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Digitized  by  the  Internet  Archive 

in  2010  with  funding  from 

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http://www.archive.org/details/textbookofanatom01cunn 


L_«B*=»ARV    OP" 

DR    HORATIO  B    WILLIAMS, 

NEW    YORK    C«TY. 


TEXT-BOOK 


OF 


ANATOMY 


EDITED    BY 


D.  J.  CUNNINGHAM,  F.R.S 

.D.     (eDIN.     ET    duel.),     D.SC,     LL.D.     (gLASG.     ET    ST.    AND.),    D.C.L.     (oXON.) 
PROFESSOR     OF     ANATOMY,     UNIVERSITY     OF    EDINBURGH 


ILLUSTRATED    WITH    936    WOOD    ENGRAVINGS    FROM    ORIGINAL 
DRAWINGS,    MOSTLY    PRINTED    IN    COLOURS 


SECOND   AND    THOROUGHLY  REVISED   EDITION 


NEW  YORK 
WILLIAM    WOOD    AND    COMPANY 

EDINBURGH    AND    LONDON:     YOUNG    J.    PENTLAND 

1905 


an 


\^o^ 


EDINBUEGH  :   PRINTED   FOR   YOUNG   J.    PENTLAND,    11   TEVIOT   PLACE,    AND 
38  WEST   SMITHFIELD,    LONDON,    EC,    BY   R.    AND   R.    CLARK,    LIMITED. 


All  rights  reserved. 


TO 

^tr  SEilUam  Euxntx,  W^MM. 

F.R.S.,    M.B.,     LL.D.,     D.C.L.,     D.SC, 

IN    RECOGNITION    OF 

HIS     EMINENCE     AS     AN     ANATOMIST 

AND     HIS     INFLUENCE     AS     A     TEACHER 

THIS    VOLUME 

IS     DEDICATED 

BY     THOSE     OF     HIS     FORMER     PUPILS     AND     ASSISTANTS 

WHO     HAVE     CONTRIBUTED 

TO     ITS     PAGES 


PKEFACE    TO    THE    SECOND    EDITION. 


The  gratifying  reception  given  to  the  Text-book  of  Anatomy,  not  only  in  this 
country  but  also  in  America,  has  rendered  it  necessary  to  prepare  a  new  edition. 
In  carrying  out  this  work  the  whole  book  has  been  carefully  revised,  and  a  large 
number  of  new  illustrations  have  been  added. 

The  sections  in  which  the  chief  changes  and  additions  have  been  made  are 
those  upon  Embryology,  the  Joints,  the  Muscles,  the  Brain  and  Spinal  Cord,  the 
Genito  -  Urinary  Organs,  the  Lymphatics,  and  Applied  Anatomy.  By  pruning 
down  in  various  directions,  it  has  been  found  possible  to  incorporate  a  considerable 
amount  of  new  matter  in  these  and  other  sections  without  materially  increasing 
the  bulk  of  the  book. 

The  lamented  death  of  Professor  Birmingham  was  felt  by  all  the  contributors 
to  be  not  only  a  personal  loss,  but  one  which  materially  affected  an  important 
section  of  the  book.  Although  in  very  bad  health.  Professor  Birmingham  was 
desirous  to  undertake  his  share  of  the  work,  and  he  had  the  sheets  on  the 
Digestive  System  in  his  possession  for  this  purpose  when  he  died.  There  was 
probably  no  part  of  the  book  which  required  less  revision  than  his,  and  the 
Editor  has  taken  upon  himself  the  duty  of  making  the  alterations  which  seemed 
essential.  In  doing  this  he  has  been  careful  to  avoid  unnecessary  changes  and  to 
preserve  throughout  the  original  character  of  the  article. 

In  the  section  upon  the  Muscular  System,  a  series  of  illustrations  has  been 
added  in  which  the  areas  of  muscle  attachment  are  delineated  upon  the  bones.  For 
the  preparation  of  the  specimens,  and  for  assistance  in  the  mapping  out  of  these 
areas,  the  Editor  is  indebted  to  Dr.  E.  B.  Jamieson.  Those  who  have  attempted 
work  of  this  kind  will  appreciate  the  amount  of  labour  and  judgment  entailed,  as 
it  is  only  by  taking  the  average  condition  in  many  specimens,  and  by  the  close 
study  of  the  bones  selected  for  the  delineations,  that  a  sufficiently  accurate 
result  can  Ije  attained. 

With  the  exception  of  the  figures  which  have  been  added  to  the  sections  of 
the  book  dealing  with  Embryology,  Osteology,  and  the  Genito-Urinary  Organs, 
the  many  new  illustrations  whicli  appear  in  this  edition  have  been  prepared  in 
the  Anatomical  Department  of  the  University  of  Edinburgh.  In  carrying  out  this 
work,  the  Editor  has  again  had  the  good  fortune  to  secure  the  co-operation  of  Mr. 

vii 


viii  PEEFACE. 

J.  T.  Murray,  an  artist  whose  ability  in  the  rendering  of  anatomical  subjects  is 
recognised  on  all  hands.  Wherever  it  was  felt  that  colour  would  increase  the 
artistic  effect  or  the  general  usefulness  of  an  illustration,  it  has  been  freely 
employed,  both  in  the  case  of  the  old  and  of  the  new  figures. 

The  Editor  cannot  conclude  this  preface  to  the  second  edition  of  the  Text-book 
without  expressing  his  grateful  acknowledgment  of  the  assistance  which  has  been 
so  freely  extended  to  him  by  his  fellow-contributors  at  every  stage  of  the  work. 
He  has  also  to  thank  many  readers  of  the  first  edition  for  calling  his  attention  to 
typographical  errors  and  other  imperfections  which  had  escaped  his  notice  in 
passing  the  sheets  through  the  press. 


18  Grosvenor  Crescent,  Edinburgh, 
August  1905. 


PREFACE  TO  THE  FIRST  EDITION. 


The  form  which  this  book  has  taken  expresses  the  desire  of  those  who  have 
contributed  the  various  sections  to  produce  something  which  they  might  dedicate 
to  their  former  teacher  and  master,  Sir  William  Turner.  With  one  exception, 
all  the  contributors  have  studied  under  Sir  William  Turner,  and  all  but  two 
have  for  longer  or  shorter  periods  acted  as  his  Assistants.  Bound  together  by  this 
common  tie,  and  animated  by  affection  and  reverence  for  their  great  master,  they 
have  sought  to  produce  a  book  worthy  of  him  whose  teaching  it  so  largely  reflects, 
and  if  this  object  has  not  been  attained  it  is  not  for  want  of  will,  but  of  power,  on 
the  part  of  the  writers. 

In  the  preparation  of  a  work  such  as  this  it  is  no  easy  matter  to  prevent  over- 
lapping of  the  different  articles  and  to  keep  the  various  sections  in  harmony  with 
each  other.  Yet  in  this  direction  it  is  believed  that  a  fair  amount  of  success  has 
been  attained.  Differences  of  opinion  on  particular  points  were  bound  to  arise, 
but  the  Editor  found  in  those  concerned  the  greatest  readiness  to  come  to  a  mutual 
understanding,  and  he  is  deeply  grateful  to  his  colleagues  for  the  manner  in  which 
they  endeavoured  to  lighten  his  work  and  assist  him  in  his  task.  Of  course  when 
totally  different  views  were  held  by  two  authors  on  a  matter  which  had  to  be  dealt 
with  in  two  sections,  no  serious  attempt  was  made  to  urge  these  writers  to  qualify 
their  statements  so  as  to  produce  an  apparent  agreement.  It  was  felt  that  if  this 
were  done  the  individuality  of  the  author,  whi^h  forms  a  characteristic  feature  of 
each  article  as  it  stands,  would  thereby  be  damaged ;  and  further,  it  was  believed 
that  the  same  question  discussed  from  two  different  points  of  view  could  not  fail 
to  be  of  advantage  to  the  reader.  At  the  same  time  it  is  right  to  state  that  the 
places  in  which  a  divergence  of  opinion  appears  are  very  few,  and  taking  into 
account  that  nine  writers  have  co-operated  with  the  Editor,  a  remarkable  degree 
of  harmony  in  the  treatment  of  the  different  sections  has  been  obtained. 

The  recent  introduction  of  Formalin  as  a  hardening  and  preserving  reagent 
imposed  an  especially  arduous  duty  upon  those  writers  who  had  undertaken  the 
chapters  dealing  with  tlie  thoracic  and  abdominal  viscera.  The  possibilities  for 
establishing  a  more  accurate  topography  and  of  improving  our  conception  of  the 
forms  assumed  by  the  viscera  under  different  conditions  have  by  this  means  been 
greatly  extended  ;  and  in  preparing  the  sections  which  treat  of  these  organs  the 
writers  have  taken  full  advantage  of  the  new  method.  Much,  therefore,  which 
appears  in  this  book  on  the  topographical  relations  of  the  viscera  departs  con- 
siderably from  the  older  and  more  conventional  descriptions  hitherto  in  vogue. 

The  arrangement  of  the   matter  treated  in  the  following  pages  is  very  much 
the  same  as  that  adopted  in  the  various  courses  of  lectures  delivered  in  the  schools 
from  which  the  different  sections  of  llic  work  have  emanated.      The  first  chapter  is 
a  2  ix 


X  PEEFACE. 

devoted  to  the  general  principles  and  elementary  facts  of  Embryology.  Then 
follow,  in  an  order  best  suited  for  the  student,  the  chapters  dealing  with  the 
various  systems  of  organs ;  whilst  the  last  seventy-five  pages  are  used  for  the 
purpose  of  applying  the  information  conveyed  in  the  preceding  part  of  the  book 
to  the  practice  of  medicine  and  surgery.  Each  chapter  is  more  or  less  complete 
in  itself,  altliough  an  effort  has  been  made  to  weld  them  all  into  one  consistent 
whole. 

The  numerous  illustrations  which  appear  in  the  text  are  all  new  in  tlie  sense 
that  in  no  case  has  an  old  drawing  or  an  old  block  been  used.  Eurther,  the  vast 
majority  of  the  illustrations  are  new  in  the  sense  that  they  are  original.  The 
very  few  that  are  not  have  been  taken  from  monographs  dealing  with  the  subjects 
so  illustrated,  and  in  every  case  the  source  from  which  these  have  been  obtained 
is  acknowledged  in  the  text.  The  drawings  for  each  section  were  prepared  under 
the  personal  supervision  of  its  author,  and,  with  the  exception  of  the  figures  in 
two  chapters,  they  are  the  work  of  Mr.  J.  T.  Murray.  This  talented  artist  has 
devoted  much  time  to  the  undertaking,  and  the  reader  can  judge  for  himself  the 
success  which  has  attended  his  efforts.  The  Editor  cannot  sufficiently  express  his 
indebtedness  to  Mr.  Murray  for  the  great  technical  skill  and  the  patience  which  he 
brought  to  bear  upon  this  extremely  trying  and  difficult  work.  The  chapter  on 
Osteology  has  been  illustrated  by  Mr.  W.  C.  Stevens  ;  that  upon  Embryology  by 
the  authors  themselves ;  whilst  the  microscopical  drawings  in  the  section  on  the 
Brain  and  Cord  were  executed  by  Mr.  Wm.  Cathie.  It  is  also  necessary  to  mention 
that  the  coloured  outlines  representing  the  attachments  of  the  muscles  on  the 
figures  of  the  bones  were  mapped  in  by  Professor  A.  M.  Paterson. 

The  Editor  has  to  thank  his  former  Assistant,  Professor  A.  F.  Dixon  of  Cardiff, 
for  much  help  in  the  correction  of  the  proofs. 


Trinity  College,  Dublin, 
June  1902. 


LIST  OF  CONTRIBUTORS. 


AMBEOSE  BIRMINGHAM,  M.D.,  F.R.C.S.I., 

Formerly  Professor  of  Anatomy,  Catliolic  University  School  of  Medicine,  Dublin. 
(The  Digestive  System.) 

D.  J.  CUNNINGHAM,  M.D.,  F.R.S., 

Professor  of  Anatomy,  University  of  Edinburgh. 

{The  Brain  and  Sinnal  Cord,  The  Resinratory  System,  The  Ductless  Glands.) 

A.  FRANCIS  DIXON,  M.B.,  D.Sc.  (Dubl), 

Professor  of  Anatomy,  Trinity  College,  Dublin. 
{The  Urinogenital  System,.) 

DAVID  HEPBURN,  M.D.,  F.R.S.E., 

Professor  of  Anatomy,  University  College,  Cardiff. 
{Arthrology.) 

ROBERT  HOWDEN,  M.A.,  M.B., 

Professor  of  Anatomy,  University  of  Durham. 
{Tlie  Organs  of  Sense  and  the  Integument.) 

A.  M.  PATERSON,  M.D., 

Professor  of  Anatomy,  University  College,  Liverpool. 

{Myology,  The  Spinal  and  Cranial  Nerves,  The  Sympathetic  Nervous  System.) 

ARTHUR  ROBINSON,  M.D., 

Professor  of  Anatomy,  University  of  Birmingham. 
(General  Embryology,  The  Vascular  System.) 

HAROLD  J.  STILES,  M.B.,  F.R.C.S.  Ed., 

Surgeon  to  the  Royal  Hospital  for  Sick  Children,  Edinburgh. 
{Surface  and  Surgical  Anatomy.) 

ARTHUR  THOMSON,  M.A.,  M.B., 

Profe.s.sor  of  Human  Anatomy,  University  of  Oxford. 
{Osteology.) 

A.  H.  YOUNG,  M.B.,  F.li.C.H., 

Profe.s.sor  of  Anatomy,  Tlie  Owens  College,  Manchester. 
{General  Embryology,  The  Vu.icalar  System.) 


The  Index  la  tlie  wojk  of  Di-.  T.  W.  P.  Lawi{7:ncio. 

-xi 


CONTENTS. 


INTEODUCTION. 
GENERAL  EMBEYOLOGY. 


The  Animal  Cell     . 

Reproduction  of  Cells 
The  Ovum 

Its  Structure 

Its  Maturation  . 
The  Spermatozoon  . 
Fertilisation  of  the  Ovum 

Segmentation  of  Ovum 

Formation  of  Blastodermic  Vesicle 

Ectoderm  and  Entoderm   . 

Embryonic  Area 

Neural  Groove  and  Tube  . 

Formation  of  Notochord    . 

Formation  of  Ccelom 

Mesodermic  Somites  . 

Folding  off  of  the  Embryo 
The  Embryo  .... 
Primitive  Alimentary  Canal  . 

Pharynx  and  Stomatodaeum 

Visceral  Clefts  and  Arches 


The  Skeleton  . 

Composition  of  Bone 

Structure  of  Bone 

Ossification  and  Growth  of  Bones 
The  Vertebral  Column    . 
True  or  Movable  Vertebrte     . 

Cervical  Vertebrte     . 

Thoracic  Vertebrae    . 

Luml^ar  Vertebrae 
False  or  Fixed  Vertebrae 

Sacrum      .... 

Coccyx       .... 
Vertebral  Column  as  a  wliole 
Cartilaginous  Vitrtebral  Column 
OH.sification  of  Verteljrai 
Serial  Honiologics  of  tlie  Vertebra' 
Sternum  . 
Ribs 

Costal  Cartilage.4 
Thorax  as  a  wdiolt;  . 
BoTies  of  tlie  Skull  . 

Frontal  Bone 

J^arictal  JioneH  . 

Occijfilal  Jionc  . 


9 
10 
10 
12 
14 
16 
17 
18 
19 
19 
21 
24 
24 
26 
26 
28 
32 
34 
35 


69 

70 

71 

72 

74 

76 

76 

80 

82 

83 

83 

86 

87 

90 

91 

94 

94 

97 

101 

101 

103 

103 

107 

109 


Mouth  and  Nose 

PAGE 

38 

External   Ear,  Tympanic    Cavity,  and 

Eustachian  Tube    .         .         .         . 

43 

Hind-gut,  Anal  Passage,  and   Post-anal 

Gut 

45 

The  Limbs 

46 

Nutrition    and    Protection  of  Embryo 

during  Intrauterine  Existence 

47 

Foetal  Membranes  and  Appendages 

48 

Yolk-Sac 

48 

Amnion     ..... 

48 

Body-Stalk        .... 

50 

AUantois 

51 

Umbilical  Cord 

61 

Chorion 

52 

The  Placenta 

52 

Primitive  Vascular  System  and  Fceta 

[ 

Circulation     .... 

60 

External  Features  of  Human  Embryo  a1 

different  periods     . 

65 

LOGY. 

Temporal  Bones 

114 

Sphenoid  Bone . 

122 

Ethmoid  Bone  . 

128 

Wormian  Bones 

131 

Bones  of  the  Face    . 

131 

Superior  Maxillary  Bones 

131 

Malar  Bones 

135 

Nasal  Bones 

137 

Lachrymal  Bones 

138 

Inferior  Turbinated  Bones 

139 

Vomer       .... 

140 

Palate  Bones 

141 

Inferior  Maxillary  Bone    . 

143 

Hyoid  Bone 

147 

Skull  as  a  whole 

148 

Norma  Frontalis 

148 

Norma  Lateralis 

152 

Norma  Occipitalis     . 

159 

Norma  Verticalis 

159 

Norma  Basal  is  . 

160 

Skull  in  Section     .... 

.       167 

Ui)i)er   Surface;  of  tlie  Base  of  thi 

Skull.         .... 

\       167 

Mesial  Sagittal  Secti<jn  of  Skii 

1 

171 

xiv 

CONTENTS. 

PAGE 

PAGE 

Skull  in  Section — Continued. 

Sesamoid  Bones 

214 

Nasal  Fossfe       ... 

173 

Bones  of  the  Lower  Limb 

214 

Nasal  Septum   ..... 

173 

Pelvic  Girdle  and  Lower  Extremity 

214 

Air-sinuses  in  connexion  with  Nasal 

Innominate  Bone 

214 

Fosste     ...... 

174 

Pelvis 

220 

Coronal  Sections 

175 

Femur 

224 

Sexual  Differences  in  Skull    . 

177 

Patella 

230 

Differences  due  to  Age    . 

177 

Tibia  . 

231 

Craniology       .... 

178 

Fibula 

235 

Development  of   Cliondro-craniun 

1  and 

Tarsus 

239 

Morphology  of  Skull 

181 

Astragalus  . 

239 

Bones  of  Upper  Extremity 

184 

Os  Calcis    . 

243 

Clavicle      .... 

184 

Navicular  Bone 

245 

Scapula 

186 

Cuneiform  Bones 

245 

Humerus    . 

190 

Cuboid  Bone 

247 

Ulna  . 

195 

Tarsus  as  a  whole 

248 

Eadius 

199 

Metatarsal  Bones 

249 

Carpal  Bones 

203 

Phalanges  . 

251 

Carpus  as  a  whole 

208 

Sesamoid  Bones 

253 

Metacarpal  Bones 

209 

Morphology  of  Limbs 

253 

Phalangeal  Bones 

212 

AETICULATIONS   OE   JOINTS. 


Arthrology       ..... 

255 

Synarthroses      .... 

255 

Movable  Joints           .         .         .         . 

256 

Structures    which,    enter    into    the 

Formation  of  Joints 

257 

Different    Kinds    of    Movement    at 

Joints 

259 

Development  of  Joints 

259 

Morphology  of  Ligaments 

261 

Ligaments  of  the  Vertebral  Column  anc 

Skull 

261 

.  Articulation  of  Atlas  with  Axis 

265 

Articulation  of  Spine  with  Cranium 

266 

Temporo-mandibular  Joint    . 

267 

Cranial    Ligaments    not    directly  asso- 

ciated with  Articulations 

269 

Joints  of  Thorax      .... 

269 

Costo-central  Joints  .         .         .         . 

269 

Costo-transverse  Joints 

270 

Articulations  between  the  Ribs  anc 

their  Cartilages 

271 

Interchondral  Joints 

271 

Costo-sternal  Joints  . 

271 

Sternal  Articulations 

272 

Articulations  of  tlie  Superior  Extremity 

273 

Articulations  of  the  Clavicle  . 

273 

Sterno-clavicular  Joint 

273 

Acromio  -  clavicular      or      Scapulo 
clavicular  Joint 

Ligaments  of  Scapula 
Shoulder-joint 
Elbow-joint 
Eadio-ulnar  Joints 
Radio-carpal  Joint 
Carj)al  Joints 
Intermetacarpal  Joints 
Carpo-metacarpal  Joints 
Metacarpo-phalangeal  Joints 
Interphalangeal  Joints    . 
Articulations  and  Ligaments  of  Pelvis 

Lumbo-sacral  Joints 

Sacro-iliac  Joint 
Symphysis  Pubis  . 
Articulations  of  Lower  Extremity 

Hip -joint   . 

Knee-joint 

Tibio-fibular  Joints 

Joints  of  Foot     . 

Ankle-joint 

Intertarsal  Joints 

Tarso-metatarsal  Joints 

Intermetatarsal  Joints 

Metatarso-jjhalangeal  Joints 

Interphalangeal  Joints 


274 
275 
276 
279 
281 
283 
284 
287 
287 
288 
288 
289 
289 
290 
292 
293 
293 
297 
304 
306 
306 
308 
313 
314 
314 
314 


MUSCULAE   SYSTEM. 


Ajjpendicular  Muscles 
Fasciae  and  Muscles  of  Ujjper  Limb 
Fasciffi  and  Superficial  Muscles  of  Back 
Fasciae  and  Muscles  of  Pectoral  Region 
Fasciae  and  Muscles  of  Shoulder 
Fasci  ae  and  Muscles  of  Ai'm     . 
Fasciae   and   Muscles   of    Forearm    and 
Hand 

Front  and  Inner  Asj)ect  of  Forearm 

Short  Muscles  of  Hand 

Muscles  on  Back  of  Forearm 
Fasciae  and  Muscles  of  Lower  Limb 

Fasciae   and   Muscles  of  Thigh  and 
Buttock 


318 
318 
318 
321 
327 
332 

336 
339 
345 
349 
355 

355 


Muscles  on  Front  of  Thigh 

Muscles  on  Inner  Side  of  Thigh 

Muscles  of  Buttock     . 

Muscles  on  Back  of  Thigh 

Fasciae  and  Muscles  of  Leg  and  Foot 
Axial  Muscles  .... 

Fasciae  and  Muscles  of  Back    . 
Fasciae  and  Muscles  of  Head  and  Neck 
Muscles  of  Thorax  .... 
Fasciae  and  Muscles  of  Abdoininal  Wall 
Fasciae  and   Muscles  of  Perineum  and 

Pelvis 

Development  and  Morphology  of  Skele- 
tal Muscles 


359 
365 
368 
372 
376 
391 
391 
399 
422 
426 

434 

441 


CONTENTS. 


XV 


NERVOUS  SYSTEM. 


Cerebrospinal  Nervous  System 

Nerve-fibres 

Nerve-cells 

Neuroglia        ..... 

Spinal  Cord 

Internal  Structure  of  Spinal  Cord 
Characters  presented  by  Cord  in  its 

Different  Regions  . 
Component  Parts  of  Gray  Matter  of 

Spinal  Cord 
Component  Parts  of  tbe  White  Matter 

of  the  Sjjinal  Cord 
Development  of  Spinal  Cord 
Brain  or  Encephalon  . 

General  Outline  of  Development  of 
Brain 

Parts  of  Encephalon  derived  from  the 
Hind-brain     .... 
Medulla  Oblongata  or  Bulb 
Pons  Varolii       .... 
Internal  Structure  of  Medulla  . 
Internal  Structure  of  Pons  Varolii 

Cerebellum 

Minute   Structure    of    a   Cerebellar 

Folium   .... 

Deep    Connexions    of    Cranial    Nerves 

attached  to  Medulla  and  Pons 
Development    of    Parts    derived    from 

Rhombencephalon 
Mesencephalon 

Internal  Structure  of  Mesencephalon 
Deep  Origin  of  Cranial  Nerves  wliicli 
arise  within  the  Mesencephalon     . 
Development  of  Mesencephalon 
Fore-brain       .         .        .         .         . 

Parts  derived  from  the  Diencephalon 
Optic  Thalamus  .... 
Subthalamic  Tegmental  Region 

Pineal  Body 

Trigonum  Habenulse 
Corpora  Mammillaria 

Pituitary  Body 

Third  Ventricle  .... 

Cerebral  Connexions  of  Optic  Tract . 
Parts  derived  from  the  Telencephalon    . 
Cerebral  Hemispheres 

Olfactory  Lobe 

Corpus  Callosum,  Septum  Lucidum, 
and  Fornix     ..... 
Lateral  Ventricle        .... 
Basal   Ganglia    of    Cerebral   Hemi- 
sphere      

Intimate  Structure  of  Cerebral  Hemi- 
sphere    ...... 

Cerebral  Cortex  .... 

Olfactory  Tract  and  Bulb  . 
White  Medullary  Centre  of  Cerebral 
Hemisphere    .         .         .         .         . 

Development  of  Parts  derived  from 
Fore-brain      .         .         .         .         . 

Weight  of  Brain         .         .         .         . 

Meninges  of  Bi'ain  and  Spinal  Cord 

Dura  Mater 

Arachnoidea 

Pia  Mater 

Spinal  Nkkvks 

Posterior   Primary 

NerveH   . 
Cervical  Nerves 


Divisions  of  Spinal 


PAGE 

443 

444 
445 
451 
452 
456 

460 

461 

465 
471 

474 

476 

481 
481 
486 
489 
499 
505 

512 

514 

526 
531 
533 

540 
542 
542 
542 
542 
546 
547 
547 
548 
549 
550 
551 
553 
553 
569 

570 
573 

579 

584 

584 
587 

588 

594 
597 
597 
597 
600 
603 
607 

610 
611 


Thoracic  Nerves  .... 
Lumbar  Nerves  .... 
Sacral  and  Coccygeal  Nerves  . 

Morphology    of    Posterior    Primar 
Divisions        .... 
Anterior  Primary   Divisions   of  Spinal 

Nerves    ..... 
Cervical  Nerves       .... 
Cervical  Plexiis       .... 
Phrenic  Nerve  .... 
Morphology  of  Cervical  Plexus 
Brachial  Plexus      .... 
Branches  of  Brachial  Plexus 
Anterior  Thoracic  Nerves 
Musculo-cutaneous  Nerve 
Median  Nerve    .... 
Ulnar  Nerve       .... 
Internal  Cutaneous  Nerve 
Lesser  Internal  CutaneoiLS  Nerve 
Circumflex  Nerve 
Musculo-spiral  Nerve 
Radial  N^rve     .... 
Posterior  Interosseous  Nerve     . 
Subscapular  Nerves   . 
Thoracic  Nerves       .... 
Lumbo-sacral  Plexus 
Lumbar  Plexus        .... 
Obttirator  Nerve 
Anterior  Crural  Nerve 
Sacral  or  Sciatic  Plexus 
Great  Sciatic  Nerve  . 
Nerves    of    Distribution    from    the 

Sacral  Plexus 
Peroneal  Nerve  .... 
Anterior  Tibial  Nerve 
Musculo-cutaneous  Nerve  . 
Tibial  Nerve      .... 
Internal  Plantar  Nerve     . 
External  Plantar  Nerve     . 
Pudendal  Plexus     .... 
Pudic  Nerve      .... 
Development  of  Spinal  Nerves 
Morphology  of  Limb-plexuses 
Distribution  of  Spinal  Nerves  to  Muscles 

and  Skin  of  Limbs 
Variations  in  Position  of  Limb-plexuses 
Significance  of  Limb-plexuses 
Cranial  Nerves  .... 
First  or  Olfactory  Nerve  . 
Second  or  Optic  Nerve 
Third  or  Oculo-motor  Nerve     . 
Fourth  or  Trochlear  Nerve 
Fifth,  Trigeminal  or  Trifacial  Nerve 
Sixth  or  Abducent  Nerve 
Seventh  or  Facial  Nerve  . 
Eighth  or  Auditory  Nerve 
Ninth  or  Glosso-pharyngeal  Nerve 
Tenth  or  Pneumogastric  Nerve 
Thoracic  Plexuses    .... 
Eleventh  or  Spinal  Accessory  Nerve 
Twelfth  or  Hypoglossal  Nerve  . 
Development  of  Cranial  Nerves      . 
Morphology  of  Cranial  Nerves 
Sy.m PATHETIC  Nervous  System    . 
Cervical  Part  of  Sympathetic  Cord 
Sui)erior  Cervical  Ganglion 
Middle  Cervical  Ganglion 
I  Inferior  Cervical  Ganglion 

Thoracic  Part  of  Sympathetic  Cord 


PAOE 

613 
613 
613 

614 

615 

617 

617 

621 

622 

622 

624 

626 

627 

627 

629 

631 

632 

632 

632 

634 

634 

635 

635 

639 

641 

643 

645 

647 

648 

649 
650 
651 
651 
652 
654 
654 
655 
658 
660 
662 

665 

673 

674 

674 

675 

675 

676 

677 

678 

686 

686 

688 

689 

690 

693 

695 

696 

698 

700 

703 

706 

706 

708 

708 

708 


CONTENTS. 


Lumbar  Part  of  Sympatlietic  Cord 
Sacral  Part  of  Gangliated  Cord 
Syiiii^athetic  Plexuses     . 


PAGE 

710 
711 

712 


Solar  and  Pelvic  Plexuses 
Development  of  Sympathetic  System 
Morpliology  of  Sympathetic  System 


PAGE 

712 
715 
716 


OKGANS  OF  SENSE  AND  THE  INTEGUMENT. 


Nose 

Cartilages  of  Nose     . 
Nasal  Fossae    .... 

Eye 

Eyeball 

Sclera      ..... 
Cornea    ..... 
Vascular  and  Pigmented  Tunic 
Retina    ..... 
Refracting  Media  of  Eyeball  . 

Eyelids 

Lachrymal  Apparatus     . 
Development  of  Eye 

Ear 

External  Ear  .... 


717 

Pinna         

717 
719 
723 

External  Auditory  Meatus 
Middle  Ear  or  Tympanic  Cavity    . 

Mastoid  Antrum  and  Mastoid  Air- 

724 

cells        ...... 

725 

Eustacliian  Tube        ..... 

726 

Tympanic  Ossicles     .... 

727 

Internal  Ear  ...... 

731 
735 

Osseous  Labyrinth  ..... 
Membranous  Lal^yrinth .... 

738 
740 

DevelojDment  of  Labyrinth 
Organs  op  Taste 

741 

Skin  or  Integument    .... 

743 
743 

Aj)pendages  of  Skin        .... 
Development  of  Skin  and  its  Appendages 

VASCULAR  SYSTEM. 


Structure  of  Blood-vessels 

780 

Heart 

783 

Chambers  of  Heart          .         .         .         . 

786 

Structure  of  the  Heart    .         .         .         . 

791 

Pericardium 

793 

Arteries 

795 

Pulmonary  Artery 

795 

Systemic  Arteries 

797 

Aorta 

797 

Thoracic  Aorta        .         .         .         .         . 

797 

Abdominal  Aorta 

798 

Branches  of  Ascending  Aorta 

800 

Coronary  Ai'teries      .         .         .         . 

800 

Branches  of  Arch  of  Aorta 

800 

Innominate  Artery          ,         .         .         . 

801 

Arteries  of  Head  and  Neck     . 

801 

Common  Carotid  Arteries 

801 

External  Carotid  Artery 

803 

Branches  of  External  Carotid  Arter;y 

^      804 

Internal  Carotid  Artery 

813 

Branches  of  Internal  Carotid  Ai'tery 

814 

Vertebral  Artery 

818 

Arteries  of  Upper  Extremity 

821 

Subclavian  Arteries 

821 

Branches  of  Subclavian  Artery 

823 

Axillary  Artery       .... 

827 

Branches  of  Axillary  Artery      . 

828 

Brachial  Artery       .... 

830 

Branches  of  Brachial  Artery     . 

831 

Radial  Artery    .... 

831 

Ulnar  Artery     .... 

.       834 

Arterial  Arches  of  Wrist  and  Hand 

835 

Branches  of  Descending  Thoracic  Aorta 

837 

Parietal     Branches     of    Descending 

5 

Thoracic  Aorta 

.       837 

Visceral    Branches     of    Descending 

r 

Thoracic  Aorta 

.       838 

Branches  of  Abdominal  Aorta 

839 

Parietal     Branches    of    Abdomina 

1 

Aorta 

.       839 

Common  Iliac  Arteries 

841 

Paired  Visceral  Branches  of  Abdomi 

nal  Aorta        .... 

.       842 

Unpaired  or  Single  Visceral  Branche 

3 

of  Aladominal  Aorta 

.       843 

Internal  Iliac  Artery 

Branches  of  Posterior  Division 

Branches  of  Anterior  Division  of  In 
ternal  Iliac  Artery 

Visceral  Branches 

Parietal  Branches  of  Anterior  Divi 
sion  of  Internal  Iliac 
Arteries  of  Lower  Extremity 
External  Iliac  Artery 
Femoral  Artery 
Popliteal  Artery 

Posterior  Tibial  Artery 

Plantar  Arteries 

Anterior  Tibial  Artery 
Veins      .        .        .        .        . 
Pulmonary  Veins    . 
Systemic  Veins 
Coronary  Sinus  and  Veins  of  Heart 
Superior   Vena    Cava    and    its    Tribii 
taries      ..... 

Azygos  Veins     .... 

Innominate  Veins 
Veins  of  Head  and  Neck 

Veins  of  Scalp   .... 

Veins  of  Orbit,  Nose,  and  Pterygo 
maxillary  Region  ... 
Venous  Sinuses  and  Veins  of  Cranium 
and  of  its  Contents 

Diploic  and  Meningeal  Veins    . 

Veins  of  Brain  .... 

Blood  Sinuses  of  Cranium 

Spinal  Veins      .... 
Veins  of  Upper  Extremity 

Dee^j  Veins  of  Upper  Extremity 

Axillary  Vein    .... 

Superficial  Veins  of   Upper   Extre 

mity 

Inferior  Vena  Cava  and  its  Tributaries 

Iliac  Veins         .... 
Veins  of  Lower  Extremity 

Deep  VeiiTS  of  Lower  Extremity 

Superficial  Veins   of  Lower   Extre 

mity 

Portal  System  .... 

Mesenteric  and  Splenic  Veins   . 


CONTENTS. 


xvii 


Lymph  Vascular  System 
Terminal  Lymph  Vessels 
Lymphatic  Vessels  and  Glands  of  Head 

and  Neck       ..... 
Lymphatic  Glands  and  Vessels  of  Upper 

Extremity      .... 
Lymphatic  Glands  and  Vessels  of  Lower 

Extremity      .         .         .         .         ' 
Lymphatic  Glands  and  Vessels  of  Ab- 
domen and  Pelvis  .... 
Lymphatic     Glands     and     Lymphatic 

Vessels  of  Thorax  .... 
Development    op    Blood    Vascular 

System 

Pericardium,  the  Primitive  Aortas, 

and  Heart      ..... 
Development  of  Heart,  of  first  part 

of    Aorta,     and     of     Pulmonary 

Artery 

Division  of  Heart  into  its  different 

Chambers,  and  Division  of  Aortic 

Bulb       .        .         .         .         .         . 

Aortic  Arches — Formation  of  Chief 

Arteries 

Primitive  Dorsal  Aortte — Formation 

of  Descending  Aorta 


PAGE 

904 
906 

909 

913 

916 

918 

923 

925 

925 


928 


929 


932 


933 


Branches  of  Primitive  Dorsal  Aortse 

Arteries  of  Limbs 
Development  of  Veins     . 

Veins  of  Limbs . 

Pulmonary  Veins 
Morphology  op  Vascular  System 

Segmental  Arteries  and  their  Ana 
stomoses  .... 

Aorta,  Pulmonary  Artery,  and  other 
Chief  Stem  Vessels 

Limb  Arteries    .... 

Morphology  of  Veins 

AB>fORMALITIES  OP  VaSCULAR  SySTEM 

Abnormalities  of  Heart  . 
Abnormalities  of  Arteries 

Branches  of  Aorta 

Arteries  of  Head  and  Neck 

Arteries  of  Upper  Limb    . 

Iliac  Arteries  and  their  Branches 

Arteries  of  Lower  Limb     . 
Abnormalities  of  Veins  . 

Superior  Vena  Cava . 

Veins  of  Upper  Extremity 

Inferior  Vena  Cava   . 

Veins  of  Lower  Extremity 
Abnormalities  of  Lymphatics 


pa';e 
933 
933 
934 
938 
938 
938 

939 

942 
943 
943 
946 
946 
947 
947 
950 
951 
952 
953 
954 
954 
955 
955 
955 
955 


EESPIRATORY   SYSTEM. 


Organs  of  Eespiration  and  Voice    . 
Larynx  or  Organ  of  Voice 
Cartilages  of  Larynx 
Joints,  Ligaments,  and   Membranes 

Larynx  .... 
Interior  of  Larynx .... 
Laryngeal  Muscles  .... 
Trachea  


of 


957 
957 

958 

961 
964 
968 
972 


Bronchi 

Thoracic  Cavity 
Pleural  Membranes 
Mediastinal  or  Interpleural  Space 
Lungs 

Root  of  Lung     . 

Structure  of  Lung 
Development  of  Respiratory  Apparatus 


975 
976 

977 
982 
983 
989 
990 
992 


DIGESTIVE   SYSTEM. 


Mouth 995 

Palate  and  Isthmus  Faucium          .         .  998 

Tongue 1000 

Glands 1007 

Salivary  Glands        ....  1009 
Development   of    Salivary    Glands, 

Palate,  and  Tongue        .         .         .  1013 

Teeth 1014 

Permanent  Teeth       ....  1016 

Milk  Teeth 1022 

Structure  of  Teeth     ....  1023 

Development  of  Teeth       .         .         .  1025 

Morphology  of  Teeth         .         .         .  1029 

Pharynx 1029 

Development  of  Pharynx  and  Tonsil  1037 

(Esophagus 1038 

Development  of  QCsophagus               .  1042 

Abdominal  Cavity 1043 

Subdivision  of  Abdominal  Cavity     .  1045 

Peritoneum      ......  1048 

Stomach 1050 


Structure  of  Stomach 

1058 

Intestines 

1060 

Structure  of  Intestines 

1061 

Small  Intestine       .... 

1064 

Duodenum 

1065 

Jejunum  and  Ileum 

1071 

Large  Intestine       .... 

1074 

Caecum  and  Appendix    . 

1076 

Colon 

1082 

Rectum   .         .         .         .         . 

1087 

Anal  Canal 

1091 

Peritoneum 

1097 

Development  of  Intestinal   Canal  and 

Peritoneum    .... 

1105 

Liver       

1108 

Gail-Bladder  and  Bile  Passages      . 

1118 

Vessels  of  Liver 

1120 

Structure  of  Liver     , 

1121 

Development  of  Liver 

1122 

Pancreas.         ..... 

1124 

Development  of  Pancreas  . 

1129 

UEINOGENITAL   SYSTEM. 


Urinary  Oroanb 
KidiieyH . 
Bladder  . 
Urethra  . 


1130 
1130 
1144 
1157 


Male  Reproductive  ORotANS 

Testis    _ 

Vas  D(!f(',r(!ii.s  .... 
Descent  of  Testis     . 


1159 
1159 
1162 
1167 


xviii 

CONTENTS. 

PAOE 

PAGE 

Spermatic  Cord       .... 

1168 

Fallopian  Tubes     . 

1185 

Scrotum 

1169 

Uterus     ..... 

1187 

Penis       ...... 

1170 

Vagina 

1192 

Prostate 

1173 

Female  External  Genital  Organs    . 

1195 

Cowper's  Glands     .... 

1176 

Glands  of  Bartholin  . 

1198 

Male  Urethra          .... 

1177 

Development  of  Urinogenital 

Organs 

1198 

Female  Reproductive  Okuans  . 

.    1181 

Mammary  Glands   . 

1207 

Ovary 

1182 

Development  of  Manimte 

1209 

DUCTLESS   GLANDS. 

Spleen 

.     1210 

Parathyroids 

.     1218 

Suprarenal  Capsules 

.     1213 

Thymus  Gland 

.     1218 

Thyroid  Body         .... 

.     1216 

Carotid  and  Coccygeal  Bodies 

.      1220 

SUEEACE   AND   SUEGICAL  ANATOMY. 


Head  and  Neck 

.     1222 

Upper  Extremity  . 

1291 

Cranium    .... 

.     1222 

Shoulder  .         .         .         . 

1291 

Face 

.     1236 

Axilla 

1293 

Neck 

.     1246 

Upper  Arm 

1295 

Thorax 

.     1253 

Elbow 

1296 

Lungs        .... 

.     1255 

Forearm  and  Hand  . 

1298 

Heart  and  Great  Vessels   . 

.     1262 

Lower  Extremity   . 

1302 

Abdomen         .... 

.     1264 

Buttock 

1302 

Anterior  Abdominal  Wall 

.     1264 

Back  of  the  Thigh     . 

1303 

Abdominal  Cavity     . 

.     1267 

Popliteal  Space . 

1305 

Male  Perineum 

.     1277 

Front  of  Thigh . 

1305 

Prostate 

.     1278 

Knee .... 

1307 

Female  Pelvis 

.     1282 

Leg    . 

1308 

Back        ..... 

.     1284 

Foot  and  Ankle 

1310 

INDEX   

1313 

LIST    OF    ILLUSTRATIONS. 


GENERAL  EMBEYOLOGT. 


FIG. 
1. 

2. 
3. 

4. 
5. 


9. 
10. 
IL 

12. 

13. 

14. 

15. 
16. 

17. 
18. 

19. 

20. 
21. 

22. 


23. 

24. 

25, 
26. 
27. 


Horizontal  Section  through  Trunk  at 
Level  of  First  Lumbar  Vertebra  . 

Diagram  of  an  Animal  Cell 

Cell  Division 

The  Ovum  and  its  Coverings    . 

Maturation  of  the  Ovum  :  Extrusion 
of  the  "  Polar  Bodies  " . 

Diagram  illustrating  the  Maturation 
of  the  Ovum         .... 

Diagram  illustrating  the  Process  of 
Cell-Division  resulting  in  the 
Formation  of  Spermatids  which 
are  afterwards  modified  into  Sper- 
matozoa       .         .         .         .         . 

Human  Spermatozoa 

Structure  of  a  Human  Spermatozoon 

Fertilisation  of  the  Ovum 

Segmentation  of  the  Fertilised  Ovum 
in  the  Eabbit        .... 

Conversion  of  the  Morula  to  the 
Blastula 

Surface  View  of  the  Blastodermic 
Vesicle 

The  Upper  Pole  of  the  Blastodermic 
Vesicle ...... 

Tran  sverse  Section  of  a  Ferret  Embryo 

Transverse  Section  of  a  Ferret 
Embryo 

Surface  Areas  of  the  Blastoderm 

Sections  showing  the  different  Areas 
of  the  Blastodermic  Vesicle 

Extension  of  Mesoderm  and  Forma- 
tion of  Ccelom       .         .         .         . 

Surface  View  of  an  Early  Embryo   . 

Early  Stages  in  the  Folding-off  of  the 
Embryo         .         .         .         .         . 

The  Kelative  Positions  of  the 
Blastodermic  Layers  in  the  Body 
of  the  Embryo  when  the  "  Fold- 
ing-off" is  completed 

Transverse  Section  of  a  Ferret 
Ernbiyo         .         .         .         .         . 

Further  Differentiation  of  the  Meso- 
derm      

Coronal  Section  of  a  liat  Embryo     . 

TraiiBverse  Section  of  a  Rat  Eiiibryc; 

Diagivam  of  a  D(;veloj)irigOvum,  seen 
in  Longitudinal  Section 


9 
11 

12 

13 


14 
15 
15 
16 

17 

18 

19 

20 
20 

21 
23 

24 

25 
25 

27 


28 

29 

29 
30 
31 


32 


FIG. 

28. 


29. 
30. 

3L 
32. 
33. 
34. 
35. 
36. 
37. 

38. 
39. 

40. 
41. 

42. 
43. 

44. 
45. 
46. 


Diagram  representing  the  Condition 
of  the  Alimentary  Canal  in  a 
Human  Embryo  about  fifteen 
days  old  (modified  from  His)        .         33 

Further  Development  of  the  Aliment- 
ary Canal,  as  seen  in  a  Human 
Embryo  about  five  weeks  old       .         34 

Stages  in  the  Formation  of  the 
Tongue  and  Upper  Aperture  of 
the  Larynx  in  the  Human  Embryo 
(after  His) 36 

Head  of  Human  Embryo  (four  views  ; 

two  after  His)       ....         39 

Head  of  Human  Embryo  (four  views ; 

two  after  His)       ....         40 

Head  of  Human  Embryo  (two  views  ; 

one  after  His)        ....         41 

Vertical   Section  through  Head   of 

Eat  Embryo  ....         42 

Transverse  Section  through  the  Head 

of  a  Rat  Embryo  ...         43 

Figures,  modified  from  His,  illustrat- 
ing the  Formation  of  the  Pinna  .         44 

Diagrams  showing  the  Separation  of 
the  Cloacal  Part  of  the  Hind-gut 
into  Genito- urinary  Tract  and 
Rectum 46 

Transverse  Sections   of  the  Uterus 

and  Developing  Ovum  of  a  Ferret        49 

Very  young  Human  Ovum  almost 
immediately  after  its  entrance 
into  the  Decidua  ....         53 

Relation  of  the  young  Human  Ovum 

to  the  Decidua      ....         53 

Further  Stage  of  Develoj^ment  of  the 
Human  Ovum  and  its  Relation  to 
the  Decidual  Tissues    ...         54 

Completion  of  the  Decidua  Capsu- 

laris,  etc 54 

Enlargement  of  the  Blood  Sinuses  in 
the  Maternal  Part  of  the  Placenta 
and  the  Closure  of  the  Amnion    .         55 

Fcjotal    Ectoderm    surrounding    the 

Maternal  Blood  Sinuses,  etc.         .         55 

Further    Growth   of   the   Placental 

Sinuses  and  Villi,  etc.  .         .         56 

Later  Stage  in    the  Development  of 

tlie  Placenta  ....         58 


XIX 


LIST  OF  ILLUSTKATIONS. 


FIG. 

47. 


Development  of  Blood-Vessels  in  the 
Vascular  Area  of  the  Rat 

The  Primitive  Blood-Vessels  of  tlie 
Eml)ryo         ..... 

Blood  -  Vessels  of  a  Mammalian 
Eml)ryo  after  the  Formation  of 
the   Heart 

Diagram  of  the  Foetal  Circulation  . 
51.  Human  Einhryo  at  the  end  of  tlie 
12th,  13th,  and  14th  days  of  De- 
velopment (after  His)  . 


48, 


49 


50. 


\fiE 

FIG. 

52. 

61 

62 

53. 

54. 

63 

64 

55. 

65 


56. 


Human  Embryo  at  the  21st,  23rd, 
and  27th  days  of  Development 
(after  His) 

Human  Embryo  at  the  29th  and  32nd 
days  of  Development  (after  His)  . 

Human  Fa3tus  at  the  sixth  week  of 
Development  (after  His) 

Human  Fostus  six  and  a  half  weeks 
old  (after  His)       .... 

Human  Foetus  eight  and  a  half 
weeks  old  (after  His)    . 


OSTEOLOGY. 


57.  Fifth  Thoracic  Vertebra   . 

58.  Fifth  Thoracic  Vertebra   . 

59.  Fourth  Cervical  Vertebra 

60.  The  Atlas  from  Above      . 

61.  Axis  from  Behind  and  Above  . 

62.  Axis  from  the  Left  Side    . 

63.  First,  Ninth,  Tenth,  Eleventh,  and 

Twelfth  Thoracic  Vertebrte  from 
the  Left  Side         .         .         .         . 

64.  Third  Lumbar  Vertebra  from  Above 

and  from  tlie  Left  Side 

65.  The  Sacrum  (anterior  view) 

66.  The  Sacrum  (posterior  view)     . 

67.  The  Coccyx 

68.  Vertebral  Column  from  the  Left  Side 

69.  Vertebral     Column    as    seen    from 

Behind  .... 

70.  Ossification  of  Vertebrae    . 

71.  Ossification  of  Vertebrae    . 

72.  Ossification  of  Sacrum 

73.  The  Sternum  (anterior  view)    . 

74.  Ossification  of  the  Sternum 

75.  Fifth     Right    Rib     as    seen     from 

Below 

76.  Fifth    Right    Rib     as    seen    from 

Behind  .... 

77.  First  and    Second    Right    Ribs   a 

seen  from  Above  . 

78.  The  Thorax  as  seen  from  the  Front 

79.  The  Thorax  as  seen  from  the  Right 

Side 

80.  Frontal  Bone  (anterior  view)     . 

81.  Frontal  Bone  as  seen  from  Below 

82.  Ossification  of  Frontal  Bone 

83.  Right  Parietal  Bone  (outer  side) 

84.  Right  Parietal  Bone  (inner  surface) 

85.  Occipital  Bone  as  seen  from  Below 

86.  Occipital  Bone  (inner  surface)  . 

87.  Ossification  of  Occipital  Bone  . 

88.  Right  Temporal  Bone  as  seen  from 

the  Outer  Side 

89.  Right  Temporal  Bone  (inner  side) 

90.  Right  Temporal  Bone  as  seen  from 

Below 

91.  Vertical  Transverse  Section  through 

Left  Temporal  Bone  (anterior  half 
of  section) 

92.  Vertical  Transverse  Section  through 

Left    Temporal    Bone    (posterior 
half  of  section)      .... 

93.  Horizontal    Section    through    Left 

Temporal    Bone    (lower    half   of 
section) 

94.  The  Outer  and  Inner  Surfaces  of  the 

Right  Temporal  Bone  at  Birth    . 

95.  Sphenoid  as  seen  from  Behind 

96.  Sphenoid  as  seen  from  the  Front 


75 
75 
77 
78 
79 
79 


81 

82 
84 
85 
86 


89 
91 
92 
93 
95 
96 

98 

99 


118 


120 


120 


121 

122 
123 
123 


97. 
98. 
99. 

100. 

101. 

102. 
103. 
104. 

105. 
106. 
107. 

108. 
109. 
110. 
111. 
112. 
113. 

114. 

115. 


99 

116. 

101 

117. 

102 

118. 

104 

119. 

105 

120. 

106 

107 

108 

121. 

110 

122. 

111 

113 

123. 

115 

124. 

116 

125. 


126. 


127. 

128. 
129. 
130. 
131. 


Ossification  of  Sphenoid . 
Ethmoid  as  seen  from  Behind 
Ethmoid  as  seen  from  the  Right 

Side 

Section   sliowiug   Nasal  Aspect  of 

Left  Lateral  Mass  of  Ethmoid 
Showing  Articulation   of  Inferior 

Turbinated  Bone  with  Ethmoid  . 
Ethmoid  as  seen  from  Above  . 
Right  Superior  Maxilla  (outer  view) 
Right     Superior     Maxilla     (inner 

aspect) 

Ossification  of  Suj^erior  Maxilla 

Right  Malar  Bone  . 

Inner   Surface   of  Malar   Bone  at 

Birth 

Right  Nasal  Bone    . 

Right  Lachrymal  Bone   . 

Right  Inferior  Turbinated  Bone 

Vomer  as  seen  from  the  Right  Side 

Right  Palate  Bone  . 

Right   Palate   Bone  as   seen   from 

Behind  .... 

The  Lower  Jaw  as  seen  from  th 

Left  Side      .... 
The  Inner  Side  of  the  Right  Half 

of  the  Lower  Jaw 
Lower  Jaw  at  Birth 
The  Hyoid  Bone  as  seen  from  the 

Front    

Norma  Frontalis 
Norma  Lateralis 
Coronal      Section      through      the 

Sjjheno  -  maxillary  Fossa   of  the 

Right  Side 

Norma  Basalis         .... 
Base   of  the   Skull    as    seen   from 

Above 

Inner  Aspect  of  Left  Half  of  Skull 

sagittally  divided 
Nasal  Septum  as  seen  from  the  Left 

Side 

Part   of  the   Frontal,    Nasal,   and 

Superior    Maxillary    Bones    re- 
moved  in   order   to   display   the 

relation   of  the   various   cavities 

exposed 

Coronal  Section  passing  inferiorly 

through   interval  between   First 

and  Second  Molar  Teeth 
View  of  the  Cliondro-Cranium  of  a 

Human  Foetus      ... 
Right  Clavicle  as  seen  from  Above 
Right  Clavicle  as  seen  from  Below 
Ossification  of  the  Clavicle 
The  Right  Scapula   as  seen   from 

Behind  .... 


LIST  OF  ILLUSTEATIONS. 


FIG.  PAGE  FIO. 

132.  The  Right  Scapula  as  seen  from  the  168. 

Front 188 

133.  Ossification  of  the  Scapula      .         .  190  169. 

134.  Anterior     View     of     the     Right  170. 

Humerus      .....  191 

135.  Posterior     View     of     the     Right  171. 

Humerus 192  172. 

136.  The  Head  of  the  Right  Humerus  as 

seen  from  Above  ....  193  173. 

137.  The  Lower  Extremity  of  the  Right  174. 

Humerus  as  seen  from  Below       .  193  175. 

138.  The    Lower    End    of    the    Right 

Humerus  as  seen  from  the  Outer  176. 

Side .193 

139.  Ossification  of  the  Humerus    .        .  195  177. 

140.  The  Right  Ulna  as  viewed  from  the  178. 

Outer  Side 196 

141.  The  Radius  and  Ulna  as  seen  from  179. 

the  Front 198 

142.  The  Ossification  of  the  Ulna  .         .  199  180. 

143.  The  Radius  and  Ulna  as  seen  from  181. 

Behind 200 

144.  The  Ossification  of  the  Radius        .  202  182. 

145.  The  Bones  of  the  Right  Wrist  and 

Hand  as  seen  from  the  Front       .  203  183. 

146.  The  Bones  of  the  Right  Wrist  and  184. 

Hand  as  seen  from  Behind  .         .  204  185. 

147.  The  Right  Scaphoid  Bone       .         .  205 

148.  The  Right  Semilunar  Bone     .         .  205  186. 

149.  The  Right  Cuneiform  Bone    .        .  206 

150.  The  Right  Pisiform  Bone        .         .  206  187. 

151.  The  Right  Trapezium     .         .         .206  188. 

152.  The  Right  Trapezoid       .         .         .207  189. 

153.  The  Right  Os  Magnum  .         .         .207 

154.  The  Right  Unciform  Bone      .         .  208  190. 

155.  Radiograph  of  the  Hand  at  Birth  .  209  191. 

156.  First  Right  Metacarpal  Bone .         .  210  192. 

157.  Second  Metacarpal  Bone         .         .  210  193. 

158.  Third  Metacarpal  Bone  .         .         .  211  194. 

159.  Fourth  Metacarpal  Bone         .         .211  195. 

160.  Fifth  Metacarpal  Bone    .         .         .211  196. 

161.  The  Phalanges  of  the  Fingers       .  213  197. 

162.  Radiographs  of  Foetal  Hands .         .  213  198. 

163.  The  Right  Innominate  Bone  as  seen 

from  the  Outer  Side     .         .         .  215  199. 

164.  The  Right  Innominate  Bone  .        .  216 

165.  Ossification     of    the     Innominate 

Bone 220 

166.  Male  Pelvis  as  seen  from  the  Front  221  200. 

167.  Female    Pelvis  as  seen   from    the  201. 

Front 221  202. 


Right    Femur    as   seen  from    the 

Front 224 

Right  Femur  as  seen  from  Behind .  225 
Back  View  of  Upper  End  of  Right 

Femur 226 

Lower  End  of  Right  Femur   .         .  228 
Lower  End  of  Right  Femur  as  seen 

from  below 228 

Ossification  of  Femur      .         .         .  230 

Right  Patella 230 

Upper    Surface    of    Superior    Ex- 
tremity of  Right  Tibia         .         .231 
Right   Tibia   and   Fibula   as  seen 

from  the  Front     ....  232 

Ossification  of  the  Tibia          .         .  235 
Right   Tibia   and   Fibula  as   seen 

from  Behind         ....  236 
Right  Fibula  as  seen  from  the  Inner 

Side 237 

Ossification  of  Fibula      .         .         .  239 
Bones  of  the  Right   Foot  as  seen 

from  Above 240 

Bones   of  the   Right  Foot  as  seen 

from  Below 241 

The  Right  Astragalus      .         .         .242 

The  Right  Astragalus     .         .         .  242 
The  Right  Os  Calcis  as  seen  from 

Above 243 

The  Right  Os  Calcis  as  seen  from 

Below 243 

The  Right  Os  Calcis  .  .  .244 
Right  Navicular  Bone  .  .  .  245 
Anterior  View  of  the  three  Cunei- 
form Bones  of  the  Right  Foot  .  246 
Right  Internal  Cuneiform  .  .  246 
Right  Internal  Cuneiform  .  .  246 
Right  Middle  Cuneiform  .  .  246 
Right  Middle  Cuneiform  .  .  246 
Right  External  Cuneiform  .  .  247 
Right  External  Cuneiform  .  .  247 
Right  Cuboid  Bone  .  .  .248 
Radiographs  of  the  Foetal  Foot  .  249 
The  First  Metatarsal  Bone  of  the 

Right  Foot 250 

View  of  the  Bases  and  Shafts  of 
the  Second,  Third,  and  Fourth 
Metatarsal    Bones   of  the  Right 

Foot 250 

Fifth  Right  Metatarsal  Bone  .         .  251 

The  Phalanges  of  the  Toes      .         .  252 

Radiographs  of  the  Foetal  Foot       .  252 


THE  AETICULATIONS   OK  JOINTS. 


203.  Vertical  Section  through  a  Suture . 

204.  Section     through     the     Occipito- 

sphenoid  Synchondrosis 

205.  Sutura  Serrata         .... 

206.  Diagram  of  a  Diarthrodial  Joint    . 

207.  Diagram  of  a  Diarthrodial  Joint     . 

208.  Mesial  Section  through  a  portion  of 

the  Lumbar  part  of  the  Spine 

209.  Anterior  Common  Ligainent  of  the 

Vertebral  Column,  and  the  Costo- 
vertebral Jointsasseen  from  Front 

210.  Posterior  Common  Ligament  of  the 

Verteljral  Column 

211.  Ligamenta  Subflava 

212.  Mesial  Section  through   the    Occi- 

pito-atloid  and  Atlo-axoid  Joints 

213.  Dissection     from     Behind    of    the 


255 

256 
256 
257 
258 

262 


262 

263 
264 

265 


214. 
215. 

216. 

217. 

218. 

219. 

220. 


Ligaments  connecting  the  Occipi- 
tal Bone,  the  Atlas,  and  the  Axis 
with  each  other    ....       266 

Temporo-mandibular  Joint     .         .       267 

Section  through  Temporo-mandi- 
bular Joint 268 

Internal  Lateral  Ligament  of  the 
Temporo-maxillary  Joint     .         .       268 

Sterno-clavicular  and  Costo-sternal 
Joints 272 

Capsule  of  the  Shoulder-joint  and 
Coraco-acromial  Ligament   .         .       276 

Capsular  Ligament  of  Shoulder- 
joint  cut  across  and  Humerus 
removed 277 

Vertical  SectioTi  through  the 
Shoulder-joint      ....       278 


LIST  OF  ILLUSTKATIONS. 


FIO. 

221.  Anterior  View  of  Elbow-joint 

222.  Elbow-joint  (inner  aspect) 

223.  Vertical  Section  tlirougli  the 
Trochlear  part  of  the  Elbow -joint 

Orbicular  Ligament  of  the  Radius . 

Carpal  Articular  Surface  of  the 
Radius,  and  Triangular  Fibro- 
Cartilage  of  the  Wrist 

Ligaments  on  Anterior  Aspect  of 
Radio-carpal,  Carpal,  and  Carpo- 
metacarpal Joints 

Coronal  Section  through  the  Radio- 
carpal, Carpal,  Carpo-metacarpal, 
and  Intermetacarpal  Joints  to 
show  Joint  Cavities  and  Inter- 
osseous     Ligaments      (diagram  - 

matic) 

228.  Metacarpo-phalangeal  and  Inter- 
phalangeal  Joints 

Coronal  Section  of  Pelvis 

Posterior  View  of  the  Pelvic  Liga- 
ments and  of  the  Hip-joint . 

Dissection  of  the  Hip-joint     . 


224. 
225. 


226. 


227. 


229. 
230. 

23L 


PAGE 

279 

280 

281 

282 


282 


284 


286 

288 
290 

291 
294 


FIG. 

232, 


Dissection  of  the  Hip-joint  from  the 
Front 296 

Dissection  of  the  Knee-joint  from 
the  Front 298 

234.  The  Knee-joint  (2:>osterior  view)      .       299 

235.  The  Knee-joint  opened  from  behind 

by  the  removal  of  the  Posterior 

Ligament 301 

Upper  End  of  Tibia        .         .         .302 
Ankle-joint  dissected  from  Behind       305 
Articular   Surfaces    of   Tibia    and 
Fibula  which  are  opposed  to  the 

Astragalus 306 

Ankle  and  Tarsal-joiuts  from  the 

Tibial  Aspect        ....       307 
Ligaments  on  the  Outer  Aspect  of 
the    Ankle-joint    and    on    the 
Dorsum  of  the  Tarsus  .         .         .       308 

241.  The  Composite  Articular  Socket  for 

the  Head  of  the  Astragalus .         .       309 

242.  Plantar  Aspect  of  Tarsal  and  Tarso- 

metatarsal Joints ....       310 


233. 


236. 
237. 
238. 


239. 


240. 


THE  MUSGULAE   SYSTEM. 


243.  Muscle-Attachments  to  the  Clavicle 

244.  Superficial  Muscles  of  the  Back 

245.  Muscle-Attachments  to  the  Scapula 

(posterior  surface) 

246.  Muscle -Attachments  to  the  Front  of 

the  Sternum 

247.  Anterior  Muscle?  of  the  Trunk 

248.  Muscle-Attachments  to  the  Clavicle 

(under  surface)      .... 

249.  The  Serratus  Magnus  Muscle . 

250.  Muscle-Attachments  to  the  Scapula 

(anterior  aspect)   .... 

251.  Deltoid  Region  and  Back   of  the 

Arm      ...... 

252.  Posterior  Wall  of  the  Axilla  and 

the  Front  of  the  Arm  . 

253.  Muscle-Attachments  to  the  Front 

of  the  Humerus    .... 

254.  Muscle-Attachments  to  the  Scapula 

(posterior  surface) 

255.  Superficial  Muscles  on  the  front  of 

the  Arm  and  Forearm . 

256.  The   Muscles  on   the  Back  of  the 

Arm,  Forearm,  and  Hand    . 

257.  Muscle-Attachments  to  the  Front  of 

the  Humerus        .... 

258.  Muscle-Attachments  to  the  Back  of 

the  Humerus        .... 

259.  The  Palm  of  the  Hand   . 

260.  The  Muscles  and  Tendons  in  the 

Palm  of  the  Hand 

261.  Section  Across  the  Forearm  in  the 

Middle  Third       .         .         .         . 

262.  The  Muscles  and  Nerves   on   the 

Front  of  the  Forearm  and  Hand  . 

263.  The  Tendons  attached  to  the  Index 

Finger  

264.  Muscle- Attachments  to  the  Radius 

and  Ulna  (Anterior  Aspects) 

265.  Deep  Muscles  on  the  Front  of  the 

Forearm  and  Hand 

266.  Short  Muscles  of  the  Hand     . 

267.  Muscle-Attachments  to  the  Palmar 

Aspect  of  the  Carpus  and  Meta- 
carpus ...... 


319 

268. 

320 

269. 

321 

270. 

322 

271. 

323 

272. 

324 

325 

273. 

274. 

325 

275. 

276. 

327 

277. 

328 

329 

278. 

330 

279. 

333 

280. 

334 

281. 

335 

335 

282. 

337 

283. 

338 

284. 

340 

285. 

341 

286. 

342 

287. 

343 

288. 

344 

289. 

345 

290. 


346 


The  Palmar  Interosseous  Muscles   .       347 

Muscle-Attachments  to  the  Dorsal 
Aspect  of  the  Metacarpus     .         .       348 

Dorsal  Interosseous  Muscles  of  the 
Hand 348 

Muscle-Attachments  to  the  Radius 
and  Ulna 351 

The  Muscles  of  the  Back  of  the 
Forearm 352 

The  Groin        .         .         .         .         .       356 

The  Groin 357 

Superficial  Muscles  of  the  Back      .       358 

The  Muscles  on  the  Front  of  the 
Thigh 360 

Muscle  -  Attachments  to  the  An- 
terior Surface  of  the  Upper  Part 
of  the  Femur        .        .         .         .       361 

Transverse  Section  of  the  Thigh 
(Hunter's  Canal)  ....       362 

Muscle-Attachments  to  the  inner 
side  of  the  Upper  Part  of  the 
Tibia .363 

Muscles  and  Nerves  of  the  Lumbo- 
sacral Plexus        ....       364 

Muscle- Attachments  to  the  Posterior 
Aspect  of  the  Upper  Part  of  the 
Femur 365 

Muscle-Attachments  to  the  Outer 
Surface  of  the  Pubis  and  Ischium       366 

Scheme  of  the  Course  and  Distri- 
bution of  the  Obturator  Nerve    .       367 

Posterior  Surface  of  the  Thigh       .       368 

Muscle-Attachments  to  the  Dorsum 
Ilii  and  Tuber  Ischii    .         .         .369 

Muscle-Attachments  to  the  Posterior 
Aspect  of  the  Upper  Part  of  the 
Femur 370 

The  Gluteus  Maximus  Muscle        .       370 

The  Muscles  and  Nerves  of  the 
Buttock 371 

Muscle-Attachments  to  the  Upper 
Asjject  of  the  Great  Trochanter 
of  the  Femur        .         .         .         .371 

Muscle-Attachments  to  the  Dorsum 
Ilii  and  Tuber  Ischii   .        .        .373 


LIST  OE  ILLUSTEATIONS. 


XXI 11 


FIG. 

291.  The  Muscles  on  the  Back  of  the 

Thigh 

292.  Muscle-Attachments  to  the  Inner 

Side  of  the  Upper  Part  of  the 
Tibia    

293.  Coronal  Section  through  the  Left 

Ankle  Joint  (Astragalus  and  Cal- 
caneum)         ..... 

294.  The   Plantar  Fascia    and   Plantar 

Cutaneous  Nerves 

295.  Muscle -Attachments  to  Tarsus  and 

Metatarsus 

296.  Muscles  of  the  Front  of  the  Right 

Leg  and  Dorsum  of  the  Foot 

297.  The    Insertions  of    the    Peroneus 

Longus  and  Tibialis  Posticus 
Muscles  in  the  Sole  of  the  Right 
Foot 

298.  The  Soleus  Muscle  .... 

299.  Muscle- Attachments  to  the  Posterior 

Surface  of  the  Tibia     . 

300.  The  Deep  Muscles  on  the  Back  of 

the  Left  Leg         .... 

301.  The  Muscles  of  the  Right  Foot 

302.  Muscle-Attachments  to  Tarsus  and 

Metatarsus 

303.  The  Muscles  of  the  Right  Foot 

304.  The  Muscles  of  the  Right  Foot 

305.  Interosseous  Muscles  of  the  Foot    . 

306.  Transverse    Section    through    the 

Abdomen,  opposite  the  Second 
Lumbar  Vertebra 

307.  Schematic   Representation  of    the 

parts  of  the  Erector  Spinae  Muscle 

308.  Scheme  of  Muscular -Attachments 

to  the  Transverse  Processes  of  the 
Cervical  Vertebrae 

309.  Deeper  Muscles  of  Back 

310.  The  Suboccipital  Triangle      . 

311.  Muscle-Attachments  to  the  Sacrum 

312.  Muscle -Attachments   to    Occipital 

Bone 

313.  Transverse  Section  in  the  Cervical 

Region 

314.  The  Muscles  of  the  Face  and  Scalp 

315.  Transverse  Vertical  Section  through 

the  Orbit  behind  the  Eyeball  to 
show  the  arrangement  of  Muscles 

316.  Muscles  of  the  Orbit 

317.  Muscles  of  the  Orbit 

318.  Schematic   Representation  of    the 

Nerves  which  traverse  the  Cavity 
of  the  Orbit 

319.  Muscle-Attachments  to  the  Outer 

Aspect  of  the  Lower  Jaw 

320.  Muscles  of  Mastication    . 

321.  Muscle-Attachments  on  the  inner 

side  of  the  Lower  Jaw 

322.  Muscles    of     Mastication,     deeper 

view      ...... 


PAGE     1     FIG. 

323. 
374      324. 


325. 


374 


377 

326 

327 

378 

328 

379 

329. 

380 

330. 

381 

331. 

382 

332 

383 

333. 

383 

384 

334. 

335. 

386 

336. 

387 

387 

388 

337. 

338. 

391 

339. 

392 

340. 

341. 

342. 

393 

343. 

394 

396 

344. 

396 

397 

345. 

400 

402 

346. 

347. 

405 

405 

406 

348. 

349. 

406 

350. 

351. 

407 

408 

352. 

408 

409 

PAGE 

Pterygoid  Region    ....       409 
Muscle -Attachments    to   Occipital 

Bone 411 

Muscles  of  the  Hyoid  Bone  and 
Styloid  Process,  and  the  Extrinsic 
Muscles  of  the  Tongue,  with  their 

Nerves 412 

Triangles  of  the  Neck     .         .         .       413 
Muscle -Attachments  on  the  inner 

side  of  the  Lower  Jaw  .         .       414 

Posterior  view  of  the  Pharynx  and 

Constrictor  Muscles      .         .         .417 
Lateral  View  of  the  Wall  of  the 

Pharynx 418 

Muscle-Attachments  to  the  Upper 
Surface  of  the  First  Rib  and  the 
Outer  Surface  of  the  Second  Rib        420 
The  Prsevertebral  Muscles  of  the 

Neck 420 

Scheme  of  Muscular-Attachments 

to  Cervical  Vertebrae   .         .         .421 
Muscle -Attachments   to    Occipital 

Bone 421 

Muscles  of  the  Thoracic  Wall  .       423 

The  Diaphragm  (from  below)  .       424 

View  of  the  Posterior  Abdominal 
Wall,  to  show  the  Muscles  and 
the  Nerves  of  the  Lumbo -sacral 

Plexus 425 

The  Groin 427 

Transverse    Section    through    the 

Abdomen 428 

The  Groin 428 

Anterior  Muscles  of  the  Trunk       .       429 

The  Groin 430 

The  Groin 431 

Sheath   of  the  Rectus  Abdominis 

Muscle 432 

View  of  the  Posterior  Abdominal 
Wall  to  show  the  Muscles  and  the 
Nerves     of    the     Lumbo -Sacral 

Plexus 433 

Muscles  and   Nerves  of  the  Male 

Perineum 435 

Muscles  of  the  Female  Perineum 

(after  Peter  Thompson)        .  436 

Triangular  Ligament  of  the  Peri- 
neum, and  the  Termination  of  the 
Pudic  Nerve         ....       437 
Dissection    of    the    Pelvic    Fascia 

from  above 438 

Oblique  Section  across  the  Pelvis  .       439 
Outer  Wall  of  the  Pelvis        .         .       439 
Fascial  and  Muscular  Wall  of  the 
Pelvis  after  removal  of  part  of 
the  Left  Innominate  Bone  .         .       440 
Scheme  to  illustrate  the  disposition 
of  the  Myotomes  in  the  Embryo 
in  relation  to  the  Head,  Trunk, 
and  Limbs 442 


353.  Nerve-fibre    from 

v.  Kolliker)  . 

354.  Three  Nerve-Ceils   from    the  An- 

terior Horn  of  Gray  Matter  of  tlio 
Human  Spinal  Cord    . 

355.  Two  Multipolar  Nerve-Cells  . 


THE  NERVOUS  SYSTEM 

a    Frog    (after 


356. 


444 


445 
446 


Nerve-Cell  from  Cerebellum  (Pro- 
f(issor  Symington) 

357.  Transverse    Section    through    t])e 

early   Neural   Tube   (Alfred    H. 
Young) 

358.  Developmental  Stages  exhibited  by 


446 


447 


LIST  OF  ILLUSTEATIONS. 


a  Pyramidal  Cell  of  the  Brain 
(after  Ram6n  y  Cajal)  . 

359.  Diagram  of  the   Connexion  estab- 

lished by  a  Ganglionic  and  a 
Motor  Neuron  (Eam6n  y  Cajal)  . 

360.  Three  Stages  in  the  development 

of  a  Cell  from  a  Spinal  Ganglion 

361.  Nerve-Cells  as  depicted  by  Bethe  . 

362.  Section  through  the  Central  Canal 

of  the  Spinal  Cord  of  a  Human 
Embryo  (after  v.  Lenhossek) 

363.  Human  Foetus  in  the  third  month 

of  Development,  Avith  the  Brain 
and  Spinal  Cord  exposed  from 
behind 

364.  The    Conus    MeduUaris    and    tlie 

Filum  Terminale  exposed  within 
the  Spinal  Canal .... 

365.  The  Roots  of  Origin  of  the  Seventh 

Dorsal  Nerve        .... 

366.  Section  through  the  Conus  Medul- 

laris  and  the  Cauda  Equina  as 
they  lie  in  the  Spinal  Canal 

367.  Diagram  of  the  Spinal  Cord  as  seen 

from  behind  .... 

368.  Transverse.  Section    through    the 

Upper  Part  of  the  Cervical  Region 
of  the  Cord  of  an  Orang 

369.  Section  through  each  of  the  Four 

Regions  of  the  Cord 

370.  Section  through  the  Fifth  Cervical 

Segment  of  the  Cord    . 

371.  Section  through  the  eighth  Dorsal 

Segment  of  the  Spinal  Cord 

372.  Section  through  the  Third  Lumbar 

Segment  of  the  Spinal  Cord  to 
show  the  grouping  of  the  Motor 
Cells     ..... 

373.  Section   through    the    first   Sacral 

Segment  of  the  Spinal  Cord 

374.  Transverse    Section    through    the 

White  Matter  of  the  Cord   . 

375.  Diagram  to  show  the  iG-rangement 

of  the  Fibres  of  the  Posterior 
Nerve -Roots  in  the  Posterior 
Columns  of  the  Cord    . 

376.  Diagram   to  show  the  manner  in 

which  the  Fibres  of  the  Posterior 
Nerve-Roots  enter  and  ascend  in 
the  Posterior  Column  of  the  Cord 
(from  Edinger)      .... 

377.  Diagrammatic  Representation  of  a 

Transverse  Section  through  the 
Spinal  Cord  .... 

378.  Schema    of   a   Transverse   Section 

through  the  Early  Neural  Tube 
(Young)         ..... 

379.  Three  Stages  in  the  Development 

of  the  Spinal  Cord  (His) 

380.  The  Base  of  the  Brain  with  Cranial 

Nerves  attached  .... 

381.  Schema  showing  the  Connexions  of 

the  several  parts  of  the  Brain 

382.  Two   Stages   in   the  Development 

of  the  Human  Brain  (after  His)  . 

383.  Two   Cross    Sections  through   the 

Fore-Brain 

384.  The  Brain  of  a  Human  Embryo  in 

the  Fifth  Week  (after  His)  . 

385.  Profile   View   of    the   Brain   of   a 

Human  Embryo  of  Ten  Weeks 
(His) 


447 


449 

449 
450 


451 


467 


FIG. 

386. 

387. 


388. 


389. 


390. 


452 

391. 
392. 

453 

453 

393. 

453 

394. 

455 

456 

458 
462 

395. 
396. 
397. 

463 

398. 

463 

399. 

464 

400. 

465 

401. 


402. 

403. 

467 

404. 

469 

405. 

471 

472 

406. 

474 

476 

407. 

477 
477 
478 

408. 
409. 
410. 

479 

411. 

Diagrams  to  illustrate  the  Alar  and 
Basal  Laminae       ....       480 

Front  View  of  the  Medulla,  Pons, 
and  Mesencephalon  of  a  full-time 
Human  Foetus      .         .         .         .481 

Back  View  of  the  Medulla,  Pons, 
and  Mesencephalon  of  a  full-time 
Human  Foetus      ....       482 

Diagram  of  the  Decussation  of  the 
Pyramids  (modified  from  van 
Gehuchten) 483 

Lateral  View  of  the  Medulla,  Pons, 
and  Mesencephalon  of  a  full-time 
Human  Foetus      ....       484 

Floor  of  the  Fourth  Ventricle         .       487 

Section  through  the  Lower  End  of 
the  Medul-la  Oblongata  of  a  Chim- 
panzee to  show  the  Decussation 
of  the  Pyramids  ....       489 

Transverse  Section  through  Lower 
End  of  the  Medulla  of  a  full-time 
Fcetus 491 

Section  through  the  Closed  Part  of 
Human  Medulla  immediately 
above  the  Decussation  of  the 
Pyramids 492 

Section  through  the  Lower  Part  of 
the  Medulla  of  the  Orang     .        .       492 

Transverse  Section  through  the 
Closed  Part  of  a  Foetal  Medulla  .       493 

Transverse  Section  through  the 
Human  Medulla  in  the  Lower 
Olivary  Region     ....       493 

Transverse  Section  through  the 
Middle  of  the  Olivary  Region  of 
the  Human  Medulla     .         .         .       495 

Inferior  Olivary  Nucleus  as  recon- 
structed and  figured  by  Miss 
Florence  R.  Sabin        .        .        .       495 

Diagram  which  shows  in  part  the 
Fibres  which  enter  into  the 
Constitution  of  the  Restiform 
Body 496 

Section  through  the  Junction  be- 
tween the  Cord  and  Medulla  of 
the  Orang 496 

Diagram  of  the  Cerebello-olivary 
Fibres 497 

Section  through  the  Lower  Part  of 
the  Human  Pons  Varolii  imme- 
diately above  the  Medulla   .        .       500 

Diagram  to  show  Connexions  of  the 
Direct  Cerebellar  and  the  Olivo- 
cerebellar Tracts  .         .         .       501 

Transverse  Section  through  the 
Pons  Varolii  at  the  Level  of  the 
Nuclei  of  the  Trigeminal  Nerve 
(Orang) 503 

Section  through  the  Upper  Part  of 
the  Pons  Varolii  of  the  Orang, 
above  the  Level  of  the  Trigeminal 
Nuclei 504 

Two  Sections  through  the  Tegmen- 
tum of  the  Pons  at  its  Upper 
Part,  close  to  the  Mesencephalon       505 

Upper  Surface  of  the  Cerebellum  .       505 

Lower  Surface  of  the  Cerebellum   .       508 

Sagittal  Section  through  the  Left 
Lateral  Hemisphere  of  the  Cere- 
bellum   509 

From  a  Dissection  by  Dr.  E.  B. 
Jamieson,  showing  Corpus  Den- 


LIST  OF  ILLUSTEATIONS. 


XXV 


Fia.  PAGE 

tatuni  and  Superior  Cerebellar 
Peduncle,  etc 509 

412.  Mesial  Section  through  the  Corpus 

Callosum,  the  Mesencephalon,  the 
Pons,  Medulla,  and  Cerebellum   .       512 

413.  Transverse  Section  through  a  Cere- 

bellar Folium  (after  Kolliker)      .       513 

414.  Section  through  the  Molecular  and 

Granular  Layers  in  the  Long 
Axis  of  a  Cerebellar  Folium 
(after  Kolliker)    ...         .514 

415.  Diagram  of  the  Spinal  Origin  of 

the  Spinal  Accessory  Nerve  (after 
Bruce)  ......       516 

416.  Section  through  the  Upper  Part  of 

the  Cervical  Region  of  the  Cord 
(Orang) 516 

417.  Diagram  showing  the  Brain  Con- 

nexions of  the  Vagus,  Glosso- 
pharyngeal, Auditory,  Facial, 
Abducent,and  Trigeminal  Nerves       518 

418.  Central  Connexions  of  the  Cochlear 

and  Vestibular  Divisions  of  the 
Auditory  Nerve    ....       520 

419.  Section  through  the  Pons  Varolii  of 

the  Orang 522 

420.  Diagram  of  the  Intrapontine  Course 

pursued  by  the  Facial  Nerve        .       523 

421.  Section  through  the  Pons  Varolii 

of  the  Orang  at  the  Level  of  the 
Nuclei  of  the  Trigeminal  Nerve         525 

422.  Three  Stages  in  the  Development 

of  the  Medulla  Oblongata  (His — 
slightly  modified)         .         .         .       527 

423.  Drawings  to  illustrate  the  Develop- 

ment of  the  Cerebellum  (from 
Kuithan) 529 

424.  Brain   of   an   Embryo   of    Eleven 

Weeks 529 

425.  Sections    throu.gh    Cerebellum    of 

Human  Foetus      ....       530 

426.  Under  Surface  of  the  Cerebellum  of 

a  Human  Foetus  ....       530 

427.  Cerebellum  of  a  Human  Foetus       .       530 

428.  Diagram  of  the  Roots  of  the  Optic 

Nerve 532 

429.  Transverse    Section    through    the 

Upper  Part  of  the  Mesencephalon      533 

430.  Transverse    Section    through    the 

Human  Mesencephalon  at  the 
Level  of  the  Inferior  Quadri- 
geminal  Body       ....       535 

431.  Transverse    Section    through    the 

Human  Mesencephalon  at  the 
Level  of  the  Superior  Quadri- 
geminal  Body       ....       536 

432.  Section  through  the  Inferior  Quadri- 

geminal  Body  and  the  Tegmentum 
of  the  Mesencei^halon  below  the 
Level  of  the  Nucleus  of  the  Fourth 
Nerve  in  tlie  Orang      .         .         .       537 

433.  Section  through  the  Inferior  Quad- 

rigeminal  Body  and  tlie  Tegmen- 
tum of  the  Mesencephalon   .         .       538 

434.  Diagram  of  the  Connexions  of  the 

Posterior  Longitudinal  Bundle 
(afier  Held— modified)  .         .       538 

435.  Diagram  of  the  Connexions  of  the 

Mesial  Fillet  and  alscj  of  certain 

of  the  Tha]anio-Corti(-al  Fibr(;H    .       539 

436.  Section  tliioiigh  the  Infcj'ior  (Jjuad- 

rigeminai  Body  and  tJie  Tegmen- 


FIO.  _  PAGE 

tum      of      the      Mesencephalon 
(Orang) 540 

437.  Section  through  the  Inferior  Quad- 

rigeminal  Body  and  the  Tegmen- 
tum of  the  Mesencejjhalon  (Orang)       541 

438.  The  Two  Optic  Thalami         .         .       543 

439.  Schema 546 

440.  Coronal  Section  through  the  Cere- 

brum of  an  Orang         .         .         .       547 

441.  Mesial  Section  through  the  Pituitary 

Region   in    a    Child   of  Twelve 
Months  old 549 

442.  Mesial  S  ection  through  the  Pituitary 

Region  in  the  Adult     .         .         .       549 

443.  Mesial  Section  through  the  Corpus 

Callosum,  Diencephalon,  etc.         .       550 

444.  Cast  of  the  Ventricles  of  the  Brain 

(from  Retzius)       .         .         .         .551 

445.  Diagram  of  the  Central  Connexions 

of  the  Opti  c  Nerve  and  Optic  Tract       552 

446.  Gyri  and  Sulci  on  the  Outer  Surface 

of  the  Cerebral  Hemisphere         .       555 

447.  Three  Stages  in  the  Development 

of  the  Insula  and  the  Insular 
Opercula 557 

448.  Development  of  the  Opercula  which 

cover  the  Insula   ....       557 

449.  Fissure  of  Rolando  fully  opened  up       558 

450.  Left  Cerebral  Hemisphere  from  a 

Foetus 559 

451.  The  Gyri  and  Sulci  on  the  Mesial 

Aspect  of  the  Cerebral  Hemisphere       559 

452.  Gyri  and   Sulci  on  the  Tentorial 

and  Orbital  Aspects  of  the  Cerebral 
Hemispheres         ....       562 

453.  Intraparietal  Sulcus  fuUy  opened  up       564 

454.  Internal  Parieto-occipital  and  the 

Calcarine  Fissures  fully  opened  up       565 

455.  Development   of  the  Parieto-occi- 

pital and  the  Calcarine  Fissures  .       566 

456.  Coronal  Section  through  the  Left 

Side  of  the  Cerebrum,  Mesen- 
cephalon, and  Pons  (Chimpanzee)       569 

457.  The  Corpus  CaUosum      .         .         .570 

458.  Profile  View  of  the  Fornix      .         .       572 

459.  Cast  of  the  Ventricular  System  of 

the  Brain  (after  Retzius)      .         .       574 

460.  Coronal  Section  through  the  Frontal 

Lobes  and  the  Anterior  Horns  of 

the  Lateral  Ventricles  .         .         .574 

461.  Dissection  to  show  the  Fornix  and 

Lateral  Ventricles        .        .        .      575 

462.  Coronal      Section      through      the 

Posterior  Horns  of  the  Lateral 
Ventricles 576 

463.  Dissection  to  show  the  Fornix  and 

the  Posterior  and  Descending 
Cornua  of  the  Lateral  Ventricle 
of  the  Left  Side    ....      677 

464.  Dissection   to   show  the   Posterior 

and  Descending  Cornua  of  the 
Lateral  Ventricle  .         .         .       578 

465.  Horizontal    Section    through    the 

Right  Cerebral  Hemisphere         .       579 

466.  Coronal  Section  through  the  Cere- 

bral Hemisplieres         .         .         .       580 

467.  Coronal  Section  through  the  Cere- 

brum      581 

468.  Coronal  Section  through  the  Left 

Sid(!  of  the  Cerebrum  of  an  Orang      582 
409.  Diagram      to     illustrate      Minute 

Structure  of  the  Cerebral  Cortex        586 


LIST  OF  ILLUSTEATIONS. 


FIG. 

470.  Diagram  of  the  Minute  Structure 

of  the  Olfactory  Bulb  . 

471.  Two  Coronal  Sections  through  the 

Cerebral  Heniisj^heres  of  an  Orang 

472.  Diagram  of  the  Leading  Association 

Bundles  of  the  Cerebral  Hemisi^here 

473.  Coronal  Section  through  the  Left 

Side  of  the  Cerebrum,  Mesen- 
cephalon and  Pons  (Chimjjanzee) 

474.  Diagrams  to  show  Flechsig's  Sensory 

and  Association  Areas  on  the  sur- 
face of  the  Cerebral  Hemi8j)here 

475.  Two  Drawings  of  the  Embryonic 

Brain  (by  His)      .... 

476.  TwoDrawingsbyHisillustratingthe 

Develojjment  of  the  Human  Brain 

477.  Sagittal  Section  through  the  Skull 

478.  Diagram  to  show  the  Eelations  of 

the  Membranes  of  the  Brain  to 
the  Cranial  Wall,  etc.  . 

479.  Membranes  of  the  Spinal  Cord,  and 

the  Mode  of  Origin  of  the  Spinal 
Nerves 

480.  Mesial  Section  through  the  Cranial 

Vault  in  the  Frontal  Region 

481.  Dissection  to  show  the  Velum  In- 

terpositum 

482.  Diagrammatic      Coronal      Section 

through  the  Optic  Thalami 

483.  Membranes  of  the  Spinal  Cord,  and 

the  Mode  of  Origin  of  the  Spinal 
Nerves 

484.  Scheme  of  the  Arrangement  of  the 

Membranes  of  the  Spinal  Cord 
and  the  Roots  of  the  Spinal  Nerves 

485.  Diagrammatic     Rej^resentation    of 

the  Origin  of  the  Spinal  Nerves  . 

486.  Scheme   of  the  Distribution  of  a 

Typical  Spinal  Nerve  . 

487.  Distribution  of  Cutaneous  Nerves 

on  the  Back  of  the  Trunk    . 

488.  Posterior  Cervical  Plexus 

489.  Distribution  of  Cutaneous  Nerves 

on  the  Front  of  the  Trunk  . 

490.  The  Cervical  Plexus 

491.  Distribution  of  Cutaneous  Nerves 

to  the  Head  and  Neck 

492.  The  Triangles  of  the  Neck      . 

493.  Muscles   of  the   Hyoid   Bone   and 

Styloid  Process,  and  the  Extrinsic 
Muscles  of  the  Tongue,  with  their 
Nerves 

494.  Nerves  of  the  Brachial  Plexus 

495.  Diagram  of  the  Origin  and  Distri- 

bution of  the  Nerves  to  the 
Pectoral  Muscles  .... 

496.  The  Posterior  Wall  of  the  AxiUa 

and  the  Front  of  the  Arm    . 

497.  The    Distribution    of    Cutaneous 

Nerves  on  the  Front  of  the  Arm 
and  Hand 

498.  The    Distribution     of     Cutaneous 

Nerves  on  the  Back  of  the  Arm 
and  Hand     

499.  Deltoid  Region  and  Back  of  Arm  . 

500.  Diagrammatic    Representation    of 

the  Branches  of  the  Musculo- 
Sjjiral  Nerve         .... 

501.  The  Muscles   of  the  Back  of  the 

Forearm 

502.  Scheme   of  the    Distribution   of  a 

Typical  Spinal  Nerve  . 


PAGE 

587 
589 
590 

592 


FIG. 

503. 

504. 
505. 


506. 


507. 
593  ,   508. 

595  i  509. 

i 

596  ;  510. 
598  I 

I  511. 
I  512. 


601 

602 
603 
604 
605 

605 

607 
608 
609 

611 

612 

615 
616 

618 
619 


620 
623 


625 
626 

628 


630 
631 


633 
634 
636 


513. 

514. 


515. 
516. 


517. 

518. 
519. 

520. 


521. 
522. 
523. 

524. 

525. 

526. 

527. 
528. 

529. 

530. 
531. 
532. 
533. 
534. 
535. 

536. 


The  Distribution  of  Cutaneous 
Nerves  on  the  Front  of  the  Trunk       637 

Nerves  of  the  Lumbo-Sacral  Plexus       640 

View  of  the  Posterior  Abdominal 
Wall,  to  show  tlie  Muscles  and 
the  Nerves  of  the  Lumbo-Sacral 
Plexus 641 

Scheme  of  the  Course  and  Distri- 
bution of  the  Obturator  Nerve     .       644 

Distribution  of  Cutaneous  Nerves 
on  the  Front  of  the  Lower  Limb  .       645 

Distribution  of  Cutaneous  Nerves 
on  the  Dorsum  of  the  Foot  .         .       651 

Distribution  of  Cutaneous  Nerves 
on  the  Back  of  the  Lower  Limb  .       653 

Scheme  of  Distribution  of  the 
Plantar  Nerves     ....       654 

Nerves  of  the  Lumbo-Sacral  Plexus       656 

The  Muscles  and  Nerves  of  the 
Male  Perineum     ....       658 

The  Triangular  Ligament  of  the 
Perineum      .....       659 

Scheme  of  the  Innervation  of  the 
Hinder  Portion  of  the  Trunk  and 
of  the  Perineum    ....       660 

Development  of  the  Spinal  Nerves       661 

Scheme  of  the  Segmental  Distribu- 
tion of  the  Muscular  Nerves  of  the 
Upper  and  Lower  Limbs     .         .       671 

View  of  the  Under  Surface  of  the 
Brain    .        .        .        .        .        .675 

Innervation  of  the  Nasal  Cavity    .       676 

Diagram  of  the  Central  Connexions 
of  the  Optic  Nerve  and  Optic  Tract       676 

Relations  of  Structures  in  the  Cav- 
ernous Sinus  and  Sphenoidal 
Fissure 677 

Dorsal  Surface  of  the  Mid -brain     .       677 

The  Base  of  the  Skull     .         .         .678 

Distribution  of  Sensory  Nerves  to 
the  Head  and  Neck      .         .         .       679 

Scheme  of  the  Distribution  of  the 
OjDhthalmic  Nerve        .         .         .       680 

Schematic  Representation  of  the 
Nerves  which  traverse  the  Cavity 
of  the  Orbit 681 

Scheme  of  the  Course  and  Distri- 
bution of  the  Superior  Maxillary 
Nerve         ......         682 

Scheme  of  the  Distribution  of  the 
Inferior  Maxillary  Nerve     .         .       684 

The  Facial  Nerve  with  its  Branches 
and  Communications  in  the  Aque- 
duct of  Fallopius  ....       687 

Distribution  of  Facial  Nerve  out- 
side the  Skull,  and  Communica- 
tions with  Trigeminal  Nerve  on 
the  Face       .        .        .    •     .        .688 

Scheme  of  the  Origin  and  Distribu- 
tion of  the  Auditory  Nerve .         .       689 

Scheme  of  the  Distribution  of  the 
Glosso-jjharjTigeal  Nerve     .         .       690 

The  Distribution  of  the  Pneumo- 
gastric  Nerve        .         .         .         .691 

The  Constitution  of  the  Cardiac 
Plexuses 694 

The  Distribution  of  the  Pneumo- 
gastric  Nerve        ....       695 

Scheme  of  the  Origin,  Connexions, 
and  Distribution  of  the  Spinal 
Accessory  Nerve  ....       696 

The  Muscles  of  the  Hyoid  Bone  and 


LIST  OF  ILLUSTEATIONS. 


XXVI 1 


537. 


538. 


Styloid  Process,  and  the  Extrinsic 
Muscles  of  the  Tongue  with  their 
Nerves 697 

Coinjjarison  of  Origins  of  Nerve- 
roots  from  S23inal  Cord  and  Hind- 
brain  (after  His)   .         .         .         .       700 

Scheme  to  illustrate  the  Disposition 
of  the  Myotomes  in  the  Embryo  in 
relation  to  the  Head,  Trunk,  and 

Limbs 702 

539.  Scheme  to  illustrate  the  Embryo- 
logical  Arrangement  of  the  Cranial 
Nerves 703 

Scheme  of  the  Constitution  of  the 
White  Ramus  Communicans  of 
the  Sympathetic  ....       704 

Scheme  of  the  Constitution  and 
Connexions  of  the  Gangliated 
Cord  of  the  Sympathetic      .         .       705 


540. 


541 


542.  The    Distribution     of    the     Sym- 

pathetic Gangliated  Cord  in  the 
Neck 707 

543.  The   Constitution    of  the   Cardiac 

Plexuses 708 

544.  The    Arrangement    of    the    Sym- 

pathetic System   in  the  Thorax, 
Abdomen,  and  Pelvis    .        .         .       709 

545.  The  Lumbar  Portion  of  the  Sym- 

pathetic   Gangliated    Cord    and 
Lumbar  Plexus     .         .         .         .711 

546.  The    Arrangement    of    the    Sym- 

pathetic  System  in  the  Thorax, 
Abdomen,  and  Pelvis   .         .         .713 

547.  The    Development    of    the    Sym- 

pathetic Gangliated  Cord     .         .       715 

548.  Section   through  the  Sympathetic 

Gangliated  Cord  of  an  Embryo    .       716 


THE  OEQANS  OF  SENSE  AND  THE  INTEGUMENT. 


549.  Lateral  View  of  Nasal  Septum       .       718 

550.  Profile  View  of  the  Bony  and  Carti- 

laginous Skeleton  of  the  Nose      .       719 

551.  Front  View  of  the  Bony  and  Carti- 

laginous Skeleton  of  the  Nose      .       719 

552.  Cartilages  of  Nose  from  Below        .       720 

553.  Coronal     Section    through    Nasal 

Fossae  ;  Anterior  Half  of  Section 
Viewed  from  Behind    .         .         .       720 

554.  Section  through   Nose   of  Kitten, 

showing  position   of    Jacobson's 
Organ 721 

555.  View  of  the  Outer  Wall  of  the  Nose       721 

556.  Section     through     the     Olfactory 

Mucous  Membrane        .         .         .       722 

557.  Olfactory  and  Supporting  Cells      .       722 

558.  Diagram    of    a    Horizontal   Section 

through  Left  Eyeball  and  Optic 
Nerve 724 

559.  Vertical  Section  of  Cornea       .         .       726 

560.  Vertical   Section  of  Chorioid  and 

Inner  Part  of  Sclera     .         .         .       727 

561.  Diagram  of  the  Circulation  in  the 

Eye  (Leber) 728 

562.  Section  through  Ciliary  Region  of 

Eyeball 729 

563.  Blood-Vessels  of  Iris  and  Anterior 

Part  of  Chorioid  (Arnold)     .         .       730 

564.  Diagrammatic      Section      of     the 

Human    Retina   (modified    from 
Schultze) 732 

565.  Perpendicular    Sections   of    Mam- 

malian Retina  (Cajal)  .         .         .       733  j 

566.  Cone    and    two     Rods     from    the 

Human  Retina      ....       733  I 

567.  Pigmented  Epithelium  of  Human 

Retina 734 

568.  Section  through   Outer   Layers  of 

Retina 734 

569.  Blood-Vessels  of  the  Retina    .         .       735 

570.  Canal     of    Petit     Distended     and 

Viewed  from  the  Front        .         .       736 

571.  Lens   liardened    in    Formalin    and 

di.Hsected  to  show  its  Conceiiti'ic 

Lam  in  if;         .....       730 

572.  iJiagraiiimatic     Representation     of 

llic.    Radii    Lentis    of   tlic.    I''a;tai 

LenH        .  .         .         .       .       737 


573.  Section  through  the  Equator  of  the 

Lens 737 

574.  Vertical    Section    through   Upper 

Eyelid 738 

575.  Sections  through   Portions  of  the 

Heads  of  Foetal  Rabbits        .         .       741 
I  576.  Optic  Cup  and  Lens  viewed  from 
I  Behind  and  Below        .         .         .       742 

i  577.  Diagrammatic  View  of  the  Organ 

of  Hearing 744 

578.  View    of    Outer   Surface    of    Left 

Pinna 744 

579.  Outer  Surface  of  Cartilage  of  Pinna       745 

580.  Inner  Surface  of  Cartilage  of  Pinna       745 

581.  Vertical  Transverse  S  ection  of  Right 

Ear 747 

582.  Horizontal  Section  through  Right 

Ear 747 

583.  Section  through  Left  Temporal  Bone       749 

584.  Left  Membrana  Tympani  and  Re- 

cessus  Epitympanicus  .        .         .       749 

585.  Left  Tympanic  Membrane       .         .       751 

586.  Transverse  Section  of  the  Cartilag- 

inous Part  of  the  Eustachian  Tube       753 

587.  Tympanic  Ossicles  of  Left  Ear        .       755 

588.  Left  Membrana  Tympani  and  Chain 

of  Tympanic  Ossicles    .         .         .       755 

589.  Left  Bony  Labyrinth       .         .         .759 

590.  Interior  of  Left  Bony  Labyrinth     .       759 

591.  Section  of  Bony  Cochlea         .         .       761 

592.  Diagrammatic    Representation    of 

the  Different  Parts  of  the  Mem- 
branous Labyrinth        .  .       762 

593.  Transverse  Section  of  Human  Semi- 

circular Canal  (Riidinger)     .         .       763 

594.  Section  across  the  Ductus  Cochlearis 

(Retzius) 764 

595.  Transverse  Section  through  Outer 

Wall      of      Ductus      Cochlearis 
(Schwalbe) 765 

596.  Transverse  Section  of  Corti's  Organ 

from  tlie  Central  Coil  of  Cochlea 
(Retzius) 766 

597.  Membranous  Labyrinth  of  a  Five 

Montlis'  Frctus  (Retzius)       .         .       768 

598.  Part  of  Cochlear  Nerve  (Henle)       .       768 

599.  Sections  tlirougli  tiu;  Region  of  the 

Hind  Brain  of  Fcjctal  Rabbits       .       769 


XXVIU 


LIST  OF  ILLUSTKATIONS. 


600.  Left  Labyrintli  of  Human  Embryo 

601.  Section    tlirougli    Papilla    Vallata 

(A)  of  Human  Tongue  and  (B)  of 
Eabbit.         ..... 

602.  Three-quarter    Surface    View  and 

Vertical  Section  of  Taste  Bud 
i'rom  the  Papilla  Foliata  of  a 
Eabbit 

603.  Isolated   Cells  from   Taste  Bud  of 

Rabbit  (Engelmann)     . 


770      604.  Vertical  Section  of  the  Skin    . 

605.  Vertical  Section  of  Epidermis  and 
Papillaj  of  Corium 

770  606.  Tactile  Corpuscles  .... 

607.  Transverse  Section  of  a  Nail  . 

608.  Lougitudinal  Section  througli  Root 
j  of  Nail 

771  609.  Transverse  Section  of  Hair  Follicle 

with  Contained  Hair    . 
771 


PAGE 

772 

773 

775 
776 

776 

777 


THE  VASCULAE  SYSTEM. 


612. 


613. 


610.  Structure  of  Blood-Vessels 

611.  Transverse    Section  through  Wall 
of  a  Large  Artery 

Transverse  Section  of  the  Wall  of  a 
Vein 

The  Base  and  Inferior  Surface  of  the 
Heart 

614.  The  Antero-superior  Surface  of  the 

Heart 

615.  The    Relation    of    the    Heart    to 

the  Anterior  Wall  of  the  Thorax 

616.  The  Cavities  of  the  Right  Auricle 
and  Right  Ventricle  of  the  Heart 

The  Bases  of  the  Ventricles  of  the 
Heart 

The  Relations  of  the  Heart  and 
the  Auriculo-ventricular,  Aortic, 
and  Pulmonary  Orifices  to  the 
Anterior  Thoracic  Wall 

Posterior  Wall  of  the  Pericardium 
after  removal  of  the  Heart  . 

The  Pulmonary  Arteries  and  Veins 
and  their  Relations 

The  Abdominal  Aorta  and  its 
Branches 

The  Carotidand  Subclavian  Arteries 
and  their  Branches 
623.  The    External    Carotid,     Internal 
Maxillary,    and    Meningeal   Ar- 
teries   ...... 

The  Carotid,  Subclavian,  and  Verte- 
bral Arteries  and  their  Main 
Branches 

Distribution  of  the  Cerebral 
Arteries  on  the  Mesial,  Tentorial, 
and  Inferior  Surfaces  of  the  Cere- 
bral Hemispheres 

Distribution  of  Cerebral  Arteries  on 
the  Outer  Surface  of  the  Cerebrum 

The  Arteries  of  the  Base  of  the 
Brain 

628.  Dissection    of    the    Back    of 

Shoulder  and  Upper  Arm    . 

629.  The     Axillary     Artery     and 

Branches  and  Relations 
The     Brachial     Artery     and 

Branches       

Superficial  Dissection  of  the  Front 

of  the  Forearm  and  Hand    . 
632.  Deep   Dissection   of  the   Front  of 

the  Forearm  and  Hand 
The  Posterior  Interosseous  Artery 

and  tlie  Second  Part  of  the  Radial 

Artery,  with  their  Branches 
The    Abdominal    Aorta     and    its 

Branches 

The  Ccfiliac  Axis  and  its  Branches 


617. 


618. 


619. 


620. 


621. 


622. 


624. 


625. 


626. 


627. 


630. 


631. 


633. 


634. 


the 


its 


its 


635. 


781 
781 

782 
784 
785 
786 
787 
788 

789 
794 
796 
799 
803 

810 

813 

815 
816 
819 
824 
827 
830 
832 
833 

835 

840 

844 


636.  The  Superior  Mesenteric  Artery  and 

its  Branches  ....       846 

637.  The  Internal  Iliac  Artery  and  its 

Branches  in  the  Female        .         .       849 

638.  The   Perineal  Distribution  of  the 

Internal    Pudic    Artery    in    the 
Male 853 

639.  The  Arteries  of  the  Buttock  and  the 

Back  of  the  Thigh  and  Knee        .       855 

640.  The  Iliac  Arteries  and  Veins  in  the 

Female 857 

641.  The     Femoral     Artery     and     its 

Branches 858 

642.  The   Femoral   Vessels   in  Scarpa's 

Triangle 860 

643.  The  Arteries  of  the  Buttock  and 

the  Back  of  the  Thigh  and  Knee  .       862 

644.  The  Popliteal  and  Posterior  Tibial 

Arteries  and  their  Branches         .       864 

645.  The    Plantar   Arteries    and    their 

Branches 866 

646.  The  Anterior  Tibial  Artery  and  its 

Branches 867 

647.  The  Dorsalis  Pedis  Artery  and  its 

Branches 869 

648.  Superficial  Veins  of  the  Head  and 

Neck     .        .        .        .        .        .878 

649.  The  Veins  of  the  Diploe         .         .       881 

650.  Dissection  of  the  Head  and  Neck, 

showing  the  Cranial  Blood  Sinuses 
and  the  Upper  Part  of  the  Internal 
Jugular  Vein         ....       884 

651.  Basal  Blood  Sinuses  of  the  Dura 

Mater 885 

652.  Superficial  Veins  on  the   Dorsum 

of  the  Hand  and  Digits        .         .       889 

653.  Superficial    Veins    on   the   Flexor 

Aspect  of  the  Upj)er  Extremity  .       890 

654.  Superficial   Veins  at  the  Bend  of 

the  Elbow 891 

655.  The   Inferior   Vena   Cava   and   its 

Tributaries 893 

656.  The  Femoral   Vessels    in    Scarpa's 

Triangle 898 

657.  The  Internal  or   Long  Saphenovis 

Vein  and  its  Tributaries       .         .       899 

658.  The  External  or  Short  Saphenous 

Vein  and  its  Tributaries       .         .       901 

659.  The  Portal  Vein  and  its  Tributaries       902 

660.  The  Thoracic  Duct  and  its  Tribu- 

taries      907 

661.  Lymphatic  Vessels  and  Glands  of 

the  Head  and  Neck      .         .         .       901 

662.  Superficial   Lymphatic    Vessels   of 

the  Trunk,  and  the  Lymphatic 
Glands  and  Vessels  Sujaerficial  and 
Deep  of  the  Limbs        .         .         .       912 


LIST  OF  ILLUSTRATIONS. 


663.  Superficial  Lymphatics  of  the  Digits 

and  of  the  Dorsal  Aspect  of  the 
Hand 915 

664.  Deep  Lymphatic  Glands  and  Vessels 

of  the  Thorax  and  Abdomen         .       919 

665.  Diagram  of  the  Primitive  Vascular 

System  before  the  Formation  of 

the  Heart 926 

666.  Diagram  of  the  Primitive  Blood- 

Vessels   after   the   Formation   of 

the  Heart     .         .         .         .         .927 

667.  Diagram  of  the  Primitive  Blood- 

vessels after  the  Formation  of 
the  Heart,  but  before  its  Sub- 
division by  Septa  into  Auricles 
and  Ventricles      ....       927 

668.  Development  of  the  Heart      .        .       928 

669.  Development  of  the  Heart  and  the 

Main  Arteries       ....       930 

670.  Diagram    of    the    Course    of    the 

Foetal  Circulation         .         .         .931 

671.  Development  of  the  Venous  System 

(Stage  L) 934 

672.  Development  of  the  Venous  System 

(Stage  II.) 935 


673.  Development  of  the  Venous  System 

(Stage  III.) 936 

674.  Development  of  the  Venous  System 

(Stage  IV.) 937 

675.  Diagram   of    the   Cephalic   Aortic 

Arches,  and  of  the  Segmental  and 
Intersegmental  Arteries  in  the 
Eegion  in  front  of  the  Umbilicus       939 

676.  Diagram  of  the  Caudal  Aortic  Arch, 

and  of  the  Segmental  and  Inter- 
segmental Arteries  in  the  Region 
behind  the  Umbilicus  .        .         .       939 

677.  Diagram  showing  the  Arrangement 

and  Communications  of  the  Seg- 
mental and  Intersegmental  Ar- 
teries at  an  Early  Stage  of  De- 
velopment      940 

678.  Diagram    of    the    Segmental    and 

Intersegmental  Arteries  at  a 
Later  Period  of  Development 
than  in  Fig.  677   .         .         .         .       941 

679.  Diagram  showing  the  Arrangement 

and  Communications  of  the  Seg- 
mental Arteries  in  the  Region  of 
the  Cephalic  Aortic  Arches .         .       941 


THE  EESPIRATORY   SYSTEM. 


680.  The     Cartilages     and     Ligaments 

of  the  Larynx  viewed  from  the 
Front 959 

681.  Profile  View  of  the  Cartilages  and 

Ligaments  of  the  Larynx      .         .       959 

682.  Cartilages  and  Ligaments  of  Larynx 

from  Behind         ....       960 

683.  Dissection  to  show  the  Lateral  Part 

of  the  Crico-thyroid  Membrane   . 

684.  Superior  Aperture  of  Larynx 

685.  Coronal  Section  through  Larynx    . 

686.  Mesial  Section  through  Larynx 

687.  Diagram  of  Rima  Glottidis     . 

688.  Specimen  showing    a    Great    Ex- 

tension  of    the    Saccule   of    the 
Larynx  ..... 

689.  The  Crico-Thyroid  Muscle      . 

690.  Dissection  of  the   Muscles  in  the 

Lateral  Wall  of  the  Larynx 

691.  Dissection  of  the  Muscles  on  the 

Posterior  Aspect  of  the  Larynx    . 

692.  Cavity  of  the  Larynx 

693.  The  Trachea  and  Bronchi 

694.  Transverse    Sections    through    the 

Trachea  and  its  Immediate  Sur- 
roundings       974 


695. 
696. 

697. 


963 

698. 

964 

965 

699. 

966 

966 

700. 

967 

968 

701. 

969 

702 

970 

972 

703 

973 

704 

Diagram  showing  Arrangement  of 
Pleural  Sacs  ....       977 

Dissection  of  a  Subject  hardened  by 
Formalin-Injection,  to  show  the 
Relations  of  the  two  Pleural  Sacs       978 

Lateral  View  of  the  Right  Pleural 
Sac  in  a  Subject  hardened  by 
Formalin-Injection       .         .         .       979 

Left  Pleural  Sac  in  a  Subject 
hardened  by  Formalin-Injection .       980 

Dissection  of  the  Pleural  Sacs  from 
Behind 981 

Dissection  of  Thorax  and  Root  of 
the  Neck  from  the  Front  to  show 
the  Relations  of  the  Lungs,  Peri- 
cardium, and  Thymus  Gland        .       984 

Mediastinal  Surfaces  of  the  two 
Lungs  of  a  Subject  hardened  by 
Formalin-Injection       .         .         .       985 

Outer  or  Costal  Surfaces  of  the  two 
Lungs 986 

Sagittal  Section  through  Left 
Shoulder  and  Left  Lung       .         .       987 

Sagittal  Section  through  the  Left 
Shoulder,  Lung,  and  Apex  of 
the  Heart 988 


THE   DIGESTIVE   SYSTEM. 


705.  General    View    of    the    Digestive 

System 994 

706.  Coronal  Section  through  the  Closed 

Moutli 996 

707.  Open   Moutli  sliowing  Palate  and 

Tonsils 999 

708.  Sagittal    Section    through    Mouth, 

Tongue,    Larynx,    Pliarynx,    and 
Nasal  Cavity         ....     1001 

709.  Horizontal  Section  thioiigli  Mfjuth 

and  Pharynx  at  the  Ijevcl  of  tlie 
TouhIIh 1002 


710.  The   Anterior  Wall  of  the  Phar- 

ynx with  its  Orifices,  seen  from 
behind  

711.  The  Pa])illai  of  Tongue   . 

712.  Open  Mouth  with  Tongue  raised, 

and  the  Sublingual  and  Apical 
Glands  exposed     .... 

713.  Sections      through      the      Tongue 

(Krause) ;  and  Lymjjhoid  Follicle 
from  Back  Part  of  Tongue  (Mac- 
alister) 

714.  Section  of  a  Serous  Gland  and  a 


1003 
1004 


1005 


1006 


LIST  OF  ILLUSTEATIONS. 


FIO. 

Mucous    Gland    (Bolim    and    v.  749. 

Davidoff) 1008 

715.  Horizontal  Section  tlirough  Mouth 
and  Pharynx  at  the  Level  of  the  750. 

Tonsils 1009  | 

716.  The    Salivary    Glands    and    their  \  751. 

Ducts 1010  I 

717.  Teeth  of  a  Child  over  seven  years  i  752. 

old  (modified  from  Testut)    .         .     1014      753. 

718.  Vertical  Section  of  Canine  Tooth   .     1015 

719.  The  Permanent  Teeth  of  the  Right  754. 

Side,  Outer  or  Labial  Aspect        .     1017 

720.  The  Permanent  Teeth  of  the  Right 

Side,  Inner  or  Lingual  Aspect     .  1018  755. 

721.  The  Upper  Permanent  Teeth  .  1018  756. 

722.  The  Lower  Permanent  Teeth  .  1020 

723.  Horizontal  Sections  through  both  757. 

the   Upi^er  and  Lower  Jaws   to 

show  the  Roots  of  the  Teeth         .     1021      758. 

724.  To  show  the  Relation  of  the  Upper 

to   the   Lower   Teeth   when   the 

Mouth  is  closed     ....     1022      759. 

725.  The  Milk  Teeth  of  the  Left  Side    .     1023      760. 

726.  Vertical  Section  of  Canine  Tooth   .     1024 

727.  Diagram  to  illustrate  the  Develop-  761. 

ment  of  a  Dermal  Tooth  in  the 

Shark 1025     762. 

728.  Diagram  to  illustrate  Development  763. 

of  a  Tooth     .         .         .         .         .     1026      764. 

729.  The  Anterior  Wall  of  the  Pharynx  765. 

with  its  Orifices,  seen  from  behind     1030 

730.  Sagittal    Section   through   Mouth, 

Tongue,    Larynx,    Pharynx,  and 

Nasal  Cavity        ....     1031      766. 

731.  The  Naso-pharynx  from  the  Front     1032 

732.  Open  Mouth   showing  Palate  and  767. 

Tonsils 1034 

733.  Horizontal  Section  through  Mouth  768. 

and  Pharynx  at  the  Level  of  the  769. 

Tonsils 1035 

734.  Diagram  to  show  the  Course  of  the  770. 

CEsophagus 1038     771. 

735.  Tracings  from  Frozen  Sections  to  772. 

show  the  Relations  of  the  (Eso-  773. 

phagus 1039 

736.  Dissection  to  show  the  Arrangement  774. 

of  the   Muscular   Fibres  on   the  775. 

Back    of    the     CEsophagus    and 

Pharynx 1041      776. 

737.  The  Lower  Part  of  the  Pharynx  and 

the  Upper  Part  of  the  CEsophagus  1042      777. 

738.  Structure  of  the  CEsophagus   .         .  1042 

739.  The  Abdominal  Viscera  in  situ       .  1044      778. 

740.  The  Front  of  the  Body   .         .         .  1046 

741.  Diagrammatic    Mesial    Section   of  779. 

Female  Body        ....     1048 

742.  Diagrammatic  Transverse  Sections  780. 

of  Abdomen 1049 

743.  Moderately  distended  Stomach        .     1050 

744.  The  Abdominal  Viscera  after  the  re-  781. 

moval  of  the  Jejunum  and  Ileum     1051 

745.  The  Stomach  Chamber  and  Stomach 

Bed 1053      782. 

746.  The   Viscera   and    Vessels   on   the 

Posterior  Abdominal  Wall  .         .     1054      783. 

747.  Longitudinal  Section  through  the 

Pyloric   Canal    and    Commence- 
ment of  the  Duodenum  in  a  New-  784. 
Born  Child 1056  785. 

748.  Abdomen  of  Female,  showing  Dis-  786. 

placements  resulting  from  Tight  787. 

Lacing 1057 


Section  through  Wall  of  Stomach, 
Cardiac  Portion  (slightly  modi- 
fied from  Stijhr) 1058 

The  Three  Layers  of  the  Muscular 

Coat  of  the  Stomach     .         .         .     1059 
Diagram    to    show    Formation    of 

Pylorus 1060 

The  Mucous  Membrane  of  Stomach     1060 
A  Portion  of  Small  Intestine,  with 

Mesentery  and  Vessels  .         .         .     1061 
Diagram  to  show  the  Structure  of 
the    Small  and   Large    Intestine 
and  the  Duodenum       .         .         .     1062 
Valvuhe  Conniventes      .         .         .     1063 
Peyer's  Patch  and  Solitary  Glands 

from  Intestine  of  Child         .         .     1064 
The   Viscera   and   Vessels   on    the 

Posterior  Abdominal  Wall  .         .     1066 
The   Peritoneal    Relations   of    the 
Duodenum,      Pancreas,     Spleen, 

Kidneys,  etc 1067 

The  Duodenal  Fossae  and  Folds      .     1069 
The  Bile  Papilla  in  the  Interior  of 

the  Duodenum      ....     1069 
The  Abdominal  Viscera  after  the  re- 
moval of  the  Jejunum  and  Ileum     1071 
Large  Intestine        ....     1074 
Caecum  showing  Ileo-csecal  Valve  .     1076 
Three  Forms  of  Ileo-caecal  Valve    .     1077 
Diagrammatic  Section  through  the 
Junction  of  Ileum  with  Caecum, 
to   show  the    Formation   of  the 
Ileo-caecal  Valve  .        .        .         .     1078 
The  Blood  Supply  of  the  Caecum 

and  Vermiform  Appendix    .         .     1079 
Structure   of  the  Vermiform  Ap- 
pendix   1080 

The  Cgecal  Folds  and  Fossae  .  .  1081 
The  Abdominal  Viscera  after  the  re- 
moval of  the  Jejunum  and  Ileum  1084 
The  Iliac  and  Pelvic  Colons  .  .  1085 
The  Rectum  from  Behind  .  .  1087 
Distended  Rectum  in  situ  .  .  1088 
The    Peritoneum    of    the    Pelvic 

Cavity 1090 

Diagram  of  Rectum        .         .         .     1093 
The  Interior  of  the  Anal  Canal  and 

Lower  Part  of  Rectum  .         .     1094 

The  Anal  Canal  and  Lower  Part  of 

Rectum  in  the  Foetus  .         .         .     1094 
Diagrammatic    Mesial    Section    of 

Female  Body        ....     1098 
The    Peritoneum    of    the    Pelvic 

Cavity 1100 

Diagrammatic  Transverse  Sections 

of  Abdomen  ....     1101 

The    Peritoneal    Relations    of  the 
Duodenum,     Pancreas,      Spleen, 
Kidneys,  etc.         ....     1103 
Two    Diagrams    to    illustrate   the 
Development    of   the    Intestinal 

Canal 1106 

Two   Diagrams    to    illustrate    the 

Development  of  the  Mesenteries  .     1 107 
Diagrams  to  illustrate  the  Develop- 
ment of  the  Great  Omentum  (after 
Hertwig)       .         ...         .         .1107 

The  Abdominal  Viscera  in  situ       .     1109 
The  Liver  from  the  Front       .         .     1111 
The  Liver  from  Below  and  Behind     1112 
The     Abdominal     and     Thoracic 
Viscera  of  a  Five  Months'  Foetus .     1117 


LIST  OF  ILLUSTEATIONS. 


788.  Structures  between  the  Layers  of 

the  Lesser  Omentum    . 

789.  Diagram    showing    the    Bile    and 

Pancreatic    Ducts    piercing    the 
Wall  of  the  Duodenum  obliquely 

790.  Liver  of  a   Pig  injected  from  the 

Hepatic  Vein  by  T.  A.  Carter 

791 .  Diagrams  illustrating  the  Structure 

of  Liver 

792.  Diagram  illustrating  the  Arrange- 

ment of  the  Blood-Vessels  and  of 


1119 


1120 


1122 


1122 


the  Hepatic  Cells  and  Bile  Ducts 
within  a  Lobule  of  the  Liver       .     1123 

793.  Two  Diagrams  to  illustrate  the  De- 

velopment of  the  Intestinal  Canal     1123 

794.  The   Viscera  and   Vessels   on   the 

Posterior  Abdominal  Wall  .         .     1125 

795.  The   Peritoneal    Relations   of   the 

Duodenum,     Pancreas,      Sjjleen, 
Kidneys,  etc.         .         .         .         .1126 

796.  The  Pancreas  and  Duodenum  from 

Behind 1128 


THE   UEINOGENITAL   SYSTEM. 


797.  Dissection  to  show  the  Position  and 

Relationships  of  the  Kidneys 

798.  Transverse    Section    through    the 

Abdomen   at    the   Level   of   the 
Second  Lumbar  Vertebra     . 

799.  The  Posterior  Relationships  of  the 

Kidneys 

800.  The  Kidneys  viewed  from  Behind  . 

801.  Right  Kidney  and  Duodenum 

802.  Left    Kidney,    the    Pancreas,    the 

Spleen,  and  the  Descending  Colon 

803.  The    Kidneys   and    Great    Vessels 

viewed  from  the  Front 

804.  Longitudinal  Section  through  the 

Kidney 

805.  Section  through  a  Portion  of  the 

Kidney 

806.  Diagrammatic    Representation    of 

the  Structures  forming  a  Kidney 
Lobe 

807.  Longitudinal  Section  of  the  Kidney 

opening  up  the  Kidney  Sinus 

808.  Mesial  Section  of  an  Adult  Male 

Pelvis 

809.  Mesial  Section  through  the  Male 

Pelvis 

810.  Mesial  Section  of  the  Male  Pelvis  . 

811.  Under  Aspect  of  the  Empty  Male 

Bladder         

812.  The  Bladder,  Prostate,  and  Seminal 

Vesicles,  viewed  from  Below 

813.  The  Bladder,  Prostate,  and  Seminal 

Vesicle,  from  the  Outer  Side 

814.  The   Bladder   and   the   Structures 

traversed  by  the  Urethra  in  the 
Male 

815.  Lateral  Aspect  of  Bladder  contain- 

ing ten  ounces  of  Fluid 

816.  View  looking  into  the  Pelvis  from 

Above  and  somewhat  Behind 

817.  View  of  the  Interior  of  the  Bladder 

in  the  Region  of  the  Urethral 
Orifice 

818.  Mesial  Section  of  the  Pelvis  in  an 

Adult  Female       .... 

819.  The  Bladder  of  a  Newly -bom  Male 

Child 

820.  Mesial  Section  through  the  Pelvis 

of  Newly-born  Child    . 

821.  View  looking  from  Above  into  the 

Pelvis  and  Lower  Part  of  the 
Abdominal  Cavity  in  a  Foetus  of 
about  the  Seventh  Month    . 

822.  View  looking  into  the  Male  Pelvis 

Hi-A:]\  from  Above  and  Homcwliat 
Beliind 


823 

1131 

824 

1132 

825. 

826. 

1133 

1134 

827. 

1135 

1135 

828. 

1136 

829. 

1137 

830. 

1138 

831. 

1139 

832. 

1141 

833. 

1142 

834. 

1145 

1146 

1147 

835. 

1147 

1148 

836. 

1149 

837. 

1150 

838. 

1150 

839. 

1151 

1152  • 

840. 

1152 

841. 

1153  ' 

842. 

843. 

1154 

844. 

845. 

il54 

.  Mesial  Section  of  the  Pelvis  in  an 

Adult  Male 1155 

.  Mesial  Section  through  the  Female 

Pelvis 1158 

.  The  Right  Testis  and  Epididymis  .     1159 
.  Right      Testis      within      Tunica 

Vaginalis 1160 

.  Transverse  Section  of  Testis  and 
Epididymis  and  of  Spermatic 
Cord  below  External  Abdominal 

Ring 1161 

.  Diagram  to  illustrate  the  Structure 

of  the  Testis  and  Epididymis      .     1162 
,  The    Peritoneum    of    the    Pelvic 

Cavity 1163 

Horizontal  Section  through  the 
Rectum  and  Bladder    .        .        .     1164 

View -of  the  Base  of  the  Bladder, 
Prostate,  Seminal  Vesicles,  and 
Vasa  Deferentia  from  Behind      .     1165 

The  Bladder,  Prostate,  and  Seminal 
Vesicle  viewed  from  the  Side       .     1166 

The  Seminal  Vesicle  and  the 
Ampulla  of  Vas  Deferens     .         .     1166 

View  looking  from  Above  into  the 
Pelvis  and  Lower  Part  of  the 
Abdominal  Cavity  in  a  Foetus  of 
about  the  Seventh  Month    .         .     1167 

Diagram  to  illustrate  the  Descent 
of  the  Testis  and  the  manner  in 
which  the  Tunica  Vaginalis  is 
derived 1168 

Transverse  Sections  of  Testis  and 
Epididymis,  and  of  Spermatic 
Cord  below  External  Abdominal 
Ring 1169 

Deep  Dissection  of  the  Inguinal 
Region 1169 

Dissection  to  illustrate  the  Com- 
ponent Parts  of  the  Penis    .         .     1171 

A  Longitudinal  Section  of  the 
Terminal  Portion  of  the  Penis, 
and  a  Tranverse  Section  through 
the  Body  of  the  Organ         .         .     1172 

Bladder,  Prostate,  and  Seminal 
Vesicles,  from  the  Outer  Side      .     1173 

Prostate,  Bladder,  and  Seminal 
Vesicles,  seen  from  Below    .        .     1174 

Transverse  Section  through  the 
Prostate 1175 

Transverse  Section  through  the 
Prostate 1176 

The  Bladder  and  the  Structures 
trav(!rsed  by  the  Urethra    .         .     1177 

Mesial  Section  of  an  Adult  Male 
Pelvis 1178 


LIST  OF  ILLUSTEATIONS. 


FIG. 

846 


847. 


849. 
850. 


851. 


853. 


854. 


FIO. 

857. 


The  Prostatic,  Membranous,  and 
the  Upper  Portion  of  the  Spongy 
Urethra        .         .         .         .        \     1178 

A  Longitudinal  Section  of  the  Ter- 
minal Portion  of  the  Penis,  and  a  '  858. 
Transverse  Section  througli  the 
Body  of  the  Organ        .         .         .1180      859. 

Mesial  Section  through  the  Female 
Pelvis 1181      860. 

Side  Wall  of  the  Female  Pelvis      .     1183 

The  Uterus  and  Broad  Ligament, 
and  Diagrammatic  Representa- 
tion of  the  Uterine  Cavity  .         .     1183      861. 

Graafian  Follicle     .         .         .         .1185 
852.  The  Uterus  and  Broad  Ligament,  ' 

and  Diagrammatic   Representa- 
tion of  the  Uterine  Cavity  .         .     1188      862. 

Mesial  Section  of  the  Pelvis  in  an 
Adult  Female       .         .         .         .1193      863. 

The  Vagina,  the  Base  of  Bladder, 
and  the  Recto-vaginal  Pouch  of  i  864. 

Peritoneum  .         .         .         .1194 

855.  Female  External  Genital  Organs   .     1196  |  865. 

856.  Dissection  of  the  Female  External  866. 

Genital  Organs     .         .         .         .     1197  | 


Dissection  of  Female  Perineum  to 
show  the  Clitoris,  the  Bulb  of 
the  Vestibule,  and  Bartholin's 
Glands.  ....     1198 

Development  of  the  Bladder, 
Ureter,  and  Kidney     .         .         .     1199 

Transverse  Section  through  the 
Body  of  a  Fowl  Embryo       .         .1200 

Diagram  to  illustrate  the  Manner 
in  which  the  Ureter,  the  Vas 
Deferens,  and  the  Bladder  arise  in 
the  Embryo 1201 

Diagrammatic  Representation  and 
Comparison  of  the  Manner  in 
which  the  Urinogenital  Passages 
arise  in  the  two  Sexes  .         .         .     1202 

Transverse  Section  through  the 
Body  of  a  Rat  Embryo         .         .     1203 

Development  of  the  External 
Genital  Organs     ....     1205 

External  Genital  Organs  in  Male 
Embryo 1206 

Dissection  of  the  Mammary  Gland     1207 

Section  through  a  Mammary  Gland     1208 


THE  DUCTLESS   GLANDS. 


867.  Dissection  of  the  Spleen,  Liver,  and 

Kidneys  from  Behind  . 

868.  The  Spleen 

869.  Anterior   Surfaces    of    Suprarenal 

Capsules       .        .         .        .         . 

870.  Posterior   Surfaces   of    Suprarenal 

Capsules        .         .         .         .         . 

871.  Transverse    Section    through    the 

Suprarenal   Capsule   of  a   New- 
born Child  in  situ 

872.  Dissection   of   the   Thyroid    Body 


1211 
1212 

1214 

1214 


1215 


and  of  the  Parts  in  immediate  re- 
lation to  it   . 

873.  Thymus  Gland  ina  FuU-timeFcetus 

hardened  by  Formalin-injection  . 

874.  Dissection    to    show   the    Thymus 

Gland  in  an  Adult  Female  . 

875.  Deej)  Surface  of  Thymus  Gland 

876.  Section  through  Carotid  Body 

877.  Schema  of  the  Relation  presented 

by  the  Carotid  Gland  and  its  ac- 
cessory outlying  Parts  to  Branches 
of  middle  Sacral  Artery 


1216 

1218 

1219 
1220 
1221 


1221 


SUEFACE  AND  SURGICAL  ANATOMY. 


878.  Diagrammatic  Representation  of  a 

Coronal  Section  through  the 
Scalp,  Cranium,  Meninges,  and 
Cortex  Cerebri      ....     1223 

879.  Cranio-Cerebral  Topography  .     1226 

880.  Scheme   showing   Relative    Topo- 

graphy of  the  Chief  Subdivi- 
sions of  the  Motor  Area  (adapted 
from  Griinbaum  and  Sherring- 
ton)         1227 

881.  Cranio-Cerebral  Topography  .     1228 

882.  View  of  the   Outer    Wall   of  the 

Middle  Ear  ....     1230 

Left  Tympanic  Membrane  .  .  1230 
View   of  the    Inner   Wall   of  the 

Middle  Ear  ....     1231 

Section    through    Left     Temporal 

Bone,    showing    Outer    Wall    of 

Tymj)anic  Cavity,  etc.  .  .  .  1231 
Section  through  Petrous  Portion  of 

Temporal  Bone  of  Adult      .         .     1232 

887.  Frontal  Sinuses  of  Average  Dimen- 

sions, with  a  Mesial  Septum 
(Logan  Turner)      ....     1234 

888.  A  Large  Right  Frontal  Sinus  with 

Septum  Oblique  to  the  Left 
(Logan  Turner)     ....     1234 


883. 
884. 

885. 


886. 


889.  Right  Frontal  Sinus  of  very  large 

Dimensions ;  Left  Sinus  unopened 
(Logan  Turner)      ....     1235 

890.  Vertical  Coronal  Section  through 

the  Nose  and  Frontal  Sinuses      .     1236 

891.  Head    of    Human    Embryo    about 

29  days  old 1240 

892.  Coronal  Section  through  the  Face  of 

a  Human  Embryo  at  the  Seventh 
Week 1241 

893.  From  a  Photograph  showingDouble 

Complete    Hare  -  LijJ    and    Cleft 
Palate  .....'.     1241 

894.  Shows   arrangement  of    Bones   in 

Double  Cleft  Palate     .         .         .     1242 

895.  Coronal  Section  through  the  Tongue 

and    Submaxillary  Region   in  a 
Plane  behind  the  Molar  Teeth     .     1243 

896.  Open  Mouth  with  Tongue  raised 

and  the  Sublingual  and  Apical 
Glands  exposed     ....     1243 

897.  Horizontal  Section  through  Mouth 

and  Pharynx  at  the  Level  of  the 
Tonsils 1245 

898.  Anterior    Aspect     of     Neck     and 

Shoulders 1247 

899.  Dissection  of  the  Front  of  the  Neck     1248 


LIST  OF  ILLUSTEATIONS. 


XXXIU 


FIO. 

900. 
901. 

902. 


903. 
904. 
905. 
906. 

907. 

908. 
909. 
910. 
911. 
912. 
913. 

914. 

915. 
916. 


PAOE 

Lateral  Aspect  of  Neck  .  .  .  1250 
Anterior  Aspect  of  Trunk,  showing 

Surface  Topography  of  Viscera  .  1254 
Dissection  of  a  Subject  to  show  the 

relations  of  the  two  Pleural  Sacs 

viewed  from  the  Front  .         .     1256 

Anterior  Aspect  of  Trunk,  showing 

Surface  Topography  of  Viscera  .  1257 
Lateral  View  of  the  Right  Pleural 

Sac 1258 

Dissection  of  the  Pleural  Sacs  from 

Behind 1259 

Dissection  from  Behind  to  show  the 

relation  of  the  two  Pleural  Sacs  to 

the  Kidneys  ....     1260 

Posterior  Aspect  of  Trunk,  showing 

Surface  Topography  of  Viscera    .     1261 

1  Relations  of  the  Cavities  and  Valves 
Y  of  the  Heart  to  Anterior  Wall  of 
I    Thorax 1263 

The  Groin 1265 

Anterior  Aspect  of  Trunk,  showing 

Surface  Topography  of  Viscera  .  1268 
Lateral  Aspect  of  Trunk,  showing 

Surface  Topography  of  Viscera  .  1269 
The  Cffical  Folds  and  Fossae  .  .  1273 
The  Blood  Supply  of  the  Ceecum 

and  Vermiform  Appendix    .         .     1274 


FIO.  PAOf: 

917.  Anterior  Aspect  of  Trunk,  showing 

Surface  Topography  of  Viscera    .  1275 

918.  Dissection  of  the  Perineum     .         .  1277 

919.  The  Interior  of  the  Anal  Canal  and 

Lower  Part  of  Rectum  .        .         .  1280 

920.  The  Rectum  from  Behind       .         .1282 

921.  Dissection  of  the  Spleen,  Liver,  aiid 

Kidneys  from  Behind  .         .         .  1286 

922.  Posterior  Aspect  of  Trunk,  showing 

Surface  Topography  of  Viscera    .  1287 

923.  Dissection  of  the  Left  Hypochon- 

drium 1288 

924.  Axilla,  Inner  Aspect  of  Upper  Arm 

and  Elbow 1294 

925.  Extensor  Aspect  of  Upper  Limb     .  1295 

926.  Transverse    Section    through    the 

Bend  of  the  Elbow        .         .         .  1297 

927.  Bend  of  Elbow,  Front  of  Forearm, 

and  Palm  of  Hand        .         .         .1298 

928.  Palm  of  Hand          ....  1299 

929.  Dorsal  Aspect  of  Hand    .         .         .  1300 

930.  Section  through  Thigh  at  the  Level  of 

the  Upper  Part  of  Hunter's  Canal  1303 

931.  Section  through  the  Thigh  immedi- 

ately above  the  Patella         .         .  1304 

932.  The  Thigh  and  Groin     .         .         .  1305 

933.  Anterior  Aspect  of  Knee         .         .  1307 

934.  Outer  Aspect  of  Knee  and  Leg        .  1309 

935.  Outer  Aspect  of  Foot  and  Ankle     .  1310 

936.  Inner  Aspect  of  Foot  and  Ankle     .  1311 


TEXT-BOOK    OF    ANATOMY. 


TEXT-BOOK    OF    ANATOMY 


INTRODUCTION. 

Anatomy  is  a  comprehensive  term,  which  includes  several  closely  related  branches 
of  study.  Primarily  it  is  employed  to  indicate  the  study  of  the  several  parts 
which  build  up  the  body,  and  the  relationship  which  these  present  to  each  other. 
But  during  the  period  of  its  existence  the  individual  exhibits  many  structural 
chanoes:  its  structure  is  not  the  same  at  all  stages  of  its  life.  The  ovum  or 
starting-point  of  every  individual  is  very  different  from  the  finished  organism  as 
represented  by  the  adult,  and  the  series  of  changes  through  which  the  organism 
passes  until  its  structure  is  perfected  and  full  growth  is  attained  constitute  the 
study  of  development.  The  general  term  "  development "  includes  not  only  the 
various  and  striking  structural  changes  which  occur  during  the  intrauterine  life  of 
the  individual,  to  the  study  of  which  the  term  embryology  is  more  specially  applied, 
but  also  many  growth  processes  which  occur  after  birth,  such  as  the  later  stages  in 
the  ossification  and  growth  of  the  bones,  the  eruption  of  the  two  series  of  teeth,  the 
adjustment  of  the  vascular  system  to  its  new  requirements,  etc.  The  actual  obser- 
vation of  the  processes  by  which  the  parts  of  the  body  are  gradually  formed,  and  of 
the  structural  arrangements  by  means  of  which  a  temporary  connexion  is  estab- 
lished between  the  ovum  and  the  mother,  through  which  an  interchange  of 
nutritive  and  other  matters  between  the  two  takes  place,  renders  embryology  one 
of  the  most  interesting  of  all  the  departments  of  anatomy.  The  term  ontogeny  is 
also  used  to  denote  the  development  of  the  individual.  There  is,  however,  another 
form  of  development,  slower,  but  just  as  certain  in  its  processes,  which  affects  not 
only  the  individual,  but  every  member  of  the  animal  group  collectively  to  which  it 
belongs.  The  theory  of  descent  or  evolution  leads  us  to  believe  that  between  man 
of  the  present  day  and  his  remote  ancestors  there  is  a  wide  structural  gap,  which, 
if  the  geological  record  were  perfect,  would  be  seen  to  be  completely  occupied  by 
long-lost  intermediate  forms.  In  the  process  of  evolution,  therefore,  structural 
changes  have  gradually  taken  place  which  have  modified  the  entire  race.  A  more 
or  less  close  or  remote  blood-relationship  links  together  all  the  members  of  the 
animal  kingdom.  These  evolutionary  phases  constitute  the  ancestral  history  or 
phylogeny  of  the  individual.  Ontogeny  and  phylogeny  are  intertwined  in  a 
remarkable  manner,  and  present  certain  extraordinary  relationships.  In  other 
words,  the  ancestral  evolutionary  development  appears  to  be  so  stamj^ed  upon  an 
iri(]ividual  that  it  repeats  certain  of  the  phylogenctic  stages  witli  more  or  less 
clearness  during  the  process  of  its  own  individual  development.  Thus  at  an  early 
l>oriod  in  the  embryology  of  man  we  recognise  evanescent  gill-slits  comparable  with 
those  of  a  fish,  wliilst  a  study  of  the  development  of  his  heart  sliows  that  it  passes 


2  TEXT-BOOK  OF  ANATOMY. 

through  transitory  structural  conditions  in  many  respects  similar  to  the  permanent 
condition  of  tlie  heart  in  certain  of  the  lower  animals.  It  is  in  connexion  with 
this  that  the  phrase  has  arisen  that  every  animal  in  its  individual  development  or 
ontogeny  climbs  up  its  own  genealogical  tree — a  saying  which,  taking  it  even  in 
the  Ijroadest  sense,  is  only  partially  true. 

The  higher  conceptions  of  anatomy,  which  are  obtained  by  taking  a  general 
survey  of  the  structural  aspects  of  the  entire  animal  kingdom,  constitute  morpliology. 
The  morphologist  investigates  the  laws  of  form  and  structure,  and  in  his  generalisa- 
tions he  gives  attention  to  detail  only  in  so  far  as  this  is  necessary  for  the  proper 
establishment  of  his  views.  The  knowledge  of  anatomy  which  is  required  by  the 
student  of  medicine  is  different.  It  is  essentially  one  of  detail,  and  often  details 
important  from  the  practical  and  utilitarian  points  of  view  have  little  or  no 
morphological  value.  This  want  of  balance  in  the  interest  attached  to  anatomical 
facts,  according  to  the  aspect  from  which  they  are  examined,  so  I'ar  from  being 
unfortunate,  affords  the  teacher  the  means  of  making  the  study  of  anatomy  at  once 
fascinating  and  attractive.  Almost  every  fact  which  is  brought  under  the  notice 
of  the  student  cari  be  accompanied  by  a  morphological  or  a  practical  application. 
This  it  is  that  lightens  a  study  which,  presented  to  the  student  of  medicine  in  any 
other  way,  would  be  at  once  dry  and  tedious. 

Certain  terms  employed  in  morphology  require  early  and  definite  explanation. 
These  are  homology,  serial  homology,  and  homoplasy.  The  same  organ  repeated  in 
two  different  animals  is  said  to  present  a  case  of  homology.  But  this  morphological 
identity  between  these  two  organs  must  be  proved  beyond  dispute  before  the 
homology  between  them  can  be  allowed.  In  deciding  this  identity  the  great  and 
essential  test  is  that  the  two  organs  in  question  should  have  a  similar  develop- 
mental origin.  Thus  the  fore-limb  of  a  quadruped  is  homologous  with  the  upper 
limb  of  man ;  the  puny  collar-bone  of  a  tiger,  the  fibrous  thread  which  is  the  only 
representative  of  this  bone  in  the  horse,  and  the  strongly  marked  clavicle  of  the 
ape  or  man,  are  all,  strictly  speaking,  homologous  with  each  other.  Homologous 
oro-ans  in  different  animals  usually  present  a  similar  position  and  a  similar 
structure,  but  not  invariably  so.  It  is  not  uncommon  for  a  muscle  to  wander 
somewhat  from  its  original  position,  and  many  cases  could  be  quoted  in  which 
parts  have  become  completely  transformed  in  structure,  either  from  disuse  or  for 
the  purpose  of  meeting  some  special  demand  in  the  animal  economy.  In  the  study 
of  the  muscles  and  ligaments  instances  of  this  will  be  brought  under  the  notice  of 
tlie  reader.  Identity  or  correspondence  in  the  function  performed  by  two  organs 
in  two  different  animals  is  not  taken  into  consideration  in  deciding  questions  of 
homology.  The  gills  of  a  fish  and  the  lungs  of  a  higher  vertebrate  perform  very 
much  the  same  physiological  office,  and  yet  they  are  not  homologous.  The  term 
analogy  is  often  used  to  express  functional  correspondence  of  this  kind.  Often 
organs  which  perform  totally  different  functions  are  yet  perfectly  homologous. 
Thus  the  wing  of  a  bat  or  the  wing  of  a  bird,  both  of  which  are  subservient  to 
flight,  are  homologous  with  the  upper  limb  of  man,  the  office  of  which  is  the 
different  one  of  prehension. 

In  the  construction  of  vertebrates  and  certain  other  animal  groups  a  series  of 
similar  parts  are  repeated  along  a  longitudinal  axis,  one  after  the  other.  Thus  the 
series  of  vertebrae  which  build  up  the  backbone,  the  series  of  ribs  which  gird  round 
either  side  of  the  chest,  the  series  of  intercostal  muscles  which  fill  up  the  intervals 
between  the  ribs,  the  series  of  nerves  which  arise  from  the  brain  and  spinal  cord, 
are  all  examples  of  this.  An  animal  exhibiting  such  a  condition  of  parts  is  said  to 
present  the  segmental  type  of  organisation,  and  in  the  early  stages  of  development 
this  segmentation  is  much  more  strongly  marked,  and  is  to  be  seen  in  parts  which 


INTIUJDUCTION.  3 

siihsoqueiitly  lose  all  trace  of  such  a  subdivisiou.  The  parts  thus  repeated  are  said 
to  be  serially  homologous.  But  there  are  other  instances  of  serial  homology  besides 
those  which  are  manifestly  produced  by  segmentation.  The  upper  limb  is  serially 
homologous  with  the  lower  limb :  each  is  composed  of  parts  which,  to  a  large 
extent,  are  repeated  in  the  other,  and  the  correct  adjustment  of  this  comparison 
between  the  several  parts  of  the  upper  and  lower  limbs  constitutes  one  of  the  most 
difficult  and  yet  interesting  problems  of  morphology. 

Homoplasy  is  a  term  which  has  been  introduced  to  express  a  form  of  corre- 
spondence between  organs  in  different  animals  which  cannot  be  included  under 
the  term  homology.  Two  animal  groups,  which  originally  have  sprung  from  the 
same  stem-form,  may  independently  develop  a  similar  structural  character  which  is 
altogether  absent  in  the  ancestor  common  to  both.  Thus  the  common  ancestor  of 
man  and  the  carnivora  in  all  probability  possessed  a  smooth  brain,  and  yet  the 
human  brain  and  the  carnivore  brain  are  both  richly  convoluted.  Not  only  this, 
but  certain  anatomists  seek  to  reconcile  the  convolutionary  pattern  of  the  one  with 
the  convolutionary  pattern  of  the  other.  What  correspondence  there  is  does  not, 
in  every  instance,  constitute  a  case  of  homology,  because  there  is  not  in  every  case 
a  community  of  origin.  Correspondence  of  this  kind  is  included  under  the  term 
"  homoplasy."  Another  example  is  afforded  by  the  heart  of  the  mammal  and  that 
of  the  bird.  In  both  of  these  groups  the  ventricular  portion  of  the  heart  consists 
of  a  right  and  a  left  chamber,  and  yet  the  ventricular  septum  in  the  one  is  not 
homologous  with  the  corresponding  septum  in  the  other,  because  the  common 
ancestor  from  which  both  have  sprung  possessed  a  heart  with  a  single  ventricular 
cavity,  and  the  double-chambered  condition  has  been  a  subsequent  and  independent 
development  in  the  two  groups. 

Systematic  Anatomy. — The  human  body  is  composed  of  a  combination  of 
several  systems  of  organs,  and  the  several  parts  of  each  system  not  only  present  a 
certain  similarity  in  structure,  but  also  fulfil  special  functions.     Thus  we  have — • 

1.  The  skeletal  system,  composed  of  the  bones  and  certain  cartilaginous  and 
membranous  parts  associated  with  them,  the  study  of  which  is  known  as  osteology. 

2.  The  articulatory  system,  which  includes  the  joints  or  articulations,  the  study 
of  which  is  termed  arthrology. 

3.  The  muscular  system,  comprising  the  muscles,  the  study  of  which  constitutes 
myology. 

4.  The  nervous  system,  in  which  are  included  the  brain,  the  spinal  cord,  the 
spinal  and  cranial  ganglia,  the  sympathetic  ganglia,  and  the  various  nerves 
proceeding  from  and  entering  these.  The  study  of  these  parts  is  expressed  by  the 
term  neurology.     In  this  system  the  organs  of  sense  may  also  be  included. 

5.  The  vascular  and  lymphatic  system,  including  the  heart,  blood-vessels,  the 
lymphatic  vessels,  and  the  lymphatic  glands.  Angeiology  is  the  term  applied  to  the 
study  of  this  system. 

6.  The  resjdralory  system,  in  which  we  place  the  lungs,  windpipe,  and  larynx. 

7.  The  digestive  system,  which  consists  of  the  alimentary  canal  and  its  associated 
glands,  and  parts  such  as  the  tongue,  teeth,  liver,  pancreas,  etc. 

8.  The  urogenital  system,  composed  of  the  urinary  organs  and  the  reprcxluctive 
organs — tlie  latter  differing  in  the  two  sexes. 

The  term  splanchnology  denotes  the  study  of  the  organs  includcul  in  the 
respiratory,  digestive,  and  genito-urinary  systems. 

9.  The  integumentary  system,  consisting  of  the  skin,  nails,  hair,  etc. 

These  numerous  organs  which  form  the  various  systems  are  themselves  built  up 
of  tissues,  the  ultimat(j  tdenients  of  which  can  only  Ijc  studied  by  the  aid  of  the 


4  TEXT-BOOK  OF  ANATOMY. 

microscope.  The  study  of  these  elements  and  the  manner  in  which  they  are 
grouped  together  to  form  the  various  tissues  of  the  body  forms  an  important  branch 
of  anatomy,  which  is  termed  histology. 

The  structure  of  the  human  body  may  be  studied  in  two  different  ways.  The 
several  parts  may  be  considered  with  reference  to  their  relative  positions,  either  as 
they  are  met  with  in  the  course  of  an  ordinary  dissection,  or  as  they  are  seen  on 
the  surface  of  a  section  through  the  body.  This  is  the  to2wgra2')Jiical  method.  On 
the  other  hand,  the  several  systems  of  organs  may  be  treated  separately  and  in 
sequence.  This  constitutes  the  systematic  method,  and  it  is  the  plan  which  is 
adhered  to  in  this  treatise. 

Descriptive  Terms. — Anatomy  is  a  descriptive  science  founded  on  observation, 
and  in  order  that  precision  and  accuracy  may  be  attained  it  is  absolutely  necessary 
that  we  should  be  provided  with  a  series  of  well-defined  descriptive  terms.  It  must 
be  clearly  understood  that  all  descriptions  are  framed  on  the  supposition  that  the 
body  is  in  the  erect  position,  with  the  arms  by  the  side,  and  the  hands  held  so  that 


Pig.  1. Horizontal  Section  through  the  Trunk  at  the  Level  op  the  First  Lumbar  Vertebra. 

the  palms  look  forwards  and  the  thumbs  outwards.  An  imaginary  plane  of 
section,  passing  longitudinally  through  the  body  so  as  to  divide  it  accurately  into  a 
right  and  left  half,  is  called  the  mesial  plane,  Fig.  1  (M.P.).  When  the  right  and 
left  halves  of  the  body  are  studied  it  will  be  found  that  both  are  to  a  large  extent 
formed  of  similar  parts.  The  right  and  left  limbs  are  alike ;  the  right  and  left 
halves  of  the  brain  are  the  same ;  there  are  a  right  and  left  kidney  and  a  right 
and  left  lung,  and  so  on.  So  far  the  organs  are  said  to  be  symmetrically  arranged. 
But  still  a  large  amount  of  asymmetry  may  be  observed.  Thus  the  chief  bulk  of 
the  liver  lies  to  the  right  side  of  the  mesial  plane,  and  the  spleen  is  an  organ 
which  belongs  wholly  to  the  left  half  of  the  body.  Indeed,  it  is  well  to  state  that 
perfect  symmetry  never  does  exist.  There  always  will  be,  and  always  must  be,  a 
certain  want  of  balance  between  symmetrically  placed  parts  of  the  body.  Thus 
the  right  upper  limb  is,  as  a  rule,  constructed  upon  a  heavier  and  more  massive 
plan  than  the  left,  and  even  in  those  organs  where  the  symmetry  appears  most 
perfect,  as  for  instance  the  brain  and  spinal  cord,  it  only  requires  a  closer  study  to 
reveal  many  points  of  difference  between  the  right  and  left  halves.  The  line 
on  the  front  of  the  body  along  which  the  mesial  plane  reaches  the  surface  is 


INTRODUCTION.  5 

termed  the  anterior  median  line  ;  whilst  the  corresponding  line  Ijehind  is  called  tlie 
posterior  median  line. 

It  is  convenient  to  employ  other  terms  to  indicate  other  imaginary  planes  of 
section  through  the  hody.  The  term  sagittal  is,  therefore,  used  to  denote  any  plane 
which  cuts  through  the  body  along  a  path  which  is  parallel  to  the  mesial  plane 
(S  S') ;  and  the  term  coronal  or  frontal  is  given  to  any  vertical  plane  which  passes 
through  the  body  in  a  path  which  cuts  the  mesial  plane  at  right  angles  (C  C). 
The  term  horizontal  as  applied  to  a  plane  of  section  requires  no  explanation. 

Any  structure  which  lies  nearer  to  the  mesial  plane  than  another  is  said  to  be 
internal  or  mesial  to  it ;  and  any  structure  placed  further  from  the  mesial  plane 
than  another  is  said  to  lie  external  or  lateral  to  it.  Thus  in  Fig.  1,  A  is  external 
to  B ;  whilst  B  is  internal  to  A. 

The  terms  anterior  and  ventral  are  synonymous,  and  are  used  to  indicate  a 
structure  (D)  which  lies  nearer  to  the  front  or  ventral  surface  of  the  body  than 
another  structure  (E)  which  is  placed  nearer  to  the  back  or  dorsal  surface  of  the 
body,  and  which  is  thus  said  to  be  posterior  or  dorsal.  In  some  respects  it  would 
be  well  to  discard  the  terms  "  anterior  "  and  "  posterior  "  in  favour  of  "  ventral " 
and  "  dorsal,"  seeing  that  the  former  are  only  applicable  to  man  in  the  erect 
attitude,  and  cannot  be  applied  to  an  animal  in  the  prone  or  quadrupedal  position. 
They  have,  however,  become  so  deeply  ingrained  into  the  descriptive  language  of 
the  human  anatomist  that  it  would  hardly  be  advisable  at  the  present  moment  to 
adopt  this  course.  A  similar  objection  may  be  raised  to  the  terms  superior  and 
inferior,  which  are  employed  to  indicate  the  relative  levels  at  which  two  structures 
lie  with  reference  to  the  upper  and  lower  ends  of  the  body.  The  equivalent  terms 
of  cephalic  and  preaxial  are,  therefore,  frequently  used  in  place  of  "superior,"  and 
caudal  and  postaxial  in  place  of  "  inferior." 

The  terms  proximal  and  distal  should  only  be  applied  in  the  description  of  the 
limbs.  They  denote  relative  nearness  to  or  distance  from  the  trunk.  Thus  the 
hand  is  distal  to  the  fore-arm,  whilst  the  upper  arm  or  brachium  is  proximal  to  the 
fore-arm. 


GENERAL    EMBRYOLOGY. 

By  Alfeed  H.  Young  and  Arthur  Eobixson. 

Although  the  tissues  and  organs  of  the  body  when  fully  formed  differ  greatly 
not  only  in  respect  of  their  functional  characteristics,  hut  also  with  regard  to  their 
structural  features,  they  are  developed  from  cell  elements  so  similar  in  appear- 
ance at  first  that  they  cannot  be  distinguished  from  one  another.  They  are  all 
the  offspring  of  parent  cells — the  female  cell  or  ovum,  and  the  male  cell  or 
spermatozoon.  Developmental  processes  apparently  take  place  in  the  female  cell 
alone,  but  they  cannot  occur  unless  the  essential  elements  of  a  sperm  or  male  cell 
previously  unite  with  it. 

Like  all  animal  cells,  the  ovum  is  a  mass  of  protoplasm  {cytoplasm)  containing 
a  nucleus.  In  many  cells  the  cytoplasm  or  cell  body  is  itself  enclosed  by  an  ex- 
ternal investing  membrane,  the  cell  wall,  and  such  a  membrane  is  present  in  the 
ovum.  Speaking  generally,  animal  cells  are  minute  structures,  those  of  the 
human  body  rarely  attaining  a  diameter  of  more  than  about  '083  mm.,  but  they 
vary  somewhat  in  size,  they  assume  different  forms,  and  they  acquire  characteristic 
peculiarities  associated  with  their  positions  and  functions  ;  thus,  whilst  the  majority 
of  the  constituent  cells  of  an  individual  form  the  various  tissues  and  organs  of  the 
body,  others  are  reproductive  or  germinal  cells. 

Ova  are  simply  specialised  cells  modified  and  adapted  for  the  purpose  of  repro- 
duction and  the  continuance  of  the  species.  They  are  enclosed,  and  partially  or 
entirely  matured,  in  the  ovaries,  or  female  generative  glands,  in  the  cell-lined 
spaces  know^n  as  Graafian  follicles. 

When  an  ovum  has  reached  a  certain  stage  of  development  it  is  discharged  from 
the  ovary,  and  passing  along  the  oviduct  or  Fallopian  tube  it  eventually  reaches 
the  cavity  of  the  uterus.  Though  mature  and  capable  of  being  fertilised  it  may 
not  be  impregnated,  in  which  case  it  does  not  remain  in  the  uterus,  but  is  cast  out 
from  that  organ.  If,  however,  it  becomes  fertilised,  by  union  with  the  male 
germinal  element,  it  is  retained  in  the  uterus,  and  develops  into  an  embryo  which 
possesses  all  the  characteristic  features  of  the  species  to  which  it  belongs  and  most 
of  the  special  j)eculiarities  of  its  parents. 

When  the  embryo,  or  the  foetus  as  it  is  termed  after  it  has  assumed  definite 
form,  is  capable  of  independent  existence,  its  intrauterine  life  terminates,  and 
it  is  separated  from  the  rest  of  the  ovum  and  is  born.  The  development  of  the 
individual,  however,  is  not  complete,  nor  does  it  become  complete  until  the  new 
being  reaches  the  adult  condition. 

The  term  embryology  is  sometimes  used  to  include  the  consideration  ol'  all  the 
developmental  changes  and  j)rocesses  which  take  place  in  the  ovum  from  the  begin- 
ning up  to  the  final  adult  stage.  It  is  more  convenient,  however,  to  restrict  its 
a])plication  to  the  study  of  those  changes  which  take  place  during  the  development 
and  growth  of  the  organism  before  the  ffjctus  is  separated  i'rom  the  rest  of  the 
ovum,  or,  in  other  words,  during  its  intrauterine  existence. 

r.riefiy  epitomised,  the  sequence  of  changes  is  as  follows : — Inqn-eguatioji  of  the 
mature  ovum  is  followed  by  segmentation  or  cleavage.  By  a  series  of  successive 
divisions  the  egg-cell  is  divided  into  two,  four,  eight,  and  ultimately  into  a  large 

7 


8  GENERAL  EMBEYOLOGY. 

number  of  cells,  and  so  is  transformed  into  a  multicellular  mass,  the  morula.  The 
majority  of  the  "  segmentatinn  masses  "  or  cells,  or  blastomeres,  as  they  are  termed, 
are  differentiated  into  tissue  elements,  but  a  certain  number  retain  the  characters 
of  the  original  germ-cells  and  become  ova  or  sperm-cells,  which  form  the  "points 
of  departure "  of  succeeding  generations.  Every  germ-cell  is  derived,  therefore, 
"  by  a  continuous  and  unbroken  series  of  cell-divisions "  which  have  extended 
through  the  past  from  the  most  primitive  ancestor,  and  it  forms  a  point  from 
which,  under  ordinary  circumstances,  all  future  generations  will  commence.  It  is 
in  this  sense  that  the  changes  through  which  a  living  being  passes  in  the  course 
of  its  life  "  may,  in  their  completest  form,  be  considered  as  constituting  a  morpho- 
logical cycle,  beginning  with  the  ovum  and  ending  with  the  ovum  again." 

To  follow  these  changes  it  is  necessary  that  the  characters  and  capabilities  of 
the  constructive  elements  should  be  clearly  understood.  The  animal  cell,  which 
plays  an  all-important  part  in  the  life-history  of  the  individual,  and  the  modified 
germ-cells  must  be  carefully  studied,  and  as  far  as  possible  the  exact  nature  of 
their  constituent  parts  ascertained. 

The  phenomena  of  impregnation  and  segmentation,  and  the  subsequent  develop- 
mental processes  and  morphological  changes  which  result  in  the  formation  of  the 
embryo,  and,  finally,  the  arrangements  for  the  nutrition  and  protection  of  the  ovum 
during  its  intrauterine  existence,  will  then  he  considered. 


THE   ANIMAL   CELL. 

Cells  are  the  structural  units  of  the  body.  Each  cell  has  an  individual  life- 
history  within  the  tissue  or  organ  to  which  it  belongs,  it  is  produced  by  a  pre- 
existing cell,  it  develops  and  grows,  is  modified  by  circumstances,  reproduces  other 
cells  similar  to  itself,  or  it  dies. 

A  cell  possesses  a  body  and  a  nucleus.  An  external  investing  membrane 
or  cell  wall  may  or  may  not  be  differentiated. 

The  cell  body  consists  of  proto- 
Nucieoiu',  -     „  ^  ^     ^    spongiopiasm        plasui — an  Unstable,  highly  complex 

(cyto-reticuium)  Qrgauic  substaucc,  the  constitution 
of  which  is  approximately  repre- 
sented by  the  formula  C^QH^ogN^gOcf,. 
It  is  colourless,  semi-fluid,  viscous, 
insoluble  in  water,  capable  of 
osmosis,  and  it  is  contractile  and 
irritable.  In  the  living  condition 
it  always  contains  a  certain  amount 
of  water  and  various  inorganic 
matters.  It  is  to  be  observed,  how- 
ever, that  there  are  many  varieties 


Nucleai  ^- 
membrane 


— ' Hyaloplasm 


Attraction  sphere 


Centrosome 


Fig.  2. — Diagram  op  an  Animal  Cell. 


of  protoplasm,  differing  somewhat  in  nature  and  qualities, 

The  protoplasm  of  the  cell  body  is  called  cytoplasm.  Under  low  powers  of  the 
microscope  it  is  homogeneous  or  slightly  granular,  but  with  higher  magnification, 
and  especially  after  the  application  of  staining  agents,  it  is  possible  to  distinguish — 

(1)  A  highly  refractile,  elastic,  and  extensile  netv^ork — the  cy  to -reticulum  or 

spongiopiasm — the  meshes  of  which  are  filled  with 

(2)  A  clear,  semi-fluid  substance — the  cytolymph  or  hyaloplasm. 

The  fibres  of  the  reticulum  present  some  few  minute  rounded  bodies  of  doubtful 
nature,  which  are  termed  microsomes. 

The  nucleus  is  a  spherical  vesicle  embedded  in  the  cell  body.  It  is  surrounded 
by  a  distinct  nuclear  membrane,  and  usually  contains  nucleoli. 

It  consists  of  modified  protoplasm,  which  is  termed  karyoplasm,  the  precise  rela- 
tion of  which  to  the  cytoplasm  is  not  clear.  Structurally  it  resembles  cytoplasm  in 
that  it  presents  a  fine  reticulum,  the  fibres  of  which  seem  to  be  continuous  with 
the  cyto-reticulum  through  the  nuclear  membrane,  whilst  its  meshes  are  occupied 
by  nuclear  juice. 


THE  ANJMAL  CELL.  9 

The  reticulum  forms  a  fine  network  composed  of  linin  fibres  (acliromatic 
substance).  There  is  also  a  coarser  network,  more  readily  stainable,  consisting  of 
chromatin,  granular  portions  of  which  may  also  be  embedded  in  the  linin.  Instead 
of  forming  a  coarse  network  the  chromatin  may  be  arranged  in  the  form  of  a  con- 
voluted cord,  or  as  a  number  of  separate  filaments,  and  in  certain  cases  it  constitutes 
a  series  of  loops  from  which  secondary  branches  are  projected,  the  apices  of  the 
loops  being  grouped  together  at  one  pole  of  the  nucleus  round  a  clear  area  known 
as  the  "  polar  field." 

The  nuclear  membrane  consists  of  both  chromatin  and  linin. 

Nucleoli  are  of  two  kinds,  true  and  false.  A  true  nucleolus  is  a  small,  retractile 
particle,  of  spherical  outline,  embedded  in  the  reticulum.  It  stains  deeply,  and  is 
said  to  consist  of  a  special  modification  of  the  karyoplasm  which  is  called  pyrenin. 
False  nucleoli  are  simply  the  nodes  of  the  chromatin  reticulum. 

The  nucleus  is  capable  of  motion ;  it  has  been  seen  to  alter  its  shape  in 
the  living  cell,  and  it  undoubtedly  plays  an  active  part  in  the  process  of  cell 
reproduction. 

In  addition  to  the  nucleus  many  cells  contain  one  or  more  small  rounded  bodies 
called  centrosomes.  The  centrosomes  are  modified  portions  of  the  protoplasm,  and 
they  lie,  as  a  rule,  in  a  modified,  clear-looking  area  of  the  cytoplasm,  which  is 
known  as  the  attraction  sphere.  This  is  generally  situated  close  to  the  nucleus, 
and  from  its  surface  a  number  of  fine  radiating  lines  project  into  the  adjacent 
cytoplasm. 

Centrosomes  become  very  evident  when  reproduction  commences,  but  are  not 
so  distinct  at  other  times. 

The  attraction  sphere  also  becomes  more  evident  when  cell-division  commences, 
and  the  radii  which  project  from  it,  as  well  as  the  contained  centrosome,  appear  to 
play  important  parts  in  the  reproductive  process. 

Reproduction  of  Cells. — Cell  division  or  reproduction  may  take  place  either — 

1.  By  direct  division — amitosis  ; 

2.  By  indirect  division — mitosis  or  karyokinesis. 

In  the  amitotic  or  direct  form  of  division  the  nucleus,  and  then  the  cell  body, 
are  equatorially  constricted,  the  constrictions  deepen  until  both  are  completely 
divided,  and  so  two  daughter  cells  are  produced.     Apparently  the  attraction  sphere 


Fio.  .3. — Cell  Division. 

Successive  stages  of  mitosis  or  karyokinesis  (diagrammatic,  modified  I'mni  liiiiiicffny).  A,  B,  C,  D,  iind  K 
illustrate,  till;  plieiioiiiciia  of  tlin  piopliasu  ;  F  tliose  of  the  metai)lia.sc'.  ;  (J  and  I!  tliosu  of  tlic  aiuijiliase  ; 
.J,  K,  aud  I>  tlio.so  of  till!  t(',lo|)lia.sc. 

and  centrosome  Jjlay  some  part   in    this   ])rocess,  Init  wbetlior  thciir  innnence   is 
initiative  or  directive  is  unknown. 

Mitosis,   the  process  of  indirect  division,   is  by   r;i,r  the  iiiosl,  coninidn   nioih;  of 


10  GENEEAL  EMBEYOLOGY. 

cell-division.  It  is  a  complex  process,  and  the  phenomena  observable  during  its 
progress  are  classified  into  four  groups :  (1)  the  pro])hase,  (2)  the  metaphase,  (3)  the 
anaphase,  and  (4)  the  telophase. 

The  phenomena  of  the  p)i'ophase  commence  with  the  division  of  the  centrosome 
and  attraction  spliere  into  two  parts  which  travel  to  opposite  poles  of  the  nucleus. 
At  tlie  same  time  the  reticulum  of  the  nucleus  disappears,  and  in  its  place  a  con- 
voluted cord  of  chromatin,  tlie  skein  or  spirem,  is  formed  (Fig.  3,  A,  B,  and  C) ; 
this  is  afterwards  broken  up  into  a  number  of  segments  which  may  be  mere  rods, 
but  which  more  frequently  have  the  form  of  V-shaped  loops  (Fig.  3,  D).  The 
nucleoli  disappear,  and  some  of  the  filaments  which  radiate  I'rom  the  newly-formed 
atti'action  spheres  seem  to  penetrate  the  nuclear  membrane  at  the  poles  of  the 
nucleus.  The  nuclear  membrane  subsequently  disappears,  and  the  filaments 
passing  from  the  attraction  spheres  into  the  nucleus  form  two  cones,  the  bases  of 
which  meet  at  the  equator  of  the  nucleus,  where  they  fuse  together,  forming  an 
achromatic  spindle  which  extends  between  the  two  attraction  spheres  (Fig.  3,  E). 

The  loops,  or  rods,  of  chromatin  are  gradually  grouped  at  the  equator  of  the 
spindle,  each  rod,  or  chromosome,  being  apparently  connected  with  one  of  the 
achromatic  fibrils ;  and  the  prophase  is  completed. 

In  the  metaphase  each  chromosome  is  split  longitudinally  into  two  halves — 
daughter  chromosomes — which  separate  from  one  another ;  the  separation  com- 
mences at  the  apex  of  each  V-shaped  chromosome,  which  appears  to  be  attached  to 
an  achromatic  fibril  (Fig.  3,  F). 

In  the  anap)hase  the  daughter  chromosomes  pass  to  the  opposite  poles  of  the 
spindle.  It  is  suggested  that  this  movement  is  brought  about  by  the  contraction 
of  the  spindle  fibrils,  but  this  is  doubtful,  though  it  is  noteworthy  that  in  some 
cases  fine  achromatic  fibrils  connecting  the  separated  daughter  chromosomes  are 
present  (Fig.  3,  G  and  H).  Slightly  before,  or  simultaneously  with,  the  completion 
of  the  anaphase  the  cell  body  is  equatorially  constricted. 

During  the  telophase  the  constriction  deepens  and  the  cell  is  divided  into  two 
daughter  cells.  Whilst  this  division  is  taking  place  the  daughter  chromosomes, 
which  are  grouped  in  the  neighbourhood  of  each  attraction  sphere  at  opposite  ends 
of  the  spindle,  unite  into  a  convoluted  cord,  round  which  a  nuclear  membrane  is 
formed,  whilst  the  cord  is  converted  into  a  reticulum,  and  nucleoli  appear  (Fig.  3, 
J,  K,  L).  Therefore  when  the  separation  of  the  daughter  cells  is  completed,  at  the 
end  of  the  telophase,  each  possesses  all  the  characteristic  features  of  the  mother  cell. 

Reproductive  Cells. — The  germinal  elements,  the  union  of  which  is  essential 
to  the  formation  of  a  new  being,  are  the  ovum  or  female  element,  and  the  sperma- 
tozoon or  male  element. 

THE  OVUM. 

Structurally  an  ovum  presents  all  the  characteristic  features  of  a  typical  cell. 
It  is  peculiar  because  of  the  large  size  of  the  nucleus  and  nucleolus  and  in  the 
possession  of  two  investing  membranes,  an  inner  one,  the  vitelline  membrane, 
which  corresponds  to  the  cell  wall,  and  an  outer  one,  the  oolemma  or  zona  pellucida. 
Moreover,  the  nucleus  always  occupies  an  excentric  position  in  the  cytoplasm,  and 
the  cell  body  contains  nutritive  material  in  the  form  of  yolk  granules. 

The  constituent  parts  of  an  ovum  have  received  distinctive  names,  however ; 
thus  the  cell  body  is  known  as  the  yolk  or  vitellus,  the  nucleus  is  termed  the 
germinal  vesicle,  and  the  true  nucleolus  is  called  the  germinal  spot. 

Vitellus  or  Yolk. — The  body  of  the  ovum,  consisting  as  in  an  ordinary  cell  of 
cytoplasm  resolvable  into  reticulum  and  cytolymph,  contains  also  numerous  granules 
of  small  but  varying  size  called  yolk  granules.  These  are  highly  retractile,  fatty, 
and  albuminoid  bodies  containing  phosphorus  and  mineral  salts ;  collectively  they 
constitute  the  deutoplasm  or  nutritive  yolk,  in  contradistinction  to  the  cytoplasm  or 
formative  yolk. 

Xutritive  or  food  yolk  plays  an  important  part  in  development.  In  some 
animals  it  is  the  only  means  of  support  for  the  embryo  in  the  early  stages  of 
development ;  in  most  mammals,  on  the  other  hand,  the  embryo  is  supplied  almost 
from  the  first  with  food  not  from  the  egg  itself,  but   directly  from  the  motb.er 


THE  OVUM. 


11 


through  the  placenta.     The  amount  of  deutoplasm  present  in  the  ova  ol'  different 
animals  therefore  varies  greatly. 

Ova  in  which  there  is  no  deutoplasm  are  spoken  of  as  alecithal.     Such  ova,  if 
they  exist,  are  very  rare  ;  most  of  those  usually  classed  under  this  head  undoubtedly 
contain  a  certain  amount  of  deutoplasm  granules  scattered  throughout  the  cyto- 
plasm, and   are  better  described    by  the 
term  oligolecithal.     The  size  of  an  ovum 
is  determined  by  the  amount  of  food  yolk 
present,  and  all  oligolecithal  ova  are  small; 
the  human  ovum,  which  may  be  taken  as 
a  type  of  the  class,  is  about  '2  mm.,  or 
-j-i^th  of  an  inch  in  diameter. 

As  the  deutoplasm  is  increased  in 
amount  the  ovum  is  increased  in  size. 
The  deutoplasm  also  tends  to  accumulate 
in  certain  situations ;  if  the  accumulation 
is  at  one  extremity  of  the  cell  the  ovum 
is  described  as  telolecithal ;  such  ova  are 
naturally  divisible  into  two  areas  or  poles, 
a  cytoplasmic  or  formative  pole,  and  a 
deutoplasmic  or  nutritive  pole. 

In  eutelolecithal  ova  the  deutoplasn] 
almost  entirely  displaces  the  cytoplasm 
from  one  pole,  as  in  the  egg  of  the  fowl, 
in  which  the  cytoplasm  is  represented  by 
a  disc  spread  over  one  pole  of  a  large 
deutoplasmic  mass.  In  many  of  the 
arthropoda  the  deutoplasm  accumulates  at 
the  centre  of  the  ovum,  which  is  there- 
fore termed  centrolecithal. 

The  germinal  vesicle  or  nucleus  of 
the  human  ovum  is  about  '05  mm.  or  --o~oth  of  an  inch  in  diameter,  i.e.  \  the 
diameter  of  the  whole  ovum.  It  lies  excentrically  in  the  yolk,  and  has  the  usual 
characters  of  a  cell  nucleus,  i.e.  it  possesses  a  nuclear  membrane  within  which  is 
the  karyoplasm,  divisible  into  reticulum  or  nucleoplasm,  and  nuclear  juice.  The 
nucleoplasm  consists  of  chromatin  and  achromatic  fibres  (linin),  and  the  nuclear 
juice  contains  one  or  more  spherical  and  highly  refractile  true  nucleoli  or  germinal 
spots ;  the  nodes  of  the  reticulum  constitute  false  nucleoli. 

In  addition  to  the  nucleus,  the  vitelhis,  at  certain  periods,  also  contains  a  structure 
known  as  the  vitelline  body,  body  of  Balbiani,  or  accessory  nucleus.  It  is  readily  seen 
in  young  OA'a  lying  near  the  nucleus.  It  contains  one  or  more  centrosomes,  and  probably 
represents  an  attraction  sphere. 

Vitelline  Membrane.  — -  The  vitelline  membrane  is  simply  the  peripheral 
portion  of  the  vitellus,  modified  and  transformed  into  a  fine  structureless  envelope 
which  covers  the  outer  surface  of  the  yolk.  It  is  usually  closely  applied  to  the 
inner  aspect  of  the  outer  membrane,  the  zona  pellucida,  and  is  best  seen  in  the 
dead  ovum  and  after  treatment  by  reagents.  It  is  therefore  thought  by  some  to 
be  merely  a  condensation  of  the  outer  part  of  the  vitellus  produced  by  the  action  of 
the  reagents.  There  is  evidence,  however,  to  show  that  it  is  present  in  the  normal 
living  ovum. 

Zona  Pellucida  or  Oolemma. — This  membrane  is  thick,  tough,  and  refractile. 
It  serves  as  a  protective  covering  f(jr  the  ovum,  and  persists  for  a  considerable 
liuK;  after  fertilisati(m,  only  disappearing  when  the  ovum  becomes  attached  to 
the  uterus.  It  is  perforated  by  numerous  fine  canals,  which  give  to  the  broad  clear 
.  membrane  a  finely  striated  aytpearance,  from  which  circumstance  it  has  been  called 
i,li(!  "zona  striata."  The  zona  ]Killucida  is  not  formed  by  the  ovum,  but  is  secreted 
i)y  th(j  cells  of  tin;  Graafian  folli(;le  in  which  tin;  ovum  lies;  it  is  consequently 
r(!gurded  as  a  secondary  membrane,  and  is  altogether  different  irom  the  vitelline 


Fig.  4. — The  Ovum  and  its  Coverinc!S 
(Diagrammatic). 

The  corona  radiata,  which  completely  surrounds  the 
ovum,  is  ouly  represented  in  the  lower  part  of 
the  figure. 

1.  Corona  radiata.  5.  Vitellus  or  Yolk. 

2.  Granular  layer.  ti.  Germinal  vesicle  (nucleus). 

3.  Vitelline  membrane.  7.  Germinal  spot  (nncleolus). 

4.  Zona  pellucida  (oolemma).  8.  Nuclear  membrane. 


12 


GENEEAL  EMBEYOLOGY. 


membrane.  The  perforatious  in  the  zona  serve  for  the  passage  of  nutritive 
material  to  the  ovum. 

When  the  ovum  leaves  the  Graafian  follicle  it  is  surrounded  by  several  layers 
of  cells,  the  innermost  of  vi^hich  are  columnar.  They  are  derived  from  the  cells  of 
the  follicle,  and  collectively  constitute  the  corona  radiata ;  the  cells  gradually 
diminish  in  size,  and  ultimately  disappear.  Their  function  is  unknown,  but 
between  them  and  the  zona  pellucida  there  is  a  layer  of  granular  matter,  proljably 
formed  by  the  cells  of  the  corona  radiata,  which  rapidly  swells  up  when  the  ovum 
is  liberated  from  the  follicle,  and  forms  a  gelatinous  elastic  layer  called  the  albumen  ; 
this  increases  in  thickness  as  the  ovum  passes  along  the  oviduct,  and  persists  for 
some  time  after  it  enters  the  uterine  cavity.  The  function  of  the  albumen  has  not 
been  definitely  ascertained ;  it  may  act  merely  as  a  protective  covering  against 
undue  pressure,  possibly  it  may  be  nutritive,  whilst  in  the  dog  it  apparently  helps 
to  fix  the  ovum  to  the  wall  of  the  uterus.  It  has  not  been  found  in  all  mammalian 
ova,  and  it  has  not  been  seen  round  the  human  ovum ;  still  it  may  be  present,  for 
human  ova  at  the  stage  when  it  might  be  expected  to  develop  have  not  yet  been 
observed. 

Special  Characters  of  the  Ovum. — The  ovum  as  it  lies  in  the  Graafian 
follicle  presents  no  obvious  structural  modifications  when  compared  with  an 
ordinary  animal  cell,  but  undoubtedly  differs  greatly  in  its  capabilities  and  life 
history.  Unlike  an  ordinary  cell,  it  has  no  inherent  power  of  division  into  two 
equal  parts,  but  before  it  is  capable  of  fertilisation  it  twice  undergoes  unequal 
division  during  the  period  of  ripening  or  maturation ;  again,  its  history  is  different 
from  that  of  ordinary  tissue  cells,  though  it  corresponds  closely  with  that  of  the 
male  germinal  elements  or  spermatozoa. 

Maturation  of  the  Ovum. — As  it  lies  in  the  Graafian  follicle  before  nuitura- 


D  E  P 

Fio.  5. — The  Maturation  of  the  Ovum  :   Extrusion  of  the  "  Polar  Bodies  "  (Diagrammatic). 

A,  An  ovum  at  the  commencement  of  the  process  ;  B,  After  the  formation  of  the  spindle.  The  chromosomes 
are  gathered  at  the  equator  of  the  spindle.  C,  One  apex  of  the  spindle  has  projected  into  a  bud  on  the 
surface,  and  half  of  the  divided  dyads  have  pas.sed  to  each  pole  ;  D,  The  se]iaration  of  the  first  polar 
hody  ;  E,  The  commencement  of  the  second  polar  body  ;  F,  The  completion  of  the  second  polar  body. 

tion  commences,  the  ovum  is,  strictly  speaking,  an  oocyte  of  the  first  order,  derived 
by  a  process  of  cell -division  and  growth  from  a  primitive  germinal  cell  which 
became  embedded  in  the  ovary.  The  more  direct  descendants  of  this  primitive 
germ  cell  are  called  oogonia,  and  from  them  oocytes  of  the  first  order  are  developed. 


THE  OVUM.  13 

The  oocyte  of  the  first  order  is  at  first  small,  but  as  the  Graafian  follicle  in  which 
it  lies  grows  the  oocyte  also  increases  in  size,  and  either  before  or  immediately 
after  its  extrusion  from  the  follicle  it  undergoes  the  changes  which  constitute 
maturation  or  preparation  for  fertilisation ;  in  other  words,  it  divides  twice  into 
unequal  parts  by  a  modified  process  of  mitotic  division. 

It  is  a  well-known  fact  that  all  animal  cells  contain  in  their  nuclei  a  definite 
number  of  chromosomes,  the  number  varying  in  different  groups  of  animals,  but 
being  constant  in  any  given  species,  and  both  the  primitive  germ  cells  and  the 
oogonia  descended  from  them  contain  the  same  number  of  chromosomes  as 
ordinary  tissue  cells.  But  when  the  oocyte  of  the  first  order  begins  to  prepare  for 
the  first  division  during  the  process  of  maturation,  it  is  seen  that  the  number  of 
chromosomes  it  contains  is  only  half  that  of  the  ordinary  tissue  cells.  Moreover, 
the  chromosomes  are  not  slender  V-shaped  loops,  but  short,  thick  rods  in  rings  or 
groups  of  four  granules,  and  if  they  are  rod-like  they  do  not  lie  in  the  prophase  with 
their  long  axes  at  an  angle  with  the  achromatic  spindle,  as  in  ordinary  mitosis,  but 
parallel  with  the  filaments  of  the  spindle.  During  the  metaphase  the  chromosomes 
do  not  split  longitudinally  as  in  ordinary  mitosis,  but  transversely.     This  modifica- 


Oocyte  of  1st  order 


Oocyte  of  2iid  order 


l«t  polar  body 


Descendant  of 
1st  polar  body 

Mature  ovum 

Fig.  6. — Diagram  illustrating  the  Maturation  of  the  Ovum.     It  must  be  remembered  that  iu  some 
cases  only  one  polar  body  is  formed,  and  in  others  the  first  polar  body  does  not  divide  into  two  parts. 

tion  of  ordinary  or  homotype  mitosis  is  known  as  heterotype  mitosis ;  it  takes  place 
not  only  in  oocytes  of  the  first  order  at  the  commencement  of  maturation,  but  also 
in  the  cells  of  malignant  tumours,  and  its  exact  signification  is  not  understood. 
If  we  imagine  that  the  nuclei  of  the  tissue  cells  of  the  animal  with  which  we  are 
dealing  contain  six  chromosomes  each,  then  at  the  commencement  of  the  first 
maturation  division  of  the  oocyte  only  three  chromosomes  will  be  seen  on  the 
spindle  which  forms.  The  spindle  at  its  appearance  is  parallel  with  one  surface 
of  the  ovum,  but  it  gradually  rotates  till  it  stands  at  right  angles  to  the  surface 
upon  which  it  impinges,  pushing  a  small  part  of  the  cytoplasm  before  it  in  the 
form  of  a  small  bud  (Fig.  5,  B  and  C).  In  the  anaphase  the  chromosomes  divide 
transversely,  and  three  half  chromosomes  pass  to  the  inner  end  of  the  spindle  and 
three  to  the  outer  end,  that  is,  into  the  bud-like  projection.  When  the  teloi)haso 
is  compk;ted  the  oocyte  of  the  first  order  is  divided  into  a  small  ]);i,rt,  the  first  polar 
body,  and  a  larger  part,  th(!  occyte  of  the  second  order,  and  each  contains  three 
f:hroinoHomcs  fKig.  5,  \)).  Almost  inimediHtely  the  hoterotype  division  is  followed  in 
the  oocyte  of  the  second  order  by  a  homotype  division,  no  resting  stage  interven- 
ing. A  n(!W  spindle  appears,  the  throe  {;hromosomes  radiate  from  its  equator 
in    the    usual    way,    and    tliey    (h'vidc    hjngitudinally.      Three    of    the    daughter 


14  GENEEAL  EMBEYOLOGY. 

chromosomes  pass  to  the  inner  end  of  the  spindle  and  three  to  the  outer,  which 
projects  into  a  second  polar  bud.  Division  u(av  occurs,  and  the  oocyte  of  the 
second  order  divides  into  the  mature  ovum  and  the  second  polar  body,  each  of  which 
contains  three  chromosomes  in  its  nucleus  (Fig.  5,  E  and  ¥).  Thus  at  the  end  of 
maturation  there  lie  within  the  zona  pellucida  the  mature  ovum  and  two  polar 
bodies,  and  the  nucleus  of  the  mature  ovum,  or  female  pronucleus  as  it  is  called, 
contains  half  the  number  of  chromosomes  which  were  present  in  the  primitive 
germ  cell.^ 

THE   SPEEMATOZOON. 

Spermatozoa  are  modified  cells  produced  in  the  testicles  or  male  generative 
glands.  They  are  formed  from  the  spermatogonia  or  sperm  mother  cells  wliich  are 
derived  from  the  primitive  germ  cells  of  the  testicle,  and  which  ultimately  produce 
the  spermatocytes  of  the  first  order  (Fig.  7),  the  latter  constituting  the  immediate 
point  of  departure  in  the  production  of  a  spermatozoon,  and  corresponding  therefore 
with  the  ovum  or  oocyte  of  the  first  order  immediately  before  its  maturation 
commences.  The  daughter  cells  of  the  spermatocytes  of  the  first  order  are 
spermatocytes  of  the  second  order,  and  their  descendants  the  spermatids  are  the 
granddaugliter  cells  of  the  spermatocytes  of  the  first  order.  The  spermatids 
become  closely  associated  with  special  sustentacular  or  nurse  cells,  and  during  this 
association  are  converted  into  spermatozoa. 

Each  spermatid  is  a  cell  possessing  a  cell  body,  a  nucleus,  two  centrosomes,  and 
a  structure  known  as  an  idiosome.     The  latter  is  believed  by  some  authorities  to 


Spermatocyte  of  1st  order 


Spermatid  Spermatid  Spermatid  Spermati 


Fig.  7. — Diagram  illustratinc;  the  Process  of  Cell-Division  resulting  in  the  Formation  of 
Spermatids  which  are  afterwards  modified  into  Spermatozoa. 

represent  the  attraction  sphere,  whilst  others  look  upon  it  as  a  special  modification 
of  the  protoplasm  only  established  during  the  process  of  mitosis,  and  distinct  from 
the  attraction  sphere.  However  this  may  be,  the  nucleus  of  the  spermatid  becomes 
the  liead  of  the  spermatozoon  (Fig.  9).  The  idiosome  forms  the  head  cap,  a  tail 
filament  grows  out  from  the  region  of  the  centrosomes,  and  the  body  of  the 
spermatid  forms  part  if  not  all  of  the  neck,  body,  tail,  and  end  piece  of  the 
spermatozoon.  The  centrosomes  become  embedded  in  the  neck,  one  at  its  cephalic 
and  the  other  at  its  caudal  end.  The  axial  filament  is  closely  connected  with 
the  posterior  centrosome,  which  has  possibly  united  with  the  cytoplasm  in  its 
formation. 

^  In  the  mouse,  and  probably  also  in  some  other  mammals,  only  one  polar  body  is  formed  in  mnny  cases. 


THE  SPERMATOZOON. 


15 


There  is  no  doubt  that  the  mature  ovum  and  the  spermatozoon,  so  far  as  their 
development  is  concerned,  are  very  similar.  Each  is  derived  from  a  primitive 
germ  cell,  which  becomes  embedded  in  the  generative  gland.  From  the  primitive 
germ  cell  in  the  one  case  oogonia  are  formed  and  in  the  other  spermatogonia,  and 
from  the  oogonia  and  spermatogonia  respectively  oocytes  and  spermatocytes  of  the 
first  order  are  derived.  The  oocyte  of  the  first  order  divides  by  heterotype  mitosis 
into  an  oocyte  of  the  second  order  and  the  first  polar  body,  and  the  spermatocyte 
of  the  first  order  divides,  also  by  heterotype  mitosis,  into  two  spermatocytes  of  the 
second  order.  By  a  second  and  homotype  mitosis  the  oocyte  of  the  second  order 
divides  into  a  mature  ovum  and  a  second  polar  body,  and  the  spermatocyte  of  the 
second  order  divides  into  two  spermatids.  Thus  the  final  result  of  the  division  of 
the  spermatocyte  of  the  first  order  is  the  formation  of  four  granddaughter  cells  or 
spermatids,  each  of  which  contains  half  the  number  of  chromatic  particles  present 
in  the  primitive  germ  cell,  whilst  the  final  result  of  the  division  of  the  oocyte  of 
the  first  order  is  the  production  in  some  cases  of  only  three  granddaughter 
cells,  the  mature  ovum  and  two  polar  bodies,  but  in  many  cases  the  first 
polar  body  divides  in  the  homotype  manner  simultaneously  with  the  division 
of  the  oocyte  of  the  second  order,  and  thus  the  final  result  of  the  division 
of  the  oocyte  is  four  granddaughter  cells,  the  mature  ovum  and  three  polar 
bodies,  each  containing  half  the  number  of  chromosomes  present  in  the  primitive 
germ  cell.     There  are,  however,  two  differences  of  importance  between  the  male 

and  the  female  elements.     The  

final  result  of  the  division  of  the 
female  element  is  one  mature 
ovum  immediately  capable  of 
fertilisation  and  further  develop- 
ment, and  two  or  three  polar 
bodies  which  are  incapable  of 
further  development  and  which 
ultimately  disappear.  On  the 
other  hand,  the  result  of  the 
division  of  the  male  element  is 
the  production  of  four  equal 
parts,  the  spermatids,  each  of 
which  undergoes  further  modi- 
fication, and  is  transformed  into 
a  spermatozoon  capable  of  fertil- 
ising a  mature  ovum. 

A    spermatozoon,   like    an 
ovum,  is  a  nucleated   mass   of 
cytoplasm,  but  it  presents  strik- 
ing  modifications  in  structure. 
It  is  very  small,  and  possesses  a 
head,  a  neck,  a  body,  a  tail,  and 
^).     In  addition  it  is  provided  with 
covers  more  than  the  anterior  half 
This  cap  is  modified  over  the  apex 


Head 


Body 


Neck 


Body. 


—  End  piece- 


iHead  cap 


Ant.  centrosome 
Post,  centrosome 

Axial  fibre 

Spiral  sheath 
Mitochondrial 
sheath 
Terminal  disc 


Fi( 


8. — Human  Spermatozoa 
(after  Retzius). 

\,  Side  view  ;  B,  Front  view. 


End  piece 


.  Sheath  of  axial 
fibre 


an  end  piece  (Fig. 

a  head  cap  which 

of  tlie  head  fFig.  9) 

of  the  head  into  a  sharp  cutting  edge,  by  means  of  which 

the  spermatozoon,  driven  forward  by  the  movement  of  the 

tail,  pierces  its  way  through  the  oolemma  of  the  ovum. 

In  the   short  neck  are  an   anterior  and   a  posterior 
'  I'ntro.some  separated  by  an  intermediate  disc,  and  from 
the    posterior    centrosome    an    axial    filament    extends 
through  the  body  and  tail,  and  terminates  ])Osteriorly  as 
the  end  piece.     The  axial  filament  is  surrounded  by  a 
sheath  which  is  thicker  in  tlie  body  than  in  the  tail.     Outside  the 
Hxial  filament,  in  the  body,  is  a  spiral  sheath,  and  this  is  enclosed 
pnnctiform  siiljstance,  the  iiiitochondria,!  sheath,  whicl)   rests  a,t  the  lower  end 
the  body  on  an  annulus  or  terininal  disc. 


Ffo.  9.   -S'niDCTUHE  OK  A  Human 
Spkumatozoon  (after  Meeves). 


sheath  of  the 
)y  a  sheath  of 


of 


16 


GENERAL  EMBEYOLOGY. 


A  transverse  striation  of  the  head,  a  spiral  filament,  a  spiral  sheatli  associated 
with  the  hody  and  tail,  and  a  terminal  spear  connected  witii  the  head  have  been 
described  by  Barclleben  and  others,  but  apparently  they  do  not  exist  normally  as 
parts  of  the  human  spermatozoon. 

The  head  of  the  spermatozoon  is  ovoid  and  laterally  compressed,  so  that  when 
viewed  from  the  side  it  appears  pointed ;  it  is  about  4"5  /x  long,  2-5  fx  broad,  and 
1-5  /x,  thick.  The  body  is  somewhat  longer  than  the  head,  and  the  tail  is  six  times 
as  long  as  the  body,  therefore  the  total  length  of  tlie  spermatozoon  is  about  one- 
fifth  of  the  diameter  of  the  ovum. 


FERTILISATION  OF  THE  OVUM  AND  THE  RESULTS  THAT  ENSUE. 

Fertilisation. — The  mature  ovum  is  fertilised  by  a  spermatozoon.  The  two 
generative  elements  meet,  and  fertilisation  takes  place  as  a  rule  in  the  upper 
part  of  the  Fallopian  tube.  The  spermatozoon  penetrates  the  zona  pellucida  of 
the  ovum,  cutting  through  it  by  means  of  the  sharp  edge  of  its  head  cap.  At  the 
same  time  a  conical  projection,  the  cone  of  attraction,  appears  on  the  surface  of 
the  ovum,  within   the  zona   pellucida,  directly   beneath  the  point  at  which   the 


_MP 

\  c. 


i-C 


-SN 


Fig.  10. — Fertilisation  of  the  Ovum  (Diagrammatic). 

A,  The  entrance  of  the  spermatozoon  and  the  formation  of  the  cone  of  attraction  ;  B,  The  appearance  of  the 
centrosome  ;  C,  The  approachment  of  the  male  ami  female  jironuclei  ;  D,  The  first  segmentation  nncleus. 


C. 
CA. 


Centrosome. 
Cone  of  attraction. 


FP.   Female  pronucleus. 
MP.  Male  pronucleus. 


P.      Polar  body. 

SN.  Segmentation  nucleus. 


spermatozoon  is  entering.  The  head,  and  probably  a  portion  of  the  body  of  the 
spermatozoon,  plunge  into  the  cone  of  attraction ;  the  remainder  of  the  body  and  the 
tail  are  cast  off  and  disappear.  The  portion  of  the  spermatozoon  which  enters  the 
cytoplasm  of  the  ovum  is  converted  into  a  nucleus,  the  male  pronucleus,  which  is 
accompanied  by  its  attraction  sphere  and  centrosome.  When  the  male  pronucleus 
is  distinctly  formed  the  granules  of  the  cytoplasm  in  its  neighbourhood  begin  to 
radiate  around  it,  as  if  under  its  influence,  and  the  pronucleus  itself  travels 
inwards. 

As  the  male  pronucleus  approaches  the  female  pronucleus  the  latter  shows 


FEETILISATION  OF  THE  OVUM. 


17 


signs  of  activity,  it  undergoes  changes  of  form,  and  moves  to  meet  the  male 
pronucleus.  For  a  time  the  two  pronuclei  lie  in  juxtaposition,  and  ultimately  they 
fuse  together,  forming  the  first  segmentation  nucleus. 

The  first  segmentation  nucleus  is  accompanied  by  two  centrosomes  which  lie  at 
its  opposite  poles,  and  are  the  products  of  the  male  centrosome  which  divides  as 
the  pronuclei  fuse. 

The  fertilised  ovum,  the  product  of  the  fusion  of  the  mature  ovum  and  the 
spermatozoon,  contains  in  its  nucleus,  the  first  segmentation  nucleus,  the  same 
number  of  chromosomes  as  the  primitive  ovum  or  the  sperm-mother  cell,  but  the 
chromosomes  of  the  segmentation  nucleus  are  derived  partly  from  a  male  and 
partly  from  a  female  individual. 

According  to  some  authorities,  both  the  male  and  female  pronuclei  are  accompanied  by 
centrosomes,  aild  at  the  moment  of  imion  of  the  pronuclei  each  centrosome  divides ;  thus  four 
half-centrosornes  are  formed,  two  male  and  two  female.  From  the  foiu'  half-centrosomes  two  new 
centrosomes  are  formed  by  the  union  of  half  a  male  centrosome  with  half  a  female  centrosome. 
If  this  view  be  correct,  each  of  the  two  centrosomes  which  accomj^any  the  first  segmentation 
nucleus  contains  both  male  and  female  elements. 

Segmentation.- — Segmentation  is  the  division  of  the  fertilised  ovum  (oosperm) 
into  a  number  of  cells.  These  cells  are  afterwards  arranged  in  layers — the  germinal 
layers  or  layers  of  the  blastoderm  ;  ultimately  they  are  differentiated  into  the  tissue 
elements  of  the  body. 


A  B  c 

Fig.  11. — Segmentation  of  the  Fertilised  Ovum  in  the  Rabbit. 

Formation  of  blastomeres  and  morula  (Diagrammatic). 

A,  Division  into  two  segments  ;  B,  Division  into  four  segments  ;  C,  Morula  ; 

P,  Polar  bodies. 

All  the  phenomena  of  segmentation  have  not  been  observed  in  the  human  ovum, 
and  it  is  to  be  understood  that  the  following  description  is  based  chiefly  upon  the 
conditions  met  with  in  rodents,  more  especially  in  the  rabbit,  an  animal  well 
adapted  for  the  study  of  these  phenomena. 

After  a  period  of  quiescence,  which  succeeds  the  fusion  of  the  male  and  female 
pronuclei,  a  period  of  activity  supervenes,  during  which  repeated  divisions  of  the 
impregnated  ovum  result  in  the  production  of  a  solid  mass  of  cells  called  a  morula. 
The  divisions  are  mitotic,  and  all  the  phenomena  associated  with  mitosis  are  readily 
observable  in  properly  prepared  specimens. 

The  planes  which  separate  the  several  segments  of  the  divided  ovum  in  its 
various  stages  are  termed  the  "  planes  of  segmentation,"  and  in  some  animals  the 
first  plane  by  which  the  ovum  is  divided  into  the  first  two  daughter  cells  coincides 
with  the  future  mid-axial  or  mesial  plane  of  the  body,  the  descendants  of  the  cell 
lying  to  the  right  of  it  being  developed  into  the  right  half  of  the  body,  and  those 
of  the  cell  to  the  left  into  the  left  half.  There  is  no  proof,  however,  that  this 
occurs  in  mammals;  all  that  is  definitely  known  is  that  the  first  division  separates 
the  ovum  into  two  parts  of  unequal  size  but  of  similar  colour  and  structure. 

The  second  plane  of  segmentation  is  at  right  angles  to  the  first,  and  it  separates 
the  two  daughter  cells  into  four  granddaughter  cells,  of  which,  in  some  cases,  two 
may  be  larger  and  two  smaller.  The  subsequent  divisions  occur  irregularly,  and 
they  result  in  the  formation  of  numerous  cells  (blastomeres)  which  a])parontly  only 
differ  in  size  in  the  rabbit,  but  which  also  differ  in  appearance  in  many  mammals. 
They  are  mixed  together  so  irregularly  that  it  is  impossil)](;  to  distinguish  the 
2 


18 


GENEEAL  EMBEYOLOGY. 


Fig.  12. — Conversion  op  the  Morula  to 

THE  Blastula. 

Formation  of  blastodermic  vesicle  and 

membrane. 

A,  Appearance  of  segmentation  cavity  and 
attachment  of  inner  cell  mass  to  ectoderm 
at  upper  pole  of  ovum  ;  B-',  Extension  and 
flattening  of  inner  cell  mass  as  it  occurs  in 
rabbit  and  some  other  mammals  ;  B",  Ex- 
tension of  entoderm  as  it  occurs  in  insec- 
tivora,  monkeys,  apes,  and  man  ;  C,  Com- 
pletion of  bilaminar  blastodermic  vesicle. 
BC,  Blastodermic  cavity  ;  EC,  Ectoderm  ; 
EE,  Embryonic  ectoderm  ;  EN,  Entoderm  ; 
I,  Inner  cell  mass  ;  SC,  Segmentation 
cavity  ;  ZP,  Zona  pellucida. 


descendants  of  one  daughter  cell  from  those  of 
the  other,  and  in  this,  the  morula  stage,  there 
is  frequently  no  indication  of  any  separation 
of  the  cells  into  layers.  In  the  meantime  the 
polar  bodies  have  disappeared. 

The  next  phenomenon  of  importance  is  the 
appearance  of  a  cavity — the  segmentation  cavity 
— in  the  morula ;  the  ovum  assumes  a  vesicular 
character,  and  is  now  termed  a  blastula.  Simul- 
taneously with  the  appearance  of  the  cavity 
the  cells  of  the  morula  are  arranged  in  two  groups 
— an  outer  and  an  inner.  The  cells  of  the  outer 
group  form  a  layer,  the  primitive'  ectoderm  or 
epiblast ;  those  of  the  inner  group  remain  massed 
together  and  constitute  the  inner  cell  mass.  The 
two  groups  are  in  contact  at  one  pole  of  the 
ovum,  and  it  is  in  this  region  that  the  embryo 
develops  (Fig.  12,  A). 

In  the  rabbit  and  in  some  other  mammals 
the  outer  cells  of  the  inner  mass  at  the  embryonic 
pole  of  the  ovum  blend  with  the  superjacent 
primitive  ectoderm  (Eauber's  cells)  to  form  the 
embryonic  ectoderm.  This  is  merely  a  modi- 
fication of  the  more  general  plan,  by  which  the 
inner  cell  mass  becomes  the  inner  layer  of  the 
now  vesicular  ovum,  but  the  conversion  of  the 
inner  mass  into  the  entoderm  may  take  place 
in  two  different  ways. 

(1)  In  the  rabbit  and  in  many  other  mam- 
mals the  inner  mass  gradually  flattens  out  till 
its  cells  form  a  layer  at  the  embryonic  pole, 
and  the  wall  of  the  vesicular  ovum,  which  is  now 
called  a  blastodermic  vesicle,  is  partly  unilaminar 
and  partly  bilaminar  (B^,  Eig.  12).  Gradually, 
however,  the  margins  of  the  entodermal  layer 
extend,  and  ultimately  the  cavity  of  the  vesicle 
is  surrounded  by  two  complete  layers,  ectoderm 
and  entoderm. 

In  the  hedgehog,  in  monkeys,  apes,  and  the 
human  subject,  a  cavity  appears  in  the  inner 
cell  mass  (B^,  Fig.  12),  and  the  cells  around  it 
assume  a  laminar  character,  constituting  the  en- 
toderm, which  is  separated  from  the  ectoderm, 
except  in  the  embryonic  area,  by  the  original 
cavity  of  the  blastodermic  vesicle. 

In  the  case  of  the  hedgehog  the  cavity 
in  the  entoderm  expands  until  the  entoderm  is 
forced  into  contact  with  the  ectoderm,  and  a 
condition  is  attained  similar  to  that  met  with 
in  the  rabbit  (C,  Fig.  12),  but  in  monkeys,  apes, 
and  the  human  subject  the  expansion  of  the 
entoderm  cavity  is  not  so  great,  and  the  entoderm 
does  not  attain  contact  with  the  ectoderm 
except  in  the  embryonic  area. 

In  amphiosus  and  many  of  the  invertebrata  the 
results  of  the  segmentation  are  nOt  quite  the  same 
as  in  mammals,  for  at  a  very  early  period,  without 
the  definite  formation  of  a  moridamass,  the  segmenta- 
tion cells  arrange  themselves  in  alayer  round  a  central 


THE  EMBEYONIC  AEEA. 


19 


cavity  and  form  a  complete  unilaminar  blastoderm.  In  these  cases  the  bilaminar  condition 
is  produced  by  the  invagination  of  a  portion  of  the  wall  of  the  vesicle.  The  opening  at 
which  the  invagination  occurs  is  called  tlie  blastopore.  The  cavity  enclosed  Vjy  the 
invaginated  cells  is  the  archenteron,  or  primitive  alimentary  cavity  or  gastrula  cavity. 
Except  at  the  blastopore  the  cavity  is  surrounded  by  two  layers  of  cells,  an  outer  the 
ectoderm,  and  an  inner  the  entoderm,  and  the  animal  at  this  period  of  its  development  is 
a  gastrula.  In  the  mammal  the  cells  which  become  invaginated  in  amphioxus  to  form 
the  entoderm  are  enclosed  in  the  interior  of  the  morula  mass  at  a  very  early  period  of  the 
segmentation,  before  the  vesicular  condition  is  attained,  but  eventually,  as  already  pointed 
out,  they  form  a  layer  inside  the  ectoderm  and  they  enclose  a  cavity,  the  blastodermic 
cavity,  which  is  homologous  with  the  archenteron  or  gastrula  cavity  of  the  lower  forms, 
but  the  cavity  is  closed  and  the  blastopore  is  not  obvious.  In  amphioxus,  however,  the 
blastopore  becomes  elongated  antero-posteriorly,  and  along  the  margins  a  third  layer,  the 
mesoderm,  grows  out  between  the  two  primitive  layers.  In  the  mammal,  on  the  other 
hand,  after  the  entoderm  and  ectoderm  are  definitely  established,  a  linear  streak,  called 
the  primitive  streak,  to  which  further  reference  will  be  made,  appears  on  the  surface  of 
the  ovum  ;  this  becomes  perforated  at  its  anterior  end,  and  from  its  margins  and  mesoderm 
extends  outwards ;  clearly,  therefore,  it  represents  the  blastopore  of  amphioxus  though 
an  actual  perforation  is  only  present  for  a  short  time,  and  the  mammalian  ovum  at  this 
period  may  be  looked  upon  as  a  gastrula. 

The  ectoderm  and  entoderm  together  constitute  the  blastoderm  or  blastodermic 
membrane,  which  is  bilaminar,  and  the  vesicle  of  which  they  form  the  wall  is  no 
longer  spoken  of  as  the  blastula,  but  as  the  blastodermic  vesicle. 

Structure  of  the  Ectoderm  and  Entoderm. — The  cells  of  the  ectoderm  are  at 
first  irregular  in  size  and  shape,  and  their  outlines  are  indistinct ;  but  after  a  short 
time  the  ectoderm  cells  at  one  pole  of  the  blastodermic  vesicle  become  cubical  or 
slightly  columnar,  whilst  the  remaining  cells  of  the  outer  layer  are  flattened  and 
have  irregular  outlines. 
The  columnar  cells 
form  the  ectoderm  of 
the  embryo,  and  the 
flattened  cells  are  util- 
ised in  the  formation  of 
nutritive  and  protec- 
tive structures-  known 
as  the  placenta  and 
foetal  membranes. 

The  cells  of  the  en- 
toderm are  also,  at  first, 
very  irregular  in  shape 
and  size,  but  after- 
wards, as  they  are 
spread  out  into  a  layer,  ^ 
they  become  more  or 
less  rounded,  and  they 
anastomose  together  by 
filamentous    processes. 


Mesoderm 


A 

Fig.  13. — Surface  View  op  the  Blastodermic  Vesicle. 

Showing  the  embryonic  area  and  the  commencenient  of  the  mesoderm. 

Before  the  appearance  of  the  primitive  streak — the  embryonic  area  is 
circular  in  form  and  bilaminar  tliroiighout  ;  B,  After  the  appearance  of 
the  primitive  streak.  The  posterior  end  of  the  primitive  streak  shows 
a  crescentic  thickening,  wliich  indicates  the  commencement  of  the  meso- 
derm or  middle  layer  of  the  blastodermic  membrane. 


At  a  still  later  period  they  are  transformed  into  polygonal  plates  which  appear 
spindle-shaped  in  section  (Fig.  12). 

Embryonic  Area.  —  When  the  upper  pole  of  the  bilaminar  blastodermic 
vesicle  is  examined  in  surface  view  from  above,  a  dark,  somewhat  opaque  circular 
area  is  visible ;  this  is  known  as  the  embryonic  area.  It  is  coextensive  with  the 
columnar  portion  of  the  ectoderm.  Very  soon  after  it  appears  the  embryonic  area 
becomes  ovoid ;  tlie  small  end  of  the  ovoid  area  is  posterior,  that  is,  it  lies  in  the 
region  which  is  afterwards  converted  into  tlie  posterior  part  of  the  embryo.  At 
the  hinder  end  of  the  ovoid  area  a  still  da,rkor  ])atcli  of  triangular  form  is  developed  ; 
this  soon  becomes  crescentic,  and  is  th(!  first  indication  of  tliu  ])rimitive  streak  atul 
of  the  formation  of  a  third  blastodermic  layer  termed  the.  mesoderm  or  mesoblast. 

The  primitive  streak  consists  of  thickened  ectoderm  which  is  seen  in  transverse 
sections  projcicting  downwards,  and  resting  upon  the  entoderm  in  the  form  of  a  ridge. 


20 


GENERAL  EMBEYOLOGY. 


From  the  sides  and  the  posterior  extremity  of  the  ectodermal  ridge  a  lamina  of 
cells  projects  outwards,  and  gradually  insinuates  itself  between  the  ectoderm  and 
the  entoderm  over  the  whole  area  of  the  vesicle,  except  in  certain  regions  to  be 
afterwards  described.  This  lamina  is  the  rudiment  of  the  mesoderm.  With  the 
formation  of  the  mesoderm  the  blastodermic  membrane  becomes  trilaminar. 


Embryonic  area 


-'  Nenriil  groove 


Ectoderm 


Entoderm 
Embryonic  area 


Primitive  groove 

Ectoderm 


Fig.  14.— The  Upper  Pole  of  the  Blastodermic  Vesicle. 

Showing  the  embryonic  area,  the  primitive  streak  with  the  extension  of  the  mesoderm  from  its  sides  and 
posterior  end,  and  the  commencement  of  the  neural  groove. 

A,  Surface  view  (diagrammatic)  ;  B  and  C,  Transverse  sections  through  the  blastoderm  of  the  ferret  at  the 
stage  represented  in  A  and  along  the  lines  h  and  c  respectively. 

The  majority  of  the  cells  of  the  mesoderm  are  derived  from  those  of  the 
primitive  streak,  but  it  is  said  that  cells  from  the  entoderm  also  take  part  in  its 
formation.  Young  mesodermal  cells  are  round  or  ovoid,  and  some  give  off  numerous 
processes.  In  later  stages  they  may  assume  various  shapes,  and  many  closely 
resemble  the  cells  of  the  ectoderm  or  those  of  the  entoderm. 

As  the  blastodermic  vesicle  grows,  the  embryonic  or  germinal  area  becomes 
pyriform  and  increases  in  length,  principally  in  the  posterior  part  of  its  extent 
where  the  primitive  streak  is  situated ;  at  the  same  time  the  streak  lengthens  and 

EG  ^ 

>SoP 
SoMJ 


Fig.  15. — Transverse  Section  of  a  Ferret  Embryo. 

Showing  neural  groove  before  the  separation  of  the  para.xial  from  the  lateral  mesoderm. 

C.      Coelom.  GC.  Germinal  cell.  PM.   Paraxial  mesoderm.  SoM.  Somatic  mesoderm. 

EC.   Ectoderm.  N.     Notochord.  SB.    Spongioblast.  SoP.   Somatopleure. 

EN.  Entoderm.  NG.  Neural  groove.  SG.    Spinal  ganglion. 

SpP.  Splanchnopleure. 


SpM.  Splanchnic  mesoderm. 


becomes  more  linear.  For  a  short  time  a  groove,  the  primitive  groove,  appears  on 
the  surface  of  the  streak.  It  is  deepest  in  front,  where  in  some  mammals,  includ- 
ing man,  a  small  transitory  perforation  is  formed,  the  neurenteric  canal. 

A  second  broader  and  shallower  groove  then  appears  in  the  embryonic  area 
immediately  in  front  of  the  primitive  streak ;  this  is  the  neural  groove,  the  rudiment 
of  the  nervous  system.  The  neural  groove,  its  bounding  folds,  and  the  nervous 
system  subsequently  developed  from  them  are  formed  entirely  of  ectodermal  elements, 
which  at  first  are  continuous  with  those  forming  the  outer  layer  of  the  embryo. 
The  posterior  eiid  of  the  neural  groove  embraces  the  anterior  end  of  the  primitive 
streak  and  groove,  and  at  this  period  the  neurenteric  canal  forms  a  communication 


THE  NEURAL  OR  MEDULLARY  GROOVE. 


21 


between  the  interior  of  t]ie  ovum  and  the  bottom  of  the  neural  groove,  which 
latter  afterwards  becomes  the  closed  canal  of  the  central  nervous  system.  In  some 
vertebrates  the  neurenteric  canal  persists  for  a  considerable  period,  and  upon  the 
development  of  the  alimentary  canal  it  constitutes  a  communicating  channel 
between  it  and  the  cavity  of  the  neural  tube. 

As  the  neural  groove  grows  backwards  the  anterior  part  of  the  primitive  streak 
is  absorbed,  and  although  the  posterior  part  continues  to  grow,  the  primitive  streak 
as  a  whole  diminishes  in  length ;  ultimately  the  greater  part  of  the  primitive 
streak  disappears,  but  a  portion  is  recognisable  for  a  considerable  time  extending 
from  the  base  of  the  tail,  a  transitory  structure  in  the  human  embryo,  to  the 
ventral  wall  of  the  body.  This  portion  forms  the  posterior  boundary  of  the 
primitive  alimentary  canal ;  it  remains  bilaminar,  and  is  called  the  cloacal 
membrane. 

The  primitive  streak  is  of  great  morphological  importance ;  recent  researches  have  shown 
that  from  it  and  the  cells  in  its  neighbourhood  the  greater  part  of  the  body  of  the  embryo, 
with  the  exception  of  the  anterior  jjart  of  the  head  and  heart  region,  is  developed.  It  possibly 
represents  the  mouth  of  a  remote  (pre-vertebrate)  ancestor,  the  fused  lips  of  which  formed  the 
body  of  a  primitive  vertebrate  animal.  The  aperture  of  this  mouth  is  still  represented  in  lower 
vertebrates  by  an  opening  known  as  the  blastopore.  The  neurenteric  canal  is  the  only  represen- 
tative of  the  opening  in  the  human  subject. 

The  neural  or  medullary  groove  is  bounded  laterally  by  medullary  folds 
which  are  continuous  in  front  of  the  groove,  but  separate    behind  where    they 


SoP 


SpP — 


a^tiiv^  f*'^,  ,e|<3p>^  ,-^ 


SpP 


r 

IMC  N  PA 

Fig.  16 — Transverse  Section  of  Ferret  Embryo. 

Showing  the  closiire  of  the  neural  groove,  the  formation  of  the  neural  crest,  the  outgrowth  of  the  spinal 
ganglia,  the  commencement  of  the  separation  of  the  paraxial  mesoderm  from  the  lateral  plates,  and  the 
differentiation  of  the  intermediate  cell  mass. 


C.      Ccelom.  GC.     Germinal  cell.  PA.  Primitive  aorta. 

CC.    Central  canal.     IMC.  Intermediate  cell  mass.       PS.  Mesodermic  somite. 
EC.   Ectoderm.  N.        Notochord.  SB.  Spongioblast. 

EN.  Entoderm.  NC.     Neural  crest.  SC.  Spinal  cord. 

SpP.  Splanchnopleure. 


SG.  Spinal  ganglion. 

SoM.  Somatic  mesoderm. 

SoP.  Somatopleure. 

SpM.  Splanchnic  mesoderm. 


embrace  the  anterior  end  of  the  primitive  streak.  The  neural  groove  increases 
in  length  both  in  front  and  behind.  The  backward  increase  takes  place  at  the 
expense  of  the  primitive  streak,  whilst  the  anterior  increase  is  due  to  the  rapid 
growth  of  the  anterior  part  of  the  embryonic  area;  at  the  same  time,  not  because 
of,  though  coincident  with,  an  increase  of  the  mesoderm  which  has  grown  beneath 
them,  the  medullary  folds  are  gradually  elevated,  and  their  apices  bending  inwards 
unite  together  over  the  neural  groove,  which  is  thus  converted  into  a  tube  or  canal 
— the  neural  tube.  The  medullary  folds  unite,  in  the  first  place,  in  the  region 
which  afterwards  becomes  the  neck ;  and  subsequently  they  unite  progressively, 
forwards  and  backwards. 

Along  the  line  of  union  the  neural  tube  is  connected,  for  a  time,  with  the 
surface  ectoderm  by  a  ridge  of  cells,  the  neural  crest.  The  crest  soon  separates 
from  tiie  surface,  but  it  remains  connected  with  the  neural  tube,  and  is  utilised  in 
the  formation  of  the  cranial  and  spinal  nerve  ganglia,  the  sympatiietic  ganglia,  the 
carotid  and  coccygeal  bodies,  and  the  medullary  parts  of  the  suprarenal  bodies, 
whilst  the  walls  of  the  neural  tube  are  converted  into  the  nervous  and  sustentacular 
tissue  elements  of  the  whole  of  the  central  nervous  system  (brain  and  spinal  cord). 


22  GENERAL  EMBEYOLOGY. 

B.efore  the  tube  is  closed  the  neural  groove  is  dilated  at  each  end  (see  Fig.  20). 
The  posterior  dilatation  is  single ;  it  constitutes  the  rhomboidal  sinus,  which  under 
ordinary  circumstances  soon  disappears.  Anteriorly,  numerous  dilatations  are 
distinguishable  at  first.  The  exact  nunil>er  of  these  dilatations  (neuromeres)  is 
said  to  be  eleven.  As  the  tulje  closes  they  resolve  themselves  into  three  distinct 
vesicles  termed  the  primary  cerebral  vesicles.  These  constitute  the  rudiments  of  the 
fore-  mid-  and  hind-brains,  and  their  respective  ventricular  cavities.  The  remainder 
of  the  cavity  of  the  tube  becomes  the  central  canal  of  the  spinal  cord. 

After  the  separation  of  the  neural  crest  from  the  surface  the  mesoderm  com- 
pletely surrounds  the  whole  of  the  neural  tujje,  and  from  it  are  formed  the 
meml)ranes  of  the  Ijrain  and  spinal  cord  and  their  skeletal  environments. 

The  ectodermal  cells  which  form  the  wall  of  the  primitive  neural  tube  are  ill- 
defined,  but  they  soon  differentiate  into  two  sets,  spongioblasts  and  germinal  cells. 
The  spongioblasts  are  the  more  numerous,  they  are  columnar  in  form,  and  all 
extend  from  an  internal  limiting  membrane  which  is  developed  round  the  periphery 
of  the  central  canal  to  an  external  limiting  membrane  which  forms  the  outer 
limit  of  the  neural  tube.  There  is  frequently  considerable  difficulty  in  recognising 
their  columnar  character,  even  in  the  early  stages,  partly  because  their  nuclei  do 
not  all  lie  at  the  same  level,  and  partly  because  they  are  so  closely  opposed.  The 
spongioblasts  are  converted  into  the  sustentacular  tissue,  or  myelospongium,  of  the 
brain  and  spinal  cord,  but  all  do  not  undergo  precisely  the  same  transformations. 
The  inner  portions  of  those  spongioblasts  whose  nuclei  lie  near  the  central  canal 
retain  a  columnar  form,  and  cilia  grow  from  their  free  surfaces  into  the  lumen  of  the 
canal;  in  other  words,  they  are  converted  into  the  ciliated  epithelium  of  the  central 
canal,  but  the  outer  portions  of  the  same  cells  are  transformed  into  fibrillar  processes 
which  terminate  externally  by  fusing  with  the  external  limiting  membrane.  The 
remaining  spongioblasts  entirely  lose  their  columnar  form,  they  become  much 
branched,  and  their  branches  interlace  with  the  fibrillar  processes  of  the  ciliated 
epithelial  cells,  and  with  similar  branches  of  neighbouring  cells,  forming  the 
reticular  sustentacular  tissue  or  myelospongium ;  the  external  limiting  membrane 
is  produced  by  the  close  interweaving  of  the  peripheral  myelospongial  fibrils. 

The  germinal  cells  are  spherical  in  outline,  and  contain  clear  protoplasm  and 
darkly-staining  nuclei.  They  lie  between  the  inner  ends  of  the  spongioblasts  close 
to  the  central  canal  where,  at  the  fourth  or  fifth  week,  they  form  an^  irregular  layer, 
and  it  is  believed  that  they  very  soon  give  rise  to  a  new  generation  of  cells,  the 
neuroblasts,  or  young  nerve-cells — at  all  events  neuroblasts  appear  as  the  germinal 
cells  disappear.  Each  neuroblast  rapidly  becomes  pyriform  by  the  outgrowth  of  an 
axial  process  or  axon,  which  projects  from  its  outer  end  towards  the  peripliery  of 
the  tube. 

Shortly  after  their  formation  the  neuroblasts  migrate  outwards,  and  ultimately 
those  of  the  cord  are  arranged  in  longer  or  shorter  columns  in  the  myelospongium, 
whilst  those  of  the  brain  are  grouped  together  in  definite  areas  to  form  the 
cerebral  nuclei. 

Each  neuroblast  as  it  develops  gives  off  many  processes,  which  vary  in  length 
and  thickness.  The  first  formed  of  these  is  the  axial  process  or  axon  already 
referred  to.  It  carries  impulses  from  the  cell,  gives  off  lateral  branches,  and 
terminates  either  in  association  with  a  special  end-organ  or  by  ramifying  amidst 
other  nerve-processes  or  round  a  nerve-cell  of  the  central  or  peripheral  nervous 
system.  The  remaining  processes  of  the  neuroblast  are  called  dendrites  or 
protoplasmic  processes.  They  are  usually  shorter  and  more  branched  than  the 
axon,  and  they  carry  impulses  to  the  cell.  The  whole  system  of  cell  body,  axon, 
and  dendrites  into  which  a  neuroblast  develops  is  termed  a  neuron. 

Every  neuron  is  probably  a  separate  and  distinct  entity.  Its  processes  neither 
anastomose  together  nor  with  the  processes  of  other  neurons.  They  lie,  however, 
in  close  contiguity  with  either  the  Ijody  or  processes  of  other  neurons,  or  with 
special  end -organs,  and  it  is  possible  for  impulses  to  pass  from  one  neuron  to 
another  although  there  is  no  structural  continuity  between  them. 

Extension  of  the  Mesoderm  and  Division  of  the  Blastodermic  Membrane 
into  Areas. — It  has  already  been  pointed  out  that  when  the  primitive  streak  first 


EXTENSION  OF  THE  MESODERM. 


Proamniotic 
area 


Bucco- 
pharyngeal 
area 


Pericardial 
area 


appears  it  consists  of  a  thickened  ridge  of  ectoderm  situated  in  the  posterior  part 
of  the  embryonic  area  and  resting  upon  the  entoderm.  The  anterior  end  of  the 
ridge  soon  fuses  with  the  entoderm  beneath  it,  and  from  its  sides  and  posterior 
extremity  a  lamelliform  outgrowth,  the  mesoderm,  is  projected  between  the 
ectoderm  and  entoderm.  At  its  commencement  the  mesoderm  is  an  outgrowth 
from  the  primitive  streak,  but  during  its  subsequent  extension  it  is  probably  added 
to  by  cells  proliferated  from  the  entoderm. 

As  it  extends  the  mesoderm  forms  a  semilunar  sheet  of  cells,  the  concavity  of 
the  semilune  being  turned  forwards,  whilst  the  convexity  is  gradually  projected 
beyond  the  margins  of  the  embryonic  area.  The  cornua  of  the  semilunar  sheet 
grow  forwards  on  either  side  of,  and  at  some  little  distance  from  the  middle  line, 
immediately  beneath  the  medullary  folds.  Each  cornu  on  reaching  the  anterior 
end  of  the  embryonic  area  bifurcates,  and  the  resulting  processes  unite  with  their 
fellows  of  the  opposite  side. 

At  the  same  time  the  mesoderm  grows  from  its  convex  margin,  and  extends 
over  the  rest  of  the  ovum  as  a  continuous  sheet.  But  even  when  the  extension  is 
completed,  in  the  majority 
of  mammals,  three  areas  on 
the  upper  aspect  of  the 
ovum  remain  devoid  of 
mesoderm,  and  consist  only 
of  ectoderm  and  entoderm. 

The  largest  of  these  areas 
lies    directly    in    front    of 
the  embryonic  region.     In 
many  mammals  it  is  folded  Notochordai 
upwards  and  backwards  in  ^^^'^ 

front  of  the  head  of  the 
embryo,  when  this  becomes 
distinguishable,  and  it  takes 
part  in  the  formation  of 
one  of  the  protecting  fcetal 
membranes,  viz.  the  amnion ; 
it  is  therefore  called  the 
proamnion,  and  the  area 
from  which  it  is  developed 
constitutes  the  proamniotic  area.  Probably  it  is  not  present  in  the  human  blasto- 
derm, or  if  it  exists  it  is  very  transitory. 

The  second  of  the  areas  into  which  the  mesoderm  does  not  extend  lies  in  the 
embryonic  region.  It  is  separated  from  the  proamniotic  area  by  a  bar  of  mesoderm 
in  which  the  pericardial  cavity  afterwards  appears.  The  anterior  part  of  this 
second  area  is  situated  in  front  of  the  neural  groove,  and  as,  at  a  later  period,  it 
forms  a  septum  between  the  primitive  mouth  and  the  pharynx,  it  may  be  termed 
the  bucco-pharyngeal  area.  The  posterior  part  of  the  area  forms  the  floor  of  the 
medullary  groove,  and  as  the  notochord  is  formed  from  its  entodermal  layer  we 
have  named  it  the  notochordai  area. 

The  third  area  corresponds  to  the  posterior  part  of  the  primitive  streak.  It 
extends  from  the  base  of  the  tail  towards  the  umbilicus,  forming  the  cloacal  mem- 
brane, which  itself  forms  the  posterior  boundary  of  the  primitive  alimentary  canal. 
It  is  eventually  perforated  by  the  genito-urinary  and  anal  apertures. 

Except  in  the  areas  just  described,  tlie  blastodermic  membrane  is  trilaminar,  and 
at  an  early  period  it  is  possible  to  distinguish  the  regions  in  which  the  heart  and 
pericardium,  tlKi  amnion,  and  the  })lacental  and  non-placental  parts  of  the  chorion 
are  subsequently  developed.  These  regions  form  fairly  well-dclined  areas,  to  the 
relative  positions  of  which  reference  may  now  be  made. 

I'he  anterior  part  of  the  embryonic  area  in  front  of  tiie  Ijucco-pharyngeal  area 
is  the  region  in  whicli  the  pericardium  and  heart  are  developed,  and  it  may  therefore 
be  termed  tlie  pericardial  area, 

"■J'lie  blaHtodeniiic    membrane    iiimicdiately    surroimding    tlie    cmljiyonic  area, 


Fig.  17. — Surface  Areas  of  the  Blastoderm. 


24 


GENEEAL  EMBEYOLOGY. 


including  the  proamniotic  part  in  those  animals  in  which  it  exists,  is  the  amniotic 
area,  and  this  is  bounded  externally  by  a  band  of  elevated  and  thickened  ectoderm 
which  indicates  the  placental  area.  Tlie  latter,  together  with  the  blastoderm  over 
the  rest  of  the  ovum,  forms  the  chorionic  area,  which  is  separable,  therefore,  into 
placental  and  non-placental  portions. 

These  areas  are  further  referred  to  in  the  description  of  the  folding  ofl"  of  the 
embryo  and  the  formation  of  the  foetal  membranes  and  placenta. 

Formation  of  the  Notochord. — The  notochord  is  the  primitive  skeletal  axis  of 
the  embryo.  When  difi'erentiated  it  forms  a  rod  which  intervenes  between  the 
ectodermal  neural  tube  and  the  entoderm  of  the  primitive  alimentary  canal.  It  is 
developed  from  the  entoderm  beneath  the  neural  groove  in  the  notochordal  area. 
A  linear  strip  of  entoderm  thickens  and  then  separates  as  a  solid  rod  of  cells,  the 
continuity  of  the  entodermal  layer  being  restored  beneath  it.  "When  it  is  completed 
the  notochord  extends  from  a  point  immediately  behind  the  primitive  fore-brain,  and 


Embryonic  arfia 

NG 


Amniotic 
area 


Placental  area 


Chorionic  area 


Notochordal  area 
Pericardial  area  I 


Primitive  streak 

Amniotic  area 


Placental  area 


Chorionic  area 


Fig.  18. — Sections  showing  the  different  Areas  of  the  Blastodermic  Vesicle  (Diagrammatic). 
I.   Transverse  section  ;  IT.  Longitudinal  section. 


EC.  Ectoderm. 


M.  Mesoderm. 


EN.  Entoderm. 


N.  Notochordal  thickening. 
NGr.  Neural  groove. 


beneath  the  anterior  end  of  the  mid-brain,  to  the  anterior  end  of  the  primitive  streak, 
and  in  later  stages,  as  the  skeleton  is  formed,  the  notochord  can  be  traced  from  the 
post-sphenoid  section  of  the  base  of  the  skull,  which  is  situated  beneath  the  mid-brain, 
to  the  tip  of  the  coccyx. 

The  separation  of  the  notochord  from  the  entoderm  commences  in  the  cervical 
region,  and  extends  forwards  and  backwards.  The  anterior  extremity  is  the  last  part 
to  be  detached,  the  separation  occurring  shortly  after  the  perforation  and  disappear- 
ance of  the  bucco-pharyngeal  membrane. 

The  cellular  notochord  develops  a  cuticular  sheath  ;  it  is  subsequently  surrounded 
by  mesoderm  which  separates  it  both  from  the  neural  tube  and  the  entoderm, 
and  which  is  ultimately  transformed  into  the  vertebrae  and  their  ligaments,  the 
intervertebral  discs,  the  basi-sphenoid  and  basi-occipital  parts  of  the  skull,  and  the 
membranes  of  the  brain  and  cord. 

As  the  surrounding  mesoderm  is  differentiated  the  notochord  becomes  nodulated  ; 
the  thickened  portions  are  situated  in  the  regions  of  the  intervertebral  discs,  and 
the  intermediate  constricted  portions  in  the  regions  of  the  vertebral  bodies.  The 
vertebral  portions  gradually  disappear,  and  the  intervertebral  parts  are  converted 
into  a  kind  of  mucoid  tissue,  the  pulp  of  the  intervertebral  discs. 

Formation  of  the  Coelom. — In  all  animals  in  which  the  entoderm  and  ectoderm 


FOKMATION  OF  THE  CGELOM. 


25 


lie   in   close  relation  with   each  other  over  the  whole  surface    of  the  ovum,   the 

r  I' 


Pericardial 
area 


Fig.  19. — Extension  of  Mesoderm  and  Formation  of  C(elom  (Diagrammatic). 

A.  Mesoderm  spreading  from  the  sides  of  the  ectodermal  primitive  streak,  and  extending  between  the  ectoderm 

and  entoderm.     B.  Further  extension  of  the  mesoderm  and   appearance  of  coelomic  cleft-like  spaces. 

C.  Complete  delamination  of  the  mesoderm  and  formation  of  ccelom. 

BC.  Blastodermic  cavity.  C.  Coelom.  EC.  Ectoderm.  EN.  Entoderm.  M.  Mesoderm. 

P.   Primitive  Streak.  SoF.  Somatopleure.  SpP.  Splanchnoplenre. 

mesoderm  as  it  extends  from  the  primitive  streak  forms  a  single  layer,  and  where 
this  exists  the  blastoderm  is  _«_  Proamniotic 

area 


trilaminar,  but  in  monkeys, 
apes,  and  the  human  subject, 
as  the  ectoderm  and  entoderm 
are  separated  from  each  other 
by  the  segmentation  cavity 
(Fig.  12,  B-),  the  mesoderm  al- 
most from  its  commencement 
extends  in  two  layers,  one  the 
splanchnic  on  the  entoderm, 
and  the  other  the  somatic  on 
the  inner  surface  of  the  ecto- 
derm. In  other  mammals 
before  the  extending  meso- 
derm entirely  separates  the 
ectoderm  from  the  entoderm, 
a  cavity  is  formed  in  it  by 
the  union  of  a  series  of  cleft- 
like spaces  which  appear  near 
the  margin  of  the  embryonic 
area  and  rapidly  fuse  together, 

formin^^    the    CCaloin    or    body  F'"-  20.— Suhfack  View  of  an  Eaui,v  Emhhvu  (Diagrammatic). 

cavity.      Thus  in  the  majority  Sliowlng  the  neural  groove,  dilated  in  tlie  head  region  but  still  un- 

of     mammalH     tlie      CfP.lom     is  closed,  and  the  first  protovertebral  somites.     The  n.argius  of  the 

,         ,                     ,.    ,  cttlomic  space  are  indicated  by  dotted  lines. 

lormed  by  trie  cleavage  ot  the 

mesoderm,  but  in  the  higlier  forms  it  represents  the  segmentation  cavity  which 

has  become  surrounded  by  two  extending  layers  of  mesoderm.     In  those  animals 


Rhomboidal 
sinus 


26  GENERAL  EMBRYOLOGY. 

in  which  it  appears  by  cleavage  of  the  mesoderm,  it  extends  towards  both  poles 
of  the  ovum,  but  in  the  higher  forms  only  towards  the  embryonic  pole,  and  in 
both  groups  its  extension  in  the  eml^ryonic  area  is  arrested  before  it  quite 
reaches  the  side  of  the  notochord  and  the  mesial  plane  of  the  primitive  streak.  It 
extends  across  the  pericardial  area,  however,  and  forms  the  rudiment  of  the 
pericardial  cavity,  which  appears  as  a  transverse  tubular  passage  continuous  on 
each  side  with  the  general  body  cavity.  The  outer  or  parietal  layer  of  the 
mesoderm  becomes  more  or  less  closely  attached  to  the  ectoderm,  and  with  it 
forms  the  somatopleure,  whilst  tlie  inner  or  visceral  layer  is  similarly  associated 
with  the  entoderm  to  form  the  splanchnopleure. 

When  the  ccelom  is  fully  formed  the  blastoderm  contains  two  cavities,  one,  the 
coelom  or  body  cavity,  situated  between  the  two  layers  of  the  mesoderm,  and  the 
other  the  cavity  of  the  blastodermic  vesicle,  usually  called  the  vitelline  cavity,  which 
lies  inside  the  entoderm. 

Mesodermic  or  Protovertebral  Somites. — During  the  formation  of  the  coelom 
the  undivided  mesoderm  at  each  side  of  the  notochord  thickens,  principally  by  a 
dorsal  upgrowth  which  is  coincident  with  the  uprising  of  the  ectodermal  medullary 
folds  which  bound  the  neural  groove.  There  are  thus  formed  two  thickened  bars  of 
mesodermal  tissue,  one  on  each  side  of  the  neural  tube,  and  they  together  constitute 
the  paraxial  mesoderm  (Fig.  15) ;  the  more  laterally  situated  portions  of  the  mesoderm 
are  known  as  the  lateral  plates. 

The  paraxial  mesoderm  is  soon  divided,  except  in  the  head  region,  by  a  number 
of  transverse  clefts  into  a  series  of  cubical  masses  termed  the  mesodermic  somites. 
These  are  at  first  partially,  and  afterwards  more  completely  separated  from  the 
lateral  plates  by  longitudinal  grooves.  After  the  longitudinal  grooves  are  formed, 
the  mesodermic  somites  of  each  side  are  connected  with  the  lateral  mesoderm  by  a 
somewhat  contracted  strand  of  cells,  the  intermediate  cell  mass  (Fig.  16).  This 
strand  is  represented  in  lower  vertebrates  by  a  series  of  separate  cords  of  cells, 
the  stalks  of  the  somites,  each  somite  possessing  one  stalk. 

The  separation  of  the  paraxial  mesoderm  from  the  lateral  plates  and  the 
segmentation  of  the  former  into  somites  extends  forwards  to  the  region  of  the  hind 
brain,  where  the  first  protovertebral  somite  is  formed.  In  front  of  this  the 
mesoderm,  in  mammals  at  least,  does  not  become  segmented. 

The  cavity  of  the  coelom  may  extend  into  the  paraxial  mesoderm  before  it  is 
segmented  into  protovertebral  somites,  or  it  may  stop  just  outside  the  limits  of  the 
paraxial  mesoderm.  In  the  former  case  each  somite,  when  separated  from  the 
lateral  plate,  contains  a  cavity,  and  the  intermediate  cell  mass  is  also  hollow  for  a 
time.  In  the  latter  case  the  protovertebral  somites  and  the  intermediate  cell  masses 
are  solid ;  at  a  later  period,  however,  a  cavity  which  contains  a  few  spherical  cells 
appears  temporarily  in  each  somite. 

Folding  Off  of  the  Embryo  from  the  Blastodermic  Vesicle. — Although  so 
many  rudiments  of  the  embryo  become  distinguishable  at  an  early  period  in  its 
development  (the  embryonic  area,  the  primitive  streak  and  groove,  the  neural 
groove,  the  notochord,  and  the  protovertebral  somites),  the  body  of  the  embryo  does 
not  assume  its  characteristic  form  until  it  becomes  raised  and  folded  off  from  the 
general  surface  of  the  blastodermic  vesicle. 

The  main  cause  of  the  folding  off  of  the  embryo  from  the  surface  of  the  vesicle 
is  the  more  rapid  growth  of  the  embryonic  area  as  contrasted  with  the  slower  growth 
and  expansion  of  the  remainder  of  the  wall  of  the  vesicle ;  and  the  moulding  of  the 
increasing  embryonic  area  into  the  form  of  the  embryo  is  due  to  differences  in  the 
rate  of  growth  of  the  various  parts  of  the  area  itself. 

The  manner  in  which  the  area  is  folded,  and  the  changes  in  the  relative 
positions  of  its  various  parts  which  necessarily  result,  will  be  easily  understood  by 
reference  to  Figs.  21  and  27. 

The  embryonic  area  at  an  early  period  increases  rapidly,  especially  in  length. 
Its  margins,  however,  appear  to  remain  comparatively  fixed,  and  hence  as  the  area 
increases  it  must  fold  upon  itself.  It  becomes  more  convex  externally,  and  is 
raised  slightly  above  the  general  surface,  but  at  the  same  time  it  apparently  sinks 
into  the  interior  of  the  ovum,  and  the  amnion  folds  close  over  it. 


FOLDING  OFF  OF  THE  EMBEYO. 


27 


The  antero-posterior  growth  is  greater  than  the  lateral;  consequently  the 
folding  of  the  emhryonic  area  is  most  marked  in  front  and  behind.  Anterior  and 
posterior,  or  cephalic  and  caudal  folds  are  formed,  which  indicate  the  head  and 
tail  extremities  of  the  embryo.  Similarly,  lateral  folds  define  the  lateral  limits  of 
the  body. 

When  the  body  of  the  embryo  thus  becomes  folded  off  it  contains  a  portion  of 
the  blastodermic  cavity  and  of  the  ccelom ;  the  former  is  the  primitive  alimentary 
canal,  and  the  latter  is  the  rudiment  of  the  pericardial,  pleural,  and  peritoneal 
cavities. 

The  communication  between  the  pleuro-peritoneal  and  the   extra-em?jryonic 


SoM   _ 


SoM 


Early  Stages  in  the  Foldixg  Off  of  the  Embryo  (Diagrammatic). 


I.  Longitudinal  section  of  a  developing  ovum.     The  folding  off  of  the  embryo  has  commenced,  and  the  head  fold, 

bending  down  in  front,  has  invaginated  the  amniotic  area.  The  tail  fold  is  j^artly  formed,  and  the 
primitive  alimentary  canal,  closed  in  front,  communicates  freely  with  the  yolk-sac  by  a  wide  umbilical 
aperture. 

II.  Transverse  section  of  a  developing  ovum  showing  the  commencement  of  the  "  folding  off. "     The  thickened 

embryonic  area  is  convex  externally,  and  it  already  appears  to  sink  below  the  surface  of  the  ovum. 

III.  Tran.sverse    section  showing    the    "  folding   off "  more    advanced.     The  changes    seen  in   II.   are   more 

marked,  and  by  apparent  constriction  at  the  junction  of  the  embryonic  area  with  the  rest  of  the 
blastodermic  vesicle  the  embryo  is  still  further  nipped  off,  and  distinct  lateral  folds  are  formed. 

The  division  of  the  cavity  of  the  blastodermic  vesicle  into  that  of  the  primitive  alimentary  canal  and  that  of 
the  yolk-sac  is  shown  in  all  tlie  figures. 

The  amniotic  area,  directed  upwards  and  inwards  in  II.,  forms  with  the  placental  area  the  amniotic  fold,  and 
in  III,  tlie  amniotic  folds  of  opposite  sides  are  approaching  one  another  over  the  back  of  the  embryo  to 
enclose  the  cavity  of  the  amnion.  The  relative  iiositions  of  the  dilierent  areas  of  tlie  blastoderm  are 
correspondingly  modified. 

PA.      Placental  area.  SpM.  Splanchnic  niesodertn. 

PAC  Primitive  alimentary  canal.    YS.     Yolk-sac. 
SoM.   Somatic  mesoderm.  V.       Villi. 

portion  of  the  cadom  is  obviously  iKnnided  Ijy  the  margins  of  tlie  emljryonic  area, 
which  constitutes  tlie  limits  of  the  umbilical  orifice. 

The  margins  of  the  embryonic  area  retain  approximately  their  original  positions, 
and  in  its  further  growth  the  embryo  extends  beyond  them  in  all  directions. 


AA. 

Amnion  fold. 

EC. 

Ectoderm. 

C. 

Ccelom. 

EN. 

Entoderm. 

EA. 

Embryonic  area. 

N. 

Notochord. 

28 


GENERAL  EMBRYOLOGY. 


THE  EMBRYO. 

The  embryo,  now  easily  distinguishaljle  from  the  rest  of  the  ovum,  is  ah'eady 
sufficiently  developed  to  give  some  indication  of  the  general  plan  of  its  organisation, 
and  of  the  ultimate  relation  and  fate  of  the  three  layers  of  the  blastoderm  which 
enter  into  its  constitution.  There  are  as  yet  no  limbs,  but  the  general  contour  of 
the  head  and  body  are  defined.  It  possesses  a  notoehord,  afterwards  replaced  by 
the  permanent  vertebral  column,  which  constitutes  a  longitudinal  central  axis. 
On  the  dorsal  aspect  of  the  notoehord  the  neural  groove  is  closing  to  form  the 
neural  canal,  or  primitive  cerebro-spinal  nervous  system,  whilst  on  its  ventral  side 
a  portion  of  the  blastodermic  cavity  is  being  included  as  a  primitive  tubular 
alimentary  canal,  which  freely  communicates  with  the  remainder  of  the  blastodermic 
cavity  now  called  the  cavity  of  the  yolk-sac. 

The  formation  of  the  mesodermic  somites  has  commenced,  and  this  is  the  first 

indication  of  that  segmenta- 
tion which  is  such  a  char- 
acteristic feature  in  the 
structure  of  the  vertebrate 
body. 

The  general  relations  of 
the  three  layers  of  the  blas- 
toderm remain  unaltered. 
Thus,  externally,  there  is  a 
layer  of  ectoderm  f  ormiu  g  the 
surface  of  the  body ;  inter- 
nally, a  layer  of  entoderm 
I  i^       Lining  the  primitive  aliment- 

FiG.  22.— The  Relative  Positions  of  the  Blastodermic  Layers  ary  canal;  and  between  them 
IN  the  Body  of  the  Embryo  when  the  "Folding  Off"  is  is  the  mesoderm  enclosing 
completed  (Diagrammatic).  f'kg  coelom 

The  surface  ectoderm 
forms  the  epithelial  ele- 
ments ^  of  the  skin  and  its 
appendages,  and  of  the  glands 
which  open  on  it.  Thus  the 
hairs  and  hair-follicles,  the  nails,  the  enamel  of  the  teeth,  the  epithelium  of  the 
sebaceous  glands,  of  the  sweat  glands,  and  of  the  mammary  glands  are  all  ectodermal. 
The  epithelium  of  the  conjunctivse  and  of  the  lachrymal  glands  is  also  derived 
from  ectoderm.  The  roof  of  the  mouth,  the  inner  surfaces  of  the  cheeks,  the  nasal 
passages  and  their  associated  cavities,  together  with  the  adjacent  part  of  the  pharynx 
and  the  anterior  lobe  of  the  pituitary  body,  as  well  as  the  external  auditory  canal 
and  the  outer  layer  of  the  tympanic  membrane,  are  all  developed  from  the  surface, 
and  their  epithelium,  with  that  of  their  glands,  is  ectodermal  in  origin.  The 
epithelium  of  the  sense  organs,  except  that  of  taste  (the  tongue),  is  derived  from 
ectoderm ;  the  auditory  and  olfactory  epithelial  elements,  and  those  of  the  lens 
and  cornea,  are  from  surface  ectoderm ;  whilst  the  epithelial  elements  of  the  retina 
are  from  neural  ectoderm. 

The  neural  ectoderm  is  removed  from  the  surface  to  form  the  neural  tube  and 
neural  crest,  from  which  the  cells  and  fibres  of  the  whole  of  the  nervous  system,"-^ 

^  The  term  "Epithelium"  is  applied  to  tissues  consisting  of  cells  which  are  united  with  oue  another 
by  means  of  a  small  amount  of  intercellular  substance. 

The  cells  constituting  epithelium  are  always  arranged  in  one  or  more  layers  ;  they  cover  free  surfaces 
and  line  the  various  cavities  of  the  body,  including  the  vascular  and  lymphatic  systems  ;  they  also  form 
the  active  elements  in  secretory  glands  and  line  their  ducts.  Epithelium  is  always  non-vascular,  and  the 
cells  receive  their  nourishment  from  blood-vessels  which  are  in  their  vicinity.  Epithelial  cells  are 
modified  in  accordance  with  the  particular  functions  they  are  called  upon  to  serve,  and  they  present  many 
variations  in  shape,  size,  and  structure,  e.g.  the  neuro-epithelial  cells  of  the  central  nervous  system  and  of 
the  peripheral  sense  organs  differ  considerably  from  the  more  ordinary  epithelial  type  ;  but  they  are 
simply  more  specialised,  and  therefore  more  modified. 

"  It  seems  jiossible  that  this  statement  may,  before  long,  require  modification,  for  evidence  is  being 
brought  forward  to  show  that  some  portions  of  the  system  are  developed  from  peripherally  situated 
ectodermal  cells 


I.   Transverse  section  through  the  umbilical  aperture. 
II.   Similar  section  in  front  of  or  behind  the  umbilicus. 

AC.  Alimentary  canal.  EN.  Entoderm.  N.  Notoehord. 

EC.  Ectoderm.  M.     Mesoderm.  SC.  Spinal  cord. 

VI.   Vitello-intestinal  duct  and  umbilical  aperture. 


THE  EMBEYO. 


29 


both  central  and  peripheral,  and  the  sustentacular  tissue  of  tlie  brain  and  spinal 


Fig.  23. — Transverse  Section  of  a  Ferret  Embryo, 

Showing  further  differentiation  of  the  mesoderm. 

SC.    Spinal  cord. 

SG.     Spinal  ganglion. 

SL.     Scleratogenoiis  layer  of  pro- 

tovertebral  somite. 
SoM.  Somatic  mesoderm. 
SoP.    Somatoplenre. 
SpM.  Splanchnic  mesoderm. 


cc. 

Central  canal. 

ML. 

Muscular  layer  of  mesoder- 

CL. 

Cutaneous  lamella  of  proto- 

mic  somite. 

vertebral  somite. 

N. 

Notochovd. 

CO. 

CcElom. 

NC. 

Neural  crest. 

EC. 

Ectoderm. 

PA. 

Primitive  aorta. 

EN. 

Entoderm. 

PS. 

Mesodermic  somite. 

GC. 

Germinal  cell. 

SB. 

Spongioblast. 

SpP.    Splanchnopleure. 

AMC 


Proto- 

vertebral- 

somite 


Cutaneons 
lamella 
Muscle 
platP 

Sclerato 

genons 

layer 


cord,  are  developed.  The  neural  ectoderm  also  furnishes  the  epithelial  elements  of 
the  retinae,  the  pineal  gland,  and  of  the  posterior  lobe  of  the  pituitary  body.  It 
forms     a     large  ^m 

part  of  the  vitre- 
ous humour  of 
the  eye,  and  con- 
tributes to  the 
formation  of  the 
carotid,  coccy- 
geal and  supra- 
renal bodies. 

The  entoderm 
lines  the  alimen- 
tary canal  and 
the  spaces  and 
glands  which 
open  into  it,  ex- 
cept the  upper 
parts  of  the 
mouth  and  phar- 
ynx and  the 
terminal  portion 
of  the  rectum ; 
thus  the  eyji- 
thelium  of  the 
Eustachian  tube 
and  tympanic 
cavity,  the 
trachea,  the 
bronchi,  the  air- 
vesicles  of  the 
lungs,  the  gall- 
bladder,      the 

urinary  Ijladder,  and  ]jart  of  ihe  urethra  is  entodermal.     It  Ibrms  the  e])ithelial 
constituents  of  the  taste  buds  or  organs  of  taste,  the  liver  and  the  pancreas,  the 


Somatopleuie 


'splanchnopleuie 


Fig.  24. — Further  Differentiation  of  the  Mesoderm. 

Transverse  section  of  a  rat  embryo,  showing  the  transformation  of  the  cells  of  the 
scleratogenous  layer  of  a  protovertel jral  somite  and  their  extension  round  the 
notochord  and  spinal  cord. 


AM.  Amnion. 

AMC.  Amnion  cavity. 

C.  Cf/doiii. 

K.C.  Ectoderm. 


N.        Notochord. 
PA.      Primitive  aorta. 
PAC.  Primitive  alimentaiy 
canal. 
VD.  Vitello-intestinal  duct. 


SC.      Spinal  cord. 
SG.      Spinal  ganglion. 
SoM.   Somatic  mesoderm. 
SpM.  Splanchnic  mesoderm. 


30 


GENEEAL  EMBEYOLOGY. 


epithelium  lining  the  vesicles  of  the  thyroid  body  and  the  cell  nests  of  the  thymus 
gland. 

From  the  mesoderm  all  the  remaining  structures  which  intervene  between  the 
surface  ectoderm  and  the  entodermal  lining  of  the  primitive  alimentary  tube  are 
formed. 

Mesodermic  Somites  and  the  Lateral  Plates. — Each  mesodermal  somite 
consists  of  numerous  cells  arranged  radially  round  a  central  cavity — the  myeloccele  \ 
this  latter,  however,  quickly  disappears. 

The  cells  of  the  somites  are  gradually  grouped  into  three  sets,  two  to  the  inner 
and  lower  side  of  the  cavity,  and  one  to  its  upper  and  outer  side.  The  two  groups. 
on  the  lower  and  inner  side  are  an  outer,  next  the  ca\dty,  the  muscle  plate,  and  an 
inner,  the  scleratogenous  layer.  The  group  on  the  upper  and  outer  side  of  the 
cavity  is  the  sulj-epithelial  or  cutaneous  lamella. 


Scleratogenous    Layer.  —  The   cells    of 


Scleratogenous 
layer 

Muscle  plate 


Blood-vessel 


Spinal  cord 


Ectoderm 


Mesoderm 


llw--.     Blood- 
r)^-^  vessels 


Fig.  25. — Coronal  Section  op  a  Eat  Embeyo. 

Showing  the  relationship  of  the  extending  scleratogenous  tissue 
to  the  sjnnal  cord  and  to  the  muscle  plates. 


this  layer  proliferate  rapidly  and 
migrate  inwards,  surrounding  the 
notochord,  and  passing  both  be- 
neath the  neural  tube  and  up- 
wards along  its  lateral  walls  to- 
its  dorsal  aspect ;  they  intermingle 
above  and  below  with  the  cells  of 
the  corresponding  layer  of  the 
opposite  side,  and  in  front  and 
behind  with  the  cells  of  the  sclerato- 
genous layers  of  adjacent  somites. 
In  this  way  the  neural  tube  and 
the  notochord  are  gradually  en- 
veloped by  a  continuous  sheath 
of  mesodermal  tissue,  which  forms 
the  membranous  vertebral  column. 
This  is  perforated  at  regular  in- 
tervals by  the  nerve-roots  issuing 
from  the  spinal  cord  and  brain, 
and  by  the  vessels  of  supply  to> 
those  structures.  From  its  sub- 
stance the  vertebrae  and  ligaments, 
the  greater  part  of  the  interverte- 
bral discs,  and  the  investing  mem- 
branes of  the  brain  and  cord  are 
afterwards  developed. 

Muscle    Plates.  —  The   cells 
of   the   muscle   plate   layer   lose 


their  original  epithelial-like  characters;  they  elongate  antero-posteriorly,  become- 
spindle-shaped  and  striated,  and  they  give  rise  to  the  striped  muscles  of  the  body. 
For  a  long  time  the  fibres  developed  from  each  muscle  plate  remain  localised  and 
quite  distinct  from  the  fibres  developed  from  neighbouring  segments ;  the  masses 
they  form  are  called  myotomes.  After  a  time,  however,  the  fibres  of  neighbouring 
myotomes  are  more  or  less  intermingled,  and  in  the  adult,  except  in  certain  situa- 
tions, the  intermyotomic  intervals  are  no  longer  recognisable. 

The  main  portions  of  the  myotomes  are  converted  into  the  muscle  masses 
situated  in  the  dorsal  part  of  the  body  wall,  that  is,  into  the  erectores  spinie 
and  their  main  subdivisions,  and  the  other  muscles  which  occupy  the  vertebral 
grooves. 

In  the  lower  vertebrates  the  ventral  ends  of  the  myotomes  descend  in  the- 
somatopleure  almost  to  the  mid-ventral  line,  and  are  transformed  into  the  muscles 
of  the  ventro-lateral  walls  of  the  body.  A  similar  descent  of  the  ventral  ends  of 
the  myotomes  into  the  lateral  walls  of  the  body  has  not  been  proved  in  the  highest 
vertebrates.  In  mammals,  including  man,  the  ventral  ends  of  the  myotomes  only 
descend  for  a  short  distance  in  the  somatopleure,  and  then  all  trace  of  their  char- 
acteristic structure  is  lost.     It  is  presumed,  however,  that  cells  budded  off  from  the- 


THE  EMBEYO.  31 

myotomes  descend  to  a  lower  level,  and  that  they  take  part  in  the  formation  of  the 
ventro-lateral  muscles. 

In  lower  vertebrates  bud-like  projections  pass  from  the  myotomes  in  the 
thoracic  and  pelvic  regions  into  the  limb  rudiments,  and  from  these  the  muscles  of 
the  limbs  are  developed.  In  the  highest  vertebrates  distinct  buds  from  the  myo- 
tomes have  not  been  observed,  but  it  is  said  that  outgrowths  of  cells  pass  from  the 
myotomes  into  the  limb  buds,  where  they  proliferate  and  form  the  limb-muscles. 
The  occurrence  of  these  outgrowths  into  the  limbs,  like  the  descent  of  the  lower 
ends  of  the  myotomes  into  the  ventral  part  of  the  body- wall,  has  not  been  proved 
in  mammals;  possibly  it  occurs,  but  if  not,  the  ventral  and  limb-muscles  of 
mammals  must  be  developed  from  the  somatopleural  mesoderm. 

Cutaneous    Lamellae  of  the  Mesodermic   Somites. — The   cells  which  form 


Hind -brain 


Auditory  ganglion 
,Eudiment  of  otic  vesicle 


Paraxial  mescderm^^       ^ — v~,^  "■ .    ^'V^''^°l£  ^^  P^.^^'^ 


SoM 


SpMl 

First  cephalic  aortic  arch. 


-Transverse  Section  of  a  Rat  Embryo. 
Showing  the  relation  of  the  paraxial  mesoderm  of  the  head  to  the  lateral  plates,  the  commencement  of  the 
formation  of  the  otic  vesicles  and  hyomandibular  clefts,  and  the  relation  of  the  primitive  heart  to  the 
pericardium  and  fore-gut. 

EC.  Ectoderm.  SoM.  Somatic  mesoderm.  SpM.  Splanchnic  mesoderm. 


the  outer  and  dorsal  walls  of  the  cavities  of  the  mesodermal  somites  retain  their 
epithelial-hke  characters  for  a  longer  period  than  those  of  other  portions  of  the 
somites,  and  at  the  borders  of  the  lamellae  they  pass  by  gradual  transition  into 
the  cells  of  the  muscle  plates.  After  a  time  they  undergo  histological  differentia- 
tion, and  they  are  utilised  in  the  formation  of  the  subcutaneous  tissues  and  fascise 
on  the  dorsal  aspect  of  the  body,  and  outgrowths,  which  descend  with  the  offsets  of 
the  muscle  plates,  enter  into  the  formation  of  the  ventro-lateral  walls  of  the  body. 

Mesodermic  Somites  of  the  Head.  —  It  ]ias  already  been  jwinted  out  (p.  26)  that 
proto vertebral  somites  are  not  recognisable  in  mammals  further  forwards  than  the  occipital 
region ;  but,  from  the  evidence  obtained  by  examination  of  lower  vertebrates,  it  is  believed  that 
originally  nine  somites  were  present  in  the  cephalic  region.  From  the  first,  second,  and  third  of 
these,  muscle  j)lates  form  which  ai-e  developed  into  the  muscles  of  the  eyeballs.  If  any  muscle 
plates  are  formed  in  connexion  with  the  fourth,  fifth,  and  sixth  somites  they  disapjjear,  leaving 
no  traces,  and  the  muscles  develojjed  fi'om  tlie  remaining  cej)halic  somites  are  those  of  the  tongue 
and  those  connecting  the  head  with  the  shoulder  girdle. 

Lateral  Plates. — At  an  (jariy  stage,  before  its  separation  from  the  paraxial 
iijfjsodcriii,  each  lateral  plate  is  divided  into  an  outer  or  somatic  and  an  inner  or 
splanchnic  layer.  'J'iic  somatic  layer  is  concerned  with  the  i'ormatiou  of  the 
parietal  layers  of  the  pleural  and  ])critoii(!al  uieiultrancs,  and  with  the  development 


32 


GENEEAL  EMBEYOLOGY. 


of  the  connective  tissues,  fasciae,  and  vessels  of  the  ventro-lateral  walls  of  the  body  ; 
and  in  mamnials,  apparently,  it  also  gives  origin  to  the  ventro-lateral  body  muscles 
and  the  muscles  of  the  limljs.  The  splanchnic  portions  of  the  lateral  plates  form 
the  fascise,  the  connective  tissues,  the  smooth  muscles  of  the  walls  of  tlie  ahmentary 
canal,  the  heart  and  great  blood-vessels,  the  visceral  layers  of  the  pleural  and 
peritoneal  membranes,  the  spleen,  and  the  germinal  epithelium,  which  becomes 
transformed  into  the  mother  cells  of  the  ova  and  spermatozoa. 

In  the  cephalic  region,  in  higher  vertebrates,  lateral  plates  are  not  recognisable, 
exceyjt  so  far  as  they  may  Ije  represented  by  the  walls  of  the  pericardium;  but  in 
some  lower  vertebrates  lateral  plates  can  be  distinguished,  corresponding  in  number 
with  the  cephalic  somites,  and  it  has  been  asserted  that  the  muscles  of  the  face 
and  the  muscles  of  mastication  are  developed  from  the  lateral  plates  associated 
with  the  second  and  third  cephahc  somites.  The  subject,  however,  is  one  which  is 
still  obscure,  and  requires  further  investigation  before  any  very  positive  conclusion 
can  be  arrived  at. 

Intermediate  Cell  Mass. — As  already  mentioned,  the  lateral  plates  and  the 
mesodermic  somites  are  connected  by  the  intermediate  cell  masses,  which  are 
intimately  associated  with  the  development  of  the  ducts  and  tubules  of  the  genital 
and  urinary  organs  in  man  and  other  mammals.  On  each  side  the  mass  soon 
separates  from  the  mesodermic  somites,  and  is  transformed  by  rapid  proliferation 
of  its  cells  into  an  elongated  body,  the  Wolffian  body  or  primitive  kidney,  which 
projects  downwards  into  the  dorsal  angle  of  the  body  cavity.  In  early  stages  it 
extends  from  the  fifth  somite  of  the  body,  backwards  to  its  posterior  end,  but  is 
most  clearly  differentiated  in  the  middle  portion.  The  Wolffian  duct  and  tubules 
and  the  Mlillerian  duct  are  developed  in  connexion  with  it;  after  the  second  month 
of  intrauterine  hfe  it  degenerates,  and  is  replaced  by  the  permanent  kidney,  which 
is  formed  dorsal  to  its  posterior  extremity. 


THE  DEVELOPMENT  OF  THE  PEIMITIVE  ALIMENTAEY  CANAL. 

When  the  cephalic,  caudal,  and  lateral  folds  are  established,  and  the  general 
outline  of  the  embryo  is  clearly  defined,  its  dorsal  and  lateral  surfaces  and  its 


Spinal  cord 


Xotocliord 


Placental  area 


Rliomboidal^iuus 

Primitive  streak 

Cloacal  membrane 


Placental  area 


SpM      SoM 
Bucco-pharyngeal  membrane 
Fig.  27. — Diagram  of  a  Developing  Ovum,  seen  in  Longitudinal  Section. 
Tlie  folding  off  of  the  embryo  has  commenced,  and  the  do^vn■^vard  bend  of  the  head  fold  in  front  lias  invagi- 
nated  the  amniotic  area.     The  tail  fold  is  partly  formed,  and  the  primitive  alimentary  canal,  closed  in 
front  by  the  bucco-pharyngeal  memljrane  and  behind  by  the  cloacal  membrane,  is  distinguishable  ;  it 
communicates  freely  with  the  yolk  sac  by  a  wide  umbilical  a]ierture. 

C.     Ccelom.  EN.  Entoderm.  SoM.  Somatic  mesoderm. 

EC.  Ectoderm.  M.     Mesoderm.  SpM.  Splanchnic  mesoderm. 

anterior  and  posterior  extremities  are  easily  recognisable,  and,  as'  the  embryo  is 
folded  off  from  the  surface  of  the  blastodermic  vesicle,  a  portion  of  the  blastodermic 
cavity  is  enclosed  within  it ;  this  is  the  primitive  alimentary  canal.  It  is  simply 
an  incomplete  tubular  cavity,  situated  beneath  the  notochorcl,  which  is  bounded  in 


THE  PRIMITIVE  ALIMENTARY  CANAL. 


front  by  the  head  fold,  beliind  by  the  tail  fold,  and  laterally  by  the  lateral  foldB, 
but  is  widely  open  below  and  continuous  with  the  cavity  of  the  yolk-sac. 

As  the  head  of  the  embryo  grows  more  rapidly  than  any  other  part,  the  head 
fold  is  more  marked  than  the  other  folds,  and  with  its  formation  the  pericardial 
area  is  bent  round  until  it  becomes  ventral  in  position,  its  original  upper  and  lower 
surfaces  being  reversed  (Fig.  27).  It  is  owing  to  this  change  of  relative  position 
that  the  ventral  wall  of  the  alimentary  canal  is  completed  in  front,  and  it  is 
obvious  that  its  anterior  limit  corresponds  to  the  bucco-pharyngeal  area  of  the 
blastoderm.  Tiie  part  of  the  blastodermic  cavity  enclosed  in  the  head  fold  con- 
stitutes the  fore-gut. 

The  tail  fold  at  this  period  is  small,  but  it  limits  the  primitive  gut  behind. 

The  ventral  closing  of  the  posterior  end  of  the  primitive  alimentary  canal  to 
form  a  hind-gut  is  produced, 
as  in  the  case  of  the  fore-gut, 
by  bending  of  the  embryonic 
area.  This  takes  place  in  the 
region  of  the  tail  fold ;  but 
the  posterior  part  of  the  em- 
bryonic area  retains  for  a  con- 
siderable time  its  original 
position,  and  forms  a  connect- 
ing stalk,  termed  the  body- 
stalk,  between  the  embryo 
and  the  chorionic  area  of  the 
blastoderm.  Ultimately,  how- 
ever, this  terminal  section  of 
the  embryonic  area  is  re- 
versed in  position,  its  posterior 
end  being  carried  forwards  till 
it  forms  the  posterior  boundary 
of  the  umbilical  orifice,  and  the 
ventral  wall  of  the  hind-gut  is 
thus  completed. 

The  rest  of  the  primitive 
alimentary  canal  constitutes 
the  mid -gut.  It  remains  for 
some  time  in  free  communica- 
tion with  the  cavity  of  the 
yolk-sac,  and  this  communica- 
tion between  the  alimentary 
canal  and  the  yolk-sac  at  a 
later  stage  forms  a  tubular 
passage,  the  vitello- intestinal 
duct. 

The  entoderm  forms  the 
lining  epithelium  of  the  ali- 
mentary canal,  but  this  is 
invested  by  the  splanchnic  layer  of  the  mesoderm,  which  is  separated  from  the 
somatopleure  or  body  wall  by  the  coelom  or  body  cavity.  As  the  splanchnic 
mesoderm  passes  on  each  side  to  its  continuity  with  the  somatic  mesoderm  it  forms 
a  fold,  by  whicli  the  gut  is  suspended  from  the  under  surface  of  the  primitive 
vertebral  column  ;  this  fold  is  the  mesentery. 

When  the  diaphragm  is  formed  at  a  later  period  it  separates  tlie  thorax  from 
the  abdomen,  and  divides  the  coelom  into  pleural  and  peritoneal  portions. 

The  y»rimitive  alimentary  canal  is  almost  a  straight  tube,  blind  at  both  its 
extremities,  and  communicating  only  with  tlie  cavity  of  the  yolk-sac.  As  yet  there 
is  no  mouth  and  no  anal  passage  or  aperture.  'I'lie  simple  tuljular  canal  is  divisible 
into  fore-gut,  mid-gut,  and  hind-gut,  parts  which  are  conveniently  associated 
developrnentally  with  definite  portions  of  the  fully-formed  alimentary  canal. 


Yolk-sac 


Cloacal  meuibraue  Body  stalk 

Fig.  28. — Diagram   representing   the   Condition   of   the  Ali- 
mentary Canal  in  a  Human  Embryo  about  Fifteen  Days 
Old  (modified  from  His). 
The  visceral  clefts  are  formed,  and  the  subdivisions  of  the  fore-gut, 
together  with  the  rudimeuts  of  the  bronchi  and  liver,  are  distinct. 


GENEEAL  EMBEYOLOGY. 


Thus  the  fore-gut  is  converted  into  the  pharynx,  cesophagus,  stomach,  and  the 
greater  part  of  the  duodenum ;  whilst  from  the  mid-gut  and  the  hind-gut  the  rest 
of  the  small  intestine  (jejunum  and  ileum),  and  the  whole  length  of  the  large 
intestine  (caecum,  colon,  and  rectum),  are  formed.  There  is  no  sharp  limit  Ijetween 
the  mid-gut  and  the  hind-gut,  or  between  the  portions  of  the  intestinal  canal 
which  develop  from  them. 

Diverticular  outgrowths  from  the  entoderm  of  the  primitive  alimentary  canal 
form  the  rudiments  of  the  intestinal  glands,  including  the  liver  and  pancreas  ;  of  the 
respiratory  apparatus ;  and  of  the  thyroid  and  thymus  glands.  Details  of  the 
formation  of  these  structures  are  given  in  the  special  description  of  the  develop- 
ment of  the  system  to  which  each  belongs. 


20    28 


Fig.  29. — Further  Development  of  the  Alimentary  Canal,  as  seen  in  a  Human  Embryo 
ABOUT  Five  Weeks  Old  (Diagrammatic). 

The  tongue  is  well  formed,  the  trachea  and  cesophagus  are  separated,  the  bronchi  have  commenced  to  branch  ; 
the  duodenal  curve  is  well  formed,  and  the  Cfficum  has  appeared  in  the  loop  of  the  mid-gut.  The 
cloaca  is  partially  separated  into  genito-urinary  and  rectal  portions. 


1 .  Hind-brain. 

2.  Month. 

3.  Tongue. 

4.  Pericardium. 

5.  Pharynx. 

6.  Heart. 


7.  Trachea. 

8.  (Esophagus. 

9.  Lung. 

10.  Liver. 

11.  Bile  duct. 

12.  Stomach. 


13.  Pancreas. 

14.  Small  intestine. 

15.  Coecum. 

16.  Intestinal  loop. 

17.  Large  intestine. 

18.  Notochord. 


19.  Vertebra. 

20.  Spinal  cord. 

21.  Bladder. 

22.  Wolffian  duct. 

23.  Kidney. 

24.  Ureter. 


25.  Rectum. 

26.  Proctodfeum. 

27.  Allantoic  diverticulum. 

28.  Vitello-intestinal  duct. 

29.  Fore-brain. 

30.  Mid-brain. 


Except  with  respect  to  the  anterior  part  of  the  fore-gut,  the  changes  in  shape 
and  position  which  the  originally  simple  alimentary  tube  undergoes  during  its 
conversion  into  its  final  or  adult  form  are  described  in  the  account  of  the 
development  of  the  digestive  organs ;  but  the  development  of  the  pharynx  and  the 
structures  associated  with  it,  and  the  formation  of  the  mouth  and  anus,  may 
be  considered  now^ 

Development  of  the  Pharynx  and  Stomatodaeum. — The  development  of  the 
anterior  part  of  the  fore-gut  into  the  pharynx  and  the  floor  of  the  mouth  is  so  inti- 
mately associated  with  the  formation  of  a  primitive  mouth,  the  stomatodteum,  that 
the  two  must  to  a  certain  extent  be  considered  simultaneously. 

The  stomatodaeum  first  appears  as  a  depression  between  the  head  and  the  peri- 


VISCEEAL  CLEFTS  AND  VISCERAL  ARCHES.  35 

cardial  region.  It  is  produced  by  the  downward  growth  of  the  fore-part  of  the 
head  in  front  and  the  bulging  forward  of  the  pericardium  behind,  and  it  is  separated 
from  the  anterior  end  of  the  fore-gut  by  the  bilaminar  bucco-pharyngeal  membrane. 
When  the  stomatodteurn  first  appears  it  is  not  enclosed  laterally ;  but  at  a  later 
period  side  boundaries  are  formed,  and  the  space  is  developed  into  the  upper  part 
of  the  mouth  and  the  nasal  cavities. 

The  fore-gut,  a  relatively  wide  space,  continuous  posteriorly  with  the  mid-gut, 
is  at  first  closed  anteriorly  by  the  bucco-pharyngeal  membrane,  which  separates 
it  from  the  stomatodseum.  About  the  fifteenth  day,  in  the  human  embryo,  the  bucco- 
pharyngeal membrane  disappears,  the  fore -gut  is  then  thrown  into  continuity 
with  the  stomatodseal  space,  and  the  anterior  opening  of  the  alimentary  canal 
is  formed. 

As  development  proceeds  the  cavity  of  the  fore-gut  is  gradually  compressed 
dorso-ventrally  until  its  transverse  section  assumes  a  triangular  outline ;  but  in 
the  earliest  stages  there  are  no  indications  of  the  various  organs  which  are  ulti- 
mately developed  from  its  walls.  After  a  short  interval,  however,  two  elevations 
appear  in  its  ventral  wall.  The  anterior  of  these  is  a  rounded  elevation,  termed 
the  tuberculum  impar.  It  is  situated  directly  behind  the  lower  ends  of  two  raised 
bars  or  arches,  called  the  mandibular  arches,  which  are  growing  down  into  the  floor 
of  the  fore-gut  from  the  anterior  parts  of  its  lateral  walls.  The  tuberculum  impar 
is  the  rudiment  of  the  anterior  two-thirds  of  the  tongue,  which  is  thus  formed  in 
the  floor  of  the  entodermal  portion  of  the  alimentary  canal.  The  more  posterior 
elevation,  termed  the  furcula,  is  a  curved  ridge,  which  bounds  a  mesial  longitudinal 
depression.  It  is  separated  from  the  lateral  walls  of  the  fore-gut  and  from  the 
tuberculum  impar  by  a  groove,  the  sinus  arcuatus.  The  anterior  part  of  the  furcula 
is  transformed  into  the  epiglottis  and  the  margins  of  the  upper  aperture  of  the 
larynx  ;  the  median  depression  becomes  the  cavity  of  the  larynx  and  of  the  trachea, 
and  from  its  posterior  end  hollow  outgrowths  extend  and  form  the  rudiments  of  the 
epithelial  lining  of  the  bronchi  and  lungs.  Still  more  posteriorly,  behind  the  region 
of  the  furcula,  a  dilatation  of  the  fore-gut  is  formed,  which  projects  forwards  and 
downwards  towards  the  pericardium.     This  is  the  first  indication  of  the  stomach. 

Visceral  Clefts  and  Visceral  Arches. — In  the  lateral  wall  of  the  anterior  part 
of  the  fore-gut,  on  each  side,  four  incomplete  and  more  or  less  transverse  clefts,  the 
visceral  clefts,  appear.  They  are  due  to  outward  linear  pouchings  of  the  entoderm, 
and  corresponding,  but  less  marked,  inward  depressions  of  the  ectoderm.  The 
anterior  cleft  is  the  best  marked,  and  the  rest  diminish  in  size  from  before  back- 
wards. At  the  bottoms  of  the  clefts  the  ectoderm  and  the  entoderm  are  in  contact, 
but  the  thin  membranes  thus  formed,  which  intervene  between  the  cavity  of  the 
fore-gut  and  the  exterior,  are  only  exceptionally  and  abnormally  perforated  in  the 
human  subject,  though  in  lower  vertebrates  they  invariably  disappear,  and  the 
pharyngeal  or  anterior  part  of  the  fore-gut  is  thrown  into  continuity,  laterally, 
with  the  exterior  by  a  number  of  narrow  slits,  the  gill  slits,  which  are  used  for 
respiratory  purposes.  In  man  and  other  mammals,  however,  the  floors  of  the 
second,  third,  and  fourth  clefts  are  utilised  in  the  formation  of  the  sides  of  the 
neck ;  that  of  the  first  cleft  is  transformed  into  the  tympanic  membrane,  which 
separates  the  external  auditory  meatus  from  the  cavity  of  the  tympanum. 

In  the  further  consideration  of  the  fate  of  the  visceral  clefts,  it  must  be  borne 
in  mind  that  each  consists  of  an  inner  or  entodermal  portion  and  an  outer  or  ecto- 
dermal portion.  The  inner  yjart  of  the  first  cleft  is  converted  into  the  tympanum 
and  the  Eustachian  tulje,  and  the  outer  part  becomes  the  external  auditory  meatus. 
No  traces  of  the  outer  part  of  the  second  cleft  are  left,  but  a  portion  of  the  inner 
part  can  be  recognised  as  a  slight  depression  above  the  tonsil  in  the  lateral  wall  of 
the  pharynx  and  in  a  recess,  the  fossa  of  Kosenmiiller,  behind  the  pharyngeal  end  of 
the  Eustachian  tube.  Both  the  outer  and  inner  portions  of  the  third  and  fourth 
clefts  diHa]jp(;ar,  but  from  their  inner  parts  diverticula  are  given  off  which  form 
the  ruchments  oi'  the  tliymus  and  the  lateral  lohes  of  the  tliyroid  l)ody.  The 
diverticula  from  whicfi  the  thymus  is  developed  are  (Uirived  from  the  third  clefts, 
wiiilst  each  lateral  lobe  of  the  thyroid  body,  in  the  majoi'ity  of  mammals,  is  formed 
I'jy  a  diverticulum  i'rom  the  fourth  cleft,  but  in  some,  mammals  the  lateral  lobes  are 


GENERAL  EMBRYOLOGY. 


derived  from  the  median  diverticulum,  and  the  outgrowths  from  the  posterior  parts 
of  the  fourth  clefts  constitute  the  post-hranchial  bodies. 

The  margins  of  the  visceral  clefts  are  thickened  by  the  growth  of  the  mesoderm 
between  the  entodermal  and  ectodermal  layers,  and  they  are  moulded  into  a  series 
of  five  rounded  bars,  the  visceral  arches,  of  which  the  fifth  is  not  recognisable 
externally,  though  it  is  easily  seen  internally.  The  dorsal  extremities  of  the  arches 
terminate  at  the  sides  of  the  head  below  the  level  of  the  neural  tube,  and  in  the 
early  stages  the  vential  ends  rest  upon  the  pericardial  region.  When  the  neck  is 
formed,  it  grows  forwards  from  the  pericardial  region  and  carries  with  it  the  lower 
ends  of  the  visceral  arches,  whicli  henceforth  terminate  in  its  ventral  wall.  As  the 
visceral  arches  are  carried  forwards  the  head  is  strongly  curved  towards  the  ventral 
aspect,  and  the  lower  ends  of  the  visceral  arches  are  pushed  backwards  over  each 

other     till     the 
^  ^^  fourtli    is    over- 

lapped by  the 
third,  and  the 
third  by  the 
second. 

The  first  arch 
is  the  mandi- 
bular, the  second 
the  hyoid,  the 
third  the  thyro- 
hyoid; the  fourth 
and  fitth  have  no 
special  designa- 
tions. Each  arch 
is  covered — ex- 
ternally by  ecto- 
derm, internally 
by  entoderm,  and 
its  core  is  formed 
of  mesoderm,  in 
which  there  is 
developed  a  bar 
of  cartilage  and 
a  blood  -  vessel 
called  a  cephalic 
aortic  arch. 

At  first  each 
arch  is  limited  to 
the  side  wall  of 
the  fore-gut;  but 
after  a  time  it  is 

prolonged  into  the  ventral  wall,  encroaching,  with  the  exception  of  the  first,  upon 
the  sinus  arcuatus. 

The  first,  or  mandibular  arch,  is  formed  between  the  first  visceral  cleft  and  the 
bucco-pharyngeal  membrane.  As  it  develops  it  forms  the  lateral  and  lower 
boundaries  of  the  stomatodseal  space,  and  it  grows  downwards  till  it  meets  its 
fellow  of  the  opposite  side  in  the  ventral  middle  line,  immediately  in  front  of  the 
tuberculum  impar.  The  greater  part  of  this  arch  is  converted  into  the  lower  jaw 
and  the  soft  tissues  which  invest  it.  From  its  upper  part  a  process  grows  forwards, 
the  maxillary  process,  from  which  the  upper  lateral  part  of  the  face,  between  the 
orbit  and  the  mouth,  is  developed,  and  in  which  the  superior  maxillary,  the  malar, 
and  the  palate  bones,  and  possibly  the  internal  pterygoid  plate  also,  are  developed 
and  ossified. 

From  the  posterior  border  of  the  outer  aspect  of  the  mandibular  arch  the  tragus 
and  a  portion  of  the  helix  of  the  pinna  of  the  external  ear  are  formed.  The  carti- 
laginous bar  in  its  interior  is  known  as  Meckel's  cartilage.     It  forms  the  primitive 


Pig.  30. 


Stages  in  the  Formation  of  the  Tongue  and  Upper  Aperture  of  the 
Larynx  in  the  Human  Embryo  (alter  His). 

Embryo  14  days  old.     II.  Embryo  23  days  old.      III.    Embryo  28  to  30  days  old. 
IV.   Embryo  2  months  old. 

Coelom.  G.  Glottis. 

Epiglottis.  SA.  Sinus  arcuatus. 

Furcula.  T.  Tongue. 

Foramen  cajcum.  TI.  Tuberculum  impar. 


1] 
2 


Visceral 


2  I   

,  (arches. 


C. 
E. 
F. 
FC. 


VENTEAL  WALL  OF  THE  FORE-GUT.  37 

skeleton  of  the  arch.  Its  upper  and  lower  extremities  are  ossified  and  remain  in 
the  adult,  the  former  as  the  malleus,  and  possibly  the  incus,  and  the  latter  as  the 
symphysial  part  of  the  lower  jaw.  The  remainder  of  the  cartilaginous  bar  dis- 
appears, but  the  fibrous  membrane  which  surrounds  the  lower  section  of  the  inter- 
mediate part  is  ossified  and  converted  into  the  main  part  of  the  lower  jaw,  whilst 
that  round  the  upper  section  of  the  intermediate  portion  persists  as  the  spheno- 
mandibular  ligament.  The  blood-vessel  developed  in  the  mandibular  arch  is,  for 
the  main  part,  a  transitory  structure,  but  its  ventral  section  is  converted  into  the 
internal  maxillary,  superficial  temporal,  facial  and  lingual  arteries. 

The  second  and  third  arches  are  continued  downwards  into  the  floor  of  the 
pharyngeal  portion  of  the  fore-gut.  There,  converging,  they  insinuate  themselves 
between  the  tuberculum  impar  and  the  furcula,  across  the  anterior  part  of  the  sinus 
arcuatus,  and  uniting  together  form  a  transverse  bar.  This  rapidly  changes  into  a 
semilunar  ridge  which  first  embraces,  and  afterwards  fuses  with  the  posterior  part 
of  the  tuberculum  impar,  and  it  forms  the  posterior  third  of  the  tongue. 

The  second  arch  takes  part  in  the  formation  of  the  side  and  anterior  part  of  the 
neck.  From  its  anterior  border  externally  a  part  of  the  helix,  the  antihelix,  the 
antitragus,  and  the  lobule  of  the  pinna  of  the  external  ear  are  developed.  The 
lower  and  upper  portions  of  its  cartilaginous  bar- — the  hyoid  bar — are  ossified ; 
the  lower  portion  forms  part  of  the  body  and  the  small  cornu  of  the  hyoid  bone  on 
its  own  side,  and  the  upper  portion  is  converted  into  the  intra-  and  extra-temporal 
sections  of  the  styloid  process  (the  tympano-hyal  and  stylo-hyal  portions  of  the 
styloid  process  of  the  temporal  bone).  The  fibrous  tissue  of  the  intermediate  part 
of  the  hyoidean  bar  persists  in  the  adult  as  the  stylo-hyoid  ligament.  The  blood- 
vessel of  the  hyoid  arch,  the  second  cephalic  aortic  arch,  almost  entirely  disappears, 
but  from  its  ventral  extremity  the  ascending  pharyngeal,  occipital,  and  posterior 
auricular  arteries  are  probably  developed. 

The  third  visceral  arch  forms  part  of  the  neck  posterior  to  the  region  of  the 
second  arch,  and,  as  already  pointed  out,  its  lower  end  takes  part  in  the  formation 
of  the  posterior  part  of  the  tongue.  The  upper  and  middle  parts  of  its  cartilaginous 
bar  disappear,  but  the  lower  part  persists,  and  is  converted  into  the  posterior  part 
of  the  body  and  the  great  cornu  of  the  hyoid  bone  on  its  own  side.  Its  blood- 
vessel, the  third  cephalic  aortic  arch,  becomes  the  lower  part  of  the  stem  of  the 
internal  carotid  artery. 

The  fourth  and  fifth  visceral  arches  also  enter  into  the  formation  of  the  neck, 
but  their  exact  limits  in  the  adult  cannot  be  defined.  Of  the  upper  sections  of  their 
cartilaginous  bars  no  trace  remains  in  the  adult,  but  their  lower  portions  are 
beheved  to  enter  into  the  formation  of  the  thyroid  cartilage  of  the  larynx.  The 
blood-vessel  of  the  fourth  arch  on  the  right  side  becomes  part  of  the  right  sub- 
clavian artery,  that  on  the  left  side  is  converted  into  the  arch  of  the  aorta.  The 
vessels  of  the  fifth  arches  form  portions  of  the  pulmonary  arteries,  and  that  on  the 
left  side  forms  also  the  ductus  arteriosus. 

Further  Development  of  the  Ventral  Wall  of  the  Fore-gut  in  the  Region 
of  the  Furcula. — ^The  sinus  arcuatus  which  surrounds  the  furcula  disappears  to  a 
great  extent  as  development  proceeds,  but  certain  parts  of  it  remain  and  are  recog- 
nisable in  the  adult.  The  anterior  portion  immediately  in  front  of  the  furcula  is 
divided  into  two  parts  as  the  lower  ends  of  the  second  and  third  arches  of  the  two 
sides  converge  and  fuse  in  the  ventral  wall  of  the  pharyngeal  portion  of  the 
fore-gut ;  the  middle  portion  of  the  sinus,  in  front  of  the  transverse  bar  formed  by 
this  fusion,  persists  in  the  adult  as  the  foramen  caecum  of  the  tongue,  and  at  a  very 
early  period  a  diverticulum  grows  backwards  from  it  in  the  fioor  of  the  pharynx, 
dorsal  to  the  cartilage  bars  which  form  the  hyoid  bone,  but  ventral  to  the  rudi- 
ments of  the  tliyroid  cartilage.  This  diverticulum  is  the  thyro-glossal  duct.  As 
soon  as  it  reaches  the  level  of  the  fcjurth  visceral  clefts  it  enlarges,  unites  with  the 
diverticula  from  those  clefts  which  form  the  lateral  lobes  of  the  thyroid  body,  and 
is  itself  converted  into  the  isthmus  of  the  thyroid,  its  pyramidal  process  and  the 
thyro-glossal  duct  or  the  fibrous  cord  into  which  that  duct  becomes  converted  in 
the  adult.  Occasionally  the  thyro-glossal  duct  is  not  wholly  transformed  into  a 
fibrous  cord,  but  portions  of  it  remain  in  the  form  of  isolated  vesicles,  lined  with 


38  GENEEAL  EMBEYOLOGY. 

columnar  (n'  cul)ical  epithelium,  or  as  cords  of  cells,  and  these  occasionally  undergo 
abnormal  development,  forming  tumours  at  the  base  of  the  tongue  or  in  the  upper 
part  of  the  neck. 

The  portion  of  the  sinus  arcuatus  which  lies  behind  the  conjoined  lower 
extremities  of  the  second  and  third  arches  of  opposite  sides,  and  in  front  of  the 
furcula,  persists  in  a  modified  form  in  the  adult,  and  is  recognisable  as  glosso- 
epiglottidean  pouches  or  valleculge  at  the  base  of  the  tongue. 

The  furcula  and  the  groove  in  the  ventral  wall  of  the  fore-gut,  which  it  embraces 
antero-laterally,  are  both  of  considerable  importance.  The  anterior  part  of  the 
furcula  is  situated  in  the  ventral  wall  of  the  pharyngeal  portion  of  the  fore-gut,  but 
its  backward  prolongations  and  the  furrow  between  them  lie  in  what  may  be 
termed  the  intermediate  part  of  the  fore-gut,  that  is,  in  that  part  of  the  fore-gut 
which  intervenes  between  the  pharyngeal  and  stomach  regions.  Gradually  the 
furrow  deepens,  and  its  posterior  extremity  dilates  on  each  side.  Afterwards  the 
margins  of  the  furrow  coalesce  from  behind  forwards,  and  in  this  manner  the 
cavity  of  the  furrow  is  separated  from  the  fore-gut,  its  walls  are  converted  into  the 
trachea  and  the  lower  part  of  the  larynx,  whilst  the  diverticula  which  are  projected 
from  its  posterior  end  form  the  rudiments  of  the  bronchi.  The  fusion  of  the 
margin  of  the  furrow  ceases  a  short  distance  behind  its  anterior  extremity,  which 
latter  persists  as  the  superior  aperture  of  the  larynx.  The  anterior  part  of  the 
furcula,  which  bounds  this  aperture  in  front,  becomes  the  epiglottis,  and  its  lateral 
extensions,  which  form  the  margins  of  the  aperture,  are  converted  into  the  aryteno- 
epiglottidean  folds  in  the  substance  of  which  the  arytenoid  cartilages  and  the 
cartilages  of  Santorini  and  Wrisberg  (cuneiform  cartilages)  are  formed. 

DEVELOPMENT   OF   THE   MOUTH   AND   THE   NOSE. 

The  nose  is  formed  entirely  from  the  stomatodseum.  The  mouth  has  a  double 
origin  ;  the  roof  and  fore-part,  including  the  teeth,  are  developed  from  the  stomato- 
dseum, whilst  the  floor  and  the  tongue  are  developed  from  the  pharyngeal  portion  of 
the  fore-gut. 

It  has  already  been  pointed  out  (p.  34)  that  the  stomatodseal  depression  lies 
between  the  anterior  part  of  the  head  {i.e.  the  tissues  forming  the  base  of  the 
primary  fore-brain)  and  the  pericardial  region,  and  that  it  is  separated  posteriorly 
from  the  fore-gut  by  the  bucco-pharyngeal  membrane.  At  first  it  has  no  distinct 
lateral  boundaries,  but  subsequently  the  mandibular  arches,  which  are  developed  at 
the  sides  of  the  bucco-pharyngeal  membrane,  project  forward  beyond  the  membrane 
and  form  lateral  limits  of  the  depression.  If  the  stomatodseal  space  is  examined 
from  the  front  at  this  period  the  following  boundaries  are  recognisable  : — Above  and 
in  front  is  the  projecting  anterior  part  of  the  head  which  is  termed  the  fronto-nasal 
process,  laterally  are  the  mandibular  arches,  and  below  and  posteriorly  is  the  anterior 
part  of  the  pericardial  region.  After  a  short  time  the  lower  ends  of  the  mandibular 
arches  meet  in  front  of  the  pericardial  region,  and,  fusing  together,  form  the 
posterior  or  lower  margin  of  the  aperture  ;  simultaneously  the  lateral  boundaries  of 
the  space  are  still  further  completed  by  the  forward  growth  of  a  nodular  projection, 
the  maxillary  process,  from  the  upper  end  of  each  mandibular  arch.  About  the 
fifteenth  day  the  bucco-pharyngeal  membrane  disappears,  and  the  stomatodeeal  space 
and  pharynx  are  thenceforth  continuous.  No  trace  of  the  bucco-pharyngeal  mem- 
brane is  recognisable  in  the  adult,  but  its  position  may  be  represented  by  an 
imaginary  plane  extending  from  the  anterior  parb  of  the  basi-sphenoid  above  to  the 
base  of  the  alveolar  process  of  the  lower  jaw,  on  its  lingual  surface,  below. 

Whilst  the  boundaries  of  the  stomatodwal  space  are  being  defined,  two  oval 
depressions,  lined  with  thickened  epithelium,  appear  in  its  upper  boundary  on  the 
lower  and  anterior  surfaces  of  the  fronto-nasal  process ;  these  are  the  olfactory  pits 
or  depressions.  A  portion  of  the  epithelium  of  their  walls  is  separated  off  and  takes 
part  in  the  formation  of  the  olfactory  bulbs,  whilst  the  remainder  is  transformed 
into  the  olfactory  epithelium,  from  which  the  olfactory  nerve-fibres  grow"  inwards 
to  the  olfactory  bulbs.  As  the  olfactory  pits  deepen  they  grow  backwards  into  the 
roof  of  the  stomatodseal  space,  and  at  the  same  time  they  separate  the  lower  portion 


THE  MOUTH  AND  NOSE. 


39 


of  the  fronto-nasal  process  into  three  parts,  constituting  a  median  and  two  lateral 
nasal  processes.  At  each  lateral  angle  of  the  median  nasal  process  a  spheroidal 
elevation,  the  globular  process,  appears.  The  part  of  the  median  nasal  process 
which  intervenes  between  the  two  globular  processes  is  divided  into  two  areas,  an 
upper  triangular  and  a  lower  quadrilateral,  by  the  appearance  of  a  transverse  ridge, 
which  is  afterwards  moulded  into  the  tip  of  the  nose.  The  upper  triangular  area 
becomes  the  dorsum  of  the  nose,  and  the  lower  quadrilateral  area  forms  the 
columella,  i.e.    the  lower  and  anterior  part  of  the  septum  between  the   anterior 


Mesencephalon 


Maxillary 
Eye  process      Mandibular  arch 


Prosencephalon 


Stomatodaeum 


Fig.  31. 

I.  Side  view  of  the  head  of  human  embryo  about  27  days  old,  showing  the  olfactory  pit  and  the  visceral  arches 

and  clefts  (from  His). 

II.  Transverse  section  through  the  head  of  an  embryo,  showing  the  relation  of  the  olfactory  pits  to  the  fore- 

braiu  and  to  the  roof  of  the  stomatodteal  space. 

III.  Head  of  human  embryo  about  29  days  old,  showing  the  division  of  the  lower  part  of  the  mesial  frontal 

process  into  the  two  globular  processes,  the  intervention  of  the  olfactory  pits  between  the  mesial 
and  lateral  nasal  processes,  and  the  approximation  of  the  maxillary  and  lateral  nasal  processes,  which, 
however,  are  separated  by  the  oculo-uasal  sulcus  (from  His). 

IV.  Transverse  section  of  head  of  embryo,  showing  the  deepening  of  the  olfactory  pits  and  their  relation  to  the 

hemisphere  vesicles  of  the  fore-brain. 

nasal  ajjertures.  The  globular  processes  are  utilised  in  the  formation  of  the  philtrum 
or  middle  part  of  tlie  upy^er  lip,  and  the  lateral  nasal  processes  form  the  ala3  of 
the  nose  or  lateral  boundaries  of  tlie  anterior  nasal  apertures.  As  the  olfactory  pits 
deepen  and  grow  backwards  into  the  roof  of  the  stomatodceum  the  maxillary  pro- 
cesses grow  forwards  from  the  lateral  boundaries  of  that  space,  that  is  from  the 
upper  ends  of  the  mandibular  arches,  and  pass  beneath  the  eyes,  which  now  form 
distinct  prominences  on  the  sides  of  the  head.  The  upper  borders  of  the  maxillary 
processes  come  into  contact  with  the  lateral  nasal  ])rocesses  from  which  they  are 
temporarily  separated  by  grooves,  the  oculo-nasal  sulci.  These  latter  pass  from  the 
depressions  round  th(;  eyeballs,  tlie  rudimentary  conjunctival  sacs,  to  the  margins 
of  the  nasal  pits.     The  anterior  extremities  (jf  the  maxillary  processes  impinge 


40 


GENEEAL  EMBEYOLOGY. 


upon  the  globular  processes,  and  ultimately  their  upper  borders  and  anterior  ex- 
tremities fuse  with  the  lateral  nasal  and  globular  processes,  completing  the  lower 
boundaries  of  the  anterior  nasal  orifices  and  the  lateral  parts  of  the  primitive 
upper  lip.  At  the  same  time  the  oculo-nasal  sulci  are  converted  first  into  solid 
cords  of  cells,  and  afterwards  into  the  lachrymal  sacs  and  the  nasal  ducts,  which 
henceforth  constitute  the  channels  of  communication  between  the  conjunctival 
sacs  and  the  nose. 

The  result  of  the  ingrowth  of  the  maxillary  processes  and  their  fusion  with  tlie 


Cerpbral  lieiiiisijlieres 


Olfactory  pit 


Globular  process 


Maxillary  proces; 


Olfactory  pit 

^  Maxillary  process 

Globular  process 
Mouth 


Aut.  nasal  orifice !;5 


Globular  process 
Maxillary  process 


Lower  jaw 


Cerebral 
lieuiisphere 


Nasal  cavity 

Jacobson's  organ 

Globular  process 
Maxillary  process 

Lower  jaw 


ir 


III 


Mouth 
Fir..  32. 

I.  Portion  of  tlie  head  and  neck  of  a  human  embryo  32  days  old.  The  floor  of  the  mouth  and  pharynx  and 
the  ventral  part  of  the  anterior  portion  of  the  body  have  been  removed.  By  the  approximation  of  the 
globular  and  maxillary  processes  the  boundaries  of  the  anterior  nares  are  almost  complete,  bnt  the 
olfactory  pits  still  open  in  the  whole  of  their  lengths  into  the  roof  of  the  mouth  (from  His). 
Transverse  section  of  the  head  of  an  embryo,  showing  the  close  apposition  of  the  globular  and  maxillary 
processes. 
Head  of  human  embryo  about  2  months  old,  showing  the  union  of  the  globular  processes  and  their  fusion, 
with  the  maxillary  processes.     The  anterior  nasal  apertures  are  now  completely  defined  (Irom  His). 

IV.  Transverse  section  of  the  head  of  an  embryo,  showing  tlie  fusion  of  the  maxillary  processes    with  the 
globular  processes,  and  the  separation  anteriorly  of  the  nose  from  the  mouth. 

lateral  nasal  and  globular  processes  is  the  division  of  the  large  orifice  which  led  into 
the  stomatodgeal  space  into  three  parts — a  large  lower,  and  two  smaller  upper  aper- 
tures. The  lower  opening  is  the  aperture  of  the  mouth ;  it  is  bounded  below  by 
the  united  mandibular  arches,  and  above  by  the  fused  mesial  nasal  and  maxillary 
processes.  The  smaller  upper  openings  are  the  anterior  nares,  which  on  their  first 
formation  are  merely  foramina  of  communication  between  the  exterior  and  the 
upper  part  of  the  stomatodseal  space ;  the  latter  is  not  yet  separated  into  nasal  and 
oral  chambers. 

Formation  of  the  Palate  and  the  Separation  of  the  Nasal  and  Buccal 
Cavities. — This  separation  is  effected  by  the  formation  of  the  palate,  which  is 
developed  to  a  slight  extent  by  the  backward  growth  of  the  globular  processes 


rOKMATION  OF  THE  PALATE. 


41 


along  the  roof  of  the  space  as  a  pair  of  ridges,  termed  the  nasal  laminse,  which  fuse 
together  to  form  a  small  anterior  portion  of  the  palate,  viz.  the  intermaxillary  pro- 
cess, in  which  the  intermaxillary  parts  of  the  superior  maxillae  are  formed.  The 
remaining  and  greater  part  of  the  palate  is  formed  by  two  ledge-like  ingrowths, 
one  from  the  inner  surface  of  each  maxillary  process,  which  meet  and  fuse  anteriorly 
with  the  intermaxillary  process,  and  behind  this  with  each  other.  In  these  pro- 
jections the  palatal  processes  of  the  superior  maxillse  and  the  horizontal  plates  of 
the  palate  bones  are  formed,  and  by  their  fusion  the  upper  part  of  the  stomatodaeal 
space  is  separated  off  from  the  remainder  as  a  common  nasal  chamber  which  com- 
municates in  front  with  the  exterior  by  the  anterior  narial  orifices,  and  behind 
with  the  pharyngeal  portion  of  the  fore-gut  by  the  choanal  apertures  or  posterior 
nares.  The  lower  part  of  the  stomatodseal  space  and  the  front  part  of  the  fore-gut 
together  form  the  mouth  or  buccal  cavity ;  this  opens  anteriorly  by  a  transverse 
aperture,  the  boundaries  of  which  have  already  been  described,  and  posteriorly  it  is 
in  direct  continuity  with  the  pharynx. 

The  division  of  the  common  nasal  chamber  into  two  parts  commences  before  its 
separation  from  the  mouth  is  completed,  and  it  is  brought  about  by  the  development 


Anterior  nasal  orifice 


Ethmo-vomerine  plate 
Nasal  cavity 


Jacobson's  organ 


Mouth 


Palatal, 
process 


Pituitary  depression 

Fig.  33. 


Mecliel's  cartilage 


I.  Portion  of  the  head  of  a  human  embryo  about  2^  mouths  old  (His).     The  lips  are  sejjarated  from  the  gums, 

and  the  line  of  the  common  dental  germ  is  visible  in  the  latter.     The  palatal  processes  are  growing 
inwards  from  the  maxillary  processes. 

II.  Transverse  section  of  the  head  of  an  embryo  after  the  fusion  of  the  palatal  processes  of  the  maxillary  pro- 

cesses with  the  nasal  septum,  which  grows  backwards  from  the  fused  globular  processes. 

of  a  septum  which  is  continuous  anteriorly  with  the  fused  nasal  laminee,  and  which 
grows  downwards  and  backwards  from  the  mesial  part  of  the  under  aspect  of  the 
fronto-nasal  process.  This  septum  fuses  below  with  the  conjoined  margins  of  the 
palatal  ledges  of  the  maxillary  processes,  and  a  vertical  plate  of  cartilage  soon 
develops  in  its  interior,  which  is  continuous  above  with  the  cartilaginous  base  of  the 
cranium  (basi-cranial  axis).  A  portion  of  this  septal  cartilage  remains  in  the  adult 
as  the  septal  cartilage  of  the  nose,  and  the  remainder  is  more  or  less  completely 
replaced  by  the  vertical  plate  of  the  ethmoid  bone  and  by  the  vomer.  The  lateral 
wall  of  each  nasal  chamber  is  formed,  in  the  lower  part  of  its  extent,  by  the 
maxillary  process  of  the  mandibular  arch,  in  which  the  superior  maxillary,  malar, 
and  palate  bones,  and  possibly  the  internal  pterygoid  plate,  are  developed,  and  in 
the  upper  part  by  the  outer  boundary  of  the  original  nasal  pit,  which  now  forms 
only  the  upper  part  of  the  nasal  cavity.  In  this  upper  section  of  the  outer  wall 
an  outgrowth  of  the  basi-cranial  axis  projects  downwards,  and  is  developed  into 
the  lateral  mass  of  the  ethmoid  bone ;  probably  it  also  takes  part  in  tlie  formation 
of  the  inferior  turbiual  bone. 

The  fusion  of  the  three  segments  of  the  palate  commences  anteriorly  at  the 
eighth  week  by  the  union  of  the  maxillary  and  globular  processes ;  it  passes  back- 
wards and  is  completed  by  the  fusion  of  the  posterior  parts  of  the  palatal  ledges  of 
the  maxillary  processes  about  the  tenth  week.  To  the  non-completion  of  this 
fusion  the  various  cases  of  hare-lip  and  cleft  palate  are  due. 

Organ  of  Jacobson.  — 'I'lie  organs  of  .facobsou  arc  rudinicntary  structures  in  num. 


42 


GENEEAL  EMBEYOLOGY. 


They  lie  in  the  lower  and  anterior  part  of  the  nasal  septum,  one  upon  each  side. 
They  are  developed  as  small  diverticula  which  grow  backwards  and  upwards  in  the 
substance  of  the  septum,  and  their  points  of  commencement  are  situated  immediately 
above  the  intermaxillary  segment  of  the  palate.  Each  diverticulum  is  partially  sur- 
rounded, on  its  inner  side,  by  a  cartilaginous  capsule,  it  ends  blindly  behind,  and  it  opens 
anteriorly  close  to  the  floor  of  the  nose  in  the  region  of  Stenson's  foramen — a  small 
aperture  left  between  the  premaxillary  and  maxillary  sections  of  the  bony  palate. 

Pituitary  Body. — The  pituitary  body  is  formed  partly  from  the  lloor  of  the 
first  primary  cerebral  vesicle,  and  partly  from  the  roof  of  the  stomatodteal  space. 
The  stomatodccal  portion  appears  as  a  small  pouch,  Eathke's  pouch,  which  grows 
upwards  into  the  base  of  the  head  immediately  in  front  of  the  dorsal  margin 
of  the  bucco-pharyngeal  membrane  and  the  anterior  end  of  the  notochord,  and 

behind  the  fore-brain.  It  is  lined  by 
ectoderm,  and  soon  becomes  a  conical 
vesicle  which  lies  beneath  the  base  of 
the  fore-brain.  Its  orifice  of  communica- 
tion with  the  stomatodaeal  space  is  gradu- 
ally constricted  until  the  lumen  dis- 
appears, and  then  for  a  time  the  vesicle 
is  connected  with  the  surface  by  a  solid 
^^  cord  of  ectodermal  cells.  This  also  dis- 
appears, and  the  vesicle  is  embedded  in 
the  base  of  the  head  in  a  region  above 
and  between  those  parts  of  the  basal 
axis  which  afterwards  are  transformed 
into  the  basi-  and  pre-sphenoid  elements 
of  the  sphenoid  bone. 

During  the  period  of  its  formation 
and  separation  the  ingrowth  from  the 
stomatodgeum  comes  into  relation  pos- 
teriorly with  a  small  diverticulum  from 
the  floor  of  the  fore-brain,  which  dilates 
at  its  lower  end  to  form  the  posterior 
or  cerebral  lobe  of  the  pituitary  body, 
whilst  its  upper  part  remains  as  the 
infundibulum,  the  connecting  stalk  be- 
tween the  pituitary  body  and  the  floor 
of  the  third  ventricle  of  the  brain.  The 
anterior  or  stomatoda^al  lobe  of  the 
pituitary  body  is  much  larger  than  the 


Fig.  34.- 


-  Vertical  Section  through  Head  of 
Rat  Embryo. 


Showing  the  formation  of  the  two  parts  of  the  pituitary 
body  (diagrammatic). 

(Ectoderm  is  represented  in  black,  entoderm  in  bhie, 
and  mesoderm  in  red.) 


At. 
Ax. 
B. 


Atlas. 

Axis. 

Cartilaginous    basi- 
cranial  axis. 

Heart. 
HB.   Hind-brain. 
MB.  Mid-brain. 
N.      Part  of  nasal  cavity 


H. 


P.     Pineal  body. 

PR.  Cerebral  hemisphere. 

Pfi.  Cerebral  part  ot  pituit-  posterior  lobe,  wliich  it  surrounds  and 

ary  body.  ^  ,     ,       ,     .       „  ,  .         .  , 


Pt^.  Buccal  part  of  jDituitary 

body. 
SG.  Spinal  ganglion. 
T.     Tonsrue. 


Th.  Thalamencephalon. 


conceals  both  in  front  and  at  the  sides. 
It  is  evident  that  in  the  early  stages 
the  pituitary  body  consists  of  two  ecto- 
dermal vesicles,  the  cavity  of  the  pos- 
terior vesicle  is  continuous  with  the 
cerebral  tube,  and  that  of  the  anterior  vesicle  with  the  cavity  of  the  primitive 
mouth.  The  cavity  of  the  posterior  vesicle  is  generally  obliterated,  and  though 
nervous  structures  are  for  a  time  developed  in  its  walls  they  entirely  disappear  in 
man  and  are  replaced  by  vascular  connective  tissue.  Occasionally  a  small  part  of 
the  cavity  remains  as  a  minute  vesicle  lined  with  columnar  ciliated  epithelium. 

The  cavity  of  the  anterior  vesicle  persists,  it  sends  out  numerous  diverticula, 
and  is  gradually  converted  into  a  number  of  tubular  spaces,  lined  with  cubical  or 
columnar  cells,  united  together  by  vascular  connective  tissue  which  has  grown 
amidst  the  tubules  from  the  surroundiuo-  mesoderm. 


THE  EXTEENAL  EAR  AND  EUSTACHIAN  TUBE. 


43 


HM 


THE  EXTERNAL  EAR,  THE  TYMPANIC  CAVITY,  AND  THE 
EUSTACHIAN  TUBE. 

The  external  ear,  the  tympanic  cavity,  and  the  Eustachian  tube  are  all  developed 
from  the  first  visceral  cleft  and  its  boundaries.  The  cleft  lies  between  the 
mandibular  (first)  and  the  hyoid  (second)  visceral  arch  in  the  side  wall  of  the 
pharyngeal  portion  of  the  fore-gut,  and,  before  a  neck  is  developed,  it  extends  from 
just  ventral  to  the  otic  vesicle,  which  lies  at  the  side  of  the  hind-brain,  above,  to 
the  pericardial  region  below.  The  membrane  which  lies  at  the  bottom  of  the  cleft 
consists  in  the  early  stages  of  ectoderm  and  entoderm,  but  in  a  short  time  a  thin 
layer  of  mesoderm  grows  between  the  two  primary  layers,  and  the  trilaminar  septum 
is  ultimately  converted    into  hb 

the  tympanic  membrane  which 
separates  the  external  from 
the  middle  ear. 

The  differentiation  of  the 
outer  part  of  the  cleft  is  initi- 
ated by  the  appearance  of  six 
tubercles  round  its  margins, 
which  are  afterwards  trans- 
formed into  the  several  parts  by" 
of  the  pinna. 

Two  tubercles  are  formed 
anteriorly  on  the  mandibular 
arch,  one  at  the  dorsal  end  of 
the  cleft  and  three  posteriorly 
on  the  hyoid  arch.  The  two 
tubercles  on  the  mandibular 
arch  are  a  small  lower,  the 
tuberculum  tragicum,  and  a 
larger  upper,  the  tuberculum 
anterius  helicis.  The  tubercle 
at  the  upper  end  of  the  cleft 
is  the  tuberculum  intermedium 
helicis.  The  upper  tubercle 
on  the  hyoid  arch  is  the  tuber- 
culum anthelicis,  the  middle  is 
the  tuberculum  antitragicum, 
and  the  lowest  is  the  tuber- 
culum lobulare.  Shortly  after  the  appearance  of  the  tubercles  a  process,  the  caudal 
process,  grows  backwards  and  downwards,  from  the  posterior  part  of  the  tuberculum 
intermedium  helicis,  behind  the  tuberculum  anthelicis  and  the  tuberculum  anti- 
tragicum to  the  tuberculum  lobulare,  with  which  it  fuses.  The  tuberculum  tragicum 
remains  more  or  less  distinct,  and  it  forms  the  prominence  called  the  tragus  which 
lies  in  front  of  the  concha  and  external  auditory  meatus. 

The  two  tubercles  of  the  helix  and  the  caudal  process  unite  to  form  the  helix 
or  marginal  portion  of  the  pinna ;  this  terminates  below  in  the  lobule  which  is 
developed  from  the  tuberculum  lobulare.  The  tuberculum  anthelicis  and  the 
tuberculum  antitragicum  are  the  rudiments  respectively  of  the  antihelix  and  the 
antitragus,  and  tlie  latter  unites  below  the  lower  part  of  the  cleft  with  the  rudiment 
of  the  tragus,  forming  the  lower  boundary  of  the  outer  part  of  the  external  meatus. 
It  should  be  noted  that  in  the  early  stages  the  tuberculum  anterius  helicis  lies  in 
front  of  the  outer  part  of  tlie  first  visceral  cleft,  but  it  does  not  retain  this  position 
in  the  later  stages  during  which  the  cleft  is  relatively  reduced  in  size,  and  when 
development  is  completed  and  the  outer  part  of  tlie  cleft  is  transformed  into  the 
external  auditory  meatus  the  commencement  of  the  helix,  which  is  developed  from 
the  tuberculum  anterius  helicis,  is  situated  just  a})0vc  tlie  outer  extremity  of  the 
external  meatus. 


Fig.  35. 


-Transverse  Section  through  the  Head 
OF  A  Rat  Embryo. 


Showing  the  rudiments  of  the  three  parts  of  the  ear  and  their 
relation  to  the  hyo-mandibular  cleft. 


BV.  Blood-vessels. 

C.      Cochlea. 

EM.  Ext.  auditory  meatus. 

ET.    Eustachian  tube. 

HB.  Hind-brain. 

HM.  Hyo-mandibular  cleft. 


N.  Notochord. 

OV.  Otic  vesicle. 

P.  Pharynx. 

EL.  Recessus  labyrinthii. 

SC.  Semicircular  canal. 

T.  Tympanum. 


44 


GENEEAL  EMBEYOLOGY. 


The  outer  part  of  the  cleft  is  moulded  into  the  external  auditory  passage.  It 
remains  relatively  shallow  and  devoid  of  bony  boundaries  till  after  birth,  but  in 
the  subcutaneous  tissue  round  the  lower  margin  of  the  tympanic  membrane  an 
incomplete  ring  of  bone  is  formed  during  the  third  month,  and  at  an  earlier  period, 
above  the  upper  part  of  that  membrane,  the  rudiment  of  the  squamous  jjart  of  the 
temporal  bone  appears.  To  the  outer  side  of  the  tympanic  ring  in  the  suljcutaueous 
tissue  of  the  pinna  and  the  outer  part  of  the  external  auditory  passage  three  pieces 
of  cartilage  appear,  and  they  afterwards  join  to  form  the  cartilage  of  the  pinna  and 
the  external  auditory  meatus. 

After  birth  the  external  meatus  is  deepened  by  the  outgrowth  of  the  tympanic 
ring  below  and  of  the  squamous  part  of  the  temporal  bone  above,  together  with  a 

coincident  in- 
crease of  the  outer 
part  of  the  canal. 
The  tympanic 
cavity  and  the 
Eustachian  tube 
are  both  formed 
from  the  inner 
part  of  the  first 
visceral  cleft,  and 
consequently  they 
are  both  lined  by 
entoderm. 

The  tympanic 
cavity  is  de\  eloped 
from  the  dorsal  or 
upper  end  of  this 
portion  of  the  cleft, 
and  it  is  prolonged 
upwards  on  the 
outer  side  of  the 
otic  vesicle  which 
simultaneously 
descends  in  the 
tissues  of  the  head. 
Thus  the  upper 
end  of  the  inner 
portion  of  the  cleft, 
which  is  somewhat 
dilated,  comes  to 
lie  between  the 
otic  vesicle,  which 
is  developed  into  the  internal  ear  on  the  inner  side,  and  the  tympanic  membrane 
which  separates  it  from  the  external  auditory  meatus  on  the  outer  side,  and  it 
remains  in  the  adult  as  a  laterally  compressed  space,  the  tympanic  cavity,  which 
is  continuous  through  the  Eustachian  tube  with  the  upper  part  of  the  pharynx.  In 
the  mesoderm  round  the  inner,  upper,  and  back  part  of  the  cavity  the  petrous  part  of 
the  temporal  bone  is  developed  and  ossified,  and  in  the  lower  and  anterior  part  the 
tympanic  ossification  extends  outwards  during  the  formation  of  the  tympanic  plate. 

The  upper  part  of  the  tympanic  space  is  prolonged  backwards  between  the  ossifying 
petrous  and  sq\iamous  parts  of  the  temporal  bone,  where  it  forms  a  recess  known  in  the 
adult  as  the  mastoid  antrum,  from  which  at  a  later  period  diverticuhi  are  projected  into 
the  mastoid  portion  of  the  temporal  bone,  forming  the  mastoid  air  cells. 

'>  The  lower  portion  of  the  inner  part  of  the  cleft  is  moved  obliquely  forwards. 
As  development  proceeds  it  is  contracted  and  carried  downwards  and  forwards  in 
front  of  the  developing  otic  vesicle.  It  is  the  rudiment  of  the  Eustachian  tube, 
and,  as  the  septum  which  separates  the  nasal  chambers  from  the  mouth  is  formed^ 


Fiu.  36.- 


-Figures,  modified  from  His,  illustrating  the  Formation  of 
THE  Pinna. 


Tuberculuiu  tragicura  =  Tragus. 
,,  anterius  helicis  "j 

,,  intermedium  helicis  ^  Helix. 

Cauda  helicis  j 

Tuberculum  iinthelicis  =  Autihelix. 


6.  Tuberculum    autitragicum  =  Anti- 

tragus. 

7.  Tubeiculum  lobulare  =  Lobule. 
HM.  Hyo-mandibular  cleft. 

OV.    Otic  vesicle. 


THE  HIND-GUT  AND  ANAL  PASSAGE.  45 

its  lower  end  attains  a  position  just  Vjehind  and  at  the  side  of  the  posterior  narial 
orifice  in  the  upper  and  lateral  part  of  the  pharynx.  Apparently,  therefore,  the 
lower  end  of  the  Eustachian  tube  has  a  much  higher  position  than  that  originally 
occupied  by  the  lower  end  of  the  cleft  from  which  it  is  formed,  for  it  will  be 
remembered  that  the  lower  end  of  the  first  visceral  cleft  is  situated,  in  the  early 
stages,  at  the  side  of  the  tuberculum  impar  from  which  the  anterior  two-thirds  of 
the  tongue  is  formed.  This  alteration  in  relative  position  is  due,  however,  not  to 
elevation  of  the  lower  end  of  the  first  visceral  cleft  during  its  transformation  into 
the  Eustachian  passage,  but  to  the  enormous  downgrowth  of  the  mandibular  arches, 
which  carry  with  them  the  tongue,  as  they  enlarge  to  form  the  lower  jaw. 

THE  HIND-GUT,  THE  ANAL  PASSAGE,  AND  THE  POST-ANAL 

OE  TAIL-GUT. 

By  the  formation  of  the  mouth  the  primitive  alimentary  canal  opens  anteriorly  ; 
it  remains  closed  posteriorly  until  a  later  date,  when  the  anal  passage  and  orifice 
are  developed. 

The  posterior  end  of  the  hind-gut  which  is  enclosed  in  the  tail- fold  is  termed 
the  cloaca.  The  cloaca  is  dilated,  and,  assuming  a  conical  form,  receives  the 
terminations  of  the  genito-urinary  ducts.  It  is  bounded  postero-inferiorly  by  the 
cloacal  membrane  which  extends  from  the  root  of  the  tail  to  the  body  stalk  by  whicli 
the  embryo  is  attached  to  the  chorion.  The  cloacal  membrane  is  modified  from  the 
posterior  part  of  the  primitive  streak ;  this  remains  on  the  surface  of  the  body  after 
the  anterior  part  has  been  separated  and  enclosed  during  the  completion  of  the 
posterior  part  of  the  neural  canal,  and  it  forms  a  septum  between  the  cavity  of  the 
cloaca  and  the  exterior.  It  consists  at  first  of  ectoderm  and  entoderm  alone,  and 
it  is  only  at  its  lower  and  anterior  part  that  it  is  subsequently  invaded  to  a  slight 
extent  by  mesoderm. 

During  the  second  month  of  intrauterine  life  the  cloaca  is  divided  into  a  ventral 
or  genito-urinary,  and  a  dorsal  or  rectal  section,  by  the  formation  and  fusion  of 
lateral  folds,  which  gradually  unite,  from  before  backwards,  till  finally  the  posterior 
end  of  the  septum  approaches  and  fuses  with  the  cloacal  membrane,  and  the 
rectum  is  separated  from  the  genito-urinary  chamber.  Before  this  separation 
is  completed  an  eminence  appears  in  the  region  of  the  anterior  part  of  the 
cloacal  membrane  at  the  junction  of  the  ventral  surface  with  the  posterior 
extremity  of  the  body,  i.e.  in  that  part  which  afterwards  becomes  the  region  of  the 
symphysis  pubis.  This  eminence  is  the  genital  eminence,  and  from  it  are  formed 
the  penis  in  the  male  and  the  clitoris  in  the  female.  The  genital  eminence  is 
surrounded  by  an  oval  fold  of  skin,  genital  fold,  which  extends  from  the  front  of 
the  eminence  to  the  root  of  the  tail  and  encloses  a  shallow  fossa,  the  cloacal  fossa, 
at  the  bottom  of  which  is  the  cloacal  membrane.  The  posterior  part  of  the  cloacal 
fossa  is  afterwards  separated  from  the  anterior  part  by  a  transverse  fold,  the  perineal 
fold,  which  crosses  the  external  surface  of  the  cloacal  membrane  in  a  position  which 
corresponds  internally  with  that  occupied  by  the  lower  end  of  the  septum  separating 
the  genito-urinary  from  the  rectal  portions  of  the  cloacal.  The  posterior  part  of 
the  cloacal  fossa,  behind  the  transverse  fold,  is  the  proctodseal  depression  or 
proctodaeum ;  at  first  its  long  axis  lies  transversely,  afterwards  it  assumes  a 
triangular  and  then  a  circular  form,  the  sphincter  ani  muscle  develops  in  its  walls, 
and  it  is  transformed  into  the  greater  part,  if  not  the  whole,  of  the  anal  canal  of 
the  adult.  It  is  separated  from  the  rectum  by  the  posterior  part  of  the  cloacal 
membrane,  Init  when  that  disappciars,  at  a  date  which  has  not  yet  been  definitely 
ascertained,  but  probably  about  the  third  month,  the  anal  passage  forms  the  canal 
by  wliich  the  rectum  communicates  with  the  exterior  of  the  body. 

1'he  orifices  of  the  alimentary  canal  are  thus  completed. 

The  Post-anal  or  Tail-Gut. — ^Whcn  the  hind-gut  is  first  enclosed  there  is  no  tail, 
but  a  rudimentary  tail  is  .subse()ueHtly  developed  as  an  outgrowth  from  the  dorsal  end  of 
the  tail-fold,  i.e.  from  the  posterior  extremity  of  the  body  of  the  embryo.  As  the  tail  is 
formed,  a  narrow  tube,  which  comminiicafces  in  front  with  the  hiiid-gut,  is  developed 
within  it.     This  is  called   the  post-anal  or  tail-gut.      As  a   rul(!   it  only  exists  for  a  short 


46 


GENEEAL  EMBEYOLOGY. 


time,  disappearing  from  before  l)ack wards  about  the  period  when  cartilage  begins  to  be 
formed  in  the  body  and  limbs,  and  before  the  cloaca  is  divided  into  its  rectal  and  genito- 
urinary portions.  In  the  few  cases  in  which  it  persists 
it  retains  its  continuity  with  the  rectum,  which  is 
formed  from  the  dorsal  part  of  the  cloaca. 

The  tail-gut  appears  in  the  human  subject  when 
the  embryo  is  3  mm.  long,  and  the  rudimeiitary  tail  is 
just  visible  as  a  small  nodule.  When  the  embryo 
attains  the  length  of  4 '8  mm.  the  anterior  part  of 
the  tail-gut  begins  to  degenerate,  its  cavity  disappears, 
and  it  is  converted  into  a  solid  cord  of  cells  which  is 
still  attached  in  front  to  the  hind-gut.  In  embryos 
11  "5  mm.  long,  when  the  tail  has  been  enclosed  in  the 
posterior  part  of  the  body,  the  connexion  of  the  tail- 
gut  with  the  hind -gut  is  lost,  and  the  tail -gut  is 
represented  by  a  small  vesicle  with  a  short  cord  of 
degenerating  cells  attached  to  its  anterior  part. 

In  larger  embryos  the  tail-gut  entirely  disappears. 
When,  as  in  the  human  siibject,  the  rudimentary  tail  is 
eventually  embedded  in  the  posterior  end  of  the  body, 
any  rudiments  of  the  tail-gut  which  persist  will  be 
found  in  this  situation ;  it  is  stated  that  such  rudi- 
ments occasionally  develop  into  tumour  formations. 
In  mammals  with  free  tails,  rudiments  of  the  tail-gut 
may  be  met  with  in  any  part  of  the  tail,  and  apparently 
the  anterior  portioii  occasionally  persists  and  maintains 
its  connexion  with  the  rectum,  from  which  it  extends 
backwards  as  a  narrow  and  blind  diverticulum. 

THE   LIMBS. 

Though  the  body  of  the  embryo  begins  to  assume 
definite  form  as  soon  as  it  is  folded  and  nipped  off 
from  the  rest  of  the  ovum,  it  does  not  present  any 
distinguishable  human  characteristics  until  the 
anterior  and  posterior  limbs  are  formed.  There  are 
no  traces  of  these  before  the  third  week  of  in- 
trauterine life  when  two  longitudinal  ridges,  the 
Wolffian  ridges,  are  developed,  one  on  each  lateral 
tion  of  the  cioacai  part  of  the  hind-  surfacc  of  the  body,  just  external  to  the  outer 
gut^  into    genito- urinary    tract    and  niargins  of  the  mesodcrmic  somitcs,  and  opposite 

the  line  of  the  intermediate  cell  mass.  The  rudi- 
ments of  the  fore-  and  hind-limbs  are  discernible, 
almost  from  the  first,  as  slight  prominehces  of  the 
Wolffian  ridges,  and  in  the  fourth  week  they  project 
as  bud-like  outgrowths  in  the  thoracic  and  pelvic 
regions  respectively.  The  development  of  the  fore-limb  or  arm  is  throughout 
slightly  in  advance  of  that  of  the  hind-limb  or  leg.  At  the  fourth  week  each 
limb-bud  is  a  flattened  semilunar  projection,  as  long  as  it  is  broad,  with  a  dorsal 
and  a  ventral  surface  and  an  anterior  or  preaxial,  and  a  posterior  or  postaxial 
border.  As  growth  proceeds  the  elongating  limb-buds  are  bent  ventrally,  and  in 
the  fifth  week  two  transverse  furrows,  on  the  ventral  aspect  of  each,  indicate  the 
positions  of  the  joints  and  the  division  of  each  limb  into  three  segments — distal, 
middle,  and  proximal — representing  the  hand,  fore-arm,  and  arm  in  the  upper  limb, 
and  the  foot,  leg,  and  thigh  in  the  lower  limb.  The  terminal  or  distal  segments 
are  broad,  flat  plates  with  rounded  margins,  but  each  is  soon  divided  into  a  some- 
what enlarged  basal  part,  and  a  thinner  and  more  flattened  marginal  part.  It  is 
where  these  two  parts  are  continuous  that  the  rudiments  of  the  digits  appear. 
They  become  distinguishable  about  the  end  of  the  fifth  week  as  small  lobes  which 
gradually  extend  outwards.  In  the  fore-limb  the  fingers  project  beyond  the  margin 
of  the  hand-segments  in  the  sixth  week,  but  the  toes  do  not  reach  the  margins  of 


Fig.  37.  — Diagrams  showing  the  separa- 


rectum. 

A.  Allantoic  stalk. 

B.  Bladder. 

C.  Cloaca. 

CM.  Cloacal  membrane 
K.      Kidney. 
II.      Rectum. 


U.      Ureter. 
Ur.     Urethra. 
VD.    Vas  deferens. 
VS.     Vesicula  semi- 

nalis. 
WD.  Wolffian  duct. 


THE  LIMBS.  47 

the  foot  till  the  early  part  of  the  seventh  week.  The  nails  appear  at  the  third 
month,  and  reach  the  ends  of  the  digits  at  the  sixth  month. 

In  the  primary  position  of  the  limbs  the  elbow  and  the  knee  appear  alike  to  be 
directed  outwards,  but  this  is  soon  altered.  At  the  end  of  the  sixth  week  each 
limb  undergoes  a  partial  rotation,  the  direction  of  which  is  different  in  the  fore-  and 
hind-limbs  respectively.  In  the  former  the  elbow  is  turned  backwards,  the  ventral 
surface  therefore  becomes  anterior,  and  the  preaxial  (thumb)  margin  is  directed 
outwards ;  in  the  hind-limb  the  knee  is  turned  forwards,  and  the  ventral  surface  of 
the  limb  becomes  posterior,  whilst  the  preaxial  (great  toe)  margin  is  directed 
inwards ;  thus  in  the  adult  the  anterior  surface  and  outer  border  of  the  upper 
extremity  correspond  with  the  posterior  surface  and  inner  border  of  the  lower 
extremity,  whilst  obviously  the  posterior  surface  and  inner  border  of  the  former 
are  homologous  with  the  anterior  surface  and  outer  border  of  the  latter. 

Each  limb-bud  may  be  regarded  as  an  extension  from  a  definite  number  of  the 
segments  of  the  body ;  it  contains  a  core  of  mesoderm,  and  the  anterior  or  ventral 
primary  divisions  of  the  corresponding  spinal  nerve  segments  are  apparently 
prolonged  into  it. 

The  central  part  of  the  mesoderm,  except  in  the  regions  of  the  joints  where 
cavities  appear,  is  condensed  and  then  converted  first  into  cartilage,  and  afterwards 
into  bone.  The  proximal  part  of  the  bony  skeleton  of  each  limb,  the  limb  girdle, 
is  not,  however,  developed  in  the  limb-bud,  but  in  the  body- wall  at  its  base.  The 
more  superficially  situated  mesoderm  is  transformed  into  muscles  and  subcutaneous 
tissues,  the  extensor  muscles  appearing  on  the  dorsal  and  the  flexor  muscles  on  the 
ventral  aspect. 

As  the  nerve  trunks  pass  into  the  free  portion  of  the  limb  they  bifurcate,  the 
branches  passing  respectively  to  the  dorsal  or  extensor  aspect  of  the  limb,  and  to 
the  ventral  or  flexor  aspect. 

Apparently  in  mammals  the  whole  of  the  mesodermal  core  of  each  limb-bud  is 
formed  from  the  somatic  mesoderm  of  the  lateral  plates.  If  this  is  the  case  the 
muscles  of  the  limbs  differ  in  origin  from  those  of  the  back,  for  the  latter  are 
developed  from  the  muscle  plates  of  the  protovertebral  somites.  In  lower  verte- 
brates (cartilaginous  fishes)  buds  are  given  off  to  the  limbs  from  the  muscle  plates 
and  cutaneous  lamellae  in  the  thoracic  and  pelvic  regions,  and  as  the  muscle  plates 
pass  downwards  in  the  somatopleure  towards  the  ventral  aspect  of  the  body,  these 
buds  grow  outwards  into  the  limb-rudiments  and  develop  into  the  muscles  of  the 
limbs.  Presumably  this  is  the  more  primitive  arrangement,  and  that  met  with  in 
man  and  other  mammals  is  secondary,  and  it  is  stated  that  although  no  distinct 
buds  from  the  muscle  plates  pass  into  the  limbs  of  mammals,  nevertheless  the 
limb-muscles  are  formed  by  cells,  proliferated  from  the  muscle  plates,  which  have 
migrated  into  the  somatopleural  mesoderm  of  the  limbs. 


THE   NUTRITION   AND   PROTECTION   OF   THE   EMBRYO 
DURING   ITS   INTRAUTERINE   EXISTENCE. 

The  impregnated  ovum  during  its  passage  down  the  Fallopian  tube,  and  for  a 
brief  period  also  after  it  enters  the  uterus,  lives  either  on  the  yolk  gTanules  (deuto- 
plasm;  embedded  in  its  own  cytoplasm,  or  upon  material  absorljed  from  the  fluids 
by  which  it  is  surrounded.  The  human  ovum  is  very  small,  and  consequently  it  is 
almost  from  the  first  dependent  for  its  nutrition  upon  sources  of  supply  outside 
itself.  The  urgent  necessity  for  adequate  arrangements  whereby  this  may  be 
effected  leads  to  that  early  establishment  of  an  intimate  vascular  connexion 
between  the  embryo  and  the  mother  which  is  so  characteristic  a  feature  in  the 
development  of  the  human  (jvum.  At  the  end  of  the  second  week,  after  fertilisa- 
tion of  tin;  ovum,  tlie  embryo  is  separated  by  a  slight  constriction  from  the  rest  of 
the  Idastodermic  vesicle,  and  iiJn^udy  a  primitive  heart  and  rudimentary  blood- 
vessels are  distinguishable. 

The  development  oi"  tin;  vascular  system,  and  the  cstaltlishmcnt  of  the  fcetal 


48  GENERAL  EMBRYOLOGY. 

circulatiou,  however,  cannot  well  be  understood  initil  the  formation  and  structural 
features  of  the  group  of  closely  associated  extra-embryonic  organs  or  appendages 
have  been  considered. 

This  group  includes  the  yolk-sac,  the  chorion,  the  amnion,  the  allantois,  and 
the  placenta. 

THE    FCETAL   MEMBRANES    AND   APPENDAGES. 

Yolk-Sac  or  Umbilical  Vesicle. — That  portion  of  the  Ijlastodermic  cavity 
and  its  wall  which  is  not  included  in  the  body  of  the  eml^ryo  to  form  the  primitive 
alimentary  canal  constitutes  the  umbilical  vesicle  or  yolk-sac.  Its  walls,  like  its 
cavity,  are  continuous  with  the  corresponding  parts  of  the  intestine,  and  their 
structural  features  are  identical,  there  being  an  inner  layer  of  entodermal  cells  and 
an  outer  layer  which  is  formed  by  the  splanchnic  layer  of  the  mesoderm. 

In  the  human  embryo  the  yolk-sac  is  a  small  iiask-like  body,  suspended  from 
the  ventral  wall  of  the  alimentary  canal  by  a  hollow  stalk,  the  vitello-intestinal 
duct,  which  passes  through  the  umbilical  orifice.  It  lies  in  the  extra-embryonic 
continuation  of  the  body-cavity  (ccelom),  aud  is  filled  with  fluid.  Possibly  the 
contents  of  the  yolk-sac  are  utilised  in  the  nutrition  of  the  embryo  in  its  earliest 
stages,  and  the  first  rudiments  of  the  blood  vascular  system,  viz.  blood  corpuscles 
and  vessels,  appear  in  its  walls.  In  the  human  embryo,  however,  it  is  of  little 
nutritional  importance  ;  it  soon  atrophies  and  almost  entirely  disappears,  but  leaves 
traces  of  its  existence  in  the  umbilical  cord. 

Amnion. — The  amnion  is  a  protective  sac  which  surrounds  the  embryo.  It 
is  formed,  after  the  development  of  the  ccelom,  from  the  amniotic  area  of  the 
blastoderm,  and  its  wall  is  continuous,  at  the  margins  of  the  umbilical  orifice,  with 
the  body-wall  of  the  embryo.  Both  walls  consist  of  a  layer  of  ectoderm  and  a 
layer  of  somatic  mesoderm,  but  whilst  in  the  body-wall  the  ectoderm  is  external 
and  the  mesoderm  internal,  the  relative  positions  of  the  layers  are  reversed  in  the 
amnion,  the  mesoderm  being  external  and  the  ectoderm  internal. 

The  cavity  enclosed  between  the  amnion  and  the  embryo,  the  amniotic  cavity, 
is  filled  with  fluid,  the  amniotic  fluid,  in  which  the  embryo  floats.  The  amniotic 
cavity  is  quite  shut  off  for  some  time  from  all  the  neighbouring  spaces,  but  after 
the  disappearance  of  the  bucco-pharyngeal  and  cloacal  membranes  it  commimicates, 
both  anteriorly  and  posteriorly,  with  the  alimentary  canal  of  the  embryo. 

The  development  of  the  amnion  in  mammals  is  closely  associated  with  the 
attachment  of  the  ovum  to  the  uterine  wall  and  with  the  subsequent  formation  of 
the  placenta.  Thus  in  the  carnivora,  before  the  ccelom  is  formed,  the  ectoderm  in 
the  chorionic  area  becomes  attached  to  the  uterine  tissues  by  small  villous  out- 
growths which  invade  the  uterine  mucous  membrane.  This  attachment  is  most 
complete  in  the  placental  region,  that  is,  around  the  margins  of  the  amniotic  area. 
As  the  embryo  is  folded  off  from  the  blastoderm  and  the  ccelom  develops,  both  the 
embryo  and  the  amniotic  area  remain  quite  free  from  the  uterine  tissues,  indeed,  it 
may  be  said  that,  at  this  period,  the  embryo  is  suspended  from  the  margins  of  the 
placental  area  by  the  amniotic  membrane. 

As  development  proceeds  the  amniotic  area  increases  in  extent  by  interstitial 
growth,  and  thereupon  the  embryo,  the  membrane  which  suspends  it  being  relaxed, 
sinks  more  and  more  into  the  interior  of  the  ovum,  or,  to  be  more  precise,  into  the 
coelomic  space,  which,  in  the  meantime,  has  considerably  increased.  At  the  same 
time  the  growth  of  the  placental  area  causes  all  parts  of  its  inner  margin  to  converge, 
and  as  the  inner  margins  of  the  placental  area  are  continuous  with  the  outer 
margins  of  the  amniotic  membrane,  the  amnion  is  gradually  carried  over  the  dorsal 
surface  of  the  embryo  till  its  margins  meet  and  fuse.  After  the  fusion  of  its 
margins  the  amnion  separates  entirely  from  the  chorionic  area,  henceforth 
known  as  the  chorion,  and  forms  a  closed  sac  which  completely  surrounds 
the  embryo. 

On  reference  to  Figs.  21  and  27  it  will  be  seen  that  as  the  wall  of  the  blasto- 
dermic vesicle  is  carried  inwards  over  the  dorsal  surface  of  the  embryo  it  is  folded  ; 
the  outer  part  of  the  fold  consists  of  the  chorionic  portion,  and  the  inner  part  of  the 


THE  FCETAL  MEMBEANES  AND  APPENDAGES. 


49 


amniotic  portion  of  the  blastoderm.  The  fold  is  called  the  amnion  fold  ;  it  is  quite 
continuous  round  the  whole  margin  of  the  embryo,  but  some  ^jarts  of  it  are  more 
advanced  than  others,  or  in  other  words  the  convergence  of  the  inner  margin 
of  the  placental  area  of  the  blastoderm  over  the  dorsal  surface  of  the  embryo  does 
not  take  place  at  the  same  rate  or  to  the  same  extent  in  all  parts.  For  convenience 
of  description  it  is  usual  to  divide  the  amnion  fold  into  four  parts — the  cephalic,  the 
caudal,  and  the  two  lateral  amnion  folds  ;  these,  however,  are  all  continuous  with 
one  another. 

The  inner  part  of  the 
fold,  which  is  formed  from 
the  amniotic  area,  is 
termed  the  true  amnion, 
and  the  outer  part,  formed 
from  the  chorionic  area, 
the  false  amnion.  The 
latter  term  is,  however, 
synonymous  with  chorion, 
and  as  it  is  misleading,  it 
should  be  avoided. 

As  the  amnion  is 
formed  from  the  amniotic 
area  of  the  blastoderm 
after  the  extension  of  the 
coelom,  it  must  consist,  as 
previously  mentioned,  of 
ectoderm  and  somatic 
mesoderm, 'and  as  the  sur- 
face of  the  amniotic  area 
is  reversed  during  the 
formation  of  the  amnion 
folds,  it  is  obvious  that  in 
the  fully-formed  amnion 
the  ectodermal  layer  is 
internal  and  the  somatic 
mesoderm  external. 

In  the  case  of  the 
human  ovum  the  phe- 
nomena of  amnion  forma- 
tion are  probably  practi- 
cally similar,  except  that 

the  ovum  develops  not  in     •showing  the  formation  and  closure  of  tlie  amnion  folds,  the  completion  of 
,  •.         p    .-I  i  the  amnion,  and  the  coincident  ingrowth  of  the  inner  margins  of  the 

the   cavity  Ot    tne   uterus,  placental  area  of  the  blastoderm. 

but  in  the  substance  of 
the  mucous  membrane  into 
which  it  has  penetrated. 
It  is  therefore  surrounded 
by  the  mucous  membrane 
on  all  sides,  and  the 
chorionic  part  of  the  surface  of  the  ovum  is  closely  attached  to  the  surrounding 
tissue,  but  the  amniotic  and  embryonic  areas  are  free.  If  this  is  the  case  the  process 
of  amnion  folding  can  take  place  in  the  human  ovum  exactly  as  in  the  ovum  of  a 
carnivorous  animal,  the  inner  margin  of  the  chorionic  area  growing  inwards  over 
the  amniotic  and  embryonic  areas,  the  only  difference  being  that  the  process  takes 
place  in  a  cavity  in  tlie  mucous  membrane  and  not  on  its  surface.  This  conclusion 
is  su])ported  by  Spec's  observations  on  human  ova  and  by  tt)ose  of  Selenka  on  the 
ova  of  monkeys  and  apes,  but  it  is,  however,  possible  that,  as  in  some  rodents  and 
inscctivora,  the  amnion  cavity  appears  in  a  mass  of  ectoderm  which  lies  at  the 
embryonic  yjole  of  the  ovuin,  tlie  mass  being  cleft  by  the  appearance  of  the  cavity 
into  CMibryonic  and  amniotic  sections.  I'lio  two  parts  are  then  continuous  at  the 
4 


Fig.  38.- 


-Transveesb  Sections  of  the  Uterus  and  Developing 
Ovum  of  a  Ferret. 


A. 

Amnion. 

EN. 

Entoderm. 

SC.        Stratum  compactum. 

AF. 

Amnion  fold 

M. 

Muscular  wall 

SS.        Stratum  spongiosum. 

C. 

Cojloni. 

of  uterus. 

SoM.     Somatic  mesoderm. 

Ch. 

Chorion. 

NG. 

Neural  groove. 

Sp.M.   Splanchnic  mesoderm. 

EC. 

Ectoderm. 

PV. 

Placental  villus. 

UL.        Unchanged    layer    of 
uterine  mucosa. 

50  GENEKAL  EMBKYOLOGY. 

margin  of  the  embryonic  area,  and  the  mesoderm  growing  round  the  amniotic 
ectoderm  separates  it  from  the  chorionic  ectoderm. 

After  the  amnion  is  completed  its  cavity  is  distended  with  fluid.  As  it  expands 
it  gradually  obliterates  the  extra-embryonic  part  of  the  coelomic  cavity,  and  finally 
its  outer  surface,  of  somatic  mesoderm,  comes  into  contact  and  fuses  with  the  somatic 
mesoderm  on  the  inner  surface  of  the  chorion.  At  this  period  the  cavities  in  the 
ovum  are  the  aumiotic  cavity,  the  remains  of  the  yolk-sac,  and  those  portions  of  the 
orio-inal  blastodermic  and  coelomic  spaces  which  have  been  included  in  the  embryo. 

In  the  human  ovum,  when  the  amnion  folds  unite  and  the  true  amnion  separates 
from  the  chorion,  the  embryo  and  its  enclosing  amnion  would  be  free  within  the 
cavity  of  the  chorion,  or  extra-embryonic  ccelom,  were  it  not  that  a  very  short  cord 
of  somatic  mesoderm  and  ectoderm,  the  body-stalk,  connects  the  posterior  end  of  the 
embryo  with  the  somatic  mesoderm  on  the  inner  surface  of  the  chorion. 

Body-Stalk. — To  thoroughly  understand  how  this  union  is  effected  in  the 
human  ovum,  and  to  comprehend  the  nature  of  the  body-stalk,  it  is  necessary  to 
refer  to  some  striking  peculiarities  which  are  to  be  observed  in  the  earlier  stages 
in  the  development  of  the  human  embryo.  When  segmentation  is  completed,  and 
the  morula  is  converted  into  a  blastula  by  the  appearance  of  a  cavity  in  its  interior, 
the  human  ovum  consists  of  an  outer  layer,  the  ectoderm,  and  an  inner  cell-mass 
(Figs.  12  and  39).  The  latter,  however,  which  is  attached  to  a  small  area  of  the 
ectoderm,  does  not,  as  in  many  mammals,  extend  itself  by  migration  round  the  inner 
surface  of  that  layer,  and  so  transform  the  unilaminar  into  a  bilaminar  blastoderm 
and  convert  the  cavity  of  the  blastula  into  the  blastodermic  cavity.  The  sequence 
of  events  is  different :  a  cavity  or  space  appears  in  the  inner  cell-mass  itself  (Figs. 
41,  42,  and  44),  and  this  expanding  rapidly,  is  ultimately  converted  into  the  yolk- 
sac  and  the  alimentary  canal  of  the  embryo ;  it  corresponds,  therefore,  with  the 
blastodermic  cavity  of  other  mammals. 

Thus  the  entoderm,  though  derived  from  the  inner  cell-mass,  never  lines  the 
inner  surface  of  the  ectoderm  except  in  the  embryonic  area,  for  soon  after  the 
appearance  of  the  cavity  of  the  inner  cell-mass  the  mesoderm  grows  rapidly  from 
the  primitive  streak  and  extends,  not  in  a  single  layer,  as  in  the  majority  of 
mammals,  but  as  two  layers,  one  over  the  outer  surface  of  the  entoderm,  the 
splanchnic  layer,  and  the  other,  the  somatic  layer,  over  the  inner  surface  of  the 
ectoderm.  The  cavity  of  the  blastula  is  thus  ultimately  enclosed  between  the 
somatic  and  splanchnic  layers  of  the  mesoderm,  and  so  becomes  converted  into  the 
coelomic  space  (Fig.  42). 

As  the  mesoderm  extends,  the  several  areas  of  the  blastoderm  are  differentiated 
as  in  other  mammals,  but  the  embryonic  and  amniotic  areas  remain  of  relatively 
small  size.  The  separation  of  the  amnion  from  the  chorion  is  effected  at  a  very 
early  period,  before  the  folding  off  of  the  embryo  has  commenced,  but  the  somatic 
mesoderm  growing  from  the  posterior  end  of  the  embryonic  area  still  retains  its 
connexion  with  the  similar  layer  on  the  inner  surface  of  the  chorion,  and  it  forms 
a  short,  and  for  a  time  a  broad  stalk  which  unites  the  embryo,  and  consequently 
the  amnion  and  the  blastodermic  cavity,  with  which  the  embryo  is  connected,  to  the 
chorion  (Fig.  42).  In  addition  to  forming  a  bond  of  union  between  the  embryo 
and  the  chorion  the  mesodermal  stalk  conducts  blood-vessels  from  the  embryo  to 
the  chorion,  and  more  especially  to  its  placental  part. 

At  an  early  period  a  pouch-like  diverticulum  projects  from  the  posterior  part 
of  the  entodermal  sac.  This  is  the  allantoic  diverticulum ;  it  lies  beneath  the 
posterior  part  of  the  embryonic  area,  and  the  area  is  curved  upon  itself  so  that  its 
convexity  looks  towards  the  entodermal  sac,  and  its  concavity  towards  the  amnion. 

After  the  embryonic  area  has  increased  in  extent,  and  when  the  folding  off  of 
the  embryo  has  commenced,  the  anterior  end  of  the  area  and  the  posterior  end  of 
the  primitive  streak  remain  relatively  stationary  as  in  other  mammals,  the  cephalic 
and  caudal  folds  appear,  and  the  curvature  of  the  greater  part  of  the  area  is 
reversed,  but  the  most  posterior  part  retains  its  original  position,  lying  for  a  time 
parallel  with  the  caudal  fold  ;  afterwards,  however,  it  assumes  a  more  horizontal 
position.  This  posterior  section  of  the  embryonic  area  contains  the  diverticular 
process  of  the  entodermal  sac  which  is  called  the  allantois ;  it  also  contains  the 


THE  ALLANTOIS  AND  UMBILICAL  COED.  51 

blood-vessels,  allantoic  arteries  and  veins,  which  pass  between  the  embryo  and  the 
placenta.  It  is  in  relation  at  first  with  the  amnion,  it  appears  to  be  entirely 
behind  the  embryo,  and  it  is  called  the  "  body-stalk."  At  a  later  period, 
when  the  stalk  of  mesoderm— the  allantoic  stalk — which  connects  it  with  the 
inner  surface  of  the  chorion  is  elongated,  this  part  of  the  embryonic  area  is 
reversed  in  position,  its  anterior  end  is  carried  forwards  till  it  forms  the  posterior 
boundary  of  the  umbilical  orifice,  and  the  area  in  question  forms  the  ventral  wall 
of  the  body  from  the  umbilical  to  the  genital  region. 

AUantois. — The  allantois  plays  an  important  part  in  the  formation  of  the 
placenta.  It  consists  of  two  portions,  an  entodermic  diverticulum  irom  the  ventral 
wall  of  the  cloacal  part  of  the  hind-gut,  and  a  mesodermal  covering.  The  ento- 
dermic diverticulum  appears  in  the  human  subject,  before  the  hind-gut  is  defined, 
as  a  hollow  blind  protrusion  from  the  blastodermic  cavity  ;  it  extends  behind  the 
primitive  streak  into  the  mesoderm  of  the  body-stalk,  but  as  the  folding  off  of  the 
embryo  proceeds,  and  the  body-stalk  is  carried  forward  into  the  ventral  wall  of  the 
embryo,  the  position  of  the  diverticulum  is  altered,  and  ultimately,  when  the 
folding  off  is  completed,  it  springs  from  the  ventral  part  of  the  cloaca,  runs  forward 
to  the  umbilical  orifice,  and  passing  through  it,  projects  for  a  short  distance  still 
invested  with  the  mesodermal  covering  primarily  obtained  from  the  body-stalk. 
The  ventral  part  of  the  cloaca  is  afterwards  converted  into  the  bladder,  while  the 
rectum  is  formed  from  the  dorsal  part. 

The  mesodermal  sheath  which  surrounds  the  entodermic  diverticulum  extends 
beyond  it  to  the  inner  surface  of  the  chorion  ;  the  part  which  extends  beyond  the 
diverticulum  is  at  first  extremely  short,  indeed  it  is  only  recognisable  as  a  layer  of 
mesoderm  uniting  the  body-stalk  and  chorion,  but  as  development  proceeds  and 
the  body-stalk  is  folded  forward  to  form  the  ventral  wall  of  the  body  of  the  embryo, 
posterior  to  the  umbilicus,  this  portion  of  the  mesoderm  is  elongated,  and  it  forms 
the  allantoic  stalk  by  which  the  embryo  retains  its  connexion  with  the  chorion, 
and  along  which  pass  the  allantoic  or  umbilical  arteries  to,  and  the  corresponding 
veins  from,  the  chorionic  villi. 

After  the  separation  of  the  cloaca  into  bladder  and  rectum,  that  portion  of  the 
allantois  which  lies  in  the  body  of  the  embryo,  between  the  apex  of  the  bladder 
and  the  umbilical  orifice,  is  gradually  converted  into  a  fibrous  cord,  the  urachus. 
The  entodermal  diverticulum  disappears,  and  after  birth,  when  the  placental  circu- 
lation ceases,  the  umbilical  arteries  are  transformed  into  fine  fibrous  strands.  The 
remainder  of  the  allantois  which  lies  outside  the  body  of  the  embryo,  and  which 
takes  part  in  the  formation  of  the  umbilical  cord  and  placenta,  is  separated  from 
the  embryo  at  birth. 

Umbilical  Cord.  —  The  umbilical  cord  is  essentially  a  mesodermal  structure 
which  connects  the  embryo  with  the  placenta,  serving  as  a  passage  for  the  allantoic 
vessels  to  and  from  the  foetal  portion  of  the  latter  organ.  It  replaces,  functionally, 
the  body-stalk  and  the  allantoic  stalk,  which  were  earlier  provisions  for  the  same 
purpose,  and  it  is  formed  by  the  fusion  of  the  allantoic  stalk  with  part  of  the 
vitello-intestinal  duct  and  the  remains  of  the  yolk-sac. 

The  vitello-intestinal  duct  is  at  first  a  relatively  wide  channel  which  connects 
the  primitive  gut  with  the  yolk-sac ;  it  passes  through  the  umbilical  orifice.  In 
later  stages,  as  the  body-stalk  is  swung  round  into  the  ventral  wall  of  the  body, 
the  allantoic  stalk,  which  projects  from  the  end  of  the  body-stalk,  is  brought  into 
close  relation  with  the  distal  end  of  the  vitello-intestinal  duct  and  the  remains  of 
the  yolk-sac ;  the  mesodermal  constituents  of  the  three  structures  then  fuse 
together,  and  the  whole  is  surrounded  by  the  expanding  amnion.  In  this  way  the 
umbilical  cord  is  formed.  It  includes,  therefore,  the  allantoic  stalk  and  its  blood- 
vessels, together  with  the  remains  of  the  yolk-sac  and  its  stalk,  the  vitello-intestinal 
duct,  all  of'  which  arc  invested  and  bound  together  by  the  amnion. 

The  mesodermal  core  of  the  cord  forms  a  fibro-mucoid  tissue  known  as 
"Wharton's  jelly,"  which  consists  of  stellate  and  irregular  cells  embedded  in  a 
gelatinous  matrix.  The  blood-vessels  of  the  cord  are  situated  in  the  core,  and 
include  two  allantoic  or  umbilical  arteries  which  run  spirally  round  a  single 
umbilical  vein.     The  terminal  portion  of  the  allantoic  diverticulum  projects  into 


52  GENEEAL  EMBEYOLOGY. 

the  embryonic  end  of  the  cord,  and  at  first  a  loop  of  intestine  protrudes   into  it  for 
a  short  distance ;  the  gut,  however,  soon  recedes  into  the  abdominal  cavity. 

The  umbilical  cord,  which  extends  from  the  umbilical  oriJ&ce  to  the  centre  of  the 
placenta,  is  at  first  short  and  straight.  As  the  amnion  expands  the  length  of  the 
umbilical  cord  increases  until,  at  the  time  of  birth  it  measures,  on  an  average, 
about  20  inches.  This  increase  in  the  length  of  the  cord  allows  the  fcetus  to  float 
freely  in  the  amniotic  fluid,  and  prevents  traction  on  the  placenta. 

After  the  middle  of  the  second  month  the  umbilical  cord  is  twisted  spirally, 
usually  from  right  to  left.  It  is  suggested  that  this  is  due  either  to  the  great 
elongation  of  the  allantoic  arteries  or  to  muscular  movements  of  the  fo-tus,  and  it 
involves  a  rotation  of  the  foetus  in  the  amniotic  fluid. 

Chorion. — The  chorionic  area,  by  far  the  largest  of  the  areas  into  which 
the  blastoderm  is  divisible,  lies  external  to  the  amniotic  area.  In  most  mammals 
it  consists  at  first  of  ectoderm  and  entoderm,  but  after  the  extension  and  cleavage 
of  the  mesoderm  has  taken  place,  it  is  formed  by  ectoderm  and  somatic  mesoderm. 
In  man,  however,  it  consists  in  the  earliest  stages  of  ectoderm  alone,  but  on  the 
formation  and  extension  of  the  mesoderm  it  also  acquires  an  inner  layer  of  somatic 
mesoderm.     In  all  cases,  therefore,  it  eventually  consists  of  the  same  two  layers. 

The  ectoderm  of  the  chorionic  area  which  immediately  surrounds  the  amniotic 
area  thickens  to  form  the  annular  placental  area,  and  in  this  way  the  chorionic  area 
becomes  divisible  into  placental  and  non-placental  regions. 

When  the  blastodermic  vesicle  enters  the  uterus  numerous  ectodermal  villous 
processes  grow  from  the  surface  of  the  chorionic  area,  both  in  its  placental  and  non- 
placental  parts,  and  attach  themselves  to  the  uterine  mucous  membrane.  As 
already  pointed  out  in  the  description  of  the  formation  of  the  amnion,  the  embryonic 
and  amniotic  areas  do  not  become  attached  to  the  viterus,  but  remain  free  from  it, 
whilst  by  the  approximation  and  fusion  of  its  inner  margins,  the  rapidly  growing 
ring-like  placental  area  is  converted  into  a  disc  which  intervenes  between  the 
amnion  and  the  uterine  wall. 

The  chorionic  area  after  the  separation  of  the  amnion  is  known  as  the  chorion 
or  chorionic  membrane. 

The  chorion  forms  the  outer  wall  of  a  vesicle,  the  chorionic  vesicle,  which  is  the 
modified  remains  of  the  blastodermic  vesicle,  and  which  contains  the  embryo,  the 
yolk-sac,  the  amnion,  and  the  allantois.  It  consists  of  an  outer  layer  of  ectoderm 
and  an  inner  layer  of  somatic  mesoderm. 

The  cavity  of  the  chorion  is  the  extra- embryonic  portion  of  the  coelom.  For  a 
time  it  remains  distinct,  and  is  traversed  by  the  allantoic  stalk  which  unites  the 
embryo  to  the  inner  or  mesodermal  layer  of  the  placental  area.  The  cavity  is 
ultimately  obliterated  by  the  growth  of  the  amnion,  the  latter  sac  expanding 
rapidly  till  its  outer  surface  is  in  contact  and  intimately  blended  with  the  inner 
surface  of  the  chorion. 

Chorionic  Villi.  —  The  villous  processes  which  begin  to  grow  from  the 
surface  of  the  chorionic  area  before  it  is  separated  from  the  amnion  continue  to 
develop  after  the  separation  of  the  two  membranes  is  completed.  They  penetrate 
the  surrounding  uterine  tissues.  At  first  each  consists  of  ectoderm  only,  but  a 
core  of  vascular  mesoderm  is  soon  acquired.  The  villi  increase  in  size  and  in  com- 
plexity also,  but  ultimately  only  those  in  the  placental  area  persist  and  continue 
to  grow ;  the  remainder  atrophy  and  disappear. 

Thus  the  placental  region  of  the  chorion  eventually  constitutes  the  main  bond  of 
union  between  the  ovum  and  the  mother,  and  it  forms  the  foetal  part  of  the  placenta. 

THE  PLACENTA. 

The  placenta  is  the  organ  of  foetal  nutrition  and  respiration. 

In  it  the  blood-vessels  of  the  foetus  and  those  of  the  uterus  are  brought  into 
such  close  relationship  with  one  another  that  free  interchanges  readily  take  place 
between  the  blood  of  the  mother  and  that  of  the  fcetus.  In  the  simplest  form  of 
placenta  the  foetal  villi  are  merely  embedded  in  the  maternal  mucous  membrane, 
and  the  relationship  between  foetal  and  maternal  blood  is  not  very  close.     In  other 


THE  PLACENTA. 


53 


forms,  e.g.  the  human  placenta,  the  relation  of  foetal  to  maternal  blood  is  much 
more  intimate  ;  this  involves  marked  complications  in  the  elements  of  the  placenta, 
and  its  structure  becomes  correspondingly  more  complex.  In  all  forms,  however, 
the  placenta  consists  of  foetal  and  maternal  portions. 

Before  the  impregnated  ovum  reaches  the  uterine  cavity  the  mucous  membrane  of 
the  uterus  undergoes  certain  changes  in  preparation  for  its  reception  and  reten- 


Decidua  Jiasalis 


Gland 


Cavity  which 
becomes  coelom 


Unchanged  layer 

itum  spongiosum  -v  uterine 

Stratum  compactum/'""°°''^ 


Ectodermal  villus  enclosiijg 
space  containing  maternal 
blood 


Inner  mass  (Entoderm) 


Decidua  vera 


Fig.  39. — Diagram  representing  a  very  young  human  ovum  almost  immediately  after  its  entrance  into  the 
decidua,  and  whilst  the  place  of  its  entrance  is  still  covered  with  a  plug  of  fibrin.  Tlie  ectoderm  has 
already  proliferated  and  embraced  spaces  which  contain  maternal  blood  and  are  continuous  with  the 
maternal  blood-vessels. 

tion,  and  the  modified  mucous  membrane  is  known  as  the  uterine  decidua.  These 
changes  are,  for  the  most  part,  hypertrophic  ;  the  vascularity  of  the  mucous  mem- 
brane is  increased  mainly  by  the  dilatation  of  its  veins  and  caxDillaries,  the  tubular 
uterine    glands     become 


Decidua  basalis 


,  C    Unchanged  part 
Gland  i  -r>  i  ^  i        ^ 
L  Dilated  pait- 


^"W-.-J — -i 


Decidua 
vera 


elongated,  irregular,  and 
tortuous,  and  they  dilate 
both  at  their  orifices  and 
in  the  deeper  part  of  the 
mucous  membrane ;  at  the 
same  time  the  inter - 
glandular  connective  tis- 
sue proliferates,  and  as  a 
result  the  decidua  is 
thicker,  softer,  and  more 
spongy  than  the  unaltered 
mucous  membrane. 

After  the  developing 
ovum  enters  the  uterus 
it  comes  into  contact 
with  the  decidua,  into 
which  it  forces  its  way 
destroying  the  surface 
epithelium,  and  destroy- 
ing, or  pushing  aside,  the 
superficial  portions  of  the 
glands.  In  this  way  it 
becomes  embedded   in    the  vascular  interglandular  tissue 


Unchanged  layer 

stratum  spongiosum 


Stiatum  compactum, 
Blnod-vessel 


Uterine 
'mucosa 


Ectodermal  villus 


Inner  cell-mass 
(Entoderm) 


Cavity  of  uterus 


Fig.  40. — Diagram,  showing 


Decidua  vera 


the  relation  of  the  young 
the  decidua. 


human  ovum  to 


The  ectoderm  is  distinct  from  the  inner  cell-mass,  but  as  yet  there  is  no 
entodermal  cavity  in  the  latter. 


Tlie  orifice  which  it 
makes  in  the  superficial  surface  of  the  decidua  is  plugged,  for  a  time,  by  a  mass  ot 
fibrin,  but  all  traces  of  the  aperture  which  the  fibrin  closes  eventually  disappear 
and  the  ovum  is  entirely  (incapsuled  in  the  decidua,  which  again  presents  an 
unbroken  surface  towards  the  uterine  cavity. 
4a 


54 


GENERAL  EMBRYOLOGY. 


Immediately  after  the  ovum  becomes  embedded  the  superficial  ectoderm  cells  of 
its  surface  ^jroliferate  rapidly  and  form  numerous  branching  processes  or  villi  which 
invade  the  surrounding  decidua,  destroying  its  cells  and  gradually  enclosing  the 

maternal     blood     spaces 


Unchanged  layer 


Deciduii  basalis 


Maternal  vessel 


Stratum  spongiosum 
Stratum  com  pactum 

Placental  villus 


Primitive  streak 
Mesoderm 

Placental  villus 


Cavity  whicli 
becomes  ccelom 


Decidua  vera 


JUecidua  vera 


with  which  they  come 
into  relation.  After  a 
time  the  maternal  tissues 
which  at  first  surrounded 
the  maternal  blood  spaces 
entirely  disappear,  and 
from  this  period  onwards 
the  maternal  blood  circu- 
lates in  the  spaces  in  the 
foetal  ectoderm.  After  a 
time  the  proliferation  of 
the  ectodermal  vilh  be- 
comes most  marked  im- 
mediately around  the 
margin  of  the  amniotic 
area  of  the  ovum,  and 
thus  a  placental  area  of 
the  chorion  is  differ- 
entiated. In  the  mean- 
time the  expanding  ovum 
has  forced  the  decidua  on 
its  superficial  surface  to- 
wards the  cavity  of  the 

uterus,  and  at  this  period  three  areas  of  the  decidua  can  be  distinguished.     The 

part   outside   the  ovum,    that  is   between  the   ovum   and   the  muscular  wall  of 

the  uterus,  is  known 

as  the  decidua  basalis  ; 

the  part  pushed  into 

the     cavity     of     the 

uterus     around     the 

growing  ovum  is  the 

decidua  capsularis ;  and 

the  remainder  of  the 

decidua  is  the  decidua 

vera. 

The    decidua    cap- 
sularis is  not  formed, 

as    was   formerly  be- 
lieved, by  folds  of  the 

decidua    which    have 

grown    up    and    sur- 
rounded     an      ovum 

merely     attached    to 

the    surface    of    the 

decidua  basalis.      On 

the     contrary     it     is 

merely  the  superficial 

part  of   that    portion 

of    the   decidua   into 


Fig.  41. — Diagram,  showing  a  ftirther  stage  of  development  of  the  human 
ovum  and  its  relation  to  the  decidual  tissues.  The  entodermal  cavity 
or  yolk-sac  has  appeared  in  the  inner  cell -mass,  and  the  mesoderm 
has  commenced  to  extend  from  the  primitive  streak  in  two  layers, 
splanchnic  on  the  yolk-sac  and  somatic  on  the  ectoderm. 


Unchanged  layer 
stratum  spongiosum. 
Stratum  compactuof^ 


^Placental  villus 


Maternal  vessel 


Body-stalk 


/"^Ectoderiii 

Somatic 

mesoderm 

Entoderm 

Splanchnic 

mesoderm 


Decidua  vera 


Decidua  vera 


Fig.  42. — Diagram,  .showing  the  completion  of  the  decidna  capsularis,  the 
enlargement  of  the  maternal  blood-vessels  in  the  stratum  conipactum  of 
the  decidua  basali.s,  the  increase  of  the  placental  villi,  the  formation  of 
the  amnion  folds,  and  the  appearance  of  the  allantoic  diverticnlum. 


which  the  ovum  has  penetrated,  therefore  it  may  contain  glands  or  the  remains  of 
glands  which  open  on  its  superficial  surface  into  the  uterine  cavity,  but  no  glands 
open  on  its  inner  surface. 

The  decidua  basalis  lies  in  contact  with  the  placental  area  of  the  chorion,  i.e. 
the  fcetal  part  of  the  placenta,  and  it  forms  the  maternal  part  of  the  organ.  In 
the  fully  developed  human  placenta,  the  foetal  and  maternal  tissues  of  which  it 


THE  PLACENTA. 


55 


DeciduaAbasalis 


Unchanged  layer 
Stratum  spongiosum 
Stratum  compactum 

Placpntal  villus 


Amnion 

Maternal  blood-vessol 

Foital  ectoderm  villus, 
enclosing  space  filled 
with  matPinal  blood 


Allantoic 
diverticulum 

Ectodeim 

Somatic 
mesoderm 
Splanchnic  mesoderm 
Entoderm 


Decidua  vera' 


Decidua  Yem 


is  formed  are  so  intimately  mingled  and  blended  together  that  it  is  impossible 
to  say  where  one  ends  and  the  other  begins.  By  a  careful  study,  however,  of  a 
series  of  placentse  of  different  ages  a  fairly  clear  and  satisfactory  idea  of  the  i^art 
played  by  the  maternal 
and  the  foetal  elements 
respectively,  as  well  as 
of  their  relations  to  each 
other,  may  be  obtained. 
The  structural  char- 
acters of  the  completed 
organ  will  be  best  under- 
stood if  the  two  con- 
stituent parts  are  first 
considered  separately. 

Foetal  Part  of 
the  Placenta.  —  The 
villi  of  the  placental 
portion  of  the  chorion 
invade  and  penetrate 
the  decidua  basalis, 
whilst  the  villi  of  the 
non-placental  chorionic 
area  of  the  ovum  enter 
the  decidua  capsularis. 

As    previously   ex- 
plained,   in     connexion  Fig.  43. — Diagram,  showing  enlargement  of  the  blood  sinuses  in  the  maternal 
with  the  formation  both  P^'^*'  °f  ^^®  placenta  and  the  closure  of  the  amnion. 

of  the  amnion  and  of 

the  chorion,  the   annular  placental   area   is  converted   into   a  circular  disc.     It 
consists,  like  the  rest  of  the  chorion,  of  ectoderm  and  mesoderm,  and  it  contains 

Decidua  basalis  ramificatious  of  the 

allantoic  vessels  ; 
but  the  ectoderm 
is  thickened  and 
increased,  its  villi 
are  larger  than 
those  of  the  non- 
placental  region 
of  the  chorion,  and 
it  is  directly  con- 
nected with  the 
allantoic  stalk. 

The  early  villi 
are  merely  ecto- 
dermal buds  which 
penetrate  the  sur- 
rounding decidual 
tissues,  destroying 
and  replacing  the 
uterine  elements. 
These  villi  grow 
and  branch,  and 
their  branches  an- 
astomose together 

Fio.  44. — DiAGUA.M,  showing  the  Itctal  ectoderm  surrounding  the  maternal  blood  SUrrOUllding  the 
sinuses,  the  commencement  of  secondary  fmtal  villi  which  project  into  the  l)lood  SDaCCS  of  the 
sinuses,  and  the  disappearance  of  the  supcrliiial  iiOTtions  oftlie  glands.  ,      .  ,  '  ^      i  •    i 

decidua  which  are 
in  the  immediate  neighliourhood  oi'  the  ovum.  As  development  proceeds  every 
ectodermal  villus  is   penetrated    Ijy   an    outgrowth   of   the   subjacent   mesoderm 


Unchanged  layer 


Stiatum 
spongiosum 


Placental  -s  illus 


Maternal  blood  sinus 
Maternal  vessel 


Placental  villus 

^Allantoic  stalk 


Foetal  villus 

Decidua  \eia 


Ectoderm 
Somatic  mesoderm 
Splanchnic  mesoderm 
Entodeim 

Decidua  vera 


56 


GENEEAL  EMBEYOLOGY. 


Unclianged  lay 

Stratum 
spoiigiosuni 

Stratum 
compactin 


Maternal  blood  sinus 


Foetal  villus 


Allantoic 
diverticulum 


^Ectodenii 


which  carries  branches  of  the  allantoic  vessels,  and  so  the  villi  become  vascularised 
with  fcetal  blood.  For  some  time  all  the  villi,  placental  and  non-placental,  grow  and 
absorb  nutriment  from  the  maternal  tissues,  pro})ably  utilising  as  food  the  tissues 
which  they  destroy  and  replace ;  but  when  the  decidua  capsularis  is  thinned  by 
the  expansion  of  the  growing  ovum,  the  villi  of  the  non-placental  region  which 
have  penetrated  it  are  no  longer  able  to  obtain  nutrient  matter,  and  they  con- 
sequently atrophy  and  disappear.  The  placental  villi,  on  the  contrary,  continue  to 
increase  ;  they  grow  in  size  and  become  more  complex,  and  secondary  branches 
growing  from  them  project  into  the  maternal  blood  spaces  which  they  have 
surrounded  and  float  in  the  maternal  blood.     When  the  formation  of  the  placenta 

is  completed,  its 
foetal  part  consists 
of  villi,  each  of 
which  possesses  an 
external  covering 
of  two  layers  of 
ectodermal  cells 
and  a  vascular 
mesodermal  core ; 
the  villi  project 
into  the  interior 
of  large  blood 
spaces  which  are 
surrounded  more 
or  less  completely 
by  foetal  ectoderm, 
and  they  are  bathed 
by  maternal  Vjlood 
from  which  they  ob- 
tain the  materials 
necessary  for  the 
nutrition  and 
growth  of  the  em- 
bryo, and  into 
which  they  trans- 
mit the  effete  ex- 
cretory matters 
from  the  embryo. 

Maternal 
Part  of  the  Pla- 
centa    and     the 

Changes  in  the  Decidua. — The  occurrence  of  further  changes  in  the  decidua,  after 
the  developing  ovum  enters  the  uterus,  is  dependent  upon  the  retention  of  the 
ovum  in  the  substance  of  the  decidua.  These  changes  only  occur,  therefore,  in ' 
what  may  be  termed  the  decidua  of  pregnancy.  They  are  intimately  associated 
with  and  essential  to  the  development  of  the  maternal  part  of  the  placenta,  and 
a  more  detailed  and  complete  account  of  the  decidua  and  the  modifications  of  its 
several  parts  is  therefore  necessary. 

The  decidua  is  formed  by  the  mucous  membrane  of  the  uterus,  which  is  a  hollow, 
thick-walled  muscular  organ,  situated  in  the  pelvic  cavity.  The  mucous  membrane 
contains  numerous  tubular  glands  embedded  in  an  interglandular  tissue  formed  of 
round  and  irregular  cells.  The  uterine  glands  are  lined  by  a  columnar  or  cubical 
epithelium,  and  they  open  into  the  cavity  of  the  uterus  on  a  surface  which  is  also 
covered  by  columnar  cells.  The  whole  of  the  nmcous  membrane  is  plentifully 
supplied  with  blood-vessels  which  pass  into  it  from  the  surrounding  muscular 
walls,  and  it  is  transformed  into  the  decidua  by  proliferation  and  hypertrophy  of 
all  its  parts.  The  interglandular  tissue  increases  in  amount  and  its  blood-vessels 
dilate,  especially  near  the  surface  of  the  membrane;  but  the  most  striking  of  the 
early   changes   occur   in    the   glands — they   become   longer,  more  tortuous,  their 


Coelom 


Somatic 
mesoderm 

Splanchnic 
mesoderm 


Entoderm 
Decidua  capsularis 


Decidua  vera 


Fig.  45. — Diagram,  showing  further  growth  of  the  placental  sinuses  and  villi ;  the 
fusion  of  the  decidua  capsularis  with  the  decidua  vera,  and  the  obliteration  of 
the  uterine  cavity. 


THE  PLACENTA.  57 

apertures  enlarge  and  assume  a  funnel-like  appearance,  and  they  dilate  a  short 
distance  from  their  terminations  into  large  iiTegular  spaces.  The  increase  of 
the  interglandular  tissue  is  most  marked  in  the  intervals  between  the  dilated 
portions  of  the  glands  and  their  apertures,  and  when  all  the  changes  are  fully 
established  it  is  possible  to  recognise  three  layers  of  the  decidual  tissue.  (1)  A 
superficial  relatively  thick  layer  in  which  the  interglandular  tissue  xjreponderates, 
the  stratum  compactum ;  (2)  A  layer  formed  principally  by  the  dilated  portions 
of  the  glands,  the  stratum  spongiosum ;  and  (3)  a  thin  deep  part  of  the  membrane 
which  contains  the  outer  extremities  of  the  glands  which  are  practically  unchanged, 
the  unchanged  layer. 

The  decidua  capsularis  differs  from  the  other  portions  of  the  decidua  in  that 
it  represents  only  the  superficial  portion  of  the  other  parts  of  the  decidua,  and 
therefore  contains  no  spongy  layer  or  deep  unchanged  layer.  This  is  obviously  the 
case,  for  after  the  ovum  has  penetrated  through  the  surface  epithelium  it  becomes 
embedded  in  the  stratum  compactum  of  that  portion  of  the  decidua  which  it  has 
invaded,  and  consequently  the  portion  of  the  stratum  which  closes  over  it  cannot 
contain  more  than  the  outer  parts  of  some  of  the  uterine  glands  with  their  orifices 
and  the  intervening  interglandular  tissue. 

The  changes  which  occur  in  the  decidua  capsularis  are  due,  first,  to  its 
connexion  with  and  invasion  by  the  chorionic  villi ;  and,  secondly,  to  the  pressure 
exerted  upon  it  by  the  enlarging  ovum.  The  former  influence  is  brought  to  bear 
whilst  the  decidua  is  still  increasing ;  the  latter  after  it  has  reached  its  full 
development. 

The  changes  which  result  from  its  union  with  the  chorion  are  the  destruction 
and  absorption  of  some  of  the  interglandular  tissue ;  they  are  due  to  the  activity 
of  the  ectodermic  cells  of  the  chorion,  which  attack  and  invade  the  uterine  tissues. 

The  changes  due  to  pressure  exerted  by  the  enlarging  ovum  are  diminution  of 
vascularity,  disappearance  of  the  lumina  of  such  portions  of  the  glands  as  remain  in 
the  decidua  capsularis,  and  the  removal  of  their  epithelium,  together  with  the  co- 
incident atrophy  of  the  fcetal  villi  which  have  penetrated  this  portion  of  the  placental 
decidua.  All  these  changes  result  in  the  reduction  of  the  decidua  capsularis  to  a 
thin  membrane  in  which  no  traces  of  the  original  structure  are  recognisable,  in  the 
fusion  of  the  altered  decidua  capsularis  with  the  decidua  vera,  and  the  consequent 
obliteration  of  the  uterine  cavity. 

After  the  fifth  month  the  decidua  vera  also  undergoes  atrophic  changes,  but  they 
do  not  proceed  so  far  as  in  the  decidua  capsularis ;  nevertheless  the  stratum  com- 
pactum is  greatly  reduced,  the  superficial  epithelium  and  the  superficial  parts  of 
the  glands  entirely  disappear  from  it,  the  interglandular  tissue  becomes  less 
vascular,  and  it  diminishes  very  considerably  in  thickness.  The  epithelium  dis- 
appears from  the  spaces  in  the  spongy  layer,  and  the  spaces  themselves  are 
flattened  out  into  long  slit -like  clefts,  in  which  condition  they  remain  till 
the  period  of  pregnancy  is  completed.  The  decidua  vera  is  thus  reduced  to  the 
condition  of  a  relatively  thin  membrane,  and  its  inner  surface  is  fused  with 
the  remains  of  the  decidua  capsularis. 

Decidua  Basalis. — This  portion  of  the  decidua  is  constituted  by  the  deeper 
part  of  the  stratum  compactum  in  which  the  ovum  is  embedded  together  with 
the  more  externally  situated  spongy  and  unchanged  layers,  and,  apart  from  the 
changes  due  to  the  invasion  of  the  foetal  villi,  the  most  important  transformations 
in  this  part  of  the  decidua  occur  in  the  stratum  compactum.  The  alterations  in 
the  spongy  layer  are  similar  to  those  which  occur  in  the  same  layer  of  the  decidua 
vera,  viz.  the  lining  epithelium  disajjpears  and  the  spaces  are  flattened  out  into  a 
layer  of  cleft-like  slits. 

In  the  stratum  compactum,  however,  much  more  striking  clianges  occur ;  all 
traces  of  the  glands  disappear,  Ijut  the  blood-vessels  become  greatly  dilated,  and, 
consequently,  tlie  layer  increases  considerably  in  thickness.  The  small  blood-vessels 
wliJcli  lie  in  the  immediate  neighljourhood  of  tlie  ovum  beconie  converted  into 
enormous  blood  sinuses,  Ijut  in  the  deeper  part  of  the  stratum  a  thin  layer,  which 
lies  next  the  stratum  spongiosum,  remains  relatively  unchanged;  this  deepc-r  part 
is  called  the  basal  layer,  and  through  it  the  blood-vessels  pass  to  and  from  the 


58 


GENERAL  EMBRYOLOGY. 


blood  sinuses  in  the  more  snperticial  portion  of  the  membrane.  When  it 
is  completed,  therefore,  the  maternal  portion  of  the  placenta,  which  is  the 
transformed  decidua  basalis,  no  longer  consists  of  the  stratum  compactum,  the 
stratum  spongiosum,  and  the  unchanged  layer,  but  it  is  formed  from  within 
outwards  of — (1)  a  layer  of  blood  sinuses,  (2)  the  basal  layer,  (3)  the  modified 
spongy  layer,  and  (4)  the  unchanged  layer.  The  difference  between  the  decidua 
Ijasalis  and  the  maternal  part  of  the  placenta  may  be  tabulated  as  follows : — 


Decidua  basalis. 

Deep  part  of  stratum  compuctuni 

Stratum  spongiosum 
Unchanged  layer 


Maternal  placenta. 

Layer  of  blood  sinuses. 
Basal  layer. 

Modified  stratum  spongiosum. 
Unchanged  layer. 


Unchanged  layer- 

Stratum 
spongiosiini^-^ 

Stiatnm 
com  pact  111  II 


PliCfntal  villu 


It  must  not  be  forgotten,  however,  that  whilst  the  changes  which  result  in  the 
formation  of  the  maternal  placenta  out  of  the  decidua  Ijasalis  are  taking  place  the 
stratum  compactum  has  been  invaded  by  the  placental  villi. 

The  first  result  of  this  invasion  is  the  destruction  of  much  of  the  decidual  tissue  by 

Placenta  the    ectodemi    of 

the  foetal  villi. 
Gradually  the  ec- 
toderm of  theA'illi, 
always  in  advance 
of  the  main  body, 
reaches  and  sur- 
rounds the  dilated 
decidual  vessels, 
destroys  the  in- 
tervening tissues, 
and  ultimately  re- 
places the  endo- 
thelial walls  of  the 
vessels,  which  by 
this  time  have 
dilated  into  enor- 
mous spaces.  Into 
these  spaces  the 
ramifications  of 
the  vilh  project, 
and,  as  the  endo- 
thelial walls  are 
destroyed,  they  lie 
directly  within 
the  cavities  of  the 
spaces,  and  are 
surrounded  on  all 
sides  by  maternal 
blood.  The  most 
peculiar  feature  of 
this  part  of  the 
placenta,  when 
fully  developed,  is 
that  the  whole  of 
the  maternal  por- 
tion of  it,  except 
the      blood,     has 

been  removed  and  replaced  by  foetal  tissues,  so  that,  although  the  maternal 
blood  continues  to  circulate  in  the  same  spaces  which  it  has  occupied  from  the 
first,  viz.  the  blood  sinuses  in  the  more  superficial  part  of  the  stratum  compactum  of 
the  maternal  decidua,  yet  the  walls  of  these  spaces  have  been  replaced  more  or  less 


Peri- 
cardium 


Fused  decidua  cap- 
sulaiis  and  decidua 
\eia 


I''used  mesoderm  of 
amnion  and  cliorion 


Fig.  46. — Diagraji.  Later  stage  in  the  development  of  the  placenta,  showing  the 
relations  of  the  fcetal  villi  to  the  placental  sinuses,  the  fusion  of  the  amnion  with 
the  inner  surface  of  the  chorion,  and  the  thinning  of  the  fused  deciduaj  (cap- 
sularis  and  vera). 


THE  PLACENTA.  59 

completely  by  foetal  ectoderm,  and,  consequently,  the  spaces  now  lie  in  the  midst  of 
the  fcetal  tissues. 

The  invasion  of  the  maternal  by  the  fcetal  part  of  the  placenta  proceeds  as  far 
as  the  basal  layer,  and  in  this  region  the  foetal  ectoderm  is  directly  continuous  with 
the  walls  of  the  maternal  blood-vessels  at  the  points  where  they  enter  the  sinuses. 

Although  the  invasion  of  the  deeidua  basalis  is  so  complete,  some  portions  of 
the  maternal  tissues  persist ;  thus  the  basal  layer  and  many  strands  of  the  stratum 
compactum  escape  destruction.  The  latter  extend  from  the  basal  layer  to  the  outer 
surface  of  the  chorion,  and  they  are  eventually  converted  into  fibrous  strands,  which 
divide  the  superficial  part  of  the  completed  placenta  into  lobular  areas. 

The  completed  placenta  consists,  therefore,  of  closely  intermingled  and  fused 
foetal  and  maternal  tissues,  through  which  both  the  foetal  and  maternal  blood 
streams  circulate.  It  is  well  adapted,  on  account  of  its  peculiarities  of  structure,  to 
fulfil  the  nutritive  and  respiratory  requirements  of  the  embryo.  The  fcetal  blood 
stream  which  flows  through  the  placental  villi  and  the  maternal  blood  stream  in 
the  placental  sinuses  are  only  separated  from  each  other  by  two  layers  of  foetal 
ectodermal  epithelium  and  a  small  amount  of  foetal  mesoderm,  the  latter  being 
practically  reduced  to  the  single  layer  of  endothelial  cells  which  form  the  walls  of 
the  foetal  vessels.  Through  these  layers,  by  osmosis,  and  possibly  by  secretion, 
materials  are  passed  both  from  mother  to  embryo  and  from  embryo  to  mother,  the 
placenta  serving  not  only  for  purposes  of  nutrition  and  respiration,  but  also  as  an 
excretory  organ. 

A^hilst  the  placenta  is  attaining  its  full  development  the  amnion  is  expanding, 
and  finally  its  outer  surface  fuses  with  the  inner  surface  of  the  chorion,  consequently, 
the  innermost  portion  of  the  placenta  is  provided  with  a  covering  of  amnion. 

The  full-time  placenta  is  a  discoid  mass  about  20  or  25  inches  (50  to  60  cm.)  in 
circumference  and  1^  in  thickness  at  its  centre  ;  it  is  much  thinner,  however, 
at  its  margins,  where  it  is  continuous  with  the  membranes  formed  by  the  fused 
chorion,  deeidua  vera,  and  deeidua  capsularis.  Its  weight  is  about  one  pound,  and 
it  consists  from  within  outwards  of  the  following  layers : — 


Foetal 


Maternal 


Amnion 


(   Ectoderm. 
(  Mesoderm. 
Allantois  with  fcetal  vessels  .  .  Mesoderm. 

Chorion \   Mesoderm. 

I    xLctoderm. 

Layer  of  maternal  blood  sinuses  and  remains  of  the  intergiandular 

tissue  of  the  stratum  compactum. 
Basal  layer. 
Modified  spongy  layer. 
Unchanged  layer. 


When  the  period  of  intrauterine  life  is  completed  the  muscular  walls  of  the 
uterus  contract  and  the  lower  orifice  of  the  uterine  cavity  is  dilated,  the  fused 
chorion  and  amnion,  which  close  the  upper  part  of  the  orifice,  rupture  and  the 
amniotic  fluid  escapes,  the  foetus  is  then  expelled,  but  it  remains  attached  to  the 
placenta  by  tlie  umbilical  cord.  The  cord  is  divided  artificially,  and  after  a  short 
period  the  jjlacenta  and  membranes  are  expelled.  The  membranes  attached' to  the 
])lacenta  consist  of  tlie  fused  anmion,  chorion,  deeidua  capsularis,  and  also  the 
deeidua  vera  internal  to  the  altered  spongy  layer ;  therefore  botli  the  placenta  and 
the  jnembranes  consist  of  maternal  and  foetal  tissues..  IBefore  tlie  placenta  and 
membranes  are  expelled  the  uterine  deeidua  is  separated  into  two  parts  l)y  a 
cleavage  which  takes  place  in  the  modified  stratum  spongiosum.  The  inner  portion 
which  includes  the  placenta  and  membranes  is  cast  off.  The  outer  portion  remains 
in  the  uterus;  it  consists  almost  entirely  of  the  deep  unchanged  layer  of  the 
deeidua,  and  from  it  the  uterine  mucous  membrane  is  reconstructed. 


60  GENEEAL  EMBRYOLOGY., 

THE   PRIMITIVE   VASCULAR    SYSTEM   AND    THE   FGETAL 

CIRCULATION. 

It  has  already  been  said  that  the  ovum  during  its  passage  down  the  Fallopian 
tube  lives  either  on  its  own  yolk  particles  or  upon  substances  absorbed  from  the 
fluids  by  which  it  is  surrounded.  For  a  time  after  it  enters  the  uterus  its  nutrition 
must  be  provided  for  in  a  similar  manner,  but  as  soon  as  the  chorionic  villi  are 
formed  it  is  probable  that  the  ectodermal  cells,  of  which  in  the  earliest  stages  they 
entirely  consist,  and  wluch  cover  their  surfaces  in  the  later  stages,  actually  eat  up 
the  decidual  tissues  which  they  invade  and  use  them  for  food.  This  source  of 
nutrition,  however,  is  only  sufficient  for  the  short  period  during  which  the  ovum 
remains  relatively  small,  and  substances  absorbed  through  the  surface  cells  can  be 
readily  transmitted  to  all  its  parts. 

In  addition  to  the  solid  decidual  tissues  devoured  by  the  ectodermal  cells  it  is 
evident  that  fluids  from  the  mother  are  also  absorbed,  for  the  yolk-sac  and  crelom 
enlarge  and  are  filled  with  fluid.  The  only  sources  from  which  this  can  have  been 
derived  are  the  uterine  glands  or  the  blood  and  lymph  vessels  of  the  decidua. 

In  all  probability  the  fluids  absorbed  into  the  ovum  contain  nutritive  material, 
and  so  long  as  the  embryo  is  constituted  by  the  thin  layers  of  the  early  blastoderm 
sufficient  food  material  can  easily  be  absorbed.  When,  however,  the  various  parts 
of  the  embryo  increase  in  thickness  and  become  moulded  into  the  form  of  organs 
they  are  no  longer  in  such  intimate  relation  with  the  surrounding  nutritive  fluids, 
whilst,  further,  as  their  development  progresses  they  require  a  greater  amount  of 
food  and  oxygen  than  they  can  obtain  from  these  fluids.  There  is,  therefore,  an 
imperative  necessity  for  a  further  supply  of  nutritive  material  by  which  their  re- 
quirements may  be  satisfied,  faihng  which,  development  must  cease  and  death  ensue. 

To  meet  this  necessity  the  vascular  system  is  formed.  It  is  essentially  an 
irrigation  system  consisting  of  a  propulsive  organ,  the  heart,  and  of  tubular 
vessels,  the  blood-vessels,  all  of  which  contain  blood.  The  heart  propels  the  blood 
through  the  blood-vessels  to  all  parts  of  the  embryo,  but  the  blood  which  is  at  first 
formed  from  the  mesoderm  of  the  ovum  must,  at  least  so  far  as  its  fluid  part  is 
concerned,  be  supplemented  largely  from  maternal  sources.  It  is  necessary,  there- 
fore, that  the  foetal  blood-vessels  be  brought  into  close  relation  with  the  maternal 
blood-vessels  at  an  early  period.  It  is  for  this  purpose,  amongst  others,  that  the 
large  blood  sinuses  are  formed  in  the  maternal  portion  of  the  placenta,  and  that 
they  are  surrounded  and  invaded  by  the  fcetal  villi,  carrying  in  their  interior 
branches  of  the  foetal  blood-vessels,  and  as  previously  shown,  the  foetal  blood- 
vessels in  the  placenta  are  only  separated  from  the  maternal  blood  in  the  sinuses 
by  their  own  thin  mesodermal  walls,  and  by  one  or  two  layers  of  ectodermal  cells. 
When  the  placenta  is  fully  formed  fluids  can  readily  pass  from  the  maternal  to 
the  foetal  vessels,  and  there  can  be  no  doubt  that  both  food  and  oxygen  pass  from 
the  maternal  blood  to  the  foetal  blood  through  and  by  the  agency  of  the  intervening 
cells,  whilst  at  the  same  time  the  waste  products  which  are  formed  in  the  embryo 
pass  outwards  to  the  maternal  blood. 

Ob\dously,  however,  a  system  of  vessels  filled  with  fluid  would  be  of  little  use 
in  the  general  economy  unless  there  w^ere  some  means  by  which  the  fluid  could  be 
kept  in  constant  movement.  In  the  first  instance  this  is  accomplished  by  rhythmical 
contractions  of  the  vessel  walls,  but  in  a  short  time  portions  of  the  two  primitive 
stem-vessels  which  appear  in  the  embryo  are  modified  into  a  single  propulsive 
organ,  the  heart,  which  forces  the  fluid,  or  blood,  in  a  definite  direction  both 
through  the  body  of  the  embryo,  along  the  body-stalk  or  umbihcal  cord,  accord- 
ing to  the  age  of  the  embryo,  and  through  the  vessels  in  the  placental  villi. 

We  have  now  to  consider  how  the  blood-vessels  and  blood  are  formed. 

Where,  or  how,  the  first  blood-vessels  appear  in  the  human  subject  is  not 
definitely  known,  but  in  other  mammals  they  are  first  seen  outside  the  body  of 
the  embryo  in  the  wall  of  the  yolk-sac.  The  outer  layer  of  the  wall  of  the  yolk- 
sac  consists  of  splanchnic  mesoderm,  and  in  that  part  of  this  layer  which  lies 
nearest  the  primitive  alimentary  canal  a  large  number  of  the  cells  proliferate 


PEIMITIVE  VASCULAR  SYSTEM  AND  FCETAL  CIRCULATION.     61 


rapidly  and,    fusing    together,    form   nmlti-nucleated    masses    of   protoplasm,  the 
"  blood  islands  "  of  Pander. 

Soon  after  their  appearance  the  blood  islands  anastomose  together  by  means  of 
nucleated  processes  which  they  throw  out  on  all  sides,  and  thus  a  nucleated  proto- 
plasmic reticulum  is  formed  in  the  substance  of  the  splanchnic  mesoderm.  The 
region  in  which  this  occurs  is  known  as  the  vascular  area.  The  solid  nucleated 
reticulum  is  soon  converted  into  a  system  of  anastomosing  canals,  the  primitive 
blood-vessels,  by  the  ap- 
pearance within  it  of 
numerous  vacuoles  which 
soon  fuse  together,  whilst 
at  the  same  time  the  nu- 
cleated protoplasm  is  trans- 
formed into  cells.  The  cells 
which  lie  nearest  the  in- 
terior separate  from  each 
other  and  form  the  primi- 
tive blood -corpuscles, 
whilst  those  situated  ex- 
ternally remain  connected 
by  their  margins  and  form 
the  endothelial  walls  of  the 
embryonic  vessels.  The 
fluid  which  fills  these  first- 
formed  vessels  in  the  vas- 
cular area  is  probably  de- 
rived either  from  thecoelom 
or  from  the  yolk-sac. 

The  primitive  blood - 
corpuscles  are  nucleated 
cells  of  a  reddish  colour ; 
white  or  colourless  blood- 
corpuscles  appear  later,  and 
it  is  stated  that  those 
first  formed  are  developed 
in  the  thymus  gland. 

Nucleated  red  cor- 
puscles persist  and  increase 
in  number  till  the  end  of 
the  second  month  of  in- 
trauterine life ;  they  are 
then  gradually  replaced  by 
non-nucleated  red  corpus- 
cles. The  majority  of  the 
nucleated  red  corpuscles  disappear  long  before  birth,  but  a  few  can  usually  be  found 
in  the  blood  of  the  new-born  child.  There  is  some  doubt  about  their  ultimate  fate, 
but  it  is  generally  believed  that  their  nuclei  disappear,  and  that  they  are  converted 
into  non-nucleated  corpuscles. 

Directly  after  the  appearance  of  the  blood  islands  in  the  vascular  area  of  the 
yolk-sac,  and  just  as  the  folding  off  of  the  embryo  commences,  two  short  tubular 
vessels  appear  in  the  splanchnic  layer  of  the  pericardial  mesoderm.  These  vessels 
at  once  extend  forwards  and  outwards  into  the  extra-embryonic  region  where  they 
become  connected  with  the  vessels  of  the  vascular  area ;  they  also  extend  back- 
wards in  the  body  of  the  embryo  beneath  the  protovertebral  somites.  In  the 
majority  of  mammals  they  at  first  terminate  behind,  as  in  front,  on  the  wall  of  the 
yolk-sac,  but  after  a  time  the  main  stems  appear  to  be  continued  along  the  allantoic 
stalk  to  tlie  placenta,  whilst  they  give  olf  branches  to  the  yolk-sac.  It  is  ])robable 
that  in  the  htmian  cnd^ryo  also,  tliough  this  has  not  a])])arently  been  actually 
ob.sorved,  these  main  stem  vessels,  the  jirimitive  aorttu,  end  at  first  on  the  wall  of 


EN 


Fig.  47. 


BV2 


-Development  of  Blood-Vessels  in  the  Vascular  Area  op 
THE  Rat. 


"  blood 


III. 


Entoderm  aud  splanchnic  mesoderm. 

Proliferation    of   cells  of   mesoderm  and  formation   of 

islands." 
Commencing  differentiation  of  islands  to  form  blood-vessels  and 
blood-corpuscles. 
IV.  Completed  vessels. 

BC  Blood-corpuscles.  BVo  Blood-vessels. 

BI  Blood  islands. 
EVj  Blood  islands   being  trans-       EN  Entoderm, 
formed  into  blood-vessels.         M  Mesoderm. 


62 


GENEEAL  EMBEYOLOGY. 


the  yolk-sac,  but  on  the  fourteenth  day  of  intrauterine  life,  before  the  heart  is 
formed,  the  two  primitive  stem  vessels  pass  backwards  along  the  body-stalk  to  the 
chorion,  their  terminal  branches  entering  the  chorionic  villi.  As  they  pass  back- 
wards the  primitive  aortse  give  off  branches  to  the  wall  of  the  yolk-sac.  Thus,  at 
this  period  the  vascular  system  of  the  human  embryo  consists  of  two  longitudinal 
vessels  which  run  parallel  with  each  other,  one  on  each  side  of  the  middle  line, 
throughout  the  whole  length  of  the  embryo.  They  comnumicate  anteriorly  with 
the  vessels  on  the  yolk-sac,  and  terminate  posteriorly  in  the  chorion.  When  the 
circulation  commences  the  blood  flows  from  the  anterior  part  of  the  vascular  area 
into  the  anterior  ends  of  the  primitive  aortse,  and  passes  backwards  through  the 
embryo.  Some  of  it  is  returned  to  the  vascular  area  by  the  branches  which  are 
given  off  to  the  walls  of  the  yolk-sac ;  but  the  greater  part  is  carried  to  the 
chorion,  whence  it  returns  by  venous  channels,  the  allantoic  veins,  which  have 
been  developed  in  the  meantime,  to  the  anterior  ends  of  the  primitive  aort^. 

As  the  cephalic  and  caudal  folds  are  developed  the  anterior  and  posterior  parts 
of  the  primitive  aortse  are  carried  into  the  ventral  wall  of  the  body  of  the  embryo, 

and  thus  each  primitive  vessel  is  divisible  into 
three  parts :  (1)  a  dorsal  part,  the  primitive 
dorsal  aorta,  which  extends  from  the  dorsal  end 
of  the  mandibular  arch  to  the  cloaca,  and  runs 
beneath  the  protovertebral  somites ;  (2)  an 
anterior  ventral  part,  situated  in  the  dorsal 
wall  of  the  pericardium  and  extending  from 
the  umbilicus  to  the  ventral  end  of  the  man- 
dibular arch ;  and  (3)  a  posterior  ventral  part, 
which  at  first  runs  in  the  ventral  wall  at  the 
side  of  the  cloaca,  and  then  turns  backwards  in 
the  body -stalk  to  the  placenta,  but  afterwards, 
when  the  posterior  part  of  the  ventral  wall  of 
the  body  is  completed,  it  extends  forwards  from 
the  pelvic  region  to  the  umbihcal  orifice,  through 
which  it  passes  to  the  umbilical  cord. 

The  three  sections  are  united  together  by  two 
arches — an  anterior  arch,  the  first  cephalic  aortic 
arch,  which  passes  through  the  mandibular  arch, 
and  a  posterior  arch,  the  caudal  arch,  which  lies 
at  the  side  of  the  cloaca. 

In  a  short  time  four  additional  communica- 
tions are  formed  between  the  anterior  ventral  and 
the  dorsal  part  of  each  primitive  aorta;  they  are  the  second,  third,  fourth,  and 
fifth  cephalic  aortic  arches,  each  of  which  lies  in  the  substance  of  the  corresponding 
visceral  arch. 

As  soon  as  the  last  cephalic  aortic  arch  is  developed  the  rudiments  of  the  main 
vessels  of  the  embryo  are  established;  and  by  a  series  of  transformations,  for  a  full 
account  of  which  the  chapter  which  deals  with  the  Vascular  System  must  be 
consulted,  there  are  formed  from  the  vessels  which  have  been  mentioned  the  heart, 
the  aorta,  the  main  vessels  of  the  head  and  neck,  the  pulmonary  artery  and  its 
primary  branches,  the  common  and  internal  iliac  arteries,  and  the  hypogastric  arteries. 
The  blood  distributed  by  the  various  arteries  is  returned  to  the  heart  by  vessels 
called  veins,  'which  are  developed  in  the  substance  of  the  mesoderm  in  the  same 
manner  as  the  arteries.  From  the  yolk-sac  the  blood  returns  by  the  vitelline 
veins  ;  from  the  alimentary  canal  and  its  appendages,  through  the  portal  and  hepatic 
veins ;  from  the  head  and  neck,  by  the  jugular  veins  and  the  superior  vena  cava ; 
and  from  the  body  and  lower  limbs,  first  by  the  cardinal  veins,  and  afterwards  by 
the  inferior  vena  cava  and  the  azygos  veins. 

The  heart  is  formed  by  the  fusion  of  portions  of  the  anterior  ventral  sections  of 
the  primitive  aortse  behind  the  origins  of  the  cephalic  aortic  arches,  and,  therefore, 
it  is  primitively  a  bilateral  organ.  Subsequently  it  possesses  for  a  time  a  single 
chamber,  but  this  is  afterwards  divided.     During  the  greater  part  of  foetal  life  the 


Cephalic 
aottic  arch 

Anterior 
vential  aorta 

Primitive 
dorsal  aorta 


Vitelline  vein 


Umbilical  vein 


Splanchnic 
arteries  to 
vascular  area 


Vitelline  artery 

Poster  or 
ventral  aorta  ■ 
Primitive 
caudal  arch 
Hypogastric 
artery 

.Chorioiiie 
vessels 


Fig. 


48. — The  Primitive  Blood- Vessels 
OF  THE  Embryo. 


PRIMITIVE  VASCULAR  SYSTEM  AND  FGETAL  CIRCULATION.      6J 


heart,  as  in  the  adult,  possesses  four  cham?jers — two  auricles  or  upper  chambers,  and 
two  ventricles  or  lower  chambers,  right  and  left.  The  two  auricles  communicate 
with  the  corresponding  ventricles  through  auriculo- ventricular  apertures,  and  with 
each  other  through  a  foramen,  the  foramen  ovale,  in  the  septum  between  them. 

In  the  adult  the  blood  enters  the  right  auricle  by  the  superior  and  inferior 
venae  cavse  and  the  coronary  sinus ;  from  the  right  auricle  it  passes  into  the  right 
ventricle,  by  which  it  is  propelled  through  the  pulmonary  arteries  and  lungs ;  re- 
turning to  the  heart  by  the  pulmonary  veins  it  passes  into  the  left  auricle,  and 
then  into  the  left  ventricle,  by  the  contraction  of  which  it  is  forced  into  the 
systemic  aorta.  From  the  aorta,  by  various  branches,  it  traverses  the  organs  and 
tissues  of  the  body,  and  is  returned  again  to  the  right  auricle. 

The  course  of  the  foetal  circulation  differs  from  that  of  the  adult ;  the  blood 
passes  out  of  the  body  into  the  placenta,  to  be  oxygenated  and  purified,  the  lungs 
of  the  fcetus  remaining  functionless  until  the  time  of  birth.  Very  little  of  the 
blood  which  is  ejected  from  the  right  ventricle  at  every  contraction  of  that 
chamber  reaches  the  lungs;  the  greater  part  is  transferred  from  the  pulmonary 


Caudal  arches 


Dorsal  aortse 


7th  pair  of 
segmental  arteries 


Vertebral 
arteries 

1st  pair  of 
segniental  arteries 


Umbilical  vein 
Splanchnic  arteries 

Hypogastric  artei-y 


1st  ceplialio  aortic  arch 
2ncl  cephalic  aortic  arch 
3rd  cephalic  aortic  arch 
4th  cephalic  aortic  arch 
5th  cephalic  aortic  arch 
Aortic  bulb 
Ventricle 


Yolk-sac 


Auricle 
Sinus  venosus 


Vitelliue  vein 
Fig.  49. — Diagram  of  the  Blood-Vessels  of  a  Mammalian  Embeto  after  the  formation  of  the  Heart. 

artery  to  the  aorta  by  an  anastomosing  channel,  the  ductus  arteriosus,  which 
disappears  after  the  pulmonary  circulation  is  established. 

During  the  later  months  of  fcetal  life,  blood  enters  the  right  auricle  by  the 
superior  and  inferior  venae  cavse  and  through  the  coronary  sinus;  only  a  small 
amount  of  blood,  viz.  that  returning  from  the  walls  of  the  heart,  enters  the  right 
auricle  through  the  coronary  sinus.  The  blood  poured  into  the  right  auricle  by 
the  superior  vena  cava  is  returned  from  the  head,  neck,  upper  extremities,  and  the 
thoracic  walls;  passing  from  the  auricle  by  the  right  auriculo-ventricular  opening 
it  enters  the  right  ventricle ;  from  the  right  ventricle  it  is  forced  into  the 
pulmonary  artery,  and  a  small  part  of  it  traverses  the  lungs  and  returns  to  the 
left  auricle  Ijy  the  pulmonary  veins ;  the  main  part,  however,  is  conducted  by  the 
ductus  arteriosus  into  the  aorta  at  a  point  beyond  where  the  main  vessel  of  supply 
to  the  left  upper  extremity,  the  left  subclavian  artery,  rises. 

The  IjIoocI  wliicli  enters  the  right  auricle  by  the  inferior  vena  cava  is  mixed ;  it 
consists  partly  of  purified  blood  from  the  placenta,  and  partly  of  impure  blood 
returning  i'rom  the  abdomen  and  lower  extremities.  The  blood  Irom  the  placenta 
is  returned  to  the  embryo  })y  the  umbilical  vein.  From  the  umbilical  vein  it  passes 
along  a  channel  called  the  ductus  venosus,  which  terminates  in  the  upper  part  of  the 
inferior  vena  cava.  I'he  mixed  l>lood  from  the  inferior  vena  cava  ])asses  through 
tlie  right  auricle,  traverses  the   foramen  ovale  in   the  interauricular  septum,  and 


64 


GENEKAL  EMBEYOLOGY. 


enters  the  left  auricle ;  from  the  left  auricle  it  is  transferred  to  the  left  ventricle 
through  the  left  auriculo-ventricular  opening,  and  the  left  ventricle  ejects  it  into 
the  aorta.  From  the  first  part  of  the  aorta  some  of  the  blood  passes  into  the 
vessels  which  supply  the  head  and  neck  and  upper  extremities,  the  remainder 


Internal  jugular  vein 
External  jugular  vein 

Right  vertebral  artery  , 

Right  subclavian  artery 

Right  subclavian  vein 

Innominate  veins 

Pulmonary  artery 

Superior  vena  cava 

Vena  azygos  major 

Right  auricle 

Right  ventricle 

Hepatic  vein 

Inferior  vena  cava 

Intercostal  veins 


1st  cephalic 
aortic  arch 

Internal  carotid  artery 

2ncl  cephalic 
aortic  arch 


Kxterual  carotid  artery 

3rd  cejjhalic 
aortic  arch 
Vertebral  artery 
~= — Subclavian  artery 

4th  cephalic  aortic  arch 
Superior  intercostal  vein 
5tli  cephalic  aortic  arch 

■Pulmonary  artery 
Vena  azygos  minor  superior 
ft  auricle 


Vena  azygos  minor  inf'eri 


Atrophied  cardinal  vein 
Poi'tal  vein 


Renal  vein 
Lumbar  vein 

Common  iliac  arfcer 
External  iliac  artery 
Internal  iliac  artery _1 


fVorta 
Atrophied  cardinal  vein 


Placenta 


pcgastric  arteries 


Middle  sacral  vein 
'Fig.  50. — Diagram  of  the  Fcetal  Circulation. 

mixes  with  the  blood  conveyed  to  the  aorta  by  the  ductus  arteriosus,  and  the 
blood,  thus  further  mixed,  is  in  part  distributed  to  the  walls  of  the  thorax  and 
abdomen  to  the  abdominal  viscera  and  to  the  lower  extremities,  and  in  part  it 
passes  to  the  placenta. 

Before  birth,  therefore,  there  is  no  pure  arterial  or  fully  oxygenated  blood  in 
the  arteries  of  the  foetus.  The  blood  entering  the  heart  by  the  superior  vena  cava 
IS  venous  blood  from  the  head,  neck,  upper  extremities,  and  thorax  ;  that  entering 
by  the  inferior  vena  cava  is  mixed  blood,  consisting  of  venous  blood  from  the  lower 


PEIMITIVE  VASCULAR  SVSTEM  AND   F(KTAJ.  (JIRCULATION.     65 

part  of  the  body  and  the  lower  extremities,  and  arterial  blood  from  the  placenta. 
The  two  streams  do  not  mix  in  the  right  auricle,  but  the  mixed  or  more  arterial 
stream  passes  directly  through  the  right  into  the  left  auricle,  thence  into  the  left 
ventricle,  and  from  the  left  ventricle  into  the  aorta  or  main  systemic  vessel,  which 
conveys  it  to  all  parts  of  the  body.  The  different  parts  of  the  body  do  not,  however, 
receive  equally  oxygenated  blood,  for  the  venous  stream  which  enters  the  right 
auricle  by  the  superior  vena  cava,  passes  through  that  cavity  into  the  right  ventricle  ; 
by  the  right  ventricle  it  is  forced  into  the  pulmonary  artery,  from  which  some  small 
part  passes  into  the  lungs,  and  so  back  to  the  left  auricle  by  the  pulmonary  veins, 
but  by  far  the  greater  part  is  carried  by  the  ductus  arteriosus  to  the  aorta,  which  it 
enters  beyond  the  origins  of  the  vessels  which  supply  the  head,  neck,  and  upper 
extremities ;  therefore  the  blood  in  the  lower  part  of  the  aorta,  which  is  distributed 
to  the  abdomen,  the  abdominal  viscera  including  the  liver,  the  lower  limbs,  and  the 
placenta,  is  much  more  mixed  or  impure  (less  oxygenated)  than  that  which  is  dis- 
tributed to  the  head,  neck,  and  upper  extremities  from  the  upper  part  of  the  aorta. 


SUMMARY   OF   THE   EXTERNAL   FEATURES    OF   THE   HUMAN 
EMBRYO   AT   DIFFERENT   PERIODS    OF   DEVELOPMENT. 

First  week. — The  phenomena  of  fertilisation  and  segmentation  have  not  been 
observed  in  the  liuman  ovum,  but  there  is  no  reason  to  beheve  that  they  differ  in  any 
essential  respect  from  those  met  witli  in  the  ova  of  other  mammals.  Fertilisation  probably 
occurs  in  the  upper  part  of  the  Fallopian  tube,  and  segmentation  is  completed  in  the 
lower  part  of  the  same  canal  by  the  sixth  or  eighth  day,  when,  presumably,  the  ovum 
becomes  a  morula,  and  passes,  either  as  such  or  as  a  blastula,  into  the  cavity  of  the  uterus. 

Second  week. — At  the  twelfth  day  the  ovum  is  embedded  in  the  uterine  wall ; 
it  is  a  lenticular  vesicle, 

which  measures  5-5  mm.  ^^    ^ 

(i  of  an  inch)  in  length  and 
3"3  mm.  (|-  of  an  inch)  in 
breadth.  Its  upper  and 
lower  surfaces  are  smooth 
and  convex,  the  latter 
being  somewhat  flatter 
than  the  former,  and  it  is 
surrounded  equatorially 
by  a  broad  band  of  villi, 
some  of  which  are  slightly 
branched.  The  wall  of 
the  vesicle  and  the  villous 
processes  which  project 
from  it    consist  of    ecto- 


AM 


A  B 

Fig.  51. 

Human  embryo  at  the  end  of  the  12th  day  of  development  ;  B.  At  the 
end  of  the  13th  day  of  development  ;  C.  At  the  end  of  the  14th  day  of 
development.     (After  His.) 

Amnion  ;  AS.  Allantoic  stalk  ;  BS.  Body-stalk  ;  CV.  Chorionic  villi  on 
a  segment  of  the  chorion  ;  E.  Embryo  ;  H.  Head  of  emVjryo  ;  PR.  Peri- 
cardial region  ;  SS.  Stomatodasal  depression  ;  YS.   Yolk-sac. 


dermal  cells,  and   in   the 

embryonic  area,  which  is  clearlj^  marked   on  the   upper  surface,  there  is  an  inner  layer 

of  granular  nucleated  corpuscles. 

By  the  end  of  the  twelfth  or  the  beginning  of  the  thirteenth  day  the  length  of  the 
ovum  has  increased  to  6  mm.  (|  inch),  and  its  breadth  to  4-5  mm.  (,l  inch).  The  embryonic 
area  is  no  longer  on  the  surface  of  the  ovum,  for  the  amnion  folds  have  closed.  The  yolk- 
sac  is  formed,  and  the  rudiment  of  the  allantoic  duct  projects  backwards  from  the  upper 
and  posterior  part  of  the  embryonic  area.  Mesoderm  has  formed,  and  it  has  extended 
round  the  yolk-sac  and  over  the  inner  siirface  of  the  chorion.  The  embryonic  area,  with 
the  yolk-sac  and  the  amnion,  are  enclosed  within  the  blastoderm,  but  they  remain 
attached  to  the  inner  surface  of  the  chorion  by  a  relatively  thick  stalk  of  ectodermal  and 
mesodermal  tissue,  the  body-stalk,  which  is  subsequently  replaced  by  the  umbilical  cord. 
The  outer  surface  of  the  ovum,  which  now  consists  entirely  of  chorion,  is  covered  witli 
small  villi  into  some  of  which  mesodermal  cores  are  projecting. 

Oliviously  the  ovum  of  the  latter  part  of  the  twelfth  day  dift'crs  considerably  from 
tliat  of  the  earlier  part  of  the  same  day,  but  the  transitional  stages  which  intervene 
between  the  two  have  not  yet  been  observed.  Probably,  however,  the  iiuier  granular 
layer  of  cells  in  the  embryonic  area,  which  rejjresent  the  ent(;derm,  increase  and  form  a 
solid  mass  in  which  a  cavity  soon  appears.  Directly  after  the  formation  of  the  cavity  in 
the  entoderm  the  primitive  streak  appears,  and  the  mesoderm,  growing  from  it,  rapidly 
5 


66 


GENERAL  EMBRYOLOGY. 


oovers  the  entodermal  sac  and  spreads  over  the  inner  surface  of  the  chorionic  area.  At 
the  same  time  the  amniotic  folds  form  and  separate  from  the  chorion,  but  tiiis  separation  is 
not  effected  till  the  mesoderm,  extending  backwards  from  the  posterior  end  of  the  embryonic 
area,  has  reached  and  becomes  connected  with  the  inner  surface  of  the  chorion.  Consequently, 
when  the  amniotic  folds  fuse  together  and  separate  from  the  remainder  of  the  blastoderm, 
the  embryonic  area  with  the  yolk-sac  and  amnion  still  remain  attached  to  the  inner 
surface  of  the  chorion. 

During  the  thirteenth  day  the  embryonic  area  is  elevated,  the  cephalic  and  caudal 
folds  are  developed,  and  the  pericardial  region  becomes  prominent  between  the  head 
extremity  of  the  embryo  and  the  upper  and  anterior  part  of  the  yolk-sac.  The  neural 
groove  and  the  neural  folds  appear ;  the  posterior  ends  of  the  folds  embrace  tlie  anterior 
extremity  of.  the  primitive  streak  on  which  the  primitive  groove  is  formed.  At  the 
anterior  end  of  the  primitive  groove  a  neurenteric  canal  appears,  forming  a  communication 
between  the  neural  groove  and  the  posterior  end  of  the  primitive  alimentary  canal 

On  tlie  fourteenth  day  the  embryo  is  more  distinctly  separated  from  the  yolk-sac  ;  the 
head  increases  considerably  in  size,  and  its  anterior  part  is  bent  downwards.  The  posterior 
part  of  the  neural  canal  is  completed,  except  at  the  extreme  end,  by  the  meeting  and  fusion 
of  the  neural  folds,  but  it  is  still  open  anteriorly,  where  traces  of  the  cerebral  vesicles  are 
present.  The  two  halves  of  the  heart  fuse  together  ;  the  single  tube  thus  formed  is 
sliglitly  bent  upon  itself,  and  its  outline  is  visible  from  the  exterior.  The  pericardial 
region  increases  in  size,  and  a  distinct  stomatodeeal  sp)ace  appears  between  it  and  the 
anterior  part  of  the  head.  The  outlines  of  fourteen  protovertebral  somites  are  visible  on 
the  outer  surface  of  the  body. 


Fig.  52. 


D. 


AS. 


Human  embryo  at  tlie  '21st  day  of  development  ;  E.    At  the  23rd  day  of  development  ; 
F.   At  the  27th  day  of  development.      (After  His. ) 

Allantoic  stalk  ;  BS.  Body-stalk  ;  CV.  Chorionic  villi  on  a  segment  of  the  chorion  ;  EY.  Eye  ;  FL,  Fore- 
limb  ;  H.  Head  ;  HA.  Hyoid  arch  ;  HL.  Hind-lirnb  ;  MA.  Mandibular  arch  ;  MB.  Mid-brain  ;  MP. 
Maxillary  process  ;  OP.  Olfactory  pit  ;  OV.  Otic  vesicle  ;  PR.  Pericardial  region  ;  PS.  Protovertebral 
somite  ;  SS.  Stomatodseal  space  ;  UC.  Umbilical  cord  ;  VC.  Visceral  cleft  ;  WR.  Wolffian  ridge  ;  YS. 
Yolk-sac. 

Third  week. — On  the  fifteenth  day  the  auditory  pits  and  two  visceral  clefts 
appear.  The  head  and  pericardial  region  enlarge,  and  the  stomatodaeal  space,  which 
increases  simultaneously,  becomes  more  defined  laterally  by  the  forward  growth  of  tlie 
maxillary  processes. 

By  the  end  of  the  third  week  Wolffian  ridges  appear  below  the  ventral  ends  of  the 
protovertebral  somites ;  they  are  most  marked  in  the  thoracic  and  pelvic  regions,  where 
bud-like  projections  form  the  rudiments  of  the  limbs.  Four  visceral  clefts  ai-e  visible,  and 
there  is  a  distinct  tail. 

Fourth  week.  —  The  embi-yo  is  curved  upon  itself,  and  its  outline  is  almost 
circular.  The  visceral  arches  begin  to  overlap  each  other.  The  rudiments  of  the  external 
ear  are  just  visible  as  small  nodules.      The  limb  rudiments  are  flat,  oval  buds. 

Fifth  week. — The  curvature  is  diminished,  and  the  head  and  neck  form  about 
half  the  embryo.  The  eye  is  recognisable  externally.  The  nose  begins  to  grow  forwards, 
but  it  is  still  broad  and  flat,  and  the  nostrils  are  widely  apart.  The  nodular  elements  of 
the  external  ear  fuse  together.  The  segments  of  the  limbs  are  defined,  but  the  digits  do 
not  project  beyond  the  ends  of  the  limb-buds.  The  genital  tubercle,  the  rudiment  of  the 
external  generative  organs,  is  formed. 

Sixth  week. — During  the  sixth  week  the  increase  in  size  is  less  rapid  than  in 
previous  stages,  but  the  embrj^o  begins  to  assume  a  more  distinctly  human  form.     The 


HUMAN  EMBRYO  AT  DIFFERENT  STAGES. 


67 


head  remains  relatively  large  and  it  is  bent  at  right  angles  to  the  body.     The  neck  is 
better  defined  and  appears  as  a  constricted  region  between  the   head  and   trunk.      The 


G  H 

Fig.  5-3. 
G.   Human  embryo  at  the  29tli  day  of  development  ;  H.   At  the  32ud  day  of  development.     (After  His.) 
EB.   Rudiment  of  ear  ;  EY.  Eye  ;  FL.  Fore-limb  ;  HA.  Hyoid  arch  ;  HL.  Hind-limb  ;  MA.   Mandibular  arch  ; 
MB.   Mid-brain  ;  MP.   Maxillary  process  ;  OP.   Olfactory  pit  ;  PR.    Pericardial  region  ;  UC.   Umljilical 
cord. 

maxillary  processes  fuse  with  the  lateral  nasal  processes,  and  the  lips  and  eyelids  begin  to 
assume  their  characteristic  form.  The  outer  parts  of  all  the  visceral  clefts  except  the 
hyo-mandibular  disappear.     The  external  ear  acquires  its  adult  form.     The  rotation  of 


Fl(i.   54.  —  HU.MAN    i<'(KTUS    AT    THK    SIXTH    WEKK  FiG.  55. — HUMAN    FCETL'S    SIX    AND    A 

01'  Devei.oi'.ment.     (After  Elis.)  half  weeks  old.     (After  His.) 

D.   Digits  ;   KE.   Rudiment  of  ear  ;  FIj.   Fore-limb  ;   HL.  Hind-limb  ;  MP.  Ma-xillary  process  ;  N.    Nose  ; 

(JO.  Umbilical  cord. 

the  limbs  commences,  and  the  fingers  reach  tiie  extremity  of  tht;  hand  ;  the  tail  is 
beginninj/  to  disappear  as  an  external  yjrojection. 

Seventh  week.  -The  flexure  of  the  head  upon  the  body  is  reduced.  The  nose 
fjrojccts  more  than  in  the  preceding  stage,  and  the  chin  a])])earH.  The  toes  reach  the 
margins  of  the  feet,  a)id  the  projecting  ])ortion  of  the  tail  is  still  further  reduced  in  length. 

Eighth    week.  —  'I'hc    flexure    of    the    licad    disappears.     The    forehead    projects. 


68 


GENERAL  EMBRYOLOGY. 


The  nose  narrows  and  becomes  more  prominent,  but  the  anterior  nasal  orifices  are  still 
directed  forwards.  The  upper  lip  is  completed  by  the  fusion  of  the  globular  processes. 
The  thumb  is  widely  separated   from   the   fingers,  and   the   hand   assumes   a  distinctly 

human  appearance.  The  tail  is  reduced  to  a  small 
nodule,  and  the  umbilical  coi-d  is  attached  to  the 
lower  part  of  the  abdominal  wall.  At  the  end  of 
the  second  month  the  total  length  of  the  foetus, 
excluding  the  legs,  is  28  mm.  (1^  in.). 

Third  month.  —  The  head  grows  less 
rapidly  and,  though  it  is  still  large,  it  is  relatively 
smaller  in  proportion  to  the  whole  body.  The 
eyelids  close,  and  their  margins  fuse  together. 
The  neck  increases  in  length.  The  various  parts 
of  the  limbs  assume  theirdefinite  proportions,  and 
nails  appear  on  the  fingers  and  toes.  The  procto- 
dseum  is  formed  and  the  external  generative  organs 
are  differentiated,  so  that  the  sex  can  be  distin- 
guished on  external  examination.  The  skin  is  a 
rosy  colour,  thin  and  delicate,  but  more  consistent 
than  in  the  preceding  stages.  By  the  end  of  the 
third  month  the  total  length  of  the  foetus,  ex- 
cluding the  legs,  is  7  cm.  (2  -|  in.),  including  the 
legs,  9-10  cm.  (34-4  in.),  and  it  weighs  from 
100-125  grammes  (31-41  oz.). 

Fourth  month. —  In  the  fourth  month 
the  skin  becomes  firmer,  and  fine  hairs  are  de- 
veloped. The  disproportion  between  the  fore 
and  hind  limbs  disappears.  If  the  foetus  is  born 
at  this  period  it  may  live  for  a  fcAV  hours.  Its 
total  length  from  vertex  to  heels  is  16-20cm.  (6|-8 
in.),  from  vertex  to  coccyx  12-13  cm.  (44-5i  in.), 
and  it  weighs  from  230-260  grammes  (S^r-Ol  oz.). 
Fifth  month. — The  skin  becomes  firmer, 
the  hairs  are  more  developed,  and  sebaceous 
matter  appears  on  the  surface  of  the  body.  The 
legs  are  longer  than  the  arms,  and  the  umbilicus 
is  farther  from  the  pubis.  At  the  end  of  the 
month  the  total  length  of  the  foetus,  from  vertex 
to  heels,  is  25-27  cm.  (10-104  in.),  from  vertex  to  coccyx  20  cm.  (8  in.),  and  its  average 
weight  is  about  half  a  kilogramme  (IjV  lbs.). 

Sixth  month. — The  skin  is  wrinkled  and  of  a  dirty  reddish  colour.  The  hairs 
are  stronger  and  darker.  The  deposit  of  sebaceous  matter  is  greater,  especially  in  the 
axillae  and  groins.  The  eyelashes  and  eyebrows  appear.  At  the  end  of  the  month  the 
total  length  of  the  foetus,  from  vertex  to  heels,  is  from  30-32  cm.  (12-12f  in.),  and  its 
average  weight  is  about  one  kilogramme  (2i  lbs.). 

Seventh  month.  —  The  skin  is  still  a  dirty  red  colour,  but  it  is  lighter  than 
in  the  previous  month.  The  body  is  more  plump  on  account  of  a  greater  deposit  of  sub- 
cutaneous fat.  The  eyelids  reopen,  and  the  foetus  is  capable  of  living  if  born  at  this 
period.  Its  total  length  at  the  end  of  the  month,  measured  from  vertex  to  heels,  is  35-36 
cm.  (14-14|  in.),  and  its  weight  is  about  one  and  a  half  kilogrammes  (3|  lbs.). 

Eighth  month. — The  skin  is  comj)letely  covered  with  sebaceous  deposit  which 
is  thickest  on  the  head  and  in  the  axillae  and  groins,  and  its  colour  changes  to  a  bright 
flesh  tint.  The  umbilicus  is  farther  from  the  pubis,  but  it  is  not  yet  at  the  centre  of  the 
body.  The  total  length  of  the  foetus,  from  vertex  to  heels,  is  40  cm.  (16  in.),  and  its  weight 
varies  from  2  to  2h  kilogrammes  (4^-5^  lbs.). 

Ninth  month.  —  The  hair  begins  to  disappear  from  the  body,  but  it  remains 
long  and  abundant  on  the  head.  The  skin  becomes  paler,  the  plumpness  increases,  and 
the  umbilicus  reaches  the  centre  of  the  body.  At  the  end  of  the  ninth  month,  when  the 
foetus  is  born,  it  measures  about  50  cm.  from  vertex  to  heels  (20  in.),  and  it  weighs  from 
3-3-^  kilogrammes  {^to''^tw  lbs.). 

Tlie  age  of  a  foetus  may  be  estimated  approximately  by  Hasse's  rule,  viz.  Uj)  to  the  fifth 
month  the  length  in  centimeters,  the  lower  limbs  being  included,  equals  the  square  of  the  age 
in  months,  and  after  the  fifth  month  the  length  in  centimeters  equals  the  age  multiplied  by  five. 


Fig.  56. — Human  Fcetus  eight  and  a  halb^ 
WEEKS  OLD.     (After  His.) 

GE.   Genital  eminence  ;  UC.    Umbilical  cord. 


OSTEOLOGY. 

THE  SKELETON. 

By  Aethue  Thomson. 

The  term  skeleton  (from  the  Greek,  cT-KeAero?,  dried)  is  applied  to  the  parts  which 
remain  after  the  softer  tissues  of  the  body  have  been  disintegrated  or  removed, 
and  includes  not  only  the  bones,  but  also  the  cartilages  and  ligaments  which  bind 
them  together.  In  the  restricted  sense  of  the  word  the  skeleton  denotes  the 
osseous  framework  of  the  body.  It  is  in  this  sense  that  it  is  generally  employed  in 
human  anatomy. 

The  skeleton  serves  to  support  the  softer  structures  which  are  grouped  around 
it,  and  also  affords  protection  to  many  of  the  delicate  organs  which  are  lodged 
within  its  cavities.  By  the  articulation  of  its  several  parts,  its  segments  are  con- 
verted into  levers  which  constitute  the  passive  portion  of  the  locomotory  system. 
Eecent  research  has  also  proved  that  certain  cells  found  in  bone -marrow  are 
intimately  associated  with  the  development  and  production  of  some  of  the 
corpuscles  of  the  blood. 

Bone  may  be  regarded  as  white  fibrous  tissue  which,  having  become  calcified, 
has  undergone  subsequent  changes,  so  as  to  be  converted  into  true  osseous  tissue. 
Most  probably  all  bone  is  of  membranous  origin,  but  it  may  pass  through  a  stage 
in  which  cartilage  plays  an  important  part  in  its  development.  In  many  instances 
the  cartilage  persists,  and  is  not  converted  into  bone,  as  in  the  case  of  the  articular 
cartilage  which  clothes  the  joint  surfaces,  the  nasal  septum,  the  cartilages  of  the 
nose,  and  the  cartilages  of  the  ribs.  A  persistence  of  the  membranous  condition 
is  met  with  in  man  in  the  case  of  the  tentorium  cerebelli,  which  in  some  groups 
of  animals  (Carnivora)  is  converted  into  a  bony  partition. 

Skeletal  structures  may  be  derived  from  each  of  the  three  layers  of  the 
trilaminar  blastoderm.  The  exo-skeleton  includes  structures  of  ectodermal,  and 
some  of  mesodermal  origin  in  the  shape  of  hair,  nails,  feathers,  teeth,  scales,  armour- 
plates,  etc.,  whilst  the  endo-skeleton,  with  which  we  are  more  particularly  concerned, 
is  largely  derived  from  the  mesoblastic  tissue,  but  also  includes  the  notocliord,  an 
entodermal  structure  which  forms  the  primitive  endo-skeleton,  around  which  the 
axial  skeleton  is  subsequently  developed  in  the  Vertebrata.  The  endo-skeleton  is 
divisible  into  an  axial  portion,  appertaining  to  the  trunk  and  head,  and  an  appen- 
dicular part  associated  with  the  limbs.  It  also  includes  the  splanchnic  skeleton, 
which  comprises  certain  bones  developed  in  the  substance  of  some  of  the  viscera, 
such  as  the  os  cordis  and  os  penis  of  certain  mammals.  In  man,  perhaps,  the 
cartilaginous  framework  of  the  trachea  and  bronchi  may  be  referred  to  this 
system. 

The  number  of  the  bones  of  the  skeleton  of  man  varies  according  to  age. 
Owing  to  a  process  of  fusion  taking  place  during  growth,  the  number  in  the  adult 
is  less  than  the  number  in  the  child.  The  following  table  does  not  include  the 
sesamoid  bones  which  are  frequently  developed  in  tendons,  the  most  constant 
ossicles  of  this  description  being  those  in  relation  to  the  metacarpo-phalangeal 
joint  of  the  thumb,  and  the  metatarso-phalangeal  joint  of  the  great  toe. 


70 


OSTEOLOG-Y. 


life 


The  table  represents  the  iiuml)er  oi  hones  distinct  and  separa])le  during'  adult 


Siiij^le  15 

jues. 

Pairs. 

Total. 

The  verteltral  c(jluiiiu 

2G 

26 

The  skull  . 

6 

8 

22 

Axial  skeleton 

The  sternum 

1 

1 

The  rihs    . 

12 

24 

The  hyoid  bone 

1 

1 

A|)|)eii(licular  skeletnii 

Tlie  upper  limbs    . 
'I'he  lowei'  liud>s     . 

32 
31 

64 
62 

ri)e  ossicles  of  the  ear 

3 

6 

34 


86 


206 


Bones  are  often  classitied  according  to  their  shape.  Thus  long  bones,  that 
is  to  say,  hones  of  elongated  cylindrical  form,  are  more  or  less  characteristic  of 
the  limbs.  Broad  or  flat  bones  are  plate-like,  and  serve  as  protective  coverings  to 
the  structures  they  overlie ;  the  bones  of  the  cranial  vault  display  this  particular 
form.  Other  bones,  such  as  the  carpus  and  tarsus,  are  termed  short  bones  ;  whilst 
the  bones  of  the  cranial  base,  the  face,  and  the  vertebrae,  are  frequently  referred  to 
as  irregular  bones. 

Various  descriptive  terms  are  applied  to  the  prominences  commonly  met  with 
on  a  bone,  such  as  tuberosity,  eminence,  'protuberance,  process,  tubercle,  spine, 
ridge,  crest,  and  line.  These  may  be  articular  in  their  nature,  or  may  serve  as 
points  or  lines  of  muscular  and  ligamentous  attachment.  The  surface  of  the  bone 
may  be  excavated  into  pits,  depressiofis,  fossm,  cavities,  furrows,  grooves,  and 
notches.  These  may  be  articular  or  non-articular,  the  latter  serving  for  the  recep- 
tion of  organs,  tendons,  ligaments,  vessels,  and  nerves.  In  some  instances  the 
substance  of  the  bone  is  hollowed  out  to  form  an  air  space,  sinus,  or  antrum. 
Bones  are  traversed  hj  foramina  and  canals  ;  these  may  be  for  the  entrance  and  exit 
of  nutrient  vessels,  or  for  the  transmission  of  vessels  and  nerves  from  one  region  to 
another.  A  cleft,  hiatus,  ov  fissure  serves  the  same  purpose.  Channels  of  this  kind 
are  usually  placed  in  the  line  of  a  suture,  or  correspond  to  the  line  of  fusion  of  the 
primitive  portions  of  the  bone  which  they  pierce. 

Composition  of  Bone. — Bone  is  composed  of  a  combination  of  organic  and 
inorganic  substances  in  about  the  proportion  of  one  to  two. 


Organic  matter  (Fat  Collagen) 
Mineral  matter — 

Calcic  phosphate  . 

Calcic  carbonate    . 

Calcic  fluoride 

Magnesic  phosphate 

Sodic  chloride 


58-23^ 

7-32 

1-41 

1-32 

•69 


31-04 


68-97 


100-00 

The  animal  matter  may  be  removed  by  boiling  or  charring.  According  to  the 
completeness  with  which  the  fibrous  elements  have  been  withdrawn,  so  the  brittle- 
ness  of  the  bone  increases.  When  subjected  to  high  temperatures  the  earthy 
matter  alone  remains.  By  soaking  a  bone  in  acid  the  salts  may  be  dissolved  out, 
leaving  only  the  organic  part.  The  shape  of  the  bone  is  still  retained,  though  it 
has  now  become  soft,  and  can  be  bent  about  in  any  direction. 

Bone  may  be  examined  either  in  the  fresh  or  dry  condition.  In  the  former, 
state  it  retains  all  its  organic  parts,  which  include  the  fibrous  tissue  in  and  around 
it,  the  blood-vessels  and  their  contents,  together  with  the  cellular  elements  found 
within  the  substance  of  the  bone  itself,  and  the  marrow  which  occupies  the  lacunar 
spaces  and  marrow  cavity.  In  the  dried  or  macerated  bone  most  'of  these  have 
disappeared,  though  a  considerable  portion  of  the  organic  matter  still  remains, 
even  in  bones  of  great  antiquity  and  in  a  more  or  less  fossil  condition.  Con- 
sidering its  nature  and  the  amount  of  material  employed,  bone  possesses  a  remark- 


STKUCTUKE  OF  T30NE.  71 

able  strength,  equal  to  nearly  twice  that  of  oak,  whilst  it  is  capable  of  resisting  a 
greater  crushing  strain  ;  it  is  stated  that  a  cubic  inch  of  bone  will  support  a  weight 
of  over  two  tons.  Its  elasticity  is  remarkable,  and  is  of  the  greatest  service  in 
enabling  it  to  withstand  the  shocks  to  which  it  is  so  frequently  subjected.  In 
regions  where  wood  is  scarce  the  natives  use  the  ribs  of  large  mammals  as  a  sub- 
stitute in  the  construction  of  their  bows.  Its  hardness  and  density  vary  in  different 
parts  of  the  skeleton,  and  its  permanency  and  durability  exceed  that  of  any  other 
tissue  of  the  body,  except  the  enamel  and  dentine  of  the  teeth.  The  osseous  remains 
of  a  race  over  eighty  centuries  old  is  now  being  excavated  in  Egypt. 

Structure  of  Bone. — The  structure  of  the  bone  varies  with  the  form  of  the 
bone  examined.  If  a  long  bone  be  studied  in  section,  the  shaft  or  diaphysis  is  seen 
to  be  hollow,  displaying  a  cavity  of  elongated  shape,  which  contains  the  soft 
cellular  marrow.  Around  this,  the  bone  is  deposited  in  spicules  so  as  to  form  a 
loose  osseous  meshwork,  which  becomes  denser  as  it  reaches  the  circumference,  and 
gradually  merges  with  the  compact  layer  which  forms  the  outer  investing  envelope. 
The  extremities  of  the  bone,  usually  developed  from  separate  or  secondary  centres 
called  epiphyses,  are  composed  of  cancellous  tissue,  usually  finer  in  the  grain  and 
not,  as  a  rule,  displaying  any  medullary  cavity.  Here  the  confining  shell  of  bone 
is  thin,  and  displays  none  of  the  stoutness  which  is  so  characteristic  of  the  outer 
layers  in  the  shaft.  In  the  recent  condition,  the  extremities  are  cartilage-covered 
where  they  enter  into  the  formation  of  joints.  In  flat  bones  the  osseous  tissue  is 
disposed  in  two  compact  layers,  with  a  layer  of  softer  cancellous  bone,  here  called 
the  diploe,  sandwiched  in  between.  There  is  no  medullary  cavity,  although  in  certain 
regions  the  substance  of  the  diploe  may  be  absorbed,  thus  forming  air-spaces  or  air- 
sinuses. 

True  bone  differs  from  calcified  cartilage  or  membrane  in  that  it  not  merely 
consists  of  the  deposition  of  earthy  salts  within  its  matrix,  but  displays  a  definite 
arrangement  of  its  organic  and  inorganic  parts.  Dense  bone  merely  differs  from 
loose  or  cancellous  bone  in  the  compactness  of  its  tissue,  the  characteristic  feature 
of  which  is  the  arrangement  of  the  osseous  lamellae  to  form  what  are  called 
Haversian  systems.  These  consist  of  a  central  or  Haversian  canal  which  contains 
the  vessels  of  the  bone.  Around  this  the  osseous  lamellae  are  arranged  con- 
centrically, separated  here  and  there  by  interspaces  called  lacunae,  in  which  the 
bone  corpuscles  are  lodged.  Passing  from  these  lacunae  are  many  fine  channels 
called  canaliculi.  These  are  disposed  radially  to  the  Haversian  canal,  and  pass 
through  the  osseous  lamellae.  They  are  occupied  by  the  slender  processes  of  the 
bone  corpuscles.  Each  Haversian  system  consists  of  from  three  to  ten  concentric 
rings  of  osseous  lamellae. 

In  addition  to  the  lamellae  of  the  Haversian  systems  there  are  others  which  are 
termed  the  interstitial  lamellae ;  these  occupy  the  intervals  between  adjoining 
Haversian  systems,  and  consist  of  Haversian  systems  which  have  undergone  a  process 
of  partial  absorption.  Towards  the  surface  of  the  bone,  and  subjacent  to  the  peri- 
osteal membrane  which  surrounds  the  shaft,  there  are  lamellae  arranged  circum- 
ferentially;  these  are  sometimes  referred  to  as  the  outer  fundamental  lamellae. 
The  periosteal  membrane  which  surrounds  the  bone,  and  which  plays  so  important 
a  part  in  its  development,  sends  in  processes  through  the  various  Haversian  systems, 
which  carry  with  them  vessels  and  cells,  thus  forming  an  organic  meshwork 
around  which  the  earthy  salts  are  deposited. 

The  interior  of  the  bone,  viz.  the  marrow  cavity,  and  the  interspaces  within  the 
cancellous  tissue,  as  well  as  some  of  the  larger  Haversian  canals,  are  occupied  by 
the  marrow  or  medulla  of  the  bone.  This  varies  considerably  in  its  composition  in 
different  bones.  In  the  medullary  cavity  of  the  shafts  of  the  long  bones  it  consists 
mainly  of  fat  cells,  together  with  a  few  marrow  cells  proper,  supported  by  a  kind 
of  retiform  tissue,  and  is  known  as  the  yellow  marrow.  In  other  situations,  viz. 
in  the  diploe  of  the  cranial  bones,  in  the  cancellated  tissue  of  the  epiphyses  of  the 
long  bones,  tbe  vertebrae,  the  sternum,  and  the  ribs,  the  marrow  is  more  fluid  in  its 
consistence,  contains  less  fat,  bub  is  characterised  by  the  presence  of  marrow-cells 
proper,  which  resemble;  in  some  respects  colourless  blood  corpuscles.  In  addition 
to  tiiese,  however,  there  are  smaller  reddish  coloured  cells,  akin  to  the  nucleated  red 


72  OSTEOLOGY. 

corpuscles  of  the  blood  of  the  embryo.  It  is  these  cells  (erythroblasts)  which  are 
concerned  in  the  formation  of  the  coloured  corpuscles  of  the  blood.  Marrow  which 
displays  these  characteristic  appearances  is  distingidshed  from  the  yellow  variety 
already  described  by  being  called  the  red  marrow.  In  the  diploe  of  the  cranial 
bones  of  aged  individuals  the  marrow,  which  has  undergone  degenerative  changes, 
is  sometimes  referred  to  as  the  gelatinous  marrow. 

Apart  from  the  adaptation  of  form  rendered  necessary  by  the  use  to  which  the 
bone  is  put,  external  influences  are  seen  to  react  upon  the  intimate  structure  of 
the  bone  itself.  Thus,  if  sections  of  different  bones  be  made,  the  structural  arrange- 
ment of  their  cancellous  and  dense  tissue  is  seen  to  vary.  In  long  bones  the  walls 
of  the  shaft  are  thick  and  strong,  more  particularly  towards  the  concave  side  if  the 
shaft  happens  to  be  bent.  The  marrow  cavity — ^largest  towards  the  centre — 
gradually  tapers  towards  the  extremities,  being  encroached  upon  by  the  surround- 
ing cancellous  tissue,  which  is  disposed  in  lines  converging  towards  the  extremities 
like  the  sides  of  a  vaulted  arch,  thereby  forming  platforms  on  which  the  epiphyses 
are  supported.  The  surfaces  of  these  platforms  are  not  smooth,  but  so  arranged 
as  best  to  withstand  the  strain  to  which  the  epiphyses  are  habitually  subjected. 
Such  provision  is  necessary  in  order  to  obviate  the  tendency  to  separation,  which 
might  otherwise  occur  prior  to  the  complete  osseous  union  of  the  diaphysis  with 
the  epiphysis.  In  the  epiphysis  itself  the  arrangement  of  the  fibres  of  the 
cancellous  tissue  is  determined  by  the  disposition  of  the  articular  surfaces.  The 
osseous  lamellae,  as  a  rule,  are  disposed  at  right  angles  to  the  planes  of  the  articular 
facets,  whilst  they  are  bound  together  by  other  lamellae  arranged  conformably  with 
these  articular  planes.  The  former  correspond  to  the  direction  of  greatest  pressure, 
whilst  the  latter  agree  with  the  lines  of  greatest  tension.  In  cases  where  there  is 
an  outstanding  process  projecting  from  the  shaft,  as,  for  example,  the  head  and 
neck  of  the  femur,  a  section  of  the  bone  displays  a  bracket-like  arrangement  of  the 
osseous  fibres  of  the  cancellous  tissue,  which  assists  materially  in  strengthening  the 
bone. 

Ossification  and  Growth  of  Bones. — For  an  account  of  the  earlier  development 
of  the  skeleton  the  reader  is  referred  to  the  section  on  Embryology.  Concerning  the 
subsequent  changes  which  take  place,  these  are  dependent  on  the  conversion  of  the 
scleratogenous  tissue  into  membrane  and  cartilage.  A  characteristic  of  this  tissue 
is  that  it  contains  elements  which  become  formed  into  bone-producing  cells,  called 
osteoblasts.  These  are  met  with  in  the  connective  tissue  from  which  the  membrane 
bones  are  formed,  whilst  they  also  appear  in  the  deeper  layers  of  the  investing 
tissue  of  the  cartilage  (perichondrium),  and  so  lead  to  its  conversion  into  the  bone- 
producing  layer  or  periosteum.  All  true  bone,  therefore,  may  probably  be  regarded 
as  of  membranous  origin,  though  its  appearance  is  preceded  in  some  instances  by 
the  deposition  of  cartilage ;  in  this  case  calcification  of  the  cartilage  is  an  essential 
stage  in  the  process  of  bone  formation,  but  the  ultimate  conversion  into  true  bone, 
with  characteristic  Haversian  systems,  leads  to  the  absorption  and  disappearance  of 
this  primitive  calcified  cartilage. 

Membrane  bones  are  such  as  have  developed  from  fibrous  tissue  without 
having  passed  through  a  cartilaginous  stage.  Of  this  nature  are  the  bones  of  the 
cranial  vault  and  the  majority  of  the  bones  of  the  face,  viz.  the  superior  maxillae, 
malars,  nasals,  lachrymals,  and  palate  bones,  as  well  as  the  vomer.  The  internal 
pterygoid  plate  is  also  of  membranous  origin. 

Cartilage  bones  are  those  which  are  preformed  in  cartilage,  and  include  most 
of  the  bones  of  the  skeleton.  Their  growth  is  often  described  as  endochondral 
and  ectochondral,  the  former  term  implying  the  deposition  of  membrane  bone  in 
the  centre  of  the  cartilage,  while  the  latter  signifies  a  deposit  of  membrane  bone  on 
the  surface  of  the  cartilage,  the  osteogenetic  layer  on  the  surface  of  the  cartilage 
being  called  the  perichondrium  till  once  bone  has  been  formed,  when  it  is  called 
the  periosteum. 

In  the  course  of  the  development  of  a  bone  from  membrane,  as,  for  example, 
the  parietal  bone,  the  fibrous  tissue  corresponding  to  the  position  of  the  primary 
centre  becomes  osteogenetic,  because  here  appear  the  bone-forming  cells  (osteoblasts), 
which  rapidly  surround  themselves  with  a  bony  deposit  more  or  less  spicular  in 


OSSIFICATION  AND  GEOWTH  OF  BONES.  73 

arrangement.  As  growth  goes  on  these  osteoblasts  become  embedded  in  the  ossify- 
ing matrix,  and  remain  as  the  corpuscles  of  the  future  bone,  the  spaces  in  which 
they  are  lodged  corresponding  to  the  lacunte  and  canaliculi  of  the  fully  developed 
osseous  tissue.  From  the  primary  centre  ossification  spreads  eccentrically  towards 
the  margins  of  the  bone,  where  ultimately  the  sutures  are  formed.  Here 
the  growth  rendered  necessary  by  the  expansion  of  the  cranium  takes  place 
through  the  agency  of  an  intervening  layer  of  vascular  connective  tissue  rich  in 
osteoblasts ;  but  in  course  of  time  the  activity  of  this  is  reduced  until  only  a  thin 
layer  of  intermediate  tissue  persists  along  the  line  of  the  suture ;  this  may  eventu- 
ally become  absorbed,  leading  to  the  obliteration  of  the  suture  by  the  osseous  union 
of  the  contiguous  bones.  Whilst  the  expansion  of  the  bone  in  all  directions  is 
thus  provided  for,  its  increase  in  thickness  is  determined  by  the  activity  of  the 
underlying  and  overlying  strata.  These  form  the  periosteum,  and  furnish  the 
lamellae  which  constitute  the  inner  and  outer  compact  osseous  layers. 

In  a  cartilage  bone  changes  of  a  similar  nature  occur.  The  cartilage,  which  may 
be  regarded  histologically  as  white  fibrous  tissue  +  chondro-sulphuric  acid  and  a 
certain  amount  of  lime  salts,  undergoes  the  following  changes : — First,  the  cartilage 
cells  being  arranged  in  rows,  become  enlarged ;  secondly,  the  matrix  between  the 
cartilage  cells  becomes  calcified  by  the  deposition  of  an  additional  amount  of  lime 
salts ;  thirdly,  the  rows  of  cells  become  confluent ;  and,  fourthly,  into  the  spaces  so 
formed  extend  the  blood-vessels  derived  from  the  vascular  layer  of  the  periosteum. 
Accompanying  these  vessels  are  osteoblasts  and  osteoclasts,  the  former  building  up 
true  bone  at  the  expense  of  the  calcified  cartilage,  the  latter  causing  an  absorption  of 
the  newly-formed  bone,  and  leading  to  its  conversion  into  a  marrow  cavity,  so  that 
in  due  course  all  the  cartilage  or  its  products  disappear.  At  the  same  time  that  this 
is  taking  place  within  the  cartilage,  the  perichondrium  is  undergoing  conversion  into 
the  periosteum,  an  investing  membrane,  the  deeper  stratum  of  which,  highly  vascular, 
furnishes  a  layer  of  osteoblast  cells  which  serve  to  develop  the  circumferential 
lamellae  of  the  bone.  It  is  by  the  accrescence  of  these  layers  externally,  and  their 
absorption  internally  through  the  action  of  the  osteoclast  cells,  that  growth  takes 
place  transversely.  A  transverse  section  of  the  shaft  of  a  long  bone  shows  this 
very  clearly.  Centrally  there  is  the  marrow  cavity,  formed  primarily  by  the 
absorption  of  the  calcified  cartilage;  around  this  the  cancellous  tissue  produced 
by  the  partial  erosion  of  the  primary  periosteal  bone  is  disposed,  whilst  externally 
there  is  the  dense  envelope  made  up  of  the  more  recent  periosteal  growth. 

Such  a  description,  whilst  explaining  the  growth  of  bone  circumferentially,  fails 
to  account  for  its  growth  in  length ;  hence  the  necessity  in  long  bones  for  some 
arrangement  whereby  ossification  may  take  place  at  one  or  both  extremities  of  the 
shaft.  This  zone  of  growth  is  situated  where  the  ossified  shaft  becomes  continuous 
with  the  cartilaginous  epiphysis.  In  addition,  within  these  epiphysial  cartilages 
calcification  of  the  cartilage  takes  place  centrally,  just  as  in  the  diaphysis.  The  two 
parts  of  the  bone,  viz.  the  diaphysis  and  epiphysis,  are  thus  separated  by  a  layer  of 
cartilage,  as  yet  uncalcified,  but  extremely  active  in  growth  owing  to  the  invasion  of 
vessels  and  cells  from  a  vascular  zone  which  surrounds  the  epiphysis.  The  nucleus  of 
the  epiphysis  becomes  converted  into  true  bone,  which  grows  eccentrically.  This 
arrangement  provides  for  the  growth  of  the  shaft  towards  the  epiphysis,  and  the 
growth  of  the  epiphysis  towards  the  shaft ;  so  that  as  long  as  the  active  intervening 
layer  of  cartilage  persists,  extension  of  growth  in  a  longitudinal  direction  is  possible. 
Subsequently,  however,  at  variable  periods  the  intervening  layer  of  cartilage  becomes 
calcified,  and  true  bony  growth  occurs  within  it,  thus  leading  to  complete  osseous 
union  between  the  shaft  and  epiphysis.  When  this  has  taken  place  all  further 
growth  in  a  longitudinal  direction  ceases.  In  cases  where  the  epiphysis  enters  into 
the  formation  of  a  joint,  tlie  cartilage  over  the  articular  area  persists  and  undergoes 
neither  calcification  nor  ossification.  In  long  bones  the  ossific  nucleus  for  the  shaft 
or  diaphysis  is  the  first  to  appear,  and  is  hence  often  called  the  primary  centre  of 
ossification.  The  centres  for  the  epiphyses  appear  subsequently  at  variable  periods, 
and  are  referred  to  as  the  secondary  centres  of  ossification. 

From  what  has  been  said  it  will  ])G  gathered  that  the  vascular  supply  of  the 
bone  is  derived  irom  the  vessels  of  the  periosteum.     These  consist  of  fine  arteries 


74  OSTEOLOGY. 

which  enter  the  surface  of  the  shaft  and  epiphysis;  but  in  addition  there  is  a 
larger  trunk  which  enters  the  diaphysis  and  reaches  the  medullary  cavity.  This  is 
called  the.  nutrient  artery  of  the  bone.  The  direction  taken  by  this  vessel  varies  in 
different  bones.  In  the  upper  limb  the  artery  runs  downwards  in  the  case  of  the 
humerus  and  upwards  in  the  radius  and  ulna ;  in  the  lower  limb  the  nutrient 
vessel  of  the  femur  is  directed  towards  the  upper  extremity  of  the  shaft,  whilst 
in  the  tibia  and  fibula  it  follows  a  downward  course.  It  is  difficult  to  account  for 
this  difference  in  the  arrangement  of  the  vessels ;  but  it  has  been  pointed  out  tliat 
when  all  the  joints  are  flexed,  as  in  the  position  occupied  by  the  foetus  in  utero, 
the  direction  taken  by  the  vessels  is  the  same,  and  corresponds  to  a  line  passing 
from  the  head  towards  the  tail-end  of  the  embryo.  Consequently,  in  the  upper 
limb  the  vessels  flow  towards  the  elbow,  whilst  in  the  lower  limb  they  pass  from 
the  knee. 

The  attention  of  anatomists  has  long  been  directed  to  the  elucidation  of  the  laws 
which  regulate  bone-growth.  Our  present  knowledge  of  the  subject  may  be  briefly 
summarised  in  the  following  generalisations : — 

1.  In  bones  with  a  shaft  and  two  epiphyses,  the  epiphysis  towards  which  the 
nutrient  artery  is  directed  is  the  first  to  unite  with  the  shaft. 

2.  In  bones  with  a  shaft  and  two  epiphyses,  as  a  rule  the  epiphysis  which  com- 
mences to  ossify  latest  unites  soonest  with  the  shaft.  (The  fibula  is  a  notable 
exception  to  this  rule.     See  p.  239.) 

3.  In  bones  with  a  shaft  and  one  epiphysis  the  nutrient  artery  is  directed 
towards  the  end  of  the  bone  which  has  no  epiphysis.  (This  arrangement  holds 
good  in  the  case  of  the  clavicle,  the  metacarpus,  metatarsus,  and  phalanges.) 

4.  When  an  epiphysis  is  ossified  from  more  than  one  centre,  coalescence  takes 
place  between  the  separate  ossific  nuclei  before  the  epiphysis  unites  with  the  shaft. 

Highly  suggestive,  too,  are  the  following  propositions — That  ossification  first 
commences  in  the  epiphysis  which  ultimately  acquires  the  largest  relative  propor- 
tion to  the  rest  of  the  bone,  and  that  the  ossification  of  the  epiphysis  is  also 
correlated  with  its  functional  importance.  In  cases  of  long  bones  with -only  one 
epiphysis,  the  epiphysis  is  placed  at  the  end  of  the  bone  where  there  is  most 
movement. 

The  veins  which  permeate  the  cancellous  texture  of  the  bone  are  large  and  thin- 
walled.  They  do  not  accompany  the  arteries,  and,  as  a  rule,  in  long  bones  they 
escape  through  large  openings  near  the  articular  surface.  In  flat  bones  they  occupy 
channels  within  the  diploe,  and  drain  into  an  adjacent  sinus,  or  form  communica- 
tions with  the  superficial  veins  of  the  scalp. 

The  lymphatics  are  mainly  periosteal,  but  enter  the  bone  along  with  the  vessels 
and  become  perivascular. 

The  nerves  which  accompany  the  arteries  are  probably  destined  for  the  supply 
of  the  coats  of  these  vessels.  Whether  they  end  in  the  bony  tissue  or  not  is 
unknown. 

THE  VERTEBRAL  COLUMN. 

The  vertebral  column  (columna  vertebralis)  of  man  consists  of  thirty-three 
segments  or  vertebrae,  placed  one  on  the  top  of  the  other.  In  the  adult,  certain  of 
these  vertebrae  have  become  fused  together  in  the  process  of  growth  to  form  bones, 
the  segmental  arrangement  of  which  is  somewhat  obscured,  though  even  in  their 
fully-developed  condition  sufficient  evidence  remains  to  demonstrate  their  com- 
pound nature.  The  vertebrte  so  blended  are  termed  the  fixed  or  false  vertebrae, 
whilst  those  Ijetween  which  osseous  union  has  not  taken  place  are  described  as  the 
movable  or  true  vertebrae.  This  fusion  of  the  vertebral  sesiments  is  met  with  at 
either  extremity  of  the  vertebral  column,  more  particularly  below%  where  the  column 
is  modified  to  adapt  it  for  union  with  the  girdle  of  the  lower  limb,  and  also  in 
the  region  of  man's  degenerated  caudal  appendage.  But  a  partial  union  of  the 
vertebral  segments  also  takes  place  above,  between  the  two  highest  vertebrae,  in 
association  with  the  mechanism  necessary  to  provide  for  the  movements  of  the 
head  on  the  column. 


THE  VEETEBRAL  COLUMN.  75 

For  descriptive  purposes  the  vertebral  column  is  subdivided  according  to  the 
regions  thi-ough  which  it  passes.  Thus  the  vertebrte  are  described  as  cervical 
(vertebrtc  cervicales),  dorsal  or  thoracic  (vertebrae  thoracales),  lumbar  (vertebra; 
Jumbales),  sacral  (vertebrae  sacrales),  and  coccygeal  (vertebrae  caudales;,  according 
as  they  lie  in  the  regions  of  the  neck,  back,  loins,  pelvis,  and  tail.  The  number  of 
vertebrae  met  with  in  these  regions  is  fairly  constant,  though,  as  will  be  hereafter 
pointed  out,  variations  may  occur  in  the  number  of  the  members  of  the  different 
series.  The  vertebrae  in  man  are  thus  apportioned — 7  cervical,  12  dorsal,  5  lumljar, 
5  sacral,  and  4  or  5  coccygeal ;  the  three  former  groups  comprise  the  true  or  mov- 
able vertebrae,  the  two  latter  the  false  or  fixed  vertebrae.  The  vertebral  formula 
may  be  thus  expressed  : — 


Movable  or  True  Vertebrae. 

Cervical.        Dorsal.        Lumbar. 
7  12  5 


Fixed  or  False  Vertebrse. 

Sacral.      Coccygeal. 

5  4  =  33. 


Sufierior 
articular  process    Pedicle 


Demi-facet 

for  head 

of  lib  Bony 


Facet  for 
tubercle  of  rib 


Demi-facet  for 
head  of  rib 


(As  viewed  from  the  right  side.) 


Spinous  process 


The  vertebrae  of  which  the  column  is  built  up,  though  displaying  great  diversity  of 
characters  in  the  regions  above  enumerated,  yet  preserve  certain  features  in 
common.  All  possess  a  solid  part, 
centrum  or  body  (corpus  vertebrae) ; 
all  have  articular  processes  by  which 
they  articulate  with  their  fellows ; 
most  have  muscular  processes  de- 
veloped in  connexion  with  them ; 
whilst  the  majority  display  a  verte- 
bral or  spinal  foramen  (foramen  verte- 
brale)  formed  by  the  union  of  a  bony 
arch  (arcus  vertebrae)  with  the  body. 
These  common  characters  ruay  best 
be  studied  by  selecting  for  descrip- 
tion an  intermediate  member  of  the 
series.  For  this  purpose  one  of  the 
middle  or  lower  thoracic  vertebrae 
may  be  chosen. 

A  typical  vertebra  may  be  de- 
scribed as  consisting  of  a  body  or 
centrum  (corpus  vertebrae)  composed 
of  a  mass  of  spongy  bone,  more  or 
less  cylindrical  in  form.  The  size 
and  shape  of  the  body  is  liable  to 
considei'able  variation  according  to 
the  vertebra  examined.  The  upper 
and  lower  surfaces  of  the  body  are 
very  slightly  concave  from  before 
backwards  and  from  side  to  side, 
due  to  the  thickening  of  the  bone 
around  its  margins.  Intherecentcon- 
dition  these  surfaces  afford  attach- 
ment for  the  intervertebral  discs 
which  are  placed  like  pads  between 
the  bodies  of  the  movable  members 
of  the  series.  The  circumference  of 
the  body,  formed  as  it  is  of  more 
compact  bone  tlian  the  interior,  is 
usually  slightly  concave  from  above 
downwards,  though  it  becomes  flat 

behind,  where  the  body  forms  the  anterior  boundary  of  the  spinal  or  vertebral 
foramen,  at  wliich  ]joint  it  is  usually  slightly  concave  from  side  to  side.  The 
vertical  surfaces  of  the  body  are  pierced  liere  and  there  by   foramina    for    the 


Facet  for 
tubercle  of 
rib 
Superior  articular 
process 


Demi-facet  for 
head  of  rilj 


(As  viewed  from  above.) 
FiG.s.  .57,  58. — Fifth  Thoracic  Vkhtehka. 


76  OSTEOLOGY. 

passage  of  nutrient  vessels,  more  particularly  on  the  posterior  surface,  where  a 
depression  of  considerable  size  receives  the  openings  of  tlie  canals  through  which 
some  of  the  veins  which  drain  the  body  of  the  bone  escape.  Connected  with  the 
body  posteriorly  there  is  a  bony  arch  (arcus  vertebrae),  which,  by  its  union  with 
the  body,  encloses  a  foramen  of  variable  size,  the  spinal  or  vertebral  foramen 
(foramen  vertebrale).  When  the  vertebrte  are  placed  on  the  top  of  each  other 
these  foramina  form  with  the  uniting  ligaments  a  continuous  canal — spinal  or 
neural  canal — in  which  the  spinal  cord  with  its  coverings  is  lodged.  The  arch, 
which  is  formed  by  the  union  of  the  pedicles  and  laminae,  besides  enclosing  the 
spinal  foramen,  also  supports  a  certain  number  of  processes ;  of  these,  some  are 
outstanding,  and  may  be  regarded  as  a  series  of  levers  to  which  muscles  are 
attached,  whilst  others  are  articular  and  assist  in  uniting  the  different  vertebrte 
together  by  means  of  a  series  of  movable  joints.  The  pedicles  are  the  bars  of 
bone  which  pass  from  the  back  of  the  body  of  the  vertebrte  on  either  side  to 
the  points  where  the  articular  processes  are  united  to  the  arch.  The  pedicles 
are  compressed  laterally,  and  have  rounded  superior  and  inferior  borders.  Since 
the  vertical  breadth  of  the  pedicles  is  not  as  great  as  the  thickness  of  the  body  to 
which  they  are  attached,  it  follows  that  when  the  vertebrae  are  placed  one  above 
the  other  a  series  of  intervals  is  left  between  the  pedicles  of  the  different  vertebrae. 
These  spaces,  enclosed  in  front  by  the  bodies  of  the  vertebrae  and  their  inter- 
vertebral discs,  and  behind  by  the  coaptation  of  the  articular  processes,  form  a 
series  of  holes  communicating  with  the  neural  or  spinal  canal ;  these  are  called  the 
intervertebral  foramina  (foramina  intervertebralia),  and  allow  of  the  transmission  of 
spinal  nerves  and  vessels.  As  each  intervertebral  foramen  is  bounded  al)Ove  and 
below  by  a  pedicle,  the  grooved  surfaces  in  correspondence  with  the  upper  and 
lower  borders  of  the  pedicles  are  called  the  upper  and  lower  intervertebral  grooves 
or  notches  (incisura  vertebralis  superior  et  inferior).  Posteriorly,  the  two  pedicles 
are  united  by  two  somewhat  flattened  plates  of  bone — the  laminae,  which  converge 
towards  the  middle  line,  and  become  fused  with  the  root  of  the  projecting  spinous 
process  (processus  spinosus).  The  breadth  of  the  laminse  and  their  sloping  arrange- 
ment are  such,  that  when  the  vertebrae,  are  articulated  together  they  leave  little 
space  between  them,  thus  enclosing  fairly  completely  the  neural  canal,  of  which 
they  form  the  posterior  wall.  The  edges  and  inner  surfaces  of  the  laminae  are 
rough  for  the  attachment  of  the  ligaments  which  bind  them  together. 

The  muscular  processes  are  three  in  number,  viz.  two  transverse  processes — one 
on  either  side  — and  one  central  or  median,  the  spinous  process.  The  former 
(processus  transversus)  project  outwards  on  either  side  from  the  arch  at  the  point 
where  the  pedicle  joins  the  lamina.  The  latter  (processus  spinosus)  extends  back- 
wards in  the  middle  line  from  the  point  of  fusion  of  the  laminae.  The  spinous 
processes  display  much  variety  of  length  and  form. 

The  articular  processes  (zygapophyses),  four  in  number,  are  arranged  in  pairs — 
one  superior,  the  other  inferior ;  the  former  are  placed  on  the  upper  surface  of  the 
arch  where  the  pedicles  and  laminae  join,  the  latter  below  the  arch  in  correspondence 
with  the  superior.  Whilst  differing  much  in  the  direction  of  their  articular 
surfaces,  the  upper  have  generally  a  backward  tendency,  whilst  the  lower  incline 
forwards. 

THE  TRUE  OR  MOVABLE  VERTEBRAE. 

The  Cervical  Vertebrae. 

The  cervical  vertebrae  (vertebrae  cervicales),  seven  in  number,  can  be  readily 
distinguished  from  all  the  other  vertebrae  by  the  fact  that  their  transverse  pro- 
cesses are  pierced  by  a  foramen.  The  two  highest,  and  the  lowest,  require  special 
description ;  the  remaining  four  conform  to  a  common  type. 

Their  bodies,  the  smallest  of  all  the  true  vertebrae,  are  oblong  in  shape,  the 
transverse  diameter  being  much  longer  than  the  antero-posterior  width.  The  upper 
surface,  which  slopes  from  behind  forwards  and  downwards,  is  concave  from  side  to 
side,  owing  to  the  marked  projection  of  its  lateral  margins.  Its  anterior  lip  is 
rounded  off,  whilst  its  posterior  edge  is  sharply  defined. 


THE  CEEVICAL  VERTEBEiE. 


77 


The  inferior  surface,  which  is  more  or  less  saddle-shaped,  is  directed  downwards 
and  backwards.  It  is  convex  from  side  to  side,  and  concave  from  before  backwards, 
with  a  slight  rounding  off  of  the  projecting  anterior  lip.  The  vertical  diameter  of 
the  body  is  small  in  proportion  to  its  width.  The  anterior  surface  is  flat  in  the 
middle  line,  but  furrowed  laterally.  The  posterior  surface,  which  is  rough  and 
pierced  by  many  small  foramina,  is  flat  from  side  to  side  and  above  downwards ;  it 
forms  in  its  entire  extent  the  anterior  wall  of  the  spinal  foramen.  The  lateral 
aspects  of  the  body,  particularly  in  their  upper  parts,  are  fused  with  the  costal 
parts  of  the  transverse  processes,  and  form  the  inner  wall  of  the  vertebrarterial 
foramen  (foramen  transversarium). 

The  pedicles  which  spring  from  the  posterior  half  of  the  lateral  aspects  of  the 
body,  about  equidistant  from  their  upper  and  lower  margins,  are  directed  hori- 
zontally backwards  and  outwards.  The  superior  and  inferior  notches  are  nearly 
equal  in  depth. 

The  laminae  are  long,  and  about  as  wide  as  the  body  of  the  bone  is  thick. 

The  spinal  foramen  is  larger  than  in  the  thoracic  and  lumbar  regions ;  its  shape 
is  triangular,  or  more  nearly  semilunar. 

The  transverse  processes,  so  called,  are  pierced  by  the  vertebrarterial  foramen 


Bifid  spine 


Superior  articular  process        Superior  notch 

Vertebrarterial  foramen 


Infeuoi  notch 
Inferior  articular  process 


Spinous  process 


Vertebrarterial  foramen 
Anterior  tubercle 
Fig.  59. — Foctrth  Cervical  Vertebra  from  Above  and  from  the  Right  Side. 


(foramen  transversarium).  They  consist  of  two  parts — the  part  behind  the  foramen, 
which  springs  from  the  neural  arch  and  is  the  true  transverse  process,  and  the 
part  in  front,  which  is  homologous  with  the  ribs  in  the  thoracic  portion  of  the 
column.  These  two  processes,  united  externally  by  a  bridge  of  bone,  which  thus 
converts  the  interval  between  them  into  a  foramen,  terminate  in  two  tubercles, 
known  respectively  as  the  anterior  and  posterior  tubercles.  The  general  direction 
of  these  processes  is  outwards,  slightly  forwards,  and  a  little  downwards,  the  anterior 
tubercles  lying  internal  to  the  posterior.  The  two  tubercles  are  separated  above  by 
a  groove  directed  outwards,  downwards,  and  forwards ;  along  this  the  spinal  nerve 
trunk  passes.  The  vertebrarterial  foramen  (foramen  transversarium),  often  sub- 
divided by  a  spicule  of  bone,  is  traversed  by  the  vertebral  artery  and  vein  in  the 
upper  six  vertebrae.  The  spinous  processes,  which  are  directed  downwards,  are  short, 
compressed  vertically,  and  bifid.  The  articular  processes  are  supported  on  cylindrical 
masses  of  bone  fused  with  the  arch  where  the  pedicles  and  laminte  join.  These 
cylinders  are  sliced  away  obliquely  above  and  below,  so  that  the  superior  articular 
facets,  more  or  less  circular  in  form,  are  directed  upwards  and  backwards,  whilst 
tlie  corresponding  inferior  surfaces  are  turned  downwards  and  forwards. 

Variations. — Hzawlowski  records  the  presence  of  an  iiidependeiit  rib  element  in  tlic  Irans- 
ver.«f,  procc-H  of  flic  (V)iirlli  (■(■rvicii]  vfvUihvd.     (Anat.  Anz.  Jena,  vol.  xx.  ji.  306.) 

First  Cervical  Vertebra  or  Atlas. — This  bone  may  be  readily  recognised  by 
tl)e  absence  of  the  Itody  und  spinous  process.  It  consists  of  two  lateral  masses, 
which  8uy)port  the  articular  and  transverse  processes.  The  lateral  masses  are 
tlieiiiselvcH  united  by  two  curved  l)ars  of  bone,  tlio  anterior  and  posterior  arches,  of 
wliich  the  former  is  tlie  stonter  and  sliorter.  Each  lateral  mass  is  irr((gula,rly  six- 
sided,  and  HO  placed  that  it  lies  closer  to  its  fellow  of  tin;  oppositti  side  in  front  than 


78 


OSTEOLOGY. 


Fig.  60. — The  Atlas  prom  Above. 


1.   Posterior  arch. 

"2.  Transverse  process. 

3.  Tuliercle  for  transverse 

ligament. 

4.  Anterior  arch. 

5.  Anterior  tubercle. 


process. 

7.  Superior  articular  process. 

8.  Foramen  for  vertebral  artery. 

9.  Groove  for  vertebral  artery. 
10.  Posterior  tubercle. 


behind.  Its  upper  surface  is  excavated  to  form  an  elongated  oval  facet,  concave 
from  before  backwards,  and  inclined  obliquely  inwards ;  not  infrequently  this 
articular  surface  displays  indications  of  division  into  two  parts.  These  facets  are 
for  the  recejitiou  of  the  condyles  of  the  occipital  bone. 

The  inferior  articular  facets  are   placed   on   the   under   surfaces  of  the   lateral 

^  masses.     Of  circular  form, 

they  display  a  slight  side- 
to -side  concavity,  though 
flat  in  the  antero-posterior 
direction.  Their  disposition 
is  such  tliat  their  surfaces 
incline  downwards  and 
slightly  inwards.  They  rest 
on  the  superior  articular 
processes  of  the  second  cer- 
vical vertebra.  Springing 
from  the  anterior  and  inner 
aspects  of  the  lateral  masses, 
and  uniting  them  in  front, 
is  a  curved  bar  of  bone, 
the  anterior  arch  (arcus 
6.  Surface  for  articulation  with  odontoid  interior) :  compressed  on 
process.  <  :;  ,  .-'■     .        ,  •   i 

either  side,  this  is  thick- 
ened centrally  so  as  to  form 
on  its  anterior  aspect  the 
rounded  anterior  tubercle 
(tuberculum  anterius).  In  correspondence  with  this  on  the  posterior  surface  of 
this  arch  is  a  circular  facet  (fovea  dentis)  for  articulation  with  the  odontoid  process 
of  the  second  cervical  vertebra  (axis). 

The  inner  surface  of  the  lateral  mass  is  rough  and  irregular,  displaying  a  little 
tubercle  for  the  attachment  of  the  tranverse  ligament  which  passes  across  the  space 
included  between  the  two  lateral  masses  and  the  anterior  arch,  thus  holding  the 
odontoid  process  of  the  axis  in  position.  Behind  each  tubercle  there  is  usually  a 
deep  pit,  opening  into  the  bottom  of  which  are  the  canals  for  the  nutrient  vessels. 

External  to  the  lateral  mass,  and  principally  from  its  upper  half,  the  transverse 
process  arises  by  two  roots  which  include  between  them  the  vertebrarterial  foramen. 
The  transverse  process  is  long,  obliquely  compressed,  and  down-turned ;  the  anterior 
and  posterior  tubercles  are  no  longer  distinguishable,  as  they  have  fused  to  form 
one  mass. 

The  posterior  arch  arises  in  part  from  the  posterior  surface  of  the  lateral  mass, 
and  in  part  from  the  posterior  root  of  the  transverse  process.  Compressed  from 
above  downwards  anteriorly,  where  it  bounds  a  groove  which  curves  around  the 
posterior  aspect  of  the  superior  articular  process,  which  groove  is  also  continuous 
externally  with  the  vertebrarterial  foramen,  the  posterior  arch  becomes  thicker 
mesially,  at  which  point  it  displays  posteriorly  a  rough  irregular  projection — the 
posterior  tubercle  (tuberculum  posterius),  the  feeble  representative  of  the  spinous 
process.  A  prominent  little  tubercle,  arising  from  the  posterior  extremity  of  the 
superior  articular  process,  overhangs  the  groove  above  mentioned,  and  not  in- 
frequently becomes  developed  so  as  to  form  a  bridge  of  bone  across  it,  converting 
the  groove  into  a  canal  through  which  the  vertebral  artery  and  the  first  cervical  or 
suboccipital  nerve  pass — a  condition  normally  met  with  in  many  animals.  It  is 
noteworthy  that  the  grooves  traversed  by  the  two  highest  spinal  nerves  lie  behind 
the  articular  processes,  in  place  of  in  front,  as  in  other  parts  of  the  column. 

The  ring  formed  by  the  lateral  masses  and  the  anterior  and  posterior  arches  is 
of  irregular  outline.  The  anterior  part,  cut  off  from  the  rest  by  the  transverse 
ligament,  serves  for  the  lodgment  of  the  odontoid  process  of  the  axis;  the  larger 
part  behind  corresponds  to  the  upper  part  of  the  neural  or  spinal  canal. 

Variations. — Tlie  vertebrarterial  foramen  is  often  deficient  in  front.  Imperfect  ossification 
occasionally  leads  to  tlie  anterior  and  posterior  arches  being  incomjilete.     The  superior  articular 


THE  CERVICAL  VERTEBRiE. 


79 


surfaces  are  occasionally  partially  or  conii^letely  divided  into  antei-ior  and  posterior  iiortions. 
In  some  instances  tlie  extremity  of  the  transverse  process  has  two  tubercles.  The  transverse 
jirocess  may,  in  rare  cases,  articulate  with  a  projecting  process  (paroccipital)  from  the  under 
surface  of  the  jugular  process  of  the  occipital  bone  (see  p.  113).  An  upward  extension  from  the 
median  jjart  of  the  anterior  arch,  due  probably  to  an  ossification  of  the  anterior  occipito-atlantal 
ligament,  may  articulate  with  the  anterior  surface  of  the  summit  of  the  odontoid  jjrocess  of 
the  axis.  Allen  has  noticed  the  articulation  of  the  superior  border  of  the  posterior  arch  with 
the  posterior  border  of  the  foramen  magnum.  Cases  of  jjartial  or  complete  fusion  of  the  atlas 
with  the  occipital  bone  are  not  uncommon  (see  p.  113). 

Second  Cervical  Vertebra,  Axis,  or  Epistropheus. — This  is  characterised  by 
the  presence  of  the  tootli-like  odontoid  process  (dens)  whicli  projects  upwards  from 
the  superior  surface  of  the  body.  Slightly  constricted  where  it  joins  the  body,  the 
odontoid  process  tapers  to  a  blunt  point  superiorly,  on  the  sides  of  which  there  are 
surfaces  for  the  attachment  of  the  odontoid  or  check  ligaments.  When  the  atlas 
and  axis  are  articulated  together  this  process  hes  behind  the  anterior  arcli  of  the 
atlas,  and  displays  on  its  anterior  surface  an  oval  or  circular  facet  which  articu- 
lates with  that  on  the  posterior  surface  of  the  anterior  arch  of  the  atlas.     On  the 


Odoutoid  process     Groove  for  transverse  ligament 

Superior  articular 
surface 


Odontoid  process 


Articular 

surface  for 

anterior  arch 

of  atlas 


Foramen  ten 

vertebi al 

arteiy 

Infenoi  aitiLuLii 
process 

Spine 

Fig.  61. — Axis  prom  Behind  and  Above. 


Inferior  articular 
jwocess 


bral  artery    Transverse  process 


Pig.  62. — Axis  from  the  Left  Side. 


posterior  aspect  of  the  neck  of  the  odontoid  process  there  is  a  shallow  groove  which 
receives  the  transverse  ligament  which  holds  it  in  position. 

The  anterior  surface  of  the  body  has  a  raised  triangular  surface,  wdiich  ends 
superiorly  in  a  ridge  passing  upwards  to  the  neck  of  the  odontoid  process.  The 
pedicles  are  concealed  above  by  the  superior  articular  processes  ;  interiorly,  they  are 
deeply  grooved.  The  laminae — prismatic  on  section — are  thick  and  strong,  ending 
in  a  stout,  broad,  and  bifid  spinous  process,  the  under  surface  of  which  is  deeply 
grooved,  whilst  its  sides  meet  superiorly  in  a  ridge.  Placed  over  the  pedicles 
and  the  anterior  root  of  the  transverse  processes  are  the  superior  articular  surfaces. 
These  are  more  or  less  circular  in  shape,  slightly  convex  from  before  backwards, 
flat  from  side  to  side,  and  have  a  direction  upwards  and  a  little  outwards.  They 
are  channelled  interiorly  by  the  vertebrarterial  foramina  which  turn  outwards 
beneath  them.  The  grooves  by  which  the  second  cervical  nerves  leave  the  neural 
canal  cross  the  laminte  immediately  behind  the  superior  articular  processes.  The 
inferior  articular  processes  agree  in  form  and  position  with  those  of  the 
remaining  njcmbors  of  the  scries,  and  are  placed  behind  the  inferior  intervertebral 
notches. 

I'he  transverse  process  is  markedly  down-turned,  with  a  single  pointed 
extremity. 

Variations.  In  somi'  iuslanfi-s  t|]c  .suinmit  of  till'  (idoiiluid  jiroccss  iirticulates  with  a-  |ii'(iiiii- 
iiciil  tiiljcrcle  oil  tlic,  aiit(!i'ior  Ijorder  of  the  foramen  magiiuiii  (tljird  o(;r,i])iial  condyle,  see  ]).  J 13;. 
I>(;imi;t  {Trann.  J'ath.  Soc.  JJuhtin,,  vo].  vii.)  records  a  case  in  whi(;li  tlici  odontoid  jjrocess  was 
doul)l<;,  due  to  the  jtersiHteiice  of  the  primitive  condition  in  which  it  is  d(!velo])ed  fi'om  two 
centres.  Occasionally  tJie  odontoid  ])rocess  fails  to  be  united  with  tlie  body  of  \\\v.  axis,  forming 
an  OS  odoritoideiiiii   comparable  to  that  met  witli   in  the  crocodilia  ((iliaconiini,  Komiti,  and 


80  OSTEOLOGY. 

Turner).     The  vertebrarterial  foramen  is  not  infrequently  incomplete,  owing  to  the  imperfect 
ossification  of  the  posterior  root  of  the  transverse  process. 

The  seventh  cervical  vertebra,  or  vertebra  prominens,  receives  the  latter  name 
from  the  outstandiug  nature  of  its  spinous  process,  which  ends  in  a  single  hroad  tubercle. 
This  forms  a  well-marked  surface  projection  at  the  back  of  the  root  of  the  neck. 
The  transverse  processes  are  broad,  being  flattened  from  above  downwards ;  they 
project  considerably  beyond  those  of  the  sixth.  The  maximum  width  between 
their  extremities  agrees  with  that  between  the  transverse  processes  of  the  atlas, 
these  two  constituting  the  widest  members  of  the  cervical  series.  The  verte- 
brarterial foramen  is  small.  Not  infrequently  the  costal  element  is  separate  from 
the  true  transverse  process,  thus  constituting  a  cervical  rib. 

Variations. — The  vertebrarterial  foramen  may  be  absent  on  one  or  other  side. 

Thokacic  Vertebra*;. 

The  thoracic  or  dorsal  vertebrae  (vertebrse  thoracales),  twelve  in  number, 
are  distinguished  by  having  facets  on  the  sides  of  their  bodies  for  the  heads  of  the 
ribs,  and  in  most  instances  also  articular  surfaces  on  their  transverse  processes  for 
the  tubercles  of  the  ribs  (Figs.  57  and  58,  p.  75). 

The  body  is  described  as  characteristically  heart-shaped,  though  in  the  upper 
and  lower  members  of  the  series  it  undergoes  transition  to  the  typical  forms  of  the 
cervical  and  lumbar  vertebrae  respectively.  Its  antero -posterior  and  transverse 
widths  are  nearly  equal ;  the  latter  is  greatest  in  line  with  the  facets  for  the  heads 
of  the  rib.  The  bodies  are  slightly  thicker  behind  than  in  front,  thus  adapting 
themselves  to  the  anterior  concavity  which  the  column  displays  in  this  region. 
The  bodies  of  the  second  to  the  ninth  thoracic  vertebrae  inclusive,  each  possess  four 
costal  demi-facets — a  superior  pair  placed  on  the  upper  margin  of  the  body,  close  to 
the  junction  of  the  pedicle  with  the  centrum,  and  an  inferior  pair  situated  on  the 
lower  edge,  close  to  and  in  front  of  the  inferior  intervertebral  grooves. 

When  contiguous  vertebne  are  articulated,  the  upper  pair  of  demi-facets  of  the  lower 
vertebra  coincide  with  the  lower  demi-facets  of  the  higher  vertebra,  and,  together  with  the 
intervening  intervertebral  disc,  form  an  articular  cup  for  the  reception  of  the  head  of 
a  rib.  Of  these  facets  on  the  body  the  upper  pair  are  the  primary  articular  surfaces 
for  the  head  of  the  rib  ;  the  lower  are  only  acquired  secondarily.  Moreover,  these  facets, 
though  apparently  placed  on  the  body,  are  in  reality  developed  on  the  sides  of  the  pedicles 
behind  the  line  of  union  of  the  pedicles  with  the  centrum  (neuro-central  synchondrosis),  as 
will  be  explained  hereafter. 

The  pedicles  are  short  and  thick,  and  directed  backwards  and  slightly  upwards. 
The  superior  notch  is  faintly  marked  ;  the  inferior  notch  is  deep.  The  laminae  are 
broad,  flat,  and  sloping,  having  sharp  upper  and  lower  margins.  When  the 
vertebrae  are  superposed  the  latter  overlap  the  former  so  as  to  form  an 
imbricated  arrangement.  The  spinal  foramen  is  smaller  than  in  the  cervical  and 
lumbar  regions,  and  nearly  circular  in  shape. 

The  spinous  processes  vary  in  length  and  direction,  being  shorter  and  more 
horizontal  in  the  upper  and  lower  members  of  the  series,  longest  and  most  oblique 
in  direction  towards  the  middle  of  this  part  of  the  column.  Nearly  all  have  a  down- 
ward inclination,  and  are  so  arranged  that  they  overlap  one  another.  Triangular  in 
section  where  they  spring  from  the  neural  arch,  they  become  laterally  compressed 
towards  their  extremities,  which  are  capped  l)y  more  or  less  distinct  tubercles.  The 
transverse  processes  are  directed  backwards  and  outwards,  and  a  little  upwards. 
They  gradually  decrease  in  size  and  length  from  above  downwards.  Each  has  a 
somewhat  expanded  extremity,  the  anterior  surface  of  which,  in  the  case  of  the  upper 
ten  vertebrae,  is  hollowed  out  in  the  form  of  a  circular  facet  for  articulation  with 
the  tubercle  of  the  rib  which  rests  in  the  upper  demi-facet  of  the  vertebra  to  which 
the  transverse  process  belongs.  The  superior  articular  processes  are  vertical  and 
have  their  surfaces  directed  backwards,  slightly  upwards,  and  a  little  outwards; 
the  inferior,  correspondingly  forwards,  downwards,  and  inwards. 

Certain  of  the  thoracic  vertebrae  display  characters  by  which  they  can  readily 


THOKACIC  VEBTEBEiE. 


81 


be  recognised.     These  are  the  first,  tenth,  eleventh,  and  twelfth,  and  sometimes  the 
ninth. 

The  first  thoracic  verte- 
bra resembles  the  seventh 
cervical  in  the  shape  of  its 
body,  and  the  length  and 
direction  of  its  spine.  There 
is  an  entire  facet  on  either 
side  of  the  bodj  for  the  head  • 
of  the  first  rib,  and  one  demi- 
facet  on  each  side  at  the 
lower  border  of  its  body,  to 
complete  the  socket  for  the 
head  of  the  second  rib.  Its 
transverse  processes  are  long, 
and  the  superior  inter- 
vertebral notch  is  better 
marked  than  in  other  mem- 
bers of  the  thoracic  series. 

The  superior  articular  sur- 
faces are  directed  backwards 
and  upwards,  not  outwards 

as  in  the  lower  members  of 

the  series. 

The     ninth      thoracic 

vertebra    occasionally    has 

only  the  upper  pair  of  demi- 

facets  on  its  body ;  at  other 

times  it  conforms  to  the  usual 

type. 

The     tenth      thoracic 

vertebra  may  have  only  one 

complete  costal  facet  on  each 

side  for  the  X.  rib,  though 

sometimes      the      articular 

socket  may  be  completed  by 

the   ninth    dorsal   vertebra. 

The  facet  on  the  transverse 

process    is    generally   small, 

and  sometimes  absent. 

The   eleventh   thoracic 

vertebra    has    a    complete 

circular  facet   on  the  outer 

side    of    each    pedicle     for  pia,  63. 

articulation  with  the  XI.  rib. 

Its    transverse   processes   are  j    inferior   articular   process    with 

short  and  stunted,  and  have        out-turned  facet. 

no  facets  ^'  ^'"s^®  ^^"^^^  ^°^  ^^^^'^  °^  ^^^-  ^^^ 

The    twelfth    thoracic  3 
vertebra  has  a  single  facet 
on  the  pedicle  on  each  side  '*• 
for  the  XII.  rib.     Its  trans-  5 
processes,  which  have 


verse 


First,  Ninth,  Tenth,  Eleventh,  and  Twelfth  Thoracic 
Vertebra  from  the  Left  Side. 

8.  Single  facet  for  head  of  I.  rib. 

9.  Facet  on  transverse  process  for 
tul)erosity  of  I.  rib. 

10.  Facet  on  transverse  process  for 
tuberosity  of  IX.  rib. 

11.  Facet  on  transverse  process  for 
tuberosity  of  X.  rib,  in  tliis 
particular  instance  well 
marked. 

S.  Superior^  Tubercles  rMiiinmillary, 
r      ,   „    ■       L     corre-     J  Accossory. 
'•     f'f™"''   r  spondiM,  \  Tnn.svorso 
10.  Kxtoi-iial  J  l(j  V     ol' luiiib.-ir. 


no  facet  on  transverse  process. 
Single  facet  for  head  of  XI.  rib  ; 

no  facet  on  transverse  process. 
Single  or  demi-facet  for  head  of 

X.  rib. 
Occasional  demi-facet   for  head 

of  X.  rib. 
Demi  -  facet    for    head    of    IX. 


no    facets,    are    broken    up 

into  smaller  tubercles,  called  7.  B^I.'^faoet  for  head  of  11.  vi 
resp(!ctively     the     external, 

8ii])Crior,  and  inferior  tubercles.     These  are  homologous  with  the  transverse  mam- 
niillary  and  accessory  ])r(K;(!Sses  of   tin;    lumbar  verteljnc      Indications  of   these 
])rocess(;s  may  also  bo  met  with  in  the  tenth  and  eleventh  thoracic  vertobrtB.     The 
G 


82 


OSTEOLOaY. 


twelfth  thoracic  vertebra  may  usually  l:)e  distinguished  from  the  eleventh  by  the 
arrangement  of  its  inferior  articular  processes,  which  resemble  those  of  the  lumbar 
series  in  being  out-turned;  but  the  eleventh  occasionally  displays  the  same 
arrangement,  in  which  case  it  is  not  always  easy  to  distinguish  between  them. 


-Barclay  Smith  {Journ.  Anat.  and  Physiul.  Lond.  1902,  p.  372)  records  five  cases 
irior  articular  processes  of  the  twelfth  thoracic  vertebra  displayed  thoracic  and 


Variations, 

in  which  the  superior  articular  processes 
lumbar  ciiaracteri sties  on  the  opposite  sides, 


Inferioi  aiticulai  procpss 

MaminiUary  process 


Lumbar  Vertebra. 

The  lumbar  vertebrae  (vertebrae  lumbales),  five  in  number,  are  the  largest  of 
the  movable  vertebrae.     They  have  no  costal  articular  facets,  nor  are  their  trans- 
verse processes  pierced  by 
®P'"^  a  foramen.     In  this  way 

they  can  be  readily  dis- 
tinguished from  the  mem- 
bers of  the  cervical  and 
thoracic  series. 

The  body  is  kidney- 
shaped  in  outline,  and  of 
large  size.  The  transverse 
diameter  is  usually  about 
a  half  greater  than  the 
antero  ~  posterior  width. 
The  anterior  thickness  is 
slightly  greater  than  the 
posterior,  being  thus 
adapted  to  the  anterior 
convex  curve  of  the 
column  in  this  region. 
The  pedicles,  directed 
horizontally  backwards, 
are  short  and  stout;  the 
superior  notches  are 
shallow,  but  deeper  than 
in  the  thoracic  region;  the 
inferior  grooves  are  deep. 
The  laminse  are  broad  and 
nearly  vertical,  sloping 
but  little.  They  support 
on  their  lower  margins 
the  inferior  articular  pro- 
cesses. The  spinal  foramen 
is  large  and  triangular. 

The  spinous  processes, 
spatula  shaped,  with  a 
thickened  posterior 
margin,  project  backwards 
and  slightly  downwards. 
The  transverse  processes, 
more  slender  than  in  the 
dorsal  region,  pass  hori- 
zontally outwards,  with  a 
slight  backward  inclina- 
tion. Arising  from  the  junction  of  the  pedicles  with  the  laminse. in  the  higher 
members  of  the  series,  they  tend  to  advance  so  as  to  become  fused  with  the  outer 
side  of  the  pedicle  and  back  of  the  body  in  the  two  lower  lumbar  vertebrte.  In 
these  latter  vertebrae  the  superior  intervertebral  grooves  are  carried  obliquely  across 
the  upper  surfaces  of  the  bases  of  the  transverse  processes.     The  transverse  processes 


Body 
Superior  articular  process 


Mamiiulliiy  piocess 


Tians\erse  process 


Fig 


Inferior  articular  process 
64. — Third  Lumbar  Vertebra  from  Above,  and  from  the 
Left  Side. 


THE  FALSE  OR  FIXED  VERTEBRA.  83 

lie  in  line  with  the  external  tubercles  of  the  lower  thoracic  vertebrae,  with  whicli 
they  are  serially  homologous,  and  are  to  be  regarded  as  representing  the  costal 
element.  Placed  on  their  base  posteriorly,  and  just  external  to  and  below  the 
superior  articular  processes,  are  the  small  accessory  tubercles  (processus  accessorii) 
which  are  in  series  with  the  inferior  tubercles  of  the  lower  thoracic  vertebrai.  The 
superior  articular  processes  are  stout,  oval,  curved  plates  of  bone,  fused  in  front  with 
the  pedicles  and  laniinse,  and  having  their  concave  articular  surfaces  vertical  and 
in-turned.  Externally,  and  on  their  posterior  edge,  the  bone  rises  in  the  form  of  an 
elongated  oval  tubercle,  the  mammillary  process  (processus  mammillaris) ;  these  are 
in  correspondence  with  the  superior  tubercles  of  the  lower  thoracic  transverse  pro- 
cesses. 

The  inferior  articular  processes  lie  on  either  side  of  the  root  of  the  spinous 
process,  supported  on  the  inferior  margin  of  the  lamina.  Their  articular  surfaces, 
oval  in  outline,  convex  from  side  to  side,  and  plane  from  above  downwards,  are 
out-turned.  The  inferior  articular  processes  are  much  closer  together  than  the 
superior ;  so  that  when  the  vertebrae  are  articulated  the  superior  articular  processes 
of  the  lower  vertebra  embrace  the  inferior  articular  processes  of  the  higher 
vertebra. 

The  fifth  lumbar  vertebra  is  characterised  by  the  size  of  its  body,  which  is 
the  largest  of  all  the  vertebrse.  Further,  the  under  surface  of  the  body  is  cut 
away  at  the  expense  of  its  posterior  part :  hence  the  thickness  of  the  centrum  in 
front  much  exceeds  that  of  the  vertical  diameter  behind.  The  transverse  process 
is  pyramidal  in  form,  and  stouter  than  those  of  the  other  lumbar  vertebree.  It 
arises  by  a  broad  base  from  the  side  of  the  back  of  the  body,  as  well  as  from  the 
pedicle,  and  is  directed  outwards  and  a  little  backwards  and  upwards.  Its  upper 
surface  is  slightly  grooved  by  the  superior  intervertebral  notch.  A  deep  notch 
separates  it  posteriorly  from  the  superior  articular  processes,  which  are  less 
in-turned  than  in  the  other  members  of  the  series,  their  articular  surfaces  being 
directed  more  backwards  than  inwards,  and  displaying  less  concavity.  The  inferior 
articular  processes  are  further  apart  than  is  the  case  with  the  other  members  of 
the  series,  they  lie  in  line  with  the  superior.  The  spinous  process  is  shorter  and 
narrower  than  the  other  lumbar  spines,  particularly  so  in  the  female. 

Variations,— The  mammillary  and  accessory  processes  are  sometimes  unduly  developed.  The 
neural  arch  of  the  fifth  lumbar  vertebra  is  occasionally  interrupted  on  either  side  by  a  synchon- 
drosis which  runs  between  the  upper  and  lower  articular  processes.  In  macerated  specimens  the 
two  parts  of  the  bone  are  thus  separate  and  independent.  The  anterior  includes  the  centrum,  to- 
gether with  the  pedicles,  transverse  and  superior  articular  processes  ;  the  posterior  comprises  the 
inferior  articular  processes,  the  laminae,  and  the  spine. — (Turner,  Challenger  Reports,  vol.  xvi.) 
Szawlowski  and  Dwight  record  instances  of  the  occurrence  of  a  foramen  in  the  transverse 
jjrocess  of  the  V.  lumbar  vertebra  {Anat.  Anz.  Jena,  vol.  xx.),  and  Ramsay  Smith  describes  a  case  in 
which  the  right  transverse  process  of  the  IV.  lumbar  vertebra  of  an  Australian  sprang  from  the 
side  of  the  body  in  front  of  the  pedicle,  being  unconnected  either  with  the  pedicle  or  articular 
process. 

THE   FALSE   OR   FIXED    VERTEBRA. 

The  Saceum. 

The  sacrum  (os  sacrum),  of  roughly  triangular  shape,  is  formed  by  the  fusion 
normally,  of  five  vertebrse.  The  anterior  surface  of  the  bone  is  slightly  hollow  from 
side  to  side  and  concave  from  above  downwards,  the  curve  being  usually  most 
pronounced  opposite  the  third  sacral  segment.  The  central  part  corresponds  to 
the  bodies  of  the  sacral  vertebrte,  the  lines  of  fusion  of  which  are  indicated  by  a 
series  of  four  parallel  ridges  which  cross  the  central  part  of  the  bone  at  gradually 
diminishing  intervals  from  above  downwards;  externally,  these  ridges  disappear 
on  either  side  on  the  inner  walls  of  the  four  anterior  sacral  foramina  (foramina 
sacralia  anterioi-a).  The  size  of  these  holes  decreases  from  above  downwards.  The 
upper  and  under  border  of  each  foramen  is  formed  by  a  stout  bar  of  bone,  of  which 
there  are  five  on  each  side,  corresponding  in  number  with  the  vertebrie  present. 
These  unite  externally  so  as  to  i'orm  the.  lateral  mass  (])ars  lateralis),  and  tlnis 
enclose  the  foramina  to  the  outer  side,  though  here  the  edge  is  not  abrupt,  but 


84 


OSTEOLOGY. 


sloped  so  as  to  pass  gradually  into  the  canal.  The  large  anterior  divisions  of  the 
sacral  nerves  pass  through  these  foramina  and  occupy  the  shallow  grooves.  The 
bone  is  broadest  across  the  first  sacral  vertebra,  tends  to  narrow  opposite  the 
second,  and  again  usually  increases  in  width  opposite  the  third.  When  this 
condition  is  well  marked,  the  edge  has  a  notched  appearance  (sacral  notch)  which 
assists  in  the  interlocking  of  the  sacro-iliac  joint ;  this  feature  is  common  in  the 
Simiidse  and  some  of  the  lower  races  of  mankind  (Paterson).  The  surface  of  bone 
between  and  external  to  the  first,  second,  third,  and  fourth  foramina  affords 
attachment  to  the  fibres  of  origin  of  the  pyriformis  which  may  in  some  instances 
extend  on  to  the  bodies  of  the  II.  and  III.  segments  (Adolphi),  whilst  on  the  edge 
external  to  and  below  the  fourth  foramen  the  coccygeus  is  inserted. 

The  posterior  surface  is  rough  and  irregular.     Convex  from  above  downwards  it 
displays  mesially  a  crest  (crista  sacralis  media)  whereon  are  seen  four  elongated 


Supei'ior  articular  processes      Transverse  process  of  first  sacral  vertebra 


Anterior  sacial 
foramen 


Inferior  lateral  antjle, 


Groove  for  fifth  sacral  nei\e 


Coccygeal  articular  surface 
Fig.  65. — The  Sacrum  (anterior  view). 

tubercles — the  spines  of  the  upper  four  sacral  vertebrte.  External  to  these  the 
bone  forms  a  groove — the  sacral  groove — the  floor  of  which  is  made  up  of  the  con- 
fluent laminae  of  the  corresponding  vertebrte.  In  line  with  the  intervals  between 
the  spines,  and  wider  apart  above  than  below,  another  series  of  tubercles  is  to  be 
seen.  These  are  due  to  the  fusion  of  the  articular  processes  of  the  sacral  vertebrae, 
and  together  they  form  faint  irregular  ridges  on  the  bone  (cristse  sacrales  articulares). 
Normally,  the  spine  of  the  lowest  sacral  segment  is  absent,  and  the  laminse  do  not 
coalesce  mesially,  thus  leaving  a  gap  in  which  the  spinal  canal  is  exposed  (hiatus 
sacralis) ;  whilst  inferiorly  the  tubercles  corresponding  to  the  inferior  articular 
processes  of  the  last  sacral  vertebra  form  little  down-projecting  processes — the 
sacral  cornua  (cornua  sacralia) — by  means  of  which  the  sacrum  is  in  part  united  to 
the  coccyx.  Just  wide  of  the  articular  tubercles  are  the  posterior  sacral  foramina 
(foramina  sacralia  posteriora),  for  the  transmission  of  the  posterior  divisions  of  the 
sacral  nerves.     These  are  in  correspondence  with  the  anterior  foramina,  so  that  a 


THE  SACRUM. 


85 


probe  can  be  passed  directly  tlirough  both  openings ;  but  it  is  to  he  noted  that  the 
posterior  are  much  smaller,  and  their  margins  much  sharper,  than  is  the  case  with 
the  anterior.  The  surface  of  the  lateral  mass  external  to  the  posterior  sacral 
foramina  is  rough  and  irregular,  owing  to  the  presence  of  four  more  or  less  elevated 
tubercles,  which  constitute  the  lateral  ridges  on  either  side  of  the  bone  (cristse 
sacrales  laterales),  and  which  are  serially  homologous  with  the  true  transverse 
processes  of  the  lumbar  vertebra. 

The  posterior  surface  of  the  bone  furnishes  an  extensive  surface  for  the  origin 
of  the  erector  spinse  muscles,  whilst  the  edge  of  the  bone  external  to  the  third  and 
fourth  foramen  gives  attachment  to  the  gluteus  maximus. 

The  base  of  the  bone  displays  features  more  in  accordance  with  a  tyi:)ical 


Superior  aperture  of 
sacral  canal 


Superior  articular  process 


Posterior  sacral  foramen 


Infpiior  lateial  angle 


Inferior  a^ierture  of  sacial  canal 
Groove  for  fifth  sacral  ner\  e 


Coceygeul  articular  surface 
Fig.  66. — The  Sacrum  (posterior  view). 

verteVjra.  Centrally,  and  in  front,  is  placed  the  body,  the  upper  surface  of  which 
articulates  with  the  last  lumbar  vertebra  through  the  medium  of  an  intervertebral 
disc.  The  anterior  margin  is  thin  and  projecting,  overhanging  the  general  con- 
cavity of  the  front  of  the  bone,  and  forming  what  is  called  the  promontory  (promon- 
torium).  Behind  the  Ijody,  the  spinal  canal,  of  triangular  form  with  slightly 
appressed  sides,  is  seen,  whilst  posteriorly  is  the  short  spinous  process  forming  the 
highest  tubercle  of  the  median  crest.  Spreading  out  from  the  sides,  and  partly  from 
the  back  of  the  body  on  either  side,  is  a  fan -shaped  mass  of  bone,  the  upper  surface 
of  which  is  sliglitly  concave  from  side  to  side,  and  convex  from  above  and  behind 
downwards  and  forwards.  I'his,  th(3  ala  (ala  sacralis),  corresponds  to  the  thick  upper 
border  of  the  lateral  mass,  and  is  forined,  as  will  be  explained  hereafter,  by  elements 
wliich  correspond  to  the  pedicles  and  transverse  processes  of  the  sacral  vertebne, 
tf>g(;ther  with  superadded  structures — the  sacral  ribs.  The  external  margin  of  the 
lateral  mass,  as  seen  from  above,  is  sharp  and  outwardly  convex,  terminating  behind 
in  a  prominent  tubercle — the  highest  of  the  series  of  elevations  seen  on  the  posterior 
surface  of  the  bone,  wliich  have  been  already  described  as  serially  homologous  with 


8Q 


OSTEOLOGY. 


the  true  transverse  processes  of  the  kimbar  vertebrse.  Fused  with  the  back  of  each 
lateral  mass,  and  separated  from  it  externally  hj  a  narrow  but  deep  notch,  is  the 
superior  articular  process.  This  supports  a  vertical  articular  surface,  which  is  of 
circular  or  oval  form,  and  concave  from  side  to  side,  having  a  general  direction 
backwards  and  a  little  inwards. 

The  borders  of  the  l^one  are  thick  above,  where  they  articulate  with  the  ilia, 
thin  and  tapering  below,  where  they  furnish  attachments  for  the  powerful  sacro- 
sciatic  ligaments.  The  iliac  articular  surfaces  are  described  as  auricular  in  shape 
(facies  auriculares),  and  overlie  the  lateral  masses  formed  by  the  first  three  sacral 
vertebrse,  though  this  arrangement  is  liable  to  considerable  variation.  Behind  the 
auricular  surface  the  bone  is  rough  and  pitted  by  three  distinct  depressions  for  the 
attachment  of  the  strong  sacro- iliac  ligaments.  Inferiorly,  the  edge  formed  by 
the  lateral  masses  of  the  fourth  and  fifth  sacral  vertebrai  becomes  gradually 
thinner,  and  at  the  inferior  lateral  angle  changes  its  direction  and  sweeps  inwards 
towards  the  body  of  the  fifth  sacral  segment. 

The  apex,  or  lower  end  of  the  sacrum,  is  formed  by  the  small  oval  body  of  the 
fifth  sacral  vertebra,  which  articulates  with  the  coccyx. 

The  sacral  canal  follows  the  curve  of  the  bone ;  more  or  less  triangular  in 
shape  above,  it  becomes  appressed  and  flattened  below.  Inferiorly,  its  posterior 
wall  is  deficient  owing  to  the  imperfect  ossification  of  the  laminee  of  the  fifth,  and, 
it  may  be,  of  the  fourth  sacral  segments.  Passing  obliquely  outwards  and  down- 
wards from  this  canal  into  the  lateral  masses  on  either  side  are  the  four  pairs  of 
intervertebral  foramina,  each  of  which  is  connected  externally  with  a  V-shaped 
canal  which  terminates  in  front  and  behind  in  the  anterior  and  posterior  sacral 
foramina.     The  hinder  limb  of  the  V  is  shorter  and  narrower  than  the  anterior. 

The  female  sacrum  is  proportionately  broader  than  the  male.  Its  curves  are 
liable  to  great  individual  variation,  though  the  absolute  depth  of  the  curve  is  less 
than  in  the  male. 

Variations. — Tlie  number  of  sacral  segments  may  be  increased  to  six  or  rediiced  to  four  (see 
p.  90).  Transition  forms  are  occasionally  met  with,  in  wbich.  the  first  sacral  segment  displays 
on  one  side  purely  sacral  characters,  i.e.  it  articulates  witli  the  innominate  bone,  whilst  on  the 
opposite  side  it  may  present  all  the  features  of  a  lumbar  vertebra.  Through  deficiency  in  the 
develojjment  of  the  laminae,  the  neural  canal  may  be  exposed  throughout  its  entire  length,  or 
to  a  greater  extent  than  is  normally  the  case.  (Paterson,  Roy.  Dublin ^Soc.  Scientific  Trans. 
vol.  v.  Series  II.)  Szawlowski  and  Barclay  Smith  record  the  occurrence  of  a  foramen  in  the 
lateral  mass  of  the  I.  sacral  vertebra  {Journ.  of  Anat.  and  Physiol.  Lond.  voL  xxxvi.  p.  372). 


Coccyx. 

The  coccyx  consists  of  four — sometimes  five,  less  frequently  three — rudimentary 

vertebrse,  which  tend  to 
become  fused.  The  first 
piece  is  larger  than  the 
others ;  it  has  an  oval 
7  hollow  facet  on  its  upper 
surface,  which  articulates 
with  the  body  of  the  last 
sacral  segment.  Pos- 
teriorly, two  processes, 
cornua  coccygea,  which 
He  in  series  with  the 
articular  processes  of 
the  sacrum,  extend  up- 
wards and  unite  with 
the  sacral  cornua,  thus 
bridging  over  the  notch 

7.  Transverse  process,  f^^,  ^|^g  ^^^^  ^f  ^j^g    gf^j^ 

8.  Transverse  process.  ,  _ 

sacral  nerve,  and  con- 
verting it  into  a  foramen,  the  last  of  the  intervertebral  series.  From  the 
outer  sides  of   the    body   project    rudimentary   transverse    processes   which  may, 


Fig.  67.- 
A.   Posterior  Surface. 

1.  Transverse  process.       3.  Sacrum. 

2.  Transverse  process.       4.  Cornu. 


The  Coccyx. 
B.  Anterior  Surface, 

5.  Sacrum. 

6.  C'ornu. 


VERTEBEAL  COLUMN  AS  A  WHOLE.  87 

or  may  not,  unite  with  the  sacrum  close  to  the  lower  lateral  angles ;  in  the 
latter  case  the  fifth  anterior  sacral  foramina  are  enclosed.  Inferiorly,  the  body  of 
the  bone  articulates  with  the  succeeding  vertebra.  The  second  coccygeal  vertebra 
displays  slight  traces  of  a  transverse  process  and  the  rudiments  of  pedicles.  The 
following  segments  are  mere  rounded  or  oval-shaped  nodules  of  bone. 

Fusion  between  the  lower  elements  occurs  normally  in  middle  life,  whilst  union  between 
the  first  and  second  segments  occurs  somewhat  later.  It  is  not  unusual,  however,  to  find 
that  the  first  coccygeal  vertebra  remains  separate  from  the  others.  Though  very  variable, 
as  a  rule,  fusion  occurs  more  commonly  in  the  male,  and  at  an  earlier  age,  than  in  the 
female.  Szawlowski  has  recorded  a  case  in  which  a  curved  process  arose  from  the  ventral 
surface  of  the  first  coccygeal  segment.  He  regards  this  as  possibly  the  homologue  of  a 
ventral  arch  (Anat.  Am.  Jena,  vol.  xx.  p.  320). 

From  the  posterior  surface  of  the  coccyx  the  gluteus  maximus  arises.  To  its 
external  borders  are  attached  the  coccygei  and  levatores  ani  muscles,  and  from  its 
tip  spring  the  fibres  of  the  sphincter  ani. 

VERTEBRAL  COLUMN  AS  A  WHOLE. 

When  all  the  vertebrae  are  articulated  together,  the  resulting  column  displays 
certain  characteristic  features.  The  division  of  the  column  into  a  true  or  movable 
part,  comprising  the  members  of  the  cervical,  thoracic,  and  lumbar  series,  and  a 
false  or  fixed  portion,  including  the  sacrum  and  coccyx,  can  now  be  readily 
recognised.  The  vertebrse  are  so  disposed  that  the  centra  or  bodies  form  an 
interrupted  column  of  solid  parts  in  front,  which  constitutes  the  axis  of  support 
for  the  head  and  trunk ;  whilst  the  neural  arches  behind  constitute  a  canal  for  the 
lodgment  and  protection  of  the  spinal  cord  and  its  membranes.  In  the  movable 
part  of  the  column  both  the  anterior  supporting  axis  and  the  neural  canal  are 
liable  to  changes  in  their  disposition  owing  to  the  movements  of  the  head  and 
trunk.  Like  the  bodies  and  neural  arches,  the  spinous  and  transverse  processes 
are  also  superposed,  and  fall  in  line,  forming  three  series  of  interrupted  ridges — 
one  (the  spinous)  placed  centrally  and  behind,  the  others  (the  transverse)  placed 
laterally.  In  this  way  two  vertebral  grooves  are  formed  which  lie  between  the 
central  and  lateral  ridges.  The  floor  of  each  groove  is  formed  by  the  laminse  and 
articular  processes,  and  in  these  grooves  are  lodged  the  muscles  which  serve  to 
support  and  control  the  movements  of  the  column. 

Further,  the  column  so  constituted  is  seen  to  display  certain  curves  in  an 
antero- posterior  direction.  These  curves  are,  of  course,  subject  to  very  great 
variation  according  to  the  position  of  the  trunk  and  head,  and  can  only  be  satis- 
factorily studied  in  a  fresh  specimen ;  but  if  care  be  exercised  in  the  articulation 
of  the  vertebrae,  the  following  characteristic  features  may  be  observed,  assuming,  of 
course,  that  the  column  is  erect  and  the  head  so  placed  that  the  axis  of  vision  is 
directed  towards  the  horizon.  There  is  a  forward  curve  in  the  cervical  region, 
which  gradually  merges  with  the  backward  thoracic  curve ;  this  becomes  con- 
tinuous below  with  an  anterior  convexity  in  the  lumbar  region,  which  ends  more 
or  less  abruptly  at  the  union  of  the  fifth  lumbar  with  the  first  sacral  vertebra, 
where  the  sacrum  slopes  suddenly  backwards,  causing  the  column  to  form  a 
marked  projection — the  sacro-vertebral  angle.  Below  this,  the  anterior  concavity  of 
the  front  of  the  sacrum  is  directed  downwards  as  well  as  forwards.  Of  these  four 
curves,  two — tlie  tlioracic  and  sacral — are  primary,  they  alone  exist  during  fcetal 
life ;  whilst  the  cervical  and  lumbar  forward  curves  only  make  their  appearance 
after  birth — the  former  being  associated  with  the  extension  and  elevation  of  the 
head,  whilst  the  latter  is  developed  in  connexion  with  the  use  of  the  hind  limb  in 
tbe  hyper-extended  position,  which  in  man  is  correlated  with  tbe  assumption  of 
tlie  erect  yjosture ;  tliis  curve,  therefore,  only  appears  after  the  child  has  begun  to 
walk.  For  tbese  reasons  the  cervical  and  lumbar  curves  are  described  as  secondary 
and  comp(!nsatory. 

Not  infrequently  there  is  a  slight  lateral  curvature  in  the  thoracic  region,  the 
f'onvexity  of  the  curve  being  usually  directed  towards  the  right  side.     This  may 


OSTEOLOGY. 


be  associated  with  a  greater  use  of  the  muscles  of  tlie  right  upper  limb,  or  may 
depend  on  the  pressure  exercised  by  the  upper  part  of  the  thoracic  aorta  on  the 

vertebrae  of  the  thoracic  region,  thus  causing  a  slight 
lateral  displacement,  together  with  a  flattening  of  the 
side  of  the  five  thoracic  vertebrse  (impressio  aortica)  as 
was  first  pointed  out  by  Wood  (Journ.  Anat.  and  Phy- 
siol, vol.  iii.)  Above  and  below  this  curve  there  are 
slight  compensatory  curves  in  the  opposite  direction. 
The  line  which  unites  the  tips  of  the  spines  is 
not  a  repetition  of  the  curves  formed  by  the  bodies. 
This  is  due  to  the  fact  that  the  length  and  direction 
of  the  spines  vary  much  in  different  regions ;  thus  in 
the  neck,  with  the  exception  of  the  second,  sixth,  and 
seventh,  the  spines  are  all  short  (absent  in  the  case 
of  the  atlas).  In  the  thoracic  region  the  spines, 
though  long,  are  obliquely  placed — a  circumstance 
which  much  reduces  their  prominence ;  that  of  the 
seventh  thoracic  vertebra  is  usually  the  longest  and 
most  slanting.  Below  this  point  the  length  of  the 
spines  gradually  decreases,  and  their  position  more 
nearly  approaches  the  horizontal.  In  the  loins  the 
spines  have  all  a  slight  downward  direction. 

Taken  as  a  wliole,  the  sjiines  of  tlie  movable  vertebras  in 
man  have  a  downward  inclination — a  character  which  he  shares 
with  the  anthropoid  apes  and  a  few  other  animals.  This 
character  serves  to  distinguish  his  column  from  those  of  lower 
mammals  in  which  the  sjjines  of  the  lumbar  vertebrjB  are 
directed  headwards  towards  the  "  centre  of  motion,"  which 
is  usually  situated  near  the  hinder  extremity  of  the  thorax, 
where  a  vertebra  is  placed  the  direction  of  whose  sj^ine  is 
vertical  to  the  horizontally  disjDosed  column ;  this  vertebra 
is  often  referred  to  as  the  anticlinal  vertebra. 

The  spines  of  the  upper  three  or  four  sacral  verte- 
brfe  form  an  osseous  ridge  with  interrupted  tubercles. 
The  ridge  formed  by  the  vertel^ral  spines  is  an 
important  determinant  of  the  surface  form,  as  it  cor- 
responds to  the  median  furrow  of  the  back,  and  here 
the  individual  spines  may  be  felt  and  counted  from 
the  seventh  cervical  down  to  the  sacral  region.  This 
is  best  done  when  the  back  is  well  bent  forwards. 

As  viewed  from  the  front,  the  vertebral  bodies 
increase  in  width  from  the  second  cervical  to  the 
first  thoracic ;  thence  a  reduction  in  breadth  takes 
place  to  the  level  of  the  fourth  thoracic,  below  which 
there  is  a  gradual  increase  in  their  transverse  diameters 
until  the  sacrum  is  reached.  Here  a  rapid  reduction 
in  width  takes  place,  terminating  inferiorly  in  the 
nodules  of  the  coccyx. 

The  transverse  processes  of  the  atlas  are  wide 
and  outstanding.  The  succeeding  four  cervical  verte- 
brae have  transverse  processes  of  nearly  equal  width  ; 
the  seventh,  however,  displays  a  marked  increase  in 
its  transverse  diameter,  and  is  about  equal  in  width 
to  the  first  thoracic  vertebra.  Below  this  a  gradual 
and  regular  diminution  in  width  characterises  the 
transverse  processes  of  the  thoracic  vertebrae,  until 
in  the  case  of  the  eleventh  and  twelfth  they  are  merely  represented  by  the  small 
external  tubercles.  In  the  lumbar  region  the  transverse  processes  again  appear 
outstanding,  and  of  nearly  equal  length. 

The  transverse  diameter  of  the  lateral  mass  of  the  first  sacral  vertebra  forms 


Fig.  68. — Vertebral  Column 
FROM  THE  Left  Side. 


VEETEBRAL  COLUMN  AS  A  WHOLE. 


89 


until  the 
diameter 


~.^M^^ 


n 


(u* 


the  widest  part  of  the  column.     Below  this  a  decrease  in  width  occurs 
level  of  the  third  sacral  segment  is  reached,  at  which  point  the  transverse 
is  somewhat  abruptly  diminished,    a   reduction    in    width 
which   is  further  suddenly  accentuated  opposite  the  fifth 
sacral  segment. 

As  viewed  from  the  side,  the  bodies  display  a  gradual 
increase  in  their  antero-posterior  width  until  the  second 
lumbar  vertebra  is  reached,  below  which  this  diameter  is 
slightly  reduced.  In  the  sacral  region  the  reduction  in 
this  diameter  is  great  in  the  first  and  second  sacral 
segments,  more  gradual  and  less  marked  in  the  last  three 
segments. 

The  facets  for  the  heads  of  the  ribs  in  the  upper  thoracic 
region  lie  on  the  sides  of  the  bodies ;  those  for  the  tenth, 
eleventh,  and  twelfth  are  placed  farther  back  on  the 
pedicles. 

The  intervertebral  foramina  increase  in  size  from  above 
downwards  in  the  movable  part  of  the  column,  being  largest 
in  the  lumbar  region.  In  the  sacral  region  they  decrease 
in  size  from  above  downwards.  In  the  cervical  region  the 
two  highest  cervical  nerves  pass  out  behind  the  articular 
processes  of  the  atlas  and  axis,  and  lie,  therefore,  behind 
the  corresponding  transverse  processes  of  these  vertebrae. 
The  succeeding  cervical  nerves  pass  out  through  the  inter- 
vertebral foramina  which  are  placed  between  the  transverse 
processes  and  in  front  of  the  articular  processes.  In  the 
thoracic  and  lumbar  vertebrae  the  intervertebral  foramina 
lie  in  front  of  both  the  articular  and  transverse  processes. 
The  arrangement  of  these  foramina  in  the  sacrum  has  been 
already  sufficiently  explained. 

The  neural  canal  for  the  lodgment  of  the  spinal  cord  and 
its  meninges  is  largest  in  the  cervical  and  lumbar  regions, 
in  both  of  which  it  assumes  a  triangular  form ;  whilst  it  is 
narrow  and  circular  in  the  thoracic  region.  These  facts  are 
correlated  with  the  movements  of  the  column  which  are 
most  free  in  those  regions  where  the  canal  is  largest,  i.e.  the 
neck  and  loins. 

The  average  length  of  the  vertebral  column  IkS  from  70  to 
73  centimeti'es,  or  from  '11\  to  28f  inches.  Of  this  the  cervical 
part  measures  from  13  to  14  cm.  ;  the  thoracic,  27  to  29  cm. ; 
lumbar,  17  to  18  cm. ;  and  the  sacro-coccygeal,  12  to  15  cm. 
The  individual  differences  in  the  length  of  the  column  are  less 
than  one  might  expect,  the  variation  in  height  of  different 
individuals  being  often  largely  dependent  on  the  length  of  the 
lower  limbs.  In  the  female  the  average  length  of  the  column 
is  about  60  centimetres,  or  23|  inches,  and  the  curve  in  the 
lumbar  region  is  iisually  more  pronounced. 

Architecture.— The  vertebrae  are  formed  of  sjjongy  bone  confined       ^  ijO  ll^ 
within  a  tliin  and  dense  envelope.     In  the  bodies  the  arrangement  of         ^  \ 
the  cuncellou.s  tissue,  which  is  traversed  by  venous  channels,  is  such  V  -Q 

as  to  display  a  vertical  striation  with  lamellag  arranged  horizontally. 
The  external,  superior,  and  inferior  walls  arc.  very  thin — that  directed 
to  the  neural  canal  being  usually  thicker  and  denser  than  the  others. 
In  the  pedicles  and  roots  of  the  transverse  processes  tlie  cancellous 
tissue  is  much  more  open.  The  outer  envelope  is  much  thicker  where  1''^"-  ^^- — Vkrtebral  Column 
it  hounds  the  neurab  ring,  and  Avhei'e  it  forms  the  bottom  of  the  '^^  ^^'^'^  '^^^^^  Behind. 
superior  and   inferior   interverteljral    notches.      In  the   laminaj    the 

snongy  tissue  is  confined  ]>etween  two  compact  layers,  of  which  that  directed  to  the  spinal  canal  is 
the  thicker,     hi  the  spiiujus  ))rocesses  the  upjier  edge  is  always  the  more  compact 

Variations.     Numerical  Variations  of  the  Column  as  a  Whole. —increase  in  the  number  of 
vertehrai  segnicnts  is  usually  du<;  to  diirriitnccs  in  the  nunihei' of  the  coccygeal  vertebrae ;  these 


Ol 


\ 


90  OSTEOLOGY. 

may  vary  from  four — wliicli  may  be  regarded  as  the  normal  number — t(j  six.  Tlie  number  of 
presacral  or  movable  vertebras  is  normally  24  (7  C,  12  D,  and  5  L).  In  which  case  the  25th 
vertebra  forms  the  first  sacral  segment  (vertebra  fulcralis  of  Welcker).  Tlie  number  of  presacral 
vertebr;e  may  be  increased  by  the  intercalation  of  a  segment  either  in  the  thoracic  or  luml)ar  region 
without  any  alteration  in  the  number  of  the  sacral  or  coccygeal  elements  :  thus  we  may  have  7  C, 
13  D,  and  5  L,  or  7  C,  12  D,  and  6  L,  or  may  be  reduced  by  the  disajipearance  of  a  A-ertebral  seg- 
ment— thus,  7  C,  12  D,  and  4  L.  Such  an  arrangement  presupposes  developmental  errors  either 
of  excess  or  default  in  the  segmentation  of  the  column.  On  the  other  liand,  the  total  number  of 
vertebral  segments  remaining  tlie  same  (24  or  25),  we  may  have  variations  in  the  uumbei'  of  those 
assigned  to  different  regions  due  to  the  addition  of  a  vertebral  segment  to  one,  and  its  conseq^uent 
subtraction  from  another  region.  Thus,  in  the  24  presacral  vertel)r8e,  in  cases  of  the  occurrence  of 
cervical  ribs  the  formula  is  reari'anged  thus — 6  C,  13  D,  and  5  L,  or,  in  the  case  of  a  thirteenth 
rib  being  present,  the  formula  would  be  7  C,  13  D,  4  L,  as  happens  normally  in  the  gorilla  and 
chimpanzee.  Similarly,  the  number  of  the  presacral  vertebr;e  (24)  may  be  increased  by  the 
withdrawal  of  a  segment  from  the  sacral  region — 7  C,  12  D,  6  L,  and  4  S — or  diminished  by  an 
increase  in  the  number  of  the  sacral  vertebrae,  as  in  the  formula  7  C,  12  D,  4  L,  and  6  S.  In- 
crease in  the  numljer  of  sacral  segments  may  be  due  to  fusion  with  a  lumlmr  vertebrae,  or  by  the 
addition  of  a  coccygeal  element :  the  latter  is  more  frequently  tlie  case.  This  varialjility  in  the 
constitution  of  the  sacrum  is  necessarily  correlated  with  a  shifting  liackAvards  and  forwards  of 
the  pelvic  girdle  along  the  vertebral  column.  Rosenburg  considers  that  the  26th,  27th,  and  28th 
vertebrae  are  the  primitive  sacral  segments,  and  that  the  sacral  characters  of  the  25th  vertebrte 
(the  first  sacral  segment  in  the  normal  adult  column)  are  only  secondarily  acquired.  He  thus 
sujjposes  that  during  development  there  is  a  forward  shifting  of  the  sacrum  and  pelvic  girdle, 
with  a  consequent  reduction  in  the  length  of  the  jsresacral  portion  of  the  column.  This  view  is 
ojjposed  by  Paterson  {Roy.  Dublin  Soe.  Scientific  Trans,  vol.  v.  Ser.  II.),  who  found  that  ossification 
took  place  in  the  ahe  of  the  25tli  vertebra  (first  adult  sacral  segment)  before  it  made  its  ap^Jear- 
ance  in  the  alse  of  the  26tli  vertebra.  He  thus  assumes  that  the  ahe  of  the  25th  vertebra  may 
be  regarded  as  the  main  and  primary  attachment  with  the  ilium.  His  conclusions,  based  on  a 
large  number  of  oljservations,  are  at  variance  with  Rosenburg's  views,  for,  according  to  his  opinion, 
liberation  of  the  first  sacral  segment  is  more  common  than  assimilation  with  the  fifth  lumbar 
vertebra,  and  assimilation  of  the  first  coccygeal  vertebra  with  the  sacrum  is  more  common  than 
liberation  of  the  fifth  sacral,  thus  leading  to  the  inference  that  the  sacrum  tends  to  shift  back- 
wards more  often  than  forwards.     (See  also  T.  D wight,  Anat.  Anz.  Jena,  vol.  xix.  j)p.  321,  337.) 

THE   CAKTILAGINOUS   VEETEBKAL   COLUMN. 

As  has  been  already  stated  (p.  30),  the  neural  tube  and  the  notochord  are 
enveloped  by  a  continuous  sheath  of  mesodermal  tissue  which  forms  the  membranous 
vertebral  column.  It  is  by  the  chondrification  of  this  that  the  cartilaginous  column 
is  developed.  This  process  commences  about  the  end  of  the  first  or  the  beginning 
of  the  second  month  of  foetal  life.  In  correspondence  with  each  vertebral  segment, 
two  symmetrical  nodules  of  cartilage  appear  on  either  side  of  the  notochord ;  these 
rapidly  surround  and  constrict  it.  By  their  fusion  they  constitute  the  body  of  a 
cartilaginous  vertebra,  and  are  so  disposed  that  they  alternate  in  position  with  the 
muscle  plates  which  are  lying  on  either  side.  In  this  way  a  vertebral  body  corre- 
sponds in  position  to  the  posterior  half  of  the  anterior  myotome,  and  the  anterior 
half  of  the  posterior  myotome,  the  intermyotomic  intervals,  which  contain  the 
connective  tissue  plates  separating  the  muscle  segments,  lie  in  line  laterally 
with  the  mid -points  of  the  sides  of  the  cartilaginous  vertebrae.  It  is  by  chondri- 
fication of  these  intersegmental  layers  that  in  certain  regions  the  ribs  are 
ultimately  developed.  Meanwhile,  the.  scleratogenous  tissue  between  the  chondri- 
fying  vertebral  bodies  undergoes  little  change  and  persists  as  the  intervertebral 
disc.  Here  the  embedded  chorda  undergoes  but  slight  compression  and  enlarges, 
so  that  if  a  length  of  the  column  be  examined  in  longitudinal  section  the  noto- 
chord displays  a  moniliform  appearance,  the  constricted  parts  of  the  chorda 
corresponding  to  the  bodies,  the  enlarged  portions  to  the  discs.  The  former 
disappear  at  a  later  stage  when  ossification  begins,  but  the  latter  persist  in  the 
adult  as  the  pulpy  core  in  the  centre  of  the  intervertebral  disc. 

The  portions  of  the  scleratogenous  tissue  which  lie  lateral  to  the  chorda 
have  next  to  be  considered ;  these  extend  dorsalwards  around  the  neural  canal, 
and  ventralwards  beneath  the  chorda.  The  former  is  sometimes  called  the 
vertebral  bow,  the  latter  the  hypochordal  bow.  The  vertebral  ■  bow  begins  to 
chondrify  on  either  side,  and  forms  the  lateral  portions  of  the  cartilaginous  neural 
arch,  the  extremities  of  which  usually  unite  dorsally  about  the  fourth  month  of 
fcetal  life ;  if  from  defective  development  this  union  should  fail  to  occur,  a 
deformity  known  as  spina  bifida  is  the  result. 


OSSIFICATION  OF  THE  VERTEBE^.  91 

From  the  cartilaginous  neural  arch  so  formed  arise  the  chondrified  rudiments 
of  the  spinous,  transverse,  and  articular  processes. 

The  chondrification  of  the  neural  arch  is  variously  described  as  being  in- 
dependent of  the  body  or  an  extension  from  it ;  in  any  case,  union  between  it  and 
the  body  is  rapidly  effected. 

The  scleratogenous  tissue  between  the  cartilaginous  neural  arches  which  does 
not  undergo  chondrification  persists  as  the  ligaments  uniting  the  neural  laminai. 

As  regards  the  so-called  hypochordal  bow,  for  the  most  part  it  disappears. 
By  some  it  is  regarded  as  being  represented  by  a  fibrous  strand  in  the  inter- 
vertebral disc  in  front  of  the  vertebra  to  which  it  belongs.  It  is,  however, 
noteworthy  that  in  the  case  of  the  atlas  vertebra  there  is  an  exception  to  this 
arrangement ;  for  here  the  hypochordal  bow  chrondrifies  and  subsequently  by 
ossification  forms  the  anterior  arch  of  that  bone — an  arch  which  lies  ventral  to, 
and  embraces  the  odontoid  process  of  the  axis  {q.v.  p.  92). 

It  is  only  in  the  thoracic  region  that  the  ribs,  developed  as  stated  above  by  the 
chondrification  of  the  intersegmental  septa,  attain  their  full  dimensions.  In  the 
cervical,  lumbar,  and  sacral  regions  they  exist  only  in  a  rudimentary  or  modified 
form,  as  has  been  described  elsewhere.  In  the  construction  of  the  chest  wall 
the  ribs  are  supported  ventrally  by  the  sternum,  as  to  the  development  of  which 
there  is  some  difference  of  opinion.  Enge  has  described  this  bone  as  formed  by 
the  fusion  of  two  cartilaginous  bands  produced  by  the  coalescence  of  the  expanded 
ends  of  the  first  five  or  seven  cartilaginous  ribs.  Paterson,  on  the  other  hand, 
regards  the  sternum  as  arising  independently  of  the  ribs  by  the  union  of  a  right 
and  left  sternal  bar  in  the  median  ventral  line.  There  are  also  reasons  for 
supposing  that  the  presternum  is  intimately  associated  with  the  development  of 
the  ventral  part  of  the  shoulder  girdle. 

Ossification   of  the  Vertebrae. — The  vertebrae   are   developed  by  ossification   of 
the  cartilage  which  surrounds  the  notochord  and  which  passes  backwards  over  the  sides  of 
the    neural    canal.      The  centres  for  the  bodies  first  appear  in  the 
lower  thoracic  vertebrae   about  the  tenth  week.      An  oval  nucleus         /^fc\ 
develops  in  each  body.      At  first  it  is  placed  dorsal    to    the   noto-  f-^llf^^^V^is^^^'^.''^^'^ 
chord,   but  subsequently  surrounds   and    causes    the   disappearance  \m  |i^"*^"'^^i 

of   that    structure.       Occasionally,    however,    the    primitive    centre     |m^         yjr    ^^'^^^ 
appears   to  be  formed  by  the  coalescence    of   two  primary  nuclei.     ^^M^^^m 
Support    is    given    to    this    view    by    the    occasional    occurrence    of     ^kg^^^mCmti-e  for 
vertebrae  in  which  the  body  is  developed  in  two  lateral  halves,  or     ^^^^^^^'^'^^ 
in  cases  where  only  one-half   of    the    body  persists  (Turner) ;   nor- 
mally,   however,    it   is  impossible  to  make  out  this  division.      From    ^^^  /O. —Ossification 
these  single  nuclei  the  bodies  are  developed,  the  process  extending 

up  and  down  the  column  until,  by  the  fifth  month,  all  the  centra  possess  ossific  deposits, 
except  the  coccygeal  segments.  About  the  seventh  week  a  single  centre  appears  in  the 
neural  arch  on  either  side.  These  commence  first  to  ossify  in  the  upper  cervical  region 
and  extend  rapidly  downwai'ds  throughout  the  column.  They  first  appear  near  the  bases 
of  the  superior  articular  processes,  and  extend  backwards  into  the  laminae,  outwards  into 
the  transverse  processes,  and  forwards  into  the  pedicles.  These  latter  project  anteriorly, 
and  form  a  considerable  portion  of  the  postero-lateral  aspects  of  the  body,  from  which, 
however,  they  ai'e  separated  by  a  cartilaginous  strip — the  neuro-central  synchondrosis — 
which  does  not  entirely  disappear  until  about  the  fifth  or  sixth  year.  It  is  important  to 
note  that  in  the  thoracic  region  the  costal  facets  lie  behind  the  neuro-central  synchondrosis, 
and  are  therefore  borne  on  the  lateral  aspects  of  the  pedicles.  Fusion  of  the  laminae  in  the 
mesial  plane  beliind  begins,  after  birth,  in  the  lumbar  region  and  extends  upwards,  so 
that  Vjy  the  fifteenth  month  or  thereabouts  the  arches  in  the  cervical  region  are  com- 
pleted behind.  fn  the  sacral  region  ossification  is  slower,  the  spinal  canal  not  being 
enclosed  till  the  seventh  to  the  tenth  year.  The  spinous  processes  are  cartilaginous  at 
birth,  but  these  y>ecome  ossified  ])y  tlie  extension  iiito  them  of  the  bony  luminfc. 

At  puljcrty  certain  secondary  centres  or  epiphyses  make  their  appearance ;  these  are 
five  in  number.  One  caps  the  summit  of  the  spinous  process,  except  in  the  cervical 
region.  A  single  epiphysis  on  either  side  apjjcars  at  the  extremity  of  the  transverse 
process,  and  in  the  tliomcic  region  assists  in  forming  the  articular  surface  for  the  tul)crclc 
of  the  riV).     Two  epiphysial  plates  are  formed — one  for  the  upper,  and  the  second  for  the 


92 


OSTEOLOG-Y. 


lower  surface  of  the  body,  including  also  that  part  which  lies  behind  the  neuro-central 
synchondrosis  and  formed  by  the  pedicle  ;  from  these  the  thickened  circumference  of  both 
upper  and  lower  aspects  of  the  body  are  derived.  Fusion  of  these  centres  with  the  rest 
of  the  bone  is  not  complete  till  the  twenty-fifth  year. 

In  the  cervical  region  independent  centres  are  described  as  occurring  in  the  anterior 
roots  of  the  transverse  processes  of  the  sixth  and  seventh  vertebraj.  These  correspond  to 
the  costal  element,  and  may  occasionally  persist  in  the  form  of  cervical  ribs.  Elsewhere 
they  are  formed  by  lateral  extensions  from  the  pedicle. 

In  the  lumbar  region  the  transverse  process  of  the  first  lumbar  vertebra  is  occasionally 
associated  with  an  independent  costal  centre,  which  may  blend  with  it,  or  persist  as  a 


Fig.  71. — Ossification  of  Vertebrae. 


Cervical  vertebra. 


appears 


22 


23 


1.  Centre  for  body. 

2.  Sujjerior  epiphysial  plate. 

3.  Anterior  bar  of  transverse  process  developed  by 

lateral  extension  from  pedicle. 

4.  Neuro-central  synchondrosis. 

5.  Inferior  epiphysial  plate. 

Limibar  vertebra. 

6.  Body. 

7.  Superior  epiphysial  plate. 

8.  Epiphysis  for  niammillary  process. 

9.  Epiphysis  for  transverse  process. 

10.  Epiphysis  for  spine. 

11.  Neuro-central  synchondrosis. 

12.  Inferior  epiphysial  plate. 

Dorsal  vertebra. 

13.  Centre  for  body. 

14.  Superior  epiphysial  plate,  appears  about  puberty  ; 

unites  at  25th  year. 

15.  Neuro-central  synchondrosis  does  not  ossify  till 

5th  or  6th  year. 

16.  Appears  at  puberty  ;  unites  at  25th  year. 

17.  Appears  at  puberty  ;  unites  at  25th  year. 
18.-  Ai:)pears  about  6th  week. 

Axis. 
19.  Centre  for  transverse   process  and  neural  arch  ; 
appears  about  8th  week. 

lumbar  rib.  The  mammillary  processes  are  derived  from  separate  epiphyses.  The  neural 
arch  of  the  fifth  lumbar  vertebra  is  occasionally  developed  from  two  centres  on  either  side, 
as  is  demonstrated  by  the  fact  that  the  arch  is  sometimes  divided  b}^  a  synchondrodial 
joint  running  obliquely  across  between  the  superior  and  inferior  articular  processes  on 
either  side.  (See  ante,  p.  83  ;  also  Fortschritte  anf  dem  Gebiete  der  Rontgenstrahlen. 
Erganzungsheft  i. ;  "die  Entwickelung  des  menschlichen  Knochengertistes  wiihrend  des 
fotalen  Lebens,"  von  Lambertz.) 

Atlas. — The  lateral  masses  and  posterior  arch  are  developed  from  twO' centres — one  on 
either  side — which  correspond  with  the  centres  from  which  the  neural  arches  of  the  other 
members  of  the  series  are  developed.  These  make  their  appearance  about  the  seventh 
week,  and  do  not  unite  posteriorly  till  after  the  third  year.  Their  point  of  union  is 
sometimes  preceded  by  the  formation  of  a  distinct  spinal  nucleus  (Quain).     The  anterior 


20.  Synchondroses  close  about  3rd  year. 

21.  Centre  for  summit  of  odontoid  process  ; 
3rd  to  5th  year,  fuses  8th  to  12th  year. 

Appears  about   5th  or   6th   month  ;   unites  with 
opposite  side  7th  to  8th  month. 
Synchondrosis  closes  from  4th  to  6th  year. 

24.  Inferior  epiphysial  plate  ;  appears  about  puberty, 
unites  about  25th  year. 

25.  Single  or  double  centre  for  body  ;  appears  about 
5th  month. 

Atlas. 

26.  Posterior  arch  and  lateral  masses  developed  from 
a  single  centre  on  either  side,  ■which  appears 
about  7th  week. 

27.  Anterior  arch  and  jiortion  of  superior  articular 
surface  developed  from  single  or  double  centre, 
ajDpearing  during  1st  year. 

Dorsal  vertebra. 

28.  Epiphysis  for  transverse  jirocess  ;  appears  about 
puberty,  unites  about  25th  year. 

29.  Ejsiphysis  apj^ears  about  puberty ;  unites  about 
25th  or  27th  year. 

30.  Centre  for  neural  arch  on  either  side  ;  appears 
about  6th  or  7th  week,  the  laminte  unite  from 
birth  to  15th  month. 

31.  Centre  for  body  ;  appears  about  6th  week,  unites 
with  neural  arch  from  5th  to  6th  year. 


OSSIFICATION  OF  THE  VEETEBR^.  93 

arch  is  devcloijecl  from  centres  variously  described  as  single  or  double,  which  appear  in 
one  of  the  hypochordal  arches  of  cartilage  described  by  Froriep  {Arch.  f.  Anat.  u. 
Physiol.,  Anat.  Ahth.  1886)  which  here  persists.  In  this  cartilage  ossification  commences 
during  the  first  year  of  life.  Union  with  the  lateral  masses  is  delayed  till  six  or  eight 
years  after  birth.  The  external  extremities  of  the  anterior  arch  assist  in  forming  the 
fore  part  of  the  superior  articular  processes. 

Axis. — The  axis  ossifies  from  five  primitive  centres.  Of  these,  two — one  on  either  side 
— appear  about  the  seventh  week,  and  form  the  articular  and  transverse  processes,  together 
with  the  laminae  and  spine.  One,  or  it  may  be  two,  nuclei  appear  in  the  lower  part  of  the 
body  about  the  fifth  month.  The  upper  part  of  the  body,  including  a  small  part  of  the 
superior  articular  process,  and  the  base  of  the  odontoid  process,  are  developed  from  two 
laterally-placed  nuclei  which  appear  shortly  after,  and  fuse  together  at  the  seventh  or 
eighth  month,  so  that  at  birth  the  bone  consists  of  four  pieces.  Fusion  between  these 
parts  takes  place  in  the  following  order : — The  odontoid  unites  with  the  body  and  lateral 
parts  about  the  third  or  fourth  year ;  union  between  the  two  lateral  portions  posteriorly 
and  the  body  and  lateral  parts  in  front,  is  complete  at  from  four  to  six  years. 

The  summit  of  the  odontoid  process  is  developed  from  a  separate  centre,  occasionally 
double,  which  appears  from  the  third  to  the  fifth  year,  and  fuses  with  the  rest  of  the  bone 
from  the  eighth  to  the  twelfth  year.  About  puberty  an  annular  epiphysis  is  developed  on 
the  under  surface  of  the  body,  with  which  it  is  comjDletely  united  during  the  twentieth  to 
the  twenty-fifth  year.  Some  authorities  state  that  a  few  granules  between  the  base  of  the 
odontoid  and  the  upper  surface  of  the  body  represent  the  superior  epiphysial  plate  ;  but 
as  fusion  between  the  odontoid  and  the  body  occurs  before  the  time  for  the  appearance  of 
these  secondary  epiphysial  plates,  this  can  hardly  be  regarded  as  correct.  The  line  of 
fusion  of  the  odontoid  with  the  body  is  defined  by  a  small  disc  of  cartilage  which  persists 
within  the  substance  of  the  bone  till  an  advanced  period  of  life. 

A  pair  of  epiphyses  placed  over  the  tubercles  of  the  spine,  if  not  always  present,  are 
at  least  frequent. 

Sacrum. — Each  of  the  sacral  segments  is  ossified  from  three  centres  :  one  for  the 
body,  and  two  for  the  neural  arch— that  for  the  body,  which  makes  its  appearance  in  the 
first    three    sacral    vertebrae 

about  the  end  of  the  third  ''v'''''5Essfesar\\ /^ 

month,  about  the  fifth  to  the 
eighth  month  for  the  last 
two  segments.  From  the  two 
centres  for  the  neural  arches, 
which  make  their  appearance  ___  ^ 

about  the  fifth  or  sixth  month  ^^^^^^^^^        ^^°-  72.— Ossification  of  Sacrum. 

in   the   higher  segments,  the  ^^^^^^Bfj^KJ'         *•«•  Centres  for  bodies  ;  h.b.  Epiphysial 

lamina3,    articular   processes,  ^^^^^^T        Pj^^«^  °"  b°^^i«« '   '^■''-  Centres  for  costal 

1,1  i.     ■         \     ^s       c  ^S&  '^ff^^  elements  ;    d.d.  Centres  for  neural  arches  : 

and    the    posterior    half    of  ^^^^^^^^^  e  ^.  Late^l  epiphyses, 

the    alae   on   either  side   are 

developed.  The  spinal  canal  is  not  enclosed  till  the  seventh  to  the  tenth  year,  the 
laminae  usually  failing  to  meet  in  the  lowest  segment,  and  occasionally^  to  a  greater  or 
less  extent,  in  some  of  the  higher  segments.  The  anterior  part  of  the  lateral  masses  is 
developed  from  separate  centres  which  represent  the  costal  elements  (Gegenbauer).  These 
appear  about  the  sixth  to  the  eighth  month,  and  may  develop  in  relation  to  the  upper 
four  sacral  segments ;  more  usually  they  are  met  with  in  connexion  with  the  first  three, 
and  exceptionally  they  may  be  found  only  in  the  upper  two.  It  is  by  fusion  of  these 
with  the  posterior  arches  that  the  lateral  masses  which  support  the  innominate  bones 
are  formed.  The  costal  elements  fuse  about  the  second  to  the  fifth  year  with  the  neural 
arches,  prior  to  their  union  with  the  centra ;  and  the  segments  of  the  lateral  masses  unite 
with  each  other  sooner  than  the  union  of  the  bodies  is  efl^ected.  The  latter  only  takes 
place  after  puberty  by  the  fusion  of  the  epiphysial  plates,  a  pair  of  which  make  their 
appearance  between  the  centra  of  each  segment.  The  lower  segments  begin  to  unite 
together  about  the  eighteenth  year,  bxit  fusion  between  the  first  and  second  sacral  verte- 
bne  is  not  completed  till  the  twenty-fifth  year  or  after.  In  addition  to  the  foregoing,  two 
thin  osseous  laminfo  are  developed  in  tlic  cartilage  covering  the  outer  surface  of  the  alar 
mass.  The  upper  of  these  overspreads  the  auricular  surface,  whilst  the  lower  forms  the 
sharp  edge  below.  The  extremities  of  the  upper  spinous  processes  arc  occasionally 
developefl  from  independent  epiphyses.  On  making  a  mesial  section  of  an  adult  bone 
the  por.sistence  of  the  intervertebral  discs  lictween  the  centra  is  indicated  by  a  scries  of 
oval  cavities. 


94  OSTEOLOGY. 

Coccygeal  Vertebras. — Tiiese  arc  cartilaginous  at  birth.  Each  has  a  separate 
centre ;  the  first  a];)pears  from  the  first  to  the  fourth  year,  the  second  from  tlie  sixth  to 
the  tenth  year,  the  third  and  fourth  segments  at  or  about  puberty.  Secondary  centres, 
for  tlie  coccygeal  cornua  and  epiphysial  plates  for  the  bodies  are  also  described.  Fusion 
of  the  various  segments  begins  below  and  proceeds  upwards,  but  is  liable  to  great  indi- 
vidual variation.     In  advanced  life  the  coccyx  is  often  ossified  to  the  sacrum. 

SERIAL  HOMOLOGIES  OF  THE  VERTEBRAE. 

It  is  a  self-evident  fact  that  the  vertebral  column  consists  of  a  number  of  segments  or  verte- 
brae all  possessing  some  characters  in  common.  These  vertebrae  or  segments  undergo  modifications 
according  to  the  region  they  occupy  and  the  functions  they  are  called  ujjon  to  serve,  so  that 
their  correspondence  and  identity  is  thereby  obscured.  There  is  no  difficulty  in  recognising  the 
homology  of  the  bodies  and  neural  arches  throughout  the  colunui.  According  to  some 
anatomists  the  neural  arch  is  the  more  primitive  element  in  the  formation  of  a  vertebra,  whilst 
others  hold  that  the  centra  are  the  foundation  of  the  column.  Be  that  as  it  may,  we  find  that  in 
the  higher  vertebrates,  at  least,  the  bodies  are  the  j^arts  Avhicli  most  persist.  They  are,  however, 
subject  to  modifications  dependent  on  their  fusion  with  one  another.  This  occurs  in  the  cervical 
part  of  the  column  where  the  centrum  of  the  first  cervical  or  atlas  vertebra  has  for  functional 
reasons  become  fused  with  the  bod}'  of  the  second  or  axis  vertebra  to  form  the  odontoid  process 
of  that  segment.  For  similar  reasons,  and  in  association  with  the  union  of  the  girdle  of  the 
hind-limb  with  the  column,  the  bodies  of  the  vertebrae  which  corresj^ond  to  the  sacral  segment 
become  fused  together  to  form  a  solid  mass.  In  the  terminal  portion  of  the  caudal  region 
the  centra  alone  represent  the  vertebral  segments. 

As  regards  the  neural  arch,  this  in  man  becomes  deficient  in  the  lower  sacral  region,  and  absent 
altogether  in  the  lower  coccygeal  segments.  The  sj)inous  processes  are  absent  in  the  case  of  the 
first  cervical,  lower  sacral,  and  all  the  coccygeal  A'ertebrte,  and  display  characteristic  difterences 
in  the  cervical,  thoracic,  and  luml»ar  regions,  which  have  been  already  described.  The  articular 
processes  (zygaj^ophyses)  are  secondary  developments,  and  disj^lay  great  diversity  of  form,  deter- 
mined l)y  their  functional  requirements.  It  is  noteworthy  that,  in  the  case  of  the  uppei'  two 
cervical  vertebra?,  they  are  so  disposed  as  to  lie  in  front  of  the  foramina  of  exit  of  the  upper 
two  spinal  nerves,  and  by  this  arrangement  the  weight  of  the  head  is  transmitted  to  the  solid 
column  formed  by  the  vertebral  bodies,  and  not  on  to  the  series  of  neural  arches.  It  is  in 
regard  to  the  homology  of  the  transverse  processes,  so  called,  that  most  ditticulty  arises.  In  the 
thoracic  region  they  can  best  be  studied  in  their  simplest  form  ;  here  the  ribs — which  Qegenbauer 
regards  as  a  differentiation  from  the  inferior  or  hfemal  arches,  in  ojDposition  to  the  view  advanced 
by  others  that  they  are  a  secondary  development  from  the  fibrous  intermuscular  septa — articulate 
with  the  transverse  processes  and  bodies  of  the  thoracic  vertebrae  through  the  agency  of  the 
tubercular  (diapophysis)  and  capitular  (parapophysis)  jjrocesses  respectively,  the  latter  being 
placed,  strictly  sjDeaking,  on  the  neui^al  arch  behind  the  line  of  the  neuro-centi-al  synchondrosis. 

An  interval  is  thus  left  between  the  neck  of  the  rib  and  the  front  of  the  transverse  j^rocess  ; 
this  forms  an  arterial  passage  which  corresj^onds  to  the  vertebrarterial  canal  in  the  transverse 
l^rocesses  of  the  cervical  vertebrae,  the  anterior  bar  of  which  is  homologous  with  the  head  and 
tubercle  of  the  thoracic  rib,  whilst  the  jjosterior  part  lies  in  series  with  the  thoracic  transverse 
231'ocess.  These  homologies  are  further  emphasised  by  the  fact  that  in  the  case  of  the  seventh 
cervical  vertebra  the  anterior  limb  of  the  so-called  transverse  jsrocess  is  develojDed  from  an 
independent  ossific  centre,  which  occasionally  persists  in  an  independent  form  as  a  cervical  rib. 

In  the  lumbar  region  the  external  or  transverse  jirocess  is  serially  homologous  with  the 
thoracic  ribs,  though  here,  owing  to  the  coalescence  of  the  contiguous  j)arts,  there  is  no  arterial 
channel  between  the  rib  element  and  the  true  transverse  process,  which  is  represented  by  the 
accessory  processes  (anaj)ophysis),  jjlaced  posteriorly  at  the  root  of  the  so-called  transverse 
process  of  human  anatomy.  Support  is  given  to  this  view  by  the  presence  of  a  distinct  costal 
element  in  connexion  with  the  transverse  process  of  the  first  lumbar  vertebra,  which  accounts 
for  the  occasional  formation  of  a  supernumerary  rib  in  this  region.  The  cases  of  foramina  in  the 
transverse  processes  of  the  lumbar  vertebrte  (see  p.  83)  are  also  noteworthy  as  supporting  this  view. 

In  the  sacrum  the  lateral  mass  of  the  bone  is  made  itp  of  comliined  transverse  and  costal 
elements,  with  only  very  exceptionally  an  intervening  arterial  channel  (see  p.  86).  In  the 
case  of  the  upjser  three  sacral  segments  the  costal  elements  are  largely  developed,  assist  in 
supporting  the  ilia,  and  are  called  the  true  sacral  vertebra; ;  whilst  the  lower  sacral  segments, 
which  are  not  in  contact  with  the  ilia,  are  referred  to  as  the  j^seudo-sacral  vertebrae. 

The  anterior  arch  of  the  atlas  vertebra  is,  according  to  Froriep,  develojied  from  a  hypochordal 
strip  of  cartilage  (hypochordal  spange). 

THE  STERNUM. 

The  sternum  or  breast  bone  occupies  the  middle  of  the  upper  part  of  the 
thoracic  wall  anteriorly.  It  is  connected  laterally  with  the  cartilages  of  the  first 
seven  ribs,  and  supports,  superiorly,  the  clavicles.  It  consists  of  three  parts,  named 
respectively  the  manubrium  or  presternum ;  the  body  (corpus  sterni),  gladiolus  or 
mesostemum ;  and  the  ensiform.  or  xiphoid  cartilage  (processus  xiphoideus)  or  the 


THE  STERNUM. 


95 


Interclavicular  notch 
CI  tviculai  facial 


Eib 
car- 
tilage 


Manubrium 


II.  Ril)  caitila, 


III.  Rib  cartila: 


metasternum.     Of  these  the   body  is  formed  by  the  fusion  in   early  life  of  four 
segments  or  sternebrte. 

The  manubrium,  usually  separate  throughout  life  from  the  rest  of  the  bone, 
though  occasionally  fused  with  it,  is  of  a  flattened  triangular  form.  The  anterior 
surface,  slightly  saddle-shaped,  affords  attachment  to  the  fibres  of  the  pectoralis 
major  and  sterno- mastoid  muscles.  It  is  bounded  above  by  a  thick  border,  the  lateral 
parts  of  which  are  hollowed  out  obliquely 
to  form  the  facets  (incisurse  claviculares) 
for  the  sternal  ends  of  the  clavicles ; 
around  the  facets,  which  have  an  upward, 
outward,  and  slightly  backward  direction, 
the  bone  is  faintly  lipped.  In  the  in- 
terval between  these  two  facets  there  is 
a  slight  notch  (incisura  jugularis)  which 
forms  the  floor  of  the  characteristic  hollow 
seen  at  the  root  of  the  neck  anteriorly- 
the  suprasternal  notch,  or  pit  of  the  neck. 
The  lateral  borders  are  excavated  im- 
mediately below  the  clavicular  facets  for 
the  reception  of  the  cartilages  of  the 
first  ribs.  Below  this,  the  margin  of  the 
l^one  slopes  inwards,  and  is  sharp,  except 
interiorly,  where  it  presents  a  facet  which 
supports  a  part  of  the  second  costal 
cartilage.  Around  this  the  bone  is  usually 
lipped  anteriorly.  The  upper  angles 
correspond  to  the  ridge  separating  the 
clavicular  facets  from  the  first  costal 
facets :  whilst  the  lower  angle,  which 
may  be  regarded  as  cut  across  trans- 
versely, forms  the  surface  which  is  united 
by  cartilage  to  the  body  of  the  sternum,  iv.  Ribcaitiiage- 
The  anterior  edge  of  this  surface  is  usually 
[)rominent.  The  posterior  aspect  of  the 
manubrium  is  smoother  than  the  anterior, 
is  pierced  by  numerous  foramina,  and 
is  slightly  concave  from  side  to  side  and 
above  downwards.  Here  are  attached 
some  of  the  fibres  of  the  sterno-hyoid 
and  sterno-thyroid  muscles. 

The  body  (corpus  sterni),  usually  ^^- ^^^^^^'^^^^sf 
twice  the  length  and  from  half  to  two- 
thirds  the  width  of  the  manubrium,  dis- 
plays evidence  of  its  composite  nature. 
If  the  anterior  surface,  which  is  slightly 
convex  from  above  down  wards,  and  I'aintly 
concave  from  side  to  side,  be  carefully 
examined,  three  ill-marked  ridges  may  be 
seen  crossing  it  transversely ;  these  cor- 
respond to  the  lines  of  fusion  between  the 
four  primitive  segments.  To  this  surface  of  the  Ijone  the  great  pectoral  muscles 
are  extensively  attached  on  eith(!r  side  of  the  middle  line.  The  lateral  borders  are 
thick  and  interruyjted  at  YX)ints  corresponding  to  the  transverse  lines  already 
mentioned  by  U-shaped  hollows,  the  edges  of  which  are  more  or  less  projecting. 
These  are  for  the  reception  of  the  cartilages  of  the  third,  fourth,  and  fifth  ribs. 
'J'he  upper  harder  is  united  to  the  manubrium  ;i,l)Ove,  and  forms  with  it  an  angle 
of  variable  degree — the  sternal  angle  ra-ngiilus  sterni).  A  small  facet  is  formed  at 
the  i'X])(iiiH('.  of  the  outer  extniuiity  of  this  border,  and  in  conjunction  with  the 
I'acet  on  the  lower  edge  of  the  manubrium  forms  a  recess  on  either  side,  in  line  with 


V.  Rib  cartilai 


VII    Rib  cartila, 


Ensifonn  procesi 


Fig.  73. — The  Sternum  (anterior  view). 


96 


OSTEOLOGY. 


the  angle,  into  which  the  cartilage  of  the  second  rib  fits.  The  lower  border  of  the 
body  is  curved,  and  is  united  in  the  middle  line  with  the  xiphoid  cartilage,  whilst  on 
either  side  it  is  pitted  to  receive  the  cartilages  of  the  sixth  and  seventh  ribs,  the 
latter  being  in  part  supported  by  the  xiphoid  cartilage.  The  middle  line  of  the  body 
of  the  sternum  anteriorly  corresponds  to  the  Hoor  of  the  median  surface  furrow,  which 
runs  down  the  front  of  the  chest  in  the  interval  between  the  two  great  pectoral 
muscles.  The  j^osterior  surface  is  slightly  concave  from  above  downwards,  and 
displays  faint  indications  of  three  transverse  lines  in  correspondence  with  those 
placed  anteriorly.  It  is  in  relation  with  the  pleura  and  pericardium,  and  affords 
attachment  at  its  lower  extremity  to  the  triangularis  sterni  muscle. 

The  xiphi- sternum  (processus  xiphoideus)  displays  many  varieties  of  i'orm  and 
structure.  It  is  a  pointed  process  of  cartilage,  supported  by  a  core  of  bone  con- 
nected above  with  the  lower  end  of  the  body  of  the  sternum,  and  having  its  lower 
extremity,  to  which  the  linea  alba  is  attached,  free.  It  lies  somewhat  posterior  to 
the  plane  of  the  anterior  surface  of  the  manubrium,  and  forms  a  floor  to  the  V- 
shaped  interval  between  the  cartilages  of  the  seventh  ribs.  In  this  way  a  depression 
is  formed,  the  surface  hollow  in  correspondence  with  which  is  called  the  pit  of  the 
stomach  or  infrasternal  depression.  To  the  sides  of  this  process  are  attached  the 
aponeuroses  of  the  abdominal  muscles,  whilst  posteriorly  the  fibres  of  the  diaphragm 
and  triangularis  sterni  muscles  derive  attachment  from  it.  It  remains  partly 
cartilaginous  until  middle  life,  at  which  time  it  generally  undergoes  ossification, 
particularly  at  its  upper  part,  which  becomes  fused  with  the  body.  Of  varied 
form,  it  may  be  met  with  of  spatula-shape,  bifid,  circular,  pierced  in  the  centre,  or 
twisted  and  deflected  to  one  or  other  side,  or  turned  forward. 

The  sternum  as  a  whole  is  broadest  above  where  the  first  rib  cartilages  are 
attached.  It  becomes  narrow  opposite  the  second  rib  cartilages,  but  again  expands 
until  the  level  of  the  fifth  rib  cartilage  is  reached,  below  which  it  is  rapidly 
reduced  in  width  and  ends  below  in  the  pointed  xiphoid  cartilage.  Its  position  in 
the  body  is  oblique  from  above  downwards  and  forwards ;  its  axis,  if  prolonged 

upwards,    would     touch     the 
column  opposite  the  third  or 
fourth    cervical   vertebra. 
}^^^ii.,=;^.^-f       ^^^  Though  liable  to  changes  in 

position  by  the  rising  and  fall- 
ing of  the  chest  wall,  its  upper 
extremity  corresponds  to  the 
level  of  the  lower  border  of 
the  second  dorsal  vertebra, 
whilst  the  lower  end  of  the 
xiphoid  cartilage  usually  falls 
in  hue  with  the  disc  between 
the  tenth  and  eleventh  dorsal 
vertebrse. 

In  women  tlie  sternum  is  usually 
narrower  and  shorter  than  in  men, 
and  its  position  less  oblique. 

Architecture. — It  consists  of 
large-celled  spongy  bone,  which  is 
highly  vascular,  and  is  contained 
between  two  layers  of  thin  comiaact 
tissue. 


At  birth. 


Fig.  74. 


At  3  years. 
-Ossification  of  the  Sternum. 


In  this  figure  the  second  as  well  as  the  third  segmeut  of  the  body 
jjossesses  two  centres. 


1.  Appears  about  5th  or  sixth  mouth.  2.  Appear  about  7th 
mouth  ;  iinite  from  20  to  25.  3.  Appear  about  Sth  or  ninth  month  ; 
III.  segment  unites  with  II.  about  pul:>erty  ;  IV.  segment  unites 
with  III.  iu  early  childhood.     4.  Appears  about  3rd  year  or  later. 


Ossification.  —  The  carti- 
laginous sternum,  developed 
from  the  fusion  mesially  of  two 
cartilaginous  bands  uniting  the 
anterior  extremities  of  the  carti- 
lages of  the  first  eight  ribs,  according  to  the  researches  of  Ruge  and  more  recently  of 
Eggeling,  begins  to  ossify  about  the  sixth  month  of  fa?tal  life.  About  this  time  a  single 
centi-e  appears  in  the  manubrium;  at  birth  this  is  well  developed.  Secondary  epiphyses  have 
been  described  in  connexion  with  the  clavicular  facets  ;  these  do  not  unite  with  tlae  rest  of 


THE  EIBS.  97 

the  manubrium  till  adult  life  is  reached.  The  body  formed  by  the  fusion  of  four  segments 
is  ossified  from  independent  centres,  either  single  or  double,  for  each  segment.  These 
appear — the  highest  as  early  as  the  sixth  month  of  intrauterine  life — in  some  cases  even 
before  the  manubrium  has  begun  to  ossify  (Lambertz),  the  lowest  towards  the  end  of 
full  term.  The  common  arrangement  met  with  at  birth  is  a  single  centre  for  the  first, 
and  double  centres  for  each  of  the  succeeding  segments.  Union  between  these  segments 
occurs  rather  irregularly,  and  is  liable  to  much  variation.  The  fourth  unites  with  the 
third  segment  in  early  childhood,  the  third  with  the  second  about  puberty,  whilst  the 
fusion  of  the  second  with  the  first  segment  may  not  be  complete  till  the  twentieth  or 
twenty-fifth  year. 

The  xiphi-sternum  usually  ossifies  from  a  single  centre,  which  may  appear  as  early  as 
the  third  year,  though  often  very  much  later.  The  xiphi-sternum  usually  unites  with  the 
body  about  forty  or  fifty,  and  in  exceptional  cases  osseous  imion  between  the  body  and 
manubrium  may  occur  in  advanced  life. 

According  to  Paterson  the  presternum  is  developed  in  association  with  the  shoulder 
girdle  and  becomes  only  secondarily  associated  with  the  ventrally  growing  ribs. 

Variations. — The  sternum  is  liable  to  considerable  individual  variations  affecting  its  length 
and  direction.  The  majority  of  bones  are  asymmetrical,  displaying  irregularities  in  the  levels  of 
the  clavicular  facets.  The  higher  costal  facets  may  be  closer  together  on  one,  iisually  the  right 
side,  than  the  other,  whilst  the  pre-mesosternal  joint  is  often  oblique,  sloping  somewhat  to  the 
right.  According  to  Birmingham,  these  are  the  result  of  the  strain  thrown  on  the  shoulder  by 
pressure  either  directly  applied  or  through  the  pull  of  a  weight  carried  in  the  hand. 

Sometimes  the  sternum  articulates  with  eight  rib  cartilages.  This  may  happen  on  one  or 
both  sides,  but  when  unilateral,  much  more  frequently  on  the  right  side — a  condition  by  some 
associated  with  right-handedness.  It  is,  however,  more  probably  a  persistence  of  the  primitive 
condition  of  the  cartilaginous  sternum,  in  which  each  half  is  connected  with  the  anterior 
extremities  of  the  first  eight  costal  arches.  In  some  rare  cases  only  six  pairs  of  ribs  articulate 
by  means  of  their  costal  cartilages  with  the  sternum.  Recently  Lickley  has  brought  forward 
evidence  to  show  that  the  seventh  rib  is  undergoing  regressive  changes.  {Anat  Anz.  vol.  xxiv. 
p.  326.) 

Occasionally  the  presternum  supports  the  first  three  ribs  ;  in  other  words,  the  manubrium 
has  absorbed  the  highest  segment  of  the  body.  Keith  has  pointed  out  that  this  is  the  condition 
most  commonly  met  with  in  the  gibbon,  and  regards  its  occurrence  in  man  as  a  reversion  to  the 
simian  type.  As  far  as  is  at  present  known,  its  occurrence  seems  more  common  in  the  lower 
races.  Through  errors  of  develojament  the  sternum  may  be  fissured  throughout,  due  to  failure 
of  fusion  of  the  cartilaginous  hemisterna.  The  two  ossified  halves  are  usually  widely  separated 
above,  but  united  together  below  by  an  arthrodial  joint.  The  heart  and  pericardium  are  thus 
uncovered  by  the  bone.  Occasionally  this  condition  is  associated  with  ectopia  cordis,  under 
which  circumstances  life  is  rendered  impossible.  Through  defects  in  ossification  the  mesosternum 
may  be  pierced  by  a  hole,  usually  in  its  lower  part,  or  through  failure  of  fusion  of  the  lateral 
centres  one  or  more  of  the  segments  of  the  body  may  be  divided  longitudinally. 

Occasionally  small  ossicles  are  found  in  the  ligaments  of  the  sterno-clavicular  articulation. 
These  are  the  so-called  episternal  bones,  the  morphological  significance  of  which,  however,  has 
not  yet  been  satisfactorily  determined.  They  are  by  some  regarded  as  the  homologues  of  the 
interclavicle  or  episternal  bone  of  monotremes. 

THE   EIBS. 

The  ribs  (costse)  of  which  there  are  twelve  pairs,  form  a  series  of  curved  osseous 
bands  which  support  the  thoracic  wall;  posteriorly  they  articulate  with  the 
thoracic  or  dorsal  vertebras,  anteriorly  each  rib  is  provided  with  a  costal  cartilage. 
The  first  seven  ribs  articulate  with  the  sternum  by  means  of  their  cartilages,  and 
are  termed  the  true  (costse  verse)  or  vertebro-sternal  ribs.  The  lower  five  ribs  are 
not  so  supported,  and  are  described  as  the  false  ribs  (costse  spurise).  Of  these  the 
eighth,  ninth,  and  tenth  are  united  by  their  cartilages  to  the  cartilage  of  the 
seventh  rib,  and  are  called  the  vertebro-chondral  ribs,  whilst  the  last  two  ribs  are 
free  at  their  anterior  extremities,  and  are  named  the  floating  or  vertebral  ribs. 

A  typical  rib  consists  of  a  head  (capitulum  oostse),  a  neck  (collum  costte),  a 
tubercle  rtul^crciilum  costae),  and  a  shaft  (corpus  costtc),  on  which,  near  its  posterior 
iTid,  is  th(;  angle  Cangulus  costcc). 

'J'he  head,  ])laced  on  the  posterior  or  vertebral  end  of  the  bone,  is  somewhat 
expanded.  Internally  its  articular  surface  is  wedge-shaped  and  divided  into  two 
parts,  an  upper  and  lower,  by  a  ridge  or  crest  (crista  (;apituli),  to  which  the  intcr- 
articiibir  ligaincnt  is  attatjlied.  Of  these  two  facets  tlic  lower  is  usually  the  larger, 
and  articidatCH  witli  the  up])cr  f;i,cet  on  the  body  of  the  vcrtcibra  in  numerical 
correspondence  with  it,  whilst  the  upper  facet  is  for  the  corresponding  area  on  the 
8 


98 


OSTEOLOGY. 


Head 


Tubercle 


lower  part  of  the  body  of  the  vertebra  above.  The  head  is  supported  by  a  more 
or  less  constricted  bar  of  bone,  the  neck.  This  becomes  continuous  with  the  shaft 
externally,  at  which  point  there  is  a  well-marked  tubercle  on  its  posterior  surface. 
The  anterior  surface  of  the  neck  is  smooth;  its  posterior  aspect  is  rough,  and 
pierced  by  numerous 
small  holes  for  vessels. 
Here  is  attached  the 
middle  costo- trans- 
verse ligament.  Not 
uncommonly  the 
upper  border  of  the 
neck  is  lipped  and 
ridged     (crista     colli 

costse),   and    affords    attachment    to    the    anterior    costo- 
transverse lio-ament. 

The  tubercle  consists  of  an  articular  and  a  non-articular 
part ;  the  former  is  internal  to  and  below  the  latter.  Its 
articular  surface,  of  rounded  or  oval  shape,  is  directed 
downwards,  backwards,  and  a  little  inwards,  and  rests  upon 
a  facet  on  the  transverse  process  of  the  vertebra  in  numerical 
correspondence  with  the  rib.  The  non-articular  part,  most 
prominent  in  the  upper  ribs,  has  the  fibres  of  the  posterior 
costo-transverse  ligament  attached  to  it.  It  is  usually 
separated  from  the  upper  border  of  the  neck  and  shaft 
by  a  groove,  in  which  lies  the  external  branch  of  the  posterior 
division  of  the  thoracic  nerve. 

The  shaft  (corpus  costse)  is  thin,  flattened,  and  band- 
like. Its  length  varies  much ;  the  seventh  and  eighth, 
which  are  usually  the  longest,  are  from  two  and  a  half  to 
three  times  the  length  of  the  first  and  twelfth  ribs  respect- 
ively. The  shafts  are  curved  so  as  to  adapt  them  to  the 
form  of  the  thoracic  wall.  More  acute  in  the  upper  members 
of  the  series,  where  the  shafts  are  shorter,  the  curve  opens 
out  in  the  middle  and  lower  parts  of  the  thorax,  where 
the  diameters  of  that  cavity  are  greater.  The  curve, 
however,  is  not  uniform.  Including  the  whole  length  of 
the  bone,  it  will  be  seen  to  be  most  accentuated  towards  the 
hinder  part,  where,  in  correspondence  with  the  point  at 
which  the  bend  is  most  pronounced,  there  is  a  rough  ridge 
placed  obliquely  across  the  outer  surface  of  the  shaft ;  this 
is  the  angle  (angulus  cost?e).  The  distance  between  the 
angle  and  the  tubercle  is  greatest  on  the  eighth  rib ;  above 
that,  the  width  between  these  two  points  gradually  decreases 
until,  in  the  case  of  the  first  rib,  the  two  coincide.  Below 
the  level  of  the  eighth  rib  the  distance  slightly  diminishes 
in  conformity  with  the  general  narrowing  of  the  thorax 
below  that  level. 

Combined  with  this  curve,  there  is  in  many  of  the  ribs 
a  twist.  This  may  best  be  understood  if  the  student  will 
take  a  strip  of  stiff  paper  and  bend  it  in  the  form  of  the 
curve  of  the  rib.  If,  after  he  has  done  this,  he  pulls  down 
the  fore  end  and  turns  up  the  hind  end  of  the  strip,  he  will  have  imparted  to  the 
strip  of  paper  a  twist  similar  to  that  met  with  in  the  rib.  This  appearance  is 
best  seen  in  the  middle  members  of  the  series,  notably  in  the  seventh  and  eighth 
ribs,  above  and  below  which  it  gradually  becomes  less  marked.  It. is  the  occurrence 
of  this  twist  which  prevents  the  extremities  of  the  ribs,  together  with  the  shaft, 
from  resting  on  the  same  plane  surface.  To  this  rule  there  are  certain  notable 
exceptions,  viz.  the  first  and  second,  the  twelfth,  and  not  infrequently  the  eleventh. 

The  shaft  has  two  surfaces,  an  internal  and  an  external,  and  two  borders,  a 


For  costal  cartilai; 


Fig.  75. — Fifth  Eight  Rib 

AS    SEEN    FROM    BeLOW. 


THE  KIBS. 


99 


Facets  on  head 


Articular  part  of  tubercle 
for  transverse  process  of 
vertebra 


Fig.  76. — Fifth  PaoHT  Kib  as  seen  from  Behind. 


superior  and  an  inferior.  The  external  surface,  which  is  smootli,  conforms  to  the 
general  vertical  convexity  of  the  thorax,  being  directed  upwards  in  tlie  first  rib, 
upwards  and  outwards  in 
the  higher  ribs,  outwards  in 
the  middle  series,  and  out- 
wards and  slightly  down- 
wards in  the  tenth,  eleventh, 
and  twelfth.  The  internal 
surfaces  are  arranged  con- 
versely and  are  covered  by 
the  parietal  pleura.  Towards 
the  sternal  end  of  the  middle 
ribs,  where  the  downward 
twist  is  most  marked,  there 
is  often  an  oblique  line  across 
the  outer  surface.  This  is 
sometimes  referred  to  as  the  anterior  angle.  The  upper  border  of  the  shaft  is  thick 
and  rounded  behind,  thinner  and  sharper  in  front ;  to  it  are  attached  the  fibres  of 
the  internal  and  external  intercostal  muscles.  The  lower  border  is  grooved  behind 
at  the  expense  of  the  inner  surface,  and  is  overhuug  externally  by  a  sharp  margin. 
Anteriorly  this  subcostal  groove  (sulcus  costalis)  fades  away,  and  its  lips  coalesce 

to  form  a  rounded  edge.  The  inter- 
costal vessels  and  nerve  are  lodged  in 
this  groove,  whilst  its  lips  afford  at- 
tachment to  the  external  and  internal 
intercostal  muscles  respectively.  On 
the  floor  of  the  groove  may  also  be  seen 
the  openings  of  the  canals  for  the 
transmission  of  the  nutrient  vessels, 
which  are  directed  towards  the  vertebral 
end  of  the  rib. 

The  anterior  or  sternal  extremity 
of  the  shaft,  often  slightly  enlarged, 
displays  an  elongated  oval  pit  into 
which  the  costal  cartilage  is  sunk. 

Peculiar  Ribs. — The  first,  second, 
tenth,  eleventh,  and  tweKth  ribs  all 
display  characters  by  which  they  can 
be  readily  recognised. 

The  first  rib  can  be  easily  distin- 
guished from  the  others  by  its  size, 
curvature,  and  flattened  form.  The 
head,  which  is  of  small  size,  has  a 
single  oval  or  circular  facet,  which  is 
directed  inwards  and  slightly  back- 
wards for  articulation  with  the  side 
of  the  body  of  the  first  thoracic  verte- 
bra. The  neck  is  flattened  from  above 
downwards,  and  is  slightly  down-turned 
towards  the  end  which  supports  the 
head.  Its  anterior  border  is  rounded 
and  smooth ;  its  posterior  edge  rough  for  the  attachment  of  ligaments.  At  the 
])oii)t  where  tlie  neck  joins  the  shaft  posteriorly,  a  prominent  tubercle  curves 
upwards  and  backwards.  The  inner  and  under  surface  of  this  process  has  a  small 
circular  facet  which  rests  on  a  corresponding  articular  surface  on  the  transverse 
process  of  the  first  thoracic  vertelira.  The  angle  coiucidos  with  tlie  tubercle,  and 
thus  assists  in  cmpliasising  its  ])rominence.  Tlic  surfaccis  of  tlio  body  of  the  rib 
are  directed  u])wardH  and  downwards,  its  Ijorders  inwards  and  outwards.  If  the 
linger  be  run  along  the  thin  inner  border,  a  distinct  spine  or  tubercle  can  be  readily 


Fio.  77. — First  and  Second  Rioht  Ribs  as  seen 
FROM  Above. 


100  OSTEOLOGY. 

felt  about  an  inch  or  an  inch  and  a  quarter  from  its  anterior  extremity.  This 
is  the  scalene  tubercle  (tubercuhim  scaleni)  for  the  attachment  of  the  scalenus 
anticus  muscle.  There  is  a  shallow,  oblique  groove  crossing  the  upper  surface 
of  the  shaft  in  front  of  this  for  the  lodgment  of  the  subclavian  vein  ;  whilst  behind 
the  tubercle  there  is  another  groove,  usually  better  marked,  and  passing  obliquely 
forwards  for  the  subclavian  artery  (sulcus  subclavise).  The  space  on  the  upper 
surface  of  the  rib  between  this  latter  groove  and  the  tubercle  posteriorly  is  some- 
what rough,  and  affords  attachment  to  the  jfibres  of  the  scalenus  medius  muscle. 
The  anterior  extremity  of  the  rib  is  thickened  and  often  expanded  for  the  reception 
of  its  costal  cartilage,  which  is  not  infrequently  ossified.  The  under  surface  of  the 
rib  is  smooth  and  is  covered  by  pleura.  The  outer  convex  border,  thin  in  front, 
is  usually  thick  and  rough  behind  the  subclavian  groove,  where  it  has  attached  to 
it  the  fibres  of  the  first  digitation  of  the  serratus  magnus.  Along  this  edge,  also, 
are  attached  the  external  and  internal  intercostal  muscles  of  the  first  intercostal 
space.  The  inner  concave  border  is  thin,  and  has  connected  with  it  the  aponeurotic 
expansion  known  as  Sibson's  fascia. 

The  second  rib  may  be  distinguished  by  the  size  of  its  curve ;  the  absence  of 
any  twist  on  its  shaft,  so  that  it  can  be  laid  flat  on  the  table ;  the  oblique  direction 
of  the  surfaces  of  its  shaft,  the  outer  being  directed  upwards  and  outwards,  whilst 
the  inner  is  turned  downwards  and  inwards ;  and  the  presence  of  a  well-marked, 
rough,  oval  area  about  the  middle  of  its  outer  surface  and  lower  border  for  part 
of  the  first,  and  the  whole  of  the  second  digitation  of  the  serratus  magnus  muscle. 
The  head  has  two  facets,  and  the  angle  is  close  to  the  tubercle  posteriorly. 

The  tenth  rib  has  usually  only  a  single  articular  facet  on  the  head,  and  may  or 
may  not  have  a  facet  on  the  tubercle. 

The- eleventh  and  twelfth  ribs  are  recognised  by  their  length.  Their  heads, 
usually  large  in  proportion  to  their  shafts,  support  a  single  facet  for  articulation 
with  the  eleventh  and  twelfth  dorsal  vertebrae  respectively.  The  tubercles  are  ill- 
developed  and  have  no  articular  facets.  The  angle  is  faintly  marked  on  the 
eleventh,  scarcely  perceptible  on  the  twelfth.  Their  anterior  extremities  are  narrow 
and  pointed  and  tipped  with  cartilage.  The  subcostal  groove  is  absent  in  the 
twelfth,  and  but  slightly  seen  in  the  eleventh.  The  twelfth  is  considerably  shorter 
than  the  eleventh  rib. 

Architecture. — Each,  rib  consists  of  a  curved  and  flattened  bar  of  bone,  tbe  interior  of  wbicli 
is  loose  and  cancellous,  whilst  tbe  investing  envelope  is  comimct.  Tbe  inner  table  is  mucb  the 
stronger,  attaining  its  maximum  thickness  opposite  tbe  angle — in  front  and  behind  which  it 
becomes  gradually  reduced.  The  outer  table,  much  thinner,  is  stoutest  opposite  the  angle  ;  on 
the  posterior  surface  of  tbe  tubercle  and  neck  it  forms  but  a  thin  layer.  Tbe  compact  layers 
forming  the  upper  and  lower  borders  are  not  so  thick  as  those  forming  the  inner  and  outer 
surfaces.  Tbe  cancellous  tissue,  loose  and  open  in  tbe  shaft,  is  most  compact  in  tbe  region  of  tbe 
bead  and  towards  the  anterior  extremity. 

Variations. — The  number  of  ribs  may  be  increased  or  diminished.  Increase  may  occur  by 
the  addition  of  a  cervical  rib  due  to  the  independent  development  of  the  costal  element  in  the 
transverse  process  of  the  seventh  cervical  vertebra.  This  may  happen  on  one  or  both  sides.  Tbe 
range  of  development  of  these  cervical  ribs  varies ;  they  may  unite  in  front  with  the  sternum, 
or  they  may  be  fused  anteriorly  with  tbe  cartilage  of  tbe  first  rib,  or  the  cervical  rib  may  be 
free.  It  may  in  some  instances  be  represented  mainly  by  a  ligamentous  band,  or  its  vertebral 
and  sternal  ends  may  be  alone  developed,  the  intermediate  part  being  fibrous.  At  times  tbe 
vertebral  end  only  may  be  formed  and  may  be  fused  with  the  first  rib,  thus  leading  to  the 
formation  of  a  bicipital  rib  such  as  occurs  in  many  cetaceans.  Increase  in  the  number  of  ribs 
may  also  be  due  to  tbe  ossification  of  the  costal  element  which  is  normally  present  in  the  embryo 
in  connexion  witb  the  first  lumbar  vertebra.  (Eosenberg,  Mvrph.  Jahrb.  i.)  Keduction  in  the 
number  of  ribs  is  less  common.  The  twelfth  rib  rarely  aborts ;  in  some  cases  tbe  first  rib  is 
rudimentary.  Cases  of  congenital  absence  of  some  of  tbe  ribs  have  been  recorded  by  Hutchinson, 
Murray,  and  Ludeke. 

Fusion  of  adjacent  ribs  may  occur.     (Lane,  Gmfs  Hosp.  Rex)orts,  1883.) 

Variations  in  form  may  be  in  great  part  due  to  tbe  occupation  of  the  individual  and  tbe  con- 
stricting influence  of  corsets.  Independently  of  these  influences,  tbe  fore  part  of  the  shaft  is 
sometimes  cleft  so  as  to  appear  double  ;  at  other  times  the  cleft  may  be  incomplete  so  as  to  form 
a  perforation.  Occasionally  adjacent  ribs  are  imited  towards  their  posterior  part  by  processes 
having  an  intermediate  ossicle  between  (Meckel),  thus  recalling  the  condition  normally  met  with 
in  birds ;  more  usually,  however,  the  bony  projections  are  not  in  contact. 

The  number  of  true  or  vertebro-sternal  ribs  may  be  reduced  to  six,  or  increased  to  eight  (see 
ante,  p.  97). 


THE  THOEAX  AS  A  WHOLE. 


101 


Ossification. — Ossification  begins  in  the  cartilaginous  ribs  about  the  sixth  week,  and 
rapidly  extends  along  the  shaft,  so  that  by  the  end  of  the  third  month  it  has  reached  the 
permanent  costal  cartilage.  The  sixth  and  seventh  ribs  are  the  earliest  to  ossify ;  the 
first  rib  being  the  last  (Lambertz).  At  puberty,  or  before,  secondary  centres  appear. 
Of  these  there  are  three — an  epiphysis  for  the  articular  surface  of  the  tubercle,  one  for  the 
non-articular  part  of  the  same  process,  and  one  for  the  head.  By  the  twenty-fifth  year 
fusion  between  these  and  the  shaft  is  complete. 

THE  COSTAL  CAETILAGES. 

The  costal  cartilages,  of  which  there  are  twelve  pairs,  are  bars  of  hyaline 
cartilage  united  to  the  anterior  extremities  of  the  ribs,  into  which  they  are  recessed 
and  held  in  position  by  the  periosteum.  Through  these  cartilages  the  first 
seven  ribs  are  connected  directly  with  the  sternum  by  means  of  synovial  joints 
corresponding  to  the  notches  along  the  margins  of  the  breast  bone.  To  this  there 
is  an  exception  in  the  case  of  the  first  rib,  the  cartilage  of  which  is  directly  blended 
with  the  manubrium  sterni.  The  eighth,  ninth,  and  tenth  are  connected  indirectly 
with  the  sternum  by  their  union  with  each  other,  and  their  articulation,  through 
the  medium  of  the  eighth,  with  the  seventh  rib  cartilage,  whilst  the  eleventh  and 
twelfth  cartilages  tip  the  ribs  to  which  they  belong,  and  lie  free  in  the  muscles  of 
the  flank.  The  costal  cartilages  increase  in  length  from  the  first  to  the  seventh, 
below  which  they  become  shorter.  The  first  inclines  obliquely  downwards  and 
inwards  to  unite  with  the  upper  angles  of  the  manubrium.  The  second  lies  more 
or  less  horizontally.  The 
third  to  the  seventh 
gradually  become  more 
and  more  curved,  inclin- 
ing downward  from  the 
extremities  of  their  re- 
spective ribs,  and  then 
turning  upwards  to  reach 
the  sternum.  The  tenth 
cartilage  articulates  by 
means  of  a  synovial  joint 
with  the  ninth,  the  ninth 
with  the  eighth,  and  the 
eighth  with  the  seventh. 
There  are  also  surfaces 
for  the  articulation  of 
the  seventh  with  the 
sixth,  and  sometimes  for 
the  sixth  with  the  fifth. 

Variations.  —  Occa- 
sionally a  costal  cartilage 
is  unduly  broad,  and  may 
be  pierced  by  a  foramen. 
The  number  of  costal 
cartilages  connected  with 
the  sternum  may  be  re- 
duced to  six  or  increased 
to  eight  (see  p.  97).  In 
advanced  life  there  is  a 
tendency  towards  ossifica- 
tion in  the  layers  under- 
lying the  perichondrium, 
more  particidarly  in  the 
case  of  the  first  rib  cartilage 


YiQ.  78. — Thk  Thouax  as  skbn  kuom  Tiiii  Fhont. 
vvliich  it  may  be  regarded  as  a  more  or  less  normal  occurrence. 


TWK  THORAX  AS  A  WJIOLK. 

The  bony  and  cartilaginous  thorax  is  barrel-shaped,  being  narrower  al)ove  than 
below,  and  compressed  from  before  ba(;kwards.     Its  posterior  wall  is  longer  than  its 
8a 


102 


OSTEOLOGY. 


anterior,  and  its  transverse  width,  which  reaches  its  maximum  opposite  the  eighth 
or  ninth  rib,  is  much  in  excess  of  its  sagittal  diameter.  This  is  largely  owing 
to  the  forward  projection  of  the  thoracic  part  of  the  vertebral  column  into  the 
thoracic  cavity. 

The   anterior  wall   is  formed   by  the  ribs   and  rib    cartilages,  together  with 
the  sternum.    The  posterior  wall  comprises  the  thoracic  part  of  the  vertebral  column 

and  the  ribs  as  far  as  their 
angles.  Owing  to  the  back- 
ward curve  of  the  ribs,  and 
the  projection  forwards  of  the 
vertebral  bodies,  the.  antero- 
posterior diameter  of  the 
thoracic  cavity  is  considerably 
greater  on  either  side  of  the 
middle  line  than  in  the  mesial 
plane,  thus  allowing  for  the 
lodgment  of  the  rounded  pos- 
terior borders  of  the  lungs. 
For  the  same  reason  the  furrow 
on  either  side  of  the  spinous 
processes  of  the  thoracic  verte- 
brae is  converted  into  a  broad 
groove  (vertebral  groove),  the 
floor  of  which  is  in  part  formed 
by  the  ribs  as  far  as  their 
angles.  The  grooves  so  formed 
are  each  occupied  by  the  fleshy 
mass  of  the  erector  spinee 
muscle. 

The  lateral  walls  are  formed 
by  the  costal  arches.  The  ribs 
which  run  obliquely  from 
above  downwards  and  forwards 
do  not  lie  parallel  to  each 
other,  but  spread  somewhat,  so 
that  the  intervals  between 
them  (intercostal  spaces)  are 
wider  in  front  than  behind. 

The  superior  aperture  or 
inlet  formed  by  the  body  of 
the  first  thoracic  vertebra  be- 
hind, the  arches  of  the  first 
rib  on  either  side,  and  the 
upper  border  of  the  manubrium  sterni  in  front,  is  contracted  and  of  reniform  shape. 
The  plane  of  the  inlet  is  oblique  from  behind  downwards  and  forwards,  so  that  in 
expiration  the  upper  border  of  the  sternum  lies  on  a  level  with  the  disc  between 
the  second  and  third  thoracic  vertebrae. 

The  lower  aperture,  of  large  size,  is  bounded  in  the  middle  line  behind  by  the 
twelfth  thoracic  vertebra ;  passing  thence  the  twelfth  ribs  slope  outwards,  down- 
wards, and  forwards.  From  these  a  line  carried  horizontally  forwards  from  their 
tips  touches  the  end  of  the  eleventh  rib,  and  then  curving  slightly  upward  reaches 
the  cartilage  of  the  tenth  rib.  Here  it  follows  the  confluent  margins  of  the  car- 
tilages of  the  tenth,  ninth,  eighth,  and  seventh  ribs,  finally  reaching  the  xiphoid 
cartilage,  where  it  forms  with  the  costal  margin  of  the  opiDosite  side  the  subcostal 
angle,  the  summit  of  which  coincides  with  the  xiphi-sternal  articulation ;  in 
expiration  this  joint  usually  lies  on  a  level  with  the  intervertebral  disc  between 
the  ninth  and  tenth  thoracic  vertebrae,  and  corresponds  with  the  surface  depression 
familiarly  known  as  the  pit  of  the  stomach.  The  inferior  aperture  of  the  thorax  is 
occupied  by  the  vault  of  the  diaphragm. 


Fig.  79. — The  Thorax  as  seen  from  the  Right  Side. 


THE  FEONTAL  BONE.  103 

In  the  foetal  condition  the  form  of  the  thorax  differs  from  that  of  the  adult.  It  is 
laterally  compressed — in  this  respect  resembling  the  simian  type.  Its  antero-posterior 
diameter  is  relatively  greater  than  in  the  adult.  At  birth  changes  in  form  take  place 
dependent  on  the  expansion  of  the  lungs ;  during  subsequent  growth,  the  further  ex- 
pansion of  the  thoracic  cavity  in  a  transverse  direction  is  correlated  with  the  assumption 
of  the  erect  posture,  and  the  use  of  the  fore-limbs  as  prehensile  organs. 

Sexual  Differences. — The  thorax  of  the  female  is  usually  described  as  being 
proportionately  shorter  and  rounder  than  the  male.  It  also  tends  to  narrowness  in  the 
lower  segment.  It  is  hardly  necessary  to  point  out  that  the  natural  form  is  often 
modified  by  the  use  of  tight  or  ill-fitting  corsets. 

THE  BONES  OF  THE  SKULL  (Ossa  Ceanii). 

The  term  skull  (cranium)  is  commonly  employed  to  signify  the  entire  skeleton 
of  the  head.  This  comprises  the  bony  envelope  which  surrounds  the  brain 
(cranium  cerebrale),  and  the  osseous  structures  which  support  the  face  (cranium 
viscerale,  ossa  faciei). 

In  catalogues  of  craniological  collections  the  terms  used  are  as  follows  : — 
Skull       =  entii-e  skeleton  of  head,  including  the  mandible. 
Cranium  =  the  skull,  minus  the  mandible. 

Calvaria  =that  part  of  the  skull  which  remains  after  the  bones  of  the  face  have 
been  removed  or  destroyed. 

The  cranium  cerebrale  is  composed  of  the  occipital  (os  occipitale),  the  sphenoid 
(os  sphenoidale),  the  ethmoid  (os  ethmoidale),  and  the  frontal  (os  frontale),  the  two 
parietals  (ossa  parietalia),  and  the  two  temporals  (ossa  temporalia) — eight  bones  in  all. 

The  bones  of  the  face  (cranium  viscerale,  ossa  faciei)  include  the  following : — 
Two  single,  viz.  the  vomer  (vomer),  and  the  inferior  maxilla  or  mandible  (mandibula), 
and  twelve  bones,  arranged  in  pairs,  viz.  the  superior  maxillary  (maxillse),  malar  (ossa 
zygomatica),  palate  (ossa  palatina),  together  with  the  lachrjmial  (ossa  lacrymalia), 
nasal  (ossa  nasalia),  and  inferior  turbinated  (conchee  inferiores) — fourteen  bones  in  all. 

According  to  the  scheme  of  international  nomenclature,  the  inferior  turbinals,  the 
lachrymals,  the  nasals,  and  the  vomer  are  included  under  the  cranium  cerebrale,  and  not 
with  the  cranium  viscerale. 

The  hyoid  bone  is  usually  described  along  with  the  skull.  If,  in  addition,  the 
bones  of  the  middle  ear,  three  on  each  side  (malleus,  incus,  and  stapes),  be  in- 
cluded, the  skeleton  of  the  head  consists  of  twenty-nine  bones. 

The  separate  bones  will  first  be  described,  and  then  the  skull  will  be  considered 
as  a  whole  and  in  section. 

THE  SEPARATE  BONES  OF  THE  SKULL. 
The  Frontal  Bone. 

The  frontal  bone  (os  frontale),  situated  in  the  fore  part  of  the  cranium,  is  a 
single  bone  formed  by  the  fusion  in  early  life  of  two  symmetrical  halves.  It  con- 
sists of  a  frontal  part,  which  corresponds  to  the  region  of  the  forehead ;  an  orbital 
part,  which  enters  in  the  structure  of  the  roof  of  the  orbits ;  and  a  nasal  part,  which 
assists  in  forming  the  roof  of  the  nasal  fossae. 

The  frontal  part  (pars  frontalis)  is  the  shell-like  portion  of  the  bone  which 
rises  uj^wards  above  the  orbital  arches.  Its  external  surface  is  rounded  from  side 
to  side  and  from  above  downwards.  This  convexity  is  most  pronounced  about 
1^  inches  above  the  orbital  margins  on  either  side  of  the  middle  line,  constituting 
what  are  known  as  the  frontal  eminences  (tubera  frontalia).  These  mark  the 
original  sites  of  the  centres  from  which  the  bone  ossifies.  The  lower  margin  of 
til  is  })art  is  formed  on  either  side  of  the  middle  line  by  the  curved  orbital 
margins  (margines  supraorbi tales),  the  outer  and  inner  extremities  of  wliich 
constitute  the  external  and  internal  angular  processes  respectively.  The  latter 
descend  to  a  lower  lever  than  the  I'ornier,  and  articulate  with  the  lachrymal 
8& 


104 


OSTEOLOGY. 


bones,  being  separated  from  each  other  by  a  rough  articulate  surface — the  nasal 
notch  for  the  nasal  and  superior  maxillary  bones.  The  curve  of  the  orbital 
margin  varies  in  different  individuals  and  races ;  towards  its  inner  third  it  is 
crossed  by  a  groove,  not  unfrequeutly  converted  into  a  foramen — the  supraorbital 
notch  or  foramen  (incisura  sive  foramen  supraorbitalis).  Through  this  there  pass 
the  supraorl)ital  nerve  and  artery.  Above  the  supraorljital  margin  the  character 
of  the  bone  displays  marked  differences  in  the  two  sexes :  in  the  male,  above  the 
interval  between  the  two  internal  angular  processes,  there  is  usually  a  well-marked 
prominence,  called  the  glabella,  from  this  the  fulness  extends  outwards  above  the 
orbital  margin,  varying  in  degree  and  extent,  and  forming  the  elevations  known  as 
the  supraorbital  or  superciliary  ridges  (arcus  superciliares).  The  prominence  of 
these  naturally  reacts  on  the  character  of  the  supraorbital  margins,  which  are  thicker 
and  more  rounded  in  the  male  than  in  the  female.  Passing  upwards  over  the  glabella, 
the  remains  of  the  suture  which  originally  separated  the  two  halves  of  the  frontal  bone 
can  usually  be  seen  ;  above  this  point  all  trace  of  the  suture  is  generally  obliterated. 


Frontal  eminences 


External  angular  process -4?*,^ 


Temporal  crest 
Superciliary  ridge 


Orlabella  and  remains  of  frontal  suture 
Internal  angular  process 


Supraorbital  notch. 
For  articulation  •\vitli  nasal  bone         l^lf 

Nasal  spine 

Fig.  80. — Frontal  Bone  (Anterior  View). 

Extending  upwards  from  the  external  angular  process  is  a  well-marked  ridge, 
which  curves  upwards  and  slightly  inwards,  then  turning  backwards  it  arches 
across  the  lateral  aspect  of  the  bone.  This  is  the  temporal  ridge  or  crest  (linea  tem- 
poralis), which  serves  to  separate  the  anterior  surface  of  the  frontal  portion^f  the 
bone  from  its  temporal  aspect.  The  latter  (facies  temporalis)  forms  the  flooMF  the 
upper  and  anterior  part  of  the  temporal  fossa,  and  serves  for  the  attachm§|MPf  the 
temporal  muscle. 

The  orbital  part  of  the  bone  (pars  orbitalis)  consists  of  two  transversely-curved 
plates,  each  having  the  form  of  a  sextant ;  their  inner  edges,  which  are  cellular,  lie 
parallel  to  each  other,  and  are  separated  in  their  posterior  half  by  the  ethmoidal 
notch  (incisura  ethmoidalis),  in  which  the  ethmoid  bone  is  lodged.  The  edges  of 
the  notch  on  either  side  are  grooved  in  front  and  behind  by  the  anterior  and  posterior 
ethmoidal  foramina,  which  are  completed  when  the  ethmoid  is  in  situ.  The  anterior 
transmits  the  internal  branch  of  the  nasal  nerve  and  the  anterior  ethmoidal  vessels  ; 
the  posterior,  the  posterior  ethmoidal  vessels.  In  front  of  the  ethmoidal  notch  is  the 
nasal  notch,  from  the  centre  of  which  the  nasal  process  projects  downwards  and  for- 
wards to  terminate  in  the  nasal  spine  (spina  nasalis),  which  lies  between,  and  articu- 
lates with  the  nasal  bones  and  perpendicular  plate  of  the  ethmoid.     On  either  side 


THE  FEONTAL  BONE. 


105 


of  the  root  of  this  process  the  bone  is  grooved  obliquely  from  above  downwards  and 
forwards,  and  enters  into  the  formation  of  the  narrow  roof  (pars  nasalis)  of  the 
nasal  fossse.  Anteriorly  the  nasal  notch  is  limited  by  a  rough  U-shaped  articular 
surface,  the  median  part  of  which  articulates  with  the  nasal  bones,  whilst  on  either 
side  the  nasal  processes  of  the  superior  maxillae  are  united  with  it.  Behind  this, 
amid  the  broken  cells,  the  passages  leading  into  the  frontal  sinuses  are  readily 
distinguished,  and  here  the  inner  edges  of  the  orbital  plates  articulate  with  the 
lachrymal  bones. 

The  orbital  plate  is  thin  and  brittle.  In  front  it  is  bounded  by  the  superior 
orbital  margin,  just  within  wliich,  midway  between  the  internal  angular  process 
and  the  supraorbital  notch  there  is  a  small  shallow  depression  (fovea  trochlearis), 
often  displaying  a  spicule  of  bone  arising  from  its  edge  (spina  trochlearis),  which 
affords  attachment  to  the  pulley  of  the  superior  oblique  mnscle  of  the  eyeball. 
Externally  the  orbital  plate  is  overhung  by  the  orbital  margin  and  the  external 
angular  process,  and  in  the  hollow  so  produced  (fossa  glandules  lachrymalis)  the 
lachrymal  gland  is  lodged.  The  extremity  of  the  external  angular  process  (pro- 
cessus zygomaticus)  articulates  with  the  frontal  process  of  the  malar  bone.     Behind 


For  articulation  with 
lesser  wing  of  sphenoid 


Superior  longitudinal 
sinus  and  falx  cerebri 


..X"^"^*!-  Meningeal  groove 


Orbital  plate 


Temporal  suiface 


External  angular  pioce&s 


Surface  for  articula- 
•  tion  with  great  wing 
of  sphenoid 


Lachrymal  fossa 


^^"^^  Internal  orbital  canals 


\"5upiaoibital  notch 
Iiochlear  fosba 


Ethmoidal  notch 

Frontal  sinus  /  -^      \ 

Nasal  suitacc     r        Nasal  notch 
Nasal  spine 
Fig.  81. — Frontal  Bone  as  seen  from  Below.  ^ 

this  the  irregular  edge  of  the  orbital  plate  is  united  with  the  great  wing  of  the 
sphenoid  by  a  triangular  area,  which  also  extends  on  to  the  inferior  aspect  of 
the  temporal  surface  of  the  frontal  bone.  The  apex  of  the  orbital  plate,  for  the 
space  of  about  half  an  inch,  articulates  with  the  lesser  wing  of  the  sphenoid. 

The  cerebral  surface  of  the  bone  forms  a  fossa  in  which  lie  the  fore  and  under 
parts  of  the  frontal  lobes  of  the  cerebrum,  the  convolutions  of  which  impress  their 
form  on  tlie  inner  aspect  of  the  bone.  Here,  too,  on  either  side  of  the  middle  line, 
may  be  seen  depressions  for  the  lodgment  of  Pacchionian  bodies.  Descending  from 
the  centre  of  the  upper  margin  of  the  bone  is  a  vertical  groove,  the  frontal  sulcus ; 
narrowing  below,  this  ends  in  a  ridge — the  frontal  crest — which  nearly  reached 
the  fore  yj^irt  of  the  ethmoidal  notch,  wliere  it  terminates  in  a  small  orifice,  the 
foramen  Ccccum,  placed  usually  in  the  suture  between  the  fore  part  of  the  ethmois 
and  the  frontal.  This  foramen  may,  or  may  not,  transmit  a  small  vein  from  the 
nose  to  the  commencement  (d"  the  superior  longitudinal  sinus.  This  sinus,  which 
is  interposed  between  the  layers  of  the  falx  cerebri,  is  at  first  attached  to  the 
frontal  crest,  but  subsequently  occupies  the  frontal  sulcus.  Deeply  concave  from 
side  to  side  and  from  above  downwards,  th(!  lateral  aspects  of  the  fossa  are  seen  to 
be  traversed  by  snifdl  grooves  for  tii(^  anterior  branches  of  the  middle  meningeal 
artfirie.s.     Below,  the  orbital  plates  bulge  into  the  floor  of  the  fossa,  so  that  the 


106 


OSTEOLOGY. 


ethmoidal  notch  appears  recessed  between  them.  On  either  side  of  the  notch  faint 
grooves  for  the  meningeal  branches  of  the  ethmoidal  vessels  may  be  seen.  The 
circumference  of  the  fossa  is  formed  by  the  serrated  edges  of  the  bone  which 
articulate  with  the  parietals  above,  and  on  either  side  below  with  the  great  and 
lesser  wings  of  the  sphenoid. 

Connexions. — The  frontal  articulates  with  twelve  bones,  viz.  posteriorly  with  the  parietals 
and  sphenoid  ;  externally  with  the  malars  ;  inferiorly  and  internally  with  the  nasals,  superior 
maxillae,  lachrymals,  and  ethmoid. 

Architecture. — The  frontal  bone  is  comj^osed,  like  the  other  bones  of  the  cranial  vault,  of 
two  layers  of  compact  tissiie,  enclosing  between  them  a  layer  of  sjjongy  cancellou.'^  texture — the 
diploe.  In  certain  definite  situations,  owing  to  the  absorption  of  this  intermediate  layer,  the 
bone  is  hollow,  forming  the  frontal  air  sinuses.  The  position  and  extent  of  these  is  to  some 
extent  indicated  by  the  degree  of  projection  of  the  su2:)erciliary  ridges,  though  this  must  not  be 
taken  as  an  absolutely  reliable  guide,  for  cases  are  recorded  where  the  ridges  were  low  and  the 
sinuses  large,  and  vice  versa.  Of  much  surgical  importance,  these  air-spaces  only  attain  their  full 
develoj)ment  after  the  age  of  puberty,  being  of  larger  size  in  the  male  than  in  the  female,  a 
circumstance  which  accounts  for  the  more  vertical  aj)pearance  of  the  forehead  in  woman  as  con- 
trasted with  man.  Usually  two  in  number,  they  are  placed  one  on  either  side  of  the  middle 
line,  and  communicate  by  means  of  the  infundibulum  with  the  nasal  fossa  of  the  same  side. 
It  is  excejDtional  to  find  the  sinuses  of  opposite  sides  in  communication  with  each  other,  as  they 
are  generally  separated  by  a  comjjlete  jjartition  which,  however,  is  occasionally  much  deflected 
to  one  or  other  side.  Logan  Turner  ("  On  the  Illumination  of  the  Air  Sinuses  of  the  Skull,  with 
some  Obsei'vations  uj^on  the  Surgical  Anatomy  of  the  Frontal  Sinus,"  Edin.  Med.  Jour.,  May  1898) 
gives  the  average  dimensions  of  these  sinuses  as  follows  : — Height,  31  mm.,  i.e.  from  the  fronto- 
nasal aj^erture  upwards ;  breadth,  30  mm.,  i.e.  from  the  septum  horizontally  outwards ;  depth,  17 
mm.,  from  the  anterior  wall  at  the  level  of  fronto-nasal  suture  backwards  along  the  orbital  roof 
Exceptionally  large  sinuses  are  sometimes  met  with  extending  backwards  oA^er  the  orbit  so  as  to 
form  a  double  roof  to  that  space.  There  is  a  specimen  in  the  Oxford  collection  in  which  the 
sinus  is  so  large,  and  extends  so  far  back,  that  the  optic  nerve  is  carried  through  it  in  a  bony 
tube.  Another  point  of  some  practical  importance  is  that  the  sinuses  are  hardly  ever  sym- 
metrical. It  is  rare  to  meet  with  cases  of  their  complete  absence,  although  sometimes  the  sinus 
on  one  or  other  side  may  be  wanting. 

The  external  angular  process,  from  the  arrangement  of  its  surfaces  and  the  density  of  its 
structure,  is  particularly  well  adapted  to  resist  the  pi'essure  to  which  it  is  subjected  when  the 
jaws  are  firmly  closed. 

Variations. — That  most  frequently  met  with  is  a  persistence  of  the  suture  which  unites  the 
two  halves  of  the  bone  in  the  infantile  condition  :  skulLs  disj)laying  this  peculiarity  are  termed 
metopic.  The  researches  of  various  observers — Broca,  Eanke,  Gruber,  Manouvrier,  Anoutchine, 
and  Papillault  {Rev.  mens,  de  I'ecole  d' Anthro2)ol.  de  Paris,  annee  6,  n.  3) — ^^oint  to  the  more 
frequent  occurrence  of  this  metopic  suture  in  the  higher  than  in  the  lower  races  of  man ;  and 
Calmette  asserts  its  greater  frequence  in  the  brachycephalic  than  the  dolichocejjhalic  type. 
Separate  ossicles  (Wormian  bones)  may  occur  in  the  region  of  the  anterior  fontanelle.  The  fusion 
of  these  with  one  or  other  half  of  the  frontal  explains  how  the  metopic  suture  is  not  always  in 

line  with  the  sagittal  suture  (Stieda,  Anat.  Anz.  1897,  p. 
227) ;  they  occasionally  jjersist,  however,  and  form  by 
their  coalescence  a  bregmatic  bone  (G.  Zoja,  Bull. 
Scientifico,  xvii.  -p.  76,  Pavia).  Turner  {Ghallenger  Reports, 
part  xxix.)  records  an  instance  of  direct  articulation  of 
the  frontal  with  the  orbital  plate  of  the  sujjerior  maxilla 
in  a  Bush  skull,  and  other  examples  of  the  same  anomaly, 
which  obtains  normally  in  the  skulls  of  the  chimpanzee 
and  gorilla,  have  been  observed  {Jour.  Anat.  and  Physiol. 
vol.  xxiv.  p.  349). 

Schwalbe  (1901)  records  the  jjresence  of  small  inde- 
j)endent  ossicles  (supranasal  bones)  in  the  anterior  part 
of  the  metopic  suture.  The  same  anatomist  has  also 
recently  directed  attention  {Zeit.  f.  Morpli.  und  Anthr. 
vol.  iii.  p.  93)  to  the  existence  of  the  metoj)ic  fontanelle, 
first  described  by  Gerdy,  and  the  occurrence  of  metopic 
ossicles  (ossa  interfrontalia)  and  canals. 


Ossification. — Ossification  begins  in  membrane 
from  two  centres,  which  appear  about  tlie  sixth  or 
seventh  Aveek,  one  on  either  side  immediately  above 
the  orbital  margin.  From  these  the  two  halves  of 
the  frontal  part  of  the  bone  are  developed,  and  by 
extension  inwards  and  backwards  from  their  lower 
part  the  orbital  plates  are  also  formed.  Serres,  Rambaud,  and  Renault  and  v.  Ihering 
describe  the  occurrence  of  three  pairs  of  secondary  centres  somewhat  later :  one  pair 
for  the  nasal  spine  on  either  side  of  the  foramen  caecum  ;    a  centre  on   either  side  in 


Fig.  82. — Ossification  of  Frontal  Bone. 

a,  Metopic  suture  still  open,  b,  Position  of 
primary  centre.  c,  Centre  for  e.Yternal 
angular  iDrocess.  d,  Centre  for  region  of 
trochlea,     e,  Centres  for  nasal  spine. 


THE  PAEIETAL  BONES. 


107 


correspondence  with  the  position  of  each  trochlear  fossa ;  and  a  centre  for  each  external 
angular  process.  Fusion  between  these  secondary  and  the  primary  centres  is  usually 
complete  about  the  sixth  or  seventh  month  of  fojtal  life.  At  birth  the  two  symmetrical 
halves  of  the  bone  are  separated  by  the  metopic  suture,  obliteration  of  which  gradually 
takes  place,  so  that  about  the  fifth  or  sixth  year  it  is  more  or  less  completely  closed,  traces 
only  of  the  suture  being  left  above  and  below.  In  about  eight  per  cent  of  Europeans, 
however,  the  suture  persists  in  the  adult  (see  ante).  At  birth  the  supraorbital  notches 
lie  near  the  middle  of  the  supraorbital  arches. 

Traces  of  the  frontal  sinuses  may  be  met  with  about  the  second  year,  but  it  is  only 
about  the  age  of  seven  that  they  can  be  definitely  recognised.  From  that  time  they 
increase  in  size  till  the  age  of  puberty,  subsequent  to  which  time  they  attain  their  maxi- 
mum development. 


The  Paeietal  Bones. 

The  parietal  bones  (ossa  parietalia),  two  in  number,  are  placed  on  either  side 
of  the  vault  of  the  cranium,  articulating  with  the  frontal  anteriorly,  the  occipital 


Parietal  eminence 


Parietal 

foramen  /  \ 


Superior  temporal  line 


Inferior  temporal  line 


For  articulation  with 
great  wing  of  sphenoid 


For  articulation  with 
squamous  temporal 


]5'or  articulation  with  mastoid-temporal 
Fig.  83. — Eight  Parietal  Bone  (Outer  Side). 


posteriorly,  and  the  temporals  and  sphenoid  inferiorly.     Each  bone  possesses  an 
external  and  internal  surface,  four  borders,  and  four  angles. 

The  external  surface,  convex  from  above  downwards  and  from  before  backwards, 
displays  towards'its  centre  a  more  or  less  pronounced  elevation,  the  parietal  eminence 
(tuber  parietale).  This  marks  the  position  of  the  primitive  ossific  centre,  and  not 
unfrequently  corresponds  to  the  point  of  maximum  width  of  the  head.  At  a 
variable  distance  from  the  lower  bordcjr  of  the  bone,  and  more  or  less  parallel  to  it,  two 
curved  lines  can  usually  be  distinguished  ;  these  together  constitute  the  temporal  crest. 
The  superior  temporal  line  (\mvAi  temporalis  superior)  serves  for  the  attachment  of 
the  temporal  fascia ;  the  inferior  temporal  line  (linea  temporalis  inferior)  delines  the 
attachment  of  the  temporal  muscle,  the  extent  and  development  of  which  necessarily 
determinfis  the  position  of  tlie  crest.  Tlie  surface  below  the  crest  enters  into  the 
formation  of  the  floor  of  the  temporal  fossa,  and  is  called  the  planum  temporals;  it 
also  affords  origin  to  tin;  tem]joral  muscl(!,  find  is  often  faintly  marked  by  grooves 
wliich  indicate  the  course  of  the  middle  temporal  artery. 


108 


OSTEOLOGY. 


Above  the  superior  temporal  line  the  bone  is  covered  only  by  the  tissues  of  the 
scalp.  Near  its  upper  border,  and  about  an  inch  from  its  posterior  superior' angle, 
is  the  small  parietal  foramen  (foramen  parietale),  through  which  y^ass  a  small 
arteriole  and  an  emissary  vein. 

The  inner  or  cerebral  aspect  is  concave  from  side  to  side  and  from  above  down- 
wards, moulded  over  the  surface  of  portions  of  the  frontal,  parietal,  occipital,  and 
temporal  lobes  of  the  cerebrum,  it  displays  impressions  corresponding  to  the  arrange- 
ment of  the  convolutions  of  these  portions  of  the  brain.  It  also  presents  a  series 
of  well-marked  grooves  for  the  lodgment  of  the  branches  of  the  middle  meningeal 
artery ;  these  radiate  from  the  anterior  inferior  angle  of  the  bone,  the  best  marked 
running  upwards  at  some  little  distance  behind  and  parallel  to  its  anterior  border. 
Within  the  upper  margin  are  a  series  of  depressions  for  Pacchionian  bodies, 
and  here  also  the  bone  is  channelled  so  as  to  form  a  groove  (sulcus  sagittalis), 
which  is  completed  by  articulation  with  its  fellow  of  the  opposite  side.     Within 


Depressions  for  Paccliioiiian  bodiijs 


Anterior  interior  angle  Grooves  for  middle 

meningeal  artery- 
Groove  for  lateral  sinus 
Fig.  84. — Right  Parietal  Bone  (Inner  Surface). 

this  groove  lies  the  superior  longitudinal  venous  sinus,  and  to  its  edges  the  falx  cerebri 
is  attached.  Close  to  the  inferior  posterior  angle  there  is  also  a  curved  groove,  the 
lateral  sulcus,  in  which  the  lateral  venous  sinus  is  lodged. 

The  anterior,  superior,  and  -posterior  horders  are  deeply  serrated.  The  anterior 
articulates  with  the  frontal  bone,  and  constitutes  the  coronal  suture ;  the  posterior  is 
united  with  the  occipital  bone,  and  forms  the  lambdoid  suture.  The  superior  border 
articulates  with  its  fellow  of  the  opposite  side  by  means  of  the  sagittal  suture  ;  in 
the  interval  between  the  two  parietal  foramina  this  suture  is  usually  simple  in  its 
outline.  The  anterior  superior  angle  (angulus  frontalis)  is  almost  rectangular,  and 
corresponds  to  the  site  of  the  anterior  fontanelle.  The  -posterior  superior  angle 
(angulus  occipitalis),  usually  more  or  less  rounded,  corresponds  in  position  to  the 
posterior  fontanelle.  The  inferior  border  is  curved,  and  shorter  than  the  others ;  it 
lies  between  the  anterior  and  posterior  inferior  angles.  Sharp  and  bevelled  at  the 
expense  of  its  outer  table,  it  displays  a  fluted  arraugement,  and  articulates  with 
the  squamous  part  of  the  temporal  bone.     The  anterior  inferior  angle  (angulu^ 


THE  OCCIPITAL  BONE.  109 

sphenoiclalis),  pointed  and  prominent,  articulates  with  the  great  wing  of  the 
sphenoid.  It  is  wedged  into  the  angle  formed  by  the  union  of  that  bone  with  the 
frontal,  and  is  bevelled  at  the  expense  of  its  inner  table  anteriorly,  whilst  inferiorly 
it  is  thinned  at  the  expense  of  its  outer  table.  The  posterior  inferior  angle  (angulus 
mastoideus)  is  a  truncated  angle  lying  between  the  inferior  and  posterior  Ijorders. 
It  is  deeply  serrated,  and  articulates  with  the  mastoid  process  of  the  temporal  bone. 
Not  unfrequently  there  is  a  channel  in  this  suture  which  transmits  an  emissary  vein. 

Connexions.  —  The  parietal  bone  articulates  with  its  fellow,  with  the  frontal,  occij^ital, 
mastoid  and  squamous  temporal,  and  with  the  sphenoid.  Occasionally  the  inferior  angle  may 
not  reach  the  great  wing  of  the  sphenoid,  being  separated  from  it  by  the  articulation  of  the 
squamous  temporal  with  the  frontal  (see  also  p.  119). 

Architecture. — Thin  towards  its  lower  part,  where  it  enters  into  the  formation  of  the 
temporal  fossa,  it  is  thickest  along  the  superior  border  and  in  the  neighbourhood  of  the  posterior 
superior  angle. 

Variations. — A  number  of  cases  have  been  recorded  in  which  the  parietal  is  divided  into  an 
upper  and  lower  part  by  an  an tero -posterior  suture  parallel  to  the  sagittal  suture.  Coraini 
{AUi.  d.  XI.  Oongr.  Med.  Internaz.  Boma,  1894,  vol.  v.)  records  a  case  in  which  the  parietal  was  in- 
completely divided  into  an  anterior  and  posterior  part  by  a  vertical  suture.  The  parietal 
foramina  vary  greatly  in  size,  and  to  some  extent  in  position.  They  are  sometimes  absent  on  one 
or  other  side,  or  both.  They  correspond  in  position  to  the  sagittal  fontanelle.  Sometimes  the 
ossification  of  this  fontanelle  is  incomplete  and  a  small  transverse  fissure  remains.  The  parietal 
foramen  represents  the  patent  external  extremity  of  this  fissure  after  its  edges  have  coalesced. 
Occasionally  in  the  region  of  the  anterior  fontanelle  an  ossicle  of  variable  size  may  be  met  with. 
This  is  the  so-called  prae-interparietal  bone.  According  to  its  fusion  with  adjacent  bones  it 
may  disturb  the  direction  of  the  sagittal  suture. 

Ossification. — Ossification  takes  place  in  membrane  by  the  deposition  of  earthy 
matter,  the  centre  for  which,  most  probably  formed  by  the  coalescence  of  two  nuclei, 
appears  over  the  parietal  eminence  about  the  sixth  or  seventh  week  of  foetal  life  ;  from  this 
it  spreads  in  a  radial  manner  towards  the  edges  of  the  bone,  where,  however,  the  mem- 
branous condition  still  for  some  time  persists  constituting  the  fontanelles.  These  corre- 
spond in  position  to  the  angles  of  the  bone.  Ossification  is  also  somewhat  delayed  in 
the  region  of  the  parietal  foramina,  constituting  what  is  known  as  the  sagittal  fontanelle, 
a  membranous  interval  which  is  not  unfrequently  apparent  even  at  birth. 

The  Occipital  Bone. 

The  occipital  bone  (os  occipitale),  placed  at  the  back  and  lower  part  of  the 
cranium,  consists  of  three  parts,  arranged  around  a  large  oval  hole,  called  the 
occipital  foramen  or  foramen  magnum.  The  expanded  curved  plate  behind  the 
foramen  is  the  tabular  or  squamous  part.  The  thick  rod-like  portion  in  front  of  the 
foramen  is  the  basilar  process.  On  either  side  the  foramen  is  bounded  by  the 
lateral  or  condylic  portions. 

The  tabular  or  squamous  part  (squama  occipitalis)  in  shape  somewhat  resembles 
a  Gothic  arch,  and  is  curved  from  side  to  side  and  from  above  downwards.  It  forms 
inferiorly  a  small  portion  of  the  middle  of  the  posterior  boundary  of  the  foramen 
magnum,  and  unites  on  either  side  of  that  with  the  lateral  parts  of  the  bone.  About 
the  centre  of  the  external  surface  of  the  squama  there  is  a  prominence — the  external 
occipital  protuberance  (protuberantia  occipitalis  externa),  which  varies  considerably 
in  its  distinctness  and  projection,  and  serves  for  the  attachment  of  the  ligamentum 
nuchse.  From  the  protuberance  on  either  side  two  lines  curve  out  towards 
the  external  angles  of  the  bone.  These  are  known  respectively  as  the  highest  and 
superior  curved  lines  (linea  nuchse  suprema  and  linea  nuchse  superior).  To  the 
upper  of  these  the  epicranial  aponeurosis  is  attached,  whilst  the  lower  serves  for 
the  origin  of  the  trapezius  and  occipitalis  muscles  and  the  insertion  of  the  sterno- 
mastoid  and  splenius  capitis  muscles.  The  two  lines  together  serve  to  divide  the 
external  surface  of  the  tabular  part  into  an  upper  or  occipital  portion  (planum 
occipitale),  covered  by  the  hairy  seal])  and  a  lower  or  nuchal  part  (planum  nuchale) 
serving  for  the  attachment  of  the  fleshy  muscles  of  the  back  of  the  neck.  As  a  rule 
the  occi]Htal  part  bulges  backwards  beyond  tlie  external  occipital  protuberance ; 
exceptionally,  however,  the  latter  process  is  the  most  outstanding  part  of  the  bone. 

The  nuchal  plane,  irregular  and  rough,  is  divided  into  two  lateral  lialves  by  a 
median  ridge — tlie  external  occipital  crest  (linea  nuchte  mediana),  which  stretches 


110 


OSTEOLOGY. 


from  the  external  occipital  protuberance  above  to  the  posterior  border  of  the  foramen 
magnum  below.  Crossing  tlie  nuchal  plane  transversely,  about  its  middle,  is  the 
inferior  curved  line  (linea  nuchte  inferior),  which  passes  outwards  and  forwards  on 
either  side  towards  the  lateral  margins  of  the  bone.  The  areas  thus  marked  out 
serve  for  the  attachment  of  the  complexus,  obliquus  superior,  and  rectus  capitis 
posticus  major  and  minor  muscles. 

The  internal  surface  of  the  squama,  concave  from  side  to  side  and  from  above 
downwards,  is  subdivided  into  four  fossai  l)y  a  crucial  arrangement  of  ridges  and 
grooves.  The  upper  pair  of  fossae  lodges  the  occipital  lobes  of  the  cerebrum,  the 
lower  pair  the  lobes  of  the  cerebellum.  Near  the  centre  of  this  aspect  of  the  bone 
is  the  internal  occipital  protuberance  (protuberantia  occipitalis  interna),  an  irregular 
elevation,  the  sides  of  which  are  variously  channelled  according  to  the  disposition 
of  the  grooves.     Leading  from  this  to  the  hinder  margin  of  the  foramen  magnum 


Higliest  curved  lino 


External  occipital  protuberance 


Supei'jor  curved  line 


Inferior 

curved 

line 


Jugular  process 


Jugular  notch 


Condyle, 
Pharyngeal  tubercle 


Fig.  85. — Occipital  Bone  as  seen  from  Below. 


is  a  sharp  and  well-defined  ridge,  the  internal  occipital  crest  (crista  occipitalis 
interna),  which  serves  for  the  attachment  of  the  falx  cerebelli,  a  process  of  dura 
mater  which  separates  the  two  cerebellar  hendspheres.  Passing  upwards  from  the 
internal  occipital  protuberance  there  is  usually  a  well-marked  ridge,  to  one  or  other 
side  of  which,  more  frequently  the  right  (with  the  bone  in  the  normal  position  and 
viewed  from  behind),  there  is  a  well-defined  groove,  the  sulcus  sagittalis,  the  outer 
lip  of  which  is  generally  less  prominent.  Placed  in  this  groove  is  the  superior 
longitudinal  venous  sinus,  and  attached  to  the  lips  is  the  falx  cerebri.  At  right 
angles  to  the  foregoing,  and  at  the  level  of  the  internal  occipital  protuberance,  with 
which  they  become  confluent,  are  two  transverse  grooves,  the  sulci  transversi.  These 
grooves,  which  have  more  or  less  prominent  edges,  lie  between  the  upper  and  lower 
pairs  of  fossae,  and  serve  for  the  attachment  of  the  tentorium  cerebelli  as  well  as 
the  lodgment  of  the  lateral  blood-sinuses.  Commonly  the  right  lateral  groove  is 
confluent  with  the  groove  to  the  right  side  of  the  median  ridge,  but  exceptions  to 
this  rule  are  not  infrequent.     The  angle  formed  by  the  union  of  the  venous  sinuses 


THE  OCCIPITAL  BONE. 


Ill 


lodged  in  these  grooves  constitutes  the  torcular  Herophili,  which  may  accordingly 
be  placed  to  one  or  other  side  of  the  internal  occipital  protuberance,  more  frequently 
the  right ;  in  some  cases,  however,  it  may  occupy  a  central  position. 

The  superior  angle,  more  or  less  sharp  and  pointed,  is  wedged  in  between  the 
two  parietal  bones,  its  position  corresponding  to  the  site  of  the  posterior  fontanelle. 
The  lateral  angle  articulates  on  either  side  with  the  posterior  extremity  of  the 
mastoid  portion  of  the  temporal  bone.  The  superior  borders,  much  serrated,  articu- 
late with  the  parietal  bones  forming  the  lambdoid  suture ;  and  the  lateral  edges, 
extending  from  the  external  angles  to  the  jugular  process  inferiorly,  are  connected 
with  the  inner  sides  of  the  mastoid  portions  of  the  temporals. 

The  lateral  or  condylic  parts  of  the  occipital  bone  (partes  laterales)  are  placed 


For  superior  longitudinal  sinus  and  falx  cerebri 
Cerebral  fossa 


Superior  angle 


Internal  occipital 
jHotuberance 


For  lateral  sinus 
and  tentorium 


Lateral  angle 


Cerebellar  fossa 


Internal  occipital 
crest 


1  ~^  Jugular  process 


Posterior  condylic 
foramen 


Jugular  notch 
Groove  for  inferior  petrosal  sinus 


Basilar  process 
Fio.   86. — Occipital  Bone  (Inner  Surface). 


Basilar  groove 


on  either  side  of  the  foramen  magnum;  on  their  under  surface  they  bear  the 
condyles  (condyli  occipitales)  by  means  of  which  the  skull  articulates  with  the 
atlas  vertebra.  Of  elongated  oval  form,  the  condyles  are  so  disposed  that  their 
anterior  extremities,  in  line  with  the  anterior  margin  of  the  foramen  magnum,  lie 
closer  togetlier  than  tlieir  posterior  ends,  which  extend  as  far  back  as  the  middle  of 
the  external  Itorders  of  the  foramen.  Convex  from  before  backwards,  they  are 
skewed  so  that  their  surfaces,  which  are  nearly  plane  from  side  to  side,  are  directed 
slightly  outwards.  Each  is  supported  on  a  boss  of  bone,  pierced  by  the  anterior 
condylic  foramen  (canalis  hyp(jglossi),  which  opens  obliquely  from  within  outwards 
and  forwards  on  the  floor  of  a  fossa  called  the  anterior  condylic  fossa,  situated  just 
external  to  the  I'orc  part  of  the  condyle.  The  foramen  transmits  the  hypoglossal  or 
XII.  cranial  nerve;,  together  with  a  meningeal  brancli  oF  the  ascending  ]>haryngeal 
art(!ry  and  its  coni])anion  veins.  15(!liind  the;  cundyh;  is  ])la(;ed  the  posterior  condylic 
foBsa,  in  the  fiofjr  of  whicli  tlie  posterior  condylic  foramen  lieipKiiitly  opcnis.    Through 


112  OSTEOLOGY. 

this  a  vein  passes  which  joins  the  lateral  sinus.  The  edge  of  the  foramen  magnum 
immediately  behind  the  condyle  is  often  grooved  for  the  passage  of  the  vertebral 
artery  around  it.  Jutting  out  from  the  posterior  half  of  the  condyle  is  a  stout  bar 
of  bone,  serially  homologous  with  the  vertebral  transverse  process — this  is  the 
jugular  process  (processus  jugularis) ;  deeply  notched  in  front,  its  anterior  border 
is  free  and  rounded,  and  forms  the  posterior  boundary  of  the  jugular  foramen. 
Curving  outwards  from  this  margin,  in  line  with  the  anterior  condylic  foramen, 
there  is  often  a  small  pointed  projection,  the  processus  intra-jugulare,  which  serves 
to  divide  the  jugular  foramen  into  two  compartments.  Externally  the  jugular 
process  articulates  by  means  of  a  synchondrosis  with  the  jugular  surface  of  the 
petrous  part  of  the  temporal  bone.  Its  posterior  border  is  confluent  with  the  lower 
and  lateral  portion  of  the  occipital  squama,  and  its  under  surface  is  rough  and 
tubercular  for  the  attachment  of  the  rectus  capitis  lateralis  muscle.  The  superior 
aspect  of  the  lateral  part  displays  on  either  side  of  the  foramen  magnum  an  elevated 
surface  of  oval  form,  the  tuberculum  jugulare ;  this  corresponds  to  the  part  of  the 
bone  which  bridges  over  the  canal  for  the  hypoglossal  nerve.  Its  upper  surface  in 
many  instances  displays  an  oblique  groove  running  across  it ;  in  this  are  lodged  the 
glosso-pharyngeal,  vagus,  and  accessory  nerves.  The  jugular  process  is  deeply 
grooved  superiorly  for  the  lower  part  of  the  lateral  blood  sinus,  which  here  turns 
round  the  anterior  free  edge  of  the  process  into  the  jugular  foramen.  Joining  this, 
close  to  its  inner  edge,  is  the  opening  of  the  posterior  condyhc  foramen  when  that 
canal  exists. 

The  basilar  part  of  the  occipital  bone  (pars  basilaris)  extends  forwards  and 
upwards  from  the  foramen  magnum.  Its  anterior  extremity  is  usually  sawn  across, 
as,  after  adult  life,  it  is  necessary  to  sever  it  in  this  way  from  the  sphenoid,  the 
cartilage  uniting  the  two  bones  having  by  that  time  become  completely  ossified. 
Broad  and  thin  behind,  it  narrows  laterally  and  thickens  vertically  in  front,  where 
on  section  it  displays  a  quadrilateral  form.  Projecting  from  its  under  surface  some 
little  distance  in  front  of  the  foramen  magnum  is  the  pharyngeal  tubercle  (tuber- 
culum pharyngeum)  to  which  the  fibrous  raphe  of  the  pharynx  is  attached ;  on 
either  side  of  this  the  rectus  capitis  anticus  major  and  minor  muscles  are  inserted. 
The  upper  surface  forms  a  broad  and  shallow  groove  which  slopes  upwards  and 
forwards  from  the  thin  anterior  margin  of  the  foramen  magnum ;  in  this  rests  the 
medulla  oblongata.  On  either  side  its  lateral  edges  are  faintly  grooved  for  the 
inferior  petrosal  venous  sinuses,  below  which  the  lateral  aspect  of  the  bone  is  rough 
for  the  cartilage  which  unites  it  to  the  sides  and  apex  of  the  petrous  part  of  the 
temporal  bone. 

The  foramen  magnum,  of  oval  shape,  so  disposed  that  its  long  axis  lies  in  the 
sagittal  plane,  is  of  variable  size  and  form.  The  plane  of  its  outlet  differs  somewhat 
in  individual  skulls ;  in  most  instances  it  is  directed  downwards  and  slightly 
forwards.  In  front  the  condyles  encroach  upon  it,  and  narrow  to  some  extent  its 
transverse  diameter.  To  its  margins  are  attached  the  ligaments  which  unite  it 
with  the  atlas  and  axis.  Through  it  pass  the  lower  part  of  the  medulla  oblongata 
where  it  becomes  continuous  with  the  spinal  cord,  the  two  vertebral  arteries,  the 
spinal  accessory  nerves,  and  the  blood-vessels  of  the  meninges  of  the  upper  part  of 
the  cord. 

Connexions. — The  occipital  bone  articulates  witli  tlie  two  jaarietals  in  front  and  above,  witli 
tbe  sphenoid  in  front  and  below,  with  the  two  temporals  on  either  side,  and  with  the  atlas 
vertebra  by  means  of  its  condyles. 

Architecture. — The  squamous  part  displays  thickenings  in  the  position  of  the  various  ridges 
and  crests,  the  stoutest  part  corresponding  to  the  internal  and  external  occij^ital  protuberances, 
though  it  should  be  noted  that  the  two  protuberances  do  not  necessarily  coincide,  the  internal 
being,  as  a  rule,  placed  at  a  higher  level  than  the  external.  If  the  bone  be  held  up  to  the  light 
it  Avill  be  at  once  apparent  that  it  is  much  thinner  where  it  forms  the  floor  of  the  inferior  fossae 
than  in  the  uj^per  part.  The  basilar  portion  consists  of  a  sj^ongy  core  surroimded  by  a  more 
compact  outer  envelope,  thickest  on  its  lower  surface.  In  the  condyles  the  spongy  tissue  is 
arranged  radially  to  their  convex  articular  surfaces,  the  hypoglossal  canal  being  surrounded  by 
particularly  dense  and  compact  bone. 

Variations. — The  most  striking  of  the  many  A^ariations  to  which  this  bone  is  subject  is  the 
separation  of  the  upper  part  of  the  occipital  squama  to  form  an  indejjendent  bone — the  inter- 
parietal bone,  called  also,  from  the  frequency  of  its  occurrence  in  Peruvian  skulls,  the  os  Incse 


THE  OCCIPITAL  BONE. 


113 


As  will  be  seen  below  (see  Ossification),  the  occurrence  of  this  anomaly  is  explained  development- 
ally.  In  place  of  forming  a  single  bone  the  interjjarietal  is  occasionally  met  with  in  two 
symmetrical  halves,  and  instances  have  been  recorded  of  its  occurrence  in  three  or  even  four 
pieces.  In  the  latter  cases  the  two  anterior  parts  form  the  pre-interparietals.  Instances  are 
recorded  of  the  j^resence  of  a  separate  ejiiphysis  between  the  basi-occipital  and  the  sphenoid,  the 
OS  basioticum  (Albrecht)  or  the  os  prte-basi-occipital.  The  articular  surface  of  the  condyles  is 
sometimes  divided  into  an  anterior  and  posterior  part.  The  so-called  third  occipital  condyle  is 
an  outstanding  j^rocess  rising  from  the  anterior  border  of  tlie  foramen  magnum,  the  extremity  of 
which  articulates  with  the  odontoid  process  of  the  axis.  Guerri  has  recorded  a  case,  in  which  in 
a  foetal  skull,  there  were  two  outstanding  tubercles  in  the  position  of  the  third  occipital  condyle, 
indejoendent  of  the  basi-occipital  jaortions  of  the  condyles  (Anat.  Anz.  vol.  xix.  p.  42).  This 
appears  to  confirm  the  view  of  Macalister  that  there  are  two  different  structures  included 
under  this  name — one  a  mesial  ossification  in  the  sheath  of  the  notochord,  and  the  second,  a 
lateral,  usually  paired  process,  caused  by  the  deficiency  of  the  mesial  part  of  the  hypochordal 
element  of  the  hindmost  occipital  vertebra,  with  thickenings  of  the  lateral  parts  of  the  arch. 
Springing  from  the  under  surface  of  the  extremity  of  the  jugular  process,  a  rough  or  smooth 
elevated  surface,  or  else  a  projecting  process,  the  extremity  of  which  may  articulate  with  the 
transverse  process  of  the  atlas,  is  sometimes  met  with.  This  is  the  paroccipital  or  paramastoid 
process.  Numerous  instances  of  fusion  of  the  atlas  with  the  occipital  bone  have  been  recorded. 
Many  are,  no  doubt,  i^athological  in  their  origin  ;  others  are  associated  with  errors  in  development. 
Interesting  anomalies  are  these  in  which  there  is  evidence  of  the  intercalation  of  a  new  vertebral 
element  between  the  atlas  and  occipital,  constituting  what  is  termed  a  proatlas. 

Ossification. — The  major  part  of  the  bone  ossifies  in  cartilage,  the  upper  part  of  the 
squama  (interparietal),  alone  developing  in  membrane.  The  basilar  part  begins  to  ossify 
about  the  sixth  week  of  foetal  life  by  the  appeai'ance  of  two  centres,  one  in  front  of  the 
other;  the  anterior,  according  to  Albrecht,  constitutes  the  basiotic,  the  posterior  the 
basi-occipital.  These  two  centres — which  there  is  some  reason  to  believe — may  themselves 
be  formed  by  the  fusion  of  pairs  placed  laterally,  rapidly  tmite,  so  that  the  occurrence  of 
one  centre  alone  is  frequently  described.  From  this  the  fore  part  of  the  margin  of  the 
foramen  magnum  is  formed,  together  with  a  portion  of  the  anterior  end  of  the  occipital 
condyle  on  either  side.  It  helps  also  to  close  up  the  front  of  the  anterior  condylic  canal. 
Union  with  the  condylic  parts  is  complete  about 
the  fourth  or  fifth  year.  Ankylosis  between  the 
basi-occipital  and  the  sphenoid  takes  place  about  the 
twenty-fifth  year. 

The  lateral,  condylic,  or  exoccipital  parts  begin 
to  ossify  from  a  single  centre  about  the  end  of  the 
second  month  of  foetal  life.  The  notch  for  the 
hypoglossal  canal  appears  about  the  third  month. 
From  this  centre  is  formed  the  posterior  three- 
fourths  of  the  occipital  condyle.  The  exoccipital 
is  usually  completely  fused  with  the  squama  by 
the  third  year  or  earlier. 

As  already  noted,  the  squama  consists  of  two 
parts — the  one  above  the  occipital  crest,  the  other 
below  it :  the  former  develops  in  membrane,  the 
latter  in  cartilage.  In  a  three-months'  foetus  this 
difference  is  very  characteristic.  The  cartilaginous 
part  (supra-occipital)  begins  to  ossify  from  two  centres 
about  the  sixth  or  seventh  week,  which  rapidly  join 
to  form  an  elongated  strip  placed  transversely  in 
the  region  of  the  occipital  protuberance.  The 
centres  for  the  upper  part  (interparietal)  appear 
later.     According  to  Maggi  {Arch.  Ital.  Biol,  tome  '^' 

26,  fas.  2,  p.  301),  they  are  four  in  number,  of  Fio.  87.— Ossification  of  Occipital  Bone 
which  two  placed  on  either  side  of  the  middle  line 
appear  about  the  second  month.  The  other  pair, 
placed  laterally,  are  seen  about  the  third  month  ; 
fu.siou  between  these  takes  place  early,  but  their 
dispo.sition  and  arrangement  explain  the  anomalies 
to  which  this   part  of  the  bone    is  subject.      The 

mesial  pair  may  persist  as  separate  ossicles,  or  fuse  to  form  the  pre-interparietals,  whilst 
the  lateral  pair  may  remain  independent  of  the  supra-occipital  as  a  single  or  double 
interparietal  bone.  Union  between  the  supra-occipital  and  the  interparietal  elements 
occurs  about  the  third   or  fourth  niontli  ;  but  evidence  of  their  separation  is  frequently 


Basilar  centre  ;  b,  Exoccipital  ;  c,  Ossicle 
of  Kerkring  ;  d,  Supra-occiiiitid  (froiri  car- 
tilage) ;  e.  Fissure  between  siqtra-oecipital 
and  interparietal  ;  ,/;  Interparietal  (from 
iiienibraiie)  ;  //,  Fissure  between  inter- 
parietals. 


114  OSTEOLOGY. 

met  with  even  in  the  adult  by  the  persistence  of  a  transverse  suture  running  inwards 
from  each '  external  angle  of  the  squama,  or,  as  above  mentioned,  there  may  be  an  os 
Incse.  The  supra-occipital  forms  a  small  part  of  the  middle  of  the  hinder  border  of  the 
foramen  ■  magnum,  though  here  a  small  independent  centre,  known  as  the  ossicle  of 
Kerkring,  is  occasionally  met  with.  Other  independent  centres  ai-e  sometimes  seen 
between  the  supra-occipital  and  the  exoccipitals. 

At  birth  the  occipital    consists  of  four   parts — the  interparietal  and  supra-occipital 
combined,  the  basi-occipital,  and  the  exoccijjitals — one  on  either  side. 


The  Temporal  Bones. 

The  temporal  bone  (us  temporale)  lies  about  the  centre  of  the  lower  half  of  either 
side  of  the  skull,  and  enters  largely  into  the  formation  of  the  cranial  base.  It  is 
placed  betv^een  the  occipital  Ijehind,  the  parietal  above,  the  sphenoid  in  front,  and 
the  occipital  and  sphenoid  internally  and  below.  At  birth  it  consists  of  three 
parts — an  iipper  and  outer  part,  the  squamous  or  squamo-zygomatic  portion ;  an  inner 
and  posterior  portion,  the  petro-mastoid,  which  contains  the  parts  specially  associated 
with  the  sense  of  hearing,  together  with  the  organ  associated  with  equilibration; 
and  an  under  or  tympanic  part,  from  which  the  floor  aud  anterior  wall  of  the 
external  auditory  meatus  is  formed. 

The  squamous  part  (pars  squamosa)  consists  of  a  thin  shell-like  plate  of  bone 
placed  vertically,  having  an  inner  (cerebral)  and  an  outer  (temporal)  surface  and  a 
semicircular  upper  border.  Inferiorly,  behind,  and  internally  it  is  fused  in  early 
life  with  the  petro-mastoid  portion  by  means  of  the  squamoso-mastoid  and  the 
petro-squamosal  sutures,  traces  of  which  are  often  met  with  in  the  adult  bone ; 
whilst  below  and  in  front  it  is  separated  from  the  tympanic  and  petrous  parts  by 
the  Griaserian  fissure.  Its  external  surface,  smooth  and  slightly  convex,  enters  into 
the  formation  of  the  floor  of  the  temporal  fossa,  and  affords  attachment  to  the 
temporal  muscle.  Near  its  hinder  part  it  is  crossed  by  one  or  more  ascending 
grooves  for  the  branches  of  the  middle  temporal  artery.  In  front  and  below  there 
springs  from  it  the  zygomatic  process  (processus  zygomaticus).  This  arises  by  a 
broad  attachment,  the  surfaces  of  which  are  inferior  and  superior ;  curving  outwards 
and  forwards,  it  then  becomes  twisted  and  narrow  so  that  its  sides  are  turned 
inwards  and  outwards  and  its  edges  directed  upwards  and  downwards.  Anteriorly 
it  ends  in  an  obhque  serrated  extremity  which  articulates  with  the  zygomatic  pro- 
cess of  the  malar  bone.  Posteriorly  the  edges  of  the  zygomatic  process  separate  and 
are  termed  its  roots.  The  upper  edge,  which  becomes  the  posterior  root,  sweeps  back 
over  the  external  auditory  meatus,  and  is  confluent  with  a  ridge,  the  supra-mastoid 
crest,  which  curves  backwards  and  slightly  upwards,  and  serves  to  define  the  limit 
of  the  temporal  fossa  posteriorly.  The  inferior  edge  turns  inwards  and  constitutes 
the  anterior  root ;  the  under  surface  of  this  forms  a  transversely-disposed  rounded 
ridge,  the  articular  eminence  (tuberculum  articulare),  behind  which  there  is  a  deep 
hollow,  the  glenoid  fossa  (fossa  mandibularis),  limited  posteriorly  by  the  tympanic 
plate,  and  crossed  at  its  deepest  part  by  an  oblique  fissure,  the  Glaserian  fissure 
(fissura  petro-tympanica).  This  cleft,  which  is  closed  externally,  transmits  about 
its  middle  the  tympanic  branches  of  the  internal  maxillary  artery,  and  lodges  the 
slender  process  of  the  malleus.  At  its  inner  end  the  lips  of  this  fissure  are 
frequently  separated  by  a  thin  scale  of  bone,  a  downgrowth  from  the  tegmen 
tympani  of  the  petrous  part,  which  here  separates  the  tympanic  from  the  squamous 
elements,  forming  in  its  descent  the  major  part  of  the  outer  wall  of  the  osseous 
Eustachian  canal,  which  lies  immediately  internal  to  it.  Between  this  scale  of  bone 
and  the  posterior  edge  of  the  fissure  there  is  a  small  canal  (canal  of  Huguier),  which 
transmits  the  chorda  tympani  nerve.  The  part  of  the  glenoid  fossa  in  front  of  the 
fissure  articulates  with  the  condyle  of  the  inferior  maxilla,  through  the  medium 
of  the  interarticular  cartilage,  which  is  here  interposed  and  rests  as  well  on  the 
tuberculum  articulare.  Posteriorly  the  part  of  the  fossa  behind  the  fissure  is  non- 
articular  and  lodges  a  portion  of  the  parotid  gland.  At  the  angle  formed  by  the 
divergence  of  the  two  roots  of  the  zygoma,  in  correspondence  with  the  outer  part 
of  the  articular  eminence,  there  is  a  rounded  tubercle ;  to  this  are  attached  the 


THE  TEMPOEAL  BONES. 


115 


fibres  of  the  external  lateral  ligament  of  the  temporo-mandibular  joint.  In  front 
of  the  inner  end  of  the  articular  eminence  there  is  a  small  triangular  surface, 
limited  in  front  by  the  edge  of  the  anterior  root,  and  internally  by  a  thick  serrated 
margin  which  articulates  with  the  outer  side  of  the  great  wing  of  the  sphenoid ; 
this  area  forms  part  of  the  roof  of  the  zygomatic  fossa.  Just  anterior  to  the 
external  auditory  meatus  and  projecting  downwards  from  the  under  surface  of  the 
posterior  root  there  is  a  conical  process,  called  the  post-glenoid  tubercle,  which  forms 
a  prominent  anterior  lip  to  the  external  extremity  of  tlie  Glaserian  fissure ;  it  is  the 
representative  in  man  of  a  process  which  occurs  in  some  mammals  and  prevents  the 
backward  displacement  of  the  lower  jaw.  By  some  anatomists  it  is  referred  to  as 
the  middle  root  of  the  zygoma. 

The  zygomatic  process  by  its  lower  margin  and  inner  surface  gives  origin  to  the 
masseter  muscle,  whilst  attached  to  its  upper  edge  are  the  layers  of  the  temporal 
fascia.     Behind  the  external  auditory  meatus,  and  below  the  supramastoid  crest,  the 


Groove  for  middle 
temporal  artery' 


Supramastoid  ^-j 
crest^c^ 


Parietal  notch 


Temporal  surface 


Zygoma 


Remains  of 

masto-squamosal 

suture 


Eminentia  articularis 
Glenoid  fossa 


Mastoid  piocess 


External  auditory  meatus    Auricular  External  Process 
fissure     auditory 
process 

Styloid  process^ 


Fig.  88.— Right  Temporal  Bone  as  seen  from  the  Outer  Side. 

squamous  element  extends  downwards  as  a  pointed  process,  which  assists  in  forming 
the  roof  and  posterior  wall  of  the  external  auditory  meatus,  where  it  unites 
inferiorly  with  the  tympanic  plate.  In  the  adult  this  process  is  occasionally 
sharply  defined  posteriorly  by  an  oblique  irregular  fissure,  the  remams  of  the 
masto-squamosal  suture. 

Professor  Macewen  has  pointed  out  that  this  suture  frequently  remains  open  till 
puberty  and  occasionally  after,  and  may  be  of  iinportance  as  a  channel  along  which  in- 
fective processes  may  extend. 

The  inner  surface  of  the  squamous  part,  less  extensive  than  the  outer  aspect 
owing  to  the  bevelling  of  the  superior  border,  is  marked  by  the  impression  of  the 
convolutions  of  the  temporal  lobe  of  the  cerebrum,  and  is  limited  below  by  tlie 
petro-squamosal  suture,  the  remains  of  which  can  frequently  be  seen.  It  is  crossed 
in  front  by  an  ascending  groove  for  the  middle  meningeal  artery,  branches  from 
\vhi(;h  course  backwards  over  the  })ono  in  grooves  more  or  less  parallel  to  its  upper 
border. 

The  superior  harder  of  tb(;  squamous  part  is  curved,  shar]),  and  scalo-libs,  being 
bevelled  at  the  expense  of  its  inner  table,  except  in  front,  where  the  margin  is  thick 
\)a 


116 


OSTEOLOGY. 


and  stout.  Here  it  articulates  with  the  great  wing  of  the  sphenoid,  its  union  with 
that  hone  extending  to  near  the  fore  part  of  the  summit  of  the  curve,  behind  which 
it  is  united  to  the  parietal  overlapping  the  lower  border  of  that  bone ;  posteriorly 
the  free  margin  of  the  squamous  part  ends  at  an  angle  formed  between  it  and  the 
mastoid  process  called  the  incisura  parietalis. 

The  tympanic  part  (pars  tympanica)  of  the  temporal  bone  forms  the  anterior, 
lower  and  part  of  the  posterior  wall  of  the  external  auditory  meatus.  Bounded 
in  front  and  above  by  the  Glaserian  fissure,  it  forms  the  hinder  wall  ot  the  non- 
articular  part  of  the  glenoid  fossa.  Fused  internally  with  the  petrous  part,  its 
lower  edge,  sharp  and  well  defined  internally,  splits  to  enclose  the  root  ot  the 
proiectincf  styloid  process,  and  is  hence  called  the  vaginal  process.  Externally  it 
unites  wfth  the  fore  part  of  the  mastoid  process,  and  higher  up  with  the  descending 
process  of  the  squamous  part,  from  both  of  which  it  is  separated  by  the  auricular 
fissure  (fissura   tympano-mastoidea)  through  which   the  auricular  branch  oi  the 


Eminence  of  superior 
'        /  M'nuciieular  canal 


Groove  for  middle 
meningeal  artery  ~"~~;;~r^~^9 


^^la^.'s,.,-'  Parietal  notch 


Groove  for  superior 
XJetrosal  sinus 


Petro-squaraous  suture- 


Groove  for  inferior  petrosal  sinus 


Groove  for  lateral  sinus 


^Aqueduct  of  the  vestibule 
1  ii'i  :  ii.'il  auditory  meatus 
Aqueduct  of  the  cochlea 
Inner  surface  of  mastoid  process 
Styloid  process 


Fig.  89.— Right  Tempokal  Bone  (Inner  Side). 

vagus  escapes.  Its  free  border,  which  forms  the  anterior,  lower,  and  part  of  the 
posterior  border  of  the  external  auditory  meatus,  is  usually  somewhat  thickened 
and  rough,  and  serves  for  the  attachment  of  the  cartilaginous  part  of  the  canal. 

The  external  auditory  meatus  (meatus  acusticus  externus)  is  directed  obliquely 
inwards  and  a  little  forwards,  and  describes  a  slight  curve,  the  convexity  of  which 
is  directed  upwards  ;  of  oval  form,  its  long  axis,  close  to  its  orifice,  is  nearly  vertical, 
but,  as  it  passes  inwards,  inclines  somewhat  forwards  so  as  to  give  a  twist  to  the 
canal.  The  depth  of  the  canal  to  the  attachment  of  the  membrana  tympani 
averages  from  14  to  16  mm.  The  upper  margin  of  the  outer  orifice  overhangs 
considerably  the  lower  edge,  but  owing  to  the  obliquity  of  the  inner  aperture,  to 
which  the  membrana  tympani  is  attached,  the  upper  wall  of  the  osseous  canal 
only  exceeds  the  length  of  the  lower  wall  by  one  or  two  millimetres. 

The  petro-mastoid  part  (pars  petrosa  et  mastoidea)  of  the  temporal  bone,  of 
pyramidal  form,  is  fused  to  the  inner  aspect  of  the  tympanic  and  squamosal 
portions,  extending  behind  them,  however,  to  form  the  well-marked  and  prominent 
mastoid  process,  which  lies  posterior  to  the  external  auditory  meatus.  This  process 
(pars  mastoidea)  forms  a  nipple-like  projection,  the  size  of  which  differs  considerably 
in  different  individuals.     Usually  larger  in  the  male  than  in  the  female,  its  rough 


THE  TEMPOEAL  BONES.  117 

outer  surface  and  lower  border  serve  for  the  insertions  of  the  sterno-mastoid, 
splenius  capitis,  and  trachelo-mastoid  muscles.  Within  and  below  its  pointed 
extremity  there  is  a  deep  groove  (incisura  mastoidea),  usually  well  marked,  which 
gives  origin  to  the  posterior  belly  of  the  digastric  muscle ;  whilst  lying  to  the  inner 
side  of  this,  and  separated  from  it  by  a  more  or  less  well-defined  rough  ridge,  there 
can  oftentimes  be  seen  a  narrow,  shallow  furrow,  which  indicates  the  course  of  the 
occipital  artery.  The  inner  surface  of  the  mastoid  portion  forms,  in  part,  the  lateral 
wall  of  the  posterior  cranial  fossa,  in  which  the  cerebellar  lobes  are  lodged. 
Coursing  across  this  aspect  of  the  bone  there  is  a  broad  curved  groove,  the  con- 
vexity of  which  is  directed  forwards  and  lies  in  the  angle  formed  by  the  base  of  the 
petrous  part  and  its  fusion  with  the  mastoid  portion.  The  depth  to  which  the  bone 
is  here  channelled  varies  considerably,  and  is  important  from  a  surgical  standpoint, 
as  herein  lies  the  sigmoid  portion  of  the  lateral  venous  sinus.  Anteriorly  the 
mastoid  is  fused  with  the  descending  process  of  the  squamosal  above,  and  below, 
where  it  is  united  with  the  tympanic,  it  enters  into  the  formation  of  the  posterior 
wall  of  the  external  auditory  meatus  and  the  cavity  of  the  tympanum.  Above,  its 
free  margin  is  rough  and  serrated,  and  articulates  with  the  posterior  inferior  angle 
of  the  parietal;  behind  and  below  it  articulates  by  a  jagged  suture  with  the 
occipital.  Traversing  this  suture,  or  near  it,  is  the  mastoid  foramen  (foramen 
mastoideum),  which  transmits  a  vein  from  the  lateral  sinus  to  the  cutaneous 
occipital  vein,  together  with  a  small  branch  of  the  occipital  artery. 

The  petrous  part  of  the  petro-mastoid  is  of  the  form  of  an  elongated  three-sided 
pyramid.  By  its  base  it  is  united  obliquely  to  the  inner  sides  of  the  squamosal 
and  tympanic  parts.  Its  apex  is  directed  inwards,  forwards,  and  a  little  upwards. 
Its  three  surfaces  are  arranged  as  follows  : — The  superior  or  anterior  looks  upwards, 
slightly  forwards,  and  a  little  outwards,  and  forms  part  of  the  floor  of  the  middle 
cranial  fossa.  The  posterior  is  directed  backwards  and  inwards,  and  forms  part  of 
the  anterior  wall  of  the  posterior  cranial  fossa.  The  inferior  is  seen  on  the  under 
surface  of  the  base  of  the  skull,  and  is  directed  downwards.  The  borders  are  named 
respectively  anterior,  superior,  and  posterior. 

The  anterior  border  is  short,  and  forms  an  acute  angle  with  the  fore  part  of  the 
squamous  part;  within  this  angle  is  wedged  the  spinous  part  of  the  great  wing  of  the 
sphenoid.  Here,  too,  the  osseous  Eustachian  canal  (canalis  musculotubarius)  may  be 
seen  leading  backwards  and  outwards  from  the  summit  of  the  angle  to  reach  the 
fore  part  of  the  cavity  of  the  tympanum.  On  looking  into  it,  the  canal  is  seen  to 
be  divided  into  two  unequal  parts  by  an  osseous  partition,  the  cochleariform  process 
(septum  tubse).  The  upper  compartment,  the  smaller  of  the  two  (semicanalis 
m.  tensoris  tympani),  lodges  the  tensor  tympani  muscle,  whilst  the  lower  (semi- 
canalis tubse  auditivse)  forms  the  osseous  part  of  a  channel  (the  Eustachian  tube), 
which  serves  to  conduct  air  from  the  pharynx  to  the  tympanum. 

The  posterior  border  is  in  part  articular  and  in  part  non-articular.  Posteriorly 
and  externally  it  corresponds  to  the  upper  margin  of  an  area  on  the  inferior 
surface  with  which  the  extremity  of  the  jugular  process  of  the  exoccipital  articulates. 
In  front  of  that  it  is  irregularly  notched,  and  forms  the  free  anterior  edge  of  the 
jugular  foramen,  internal  to- which  it  has  a  sharp  curved  border,  often  grooved, 
reaching  to  the  apex.  This  groove,  which  is  completed  by  articulation  with  the 
outer  side  of  the  basi-occipital,  lodges  the  inferior  petrosal  venus  sinus. 

The  superior  harder  is  a  twisted  edge  which  is  continuous  with  the  upper  margin 
of  the  groove  for  the  lateral  sinus  posteriorly,  and  anteriorly  and  internally  reaches 
the  apex  of  the  bone.  Eunning  along  it  there  is  usually  a  well-marked  groove  for 
the  superior  petrosal  venous  sinus,  and  near  its  inner  extremity  it  is  slightly  notched 
for  the  passage  of  the  trigeminal  nerve.  Along  the  entire  length  of  this  border  the 
tentorium  cerebelli  is  attached. 

On  the  inferior  surface  of  the  petrous  part,  which  is  bounded  in  front  by  the 
anterior  border  intfsrnally,  and  the  tympanic  plate  externally,  and  behind  by  the 
]>ost(;rior  }>order,  the  following  structures  are  to  be  noted : — tSpringing  from  and 
ensheathed  by  the  vaginal  process  is  the  slender  and  pointed  styloid  process  (pro- 
cessus styloideus),  the  length  of  which  varies  mucli.  Projecting  downwards  and 
slightly  forwards  and  inwards,  it  affords  attachments  for  the  stylo-glossus, 
9& 


118 


OSTEOLOGY. 


Zygoma 


Zygomatic  surface 

Canal  for  chorda  tympani 
Eustachian  canal 
Carotid  canal 


Groove  for 
inferior 
jjetrosal  sinus 


stylo-hyoicl,  and  stylo-pharyngeus  muscles  as  well  as  the  stylo-hyoid  and  stylo- 
mandilnilar  ligaments.  Just  behind  it,  and  between  it  and  the  mastoid  process, 
is  the  stylo-mastoid  foramen  (foramen  stylomastoideum),  which  lies  at  the  anterior 
end  of  the  digastric  groove,  and  transmits  the  facial  nerve  and  the  stylo-mastoid 
artery.  Immediately  internal  to  the  styloid  process  there  is  a  deep,  smooth, 
excavated  hollow,  tlie  jugular  fossa  (fossa  jugnlaris),  which  is  converted  into  a 
foramen  (jugular)  by  articulation  with  the  occipital  bone.  Behind  and  external  to 
the  fossa  there  is  a  small  quadrilateral  surface  of  variable  size,  which  is  united  to 
the  extremity  of  the  jugular  process  of  the  exoccipital  by  a  synchondrosis.  Inside 
the  fossa,  on  its  outer  aspect,  or  placed  on  its  external  border,  is  the  opening  of  a 
small  canal  (canaliculus  mastoideus),  which  passes  outwards  to  open  into  the  can  alls 
faciahs,  and  transmits  the  auricular  branch  of  the  vagus  (Arnold's  nerve),  which 
ultimately  escapes   through   the  auricular  fissure   (see  ante).      In   front   of   the 

jugular  fossa  and  separated 
Temporal  surface  IVom  it  by  a  sliarp  crcst,  and 

just  internal  to  the  tympanic 
plate,  is  the  circular  opening 
of  the  inferior  orifice  of  the 
carotid  canal  (canalis  caroti- 
cus).  Directed  at  first  up- 
wards, this  canal  bends  at  a 
right  angle  and  turns  for- 
wards and  inwards,  lying 
parallel  to  the  anterior 
border ;  reaching  the  fore 
part  of  the  apex  of  the  bone, 
it  opens  in  front  by  an 
oblique  ragged  orifice. 
-Aqueduct  of  cochlea  ^hrough  the  caual  the  in- 

janal  for  Jacobson  s  o 

ternal  carotid  artery,  accom- 
panied by  a  plexus  of  sym- 
pathetic nerves,  passes  into 
the  cranium.  On  the  ridge 
of  bone  separating  the  jugular 
fossa  from  the  carotid  canal  is 
the  opening  of  a  small  canal 
(canaliculus  tympanicus), 
through  which  the  tympanic 
branch  of  the  glosso-pharyu- 
geal  (nerve  of  Jacobson) 
passes  to  reach  the  tym- 
panum. Within  the  orifice 
of  the  carotid  canal  another 
small  opening  or  openings  (canaliculi  carotici  tympanici)  may  be  noticed  which 
afford  passage  to  the  tympanic  branches  of  the  internal  carotid  artery  and  carotid 
sympathetic  plexus.  Occupying  the  interval  between  the  jugular  fossa  and 
the  carotid  canal  on  the  inner  side  is  a  V-shaped  depression  (fossula  fenestrte 
cochlese),  on  the  floor  of  which  and  close  to  the  posterior  border  is  the  orifice  of 
the  aqueduct  of  the  cochlea  (apertura  externa  aquseductus  cochleae).  In  the  fossa 
is  lodged  the  petrous  ganglion  of  the  glosso-pharyngeal  nerve,  and  the  aqueduct 
transmits  a  tubular  prolongation  of  the  dura  mater,  wliich  forms  a  channel  of 
communication  between  the  perilymph  of  the  cochlea  and  the  subarachnoid  space. 
A  small  vein  also  passes  through  it.  In  front  of  and  internal  to  the  orifice  of  the 
carotid  canal  the  under  surface  of  the  apex  of  the  bone  corresponds  to  a  rough 
quadrilateral  surface  which  forms  the  floor  of  the  carotid  canal,  and  also  serves  for 
the  attachment  of  the  cartilaginous  part  of  the  Eustachian  tube  as  well  as  the 
origin  of  the  levator  palati  muscle ;  elsewhere  it  has  attached  to  it  the  dense 
fibrous  tissue  which  fills  up  the  cleft  (petro-basilar  fissure)  between  it  and  the 
basilar  process  of  the  occipital  bone. 


Tubercle 


Eminentia 
articularr 
Glenoid  fobsa 

Glasenan  fissure 

Tympanic  plate 

Ext.  auditoiy  meatus 
Styloid  process 

Vaginal  process 

Auricular  Assure 

Stylo-mastoiil 

foramen 

Mastoid  process 
Digastric  groove 

Groove  foi 
occipital  artery 


nerve 
Jugular  fossa 


Canal  for  Ai-nold 
nerve 


■Jugular  surface 


Fig.  90. — Ric4ht  Temporal  Bone  as  seen  from  Below 


THE  TEMPOEAL  BONES.  119 

The  superior  or  anterior  surface  bears  the  impress  of  the  convolutions  of  the 
under  surface  of  the .  temporal  lobe  of  the  cerebrum,  which  rests  upon  it ;  in 
addition,  there  is  a  distinct  hut  shallow  depression  (impressio  trigemini)  near  the 
apex,  corresponding  to  the  roof  of  the  carotid  canal ;  in  this  is  lodged  the 
Gasserian  ganglion  on  the  sensory  root  of  the  V.  cranial  nerve.  External  to  the 
middle  of  the  upper  surface,  and  close  to  its  posterior  border,  is  the  elevation 
(eminentia  arcuata),  more  or  less  pronounced,  which  marks  the  position  of  the 
superior  semicircular  canal  here  lodged  within  the  bone.  A  little  in  front  of  this,  and 
in  line  with  the  angle  formed  by  the  anterior  border  and  the  squamous  part,  is  the 
slit-like  opening  of  the  hiatus  Fallopii  (hiatus  canalis  facialis),  within  the  projecting 
lip  of  which  two  small  orifices  can  usually  be  seen.  These  are  the  openings  of  the 
aciuseductus  Fallopii  (canalis  faciahs) ;  if  a  bristle  be  passed  through  the  inner  of  the 
two  openings  it  will  be  observed  to  pass  into  the  bottom  of  the  internal  auditory 
meatus,  if  into  the  outer,  it  will  pass  through  the  aqueduct  of  Fallopius,  and,  provided 
the  channel  be  clear,  will  appear  on  the  under  surface  of  the  bone  at  the  stylo- 
mastoid foramen.  Leading  forwards  and  inwards  from  the  hiatus  towards  the 
anterior  border  is  a  groove ;  in  this  lies  the  great  superficial  petrosal  nerve  which 
passes  out  of  the  hiatus.  A  small  branch  of  the  middle  meningeal  artery  also 
enters  the  bone  here.  A  little  external  to  the  hiatus  is  another  small  opening 
(apertura  superior  canahs  tympanici),  often  difficult  to  see  ;  from  this  a  groove  runs 
forwards  which  channels  the  upper  surface  of  the  roof  of  the  canal  for  the  tensor 
tympani  muscle.  Through  this  foramen  and  along  this  groove  passes  the  lesser 
superficial  petrosal  nerve.  Behind  this,  and  in  front  of  the  arcuate  eminence,  the 
bone  is  usually  thin  (as  may  be  seen  by  holding  it  up  to  the  light  falling  through 
the  external  auditory  meatus),  roofing  in  the  cavity  of  the  tympanum  and  forming 
the  tegmen  tympani.  Externally  the  line  of  fusion  of  the  petrous  with  the  squamous 
part  is  often  indicated  by  a  faint  and  irregular  petro-squamous  fissure. 

The  most  conspicuous  object  on  the  posterior  surface  of  the  petrous  part  of  the 
bone  is  the  internal  auditory  meatus  (meatus  acusticus  internus)  about  8  mm.  deep 
in  the  adult,  which  has  an  obhque  oval  aperture  and  leads  outwards  and  slightly 
downwards  into  the  substance  of  the  bone,  giving  passage  to  the  auditory  and 
facial  nerves,  together  with  the  pars  intermedia  and  the  auditory  branch  of  the 
basilar  artery.  The  canal  appears  to  end  blindly ;  but  if  it  be  large,  or  still  better,  if 
part  of  it  be  cut  away,  its  fundus  will  be  seen  to  be  crossed  by  a  horizontal  ridge,  the 
falciform  crest,  which  divides  it  into  two  fossse,  the  floors  of  which  (laminae  cribrosse) 
are  pierced  by  numerous  small  foramina  for  the  branches  of  the  auditory  nerve  and 
the  vessels  passing  to  the  membranous  labyrinth,  whilst  in  the  fore  and  upper  part 
of  the  higher  fossa  the  orifice  of  the  Fallopian  aqueduct  (canalis  facialis),  through 
which  the  facial  nerve  passes,  is  seen  leading  in  the  direction  of  the  hiatus  Fallopii 
(see  ante).  External  to  the  internal  auditory  meatus  and  above  it,  close  to  the 
superior  border,  an  irregular  depression,  often  faintly  marked,  with  one  or  two  small 
foramina  opening  into  it,  is  to  be  noticed.  This  is  the  floccular  fossa  (fossa  subarcuata), 
best  seen  in  young  bones,  where  it  forms  a  distinct  recess,  which  is  bounded  above 
by  the  bulging  caused  by  the  superior  semicircular  canal,  within  the  concavity  of 
which  it  is  placed  ;  it  lodges  a  process  of  the  dura  mater.  Below  and  external  to 
this,  separated  from  it  by  a  smooth,  elevated  curved  ridge,  is  the  opening  of  the 
aqueduct  of  the  vestibule  (apertura  externa  aqu^eductus  vestibuli),  often  concealed 
in  a  narrow  curved  fissure  overhung  by  a  sharp  scale  of  bone.  In  this  is  lodged  the 
saccus  endolymphaticus.  The  ridge  above  it  corresponds  to  the  upper  half  of  the 
posterior  semicircular  canal. 

Connexions. — Tlie  temporal  lK))ie  tu'ticulates  witli  tlie  malar,  sphenoid,  parietal,  and  occipital 
liones,  and  by  a  movable  joint  witli  the  inferior  maxilla.  Occasionally  the  temporal  articulates 
with  the  frontal,  as  happens  noi'inally  in  tlie  anthropoid  apes ;  although  the  region  of  the 
plerion  (see  p.  1.04)  is  cliaracterised  by  an  X-like  form  in  the  lower  races  of  man  there  is  no 
evidence  that  the  occurrence  of  a  fronto-squamosal  suture  is  more  frerinent  in  the  lower  than  the 
liiglier  races,  its  occurnnice  being  due  to  the  manner  of  fusion  of  the  so-called  ejiipteric  ossicles 
with  the  surrounding  Ijones. 

Architecture. — Tlie  temporal  bone  is  remarkable  for  the  liardn(!ss  and  d(;nsity  of  its  petrous 
part,  wlierein  is  lodgr;d  the  osseous  hibyi'intli  wliirli  contains  tlie  delicate  organs  associated  with 
the  senses  ni  lieariiig  and  efpiilibration.     Tlie  middle  ear  or  tympanum  is  a  cavity  which  contains 


120 


OSTEOLOGY. 


the  small  auditory  ossicles,  and  is  separated  from  the  external  auditory  meatus  by  the  membrana 
tympani.  In  front  it  communicates  witli  tlie  pharynx  by  the  Eustachian  tube;  behind,  it  opens 
into  the  mastoid  antrum  and  mastoid  air-cells  by  the  aditus  ad  antrum.      Siq^eriorhj,  it  is 

separated  from  the  middle  cranial  fossa  by  a 
thin  plate  of  bone  called  the  tegmen  tympani. 
Inferiorly,  its  lioor  is  formed  in  jjart  by  the 
roof  of  the  jugular  fossa  and  the  carotid  canal. 
Internally,  it  is  related  to  the  structures  wliich 
form  the  inner  ear,  notably  the  cochlea  and 
vestibule,  in  front  of  which  it  is  separated  by  a 
thin  plate  of  bone  from  the  caiotid  canal. 
Curving  OA'er  the  cavity  of  the  tymj^anum  is 
the  aquDeductus  Fallopii,  the  thin  walls  of 
which  are  occasionally  deficient.  These  details 
will  be  further  dealt  with  in  the  section  de- 
voted to  the  Organs  of  Sense. 

Variations. — The  occurrence  of  a  deficiency 
in  the  floor  of  the  external  auditory  meatus  is 
not  uncommon  in  the  adult.  It  is  met  M'ith 
commonly  in  the  child  till  about 
the  age  of  five,  and  is  due  to  incom- 
plete ossification  of  the  tjanpanic 
plate.  The  line  of  the  petro- 
squamosal  suture  is  occasionally 
grooved  for  the  lodgment  of  a  sinus 
(petro-squamosal) ;  sometimes  the 
posterior  end  of  this  is  continuous 
with  a  canal  which  pierces  the 
superior  border  of  the  bone  and 
opens  into  the  lateral  sinus.  An- 
teriorly the  groove  may  pass  into 
a  canal  which  pierces  the  root  of 
the  zygoma  and  ajsj^ears  externally 
above  the  external  extremity  of  the  Glaserian  fissure.  These  are  the  remains  of  channels  through 
which  the  blood  passed  in  the  foetal  condition  (see  cmte).  Symington  has  described  a  case  in 
which  the  squamous  part  was  distinct  and  separate  from  the  rest  of  the 
temjjoral  bone  in  an  adult ;  whilst  Hyrtl  has  observed  the  division  of 
the  temjjoral  squama  into  two  by  a  transverse  suture.  P.  P.  Laidlaw 
{Journ.  Anat.  and  Physiol,  vol.  xxxvii.  p.  364)  describes  a  temporal  bone 
in  which  there  was  absence  of  the  internal  auditory  meatus  and  of  the 
stylo-mastoid  foramen.  The  jugular  fossa  also  was  absent,  and  there 
was  partial  absence  of  the  groove  for  the  lateral  sinus  associated  with 
the  presence  of  a  large  mastoid  foramen.  An  instance  of  a  rudimentary 
condition  of  the  carotid  canal  is  also  referred  to  in  the  same  volume  by 
G.  H.  K.  Macalister. 

G.  Caribbe  {Anat.  Anz.  vol.  XX.  External  semicircular  canal 

p.  81)  notes  the  occurrence  in  idiots 
and  imbeciles  of  a  more  pronounced 
form  of  j)ost-glenoid  tubercle,  and 
associates  it  with  regressive  changes 
in  the  develoj^ment  of  the  temporal 
bone. 


External  auditoiy 

meatus 

Osseous  Eustachian 

canal 


Superior  opening  of  the  canal  for  the 
tympanic  branch  of  glosso-pharyngeal 


\  estibule 
Aqu.Liluctus  Fallopii 
Fenestia  o^alls  cut  across 
Fenestra  rotunda  cut  across 


Fig. 


91. — Vertical  Transverse  Section  through  Left 
Temporal  Bone  (Anterior  Half  of  Section). 


Superior  semicircular 
canal 


Ossification.  —  The  petro- 


Fenestra  ovalis. 
cut  across 
P'enestra  rotunda 
cut  across 


Vestibule  into 

openings  ol 

semicircular  canals 

mastoid  portion  of  the  bone-  is  auditory  meatus 
developed  by  the  deposition  of 
earthy  matter  in  the  cartila- 
ginous ear  capsule  and  the  peri- 
chondrium lining  the  labyrinth. 
The  squamous  and  tympanic 
parts  are  ossified  in  membrane. 
Ossification  commences  in 
the  ear  capsule  in  the  fifth 
month,  and  proceeds  so  rapidly 
that   by  the  end    of    the  sixth 

month  the  individual  centres  are  more  or  less  fused.  Of  these,  one  which  appears  ni 
the  vicinity  of  the  eminentia  arcuata  is  the  most  definite  in  position' and  form;  from 
this  a  lamina  of  bone  of  spiral  form  is  developed,  which  covers  in  the  inner  limb  of 
the  superior  semicircular  canal,  and  forms  the  roof  of  the  internal  auditory  meatus, 
together  with  the  commencement  of  the  Fallopian  aqueduct.  Reaching  forwards,  it 
extends  to  the  apex  of  the  petrous  part;    whilst  externally  it  forms  part  of  the  inner 


Opening  leading 
into  mastoid 
antrum. 

„.    Aquicductus 

/'  Fallopii 

J — ^Canalis  stapedii 

Tympanum 

External 
auditory  nieat\is 


Fig.  92.— Vertical  Transverse  Section  through  Left 
Temporal  Bone  (Posterior  Half  of  Sectiou). 


THE  TEMPOEAL  BONES. 


121 


styloid  process 
broken  otf 


Glenoid  fossa 

Groove  for 

membrana 

tympani 

Extei'ual 

auditory 

meatus 

Mastoid  air-cells 


Carotid  canal 


Tyinpanuni 


Cochlea 

Internal  auditory 
meatus 
Vestibule,  fenestra 
ovalis  cut  across 
Superior  semicircular 
canals 

AqucCductus  Falloxni 


External  semicircular  canal 


Fig. 


93. — Horizontal  Section  through  Left  Temporal  Bone 
(Lower  Half  of  Sectiou). 


wall  of  the  tympanum,  surrounds  the  fenestra  ovalis,  and  encloses  within  its  substance 
portions   of    the  cochlea,  vestibule,  and   superior   semicircular   canal.       Another   centre 
appears  in  the   vicinity  of  the 
promontory  on  the   inner  wall  /^' 

of  the  tympanum,  surrounds  the  /     /     Osseous  Eustacliian  canal 

fenestra  rotunda,  forms  the  floor  ■'   ' 

of   the    vestibule,   and    extends 

inwards    to  complete   the    floor 

of  the  internal  auditory  meatus. 

Surrounding    the    cochlea    in- 

feriorly  and  externally,  it  com- 
pletes the  floor  of  the  tympanum, 

and  ultimately  blends  with  the 

fore    and    under    part    of    the 

tympanic    ring.       The    carotid 

canal  at  first  grooves  it,  and  is 

then    subsequently    surrounded 

by  it.     According  to  Lambertz 

the  lamina  spiralis  of  the  cochlea 

ossifies  in  membrane.     The  roof 

of  the  tympanum  is  formed  from 

a  separate  centre,  which  extends 

backwards  towards  the  superior 

semicircular  canal,  and  encloses 

the  tympanic  part  of  the  aque- 
duct  of    Fallopius ;    externally 

this  centre  unites  by  suture  with 

the  squamosal,  and  sends  down 

a  thin   process,  which    appears 

between  the  lips  of  the  Glaserian 

fissure,  and  forms  the  outer  wall 
of  the  Eustachian  tube.  Nuclei, 
either  single  or  multiple,  appear  in  the  base  of  the  petrous  part,  and  envelop  the  posterior 
and  external  semicircular  canals.  It  is  by  extension  from  this  part  that  the  mastoid  process 
is  ultimately  developed.  To  these  centres  the  terms  pro-otic,  opisthotic,  pterotic,  and 
epiotic,  respectively,  have  been  applied  by  Huxley  and  others.  The  styloid  process,  an 
independent  development  from  the  upper  end  of  the  cartilage  of  the  second  visceral  arch, 
is  ossified  from  two  centres.  The  upper  or  basal  appears  before  birth,  and  rapidly  unites 
with  the  petro-mastoid,  the  tympanic  plate  encircling  it  in  front.  This  represents  the 
tympanohyal  of  comparative  anatomy.  At  birth,  or  subsequent  to  it,  another  centre 
appears  in  the  cartilage  below  the  above  :  this  is  the  stylohyal.  Ankylosis  usually  occurs 
in  adult  life  between  the  tympanohyal  and  stylohyal,  the  union  of  the  two  constituting 
the  so-called  styloid  process  of  human  anatomy. 

The  centre  from  which  the  squamo-zygomatic  develops  appears  in  membrane  about 
the  end  of  the  second  month.  Situated  near  the  I'oot  of  the  zygoma,  it  extends  forwards 
and  outwards  into  that  process,  inwards  to  form  the  floor  of  the  glenoid  fossa,  and 
upwards  into  the  squamosal.  From  this  latter  there  is  a  downward  and  backward  exten- 
sion, which  forms  the  post-auditory  process  ;  this  ultimately  blends  with  the  posterior  limb 
of  the  tympanic  ring,  being  separated  from  it  in  the  adult  by  the  auricular  fissure.  It  forms 
the  outer  wall  of  the  mastoid  antrum,  and  constitutes  the  fore  and  upper  part  of  the 
mastoid  process  in  the  adult.  About  the  third  month  a  centre  appears  in  the  outer 
membranous  wall  of  the  tympanum  :  from  this  the  tympanic  ring  is  developed.  Incom- 
plete above,  it  displays  two  free  extremities.  Of  these,  the  anterior  is  somewhat  enlarged, 
and  unites  in  front  with  the  glenoid  portion  of  the  squamo-zygomatic,  being  separated 
from  it  by  the  Glaserian  fissure  and  the  downgrov/th  from  the  tegmen  tympani  ;  the 
posterior  joins  the  post-auditory  process  of  the  squamo-zygomatic  above  mentioned. 
Below,  it  blends  internally  with  the  portion  of  the  pctro-mastoid  which  forms  the  floor  of 
the  tympanum,  and  enshcathcs  the  tympanohyal  behind.  From  the  outer  side  of  the 
lower  part  of  this  ring  two  tubercles  arise ;  these  grow  outwards,  and  so  form  the  floor 
of  the  external  auditory  meatus.  '^J'he  interval  between  them  remains  vuiossificd  till 
aljoiit  the  age  of  five  or  six,  after  which  closure  takes  place.  This  deficiency  may,  how- 
ever, persist  even  in  adult  life  (see  ante,  Variations). 

At  birth  the  temporal   bone  can  usually  be  separated  into  its  component  parts.     The 


122 


OSTEOLOGY. 


outer  surface  of  the  petrous  part  not  only  forms  the  inner  wall  of  the  tympanum,  but  is 
hollowed  out  behind  and  above  to  form  the  inner  side  of  the  mastoid  antrum,  the 
outer  wall  of  which  is  completed  by  the  post-auditoiy  process  of  the  squamo-zj^gomatic. 
As  yet  the  mastoid  process  is  undeveloped.  It  only  assumes  its  nipple-like  form  about  the 
second  year.     Towards  puberty  its  cancellous  tissue  becomes  permeated  with  air  spaces, 


Fig.  94. — a.  The  Outer  SaRFACE  of  the  Eight  Temporal  Bone  at 
Birth.     B.  The  same  with  Squamo-zygomatic  Portion  Removed. 

(The  lettering  is  tlie  same  in  both  A  and  B.)  a,  Tympanic  ring,  b,  Inner  wall 
of  tympanum,  c,  Fenestra  rotunda,  d,  Foramen  ovale,  e,  Mastoid. 
/,  Mastoid  process.  g.  Masto- squamosal  suture,  with  foramen  for 
transmission  of  vessels.  A,  Squamo-zygomatic,  removed  in  figure  B  to 
show  how  its  descending  process  forms  the  outer  wall  of  the  mastoid 
antrum. 


Fig.  94. — C.  Inner  Surface  of  the 
Eight  Temporal  Bone  at  Birth. 

a,  Squamo-zygomatic.  b,  Petro- 
squamosal  suture  and  foramen  (just 
above  the  end  of  the  lead  line). 
f,  Subarcuate  fossa,  d,  Aqufeductus 
vestibuli.  e,  Aquseductus  cochlete. 
/,  Internal  auditory  meatus.  g. 
Upper  end  of  carotid  canal. 


which  are  in  communication  with  and  extensions  from  the  mastoid  antrum.  The  external 
auditory  meatus  is  unossified  in  front  and  below,  the  outgrowth  from  the  tympanic  ring 
occurring  subsequent  to  birth.  The  glenoid  fossa  is  shallow  and  everted ;  the  jugular 
fossa  is  ill-marked  ;  whilst  the  subarcuate  fossa  is  represented  by  a  deep  pit,  the  so-called 
floccular  fossa  of  comparative  anatomy.  The  hiatus  Fallopii  is  an  open  groove,  displaying 
at  either  end  the  openings  of  the  inner  and  outer  portions  of  the  Fallopian  aqueduct. 


The  Sphenoid  Bone. 

The  sphenoid  bone  (os  sphenoidale)  lies  in  front  of  the  basi-occipital  mesially, 
and  the  temporals  on  either  side.  It  enters  into  the  formation  of  the  cranial, 
orbital,  and  nasal  cavities,  as  well  as  the  temporal,  zygomatic,  pterygoid,  and 
spheno-maxillary  fossae.  It  consists  of  a  body  with  three  pairs  of  expanded  pro- 
cesses, the  great  wings,  the  lesser  wings,  and  the  pterygoid  processes. 

The  body  (corpus),  more  or  less  cubical  in  form,  is  hollow,  and  contains  within 
it  the  two  large  sphenoidal  air  sinuses.  These  are  separated  by  a  partition,  which 
is  usually  deflected  to  one  or  other  side  of  the  middle  line.  Each  sinus  extends 
outwards  for  a  short  distance  into  the  root  of  the  great  wing,  and  downwards  and 
outwards  towards  the  base  of  the  pterygoid  process  of  the  same  side.  They 
communicate  by  apertures  with  the  upper  and  back  part  of  the  nasal  fossae.  In  the 
adult  the  j^osterior  aspect  of  the  body  displays  a  sawn  surface  due  to  its  separation 
from  the  basi-occipital  with  which  in  the  adult  it  is  firmly  ankylosed.  The  sujperior 
surface,  from  the  fore  angles  of  which  the  lesser  wings  arise,  displays  an  appearance 
comparal:)le  to  that  of  an  oriental  saddle,  over  its  middle  there  is  a  deep  depression, 
the  sella  turcica  or  pituitary  fossa  (fossa  hypophyseos),  in  which  is  lodged  the 
pituitary  l;)ody.  Behind,  this  is  overhung  by  a  sloping  ridge,  the  dorsum  sella,  the 
posterior  surface  of  which  is  inclined  upwards,  and  is  in  continuation  with  the 
basilar  groove  of  the  occipital  bone.  Anteriorly  and  externally  the  angles  of  this 
ridge  project  over  the  pituitary  fossa  in  the  form  of  prominent  tubercles,  called  the 
posterior  clinoid  processes  (processus  clinoidei  posteriores).  In  front  of  the  pituitary 
fossa  there  is  a  transverse  elevation,  the  olivary  eminence  (tuberculum  sellae), 
towards  the  outer  extremities  of  which,  and  somewhat  behind,  there  are  often- 


THE  SPHENOID  BONE. 


123 


times  little  spurs  of  bone,  the  middle  clinoid  processes  rprocessus  clinoidei  ruediij. 
In  front  of  the  olivary  eminence  is  the  optic  groove  (sulcus  chiasmatis),  which 
passes  outwards  on  either  side  to  become  continuous,  between  the  roots  of  the 
lesser  wings,  with  the  optic  foramina. 


Foramen 
rotunduni 
Groove  for 
Eubtachiaii  tube 

Vidian  canal 


External  pterygoid  plate  - 


Internal  pterygoid  plate 


Pterygoid  notch 


Hainular  process 
Fig.  95. — Sphenoid  as  seen  from  Behind. 


Tliis  groove  is  Hal  ile  to  considerable  variations,  and  apparently  does  not  always  serve  for  the 
lodgment  of  the  optic  chiasma.  (Lawrence,  "  Proc.  Soc.  Anat.,"  Journ.  Anat.  and  Physiol. 
vol.  xxviii.  p.  18.) 

In  front  of  the  optic  groove,  from  which  it  is  often  separated  by  a  thin  sharp  edge, 
the  superior  surface  continues  forwards  on  the  same  plane  as  the  upper  surfaces  of 


Oi  bital  surface 

Infra  temporal  crest 

^   Spine 
Spheno-maxiUary  surface 

External  pterygoid  plate 


laiiiiilar  process  of 
nternal  jjteiygoid  plato 


Pterygoid  notcl 

Fig.  96. — Sphenoid  as  shen  khom  the  Front. 

the  IcHHfir  wings,  and  terminates  anteriorly  in  a  ragged  edge,  wliich  articulates  with 
the  cribriform  plate  of  the  ethmoid,  and  has  often  projecting  from  it,  mesially,  a 
pointed  process,  the  ethmoidal  spine.  The  lateral  aspects  of  the  body  are  fused 
with  the  great  wings,  and  in  ])art  also  with  the  roots  of  the  pterygoid  processes. 
Curving  along  the  side  of  the  body,  sii])erior  to  its  attachment  to  the  great  wing, 
is  an    jT-sliaped  groove,  the  carotid  groove   (sulcus  caroticus),   which   marks  the 


124  OSTEOLOGY. 

position  and  course  of  the  internal  carotid  artery.  Posteriorly,  the  hinder  margin 
of  this  groove,  formed  by  the  salient  outer  edge  of  the  posterior  surface  of  the 
body,  articulates  with  the  apex  of  the  petrous  portion  of  the  temporal  bone,  and 
is  hence  called  the  petrosal  process ;  just  above  this,  on  the  lateral  border  of  the 
dorsum  sellae,  there  is  often  a  groove  for  the  sixth  nerve. 

The  anterior  surface  of  the  body  displays  a  vertical  mesial  sphenoidal  crest 
(crista  sphenoidalis),  continuous  above  with  the  ethmoidal  syjine,  and  below  with 
the  pointed  projection  called  the  rostrum.  This  crest  articulates  in  front  with  the 
perpendicular  plate  of  the  ethmoid.  On  either  side  of  the  middle  line  are  seen  the 
irregular  openings  leading  into  the  sphenoidal  air  sinuses,  the  thin  anterior  walls 
of  which  are  in  part  formed  by  the  absorption  of  the  sphenoidal  turbinated  bones 
with  which  in  early  life  they  are  in  contact.  With  the  exception  of  a  broad  groove 
leading  downwards  from  the  apertures  above  mentioned,  which  enters  into  the 
formation  of  the  roof  of  the  nasal  fossa  of  the  corresponding  side,  the  lateral 
aspects  of  this  surface  of  the  bone  are  elsewhere  in  articulation  with  the  lateral 
masses  of  the  ethmoid  and  the  orbital  processes  of  the  palate  bones.  The  rostrum 
is  continued  mesially  for  some  distance  along  the  inferior  surface  of  the  body, 
where  it  forms  a  prominent  keel  which  fits  into  the  recess  formed  by  the  al£e  of 
the  vomer.  The  edges  of  the  latter  serve  to  separate  the  rostrum  from  the  incurved 
vaginal  processes  at  the  roots  of  the  internal  pterygoid  plates.  Posteriorly  the 
under  surface  of  the  body  of  the  sphenoid  is  rougher,  and  covered  by  the  mucous 
membrane  of  the  roof  of  the  pharynx ;  here,  occasionally,  a  median  depression  may 
be  seen  which  marks  the  position  of  the  inferior  extremity  of  a  foetal  channel, 
called  the  canalis  cranio -pharyngeus. 

The  lesser  or  orbital  wings  (alee  parvse)  are  two  flattened  triangular  plates  of 
bone  which  project  forwards  and  outwards  from  the  fore  and  upper  part  of  the 
body  of  the  bone,  with  which  they  are  united  by  two  roots  which  enclose  between 
them  the  optic  foramina  (foramina  optica)  for  the  transmission  of  the  optic  nerves 
and  ophthalmic  arteries.  Of  these  roots,  the  posterior  springs  from  the  body  just 
wide  of  the  olivary  eminence,  separating  the  carotid  groove  behind  from  the  optic 
foramen  in  front ;  externally  this  root  is  confluent  with  the  recurved  posterior  angle 
of  the  lesser  wing,  forming  the  projection  known  as  the  anterior  clinoid  process 
(processus  clinoideus  anterior),  which  overhangs  the  fore  part  of  the  body  of  the 
bone.  The  anterior  root,  broad  and  compressed,  unites  the  upper  surface  of  the 
lesser  wing  with  the  fore  and  upper  part  of  the  body.  Externally  the  outer 
angle  terminates  in  a  pointed  process  which  reaches  the  region  of  the  pterion  and 
there  articulates  with  the  frontal,  and  may  come  in  contact  with  the  great  wing. 
The  superior  aspect  is  smooth,  and  forms  in  part  the  floor  of  the  anterior  cranial 
fossa.  The  inferior  surface  constitutes  part  of  the  posterior  portion  of  the  upper 
wall  of  the  orbit,  and  also  serves  to  roof  in  the  sphenoidal  fissure  which  separates 
the  lesser  from  the  greater  wings  below.  The  anterior  edge  is  ragged  and  irregular, 
and  articulates  with  the  orbital  plates  of  the  frontal.  The  posterior  margin, 
sharp  and  sickle-shaped,  separates  the  anterior  from  the  middle  cranial  fossa,  and 
corresponds  to  the  position  of  the  Sylvian  fissure  on  the  surface  of  the  cerebrum. 

The  greater  or  temporal  wings  (alee  magnse),  as  seen  from  above,  are  of  a 
somewhat  crescentic  form.  If  the  inner  convex  edge  of  the  crescent  be  divided 
into  fifths,  the  posterior  fifth  extends  backwards  and  outwards  beyond  the  body  of 
the  bone,  presenting  a  free  posterior  edge,  which  forms  the  anterior  boundary  of  the 
foramen  lacerum  medium.  This  border  ends  behind  in  the  horn  of  the  crescent, 
from  which  a  pointed  process  projects  downwards,  called  the  alar  or  sphenoidal  spine 
(spina  angularis),  this  is  wedged  into  the  angle  between  the  petrous  and  squamous 
parts  of  the  temporal  bone.  The  inner  surface  of  the  posterior  border  and  spine  is 
furrowed  for  the  cartilaginous  Eustachian  tube  (sulcus  tubse),  whilst  on  the  inner 
side  of  the  spine  the  course  of  the  chorda  tympani  nerve  is  indicated  by  a  groove 
(Lucas).  The  second  fifth  of  the  convex  border  of  the  crescent  is  fused  to  the  side 
of  the  body  and  united  below  with  the  root  of  the  pterygoid  process.  The  angle 
formed  by  the  union  of  the  great  wing  with  the  side  of  the  body  posteriorly  corre- 
sponds to  the  hinder  end  of  the  carotid  groove,  the  outer  lip  of  which  is  formed  by 
a  projecting  lamina  called  the  lingula.     The  remaining  three-fifths  of  the  convex 


THE  SPHENOID  BONE.  125 

border  is  divisible  into  two  nearly  equal  ]3arts ;  the  inner  is  a  free,  curved,  sharp 
margin,  which  forms  the  inferior  margin  of  the  sphenoidal  fissure  (fissura  orbitalis 
superior),  the  cleft  which  separates  the  great  wing  from  the  lesser  wing,  and  which 
establishes  a  wide  channel  of  communication  between  the  middle  cranial  fossa  and 
the  cavity  of  the  orbit,  transmitting  the  third,  fourth,  ophthalmic  division  of  the 
fifth,  and  the  sixth  cranial  nerves,  together  with  the  ophthalmic  veins.  Wide  of 
the  sphenoidal  fissure  this  edge  becomes  broad  and  serraj;ed,  articulating  with  the 
frontal  bone  internally,  and  at  the  part  corresponding  to  the  anterior  horn  of  the 
crescent,  by  a  surface  of  variable  width,  it  unites  with  the  anterior  inferior  angle 
of  the  parietal  bone.  The  external  lorder  corresponds  to  the  concave  side  of 
the  crescent,  and  is  serrated  for  articulation  with  the  squamous  temporal,  being 
thin  and  bevelled  at  the  expense  of  its  outer  surface  above  and  externally,  and 
broad  and  thick  behind  as  it  passes  towards  the  alar  spine.  The  swperior  or 
cerebral  surface  is  concave  from  behind  forwards,  and  in  its  fore  part  from  side  to 
side  also ;  it  forms  a  considerable  part  of  the  floor  of  the  middle  cranial  fossa,  and 
bears  the  impress  of  the  convolutions  of  the  extremity  of  the  temporal  lobe  of  the 
cerebrum  which  rests  upon  it ;  towards  its  outer  side  it  is  grooved  obliquely  by  an 
anterior  branch  of  the  middle  meningeal  artery.  The  following  foramina  pierce 
the  great  wing :  close  to  and  in  front  of  the  alar  spine  is  the  foramen  spinosum 
for  the  transmission  of  the  middle  meningeal  artery  and  its  companion  vein, 
together  with  a  recurrent  branch  from  the  third  division  of  the  V.  nerve.  In 
front  of  and  internal  to  this,  and  close  to  the  posterior  free  border,  is  the 
foramen  ovale,  of  large  size  and  elongated  form.  This  gives  passage  to  the 
motor  root  and  inferior  sensory  division  of  the  V.  nerve,  and  admits  the  small 
meningeal  branch  of  the  middle  meningeal  artery ;  a  small  emissary  vein  from  the 
cavernous  sinus  usually  passes  through  this  foramen,  and  occasionally  also  the 
small  superficial  petrosal  nerve.  Near  the  fore  part  of  the  root  of  the  great  wing, 
and  just  below  the  sphenoidal  fissure,  is  the  foramen  rotundum,  of  smaller  size  and 
circular  form.  Through  this  the  second  division  of  the  V.  nerve  escapes  from  the 
cranium.  Occasionally  there  is  a  small  canal — the  foramen  of  Vesalius — which 
pierces  the  root  of  the  great  wing  to  the  inner  side  of  the  foramen  ovale.  This 
opens  below  into  the  scaphoid  fossa  at  the  base  of  the  internal  pterygoid  plate,  and 
transmits  a  small  vein.  Occasionally  there  is  a  small  foramen  (canaliculus 
innomiuatus)  to  the  inner  side  of  the  foramen  spinosum  for  the  transmission  of 
the  small  superficial  petrosal  nerve. 

The  outer  surface  of  the  great  wing  is  divided  into  three  well-marked  areas ;  of 
these  the  upper  two  are  separated  by  an  oblique  jagged  ridge,  the  malar  crest 
(margo  zygomaticus),  for  articulation  with  the  orbital  process  of  the  malar  bone. 
The  lower  part  of  this  ridge  may  occasionally  articulate  with  the  malar  process  of 
the  superior  maxilla.  Of  these  two  areas  the  orbital  (facies  orbitalis)  is  directed 
forwards  and  a  little  inwards ;  of  quadrilateral  shape,  it  forms  the  back  and  outer 
wall  of  the  orbit ;  plane  and  smooth,  it  is  bounded  behind  by  the  sharp  inferior 
free  margin  of  the  sphenoidal  fissure,  towards  the  inner  extremity  of  which  a 
pointed  spine  for  the  attachment  of  the  inferior  common  ligament  of  origin  of  the 
ocular  muscles  can  usually  be  seen.  It  is  limited  superiorly  by  the  edge  of  a  rough 
triangular  area  which  articulates  with  the  frontal  bone ;  anteriorly  by  the  malar 
crest ;  whilst  inferiorly  a  free,  well-defined  horizontal  margin  constitutes  the 
posterior  and  external  boundary  of  the  spheno-maxillary  fissure  (fissura  orbitalis 
ini'erior),  which  separates  this  part  of  the  bone  from  the  orbital  plate  of  the  superior 
maxilla.  Below  this  border  there  is  a  grooved  surface  which  leads  inwards  toward 
the  orifice  of  the  foramen  rotundum.  In  the  articulated  skull  this  forms  part  of 
the  posterior  wall  of  the  spheno-maxillary  fossa. 

To  the  outer  side  of  the  malar  crest,  which  })ounds  it  in  front,  is  the  temporal 
area  (facies  temporalis),  concavo-convex  from  Ijcforc;  backwards.  It  slopes  inwards 
below,  where  it  is  se])arated  from  the  zygomatic  area  by  a  well-marked  muscular 
ridge,  the  infra-temporal  crest  or  pterygoid  ridge  (crista  infratemporalis).  Behind, 
the  tem])oral  surface  is  l^ounded  by  the  margin  of  the  great  wing  which  articulates 
with  the  sfinamous  tem])oral,  and  above  by  the  edge  which  unites  it  with  the 
anterior  inferior  angle  of  the  parietal  and  the  frontal  bone.     The  temporal  surface 


126  OSTEOLOGY. 

enters  into  the  formation  of  the  floor  of  the  fossa  of  the  same  name,  and  affords  an 
extensive  attachment  to  the  fibres  of  origin  of  the  temporal  muscle.  The  zygomatic 
surface  (facies  infratemporalis),  situated  below  the  infra-temporal  crest,  corresponds 
to  the  under  surface  of  the  posterior  half  of  the  great  wing ;  it  extends  as  far  back 
as  the  alar  spine  and  posterior  border.  Opening  on  it  are  seen  the  orifices  of  the 
foramen  spinosum  and  ovale.  It  is  slightly  concave  from  side  to  side,  and  is 
confluent  internally  with  the  outer  surface  of  the  external  pterygoid  plate.  In 
front  it  is  bounded  by  a  ridge  which  curves  upwards  and  outwards  from  the  fore 
part  of  the  external  pterygoid  plate  to  join  the  infratemporal  crest.  In  the 
articulated  skull  this  ridge  forms  the  posterior  boundary  of  the  pterygo-maxillary 
fissure.  The  zygomatic  surface  overhangs  the  zygomatic  fossa,  and  affords  an  origin 
for  the  upper  head  of  the  external  pterygoid  muscle. 

The  pterygoid  processes  (processus  pterygoidei)  spring  from  the  inferior 
surface  of  the  lateral  aspect  of  the  body  as  well  as  the  under  side  of  the  root  of 
the  great  wings,  and  pass  vertically  downwards.  Each  consists  of  two  laminse,  the 
external  and  internal  pterygoid  plates,  fused  together  anteriorly,  and  enclosing 
between  them  posteriorly  the  pterygoid  fossa  (fossa  pterygoidea).  The  external 
pterygoid  plate  (lamina  lateralis  processus  pterygoidei),  thin  and  expanded,  is 
directed  obliquely  backwards  and  outwards,  its  lower  part  being  often  somewhat 
everted.  Its  hinder  edge  is  sharp,  and  often  has  projecting  from  it  one  or  two 
spines,  to  one  of  which  (processus  pterygo-spinosus)  the  pterygo-spinous  ligament 
which  stretches  towards  the  alar  spine  is  attached.  Externally  it  furnishes  an 
origin  for  the  lower  head  of  the  external  pterygoid  muscle,  and  on  its  inner  side, 
where  it  forms  the  lateral  wall  of  the  pterygoid  fossa,  it  supplies  an  attachment  for 
the  internal  pterygoid  muscle.  ' 

The  internal  pterygoid  plate  (lamina  medialis  processus  pterygoidei)  is  narrower 
and  somewhat  stouter.  By  its  inner  aspect  it  forms  the  posterior  part  of  the 
lateral  wall  of  the  nasal  fossse;  externally  it  is  directed  towards  the  pterygoid 
fossa.  Its  posterior  edge  ends  below  in  the  hook -like  hamular  process  (hamulus 
pterygoidei),  which,  reaching  a  lower  level  than  the  external  plate,  curves  back- 
wards and  outwards,  furnishing  a  groove  in  which  the  tendon  of  the  tensor  palati 
muscle  glides ;  superiorly,  the  sharp  posterior  margin  of  the  inner  plate  bifurcates, 
so  as  to  enclose  the  shallow  scaphoid  fossa  from  which  the  tensor  palati  muscle 
arises,  and  wherein  may  occasionally  be  seen  the  inferior  aperture,  of  the  foramen 
Vesalii.  To  the  inner  edge  of  this  fossa,  as  well  as  to  the  posterior  border  of  the 
internal  pterygoid  plate,  the  pharyngeal  aponeurosis  is  attached.  Here,  too,  the 
cartilage  of  the  Eustachian  tube  is  supported  on  a  slight  projection,  and  the  palato- 
pharyngeus  muscle  receives  an  origin,  whilst  the  superior  constrictor  of  the  pharynx 
arises  from  the  lower  third  of  the  same  border  and  from  the  hamular  process. 
Superiorly  and  internally  the  inner  plate  forms  an  incurved  lamina  of  bone,  the 
vaginal  process  (processus  vaginalis),  which  is  applied  to  the  under  surface  of  the 
lateral  aspect  of  the  body  reaching  inwards,  towards  the  root  of  the  rostrum,  from 
which,  however,  it  is  separated  by  a  groove,  in  which,  in  the  articulated  skull,  the 
ala  of  the  vomer  is  lodged.  The  angle  formed  by  the  vaginal  process  and  the 
internal  edge  of  the  scaphoid  fossa  forms  a  projection  called  the  pterygoid  tubercle, 
immediately  above  which  is  the  posterior  aperture  of  the  Vidian  canal  (canalis 
pterygoideus),  through  which  the  Vidian  nerve  and  artery  are  transmitted.  On  its 
under  surface  the  vaginal  process  displays  a  groove  (sulcus  pterygo-palatinus) 
which  in  the  articulated  skull  is  converted  into  the  pterygo-palatine  canal  by  its 
union  with  the  palate  bone.  In  front,  at  its  root,  the  pterygoid  process  displays  a 
broad  smooth  surface  (facies  spheno-maxillaris),  which  is  confluent  above  with  the 
root  of  the  great  wing  around  the  foramen  rotundum,  and  forms  the  posterior  wall 
of  the  spheno-maxillary  fossa.  Here,  to  the  inner  side  of  the  foramen  rotundum, 
is  seen  the  anterior  opening  of  the  Vidian  canal.  Below,  the  pterygoid  plates  are 
separated  by  an  angular  cleft,  the  pterygoid  notch  (fissura  pterygoidea) ;  in  this  is 
lodged  the  tuberosity  of  the  palate  bone,  the  margins  of  which  articulate  with  the 
serrated  edges  of  the  recess. 

Connexions. — The  spLenoid   articulates  with    the   occij^ital,    temporals,  parietals,  frontal, 


THE  SPHENOID  BONE. 


127 


ethmoid,  sphenoidal  turbinals,  vomer,  palate  and  malar  bones,  and  occasionally  v/ith  the  superior 
maxillae. 

Architecture. — In  the  adult  the  body  of  the  bone  is  hollow  and  encloses  the  sphenoidal  air 
cells,  usually  two  in  number,  sejjarated  by  a  septum.  The  arrangement  and  extent  of  these  air 
cells  vary  ;  sometimes  they  are  multilocular,  at  other  times  simple,  while  occasionally  they  extend 
backwards  into  the  basi-occipital  and  outwards  and  downwards  into  the  roots  of  the  great  wings 
and  pterygoid  processes.  Cases  are  on  record  in  which  in  the  adult  the  body  of  the  bone  was  not 
pneumatic. 

Variations. — Through  imperfect  ossification  the  foramen  spinosum  and  foramen  ovale  are 
sometimes  incomplete  posteriorly.  Le  Double  (Bull,  et  mim.  de  la  Soc.  d'Anth.  de  Paris,  5*^  ser. 
vol.  iii.  p.  550),  records  a  case  in  which  the  foramen  rotundum  and  the  sphenoidal  fissure  were 
united  so  as  to  form  a  single  cleft. 

Through  deficiency  of  its  external  wall,  the  optic  foramen,  in  rare  instances,  communicates 
with  the  sphenoidal  fissure.  Duplication  of  the  optic  foramen  is  also  recorded  as  a  rare 
occurrence,  the  artery  passing  through  one  canal,  the  nerve  through  the  other.  Persistence  of 
the  cranio -pharyngeal  canal  is  also  occasionally  met  with.  On  the  other  hand,  owing  to  the 
ossification  of  fibrous  bands  connecting  the  several  bony  points,  anomalous  foramina  are 
frequently  met  with.  Cases  of  persistence  of  the  cranio -pharyngeal  canal  have  been 
recorded. 

Ossification. — The  sphenoid  of  man  is  formed  by  the  fusion  of  two  parts,  the  pre- 
sphenoid  and  the  post-sphenoid,  each  associated  with  certain  processes.  In  most  manmials 
the  orbito-sphenoids  or  lesser  wings  fuse  with  the  pre-sphenoid,  whilst  the  alisphenoids  or 
greater  Avings,  together  with  the  internal  pterygoid  plate,  ankylose  with  the  post-sphenoid. 
The  ossification  of  these  several  parts  takes  place  in  cartilage,  with  the  exception  of  the 
internal  pterygoid  plate,  which  is  developed  from  an  independent  centre  in  the  connective 
tissue  of  the  lateral  wall  of  the  oral  cavity  (Hertwig). 

At  the  end  of  the  second  month  a  centre  appears  in  the  root  of  the  great  wing  between 
the  foramen  ovale  and  foramen  rotundum;  from  this  the  ossification  spreads  outwards  and 
backwards  and  also  downwards  into  the  external  pterygoid  plate.  Meanwhile  two  centres 
appear  about  the  same  time  in  the  basi-sphenoid  in  relation  to  the  floor  of  the  sella  turcica  and 
on  either  side  of  the  cranio-pharyngeal  canal,  around  which  they  ossify,  ultimately  leading 
to  the  obliteration  of  this  channel.  Somewhat  later  a  centre  appears  on  either  side,  from 
which  the  lateral  aspect  of  the  body  and  the  lingula  are  developed.  Fusion  between  these 
four  centres  is  usually  complete  by  the  sixth  month. 

In  the  pre-sphenoid  a  pair  of  lateral  nuclei  make  their  appearance  about  the  middle  of 
the  third  month,  just  external  to  the  optic 
foramina ;  from  each  of  these  the  orbito- 
sphenoids  (lesser  wings)  and  their  roots  are 
developed.  About  the  same  time  another 
pair  of  centres,  placed  mesial  to  the  optic 
foramina,  constitute  the  body  of  the  pre- 
sphenoid.  By  the  coalescence  of  these  in 
front,  and  their  ultimate  union  with  the  basi- 
sphenoid  behind,  a  cartilaginous  interval  is 
enclosed,  of  triangular  shape,  which,  however, 
becomes  gradually  reduced  in  size  by  the 
ingrowth  of  its  margins  so  as  to  form  two 
mesially  -  placed  foramina,  as  may  be  fre- 
quently observed  in  young  bones — one  open- 
ing on  the  surface  of  the  olivary  eminence,  the  other  being  placed  anteriorly. 
"  Proc.  Soc.  Anat.,"  Journ.  Anat.  and  Physiol,  vol.  xxviii.  p.  19.) 

As  has  been  seen,  the  internal  pterygoid  plates  are  developed  in  membrane  and  are  the  first 
parts  of  the  sphenoid  to  ossify.  (Fawcett,  Anat.  Auz.,  vol.  xxvi.  1905,  p.  280.)  Each  is  derived 
from  a  single  nucleus  which  appears  about  the  ninth  or  tenth  week,  and  fuses  with  the  under 
surface  of  the  great  wing,  there  forming  a  groove  which  is  converted  into  the  Vidian  canal 
when  the  alisplienoid  and  internal  pterygoid  plates  fuse  later  with  the  body  of  the  post- 
sphenoid.  The  hamular  process,  however,  chondrifies  before  it  ossifies  during  the  third 
month.     Fawcett  also  regards  the  external  pterygoid  plate  as  of  membranous  origin. 

At  birth  the  sphenoid  consists  of  three  parts  :  one  comprising  the  orbito-sphenoids 
together  with  the  body  of  tlie  pre-sphcu(jid  and  the  basi-sphenoid,  the  others  consisting  of 
the  alisphenoids,  one  on  eitlier  side.  Fusion  of  the  latter  witli  the  former  occurs  near  the 
end  of  the  first  year.  The  dorsum  sella  at  birth  consists  of  a  cartilaginous  plate  which 
M!parates  the  body  of  the  f)Ost-sphcnoid  from  the  basi-occipital.  This  slowly  ossifies,  but 
the  curtilage  does  not  entirely  disappear  till  the  age  of  twenty-five,  by  which  time  bony  anky- 
losis of  the  basi-craniul  axis  is  complete.      For  a  considerable  time  the  under  surface  of  the 


Fig.  97. — Ossification  of  Sphenoid. 

«,  Pre-spheuoid  ;  b,  Orbito-spheuoids  ;  c,  Alisphenoids  ; 
d,  Internal  pterygoid  plates  ;  e,  Basi-sphenoid. 


(Lawrence, 


128 


OSTEOLOaY. 


body  of  the  pre-sphenoid  displays  a  bullate  appearance,  with  the  sides  of  whicli  the 
sphenoidal  turbinated  bones  articulate.  It  is  only  after  the  seventh  or  eighth  year  is 
reached  that  the  cancellous  tissue  within  this  part  of  the  bone  becomes  absorbed  to  form 
the  sphenoidal  sinuses. 

The  sphenoidal  turbinals  (conchte  sphenoidales),  or  bones  of  Bertin,  best  studied  in 
childhood,  are  formed  by  tlie  fusion  of  four  distinct  ossicles  (Cleland),  the  centres  for 
which  appear  in  the  later  months  of  utero-gestation.  Each  bone  consists  of  a  hollow,  three- 
sided  pyramid,  the  apex  of  which  is  in  contact  with  the  fore  part  of  the  vaginal  process  of 
the  internal  pterygoid,  whilst  the  base  fits  on  to  the  posterior  surface  of  the  lateral  mass 
of  the  ethmoid.  The  inferior  surface  of  each  forms  the  roof  of  the  corresponding  nasal 
fossa,  and  completes  the  formation  of  the  spheuo-palatine  foramen,  whilst  the  external 
aspect  is  united  with  the  palate  bone  and  forms  the  inner  wall  of  the  spheno-maxillaiy 
fossa,  and  occasionally  constitutes  a  part  of  the  orbital  wall  posterior  to  the  os  planum  of 
the  ethmoid.  The  superior  surface  of  the  sphenoidal  turbinal  is  applied  to  the  fore  and 
under  surface  of  the  body  of  the  pre-sphenoid  on  either  side  of  the  rostrum.  It  is  by  the 
absorption  of  this  wall  that  the  sphenoidal  sinuses  are  ultimately  opened  up.  The  base 
of  the  pyramid  forms  the  aperture  through  which  each  of  these  sinuses  opens  into  the 
nasal  fossse  in  the  adult.  Owing  to  their  firm  ankylosis  with  the  surrounding  bones,  these 
ossicles  are  merely  represented  in  the  adult  disarticulated  skull  by  the  irregular  fragments 
adherent  to  the  separated  borders  of  the  ethmoid,  palate,  and  sphenoid  bones. 

The  Ethmoid  Bone. 

The  ethmoid  bone  (os  ethmoidale)  lies  in  front  of  the  sphenoid,  and  occupies 
the  interval  between  the  orbital  plates  of  the  frontal,  thus  entering  into  the  forma- 
tion of  the  anterior  cranial  fossa  as  well  as  the  inner  walls  of  the  orbits  and  the 
roof  and  inner  and  outer  walls  of  the  nasal  fossse.  The  bone,  which  is  extremely 
light,  consists  of  two  cellular  parts — the  lateral  masses,  which  are  united  superiorly 
to  a  mesial  vertical  plate  by  a  thin  horizontal  lamina  which,  from  its  perforated 
condition,  is  called  the  cribriform  plate. 

The  study  of  this  bone  will  be  much  facilitated  by  cutting  through  the  cribriform 
plate  on  one  side  of  the  vertical  plate,  thus  removing  the  lateral  mass  of  one  .side  and 
exposing  more  fully  the  central  perpendicular  lamina. 

The  vertical  plate  (lamina  perpendicularis),  of  irregular  pentagonal  shape,  forms 
the  upper  part  of  the  nasal  septum.     Its  superior  border  projects  above  the  level  of 

the  cribriform  plate  so  as  to  form  a 
crest,  which  is  much  elevated  an- 
teriorly, where  it  terminates  in  a 
bullate  process  called  the  crista  galli, 
the  upper  edge  of  which  is  sharp  and 
pointed,  and  affords  attachment  to 
the  falx  cerebri.  In  front  of  this 
process  there  is  a  groove  which 
separates  the  alar  processes  (pro- 
cessus alares)  which  project  from  the 
crista  galH  on  either  side.  By  ar- 
ticulation with  the  frontal  bone  this 
groove  is  converted  into  a  canal, 
the  foramen  cascum ;  this,  however, 
is  not  always  bhnd,  but  frequently 
transmits  a  vein  to  the  roof  of  the 
nose.  The  posterior  margin  of  the 
vertical  plate  is  thin,  and  articulates 
with  the  crest  of  the  sphenoid. 
The  posterior  inferior  border  in  the  adult  is  ankylosed  with  the  vomer;  and 
the  anterior  inferior  edge,  which  is  usually  thicker  than  the  others,  unites  with 
the  cartilaginous  nasal  septum.  The  a7iterior  sitperior  border  articulates  with  the 
nasal  spine  of  the  frontal  bone  and  with  the  median  crest  formed  by  the  union  of 
the  two  nasal  bones.  The  vertical  plate,  which  is  usually  deflected  to  one  or  other 
side,  has  generally  smooth  surfaces,  except  above,  where  they  are  channelled  by 


Alar  process 


Crista  sfalli 


Os  planum 


piocess 


98. — ETHMOm   AS    SEEN    FROM   BEHIND. 


THE  ETHMOID  BONE. 


129 


Ciista  fralli 


Anterior  and  ijosterior 
ethmoidal  grooves 


Alar  process 


Os  planum 
(orbital  surface) 


Middle  meatus 


Infuudibuluii] 


Vertical  plate 


Middle  turbinated  bone.  Uncinate  process 

Fig.  99. — Ethmoid  as  seen  from  the  PiTght  Side. 


short  and  shallow  grooves  leading  to  the  foramina  which  pierce  the  cribriform  plate  ; 
these  are  for  the  lodgment  of  the  olfactory  nerves. 

The  lateral  mass  or  labyrinth  (labyrinthus)  is  composed  of  papery  bone, 
enclosing  a  large  number  of  air-cells ;  these  are  arranged  in  three  groups — an 
anterior,  a  middle,  and 
a  posterior,  the  walls  of 
which  have  been  broken 
in  front,  above,  behind, 
and  below,  in  the  pro- 
cess of  disarticulation. 
Externally  they  are 
closed  in  by  a  thin,  ob- 
long lamina,  the  orbital 
plate  or  os  planum 
(lamina  papyracea), 
which  forms  a  part  of 
the  inner  wall  of  the 
orbit,  and  articulates 
above  with  the  orbital 
plate  of  the  frontal, 
which  here  roofs  in  the 

ethmoidal  cells.  The  line  of  this  suture  is  pierced  by  two  canals,  the  anterior  and 
posterior  ethmoidal  canals,  both  of  which  transmit  small  ethmoidal  vessels,  whilst 
the  anterior  also  gives  passage  to  the  nasal  nerve.  In  front  the  os  planum  articu- 
lates with  the  lachrymal  bone ;  whilst  heloio,  by  its  union  with  the  orbital  surface 
of  the  superior  maxillary  bone,  the  air-sinuses  in  both  situations  are  completed. 
Posteriorly  the  os  planum  articulates  with  the  sphenoid,  and  at  its  posterior 
inferior  angle  for  a  variable  distance  with  the  orbital  process  of  the  palate  bone, 
both  of  which  serve  to  close  in  the  air-cells.  The  mesial  aspect  of  the  lateral  mass 
displays  the  convoluted  turbinated  processes,  usually  two  in  number,  though 
occasionally  there  may  be  three — rarely  more.  In  cases  where  there  are  two 
ethmo-turbinals  they  are  separated  posteriorly  by  a  deep  groove.  A  channel  is 
thus  formed  in  the  back  part  of  the  lateral  and  upper  aspect  of  the  nasal  fossae, 
called  the  superior  meatus,  which  is  roofed  in  by  the  superior  turbinated  process 
(concha  superior),  whilst  its  floor  is  formed  by  the  upper  surface  of  the  middle 
turbinated  process  (concha  media).     The  posterior  ethmoidal  cells  open  into  this 

meatus.  In  front  of  the  superior  meatus, 
which  only  grooves  the  posterior  half  of 
this  aspect  of  the  bone,  the  surface  is 
rounded  from  above  downwards  and  before 
backwards,  and  forms  the  inner  wall  of 
the  anterior  and  middle  ethmoidal  ceUs. 
Eunning  obliquely  from  above  downwards 
and  backwards  over  the  mesial  surface  of 
the  superior  concha,  are  a  number  of  fine 
grooves  continuous  above  with  the  fora- 
mina in  the  cribriform  plate ;  these  are 
fewer  and  more  scattered  in  front,  do  not 
pass  on  to  the  middle  concha,  and  are  for 
the  olfactory  nerves. 

The  middle  turbinated  process  (concha 
media)  is  nearly  twice  the  length  of  the  superior.  Its  anterior  extremity  is  united 
for  a  short  distance  to  the  superior  turbinated  crest  on  the  inner  side  of  the 
frontal  process  of  the  superior  maxilla.  By  its  thickened,  free  convoluted  border 
it  overhangs  a  deep  grorjve  which  runs  along  the  under  surface  of  the  lateral  mass. 
Til  is  is  the  middle  meatus  of  the  nose.  It  r<}ceives  the  openings  of  the  middle 
ethmoidal  cells  and  a  passage  which  runs  upwards  and  forwards  from  it,  the 
infundibulum.  This  communicates  with  the  anterior  ethmoidal  cells  and  the 
froiiUiI  sinus.  'I'he  out(!r  side  of  the  niiddle  meatus  is  formed  by  tlie  thin  inner 
10 


Suijerior 
turbinated  bone 


Anterior  ethmoidal 
groove 


Uncinate  process 

Fig.   100. — Section  showing  Na.sal  Aspect  of 
Left  Lateral  Mass  of  Ethmoid. 


130 


OSTEOLOGY. 


Os  pliinmii 


Alar  process 


Lacliryiiial  process 


walls  of  the  ethmoidal  cells.  Curving  downwards,  backwards,  and  a  little  out- 
wards from  the  roof  of  the  fore-part  of  this  meatus  is  the  uncinate  process  (pro- 
cessus unciuatus).    This  bridges  across  the  irregular  opening  on  the  inner  wall  of 

the  maxillary  sinus,  and  articu- 
Cristagaiii  lates    iuferiorly   with    the    eth- 

moidal process  of  the  inferior 
turbinated  bone.  The  hinder 
extremity  of  the  middle  turbin- 
ated bone  articulates  with  the 
ethmoidal  crest  on  the  vertical 
plate  of  palate  bone. 

The  cribriform  plate  (lamina 
cribrosa)  is  the  horizontal 
lamina  which  connects  the 
lateral  masses  with  the  vertical 
plate,  much  in  the  same  manner 
as  the  cross  limb  of  a  capital  T 
is  arranged.  It  occupies  the 
interval  between  the  orbital 
plates  of  the  frontal  bone, 
roofinff  in   the  nasal  fossae  in- 

^■^^  Iiiierior 

turbinated  bone  fcriorly,  and  Superiorly  forming 
on  either  side  of  the  crista  galli 

FIG.  lOi.-SHowiNG  ARTICULATION  OF  Inpekioh  TURBINATED    ^^^o  shallow  olfactory  grooves  in 
Bone  with  Ethmoid.  which,  m    the  recent  condition, 

the  olfactory  lobes  of  the  cere- 
brum are  lodged.  Numerous  foramina  for  the  transmission  of  the  olfactory  nerves 
pierce  this  part  of  the  bone ;  those  to  the  inner  and  outer  sides  of  the  groove 
are  the  largest  and  most  regular  in  their 
arrangement.  Along  the  outer  edges  of  the 
cribriform  plate  two  notches  can  usually  be 
distinguished ;  when  articulated  with  the 
frontal  bone  these  form  the  inner  openings  of 
the  ethmoidal  canals.  Leading  forward  from 
the  anterior  of  these  there  is  often  a  groove 
which  crosses  to  the  side  of  the  crista  galli, 
where  it  ends  in  a  slit  which  allows  of  the 
transmission  of  the  nasal  nerve  to  the  nose. 
Posteriorly  the  cribriform  plate  articulates 
with  the  ethmoidal  spine  of  the  sphenoid. 


MaxiUaiy  process 


Ethinoidal  process 


Vertical  plate 


Alar  process 


Crista  aalli 


t  for  nasal  nerve 


Us  planum 


Lateral  mass 


Fig.  102. — Ethmoid  as  seen  from  Above. 


Connexions. — The  ethmoid  articulates  with  the 
sphenoid  and  sphenoidal  turbinals,  the  frontal,  the 
two  nasals,  two  superior  maxillte,  two  lachrymals, 
two  inferior  turbinals,  two  palates,  and  the  vomer. 

Variations. — The  size  of  the  os  planum  is  liable 
to  considerable  variations.  In  the  lower  races  it  tends  „  ,  „ 
to  be  narrower  from  above  downwards  than  in  the  ii'nni'upae 
higher,  in  this  resjiect  resembling  the  condition  met 
with  in  the  anthropoids.  The  os  planum  may  fail  to 
articulate  with  the  lachrymal  owing  to  the  union  of  the  frontal  with  the  orbital  process  of  the 
superior  maxilla  in  front  of  it.  (Orbito-maxillary  frontal  suture.  A.  Thomson,  Journ.  Anat. 
and  Physiol,  vol.  xxiv.  p.  349.)  Division  of  the  os  planum  by  a  vertical  suture  into  an  anterior 
and  posterior  part  has  been  frequently  recorded.  The  number  of  the  turliinals  may  be  increased 
from  two  to  four,  or  may  be  reduced  to  one.  (Report  of  Committee  of  Collect.  Invest.,  Journ. 
Anat.  and  Physiol.,  vol.  xxviii.  p.  74.) 

Ossification  takes  place  in  the  cartilage  of  the  nasal  capsule.  Each  lateral  mass  has 
one  centre,  Avhich  appears  about  the  fourth  or  tifth  month  in  the  neighbourhood  of  the 
OS  planum.  From  this  the  laminae  around  the  ethmoidal  air  cells  are  formed  which  are 
complete  at  bii'th,  the  air-sinuses  in  this  instance  not  being  formed  by  the  absorption 
of  cancellous  bone.  From  these  centres  the  turbinals  are  also  developed,  and  these,  too, 
are  ossified  at  the  ninth  month. 


BONES  OF  THE  FACE.  131 

At  birth  the  ossified  lateral  masses  are  united  to  the  central  cartilaginous  plate  by  a 
fibrous  layer.  Two  centres  make  their  appearance  in  the  mesial  cartilage  on  either  side 
of  the  root  of  the  crista  galli  about  the  end  of  the  first  year ;  from  these,  the  crista  galli 
and  the  vertical  plate  are  ossified  as  well  as  the  mesial  part  of  the  cribriform  plate,  the 
lateral  portions  of  which  are  derived  from  an  inward  extension  of  the  lateral  mass. 

Ossification  is  usually  complete  about  the  fifth  or  sixth  year.  About  the  twenty-fifth 
year  bony  union  has  taken  place  between  the  cribriform  plate  and  the  sphenoid,  but 
ankylosis  between  the  vertical  plate  and  the  vomer  is  not  usual  till  the  fortieth  or  forty- 
fifth  year. 

Wormian  Bones. 

Along  the  line  of  the  cranial  sutures  and  in  the  region  of  the  fontanelles,  isolated 
bones  of  irregular  form  and  variable  size  are  occasionally  met  with.  These  are  the 
so-called  Wormian  bones,  named  after  the  Danish  anatomist  Wormius.  They  are  also 
called  sutural  or  epactal  bones.  Their  presence  depends  on  the  fact  that  they  are  either 
developed  from  distinct  ossific  nuclei,  or  it  may  be  from  a  division  of  the  primary  ossific 
deposit.  Their  occurrence  may  also  be  associated  with  certain  pathological  conditions 
which  modify  the  development  of  the  bone.  They  usually  include  the  whole  thickness 
of  the  cranial  wall,  or  it  may  be  only  involve  the  outer  or  inner  tables  of  the  cranial 
bones.  They  are  most  frequent  in  the  region  of  the  lambda  and  the  lambdoid  suture. 
They  occur  commonly  about  the  pterion,  and  in  this  situation  are  called  epipteric  bones 
(Flower).  By  their  fusion  with  one  or  other  of  the  adjacent  bones  they  here  lead  to  the 
occurrence  of  a  fronto-squamosal  suture.  Their  presence  has  also  been  noted  along  the 
line  of  the  sagittal  suture,  and  sometimes  in  metopic  skulls  in  the  inter-frontal  suture. 
They  are  occasionally  met  with  at  the  asterion  and  more  rarely  at  the  obelion.  They 
appear  less  frequently  in  the  face,  but  their  presence  has  been  noted  around  the  lachrymal 
bone,  and  also  at  the  extremity  of  the  spheno-maxillary  fissure,  where  they  may  form  an 
independent  nodule  wedged  in  between  the  great  wing  of  the  sphenoid,  the  malar,  and 
the  superior  maxillary  bones. 

BONES  OF  THE  FACE. 

The  bones  of  the  face  (ossa  faciei),  fourteen  in  number,  comprise  two  superior 
maxillee,  two  palates,  two  malars,  two  lachrymals,  and  two  nasals,  together  with  the 
vomer  and  inferior  maxilla. 

The  Supeeior  Maxillary  Bones. 

The  superior  maxillae  (maxillse),  of  which  there  are  two,  unite  to  form  the 
upper  jaw.  Each  consists  of  a  body,  with  which  are  connected  four  projections, 
named  respectively  the  zygomatic,  frontal,  alveolar,  and  palatal  processes. 

The  body  (corpus)  is  of  pyramidal  form,  and  contains  within  it  a  hollow  called 
the  antrum  or  maxillary  air-sinus.  It  has  four  surfaces — an  antero-external  or  facial, 
a  postero-external  or  zygomatic,  a  supero-external  or  orbital,  and  an  internal  or 
nasal.  The  antero-external  or  facial  surface  (facies  anterior)  is  confluent  below  with 
the  alveolar  process.  Above,  it  is  separated  from  the  orbital  aspect  by  the 
infraorbital  margin  (margo  infraorbitalis),  whilst  internally  it  is  limited  by  the  free 
margin  of  the  nasal  notch,  which  ends  below  in  the  pointed  anterior  nasal  spine 
(spina  nasalis  anterior).  Posteriorly  it  is  separated  from  the  zygomatic  surface  by 
the  inferior  border  of  the  zygomatic  process.  The  facial  aspect  of  the  bone  is  ridged 
by  the  sockets  of  the  teeth  (juga  alveolaria).  The  ridge  corresponding  to  the  root 
of  the  canine  tooth  is  usually  the  most  pronounced ;  internal  to  this,  and  overlying 
the  roots  of  the  incisor  teeth,  is  the  shallow  incisive  or  myrtiform  fossa,  whilst 
placed  externally,  on  a  higher  level,  is  the  deeper  canine  fossa,  the  floor  of  which 
is  formed  in  part  by  the  projecting  zygomatic  process.  Above  this,  and  near  the 
infraorbital  margin,  is  the  infraorbital  foramen,  the  external  opening  of  the 
infraorbital  canal,  which  transmits  the  infraorbital  nerve  and  artery.  The  postero- 
external, or  zygomatic  surface  is  separated  above  from  the  orbital  asyicct  l)y  a 
rounded  free  edge,  which  f'ornis  the  anterior  margin  of  the  spheno-maxillary  fissure 
in  th<;  articulated  skull.  Inferioi'ly  and  in  fnnit  it  is  scjparated  from  the  facial 
surface  by  the  zygomatic  process  and  its  free  lower  border.     Internally  it  is  limited 


132 


OSTEOLOGY, 


Nasal  process 


LiohtM  nl  gioo\e 


liilVaorbital 
foramen 


Incisor  fossa 


Tuberositj 


Right  superior  Maxilla  (Outer  View). 


by  a  sharp,  irregular  margin  with  which  the  palate  bone  articulates.  This  surface 
is  more  or  less  convex,  and  is  directed  towards  the  zygomatic  and  spheno-maxillary 
fossae.     It  is  pierced  in  a  downward  direction  by  the  apertures  of  the  posterior 

dental  canals  (foramina 
alveolaria),  two  or 
more  in  number,  which 
transmit  the  corre- 
sponding nerves  and 
vessels  to  the  molar 
teeth.  Its  lower  part, 
slightly  more  proDii- 
nentwhere  it  overhangs 
the  root  of  the  wisdom 
molar,  is  often  called 
the  tuberosity  (tuber 
maxillare).  Thesi'/pero- 
external  or  orbital  sur- 
face (planum  orbitale), 
smooth  and  plane,  is 
triangular  in  shape  and 
forms  part  of  the  floor 
of  the  orbit.  Its  an- 
terior edge  corresponds 
to  the  iniraorbital 
margin ;  its  posterior 
border  coincides  with 
the  anterior  boundary 
of  the  spheno  maxillary  fissure.  Its  thin  inner  edge,  which  may  be  regarded  as  the 
base  of  the  triangle,  is  notched  in  front  to  form  the  lachrymal  groove  (sulcus  lacri- 
malis),  behind  which  it  articulates  with  the  lachrymal  bone  for  a  short  distance, 
then  for  a  greater  length 

with  the  OS  planum  of  the  ^^"'"'  i'™'-'*'-^' 

ethmoid,  and  terminates 
posteriorly  in  a  surface 
for  articulation  with  the 
orbital  process  of  the 
palate  bone.  Its  ex- 
ternal angle  corresponds 
to  the  outspring  of  the 
zygomatic  process.  Tra- 
versing its  substance  is 
the  infraorbital  canal,  the 
anterior  opening  of  which 
has  been  already  noticed 
on  the  facial  aspect  of  the 
body.  Behind,  however, 
owing  to  deficiency  of  its 
roof,  the  canal  forms  a 
groove  which  lips  the 
edge  of  the  bone  which 
constitutes  the  anterior 
boundary  of  the  spheno- 
maxillary fissure.  If  this 
canal  be  laid  open,  the 
orifices  of  the  middle  and 
anterior     dental    canals 

will  be  seen,  which  transmit  the  corresponding  vessels  and  nerves  to  the  bicuspid 
and  incisor  teeth.  The  inner  or  nasal  surface  (facies  nasalis)  of  the  body  is 
directed  inwards  towards  the  nasal  fosscC.     Below  it  is  confluent  with  the  upper 


Ridge  for  middle 
turbinated  bone 


Middle  meatus- 


Ridge  for  inferior 
turbinated  bone 


Inferior  meatus 


Incisor  crest 

Anterior  na 
spi 


Alveolar 

process 


Nasal  crest 
Fk;.  104. — RicHT  Superior  Maxilla  (Inner  Aspect). 


THE  SUPERIOK  MAXILLAE Y  BONES.  133 

surface  of  the  palatal  process ;  in  front  it  is  linjited  by  the  sharp  edge  of  the 
nasal  notch ;  above  and  in  front  it  is  continuous  with  the  inner  surface  of  tlie 
frontal  process ;  behind  this  it  is  deeply  channelled  by  the  lachrymal  groove,  which 
is  converted  into  a  canal  by  articulation  with  the  lachrymal  and  inferior  turbinated 
bones.  The  channel  so  formed  conveys  the  nasal  duct  from  the  orbital  cavity 
above  to  the  inferior  nasal  meatus  below.  Behind  this  groove  the  upper  edge  of 
this  area  corresponds  to  the  inner  margin  of  the  orbital  surface,  and  articulates 
from  before  backwards  with  the  lachrymal,  os  planum  of  the  ethmoid,  and  the 
orbital  process  of  the  palate  bone.  The  posterior  border,  rough  for  articulation 
with  the  palate  bone,  is  traversed  obliquely  from  above  downwards  and  slightly 
inwards  by  a  groove,  which,  by  articulation  with  the  palate  bone,  is  converted  into 
the  posterior  palatine  or  palato-maxillary  canal  which  transmits  the  descending  pala- 
tine artery  and  great  palatine  nerve.  Towards  its  upper  and  hinder  part  the  nasal 
surface  of  the  body  displays  the  irregular,  more  or  less  triangular,  opening  of  the 
antrum  (sinus  maxillaris).  This  aperture,  which,  in  the  articulated  skull  opens 
into  the  middle  meatus  of  the  nose,  is  much  reduced  in  size  by  articulation  with 
the  lachrymal,  ethmoid,  palate,  and  inferior  turbinal  bones.  In  front  of  the 
lachrymal  groove  the  inner  surface  is  ridged  horizontally  by  the  inferior  turbinated 
crest  (crista  conchalis),  to  which  the  inferior  turbinated  bone  is  attached.  Below 
this  the  bone  forms  the  outer  wall  of  the  inferior  nasal  meatus,  receiving  the 
termination  of  the  lachrymal  groove.  Above,  and  for  some  little  distance  also  on 
the  inner  side  of  the  frontal  process,  it  constitutes  the  smooth  outer  wall  of  the 
atrium  of  the  middle  meatus. 

The  zygomatic  or  malar  process  (processus  zygomaticus),  which  is  placed  on 
the  outer  surface  of  the  body,  is  confluent  anteriorly  with  the  facial  surface  of  the 
body ;  posteriorly,  where  it  is  concave  from  side  to  side,  with  the  zygomatic  surface ; 
whilst  superiorly,  where  it  is  rough  and  articular,  it  forms  the  apex  of  the  triangular 
orbital  plate,  and  supports  the  malar  bone.  Inferiorly,  its  anterior  and  posterior 
surfaces  meet  to  form  an  arched  border,  which  fuses  with  the  alveolar  process 
opposite  the  root  of  the  first  molar  tooth,  and  serves  to  separate  the  facial  from  the 
zygomatic  aspects  of  the  body. 

The  frontal  or  nasal  process  (processus  frontalis)  rises  from  the  upper  and 
fore-part  of  the  body.  It  has  two  surfaces — one  external,  the  other  internal.  The 
external  is  divided  into  two  by  a  vertical  ridge  (crista  lachrymalis  anterior),  which 
is  the  upward  extension  of  the  infraorbital  margin.  The  narrow  strip  of  bone 
behind  this  ridge  is  hollowed  out,  and  leads  into  the  lachrymal  groove  below. 
Posteriorly  the  edge  of  the  frontal  process  here  articulates  with  the  lachrymal,  and 
so  forms  the  fossa  for  the  lodgment  of  the  lachrymal  sac  (fossa  sacci  lacrimalis). 
In  front  of  the  vertical  crest,  to  which  the  tendo  oculi  is  attached,  the  external 
surface  is  confluent  below  with  the  facial  aspect  of  the  body,  and  forms  the  side  of 
the  root  of  the  nose.  Its  anterior  edge  is  rough,  or  grooved,  for  articulation  with 
the  nasal  bone.  Superiorly  the  summit  of  the  process  is  serrated  for  articulation 
with  the  nasal  notch  of  the  frontal  bone.  The  inner  surface  of  the  nasal  process  is 
directed  towards  the  nasal  fossse.  It  is  crossed  obliquely  from  below  upwards  and 
backwards  by  a  ridge — the  agger  nasi  or  superior  turbinated  crest  (crista  ethmoidalis). 
Below  this  the  bone  is  smooth  and  forms  the  upper  part  of  the  atrium,  whilst  the 
ridge  itself  articulates  posteriorly  with  the  fore-part  of  the  middle  turbinated  bone, 
formed  by  the  inferior  turbinated  process  of  the  ethmoid  bone. 

The  alveolar  process  (processus  alveolaris)  projects  from  the  under  surface  of 
the  body  of  the  bone  below  the  level  of  the  palatal  process.  (Jf  curved  form,  it 
completes,  with  its  fellow  of  the  opposite  side,  the  alveolar  arch,  in  which  are 
embedded  in  sockets  or  alveoli  the  roots  of  the  teeth  of  the  upper  jaw ;  ordinarily 
in  the  adult,  when  dentition  is  complete,  each  alveolar  process  supports  eight  teeth. 
Piercing  the  inner  surface  of  the  alveolar  border  behind  the  incisor  teeth  two 
small  vascular  foramina  are  usually  visible.  When  any  or  all  the  teeth  are  shed 
the  alveoli  become  absorbed,  and  the  process  may  under  these  circumstances  be 
reduced  to  tbe  level  of  the  plane  of  the  ])alatal  process.  Posteriorly  the  alveolar 
jjroccHS  cuds  below  the  tuberosity  of  the  body ;  anteriorly  it  shares  in  the  formation 
of  the  intermaxillary  suture. 


134  OSTEOLOGY. 

The  palatal  process  (processus  palatinus),  of  the  form  of  a  quadrant,  lies  in  the 
horizontal  plane;  it  has  two  surfaces — upper  and  under — and  three  borders,  a  straight 
internal,  a  more  or  less  straight  posterior,  and  a  curved  external,,  by  which  latter 
it  is  attached  to  the  inner  side  of  the  body  and  alveolar  process  as  far  back  as  the 
interval  between  the  second  and  third  molar  teeth.  Its  under  surface,  together 
with  that  of  its  fellow,  forms  the  anterior  three-fourths  of  the  vaulted  hard  palate; 
it  is  rough  and  pitted  for  the  glands  of  the  mucous  membrane  of  the  roof  of  the 
mouth,  and  is  grooved  on  either  side  near  the  alveolar  margin  by  a  channel  which 
passes  forward  from  the  posterior  palatine  canal  and  transmits  the  great  palatine 
nerve  and  descending  palatine  artery.  Its  superior  surface,  smooth  and  concave 
from  side  to  side,  forms  the  floor  of  the  corresponding  nasal  fossa.  Its  internal  or 
mesial  border,  broad  and  serrated,  rises  in  a  ridge  superiorly,  so  as  to  form  with  its 
fellow  of  the  opposite  side  the  nasal  crest  (crista  nasalis),  which  is  grooved  superiorly 
to  receive  the  lower  border  of  the  vomer.  In  front  of  its  articulation  with  the 
vomer  this  ridge  rises  somewhat  higher,  being  named  the  incisor  crest,  anterior  to 
which  it  projects  beyond  the  free  border  of  the  nasal  notch,  and  together  with  its 
fellow  forms  the  pointed  projection  called  the  anterior  nasal  spine  (spina  nasalis 
anterior).  These  parts  support  the  septal  cartilage  of  the  nose.  Immediately  to 
the  outer  side  of  the  incisor  crest  the  superior  surface  of  the  palatal  process  is 
pierced  by  a  foramen  which  leads  downwards,  forward,  and  a  little  inwards,  to  open 
into  a  broad  groove  on  the  mesial  border  of  the  bone  immediately  behind  the 
central  incisor  tooth.  When  the  two  maxillse  are  articulated,  the  two  grooves 
form  the  oval  anterior  palatine  canal  or  fossa,  into  which  the  two  aforementioned 
foramina  open  like  the  limbs  of  a  Y ;  these  are  called  the  incisor  foramina,  or  the 
foramina  of  Stensen,  and  contain  the  remains  of  uhe  organs  of  Jacobson.  In  front 
and  behind  these,  and  lying  within  the  fossa  and  in  the  line  of  the  suture,  are  the 
smaller  foramina  of  Scarpa,  which  transmit  the  naso-palatine  nerves,  the  right  nerve 
usually  passing  through  the  posterior  foramen,  the  left  through  the  anterior.  The 
posterior  border  of  the  palatal  process,  which  is  sharp  and  thin,  falls  in  line  with 
the  interval  between  the  second  and  third  molar,  and  articulates  with  the  horizontal 
plate  of  the  palate  bone. 

The  maxillary  sinus  or  antrum  of  Highmore  (sinus  maxillaris)  lies  within  the 
body  of  the  bone,  and  is  of  corresponding  pyramidal  form,  its  base  being  directed 
towards  the  nasal  fossa,  with  the  middle  meatus  of  which  it  communicates,  its 
summit  extending  outwards  into  the  root  of  the  zygomatic  process.  It  is  closed 
in  externally  and  above  by  the  thin  walls  which  form  the  facial,  zygomatic,  and 
orbital  surfaces  of  the  body.  Inferiorly  it  overlies  the  alveolar  process  in  which 
the  molar  teeth  are  implanted,  the  sockets  of  which  are  separated  from  it  by  a  thin 
layer  of  bone. 

Advantage  is  taken  of  this  circumstance  to  pierce  the  floor  of  the  antrum  in  such  conditions 
as  necessitate  its  tliorough  drainage,  as  its  natural  outlet  into  the  middle  meatus  is  of  the  nature 
of  an  overflow  aj^erture,  and  so  preveiats  purulent  fluids,  which  may  here  accumulate,  from  being 
readily  discharged. 

The  angles  and  corners  of  this  cavity  are  frequently  groined  by  narrow  ridges 
of  bone,  one  superiorly  corresponds  to  the  relief  formed  by  the  infraorbital  canal. 
A  vascular  and  nervous  groove  is  often  exposed,  curving  along  the  floor  of  the 
antrum  just  above  the  alveoli  of  the  teeth.  The  interior  of  the  cavity  is  lined  by 
an  extension  from  the  mucous  membrane  of  the  nose. 

Connexions. — The  superior  maxillary  bone  articulates  with  the  nasal,  frontal,  lachrymal, 
and  ethmoid  bones  above,  externally  with  the  malar,  and  occasionally  with  the  siDlienoid, 
posteriorly  and  internallj^  with  the  'pala.te,  whilst  on  its  inner  side  it  unites  with  its  fellow  of 
the  op23osite  side,  and  also  sujij^orts  the  inferior  turl)inated  bone  and  tlie  A^omer. 

Architecture. — The  disjiosition  of  the  maxillary  sinus  within  the  body  of  the  bone  has  been 
already  referred  to.  In  union  with  its  fellow,  the  A'aulted  arrangement  of  the  hard  palate  is  well 
displayed,  and  the  arched  arrangement  of  the  suj^erior  alveolar  processes  is  obA'ious.  It  is  in 
these  latter  processes  around  the  sockets  for  the  reception  of  the  teeth  that  the  cancellous  tissue 
of  the  bone  is  seen  ;  elsewhere  its  walls  are  formed  by  thin  and  dense  bone. 

Variations. — Not  unfrequently  there  is  a  suture  running  vertically  through  the  bar  of  bone 
which  separates  the  infraorl:)ital  foramen  from  the  infraorbital  margin.  Through  imperfections 
in  ossification  the  infraoi'bital  canal  may  form  an  open  groove  along  the  floor  of  the  orbit. 


THE  MALAR  BONES. 


135 


Ossification. — The  superior  maxilla;  are  developed  in  the  connective  tissue  around 
the  oral  aperture  of  the  embryo.  The  centres  from  wliich  the  bone  ossifies  are  not 
preceded  by  a  cartilaginous  stage.  Their  number  is  uncertain,  as  early  fusion  occurs 
between  them.  They  first  make  their  appearance  in  the  second  month  of  intrauterine 
life,  shortly  after  the  clavicle  has  begun  to  ossify.  By  the  sixth  montli  they  are  so  united 
that  their  independent  character  is  obscured.  Five  centres  are  described — an  external  or 
malar,  which  forms  the  bone  to  the  outer  side  of  the  infraorbital  canal ;  an  inner  or 
orbito-nasal,  from  which  is  developed  the  iimer  part  of  the  floor  of  the  orbit,  the  frontal 
process,  and  the  wall  of  the  antrum ;  a  palatine,  for  the  posterior  three-fourths  of  the 
palatal  process ;  a  nasal,  situated  between  the  frontal  process  and  the  canine  tooth  ;  and 
within  this  and  nearer  the  middle  line  and  below,  an  incisive  centre,  from  which  the  pre- 
masillse  are  developed,  thus  forming  the  anterior  fourth  of  the  palatal  process  in  the 
adult.  In  the  early  stages  of  the  development  of  the  bone  the  alveolar  groove,  in  which 
the  teeth  are  developed,  lies  close  below  the  infraorbital  groove,  and  it  is  not  till  later 
that  they  become  separated  by  the  growth  of  the 
antrum,  which  first  makes  its  appearance  as  a  shallow 
fossa  to  the  inner  side  of  the  orbito-nasal  element  about 
the  fourth  month.  In  the  adult  bone  the  course  of  the 
infraorbital  canal  and  foramen  indicates  the  line  of  fusion 
of  the  orbito-nasal  and  malar  elements,  whilst  the  position 
of  the  anterior  palatine  canal  serves  to  determine  the  line 
of  union  of  the  incisive  with  the  palatal  elements.  In 
addition  to  the  foregoing  centres,  Rambaud  and  Renault 
describe  another  which,  together  with  its  fellow,  is  wedged 
in  between  the  incisive  and  the  palatal  elements  beneath 
the  vomer,  thus  explaining  the  Y-shaped  arrangement  of 
the  foramina  of  Stensen,  which  open  into  the  anterior 
palatine  canal. 

The  premaxillae,  which  in  most  vertebrates  are  in- 
dependent bones  lying  in  front  of  the  superior  maxillae, 
constitute  in  man  and  apes  the  portions  of  the  upper 
jaw  which  lie  in  front  of  the  anterior  palatine  foramen, 
and  support  the  superior  incisor  teeth.  They  are  de- 
veloped from  the  incisive  centres  above  described ;  the 
line  of  fusion  of  these  elements  with  the  maxillse  proper 
can  readily  be  seen  in  young  skulls,  and  occasionally 
also  in  the  adult.  It  corresponds  to  a  suture  which 
passes  on  the  palate  obliquely  outwards  and  forwards, 
from  the  anterior  palatine  foramen  to  the  interval 
between  the  lateral  incisor  and  the  canine  tooth.  In 
cases  of  alveolar  cleft  palate  the  adjacent  bones  fail  to 
unite  along  the  line  of  the  suture.  In  some  instances, 
however,  the  cleft  passes  outwards  between  the  central 
and  lateral  incisor  teeth,  and  this  condition  sviggests  the 
explanation  that  the  preniaxillary  element  is  derived 
from  two  centres — a  lateral  and  a  mesial.  The  researches 
of  Albrecht  and  Warinski  have  confirmed  this  view. 
The  latter  anatomist  further  observes  that  the  lateral  cleavage  may  lead  to  a  division  of  the 
dental  germ  of  the  lateral  incisor  tooth,  and  so  explain  the  occurrence  of  the  supernumer- 
ary incisor  which  is  occasionally  met  with.  In  this  way  the  different  varieties  of  cleft 
palate  are  x'eadily  explained  ;  mesial  cleft  palate  being  due  to  failure  of  union  between  the 
two  preniaxillary  bones.  Lateral  cleft  palate  may  be  of  two  types :  the  cleft  in  one  case 
passing  forward  between  the  central  and  lateral  incisor,  and  being  due  to  the  non-union 
of  the  two  elements  from  which  the  premaxilla  is  primarily  developed ;  the  other,  in 
which  the  cleft  passes  between  the  lateral  incisor  and  the  canine,  or  between  the  lateral 
incisor  and  a  supernumerary  incisor,  owing  to  the  imperfect  fusion  of  the  premaxilla 
laterally  with  the  maxilla. 


Fig.  105. — Ossification  of  Superior 
Maxilla. 

A,  Outer  side  ;  B,  luuer  side  ;  C, 
Under  side,  a,  Nasal  process ;  6, 
Orbital  plate  ;  c,  Anterior  nasal 
spine  ;  d,  Infraorbital  groove  ;  e. 
Infraorbital  foramen  ;  /,  Anterior 
l^alatine  groove  ;  g,  Palatal  process  ; 
h,  Premaxillary  suture  ;  i.  Alveolar 
process. 


The  Malar  Bones. 


The  malar  bone  fos  zygomaticum)  underlies  the  most  prominent  part  of  the 
cheek,  and  is  hence  often  called  the  cheek-bone.  Placed  to  the  outer  side  of  the 
orbital  cavity,  it  forms  the  sharp  external  border  of  that  hollow,  and  serves  to 


136 


OSTEOLOGY. 


separate  that  space  from  the  temporal  and  zygomatic  foss»  which  lie  behind; 
below,  it  rests  upon  and  is  united  to  the  superior  maxilla ;  behind,  it  enters  into 
the  formation  of  the  zygomatic  arch  which  bridges  across  the  temporal  fossa. 

As  viewed  from  the  outer  side,  the  bone  is  convex  from  side  to  side,  and  has 
four  angles,  of  which  three  are  prominent.  These  are  the  ascending  or  frontal 
(processus  fronto-sphenoidalis),  the  anterior  or  pointed  extremity  of  the  maxillary 
border,  and  the  posterior  or  temporal  (processus  temporalis). 

The  most  elevated  part  of  the  convex  outer  surfaa  (facies  anterior)  forms  the 
malar  tuberosity.  The  processus  temporalis,  sometimes  called  the  zygomatic  process, 
ends  posteriorly  in  an  oblique  edge,  which  articulates  with  the  extremity  of  the 
zygomatic  process  of  the  temporal  bone.  The  frontal,  the  most  prominent  of  its 
processes,  is  united  superiorly  to  the  external  angular  process  of  the  frontal  bone. 
The  edo-e  between  the  frontal  and  temporal  processes  is  thin  and  sharp ;  it  affords 
attachment  to  the  temporal  fascia,  and  near  its  upper  end  there  is  usually  a 
pronounced  angle  (processus  marginalis),  formed  by  a  sudden  change  in  the  direc- 
tion of  the  border  of  the  bone.  It  is  just  below  this  point  that  the  temporal 
branch  of  the  orbital  nerve  becomes  cutaneous.  The  lower  margin  of  the  temporal 
process  is  somewhat  thicker  and  rounded ;  it  extends  downwards  and  forwards 
towards  the  inferior  angle,  where  the  bone  articulates  with  the  superior  maxilla. 


Frontal  process 


PYontal  process 


Temporal  border 


Temporal  canal 
Orbital  surface 


Temporal 
process  ■p' 


Masseteric 
border 


For  articulation 

with  superior 

maxilla 


Orbital  process 

Temporal 
process 


Temporo- 
zygomatic 
surface 


Fig.  106.— Right  Malar  Bone.     A,  Outer  Bide  ;  B,  Inner  Side. 

and  is  there  confluent  with  the  ridge  which  separates  the  facial  from  the  zygomatic 
aspect  of  the  upper  jaw.  This  edge  of  the  bone  is  sometimes  called  the  masseteric 
border,  since  it  affords  attachment  to  the  fibres  of  origin  of  the  masseter  muscle. 
Sweeping  downwards  in  front  of  the  frontal  process  is  a  curved  edge  which 
terminates  inferiorly  in  a  pointed  process.  This  border  forms  the  outer  and,  in 
part,  the  inferior  margin  of  the  orbital  cavity.  Between  the  anterior  extremity  of 
the  masseteric  edge  and  the  pointed  anterior  angle  there  is  an  irregular  suture  by 
which  the  bone  is  joined  to  the  maxilla.  The  opening  of  the  malar  canal  (foramen 
zygomatico-faciale)  is  seen  on  the  outer  surface  of  the  bone ;  its  size  and  position 
are  very  variable. 

The  mesial  as'pect  of  the  bone  is  distinguished  by  a  curved  elevated  crest,  called 
the  orbital  process,  which  extends  inwards  and  backwards,  and  is  confluent 
externally  with  the  orbital  margin.  This  process  has  two  surfaces — one  anterior, 
which  forms  a  part  of  the  outer  and  lower  wall  of  the  orbit,  and  one  posterior, 
which  is  directed  towards  the  temporal  fossa  above  and  the  zygomatic  fossa  below. 
The  free  edge  of  the  orbital  process  is  thin  and  serrated  ;  a  little  below  its  middle  it 
is  usually  interrupted  by  a  non-articular  notch,  which  corresponds  to  the  anterior 
extremity  of  the  spheno-maxillary  fissure.  The  part  above  this  articulates  with  the 
great  wing  of  the  sphenoid,  the  portion  below  with  the  orbital  plate  of  the  superior 
maxilla.  Behind  the  orbital  process  the  inner  surface  of  the  bone  is  concave  from 
side  to  side,  and  extends  backwards  along  the  mesial  aspect  of  the  temporal  process 
and  upwards  over  the  posterior  half  of  the  inner  side  of  the  frontal  process,  thus 
entering   into  the    formation   of  the  zygomatic   and  temporal  fossae   respectively. 


THE  NASAL  BONE.S.  137 

The  orbital  surface  of  the  orljital  process  usually  displays  the  openings  of  two 
canals  (foramina  zygomatic -orbitalia) — one  which  traverses  the  bone  below  the 
orbital  margin  and  appears  on  the  front  of  the  bone  as  already  described,  the  other 
which  passes  obliquely  upwards  and  outwards  through  the  orbital  process  and 
appears  in  the  temporal  fossa,  to  the  inner  side  of  the  frontal  process  (foramen 
zygoma tico-temporale).  The  former  transmits  the  ramus  subcutaneous  malai ;  the 
latter  the  temporal  branch  of  the  orbital  nerve. 

Below  the  orbital  process  there  is  a  rough  triangular  area,  bounded  externally 
by  the  maxillary  border.  This  articulates  with  the  malar  process  of  the  superior 
maxilla,  and  occasionally  forms  the  outer  wall  of  the  antrum. 

Connexions.- — The  malar  bone  articulates  with  the  frontal,  sphenoid,  superior  maxilla,  and 
temporal  bones. 

Architecture. — In  structure  the  bone  is  compact,  witli  little  cancellous  tissue.  Together 
with  the  zygomatic  process  of  the  temporal  bone  it  forms  the  buttress  which  supports  the  superior 
maxilla  and  the  outer  orbital  wall  externally.  Additional  strength  is  imparted  to  the  bone  by 
the  angular  mode  of  union  of  its  orbital  and  facial  parts. 

Variations.' — Cases  of  division  of  the  malar  bone  by  a  horizontal  suture  have  been  recorded, 
as  well  as  instances  of  its  separation  into  two  parts  by  a  vertical  suture.  Owing  to  the  supposed 
more  frequent  occurrence  of  this  divided  condition  in  Asiatics  the  malar  has  been  named  the  os 
Japonicum.  Barclay  Smith  ("  Proc.  Anat.  Soc,"  Joihr.  Anat.  and  Phijsiol,  April  1898,  p.  40) 
describes  a  case  in  v/hich  the  malar  bone  was  divided  into  two  parts,  an  upper  and  lower,  by  a 
backward  extension  of  the  maxilla,  which  articulated  with  the  zygomatic  process  of  the  temporal, 
thus  forming  a  temporo-maxillary  arch.  Varieties  of  a  like  kind  have  also  been  described  by 
Gruber  and  others.  Cases  have  been  noted  where,  owing  to  deficiency  in  the  development  of  the 
malar,  the  continuity  of  the  zygomatic  arch  has  been  incomplete. 

Ossification. — The  malar  ossifies  in  membrane.  Its  basis  appears  about  tlie  tenth 
week  as  a  thin  ossifying  lamina  which  corresponds  to  the  orbital  margin,  attached  to 
which  there  is  a  backward  expansion  corresponding  to 
the  body  of  the  bone  ;  from  this  posteriorly  there  extends 
the  element  of  the  temporal  process.  On  the  inner  side, 
and  above  the  angle  formed  by  the  orbital  and  temporal 
margins,  there  appears  a  secondary  thickening,  which 
develops  into  a  cap-shaped  layer  which  fits  into  the 
recess    and    ultimately  forms   the    surface    of   the  bone 

directed    to    the    temporal    fossa.       Below    the    orbital  ciub-shap'ed  process 

margin    on    the   inner    side,    and     extending    backwards         ^j^^  107.— Inner  Surface  op 
towards    the    temporal    process,    is    another    secondary  Malar  Bone  at  Birth. 

thickening  which  forms  a  club-shaped  nodule,  the  thick 

end  of  which  is  directed  forwards,  whilst  posteriorly  it  forms,  in  part,  the  lower  margin 
of  the  body  and  temporal  process.  The  overlap  of  these  several  parts  leads  to  the 
formation  of  grooves  which  may  persist  in  the  adult  as  sutures.  (Karl  Toldt,  junr., 
Sitzshr.  des  Akad.  des  Wiss.,  Wien.  July  1902.) 


The  Nasal  Bones. 

The  nasal  bones  (ossa  nasalia),  two  in  number,  lie  in  the  interval  between  the 
frontal  processes  of  the  superior  maxillae,  there  forming  the  root  or  bridge  of  the 
nose.  Each  bone  is  of  elongated  quadrangular  form,  having  two  surfaces — an 
inner  and  outer — and  four  borders.  The  external  surface,  somewhat  constricted 
about  its  middle,  is  convex  from  side  to  side,  and  slightly  concavo-convex  from 
above  downwards.     Near  its  centre  there  is  usually  the  opening  of  a  nutrient  canal. 

The  internal  surface  is  not  so  extensive  as  the  external,  as  the  superior  and 
anterior  articular  borders  encroach  somewhat  upon  it  above.  Concave  from  side  to 
side,  and  also  from  above  downwards,  it  is  covered,  in  the  recent  condition,  by  the 
mucous  membrane  of  the  nose.  Eunning  downwards  along  this  surface  is  a 
narrow  groove  Tsulcus  ethmoidalis)  which  transmits  the  internal  nasal  nerve.  The 
anterior  or  internal  })order,  narrow  below,  is  thick  above,  and,  in  conjuncjtion  with 
its  fellow  at  the  opj>osite  side,  with  which  it  articulates,  forms  a  median  crest 
posteriorly,  which  is  united  to  the  nasal  spine  of  the  frontal,  the  vertical  plate  of 
the  ethmoid,  and  the  septal  cartilage  of  the  nose,  in  that  order  frou)  above  down- 
wards.     The  posterior  or   external   border,  usually  the    longest,  is   serrated  and 


138 


OSTEOLOGY. 


bevelled  to  fit  on  to  the  anterior  edge  of  the  frontal  process  of  the  superior  maxilla. 

The  superior  border  forms  a  wide  toothed  surface,  which  articulates  with  the  inner 

part  of  the  nasal  notch  of  the  frontal 
bone  anteriorly ;  whilst,  behind,  it  rests 
in  contact  with  the  root  of  the  nasal 
process  of  the  same  bone.  The  inferior 
border  is  thin  and  sharp,  and  is  con- 
nected below  with  the  lateral  cartilage 
of  the  nose,  and  is  usually  deeply 
notched  near  its  mesial  extremity. 

Connexions. — The  nasal  bone  articulates 
witli  its  fellow  of  the  opposite  side,  with 
the  frontal  above,  behind  with  the  mesial 
jDlate  of  the  ethmoid  and  with  the  frontal 
process  of  the  suijerior  maxilla.  It  is  also 
A,  Outer  side  ;  united  to  the  septal  and  upj^er  lateral  carti- 
lages of  tlie  nose. 

Architecture.  —  Formed  of  dense  and 
compact  bone  ;  the  strength  of  the  nasal  bones  is  increased  by  their  mode  of  union  and  the 
formation  of  a  median  crest  jjosteriorly. 

Variations. — The  size  and  configuration  of  the  nasal  bones  vary  greatly  in  different  races, 
being,  as  a  rule,  large  and  prominent  in  the  white  races,  and  flat  and  reduced  in  size,  as  well  as 
depressed,  in  the  Mongolian  and  Negro  stock.  Obliteration  of  the  internasal  suture  is  unusual  ; 
it  is  stated  to  occur  more  frequently  in  negroes,  and  is  the  recognised  condition  in  adult  apes. 

Duckworth  has  recorded  a  case  {Journ.  Anat.  and  Physiol.,  vol.  xxxvi.  j).  257)  of  undue  extension 
downwards  of  the  nasal  bone,  which  may  be  perhaps  accounted  for  on  the  supposition  that  the 
lower  part  is  a  persistent  portion  of  the  premaxilla. 

Ossification. — The  nasal  bones  are  each  developed  from  a  single  centre,  which  makes 
its  appearance  about  the  end  of  the  second  month  in  the  membrane  covering  the  fore- 
part of  the  cartilaginous  nasal  capsule.  Subsequent  to  birth  the  underlying  cartilaginous 
stratum  disappears,  persisting,  however,  below  in  the  form  of  the  lateral  nasal  cartilage, 
and  behind  as  the  septal  cartilage  of  the  nose. 


Fig.  108.- 


-RiGHT  Nasal  Bone. 
B,  Inner  side. 


Orbital  surface 


The  Lachrymal  Bones. 

The  lachrymal  bone  (os  lachrymale),  or  os  unguis,  a  thin  scale  of  bone  about  the 
size  of  a  finger-nail,  forms  part  of  the  inner  orbital  wall  behind  the  frontal  pro- 
cess of  the  superior  maxilla.  Irregularly  quadrangular,  it  has  two  surfaces — an 
inner  and  outer — and  four  borders. 

Its  external  or  orbital  surface  has  a  vertical  ridge,  the  lachrymal  crest  (crista 
lachrymalis  posterior),  running  downwards  upon  it.  In  front  of  this  is  the  lachrymal 
groove  (sulcus  lachrymalis)  for  the  lodgment  of  the  lachry- 
mal sac.  The  floor  of  this  groove  descends  below  the  level 
of  the  bulk  of  the  bone,  and  forms  the  descending  process, 
which  helps  to  complete  the  osseous  canal  for  the  nasal 
duct,  and  articulates  inferiorly  with  the  inferior  turbinal. 
The  lower  end  of  the  lachrymal  crest  terminates  in  a 
hook- like  projection,  the  hamular  process  (hamulus  lachry- 
malis), which  curves  round  the  posterior  and  outer  edge 
of  the  lachrymal  notch  of  the  superior  maxilla,  and  thus 
defines  the  upper  aperture  of  the  canal  for  the  nasal  duct. 
To  the  free  edge  of  the  crest  behind  the  lachrymal  groove 
are  attached  the  reflected  portion  of  the  tendo  oculi,  and 
the  tensor  tarsi  muscle.  The  part  of  the  bone  behind  the 
lachrymal  crest  is  smooth  and  continuous  with  the  surface  of  the  os  planum  of 
the  ethmoid.  The  inner  surface  is  irregular  and  cellular  above  ;  it  closes  in  some 
of  the  anterior  ethmoidal  cells.  Where  it  is  smoother  it  forms  a  part  of  the 
lateral  wall  of  the  middle  meatus  of  the  nose  immediately  behind  the  frontal 
process  of  the  superior  maxilla,  and  above  the  inferior  turbinated  bone.  The 
superior  border  articulates  with  the  orbital  plate  of  the  frontal ;  the  anterior  edge 
with  the   posterior   border  of  the  frontal   process  of  the  superior  maxilla,  with 


Fig.  109. — Right  Lachrymal 
Bone  (Orbital  Surface). 


THE  INFERIOE  TURBINATED  BONES. 


139 


which  it  completes  the  lachrymal  groove  for  the  lodgment  of  the  lachrymal  sac. 
The  inferior  margin  articulates  with  the  orbital  surface  of  the  superior  maxilla, 
and  in  front  by  its  descending  process  with  the  inferior  turbinal.  Posteriorly  the 
bone  articulates  with  the  anterior  border  of  the  os  planum  of  the  ethmoid. 

Connexions. — The  lachrymal  bone  articulates  with  four  bones — the  frontal,  ethmoid,  inferior 
turbinal,  and  the  suj^erior  maxilla. 

Architecture. — The  bone  consists  of  a  thin  pajaery  translucent  lamina,  somewhat  strength- 
ened by  the  addition  of  the  vertical  crest. 

Variations. — The  lachrymal  is  occasionally  absent.  In  some  cases  it  is  divided  into  two 
parts  ;  in  others  replaced  by  a  number  of  smaller  ossicles.  In  rare  instances  the  hamular  process 
may  extend  forwards  to  reach  the  orbital  margin,  and  so  bear  a  share  in  the  formation  of  the  face, 
as  in  lemurs  (Gegenbauer).  In  other  instances  the  hamulus  is  much  reduced  in  size.  Occasion- 
ally the  lachrymal  is  separated  from  the  os  planum  of  the  ethmoid  by  a  down-growth  from  the 
frontal,  which  articulates  with  the  orbital  process  of  the  superior  maxilla,  as  is  the  normal 
disposition  in  the  gorilla  and  chimpanzee.  (Turner,  Challenger  Reports,  "  Zoology,"  voL  x. 
Part  IV.  Plate  I. ;  and  A.  Thomson,  Journ.  Anat.  and  Physiol.,  London,  vol.  xxiv.  p.  349.) 

Ossification. — The  lachrynaal  is  developed  from  a  single  centre,  which  makes  its 
appearance  about  the  end  of  the  second  or  the  beginning  of  the  third  month  of  intra- 
uterine life  in  the  membrane  around  the  cartilaginous  nasal  capsule. 


The  Infeeior  Turbinated  Bones. 

The  inferior  turbinated  or  spongy  bone  (concha  inferior)  is  a  shell-like  lamina 
of  bone  lying  along  the  lower  part  of  the  outer  wall  of  the  nasal  fossa.  Of 
elongated  form,  the  bone  displays  two  curved  borders  enclosing  an  internal  and 
external  surface. 

The  superior  or  attached  border  is  thin  and  sharp  in  front  and  behind,  where 


Lachrymal  process 


Ethmoidal  process 


Lachrymal  process 


Ethmoidal  process 


A 


Maxillary  process 
B 


Fig.  110. — PiiGHT  INFEKIOE  TURBINATED  BoNE.     A,  luiier  Surface  ;  B,  Outer  Surface. 

it  articulates  with  the  inferior  turbinal  crests  on  the  inner  surface  of  the  body 
of  the  superior  maxilla  and  the  vertical  plate  of  the  palate  bone  respectively. 
Between  these  two  borders  the  central  part  of  the  upper  edge  rises  in  the  form  of 
a  sharp  crest,  the  fore-part  of  which  forms  the  upstanding  lachrymal  process  (pro- 
cessus lachrymalis),  which  articulates  above  with  the  descending  process  of  the 
lachrymal  bone,  as  well  as  with  the  edges  of  the  nasal  groove  of  the  superior 
maxilla,  thus  completing  the  osseous  canal  of  the  nasal  duct.  The  posterior  end 
of  this  crest  is  elevated  in  the  form  of  an  irregular  projection  called  the  ethmoidal 
process  (processus  ethmoidalis).  This  unites  with  the  uncinate  process  of  the 
ethmoid  bone  (see  Fig.  101).  Spreading  downwards  from  the  middle  of  the 
superior  border,  on  its  outer  side,  is  a  thin,  irregular  plate  of  bone,  the  maxillary 
process  (processus  maxillaris),  which  partially  conceals  the  outer  concave  surface 
of  the  bone,  and,  by  its  union  with  the  inner  wall  of  the  maxillary  sinus,  assists  in 
the  completion  of  the  partition  which  separates  that  cavity  from  the  inferior  nasal 
meatus.  The  inferior  or  free  border,  gently  curved  from  before  backwards  and 
slightly  out-turned,  is  roundfid  and  full,-and  formed  of  bone  which  is  deeply  pitted 
and  of  a  somewhat  cellular  cliaracter.  The  anterior  and  posterior  extremities  of 
tlie  bone,  formed  by  the  convergcmce  of  the  upper  and  lower  borders,  are  thin  and 
sharp;  as  a  rule  the  hinder  end  is  the  mon;  pointed  of  the  two.  The  internal 
surface  projects  into  the  nasal   fossa  ;  convcix  from  above  downwards,  and  slightly 


140 


OSTEOLOGY. 


curved  from  before  backwards,  it  forms  the  floor  of  the  middle  meatus.  It  is 
rough  and  pitted,  and  displays  some  scattered  and  longitudinally  directed  vascular 
grooves.  The  outer  surface  overhangs  the  inferior  nasal  meatus.  Concave  from 
above  downwards,  and  to  some  extent  from  before  backwards,  it  is  directed  towards 
the  outer  wall  of  the  nasal  fossa.  It  is  smooth  in  front,  where  it  corresponds  to 
the  opening  of  the  canal  for  the  nasal  duct ;  behind  and  towards  its  lower  border 
it  is  irregular  and  pitted.  In  the  disarticulated  bone  this  surface  is  in  part  con- 
cealed by  the  downward  projecting  maxillary  process. 

Connexions.  —  The  inferior  turbinal  articulates  with  the  su2:'erior  maxilla,  lachrymal, 
ethmoid,  and  palate  bones. 

Variation. — A  case  in  which  the  inferior  turbinals  were  absent  has  been  recorded  by 
Hyrtl. 

Ossification.  —  The  infei-ior  turbinate  bone,  the  maxillo- turbinal  of  comparative 
anatomy,  is  derived  from  the  cartilage  forming  the  outer  wall  of  the  nasal  capsule,  the 
upper  portion  of  which  forms  the  ethmo-turbinals.  It  ossifies,  however,  from  a  separate 
centre,  which  appears  about  the  fifth  month  of  foetal  life,  and  later  contracts  a  union 
by  a  horizontal  lamella  on  its  outer  side  with  the  superior  maxillary  bone. 


Fm.  111. 


Palate  Superior  maxilla 

-Vomer  as  seen  from  the  Right  Side. 


The  Vomer. 

The  vomer,  a  bone  of  irregular  quadrilateral  shape,  is  placed  mesially  in  the 
hinder  part  of  the  nasal  septum.  It  has  four  borders  and  two  surfaces.  The 
superior  border,  which  can  readily  be  distinguished  by  the  presence  on  either  side 

of  an  everted  lip  or  ala,  slopes  from  behind 
upwards  and  forwards,  and  articulates 
with  the  under  surface  of  the  body  of  the 
sphenoid,  the  pointed  rostrum  of  which 
is  received  into  the  groove  formed  by  the 
projecting  alee.  Laterally  these  alae  are 
wedged  in  between  the  sphenoidal  pro- 
cesses of  the  palate  bone  in  front,  and 
the  vaginal  processes  at  the  root  of  the 
internal  pterygoid  plates  behind.  The 
posterior  harder,  which  slopes  from  behind 
downwards  and  forwards,  is  free,  and  forms  a  sharp,  slightly  curved  edge ;  this 
constitutes  the  posterior  margin  of  the  nasal  septum,  and  serves  to  separate  the 
openings  of  the  posterior  nares.  The  inferior  border,  more  or  less  horizontal  in 
direction,  articulates  with  the  nasal  crest  formed  by  the  superior  maxillary  and 
palate  bones.  The  anterior  edge  is  the  longest ;  it  slopes  obliquely  from  above 
downwards  and  forwards.  In  its  upper  half  it  is  ankylosed  to  the  perpendicular 
plate  of  the  ethmoid ;  in  its  lower  half  this  margin  is  grooved  for  the  reception 
of  the  septal  cartilage  of  the  nose.  The  anterior  extremity  of  the  bone  forms  a 
truncated  angle,  which  articulates  with  the  hinder  border  of  the  incisor  crest  of 
the  superior  maxillse,  and  sends  downwards  a  pointed  process  which  passes  between 
the  incisor  foramina.  The  right  and  left  surfaces  of  the  bone  are  smooth,  and 
covered  by  mucous  membrane.  It  is  not  uncommon  to  find  them  deflected  to 
one  or  other  side.  A  few  vascular  grooves  may  be  noticed  scattered  over  these 
surfaces,  and  one,  usually  more  distinct  than  the  others,  running  obliquely  down- 
wards and  forwards,  indicates  the  course  of  the  naso-palatine  nerve. 

Connexions. — The  vomer  articulates  with  the  sjjhenoid,  the  ethmoid,  the  palates,  and  the 
superior  maxillpe.     In  front  it  supports  the  septal  cartilage. 

Architecture. — The  bone  is  composed  of  two  comi^act  layers  fused  below,  but  separated  above 
by  the  groove  for  the  lodgment  of  the  rostrum  of  the  sphenoid  behind,  and  the  sejDtal  cartilage  in 
front.  The  lamellae  are  also  sej^arated  from  each  other  by  a  canal  which  runs  horizontally  from 
behind  forwards  in  the  substance  of  the  bone,  and  which  transmits  the  nutrient  vessel  of 
the  bone. 

Variations. — Owing  to  imperfect  ossification  there  may  be  a  deficiency  in  the  boue,  filled  up 
during  life  by  cartilage.  The  se23aration  of  the  two  lamellae  along  the  anterior  border  varies 
considerably,  and  instances  are  recorded  where  they  were  separated  by  a  considerable  cavity 
within  the  substance  of  the  bone.      The  spheno-vomerine  canal  is  a  minute  opening  behind 


THE  PALATE  BONES. 


141 


the  rostrum  of  the  sphenoid,  and  between  it  and  the  alas  of  the  vomer,  by  which   the  nutrient 
artery  enters  the  bone. 

Ossification. — The  vomer,  primitively  double,  begins  to  ossify  about  the  end  of  the 
second  month  of  foetal  life.  A  nucleus  appears  on  either  side  in  the  membrane  overlying 
the  back  and  lower  part  of  the  vomerine  cartilage ;  these  form  the  primitive  lamellge 
developed  on  either  side  of,  and  not  from,  the  cartilage.  About  the  third  month  these 
laminae  become  fused  behind  and  below,  thus  forming  a  deep  groove  in  which  the  cartilage 
is  lodged.  As  growth  goes  on  the  groove  becomes  reduced  by  the  further  fusion  of  the 
lateral  plates  and  the  absorption  of  the  cartilage,  until  the  age  of  puberty,  by  which 
time  the  lateral  laminae  have  united  to  form  a  mesial  plate,  the  primitively  divided  con- 
dition of  which  is  now  only  represented  by  the  eversion  of  the  alse  and  the  grooving 
along-  the  anterior  border. 


The  Palate  Bones. 

The  palate  bone  (os  palatinum),  of  irregular  shape,  assists  in  the  formation  of 
the  outer  wall  of  the  back  part  of  the  nasal  fossae,  the  posterior  portion  of  the  hard 
palate,  the  orbit,  the  spheno-maxillary,  zygomatic,  and   the  pterygoid  fossae.     It 


Sphenoid 


Spheno- 
maxillary fossa 


Sphenoidal 
process  ,>-^ 


Orbital  process 
^\    ^Ethmoid 


Orbital  surface 


For  superior  maxilla 


Orbital  process 


Orbital  surface 
Ethmoid 


Sphenoid 


Ethmoidal  crest  — -* 
Spheno-palatine  notch 


Middle  meatus 


Inferior  meatus 

Pterygoid  fossa  J 
]\  Tuberosity 

Surface  for  attach.'    Surface    Posterior  palatine  canal  ""'""plate"  Posteuor         Internal 

of  pterygoideus     for  superior  nasal  spine         pterygoid  plate 

extemus  maxilla 

A 

Fig.  112.— Right  Palate  Bone. 
A,  As  seen  from  the  Outer  Side  ;  B,  As  viewed  from  the  Inuer  Side. 

consists  of  a  horizontal  and  a  vertical  plate,  united  to  each  other  like  the  hmbs  of 
the  letter  L.  At  their  point  of  union  there  is  an  irregular  outstanding  process 
called  the  tuberosity,  whilst  capping  the  summit  of  the  vertical  plate  and  separated 
by  a  deep  cleft  are  two  irregular  pieces^  of  bone,  called  the  sphenoidal  and  orbital 

processes.  ^  j    r        -u    a 

The  horizontal  plate  (pars  horizontalis)  has  two  surfaces  and  four  borders 
As  its  name  implies,  it  is  horizontal  in  position,  and  forms  the  posterior  third  ot 
the  hard  palate.  Its  upper  surface,  which  is  smooth,  is  slightly  concave  from  side 
to  side,  and  forms  the  floor  of  the  hinder  part  of  the  nasal  fossae.  Its  inferior 
surface,  rougher,  is  directed  towards  the  mouth,  and  near  its  posterior  edge  otten 
displays  a  transverse  ridge  for  the  attachment  of  a  part  of  the  aponeurosis  ot  the 
tensor  palati  muscle.  The  anterior  border  articulates  by  means  ot  an  irregular 
suture  with  the  hinder  edge  of  the  palatal  process  of  the  superior  maxilla.  Ihe 
posterior  raan/m  is  i'rce  and  concave  from  side  to  side ;  by  its  sharp  edge  it  furnishes 
attachment  to  the  aponeurosis  of  the  soft  palate.  The  internal  border  is  upturned, 
and  when  it  articulates  with  its  fellow  of  the  opposite  side  it  iorms  superiorly  a 
central  crest  continuous  in  front  with  the  nasal  crest  of  the  superior  maxiiia ;  it 
supports  the  hinder  part  of  the  lower  border  oi'  the  vomer,  and  j)ro.jectmg  beyond 
the  line  of  the  i;ost(;rior  border  forms  tlu;  posterior  nasal  or  palatine  spine  (spina 
iiasalis  posterior;.     Tlie  external  larder  fuses  with  the  vertical  plate,  forming  with 


142 


OSTEOLOGY. 


Orbital  process 


Sphenoid 

Sphenoidal  process 

Pterygo-palatme 
groo\ e 


Orbital 
/'surface 


it  a  right  angle.     The  liinder  extremity  of  this  edge  is  grooved  bj  the  lower  end  of 
the  posterior  palatine  canal. 

The  vertical  plate  (pars  perpeudicularis)  is  very  much  broader  below  than 
above.  Composed  of  thin  bone,  it  is  liable  to  be  broken  in  the  process  of  disarticu- 
lation, particularly  at  its  upper  part,  so  that  it  is  somewhat  uncommon  to  meet 
with  a  perfect  specimen.  It  may  be  described  as  possessing  two  surfaces  and 
four  borders.  Its  inner  surface,  which  is  directed  towards  tbe  cavity  of  the  nose, 
is  crossed  horizontally  about  its  middle  by  the  inferior  turbinated  crest  (crista 
turbinalis)  with  which  the  hinder  end  of  the  superior  border  of  the  inferior 
turbinated  bone  articulates ;  above  and  below  this  it  enters  into  the  formation  of 
the  outer  wall  of  the  middle  and  inferior  meatuses  of  the  nose  respectively.  Near 
the  upper  extremity  of  the  vertical  plate,  and  below  the  processes  which  spring 
from  it,  there  is  another  ridge  more  or  less  parallel  to  that  already  described. 
This  is  the  superior  turbinated  or  ethmoidal  crest  (crista  ethmoidalis),  and  with  this 
the  hinder  extremity  of  the  middle  turljinated  Ijone  is  united.  The  external  surface, 
which  forms  the  inner  wall  of  the  spheno- maxillary  fossa,  is  channelled  by  a 
vertical  groove  (sulcus  pterygo-palatinus),  converted  into  a  canal  by  articulation 

with  the  superior  maxillary  bone.  This 
canal,  called  the  posterior  palatine  canal 
transmits  the  large  palatine  nerve  and 
descending  palatine  vessels.  Anteriorly 
the  external  surface  projects  forwards  to 
a  variable  extent,  and  helps  to  close  in 
the  antrum  of  the  maxilla  by  its  maxillary 
Middle  meatus         Mpi  ""''^"  process.      The   anterior    border   is  a  thin 

edge  of  irregular  outline  which  articu- 
lates above  with  the  ethmoid,  with  the 
posterior  edge  of  the  maxillary  process 
of  the  inferior  turbinated  bone  about  its 
middle,  and  below  with  the  superior 
maxilla.  The  posterior  border,  thin  above, 
where  it  articulates  with  the  fore-part 
of  the  internal  pterygoid  plate,  expands 
below  into  a  pyramidal  process  called  the 
tuberosity.  The  inferior  border  of  the 
vertical  plate  is  confluent  with  the  outer 
edge  of  the  horizontal  plate ;  posteriorly, 
and  immediately  in  front  of  the  tuberosity,  it  is  notched  by  the  lower  extremity 
of  the  posterior  palatine  canal.  The  superior  border  supports  the  orbital  and 
sphenoidal  processes ;  the  former — the  anterior — is  separated  from  the  latter  by  a 
notch  (incisura  spheno-palatina),  which  is  converted  into  the  spheno -palatine  foramen 
by  the  articulation  of  the  palate  bone  with  the  under  surface  of  the  sphenoid. 
Through  this  communication  between  the  spheno-maxillary  and  nasal  fossae  pass 
the  spheno-palatine  artery  and  the  nasal  branches  of  the  spheno-palatine  ganglion. 
The  tuberosity  (processus  pyramidalis)  is  directed  backwards  and  outwards 
from  the  angle  formed  by  the  vertical  and  horizontal  plates,  and  presents  on  its 
posterior  stirface  a  central  smooth  vertical  groove,  bounded  on  either  side  by  rough 
articular  furrows  which  unite  above  in  a  V-shaped  manner  with  the  upper  thin 
posterior  edge.  These  latter  articulate  with  the  fore-parts  of  the  lower  portions  of  the 
internal  and  external  pterygoid  plates,  while  the  central  groove  fits  into  the  wedge- 
like interval  between  the  two  pterygoid  plates,  thus  entering  into  the  formation  of 
the  pterygoid  fossa.  The  outer  surface  of  the  tuberosity  is  rough  above,  where  it 
is  confluent  with  the  outer  surface  of  the  vertical  plate  which  articulates  with  the 
tuberosity  of  the  superior  maxilla ;  beloiv,  there  is  a  small,  smooth,  triangular  area 
which  appears  between  the  tuberosity  of  the  superior  maxilla  and  the  outer  surface 
of  the  external  pterygoid  plate,  and  so  enters  into  the  floor  of  the  zygomatic  fossa. 
Passing  through  the  tuberosity  in  a  vertical  direction  are  the  posterior  and  external 
accessory  palatine  canals  (foramina  palatina  minora)  for  the  transmission  of  the 
smaller  palatine  nerves  and  vessels. 


Inferior  turbinated 
crest 

Inferior  meatus 
Nasal  crest 


Posterior 
nasal 
spine 
Horizontal  plate 


For  internal  pterygoid  plate 

Fig.  113. — Right  Palate  Bone. 
As  seen  from  Behind. 


THE  INFERIOE  MAXILLAEY  BONE.  143 

The  orbital  process  (processus  orbitalis),  shaped  like  a  hollow  cube,  surmounts 
the  fore-part  of  the  vertical  plate.  The  open  mouth  of  the  cube  is  usually  directed 
backwards  and  inwards  towards  the  fore-part  of  the  body  of  the  sphenoid,  with  the 
cavity  of  which  it  commonly  communicates ;  the  fore-part  of  the  cube  articulates 
with  the  inner  end  of  the  angle  formed  by  the  orbital  plate  and  zygomatic  surface 
of  the  superior  maxilla.  Of  the  remaining  four  surfaces,  one  directed  forwards  and 
inwards  articulates  with  the  ethmoid.  The  others  are  non-articular :  the  superior 
enters  into  the  formation  of  the  floor  of  the  orbit ;  the  external  is  directed  towards 
the  spheno-maxillary  fossa ;  whilst  the  inferior,  which  is  confluent  with  the  inner 
surface  of  the  vertical  plate,  is  of  variable  extent,  and  overhangs  the  superior 
meatus  of  the  nose. 

The  sphenoidal  process  (processus  sphenoidalis),  much  smaller  than  the  orbital, 
curves  upwards,  inwards,  and  backwards  from  the  hinder  part  of  the  summit  of  the 
vertical  plate.  Its  superior  surface,  which  is  grooved,  articulates  with  the  fore-part 
of  the  under  surface  of  the  body  of  the  sphenoid  and  the  root  of  the  internal 
pterygoid  plate,  thereby  converting  the  groove  into  the  pterygo-palatine  canal,  which 
transmits  an  artery  of  the  same  name  together  with  a  pharyngeal  branch  from  the 
spheno-palatine  ganglion.  Its  outer  side  enters  into  the  formation  of  part  of  the 
inner  wall  of  the  spheno-maxillary  fossa.  Its  internal  curved  aspect  is  directed 
towards  the  nasal  fossa,  whilst  its  inner  edge  is  in  contact  with  the  ala  of  the 
vomer. 

Connexions. — The  palate  bone  articulates  with  its  fellow  of  tlie  opj^osite  side,  with  the 
ethmoid,  vomer,  sphenoid,  sujjerior  maxilla,  and  inferior  turbinated  bones. 

Ossification. — The  palate  bones  are  developed  from  the  ossification  of  the  membrane 
covering  the  sides  of  the  oral  cavity.  According  to  Rambaud  and  Renault,  two  primitive 
centres  appear  about  the  sixth  week  of  foetal  life.  From  one  of  these  the  tuberosity  and 
the  part  of  the  vertical  plate  behind  the  posterior  palatine  groove  is  developed ;  from  the 
other  the  remainder  of  the  bone  is  formed,  with  the  exception  of  the  orbital  and  sphenoidal 
processes  which  are  derived  from  secondary  centres  that  make  their  appearance  some- 
what later.  Other  authorities  describe  the  bone  as  ossifying  from  a  single  centre  which 
appears  about  the  end  of  the  second  month  in  the  angle  between  the  vertical  and  hori- 
zontal plates. 

At  birth  the  bone  is  much  longer  in  its  antero-posterior  diameter  than  in  its  vertical 
height,  the  converse  of  its  typical  adult  form. 

The  Infeeior  Maxillary  Bone. 

The  inferior  maxilla  (rnandibula)  or  mandible,  of  horse-shoe  shape,  with  the 
extremities  upturned,  is  the  only  movable  bone  of  the  face.  Stout  and  strong,  it 
supports  the  teeth  of  the  lower  dental  arch,  and  articulates  with  the  base  of  the 
cranium,  by  the  joints,  on  either  side,  between  its  condyles  and  the  glenoid  fossse 
of  the  temporal  bones.  The  anterior  or  horizontal  part,  which  contains  the  teeth, 
is  called  the  body  (corpus) ;  the  posterior  or  vertical  portions  constitute  the  rami 
(rami  mandibulse). 

The  body  (corpus  mandibulse)  displays  in  the  middle  line  in  front  a  faint 
vertical  ridge,  the  symphysis,  which  indicates  the  line  of  fusion  of  the  two 
symmetrical  halves  from  which  the  bone  is  primarily  developed.  Inferiorly  this 
ridge  divides  so  as  to  enclose,  in  well-marked  specimens,  a  triangular  area — the 
mental  protuberance  Tprotuberantia  mentalis),  the  centre  of  which  is  somewhat 
depressed,  thus  emphasising  the  inferior  angles,  which  are  known  as  the  mental 
tubercles  ftubera  mentalia).  The  outer  surface  is  crossed  by  a  faint,  elevated  ridge, 
the  external  oblique  line  (linea  obliqua),  which  runs  upwards  and  backwards  from 
the  mental  tubercle  to  the  fore-part  of  the  anterior  border  of  the  ramus,  with 
which  it  is  confluent.  A  little  ab(jve  this,  midway  between  the  upper  and  lower 
borders  of  the  jaw,  and  in  line  with  the  root  of  the  second  bicuspid  tooth,  the  bone 
is  pierced  by  the  mental  foramen  (foramen  mentale) ;  this  is  the  anterior  opening 
of  the  inferior  dental  canal,  wliifib  traverses  the  body  of  the  bone.  Through  this 
aperture   the   mental   vessels   and   nerves   reach  the  surface.     The  up'per  harder 


144 


OSTEOLOGY, 


supports  the  sixteen  teeth  of  the  lower  jaw.  It  is  thick  behind  and  thinner  in 
front,  in  correspondence  with  the  size  of  the  roots  of  the  teeth.  Anteriorly  the 
sockets  of  the  incisor  and  canine  teeth  produce  a  series  of  vertical  elevations  (juga 
alveolaria),  of  which  that  corresponding  to  the  canine  tooth  is  the  most  prominent. 
When  this  is  outstanding  it  gives  rise  to  a  hollowing  of  the  surface  between  it  and 
the  symphysis,  often  referred  to  as  the  incisor  fossa ;  frequently,  however,  this 
is  only  faintly  marked.  Below  the  external  ol)li(jue  line  the  bone  is  full  and 
rounded,  and  ends  below  in  the  inferior  horde?'  or  base.  This  slopes  outwards  at 
the  sides,  and  forwards  in  front,  where  it  is  thick  and  hollowed  out  on  either  side 
of  the  symphysis  to  form  the  digastric  fossae  (fossai  digastricije),  to  which  the 
anterior  bellies  of  the  digastric  muscles  are  attached;  narrowing  somewhat  behind 
this,  the  inferior  border  again  expands  opposite  the  molar  teeth,  and  finally 
becoming  reduced  in  width,  terminates  posteriorly  at  the  angle  formed  between  it 
and  the  posterior  border  of  the  ramus.  The 
deep  or  inner  surface  of  the  body  is  crossed 
by  the  internal  oblique  line  or  mylo-hyoid  ridge 
(linea  mylo-hyoidea).  This  slants  from  above 
downwards  and  forwards  towards  the  lower 
part  of  the  symphysis.  It  serves  for  the 
origin  of  the  mylo-hyoid  muscle,  and  also 
furnishes  an  attachment  to  the  superior  con- 
strictor of  the  pharynx  just  behind  the  last 
molar  tooth.  Below  the  hinder  part  of  this 
ridge  the  surface  is  hollowed  to  form  a  fossa 
for  the  lodgment 
of  the  submaxil- 
lary gland.  Above 
the  fore -part  of 
the  internal  ob- 
lique line  the 
bone  is  smooth 
and  usually  con- 
vex. Here  the 
sublingual  gland 
lies  in  relation  to 
it.  In  the  angle 
formed  by  the 
convergence  of  i 
the  two  internal 
oblique  lines,  and 
in  correspondence 
with  the  back  of 
the  lower  part  of 

the  symphysis,  there  is  a  raised  tubercle  surmounted  by  two  laterally  placed 
spines,  the  mental  or  genial  spines  (spinse  meutales).  Occasionally  these  are 
ao-ain  subdivided  into  an  upper  and  lower  pair,  or  it  may  be  that  the  lower 
pair  may  fuse  to  form  a  rough  median  ridge.  To  the  upper  pair  of  spines 
the  genio-hyoglossi  muscles  are  attached,  whilst  the  lower  pair  serve  for  the 
origin  of  the  genio-hyoid  muscles.  Immediately  above  the  tubercle  there  is 
a  median  foramen  for  the  transmission  of  a  nutrient  vessel,  and  close  to  the 
alveolar  border  opposite  the  intervals  between  the  central  and  lateral  incisors,  there 
are  two  little  vascular  canals. 

The  ramus  (ramus  mandibulse)  passes  upwards  from  the  back  part  of  the  bone, 
forming  by  the  junction  of  its  posterior  border  with  the  base  of  the  body  tlie  angle 
(angulus  mandibulse),  which  is  usually  rounded  and  more  or  less  everted.  The 
outer  surface  of  the  ramus  affords  attachment  to  the  masseter  muscle,  and  when 
that  muscle  is  powerfully  developed  the  bone  is  usually  marked  by  a  series  of 
oblique  curved  ridges,  best  seen  towards  the  angle.  About  the  middle  of  the  deep 
.  or  inner  surface  is  the  large  opening  (foramen  mandibulare)  of  the  inferior  dental 


Fig.  114. — The  Lower  .Jaw  as  seen  from  the  Left  Side. 


1.  Meutal  tubercle. 

2.  Mental  prominence. 

3.  Symphysis. 


4.  Coronoid  i^rocess. 

5.  Condyles. 

6.  Neck. 


7.  Angle. 

8.  E.xternal  oblique  line. 

9.  Mental  foramen. 


THE  INFERIOE  MAXILLAEY  BONE. 


145 


canal,  which  runs  downwards  and  forwards  to  reach  the  body,  and  transmits  the 
inferior  dental  vessels  and  nerves.  This  aperture  is  overhung  in  front  by  a  jjointed 
scale  of  bone,  the  lingula,  to  the  edges  of  which  the  internal  lateral  ligament  of  the 
temporo-maxillary  articulation  is  attached.  Behind  the  lingula  and  leading  down- 
wards and  forwards  for  an  inch  or  so  from  the  opening  of  the  inferior  dental  canal 
is  the  mylo-hyoid  groove  (sulcus  mylo-hyoideus),  along  which  the  mylo-hyoid  artery 
and  nerve  pass.  Behind  and  below  this  groove  the  inner  surface  of  the  angle  is 
rough  for  the  attachment  of  the  internal  pterygoid  muscle.  Superiorly  the  ramus 
supports  the  coronoid  process  in  front,  and  the  condyle  behind,  the  two  being 
separated  by  the  wide  sigmoid  notch  (incisura  mandibul&e),  over  which  there  X-»as8 
in  the  recent  condition  the  vessels  and  nerve  to  e 

the  masseter  muscle.  The  coronoid  process,  of 
variable  length  and  beak-shaped,  is  limited  behind 
by  a  thin  curved  margin,  which  forms  the  anterior 
boundary  of  the  sigmoid  notch.  In  front  its 
anterior  edge  is  convex  from  above  downwards 
and  forwards,  and  becomes  confluent  below  with 
the  anterior  border  of  the  ramus  and  the  external 
oblique  line.  To  the  inner  side  of  this  edge  there 
is  a  grooved  elongated  triangular  surface,  the  inner 
margin  of  which,  commencing  above  near  the 
summit  of  the  coronoid  process,  leads  downwards 
along    the    inner  3 

side  of  the  root  of 
the  last  molar 
tooth  towards  the 
internal  oblique 
line.  Behind  this 
ridge  the  thick- 
ness of  the  ramus 
is  much  reduced. 
The  temporal 
muscle  is  inserted 
into  the  margins 
and  inner  surface 
of  the  coronoid 
process.  The  pos- 
terior border  of 
the  ramus  is  con- 
tinued upwards  to 
support  the  con- 
dyle (capitulum  mandibulse),  below  which  it  is  somewhat  constricted  to  form 
the  neck  (collum  mandibulse),  which  is  compressed  from  before  backwards,  and 
bounds  the  sigmoid  hollow  posteriorly.  To  the  inner  side  of  the  neck,  im- 
mediately below  the  condyle,  there  is  a  little  depression  (fovea  pterygoidea) 
for  the  insertion  of  the  external  pterygoid  muscle.  The  convex  surface  of 
the  condyle  is  transversely  elongated,  and  so  disposed  that  its  long  axis  is 
inclined  nearly  horizontally  from  within  outwards  and  a  little  forwards.  The 
convexity  of  the  condyle  is  more  marked  in  its  antero-posterior  than  in  its 
transverse  diameter. 


Fig.  115. — The  Inneu  Side  of  the  Eight  Half  of  the  Lower  Jaw. 


1.  Mental  spines. 

2.  Surface   in   relation   to 

the  sublingual  gland. 

3.  Alveolar  border. 

4.  Lingula. 


5.  Coronoid  process. 

6.  Condyles. 

7.  Inferior  dental  foramen. 

8.  Mylo-hyoid  groove. 

9.  Angle. 


10.  Fossa  for  submaxillary 

gland. 

11.  Internal  oblique  line. 

12.  Digastric  fossa. 


Architecture. — The  mandiljle  is  rcanai'kable  for  the  density  and  thickness  of  its  inner  and 
outer  walls.  Wliere  these  coalesce  below  at  the  base  of  the  body,  the  bone  is  i^articularly  stout. 
Superiorly,  w'here  they  form  the  walls  of  the  alveoli,  they  gradually  thin,  being  thicker, 
however,  on  the  inner  than  the  outer  side,  except  in  the  region  of  the  last  molar  tooth, 
where  the  inner  wall  is  the  thinner.  The  cancellous  substance  is  open-jneshed  below,  finei' 
and  more  condensed  where  it  surrounds  the  alveoli.  The  inferior  dental  canal  is  large  and 
lias  no  very  definite  wall  ;  it  is  prolonged  beyond  the  mental  foramen  t(j  reach  the  incisor 
teeth.  From  it  nume,roiis  channels  j)ass  upwards  to  the  sockets  of  the  teeth,  and  it  com- 
municates freely  with  the  surronrifling  cancellous  tissue.  Above  the  canal  the  substance  of  the 
bone  is  broken  up  by  the  alveoli  for  the  recejjtion  of  the  roots  of  the  teeth.  In  the  substance 
11 


146 


OSTEOLOGY. 


of  the  condyle  the  cancellous  tissue  is  more  compact,  with  a  general  striation  vertical  to  the 
articular  surface. 

The  mental  prominence  is  an  essentially  human  characteristic;  by  some  it  is  associated  with  the 
development  of  speech  in  man,  others  regard  it  as  due  to  the  reduction  in  the  size  of  the  teeth. 

Variations.^Considerable  differences  are  met  with  in  the  height  of  the  coronoid  process: 
usually  its  sumiuit  reaches  the  same  level  as  the  condyle,  or  slightly  above  it ;  occasionally,  how- 
ever, it  rises  to  a  much  liigher  level ;  in  other  cases  it  is  much  reduced.  These  difi'erences 
naturally  react  on  the  form  of  the  sigmoid  notch.  The  projection  of  the  mental  protuberance 
is  also  liable  to  vary.  Occasionally  the  mental  foramen  is  douljle,  and  sometimes  the  mylo-hyoid 
groove  is  for  a  short  distance  converted  into  a  canal. 

Ossification.  —  The  development  of  the  lower  jaw  is  intimately  associated  with 
Meckel's  cartilage,  the  cartilaginous  bar  of  the  first  visceral  or  mandibular  arch.  Meckel's 
cartilages,  of  which  there  are  two,  are  connected  proximally  with  the  periotic  capsule  and 
cranial  base.  Their  distal  ends  are  united  in  the  region  of  the  symphysis.  It  is  in  the 
connective  tissue  overlying  the  outer  surface  of  this  cartilaginous  arch  that  the  bulk  of 
the  lower  jaw  is  developed.     The  cartilage  itself  is  not  converted  into  bone,  but  undergoes 

resorption,  except  its 
h  £S!Wh  anterior     extremity, 

which  is  stated  to 
undergo  ossification 
to  form  the  part  of 
the  jaw  lying  be- 
tween the  mental 
foramen  and  the 
symphysis.  Inathird 
or  fourth  month 
foetus  the  cartilage 
can  be  traced  from 
the  under  surface  of 
the  fore-part  of  the 
tympanic  ring  down- 
Avards  and  forwai'ds 
to  reach  the  jaw,  to 
which  it  is  attached 
at  the  opening  of  the 
inferior  dental  canal ; 
from  this  it  may  be 
traced  forwards  as  a 
narrow  strip  applied 
to  the  inner  surface  of 
the  mandible,  which 
it    sensibly    grooves. 

The  proximal  end  of  this  furrow  remains  permanently  as  the  mylo-hyoid  groove.  The 
part  of  the  cartilage  between  the  tympanic  ring  and  the  jaw  becomes  converted  into 
fibrous  tissue,  and  persists  in  the  adult  as  the  so-called  internal  lateral  ligament  of  the 
temporo-maxillary  articulation,  its  proximal  end  through  the  Glaserian  fissure  being  con- 
tinuous with  the  slender  process  of  the  malleus.  J.  Chain e  (Cmnptes  Rendus.  Biologie, 
1903)  takes  exception  to  this  view  and  regards  the  internal  lateral  ligament  as  the  remnant 
of  a  muscular  slip.  The  part  which  is  applied  to  the  inner  surface  of  the  lower  jaw 
disappears.  In  the  tissue  overlying  the  cartilage  ossification  begins  by  several  centres  as 
early  as  the  sixth  or  seventh  week  of  foetal  life,  in  this  respect  resembling  the  clavicle,  by 
which  it  is  alone  preceded.  The  dentary  or  basal  centre  forms  the  outer  wall  and  lower 
border.  With  this  is  united  the  splenial  portion,  which  appears  somewhat  later,  forming 
the  inner  table  from  near  the  symphysis  backwards  towards  the  opening  of  the  inferior 
dental  canal  where  it  terminates  in  the  lingula.  By  the  union  of  these  two  parts  a  groove 
is  formed,  which  ultimately  becomes  covered  in,  and  in  which  the  inferior  dental  nerve 
and  vessels  are  lodged.  As  has  been  already  stated,  the  part  of  the  body  between  the 
symphysis  and  the  mental  foramen  is  regarded  as  directly  developed  by  the  ossification  of 
the  fore-part  of  the  Meckelian  cartilage.  As  Avill  have  been  gathered  from  the  above 
description,  the  upper  part  of  the  I'amus  and  its  processes  have  no  connexion  with  Meckel's 
cartilage.  The  condyle  and  the  coronoid  process  arc  each  developed  from  a  separate 
centre,  pi-eceded  by  a  cartilaginous  matrix.  These  several  centres  are  all  united  about  the 
fourth  month. 

At  birth  the  lower  jaw  consists  of  two  lateral  halves  united  at  the  symphysis  by  fibrous 


Fig.  116. 


-Lower  Jaw  at  Birth.     A,  As  seen  from  a1>ove 
B,  Outer  side  :  C,  Inner  side. 


a,  Mental  foramen  ;  &,  Inferior  dental  canal ;  c,  Lingula  ;  d,  Sockets  for  the  dental  sacs 


THE  HYOID  BONE. 


147 


tissue ;  towards  the  end  of  the  first,  or  during  the  second  year,  osseous  union  between  the 
two  halves  is  complete.  In  infancy  the  jaw  is  shallow  and  the  rami  proportionately  small; 
fiirthei',  owing  to  the  obliquity  of  the  ramus  the  angle  is  large,  averaging  about  150". 
The  mental  foramen  lies  near  the  lower  border  of  the  bone.  Coincident  with  the  eruption 
of  the  teeth  and  the  use  of  the  jaw  in  mastication,  the  rami  rapidly  increase  in  size,  and 
the  angle  becomes  more  acute.  After  the  completion  of  the  permanent  dentition  it 
approaches  more  nearly  a  right  angle  varying  from  110°  to  120'.  The  body  of  the  bone 
is  stout  and  deep,  and  the  mental  foramen  xisually  lies  midway  between  the  upper  and 
lower  borders.  As  age  advances,  owing  to  the  loss  of  the  teeth  and  the  consequent 
shrinkage  and  absorption  of  the  alveolar  border  of  the  bone,  the  body  becomes  narrow  and 
attenuated,  and  the  mental  foramen  now  lies  close  to  the  upper  border.  At  the  same  time 
the  angle  opens  out  again  (1.30°  to  140°),  in  this  respect  resembling  the  infantile  condition. 
In  old  age  the  coronoid  process  and  the  condyle  form  a  more  open  angle  with  each  other 
than  in  the  adult. 

The  Hyoid  Bone. 

The  hyoid  bone  (os  hyoideum),  or  os  linguae,  though  placed  in  the  neck,  is 
developmentally  connected  with  the  skull.  It  lies  between  the  mandible  above 
and  the  larynx  below,  and  is  connected  with  the  root  of  the  tongue.  Of  U-shaped 
form,  as  its  name  implies  (Greek  v  and  e'l8o<;,  like),  it  consists  in  the  adult  of  a 
central  part,  or  body,  with  which  on  either  side  are  united  two  long  processes 
extending  backwards — the  great  cornua.  At  the  point  where  these  are  ossified 
with  the  body,  the  lesser  cornua,  which  project  upwards  and  backwards,  are  placed. 

The  body  (basis)  is  arched  from  side  to  side  and  compressed  from  before  back- 
wards, so  that  its  surfaces  slope  downwards  and  forwards.  Its  cmterior  surface 
displays  a  slight  median  ridge,  on  either  side  of 
which  the  bone  is  marked  by  the  attachment 
of  the  mylo-hyoid  muscles.  Its  'posterior  surface, 
deeply  hollowed,  is  concave  from  side  to  side  and 
from  above  downwards.  Herein  lie  a  quantity 
of  fat  and  a  bursa  which  separates  this  aspect 
from  the  thyro-hyoid  membrane.  The  upper 
border  is  broad ;  it  is  separated  from  the  anterior 
surface  by  a  transverse  ridge,  behind  which  are 
the  impressions  for  the  attachment  of  the  genio- 
hyoid muscles.  Its  hinder  edge  is  thin  and  sharp; 
to  this,  above,  are  attached  the  genio-glossi,  whilst 
behind  and  below  the  thyro-hyoid  membrane  is 
connected  with  it.  The  inferior  border  is  well  defined  and  narrow ;  it  serves  for  the 
attachment  of  the  omo-hyoid,  sterno-hyoid,  thyro-hyoid,  and  stylo-hyoid  muscles. 

The  great  cornua  are  connected  on  either  side  with  the  lateral  parts  of  the 
body.  At  first,  union  is  effected  by  synchondroses,  which,  however,  ultimately 
ossify.  These  cornua  curve  backwards  as  well  as  upwards,  and  terminate  ia  more  or 
less  rounded  and  expanded  extremities.  Compre.-sed  laterally,  they  serve  for  the 
attachments  externally  of  the  thyro-hyoid  and  hyo-glossi  muscles,  and  the  middle 
constrictor  of  the  pharynx  from  below  upwards,  whilst  internally  they  are  con- 
nected with  the  lateral  expansions  of  the  thyro-hyoid  membrane,  the  free  edges  of 
which  are  somewhat  thickened,  and  connect  the  extremities  of  the  great  cornua 
with  the  ends  of  the  superior  cornua  of  the  thyroid  cartilage  below. 

The  lesser  cornua,  frequently  cartilaginous  in  part,  are  about  the  size  of  grains 
of  wheat.  They  rest  upon  the  upper  surface  of  the  bone  at  the  junctions  of  the 
great  cornua  with  the  body.  In  youth  they  are  separated  from,  but  in  advanced 
life  become  ossified  with,  the  rest  of  the  bone,  from  which  they  are  directed  upwards, 
backwards,  and  a  little  outwards.  Their  summits  are  connected  with  the  stylo- 
hyoid ligaments ;  they  also  serve  for  the  attachment  of  muscles. 

Connexions.  Tlie  liyoid  jh  Hhnig  from  the  styloid  proce.sse.s  of  the  temporal  bones  by  the 
fltylo-liyoi'l  lif,'aiiic,iits.  Inferiorly  it  is  connected  with  tlie  thyi'oid  cartilage  of  the  larynx  by 
the  ihyro-liyoid  ligariients  and  niiMiil)iane.  Posteriorly  it  is  intimately  associated  with  the 
epiglottis. 


Fig.  117. — The  Hyoid  Bone  as  seen 
FROM  THE  Front. 


148  OSTEOLOGY. 

Ossification. — In  considering  the  development  of  the  hyoid  bone  it  is  necessary  to 
refer  to  the  arrangement  and  disposition  of  the  cartilaginous  laars  of  the  second  and  third 
visceral  arches.  That  of  the  second  visceral  arch,  the  hyoid  bar — or  Reichert's  cartilage, 
as  it  is  sometimes  called — is  united  above  to  the  petrous  tempoi'al,  whilst  ventrally  it  is 
joined  to  its  fellow  of  the  opposite  side  by  an  independent  mesial  cartilage.  Chondrifica- 
tion  of  the  third  visceral  arch  only  occurs  towards  its  ventral  extremity,  forming  what  is 
known  as  the  thyro-hyoid  bar.  This  also  unites  with  the  mesial  cartilage  above  mentioned. 
In  these  cartilaginous  processes  ossific  centres  apj^ear  in  certain  definite  situations. 
Towards  the  end  of  fcctal  life  a  single  centre  (by  some  authorities  regarded  as  primarily 
double)  appears  in  the  mesial  cartilage,  and  forms  the  body  of  the  bone  (basihyal). 
About  the  same  time  ossification  begins  in  the  lower  ends  of  the  thyro-hyoid  bars,  and 
from  these  the  great  cornua  are  developed  (thyro-hyals).  During  the  first  year  the  lower 
ends  of  the  hyoid  bars  begin  to  ossify  and  form  the  lesser  cornua  (cerato-hyals).  The 
cephalic  ends  of  the  same  cartilages  meanwhile  ossify  to  form  the  styloid  processes  (stylo- 
hyals)  (see  p.  121),  whilst  the  intervening  portions  of  cartilage  undergo  resorption  and 
become  converted  into  the  fibrous  tissue  of  the  stylo-hyoid  ligaments,  which  in  the  adult 
connect  the  lesser  cornua  with  the  styloid  processes  of  the  temporal  bone.  The  great 
cornua  fuse  with  the  body  in  middle  life ;  the  lesser  cornua  only  at  a  more  advanced 
period.  Variations  in  the  course  of  development  lead  to  interesting  anomalies  of  the 
hyoid  apparatus.  The  lesser  cornua  may  be  unduly  long  or  the  stylo-hyoid  ligament  may 
be  bony ;  in  this  case  the  cartilage  has  not  undergone  resorption,  but  has  passed  on  to  the 
further  stage  of  ossification,  thus  forming  an  epihyal  element  comparable  to  that  in  the 
dog.  The  ossified  stylo-hyoid  ligament,  as  felt  thi'ough  the  pharyngeal  wall,  may  be 
mistaken  for  a  foreign  body.     (Farmer,  G.  W.  S.,  Brit.  Med.  Journ.  1900,  vol.  i.  p.  1405.) 

THE   SKULL   AS   A   WHOLE. 

The  skull  as  a  whole  may  be  studied  as  seen  from  the  front  (norma  frontahs), 
from  the  side  (norma  lateralis),  from  the  back  (norma  occipitalis),  from  above 
(norma  verticalis),  and  from  below  (norma  basalis). 

NOKMA    FkONTALIS. 

In  front,  the  smooth  convexity  of  the  frontal  bone  limits  this  region  above, 
whilst  inferiorly,  when  the  lower  jaw  is  disarticulated,  the  teeth  of  the  upper  jaw 
form  its  lower  boundary.  The  large  openings  of  the  orbits  are  seen  on  either  side ; 
whilst  placed  mesially  and  at  a  somewhat  lower  level  is  the  anterior  nasal  aperture 
(apertura  pyriformis)  leading  into  the  nasal  fossae. 

The  frontal  region,  convex  from  above  downwards  and  from  side  to  side,  is 
limited  externally  by  two  ridges,  which  are  the  anterior  extremities  of  the  temporal 
lines.  Superiorly  the  fulness  of  the  bone  blends  with  the  convexity  of  the  vertex. 
Inferiorly  the  frontal  bone  forms  on  either  side  the  arched  superior  border  of  the 
orbit  (margo  supraorbitalis).  The  space  between  these  borders  corresponds  to  the 
root  of  the  nose,  an  1  here  are  seen  the  sutures  which  unite  the  frontal  with  the 
nasal  bones  in  the  middle  line,  and  with  the  nasal  process  of  the  superior  maxilla 
on  either  side,  called  the  naso-frontal  and  fronto-maxillary  sutures  respectively.  The 
orbital  arch  is  thin  and  sharp  externally,  but  becomes  thick  and  more  rounded 
towards  its  inner  side,  where  it  forms  the  internal  angular  process  and  unites  with 
the  frontal  process  of  the  superior  maxilla  and  the  lachrymal  bone  on  the  inner 
wall  of  the  orbit.  This  arched  border  is  interrupted  towards  the  inner  side  by 
a  notch  (incisura  supraorl:)italis),  sometimes  converted  into  a  foramen,  for  the 
transmission  of  the  supraorbital  nerve  and  artery.  In  the  middle  line,  just  above 
the  naso-frontal  suture,  there  is  often  the  remains  of  a  median  suture  (sutura 
frontalis),  which  marks  the  fusion  of  the  two  halves  from  which  the  bone  is 
primarily  ossified.  Here  also  a  prominence,  of  variable  extent — the  glabella — is  met 
with ;  from  this  there  passes  out  on  either  side  above  and  over  the  orbital  margin 
a  projection  called  the  superciliary  ridge  (arcus  superciliaris). 

The  orbital  fossae,  of  more  or  less  conical  form,  display  a  tendency  to  assume 
the  shape  of  four-sided  pyramids  by  the  flattening  of  the  superior,  inferior,  and 
lateral   walls.      The    base,   which    is    directed    forwards    and   a    little   outwards, 


NOEMA  FEONTALIS  OF  THE  SKULL.  149 

corresponds  to  the  orbital  aperture.  Tlie  shape  of  this  is  liable  to  individual  and 
racial  variations,  being  nearly  circular  in  the  Mongoloid  type,  whilst  it  displays  a 
more  or  less  quadrangular  Ibrm  in  Australoid  skulls.  The  upper  margin,  as  has 
been  already  stated,  is  formed  by  the  frontal  bone  between  the  internal  and  external 
angular  processes.  The  outer,  and  about  half  the  lower,  margin  are  formed  by  the 
sharp  curved  edge  between  the  facial  and  orbital  surfaces  of  the  malar  bone.  The 
internal  border  and  the  remainder  of  the  lower  margin  are  determined  by  the 
outer  surface  of  the  frontal  process  of  the  superior  maxilla,  and  the  sharp  edge 
separating  the  facial  from  the  orbital  surface  of  the  same  bone.  Three  sutures 
interrupt  the  continuity  of  the  orbital  margin — the  fronto-malar  (sutura  zygomatico- 
frontalis)  externally,  the  fronto-maxillary  (sutura  fronto-maxillaris)  internally,  both 
lying  about  the  same  level,  and  the  malo-maxillary  (sutura  zygomatico-maxillaris) 
inferiorly.  The  apex  of  the  space  is  directed  backwards  and  inwards,  so  that  the 
inner  walls  of  the  two  orbits  lie  nearly  parallel  to  each  other,  whilst  the  outer 
walls  are  so  disposed  as  to  form  nearly  a  right  angle  with  each  other.  The  depth  of 
the  orbit  measures,  on  an  average,  about  two  inches  (5  cm.).  At  the  apex  there  are 
two  openings ;  the  larger,  known  as  the  sphenoidal  fissure  (fissura  orbitalis  superior), 
passes  from  the  apex  of  the  space  outwards  and  a  little  upwards  for  the  distance 
of  three-quarters  of  an  inch  or  so,  between  the  roof  and  outer  wall  of  the  orbit.  The 
inner  third  of  this  fissure  is  broad  and  of  circular  form.  Externally  it  is  consider- 
ably reduced  in  width.  Through  this  the  third,  fourth,  ophthalmic  division  of  the 
fifth,  and  the  sixth  nerves  enter  the  orbit,  whilst  the  ophthalmic  veins  pass 
backwards  through  it.  Above  and  internal  to  the  inner  end  of  the  sphenoidal 
fissure  there  is  a  smaller  circular  opening,  the  optic  foramen  (foramen  opticum),  for 
the  transmission  of  the  optic  nerve  and  ophthalmic  artery. 

The  roof  of  the  orhit,  which  is  very  thin  and  brittle  towards  its  centre,  is  formed 
in  front  by  the  orbital  plate  of  the  frontal  bone  (pars  orbitalis)  and  behind  by  a 
small  triangular  piece  of  the  lesser  wing  of  the  sphenoid,  which  surrounds  the 
optic  foramen  and  forms  the  upper  border  of  the  sphenoidal  fissure.  Externally 
this  surface  is  separated  from  the  outer  wall  by  the  sphenoidal  fissure  posteriorly, 
anteriorly  by  an  irregular  suture  between  the  orbital  part  of  the  frontal  and 
the  upper  margin  of  the  orbital  surface  of  the  great  wing  of  the  sphenoid,  ex- 
ternal to  which  the  external  angular  process  of  the  frontal  articulates  with  the 
malar.  Internally  the  roof  is  marked  off  from  the  inner  wall  by  a  suture,  more 
or  less  horizontal  in  direction,  between  the  orbital  plate  of  the  frontal  and  the 
following  bones  in  order  from  before  backwards,  viz.  the  frontal  process  of  the 
superior  maxilla,  the  lachrymal  bone,  and  the  os  planum  of  ethmoid.  In  the 
suture  between  the  last-mentioned  bone  and  the  frontal  there  are  two  foramina, 
the  anterior  and  posterior  internal  orbital  or  ethmoidal  canals  (foramen  ethmoidale 
anterius  et  posterius);  both  transmit  ethmoidal  vessels — the  anterior  affording 
passage  to  the  nasal  nerve  as  well.  The  roof  is  concave  from  side  to  side,  and 
to  some  extent  also  from  before  backwards.  About  midway  between  the 
fronto  -  maxillary  suture  and  the  supraorbital  notch  or  foramen,  but  within 
the  margin  of  the  orbit,  there  is  a  small  depression,  occasionally  replaced  by  a 
spine  (fovea  vel.  spina  trochlearis),  for  the  attachment  of  the  cartilaginous  pulley 
of  the  superior  oblique  muscle  of  the  eyeball.  Under  cover  of  the  external 
angular  process  the  roof  is  more  deeply  excavated,  forming  a  shallow  fossa  for  the 
lodgment  of  the  lachrymal  gland  (fossa  glandulte  lachrymalis).  In  front,  the  roof 
separates  the  orbit  from  the  frontal  sinus,  and  along  its  inner  border  it  is  in  relation 
with  the  ethmoidal  air-cells.  The  relation  to  these  air  spaces  is  variable,  depending 
on  the  development  and  size  of  the  sinuses.  The  rest  of  the  roof,  which  is  very  thin, 
forms  by  its  upper  surface  the  floor  of  the  anterior  cranial  fossa,  in  which  are  lodged 
the  frontal  lobes  of  the  cerebrum. 

The  floor  of  the  orlit  is  Ibrmed  by  the  orbital  plate  of  the  superior  maxilla, 
together  with  part  of  the  orbital  surface  of  tluj  malar  bone,  and  a  small  triiingular 
])iece  of  bone,  the  orbital  process  of  the  palate,  which  is  wedged  in  posteriorly. 
Externally,  for  three-quarters  of  its  length  posteriorly,  it  is  s(iymrated  I'rom  the  outer 
wall,  wliich  is  here  ffjrmed  by  the  great  wing  of  the  sphenoid,  by  a  cleft  called  the 
spheno- maxillary  fissure  (fissura  orbitalis  inferior).     Through  this  there  pass  the 


150 


OSTEOLOGY. 


superior  maxillary  division  of  the  fifth  nerve  on  its  way  to  the  infraorbital  canal,  the 
orbital  or  temporo-malar  branch  of  the  same  nerve,  the  infraorbital  vessels,  and  some 


1.  Mental  protuberance. 

2.  Body  of  lower  jaw. 

3.  Eamus  of  lower  jaw. 

4.  Anterior  nasal  spine 

5.  Canine  fossa. 

6.  Infraorbital  canal. 

7.  Malar  canal. 

8.  Orbital  surface  of  superior 

maxilla. 

9.  Temporal  fossa. 

10.  Os  planum  of  ethmoid. 

11.  Sphenoidal  fissure. 

12.  Lachrymal  bone  and  groove. 


Fig.  118. — Norma  Frontalis. 

13.  Optic  foramen. 

14.  Orbital  foramina. 

15.  Temporal  ridge. 

16.  Supraorbital  notch. 

17.  Glabella. 

18.  Frontal  eminence. 

19.  Superciliary  ridge. 

20.  Parietal  bone. 

21.  Fronto-nasal  suture. 

22.  Pterion. 

23.  Great  wing  of  sphenoid. 

24.  Orbital  surface  of  great  wino 

of  sphenoid. 


25.  Squamoiis  temporal. 

26.  Left  nasal  bone. 

27.  Malar  bone. 

28.  Siiheno-maxillary  fissure. 

29.  Zygomatic  arch. 
Anterior  nasal  aperture,  displaying 

nasal    septum   and    inferior   and 
middle  turbinated  bones. 

Mastoid  process. 

Incisor  fossa. 

Angle  of  jaw. 

Mental  foramen. 

Symphysis. 


30 


31. 
32. 
33. 
34. 
35. 


twigs  from  Meckel's  (spheno-palatine)  ganglion.  By  means  of  this  fissure  the  orbit 
■communicates  with  the  spheno-maxillary  fossa  behind  and  the  zygomatic  fossa  to 
the  outer  side.     Internally  the  floor  is  limited  from  behind  forwards  by  the  suture 


NOKMA  FRONTALIS  OF  THE  SKULL.  151 

between  the  i'ollowing  bones,  viz.  the  orbital  process  of  the  palate  below  with  the 
body  of  the  sphenoid  above  and  behind,  and  the  os  planum  of  the  ethmoid  above  and 
in  front — anterior  to  which  the  orbital  plate  of  the  superior  maxilla  below  articulat(i8 
with  the  OS  planum  of  the  ethmoid  and  the  lachrymal  above  and  in  front.  At  the 
anterior  extremity  of  this  line  of  sutures  the  inner  edge  of  the  orbital  plate  of  the 
superior  maxilla  is  notched  and  free  between  the  point  where  it  articulates  with  the 
lachrymal  posteriorly  and  the  part  from  which  its  frontal  process  rises.  Here  it 
forms  the  outer  edge  of  a  canal,  down  which  the  membranous  nasal  duct  passes  to 
the  nose.  The  floor  of  the  orbit  is  thin  behind  and  at  the  sides,  but  thicker  in 
front  where  it  blends  with  the  orbital  margin.  Passing  in  a  sagittal  direction 
through  its  substance  is  the  infraorbital  canal,  the  roof  of  which  is  usually  deficient 
behind,  where  it  becomes  continuous  with  a  broad,  shallow  groove,  which  leads 
forwards  from  the  anterior  margin  of  the  spheno-maxillary  fissure.  This  canal 
(canalis  infraorbitalis)  opens  on  the  facial  surface  of  the  superior  maxillary  imme- 
diately below  the  orbital  margin  (foramen  infraorbitale)  and  transmits  the  superior 
maxillary  division  of  the  fifth  nerve,  together  with  the  infraorbital  vessels.  The 
floor  forms  a  thin  partition  which  separates  the  orbit  from  the  antrum  or  sinus  of 
the  superior  maxilla,  which  lies  below.  Internally  it  completes  the  lower  ethmoidal 
air-cells,  and  separates  the  orbit  from  the  middle  meatus  of  the  nasal  fossae. 

The  outer  loall  of  the  orbit,  which  is  the  strongest,  is  formed  by  the  orbital 
surface  of  the  great  wing  of  the  sphenoid  and  the  upper  part  of  the  orbital  surface 
of  the  malar  bone.  Above  it,  behind,  is  the  sphenoidal  fissure,  whilst  below, 
and  extending  much  farther  forward,  is  the  spheno-maxillary  fissure.  The  anterior 
margin  of  the  outer  wall  is  stout  and  formed  by  the  malar  bone,  behind  which, 
formed  in  part  by  the  orbital  process  of  the  malar  bone  and  the  malar  edge  (margo- 
zygomaticus)  of  the  great  wing  of  the  sphenoid,  it  forms  a  fairly  thick  partition 
between  the  orbit  in  front  and  the  temporal  fossa  behind.  Crossing  this  surface 
from  above  downwards,  close  to  the  anterior  extremity  of  the  spheno-maxillary 
fissure,  is  the  suture  between  the  malar  bone  and  the  great  wing  of  the  sphenoid 
(sutura  spheno  -  zygomatica).  This  wall  is  pierced  in  front  by  one  or  two 
small  canals  (foramen  zygomatico-orbitale),  which  traverse  the  malar  bone  and 
allow  of  the  transmission  of  the  temporal  and  malar  branches  of  the  orbital  portion 
of  the  superior  maxillary  division  of  the  fifth  nerve. 

The  inner  wall  of  the  orbit  is  formed  from  before  backwards  by  a  small  part  of 
the  frontal  process  of  the  superior  maxilla,  by  the  lachrymal,  and  by  the  os  planum  or 
orbital  plate  of  the  ethmoid  (lamina  papyracea  ossis  ethmoidalis),  posterior  to  which 
is  a  small  part  of  the  lateral  aspect  of  the  body  of  the  sphenoid  in  front  of  the 
optic  foramen.  Above,  the  orbital  plate  of  the  frontal  bone  forms  a  continuous 
suture  from  before  backwards  with  the  bones  just  enumerated ;  whilst  below,  the 
lachrymal  and  the  os  planum  of  the  ethmoid  articulate  with  the  orbital  plate  of 
the  superior  maxilla ;  posteriorly  the  hinder  extremity  of  the  os  planum  and  the 
fore-part  of  the  body  of  the  sphenoid  articulate  with  the  orbital  process  of  the 
palate.  The  orbital  surface  of  the  lachrymal  bone  is  divided  into  two  by  a  vertical 
ridge — the  lachrymal  crest  (crista  lachrymalis  posterior) — which  forms  in  front  the 
posterior  half  of  a  hollow,  the  lachrymal  groove  (sulcus  lachrymalis),  the  anterior 
part  of  which  is  completed  by  the  channelled  posterior  border  of  the  frontal  process 
of  the  superior  maxilla.  In  the  lachrymal  groove  or  fossa  (fossa  sacci  lachrymalis) 
is  lodged  the  lachrymal  sac,  whilst  passing  from  it  and  occupying  the  canal,  of 
which  the  upper  opening  is  at  present  seen,  is  the  membranous  nasal  duct.  The 
extremely  thin  wall  of  the  lower  part  of  the  lachrymal  fossa  separates  the  orbit 
from  the  fore-part  of  the  middle  meatus  of  the  nasal  fossa.  To  the  inner  side  of 
the  upper  and  fore  j>art  of  the  lachrymal  bone,  and  separated  from  the  orbit  merely 
by  the  thickness  of  that  bone,  is  the  passage  leading  from  the  nose  to  the  frontal 
sinus  (infundibulum  ethmoidale),  whilst  the  part  of  the  bone  behind  the  lachrymal 
crest  forms  the  thin  partition  between  the  orbit  and  the  anterior  ethmoidal  cells. 
Behind,  wliore  tlie  body  of  the  8])henoid  forms  part  of  the  inner  wall  of  the  orbit, 
the  sphenoidal  air  sinus  is  in  relation  to  the  apex  of  that  space,  though  here  the 
jjartitioti  wall  l)(jtvvc(!ii  the  two  cavities  is  much  thicker. 

The  skeleton  of  the  face  on  its  anterior  surface  is  formed  by  the  two  superior 


152  OSTEOLOGY. 

maxillffi,  the  frontal  processes  of  which  have  been  ah'eady  seen  to  pass  up  to  articu- 
late with  the  internal  angular  processes  of  the  frontal  bone,  thus  forming  the  lower 
halves  of  the  inner  margins  of  the  orbit.  Joined  to  the  upper  jaws  externally  are 
the  malar  or  cheek  bones  (ossa  zygomatica),  which  are  supported  by  their  union 
with  the  temporal  bones  posteriorly  through  the  medium  of  the  zygomatic  arches. 
The  suture  which  separates  the  malar  from  the  superior  maxilla  (sutura  zygomatico- 
maxillaris)  commences  above  about  the  centre  of  the  lower  orbital  margin  and 
passes  obliquely  downward  and  outward,  its  lower  end  lying  in  vertical  line  with 
the  outer  orbital  margin.  The  two  superior  maxillee  are  separated  by  the  nasal 
fossse,  which  here  open  anteriorly.  Above,  the  two  nasal  bones  are  wedged  in 
between  the  frontal  processes  of  the  maxillaB ;  whilst  below  the  nasal  aperture,  the 
maxillfe  themselves  are  united  in  the  middle  line  by  the  intermaxillary  suture 
(sutura  intermaxillaris). 

The  nasal  aperture  (apertura  pyriformis),  which  lies  below  and  in  part  between 
the  orbits,  is  of  variable  shape  and  size — usually  pyriform,  it  tends  to  be  long  and 
narrow  in  Europeans,  as  contrasted  with  the  shorter  and  wider  form  met  with  in 
the  negroid  races.  Its  edges  are  formed  below  and  on  either  side  by  the  free 
curved  margin  of  the  body  and  the  frontal  process  of  the  superior  maxilla ;  and 
above,  and  partly  at  the  sides,  by  the  free  border  of  the  nasal  bones.  In  the 
middle  line,  inferiorly,  corresponding  to  the  upper  end  of  the  intermaxillary 
suture  there  is  an  outstanding  process — the  anterior  nasal  spine  (spina  nasalis 
anterior)  formed  by  the  coalescence  of  spicules  from  both  maxillae ;  arising  from 
this,  and  passing  backwards  and  upwards,  is  a  thin  bony  partition — the  osseous 
septum  of  the  nose.  Often  deflected  to  one  or  other  side,  it  divides  the  cavity  of 
the  nose  (cavum  nasi)  into  a  right  and  left  half.  Projecting  into  these  chambers 
from  their  outer  walls  can  be  seen  the  inner  surfaces  and  free  borders  of  the  middle 
(concha  media)  and  inferior  (concha  inferior)  turbinated  bones,  the  spaces  below 
and  between  which  form  the  inferior  and  middle  meatuses  of  the  nose  respectively. 

Below  the  orbit,  and  to  the  outer  side  of  the  nasal  aperture,  the  anterior  or 
facial  surface  of  the  body  of  the  superior  maxilla  (corpus  maxillte)  is  seen  ;  this  is 
continuous  inferiorly  with  the  outer  surface  of  the  alveolar  process  (process  alveo- 
laris),  in  which  are  embedded  the  roots  of  the  upper  teeth. 

A  horizontal  line  drawn  round  the  jaw  on  the  level  of  a  point  midway  between 
the  lower  border  of  the  nasal  aperture  and  the  alveolar  edge  corresponds  to  the 
plane  of  the  bard  palate.  Below  that  the  alveolar  process  separates  the  cavity  of 
the  mouth  from  the  front  of  the  face ;  whilst  above,  the  large  air  space,  the  maxil- 
lary sinus  (sinus  maxillaris),  or  antrum  of  Highmore,  lies  within  the  body  of  the 
superior  maxilla. 

The  malar  or  cheek  bone  (os  zygomaticum)  forms  the  lower  half  of  the  outer, 
and  outer  half  of  the  lower  border  of  the  orbit.  Its  external  aspect  corresponds  to 
the  point  of  greatest  width  of  the  face,  the  modelling  of  which  depends  on  the 
flatness  or  projection  of  this  bone. 

When  the  lower  jaw  (mandibula)  is  in  position,  and  the  teeth  in  both  jaws  are 
complete,  the  lower  dental  arch  will  be  seen  to  be  smaller  in  all  its  diameters  than 
the  upper,  so  that  when  the  jaws  are  closed  the  upper  teeth  slightly  overlap  the 
lower  both  in  front  and  at  the  sides.  Exceptionally  a  departure  from  this  arrange- 
ment is  met  with. 

Norma  Lateralis. 

Viewing  this  aspect  of  the  skull,  in  the  first  instance,  without  the  lower  jaw^,  it 
is  seen  to  be  formed  in  part  by  the  bones  of  the  cranium,  and  in  part  by  the  bones 
of  the  face.  A  line  drawn  from  the  fronto-nasal  suture  to  the  tip  of  the  mastoid 
process  serves  to  define  roughly  the  boundary  between  these  portions  of  the  skull. 
Of  ovoid  shape,  the  cranium  is  formed  above  by  the  frontal,  parietal,  and  occipital 
bones  from  before  backwards;  whilst  below,  included  within  these  are. the  sphenoid 
and  temporal  bones.  The  sutures  between  these  several  bones  are  arranged  as 
follows :  Commencing  at  the  external  angular  process  of  the  frontal,  the  suture 
between  that  bone  and  the  malar  is  first  seen ;  tracing  this  backwards  and  a  little 


NOEMA  LATEEALIS  OF  THE  SKULL. 


15J 


upwards,  the  lower  edge  of  the  frontal  next  articulates  with  the  upper  margin  of  the 
great  wing  of  the  sphenoid  for  a  distance  varying  from  three-quarters  of  an  inch  to 
one  inch.  Here  the  posterior  border  of  the  frontal  turns  upwards  and  slightly  back- 
wards, forming  with  the  parietal  the  coronal  suture  (sutura  coronalis).  The  lower 
border  of  the  parietal  bone,  which  is  placed  immediately  behind  the  frontal,  articulates 


Fig.  119. — Norma  Lateralis. 

12.  Lambcloid  suture. 

13.  Occipital  1:10116. 

14.  Lambda. 

15.  Obelion  placed  between  the  two 
parietal  foramina. 

16.  Parietal  bone. 

17.  Lower  temporal  ridge. 

18.  Upper  temporal  ridge. 

19.  Squamous    j^art    of    temporal 
bone. 

20.  Bregma. 

21.  Coronal  suture. 


22.  Stejiliaiiiou. 

23.  Frontal  bone. 

24.  Pterion. 

25.  Temporal  fossa. 

26.  GreM;  wing  of  sphenoid. 

27.  Malar  bone. 

28.  Malar  canal. 

29.  Lachrymal  bone. 

30.  Nasal  bone. 

31.  InfraorVjital  canal. 

32.  Anterior  nasal  aperture. 


1.  Mental  foramen. 

2.  Body  of  low£r  jaw. 

3.  Superior  maxilla. 

4.  Eamus  of  lower  jaw. 

5.  Zygomatic  arch.- 

6.  Styloid  process. 

7.  External  auditory  meatus. 

8.  Mastoid  process. 

9.  Asterion. 

10.  Superior  curved  line  of  occipital 

bone. 

11.  External  occipital  protuberance. 

anteriorly  with  the  hinder  part  of  the  upper  edge  of  the  great  wing  of  the  sphenoid. 
The  extent  of  this  suture  (sutura  spheno-parietalis)  is  liable  to  very  great  indi- 
vidual variation — at  times  being  broad,  in  other  instances  being  pointed  and 
narrow,  whilst  occasionally  the  parietal  does  not  articulate  with  the  sphenoid  at  all. 
JJehind  the  spheno-pari(;tal  suture  Uw,  parietal  articulates  witli  the  squamous  part 
of  the  temporal  THutura  Hquamf)sa).  This  re])oats  to  a  certain  extent  the  curve 
formed  l^y  tfie  outline  oi'  the  calvaria,  and  ends  posteriorly  about  one  inch  beliind 
the  external  auditory  meatus.  Here  the  suture  alters  its  character  aiui  direction, 
and  in  jdace  of  being  scaly,  becomes  toothed  and  irregular,  uniting  for  the  space  of 


154  OSTEOLOGY. 

an  inch  or  so  the  posterior  inferior  angle  of  the  parietal  with  the  mastoid  process 
of  the  temporal  bone.  This  suture  (sutura  parieto-mastoid)  is  more  or  less  hori- 
zontal in  direction,  and  lies  in  line  and  on  a  level  with  the  upper  border  of  the 
zygomatic  arch.  At  a  point  about  two  inches  behind  the  external  auditory  meatus 
the  posterior  border  of  the  parietal  bone  turns  obliquely  upwards  and  backwards, 
and  forms  with  the  tabular  part  of  the  occipital  bone  the  strongly-denticulated 
lambdoid  suture  (sutura  lambdoidea).  Inferiorly  this  suture  is  continued  obliquely 
downwards  between  the  occipital  bone  and  the  hinder  border  of  the  mastoid  portion 
of  the  temporal,  where  it  forms  the  occipito- mastoid  suture  (sutura  occipito- 
mastoidea),  much  simpler  and  less  serrated  than  the  two  previously  mentioned. 
These  three  sutures  just  described  meet  in  tri-radiate  fashion  at  a  point  called 
the  asterion. 

Anteriorly  the  curve  of  the  squamous  suture  is  continued  downward  between 
the  anterior  edge  of  the  squamous  part  of  the  temporal  and  the  posterior  border  of 
the  great  wing  of  the  sphenoid ;  inferiorly  it  lies  in  plane  with  the  middle  of  the 
zygomatic  arch. 

The  sutures  around  the  summit  of  the  great  wing  of  the  sphenoid  are  arranged 
like  the  letter  H  placed  obliquely,  the  cross-piece  of  the  H  corresponding  to  the 
spheno-parietal  suture.  When  this  is  short,  and  becomes  a  mere  point  of  contact, 
the  arrangement  then  resembles  the  letter  X-     This  region  is  named  the  pterion. 

Curving  over  the  lateral  region  of  the  calvaria  in  a  longitudinal  direction  is 
the  temporal  crest  (linea  temporalis).  This  is  often  double.  The  lower  line  marks 
the  limit  of  the  attachment  of  the  temporal  muscle,  whilst  the  upper  ridge  defines 
the  attachment  of  the  temporal  fascia.  Commencing  in  front  at  the  external 
angular  process  of  the  frontal,  the  crest  sweeps  upwards  and  backwards  across  the 
lower  part  of  that  bone,  and  then  crossing  the  coronal  suture — a  point  called  the 
stephanion — it  passes  on  to  the  parietal,  over  which  it  curves  in  the  direction  of  its 
posterior  inferior  angle.  Here  it  is  continued  on  to  the  temporal  bone,  where  it 
sweeps  forward  to  form  the  supramastoid  crest,  which  serves  to  separate  the  squamous 
from  the  mastoid  portion  of  the  temporal  bone  externally.  Carried  forward,  this 
ridge  is  seen  to  become  continuous  with  the  upper  border  of  the  zygomatic 
arch  over  the  external  auditory  meatus.  In  front,  the  temporal  ridge  separates 
the  temporal  fossa  from  the  region  of  the  forehead ;  above  and  behind,  it  bounds 
the  temporal  fossa  which  lies  within  its  concavity,  and  serves  to  separate  that  hollow 
from  the  surface  of  the  calvaria  which  is  overlain  by  the  scalp.  Above  the  level 
of  the  temporal  Knes  the  surfaces  of  the  frontal  and  parietal  bones  are  smooth, 
the  latter  exhibiting  an  elevation  of  varying  prominence  and  position,  but  usually 
situated  about  the  centre  of  the  bone,  called  the  parietal  eminence  (tuber  parietale). 
A  slight  hollowing  of  the  surface  of  the  parietal  behind  and  parallel  to  the  coronal 
suture  is  not  uncommon,  and  is  referred  to  as  the  post -coronal  depression.  As 
seen  in  profile,  the  part  of  the  calvaria  behind  and  below  the  lambdoid  suture  is 
formed  by  the  tabular  part  of  the  occipital  bone.  In  line  with  the  zygomatic  arch 
this  outline  is  interrupted  by  the  external  occipital  protuberance  or  inion  (protuber- 
antia  occipitalis  externa).  The  projection  of  this  point  is  variable ;  but  its 
position  can  usually  be  easily  determined  in  the  living.  Passing  forwards  from 
it,  and  blending  anteriorly  with  the  posterior  border  of  the  mastoid  process  of  the 
temporal  bone,  is  a  rough  crest,  the  superior  curved  line  (linea  nuchse.  superior),  a 
little  above  which  there  is  often  a  much  fainter  line,  the  highest  curved  line  (linea 
nuchse  suprema) ;  this  affords  attachment  to  the  epicranial  aponeurosis.  These  two 
lines  serve  to  separate  the  part  of  the  cranium  above,  which  is  covered  by  scalp, 
from  thab  below,  which  serves  for  the  attachment  of  the  fleshy  muscles  of  the  back 
of  the  neck,  the  latter  surface  (planum  nuchale)  being  rough  and  irregular  as 
contrasted  with  the  smooth  superior  part  (planum  occipitale).  The  fulness  of 
these  two  parts  of  the  occipital  bone  varies  much.  There  is  frequently  a  pronounced 
bulging  of  the  planum  occipitale,  and  the  position  of  the  lambda  can  often  be 
easily  determined  in  the  living ;  similarly  the  planum  nuchale  may  be  either  com- 
paratively flat  or  else  full  and  rounded.  These  differences  are  of  course  associated 
with  corresponding  differences  in  the  development  of  the  cerebral  and  cerebellar 
lobes  which  are  lodged  in  relation  to  the  internal  aspect  of  these  parts  of  the  bone. 


NOEMA  LATERALIS  OF  THE  SKULL.  155 

The  further  description  of  the  planum  nuchale  is  best  deferred  till  the  base  of 
the  skull  (norma  basalis)  is  studied. 

Temporal  Fossa. — Within  the  limits  of  the  temporal  lines  the  side  of  the  cranium 
slopes  forwards,  inwards,  and  downwards,  thus  leaving  a  considerable  interval  between 
its  lower  part  and  the  zygomatic  arch.  This  space  or  hollow  is  called  the  temporal 
fossa  (fossa  temporalis) ;  bounded  above  and  behind  by  the  temporal  lines,  its  inferior 
limit  is  defined  by  the  level  of  the  zygomatic  arch.  Deepest  opposite  the  angle  formed 
by  the  frontal  and  temporal  processes  of  the  malar  bone,  the  fossa  becomes  shallow 
towards  its  circumference.  Its  floor,  which  is  slightly  concavo-convex  from  before 
backwards  about  mid-level,  is  formed  above  by  the  temporal  surface  (facies  temporalis) 
of  the  frontal,  behind  by  the  anterior  inferior  angle  (angulis  sphenoidalis)  of  the 
parietal,  as  well  as  the  lower  portion  of  that  bone,  below  the  temporal  crest ;  below 
and  in  front  by  the  temporal  surface  of  the  great  wing  of  the  sphenoid,  and  behind 
and  below  by  the  squamous  portion  of  the  temporal  bone.  Inferiorly  the  floor  is 
limited  in  front  by  the  free  inferior  border  of  the  great  wing  of  the  sphenoid,  which 
forms  the  upper  boundary  of  the  spheno-maxillary  fissure ;  behind  that,  by  a  rough 
ridge,  the  infratemporal  crest  or  pterygoid  ridge  (crista  infratemporalis),  which 
crosses  the  external  surface  of  the  great  wing  of  the  sphenoid,  to  become  con- 
tinuous posteriorly  with  a  ridge  on  the  lower  surface  of  the  squamous  temporal, 
from  which  the  anterior  root  of  the  zygomatic  process  springs.  In  front  the 
temporal  fossa  is  separated  from  the  orbit  by  the  external  angular  process  of  the 
frontal  above,  and  by  the  orbital  process  of  the  malar  and  its  junction  with  the 
external  border  of  the  great  wing  of  the  sphenoid  between  the  orbital  and  temporal 
surfaces  of  that  process.  Externally  and  in  front,  the  fossa  is  overhung  by  the 
backward  projection  of  the  frontal  process  of  the  malar  bone,  and  it  is  under  cover 
of  this,  and  within  the  angle  formed  by  the  frontal  and  orbital  processes  of  the  malar, 
that  we  see  the  opening  of  the  temporal  canal,  which  pierces  the  orbital  plate  of  the 
malar  and  transmits  the  temporal  branch  of  the  orbital  nerve — a  filament  of  the 
superior  maxillary  division  of  the  V  nerve.  The  fore-part  of  the  spheno -maxillary 
fissure  (fissura  orbita  inferior)  opens  into  the  lower  part  of  the  temporal  fossa,  and 
thus  establishes  a  communication  between  it  and  the  orbit.  If  the  floor  of  the 
fossa  be  carefully  examined,  some  more  or  less  distinct  vascular  grooves  may 
be  seen.  One  passing  upwards  over  the  posterior  part  of  the  squamous 
temporal,  immediately  in  front  of  and  above  the  external  auditory  meatus,  is  for 
the  middle  temporal  artery ;  two  others,  usually  less  distinct,  pass  up,  one  over  the 
temporal  surface  of  the  great  wing  of  the  sphenoid,  the  other  over  the  fore-part  of 
the  squamous  temporal;  these  are  for  the  anterior  and  posterior  deep  temporal 
branches  of  the  internal  maxillary  artery.  The  fossa  contains  the  temporal  muscle 
with  its  vessels  and  nerves,  together  with  the  temporal  branch  of  the  orbital  nerve 
.and  some  fat ;  all  of  which  are  enclosed  by  the  fascia  which  stretches  over  the  space 
from  the  upper  temporal  line  above  to  the  superior  border  of  the  zygomatic  arch 
below.  The  extent  of  the  fossa  depends  on  the  size  of  the  temporal  muscle, 
the  development  of  which  is  correlated  with  the  size  and  weight  of  the  lower  jaw. 

Springing  from  the  front  and  lower  part  of  the  squamous  temporal  is  the 
zygomatic  process  of  that  bone  ;  it  has  two  roots,  an  anterior  and  a  posterior,  between 
and  below  which  are  placed  the  glenoid  fossa  (fossa  mandibularis)  in  front,  and  the 
•opening  of  the  external  auditory  meatus  behind.  Of  compressed  triangular  form,  the 
process  at  first  has  its  surfaces  directed  upwards  and  downwards,  but  curving  out- 
wards and  forwards,  it  twists  on  itself,  so  that  its  narrowed  surfaces  are  now  turned 
outwards  and  inwards,  and  its  edges  upwards  and  downwards ;  passing  forwards,  it 
•expands  somewhat,  and  ends  in  an  oblique  serrated  surface,  which  unites  with  the 
temporal  process  of  the  malar  bone  and  comj^ietes  the  zygomatic  arch.  It  is  the 
upper  edge  of  this  bridge  of  bone  which  forms  the  posterior  root.  The  lower  border, 
turning  inwards,  forms  the  anterior  root,  and  serves  to  separate  the  temporal  from 
the  zygomatic  surface  of  the  squamous  temporal,  blending  in  front  with  tlie  infra- 
temporal crest  on  the  outer  surface  of  the  great  wing  of  the  sphenoid.  The  under 
■surface  of  this  root  is  convex  from  })efore  backwards,  and  is  thrown  into  relief  by 
the  glenoid  hollow,  which  ])asse.s  u])  }>ehind  it.  In  this  way  a  downward  projection, 
whicii  is  called  the  eminentia  articularis,  is  formed. 


156  OSTEOLOGY. 

The  alar  spine  of  the  sphenoid  (spina  angularis)  lies  immediately  to  the 
inner  side  of  the  articular  part  of  the  glenoid  fossa.  Its  size  and  projection  vary. 
It  is  well  to  remember  its  relation  to  the  condyle  of  the  lower  jaw  when  that  bone 
is  in  position  ;  lying,  as  it  does,  to  the  inner  side  and  a  little  in  front  of  that  pro- 
cess, it  affords  attachment  to  the  so-called  long  internal  lateral  ligament  (spheno- 
mandibular)  of  the  temporo-maxillary  articulation.  As  will  be  seen  hereafter,  the 
anterior  extremity  of  the  osseous  Eustachian  canal  lies  immediately  to  its  inner 
side  (p.  164).  A  noteworthy  feature  about  the  articular  part  of  the  glenoid  fossa 
is  the  thinness  of  the  bony  plate  which  serves  to  separate  it  from  the  middle 
cranial  fossa  above.  The  vaginal  process  is  a  crest  of  bone  which  runs  obHquely 
forwards  from  the  front  and  inner  side  of  the  mastoid  process,  just  below  the 
external  auditory  meatus,  to  the  alar  spine  of  the  sphenoid.  Passing  downwards 
and  slightly  forwards  from  the  centre  of  this,  and  ensheathed  by  it  in  front  and 
at  the  sides,  is  the  pointed  styloid  process,  the  length  of  which  is  extremely  variable. 

In  the  recess  between  the  posterior  root  of  the  zygoma  and  the  upper  curved 
edge  of  the  meatus  there  is  usually  a  depression,  though  in  some  instances  this 
may  be  replaced  by  a  slight  bulging  of  the  bone.  If  from  the  posterior  root  of 
the  zygoma  a  vertical  line  be  let  fall,  tangential  to  the  posterior  edge  of  the  meatus, 
a  small  triangular  area  is  mapped  off  which  has  been  named  Ijy  Macewen  the  supra- 
meatal  triangle.  Surgically  this  is  of  importance,  as  it  is  the  spot  selected  in  which 
to  trephine  the  bone  to  reach  the  mastoid  antrum  (see  p.  120). 

In  the  suture  between  the  posterior  border  of  the  mastoid-temporal  and  the 
tabular  plate  of  the  occipital,  there  is  usually  a  foramen  (mastoid)  for  the  trans- 
mission of  an  emissary  vein  from  the  lateral  sinus  within  the  cranium  to  the 
cutaneous  occipital  vein  of  the  scalp ;  this  opening,  which  may  be  double,  varies 
greatly  in  size,  and  is  usually  placed  on  a  level  with  the  external  auditory 
meatus. 

Zygomatic  Fossa. — The  side  of  the  cranium  in  front  of  the  anterior  root  of  the 
zygomatic  process  of  the  temporal  bone  is  deeply  hollowed,  forming  the  zygomatic 
or  infratemporal  fossa  (fossa  infratemporalis) ;  this  in  topographical  anatomy 
corresponds  to  the  pterygo-maxillary  region.  The  student  must  bear  in  mind 
that,  in  examining  this  space,  the  ramus  and  coronoid  process  of  the  lower 
jaw  form  its  outer  wall ;  but  this  bone  for  the  present  being  withdrawn,  enables  us 
to  get  a  better  view  of  the  boundaries  of  the  space.  In  front  its  anterior  luall 
is  formed  by  the  convex  posterior  or  zygomatic  surface  (facies  infratemporalis) 
of  the  superior  maxilla,  which  rises  behind  the  socket  for  the  last  molar  tooth  to 
form  the  tuberosity  (tuber-maxillare).  Anteriorly  the  zygomatic  surface  of  the  upper 
jaw  is  separated  from  its  facial  aspect  by  the  rounded  inferior  margin  of  the  malar 
or  zygomatic  process  which  supports  the  malar  bone.  This  latter  curves  outwards 
and  backwards,  forming  part  of  the  upper  and  anterior  wall  of  the  fossa.  On  the  inner 
surface  of  this  wall  will  be  seen  the  suture  uniting  the  malar  and  superior  maxillary 
bones  (sutura  zygomatico-maxillaris),  which  runs  obliquely  upwards  and  inwards 
to  reach  the  external  extremity  of  the  spheno-maxillary  fissure,  the  lower  border  of 
which  forms  the  superior  boundary  of  the  zygomatic  surface  of  the  upper  jaw.  On 
this  aspect  of  the  bone  are  to  be  seen  the  openings  of  the  posterior  dental  canals 
(foramina  alveolaria)  two  or  more  in  number,  which  transmit  the  nerves  and 
vessels  to  the  upper  molar  teeth.  The  inner  ivall  of  the  zygomatic  fossa  is  formed 
by  the  outer  surface  of  the  external  pterygoid  plate  (lamina  lateralis  processus 
pterygoidei),  the  width  and  shape  of  which  varies  greatly  ;  its  posterior  border  is 
thin  and  sharp,  and  often  furnished  with  spiny  points,  to  one  of  which  the  pterygo- 
spinous  ligament,  which  stretches  from  this  border  to  the  alar  spine  of  the  sphenoid, 
is  attached.  It  occasionally  happens  that  this  ligament  becomes  ossified. 
Anteriorly  the  external  pterygoid  plate  is  separated  from  the  superior  maxilla 
above  by  an  interval  called  the  pterygo-maxillary  fissure.  Below  this  the  bones  are 
apparently  fused,  but  a  careful  inspection  of  the  skull,  together  with  an  examina- 
tion of  the  disarticulated  bones,  will  enable  the  student  to  realise  that,  wedged  in 
between  the  two  bones  at  this  point,  is  a  part  of  one  of  the  smaller  bones  of  the 
face,  the  tuberosity  of  the  palate  bone  (processus  pyramidalis  ossis  palatini). 

The  lower  border  of  the  external  pterygoid  plate  is  usually  curved  and  slightly 


'    NORMA  LATERALIS  OF  THE  SKULL.  L57 

everted.  Superiorly,  where  the  external  pterygoid  plate  is  generally  narrower,  it 
sweeps  upwards  to  become  continuous  with  the  broad  under  surface  of  the  great 
wing  of  the  sphenoid ;  this,  which  overhangs  in  part  the  zygomatic  fossa  superiorly, 
is  limited  above  by  the  infratemporal  crest  which  separates  its  zygomatic  from  its 
temporal  surface.  The  zygomatic  surface  of  the  great  wing  of  the  sphenoid  is 
limited  in  front  and  below  by  the  edge  which  forms  the  upper  boundary  of  the 
spheno-maxillary  fissure,  whilst  behind  it  reaches  as  far  back  as  the  inner 
extremity  of  the  Glaserian  fissure,  where  it  terminates  in  the  alar  spine.  It  is 
from  this  point  that  the  suture  (sutura  spheno-squamosa)  curves  forward  and 
upwards  to  reach  the  region  of  the  pterion.  The  infratemporal  or  zygomatic 
■surface  of  the  great  wing  of  the  sphenoid,  and  the  outer  surface  of  the  external 
pterygoid  plate,  alike  afford  extensive  attachments  for  the  external  j)terygoid 
muscle,  whilst  the  former  is  pierced  by  minute  canals  for  the  transmission  of 
emissary  veins.  Occasionally  a  larger  vascular  foramen  is  present  (foramen  Vesalii), 
through  which  a  vein  runs  from  the  cavernous  sinus  within  the  cranium  to  the 
pterygoid  venous  plexus  situated  in  the  pterygo-maxillary  region.  Immediately 
behind  the  root  of  the  external  pterygoid  plate  there  is  a  large  oval  hole,  the  foramen 
ovale,  and  behind  that,  and  in  line  with  the  alar  spine,  is  the  smaller  foramen 
spinosum.  These  two  foramina  cannot  usually  be  seen  in  a  side  view  of  the  skull, 
and  are  better  studied  when  the  base  is  examined ;  they  are  mentioned,  however, 
because  they  transmit  structures  which  here  pass  from  and  enter  the  cranium,  viz. 
the  inferior  maxillary  division  of  the  fifth  nerve,  together  with  its  motor  root,  and 
the  small  meningeal  artery  through  the  foramen  ovale,  and  the  middle  meningeal 
artery  and  its  companion  veins  through  the  foramen  spinosum.  A  part  of  the 
squamous  temporal  also  forms  a  small  portion  of  the  roof  of  this  fossa ;  it  consists 
of  a  triangular  area  immediately  in  front  of  the  eminentia  articularis,  and  between 
it  and  the  anterior  root  of  the  zygomatic  process  of  the  temporal,  which  is  here 
curving  inwards  and  forwards,  to  become  continuous  with  the  infratemporal  crest. 
Internally  this  surface  is  continuous  with  the  zygomatic  surface  of  the  great  wing 
of  the  sphenoid,  separated  from  it,  however,  by  the  hinder  part  of  the  spheno- 
squamosal  suture. 

When  the  lower  jaw  is  in  position,  the  zygomatic  fossa  is  concealed  by  the 
ramus  of  the  mandible,  the  inner  surface  of  which,  in  its  upper  half,  forms  the  outer 
wall  of  that  space.  Viewed  from  the  outer  side,  the  ramus  of  the  inferior  maxilla 
displays  considerable  differences  in  different  skulls.  These  are  mainly  due  to  varia- 
tions in  its  width  and  in  the  nature  of  the  angle  which  it  forms  at  its  fusion  with 
the  body  of  the  bone.  A  considerable  interval  separates  the  posterior  border  of  the 
ramus  from  the  front  of  the  mastoid  process.  Within  this  space  may  be  seen  the 
free  inferior  edge  of  the  tympanic  plate  (vaginal  process),  from  which,  just  below 
the  external  auditory  meatus,  the  styloid  process  of  the  temporal  bone  is  observed 
passing  downwards  and  slightly  forwards.  The  width  and  height  of  the  coronoid 
process  vary  much,  oftentimes  reaching  the  level  of  the  top  of  the  condyle.  Its 
extremity,  when  the  lower  jaw  is  closed,  lies  just  within  the  fore-part  of  the  zygo- 
matic arch  ;  at  other  times  it  rises  to  a  much  higher  level,  so  that  its  point  may  be 
seen  above  the  level  of  the  upper  border  of  the  zygomatic  arch.  The  posterior 
edge  of  the  coronoid  process  forms  the  anterior  border  of  the  sigmoid  notch,  and 
limits  in  front  the  interval  left  between  the  lower  border  of  the  posterior  half  of 
the  zygomatic  arch  and  the  upper  hollowed  edge  of  the  ramus.  On  looking  into 
this  interval,  the  floor  of  the  zygomatic  fossa  may  be  seen,  formed  anteriorly  by  the 
external  jjterygoid  plate ;  whilst  posteriorly  it  is  possible  to  pass  a  prol)e  right 
across  the  base  of  the  skull  from  one  sigmoid  notch  to  the  other,  the  shaft  of  the 
probe  lying  immediately  behind  the  pterygoid  processes  of  the  sphenoid,  and  cross- 
ing the  foramina  ovalia,  tlirough  which  the  inferior  maxillary  divisions  of  the  fifth 
nerves  ])ass. 

The  ramus  and  coronoid  process  are  so  placed  as  to  occupy  a  position  inter- 
mediate between  the  zygomatic  arc!)  externally  and  the  external  pterygoid  plate 
internally ;  their  inner  surface,  therefore,  forms  the  outer  wall  of  the  zygomatic  fossa. 
On  a  level  with  the  surface  of  the  crowns  of  the  teeth  of  the  lower  jaw,  and 
situated  about  the  middle  of  this  aspect  of  the  ramus,  is  the  inferior  dental  foramen 


158 


OSTEOLOGY. 


(foramen  mandibulare),  the  superior  opening  of  the  inferior  dental  canal  (canalis 
mandibulse),  which  traverses  the  body  of  the  bone.  Through  this  foramen  there 
pass  the  inferior  dental  branch  of  the  inferior  maxillary  division  of  the  fifth  nerve, 
together  with  the  inferior  dental  artery  and  its  companion  veins.  As  will  now  be 
seen,  when  the  lower  jaw  is  in  position,  the  zygomatic  fossa  is  closed  in  externally 
by  the  ramus  of  the  mandible.  In  front  there  is  an  interval  between  the  anterior 
border  of  the  ramus  and  the  zygomatic  surface  of  the  superior  maxilla,  through 
which  pass  the  buccal  branch  of  the  fifth  nerve  and  the  communicating  vein 
between  the  pterygoid  plexus  and  the  facial  vein.  Above,  in  the  interval  between 
the  sigmoid  edge  and  the  lower  border  of  the  zygomatic  arch,  there  pass  from  the 
fossa  the  vessels  and  nerves  which  supply  the  masseter  muscle.  Between  the 
posterior  border  of  the  ramus  and  the  styloid  process  there  enter  and  leave  the 
large  vessels  which  are  found  within  the  space.  Superiorly,  under  cover  of  the 
zygomatic  arch,  the  zygomatic  fossa  communicates  with  the  temporal  fossa,  whilst 
inferiorly  it  is  continuous  with  the  inframaxillary  region.  Internally,  on  the 
floor  of  the  fossa  there  is  an  f-shaped  fissure,  the  horizontal  limb  of  which 
corresponds  to  the  spheno-maxillary  fissure,  forming  a  channel  of  communication 
between  the  fossa  and  the  orbit,  through  which  passes  the  orbital  branch  of  the 
superior  maxillary  division  of  the  fifth  nerve  ;  whilst  the  vertical  cleft  is  the  pterygo- 
maxillary  fissure,  which  leads  into  a  small  fossa  placed  between  the  front  of  the  root 
of  the  pterygoid  process  of  the  sphenoid  and  the  back  of  the  superior  maxilla,  called 
the  spheno-maxillary  fossa  (fossa  pterygo-palatina). 

The  following  foramina  open  into   the  zygomatic  fossa — the  foramen  ovale. 


24     23         22 

Fig.  120. — Coronal  Section  through  the  Spheno- Maxillary  Fossa  of  the  Right  Side. 

A.  Anterior  Wall.     B.  Posterior  Wall.     C.   Diagrammatic  representation  of  a  horizontal  section  across  the 

fossa. 


1.  Spheno-palatiiie  foramen. 

2.  Apex  of  orbital  cavity. 

3.  Spheno-maxillary  fissure. 

4.  Spheno-maxillary  fissure. 

5.  Pterygo-niaxillary  fissure. 

6.  Dental  foramina. 

7.  Part  of  pterygoid  fossa. 


S,  9,  10.  Posterior  palatine   and   ac- 
cessory palatine  canals. 

11.  Foramen  rotunduin. 

12.  Sphenoidal  fissure. 

13.  Optic  foramen. 

14.  Sphenoidal  sinus. 

15.  Pterygo-palatine  canal. 

16.  Vidian  canal. 


IT.  Spheiio-palatine  foramen. 

18.  Spheno-maxillary  fossa. 

19.  Infra-orbital  groove. 

20.  Spheno-maxillary  fissure. 

21.  Pterygo-niaxillary  fissure. 

22.  Foramen  rotundum. 

23.  Vidian  canal. 

24.  Pterygo-palatine  canal. 


foramen  spinosum,  posterior  dental  foramina,  inferior  dental  foramen,  minute 
foramina  for  the  transmission  of  emissary  veins ;  of  these  one  of  large  size  is 
occasionally  present,  the  foramen  of  Vesalius. 

Spheno-Maxillary  Fossa. — This  space,  which  corresponds  to  the  angular  interval 


.NOEMA  OCGiriTALIS  OF  THE  SKULL.  L59 

between  the  pterygo-maxillary  and  spheno-inaxillary  fissures,  and  which  lies 
between  the  maxilla  in  front  and  the  root  of  the  pterygoid  process  behind,  is 
bounded  internally  by  the  vertical  plate  of  the  palate  bone,  which  separates  it 
from  the  nasal  cavity,  with  which,  however,  it  communicates  by  means  of  the 
spheno-palatine  foramen,  which  lies  between  the  orbital  and  sphenoidal  processes  of 
the  palate  bone  and  the  under  surface  of  the  body  of  the  sphenoid.  Opening 
into  this  fossa,  above  and  behind,  are  the  foramen  rotundum,  the  Vidian  canal  and 
the  pterygo-palatine  canal  from  without  inwards,  whilst  below  is  the  superior 
orifice  of  the  posterior  palatine  canal,  together  with  openings  of  the  accessory 
posterior  palatine  canals.  Its  roof  is  formed  by  the  under  surface  of  the  body  of 
the  sphenoid  and  the  orbital  plate  of  the  palate  bone.  Anteriorly  it  lies  in  relation 
to  the  apex  of  the  orbit,  with  which  it  communicates  by  means  of  the  spheno- 
maxillary fissure ;  whilst  externally,  as  already  stated,  it  communicates  with  the 
zygomatic  fossa  through  the  pterygo-maxillary  fissure. 

Norma  Occipitalis. 

This  view  of  the  cranium  includes  the  posterior  halves  of  the  two  parietal 
bones  above,  the  tabular  part  of  the  occipital  bone  below,  and  the  mastoid  portions 
of  the  temporal  bones  on  either  side  inferiorly.  The  shape  of  this  aspect  of  the 
skull  varies  much,  but  ordinarily  the  greatest  width  corresponds  to  the  level  of  the 
parietal  eminences.  The  sutures  on  this  view  of  the  calvaria  display  a  tri-radiate 
arrangement,  one  limb  of  which  is  vertical,  and  corresponds  to  the  posterior  part  of 
the  interparietal  or  sagittal  suture  (sutura  sagittalis).  The  other  two  limbs  pass 
outwards  and  downwards  in  the  direction  of  the  mastoid  processes,  uniting  the  two 
parietal  bones  in  front  with  the  occipital  bone  behind ;  these  constitute  the  A-shaped 
lambdoid  suture  (sutura  lambdoidea).  The  point  of  confluence  of  the  sagittal  and 
lambdoid  sutures  is  called  the  lambda.  This  can  generally  be  felt  in  the  living, 
owing  to  the  tendency  of  the  tabular  part  of  the  occipital  to  project  slightly 
immediately  below  this  spot.  About  one  inch  and  a  quarter  above  the  lambda  the 
two  small  parietal  foramina  (foramina  parietalia)  are  seen,  through  which  pass  the 
small  emissary  veins  of  Santorini,  which  connect  the  intracranial  venous  system 
with  the  superficial  veins  of  scalp.  These  small  holes  lie  about  y^g-  of  an  inch  apart 
on  either  side  of  the  sagittal  suture,  which  here,  for  the  space  of  about  an  inch, 
displays  a  simplicity  of  outline  in  striking  contrast  with  its  serrated  arrangement 
elsewhere.  The  term  obelion  is  applied  to  a  point  on  the  sagittal  suture  in  line 
with  the  two  parietal  foramina.  The  lambdoid  suture  is  characterised  by  great 
irregularity  of  outline,  and  not  unfrequejitly  chains  of  separated  ossicles  are  met 
with  in  it,  the  so-called  Wormian  bones.  The  tabular  part  of  the  occipital  bone  is 
divided  into  two  parts  by  the  superior  curved  line  (linea  nuchse  superior),  the 
central  part  of  which  forms  the  external  occipital  protuberance  (protuberantia 
occipitalis  exterior).  The  part  above,  called  the  occipital  surface  (planum  occipitale), 
comes  within  our  present  consideration  ;  the  part  below,  the  nuchal  surface  (planum 
nuchale),  though  seen  in  perspective,  had  best  be  considered  when  the  base  is 
examined.  A  little  above  the  level  of  the  superior  curved  line  the  occipital  surface 
is  crossed  on  either  side  by  a  faint  lunated  line,  the  highest  curved  line  (linea 
nuchse  suprema)  to  which  are  attached  the  occipitales  muscles  and  the  epicranial 
aponeurosis.  The  projection  of  the  occipital  surface  varies  much  in  individual 
skulls  ;  most  frequently  it  overhangs  the  external  occipital  protuberance,  forming  a 
distinct  boss ;  exceptionally,  however,  the  latter  may  be  the  most  projecting  part  of 
the  bone.  The  extremity  of  the  superior  curved  line  on  either  side  corresponds  to 
the  position  of  the  asterion  (jj.  154).  External  to  these  points  the  outline  of  the 
skull  is  determined  by  the  downward  projection  of  the  mastoid  processes,  the  inner 
surfaces  of  whicli  are  deeply  grooved  for  tlie  attachment  of  the  posterior  bellies  of 
the  digastric  muscles,  thus  causing  these  processes  to  appear  more  pointed  when 
viewed  from  this  aspect. 

Norma  Verticalis. 

This  is  the  view  of  the  (;alvaria  as  seen  from  above.      It  is  liable  to  great 


160  OSTEOLOGY. 

diversities  of  form.  Thus  its  shape  may  vary  from  an  elongated  oval  to  an  outline 
more  nearly  circular.  These  differences  have  been  classified,  and  form  important 
distinctions  from  a  craDiometrical  standpoint  (p.  178),  the  rounder  varieties  being 
termed  tlie  brachycephalic,  whilst  the  elongated  belong  to  the  dolichocephalic  group. 
Another  noteworthy  point  in  this  view  is  the  fact  that  in  some  instances  the 
zygomatic  arches  are  seen,  whilst  in  others  tliey  are  concealed  by  the  overhang 
and  l:)ulge  of  the  sides  of  the  fore-part  of  the  cranium.  The  former  condition  is 
described  as  phoenozygous,  the  latter  as  cryptozygous,  and  each  is  more  or  less  closely 
associated  with  the  long  or  round  varieties  of  head-form  respectively. 

The  sutures  displayed  have  a  T-shaped  arrangement.  Placed  mesially  between 
the  two  parietal  bones  is  the  sagittal  suture.  This  is  finely  denticulated,  except  in 
the  region  of  the  obelion,  though,  of  course,  this  will  not  be  apparent  if  obliteration 
of  the  suture  has  taken  place  through  fusion  of  the  two  parietal  l)ones.  Posteriorly 
the  sagittal  suture  unites  with  the  lambdoid  suture  at  the  lambda,  which  marks 
in  the  adult  the  position  of  the  posterior  fontanelle  of  the  foetus.  Anteriorly  it 
terminates  by  joining  the  transverse  suture  which  separates  the  frontal  bone 
anteriorly  from  the  parietals  behind ;  this  latter  is  called  the  coronal  suture,  and  the 
point  of  junction  between  the  sagittal  and  coronal  sutures  is  known  as  the  bregma 
which  corresponds  in  position  to  the  anterior  fontanelle  of  the  foetus.  The  summit 
of  the  vault  of  the  calvaria  corresponds  to  a  variable  point  in  the  line  of  the  sagittal 
suture,  and  is  named  the  vertex.  The  coronal  suture  is  less  denticulated  centrally  than 
laterally.  Occasionally  there  is  a  persistence  of  the  suture  which  unites  the  two 
halves  of  the  frontal  bone;  under  these  conditions  the  line  of  the  sagittal  suture  is 
carried  forward  to  the  fronto-nasal  suture,  and  a  skull  displaying  this  peculiarity  is 
described  as  metopic.  Behind  the  coronal  suture  may  occasionally  be  seen  the 
post-coronal  depression  (p.  154),  and  in  some  instances  the  vault  of  the  calvaria  forms 
a  broad,  slightly  elevated  crest  along  the  line  of  the  sagittal  suture.  On  either 
side,  the  temporal  ridges  can  be  seen  curving  over  the  lateral  and  superior  aspects 
of  the  parietal  bones.  As  the  lower  of  these  crosses  the  coronal  suture  in  front  it 
marks  a  spot  known  as  the  stephanion,  useful  as  affording  a  fixed  point  from  which 
to  estimate  the  bi-stephanic  diameter.  The  interval  between  the  temporal  ridges 
on  either  side  will  vary  according  to  the  form  of  the  skull  and  the  development  of 
the  temporal  muscle.  In  this  view  of  the  calvaria  a  small  part  of  the  lambdoid 
suture  on  either  side  of  the  lambda  is  visible  posteriorly. 

Norma  Basalis. 

The  base  of  the  cranium — i.e.  the  skull  without  the  mandible — includes  a  descrip- 
tion of  the  under  surfaces  of  the  skeleton  of  the  face  (cranium  viscerale)  and  the 
cranium  (cranium  cerebrale).  The  former  includes  the  hard  palate  formed  by  the 
superior  maxillae  and  palate  bones,  the  superior  dental  arch,  and  the  bodies  of  the 
superior  maxillae  as  seen  from  below  ;  whilst  externally,  and  united  with  the  bodies  of 
the  superior  maxilla,  the  malar  bones  are  displayed,  curving  backwards  to  form  the 
anterior  halves  of  the  zygomatic  arches.  In  the  middle  line,  passing  from  the  upper 
surface  of  the  hard  palate,  is  the  osseous  septum  of  the  nose,  here  formed  by 
the  vomer,  which  is  united  above  to  the  under  surface  of  the  body  of  the 
sphenoid. 

The  under  surface  of  the  cranium  is  pierced  by  the  foramen  magnum  for  the 
transmission  of  the  spinal  cord  and  its  membranes.  In  front  of  this  a  stout  bar  of 
bone  extends  forwards  in  the  middle  line,  formed  by  the  union  of  the  body  of  the 
sphenoid  in  front  with  the  basilar  process  of  the  occipital  bone  behind.  In  adult 
skulls  all  trace  of  the  fusion  of  these  two  bones  has  disappeared  ;  when  union  is  in- 
complete, it  indicates  that  the  skull  is  that  of  a  person  below  the  age  of  twenty-five. 
The  sphenoid  comprises  that  part  of  the  calvaria  which  forms  the  roof  and  sides  of 
the  apertvires  which  lie  on  either  side  of  the  nasal  septum  above, the  hard  palate 
— the  choanse  or  posterior  nares.  Laterally  the  under  surfaces  of  the  great 
sphenoidal  wings  extend  as  far  forward  as  the  posterior  border  of  the  spheno- 
maxillary fissure ;  whilst  posteriorly  they  reach  as  far  as  the  alar  spine,  external  to 
which  the  spheno-squamosal  suture,  separating  the  great  wing  of  the  sphenoid  from 


NORMA  BASALIS  OF  THE  SKULL. 


IGl 


1.  External  occipital  crest. 

2.  Superior  curved  line  of 

the  occipital  bone. 

3.  Foramen  magnum. 

4.  Occipital  condyle. 

5.  Digastric  groove. 

6.  Mastoid  process. 

7.  External  auditory  meatus. 

8.  Styloid  process. 

9.  Glenoid  fossa. 

10.  Foramen  spinosum. 

11.  Sphenoidal  spine. 

12.  Foramen  ovah;. 

13.  External  pterygoid  filate. 


Fig.  121. — Norma  Basalis. 

14.  Haniular  process  of  internal  27. 

pterj'goid  i:ilate.  28. 

1.5.  Nasal  septum.  29. 

16.  Posterior  nasal  spine.  30. 

17.  Horizontal  plate  of  palate  bone. 

18.  Palatal  process  of  superior  maxilla.  31. 

19.  Anterior  jjalatine  canal.  32. 

20.  Intermaxillary  suture.  33. 

21.  Posterior  palatine  canal.  34. 

22.  Malar  process  of  superior  maxilla.  35. 

23.  Spheno-niaxillary  fissure.  36. 

24.  Zygomatic  fossa.  37. 

25.  Zygomatic  arch.  38. 

26.  Posterior  open! iig  of  left  nasal  fossa.  39. 


Pterygoid  fossa. 

Scaphoid  fossa. 

Foramen  lacerum  medium. 

Opening  of  osseous  Eu.stachian 

canal. 
Carotid  canal. 
Jugular  fossa. 
Stylo-niastoid  foramen. 
Jugular  process  of  occipital  bone. 
Groove  for  occipital  artery. 
Mastoid  foramen. 
Posterior  condylic  foramen. 
Inferior  curved  lineof  occii)ital  bone 
External  occipital  protuberance. 


the  squamous  portion  of  the  temporal,  curves  forwards  and  upwards,  internal  to  the 
eminentia  articularis,  to  reach  the  fi<jf)r  of  the  temporal  fossa,  along  which  its  course 
12 


162  OSTEOLOGY. 

has  been  already  traced  (p.  155).  On  a  level  with  the  front  of  the  foramen 
magnum  the  jugular  process  of  the  occipital  bone  forms  an  irregular  curved  border, 
which  sweeps  outwards  to  terminate  at  a  point  just  internal  to  the  root  of  the 
styloid  process.  Here,  in  line  with  the  spheno-squamosal  suture,  from  which,  how- 
ever, it  is  separated  by  a  considerable  interval,  its  extremity  turns  backwards,  and 
may  be  traced  at  first  internal  to,  and  then  turning  upwards,  behind  the  mastoid 
process  of  the  temporal  bone,  separated  from  this  latter  by  the  occipito-mastoid 
suture.  The  bone  behind  the  foramen  magnum,  which  is  included  between  the 
two  occipito-mastoid  sutures,  comprises  the  nuchal  surface  of  the  tabular  portion  of 
the  occipital  bone,  an  area  which  is  limited  behind  by  the  superior  curved  line 
which  separates  it  from  the  occipital  surface  of  the  same  bone.  The  remaining 
portions  of  the  base  of  the  calvaria,  as  at  present  exposed,  are  formed  by  the 
squamous  and  tympanic  portions  of  the  temporal  bone  together  with  the  petro-mastoid 
part  of  the  same  bone,  the  latter  of  which  is  wedged  in  between  the  great  wing  of 
the  sphenoid  in  front  and  the  occipital  bone  behind.  Stretching  forwards  from  the 
squamous  temporal  in  front  is  seen  the  zygomatic  process  which,  by  its  union  with 
the  malar,  completes  the  formation  of  the  zygomatic  arch. 

Studying  next  the  various  parts  in  detail,  the  hard  palate  (palatum  durum)  may 
be  first  examined.  Of  horse-shoe  shape  as  a  rule,  it  presents  many  varieties  of  out- 
line and  size.  Formed  by  the  palatal  processes  (processus  palatini)  of  the  superior 
maxillae  in  front  and  the  horizontal  plates  (partes  horizontales)  of  the  palate  bones 
behind,  its  circumference  in  front  and  at  the  sides  corresponds  to  the  superior 
alveolar  arch,  in  which  are  embedded  the  sixteen  teeth  of  the  upper  jaw ; 
posteriorly  the  edge  of  the  hard  palate  is  thin,  ending  mesially  in  a  pointed 
process,  the  posterior  nasal  spine  (spina  nasalis  posterior),  on  either  side  of  which  the 
posterior  free  border  is  sharp  and  lunated.  The  vault  of  the  palate,  which  is 
concave  from  side  to  side,  and  from  before  backwards,  varies  in  depth  according  to 
the  projection  and  development  of  the  alveolar  processes.  When  the  teeth  are  shed 
and  the  alveoli  are  absorbed,  the  palate  becomes  shallow  and  flat.  Eunning 
throughout  its  entire  length  in  the  middle  line  is  the  middle  palatine  suture 
(sutura  palatina  mediana),  which  separates  the  palatal  processes  of  the  superior 
maxillae  in  front  and  the  horizontal  plates  of  the  palate  bones  behind.  A  little 
behind  the  central  incisor  teeth,  and  in  the  line  of  this  suture,  is  a  little  pit,  the 
anterior  palatine  canal  or  fossa  (foramen  incisivum).  At  the  bottom  of  this  may  be 
seen  the  openings  of  some  small  canals,  varying  in  number  from  one  to  four ;  these 
are  usually  described  as  arranged  in  two  pairs,  the  one  pair  placed  side  by  side, 
the  other  lying  mesially  in  front  and  behind.  The  former  are  called  the  incisor 
foramina,  or  foramina  of  Stenson,  and  transmit  the  terminal  twigs  of  the  superior 
or  descending  palatine  arteries  which  ascend  to  reach  the  nasal  fossae.  The  latter, 
called  the  foramina  of  Scarpa,  open,  the  anterior  into  the  left,  the  posterior  into  the 
right  nasal  fossa,  and  afford  passage  for  the  fine  filaments  of  the  left  and  right  naso- 
palatine nerves  respectively.  About  half  an  inch  (12  mm.)  in  front  of  the  posterior 
nasal  spine  the  middle  palatine  suture  is  crossed  at  right  angles  by  the  transverse 
palatine  suture  (sutura  palatina  transversa).  This,  which  indicates  the  line  of 
union  of  the  palatal  processes  of  the  superior  maxillae  with  the  horizontal  plates  of 
the  palate  bones,  passes  transversely  outwards  on  either  side  until  it  reaches  the 
inner  aspect  of  the  base  of  the  alveolar  process,  along  which  it  turns  backward,  to 
disappear  within  the  posterior  palatine  canal  (foramen  palatinum  majus),  the  aperture 
of  which  lies  immediately  internal  to  the  root  of  the  wisdom  molar.  Through  this 
there  pass  the  superior  or  descending  palatine  artery  and  the  large  descending 
palatine  nerve.  Leading  from  this  foramen  is  a  groove  which  curves  forward  im- 
mediately to  the  inner  side  of  the  alveolar  arch ;  not  unfrequently  the  inner  edge 
of  this  groove  forms  a  thin  and  sharp  ridge  on  the  surface  of  the  palate.  In  this 
groove  are  lodged  the  aforementioned  vessels  and  nerves.  The  surface  of  the  palate 
in  front  of  the  transverse  suture  is  rough,  pitted  for  the  palatine  glands,  and  pierced  by 
numerous  small  vascular  foramina ;  the  part  of  the  palate  behind  the  suture,  formed 
by  the  under  surface  of  the  horizontal  plate  of  the  palate  bone,  is  much  smoother. 
From  this  there  rises,  just  posterior  to  the  orifice  of  the  posterior  palatine  canal,  a 
thin  sharp  crest  which  curves  inwards  immediately  in  front  of  the  posterior  free 


NOEMA  BASALIS  OF  THE  SKULL.  103 

edge ;  to    this   are    attached    some  of   the   tendinous   libres  of   tlie   tensor  pulati 
muscle. 

Pterygoid  Processes. — Buttressed  against  tlie  hinder  extremities  of  the  alveolar 
arch  are  the  pterygoid  processes  of  the  sphenoid.  If  carefully  examined,  these 
will  be  seen  not  to  lie  in  actual  contact  with  the  maxillse,  but  to  be  separated  from 
them  by  the  triangular  wedge-shaped  tuberosities  (proc.  pyramidales)  of  the  palate 
bones.  It  is  these  latter  which  are  jjierced  by  the  posterior  and  external  accessory 
palatine  canals  (foramina  palatina  minora)  which  lie  just  beliind  the  jjosterior  pala- 
tine canal,  and  through  which  pass  the  lesser  palatine  nerves.  As  here  displayed, 
the  pterygoid  processes  (processus  pterygoidei)  of  the  sphenoid  lie  on  either  side  of 
the  opening  of  the  posterior  nares ;  each  consists  of  two  plates,  an  internal  (lamina 
medialis)  and  an  external  (lamina  lateralis) ;  the  latter  is  the  broader,  and  is 
directed  backwards  and  slightly  outwards.  Its  external  surface  has  been  already 
studied  in  connexion  with  the  zygomatic  fossa  (p.  156).  Internally  it  is  separated 
from  the  inner  pterygoid  plate  by  the  pterygoid  fossa  (fossa  pterygoidea),  wherein 
is  lodged  a  considerable  part  of  the  internal  pterygoid  muscle.  The  floor  of  the 
fossa  is  formed  in  greater  part  by  the  coalescence  of  the  two  pterygoid  plates ;  but 
at  the  level  of  the  hard  palate  the  tuberosity  of  the  palate  bone  appears  wedged  in 
between  the  two  plates,  and  so  enters  into  the  formation  of  the  floor  of  the 
pterygoid  fossa.  The  internal  pterygoid  plate  separates  the  nasal  from  the 
pterygoid  fossa ;  to  the  hinder  edge  of  the  internal  pterygoid  plate  are  attached  the 
pharyngeal  aponeurosis,  the  superior  constrictor  of  the  pharynx,  and  the  palato- 
pharyngeus  muscle.  Above,  the  posterior  border  of  this  plate  is  channelled  to 
form  the  small  scaphoid  fossa  (fossa  scaphoidea),  which  curves  outwards  over  the 
summit  of  the  pterygoid  fossa,  and  furnishes  a  surface  for  the  origin  of  the  tensor  palati 
muscle.  The  sharp  inner  margin  of  this  fossa,  continuous  below  with  the  posterior 
border  of  the  internal  pterygoid  plate,  extends  upwards,  and  on  either  side  of  the 
body  of  the  sphenoid  forms  a  blunt  pointed  process,  the  pterygoid  tubercle,  which 
extends  backwards  towards  the  apex  of  the  petrous  part  of  the  temporal  bone. 
Just  external  to  this,  and  concealed  by  it,  is  the  hinder  extremity  of  the  Vidian 
canal  (canalis  Vidianis),  through  which  pass  the  Vidian  vessels  and  nerve.  The 
inner  surface  of  the  internal  pterygoid  plate  is  directed  towards  the  nasal  fossae. 
Superiorly  this  surface  curves  inwards  to  meet  the  under  surface  of  the  body  of  the 
sphenoid,  forming  on  either  side  a  lipped  edge,  the  vaginal  process  (processus  vaginalis), 
between  which  the  alae  of  the  vomer,  which  here  forms  the  nasal  septum,  are 
wedged.  Between  the  two  a  small  interval,  however,  is  occasionally  left,  which  forms 
on  either  side  the  basi-pharyngeal  canal.  A  little  external  to  the  line  of  union  of 
the  vaginal  process  with  the  vomer  is  the  opening  of  the  pterygo-palatine  canal 
(canalis  pharyngeus).  This  lies  between  the  under  surface  of  the  vaginal  process 
and  the  sphenoidal  process  of  the  palate  bone,  which  here  articulates  with  the 
inferior  surface  of  the  body  of  the  sphenoid.  The  pharyngeal  branch  of  the 
spheno-palatine  ganglion  and  the  pterygo-palatine  artery  pass  through  this  canal. 
Inferiorly  the  pterygoid  processes  project  below  the  level  of  the  hard  palate.  The 
inner  plate  ends  in  a  slender  recurved  process,  called  the  hamular  process  (hamulus 
pterygoideus),  which  turns  backwards  and  outwards  ;  this  is  frequently  broken  off  in 
skulls  which  have  been  roughly  handled.  It  reaches  as  low  as  the  level  of  the 
alveolar  margin,  and  lies  just  within  and  behind  the  posterior  extremity  of  the 
alveolar  jjrocess.  It  can  readily  be  felt  in  the  living  by  placing  the  finger  against 
the  soft  palate  behind  and  just  within  the  gum  around  the  root  of  the  wisdom 
tooth.  On  the  front  of  and  below  this  process  the  tendon  of  the  tensor  palati 
muscle  glides  in  a  groove. 

The  posterior  nares  (choanse)  lie  within  and  between  the  pterygoid  processes. 
Of  a  shape  much  resembling  two  Gothic  windows,  their  bases  or  inferior  boundaries 
are  formed  by  the  horizontal  plates  of  the  j)alate  bone.  Externally  they  are 
bounded  by  the  inner  surfaces  of  the  internal  pterygoid  plates,  whilst  above,  the 
outer  side  of  the  arch  is  formed  by  the  vaginal  processes  of  the  same  plate;  intern- 
ally they  are  separated  by  the  thin  vertical  posterior  border  of  the  vomer,  wliilst 
above  the  everted  alte  of  the  same  bone  form  the  inner  sides  of  the  arch.  The 
plane  of  these  ajjertures  is  not  vortical  Ijut  ol^lique,  corresponding  usually  to  a 
12a 


164  OSTEOLOGY. 

line  drawn  from  the  bregma  above  through  the  last  molar  tooth  of  the  upper 
jaw  below.  Their  size  varies  considerably,  but  the  height  is  usually  equal  to  twice 
the  width. 

The  region  of  the  cranium  which  lies  external  to  the  superior  maxilla  and 
external  pterygoid  plate  corresponds  to  the  zygomatic  fossa,  which  has  been  already 
described  as  seen  from  the  side  (norma  lateralis,  p.  156).  Viewed  from  below,  the 
zygomatic  fossa  is  bounded  in  front  by  the  posterior  surface  of  the  body  of  the 
superior  maxilla  and  the  internal  surface  of  the  malar  bone.  The  roof,  which  is 
traversed  by  the  spheno-squamosal  suture,  is  formed  in  front  by  the  under  surface 
of  the  great  wing  of  the  sphenoid,  and  behind  by  a  small  triangular  surface  of  the 
under  side  of  the  squamous  part  of  the  temporal  bone  immediately  in  front  of  the 
eminentia  articularis. 

Circumscribed  externally  and  behind  by  the  anterior  root  of  the  zygoma,  which 
curves  forward  to  become  continuous  in  front  with  the  infra-temporal  crest  crossing 
the  external  surface  of  the  great  wing  of  the  sphenoid,  the  roof  of  the  fossa  is 
separated  from  its  anterior  wall  by  the  spheno-maxillary  fissure,  which  is  so  inclined 
that  with  its  fellow  of  the  opposite  side  it  forms  an  angle  of  90".  Superiorly  the 
zygomatic  fossa  communicates  freely  with  the  temporal  fossa  beneath  the  zygo- 
matic arch,  though  the  student  must  bear  in  mind  the  fact  that  when  the  inferior 
maxilla  is  in  position  the  external  limits  of  the  space  are  very  much  reduced  (p.  160). 

The  under  surface  of  the  great  wing  of  the  sphenoid  is  here  V-shaped.  The 
angle  corresponds  to  the  spine,  the  outer  limb  to  the  spheno-squamosal  suture, 
whilst  the  inner  limb  corresponds  to  a  narrow  cleft,  the  fissura  spheno-petrosa, 
which  separates  it  from  the  petrous  portion  of  the  temporal  bone  to  which  it  is 
united  in  the  recent  condition  by  a  synchondrosis.  Along  the  line  of  this  latter 
fissure  the  edges  of  the  adjacent  bones  (sphenoid  and  petrous  temporal)  are 
bevelled  so  as  to  form  a  groove,  which  extends  from  the  root  of  the  inner  pterygoid 
plate  internally,  to  the  inner  side  of  the  base  of  the  alar  spine  externally,  where 
the  groove  ends  by  entering  an  osseous  canal.  In  the  groove  (sulcus  tubee  auditivse) 
is  lodged  the  cartilaginous  part  of  the  Eustachian  tube,  whilst  the  osseous  canal 
includes  the  bony  part  of  the  same  tube,  together  with  the  tensor  tympani  muscle, 
which  is  lodged  in  a  separate  compartment  immediately  above  it.  The  anterior 
extremity  of  the  cartilaginous  part  of  the  Eustachian  tube  is  supported  by  the 
posterior  edge  of  the  internal  pterygoid  plate,  which  is  often  notched  for  its  recep- 
tion. Between  the  root  of  the  external  pterygoid  plate  and  the  alar  spine  there 
are  two  foramina  which  lie  immediately  in  front  of  the  sulcus  tubee  auditivse. 
Of  these  the  larger  and  anterior  is  the  foramen  ovale,  through  which  pass  the 
motor  root  and  inferior  maxillary  division  of  the  fifth  nerve,  together  with  the 
small  meningeal  artery.  The  smaller,  which  from  its  position  immediately  in 
front  of  the  alar  spine  is  called  the  foramen  spinosum,  transmits  the  middle  menin- 
geal artery  and  sympathetic  plexus  surrounding  that  vessel.  The  lesser  superficial 
petrosal  nerve  here  passes  through  the  base  of  the  skull  to  join  the  otic  ganglion 
either  through  a  small  foramen  (canalis  innominatus)  placed  between  the  foramen 
ovale  and  the  foramen  spinosum,  or  through  the  foramen  ovale  or  through  the 
spheno-petrosal  fissure.  The  position  of  the  suture  between  the  basi-occipital  and 
basi-sphenoid  corresponds  to  a  line  connecting  the  tips  of  the  pterygoid  tubercles  at 
the  root  of  the  internal  pterygoid  plates. 

Occasionally  in  the  centre  of  this  line  there  is  a  small  pit  with  a  foramen  leading  from  it.    This 
probably  represents  the  lower  end  of  the  cranio -pharyngeal  canal. 

The  under  surface  of  the  basi-occipital  (pars  basilaris)  stretches  between  the 
body  of  the  sphenoid  in  front  and  the  anterior  margin  of  the  foramen  magnum 
behind  ;  projecting  from  its  centre  is  a  slight  elevation,  the  pharyngeal  tubercle 
(tuberculum  pharyngeum),  to  which  the  pharyngeal  aponeurosis,  together  with  the 
central  part  of  the  anterior  occipito-atlantal  ligament,  is  attached.  It  should  be 
noted,  that  when  the  atlas  is  in  position  the  pharyngeal  tubercle  lies  in  line  with 
the  tubercle  on  the  anterior  arch  of  that  bone.  Curving  outwards  and  backwards 
from  the  pharyngeal  tubercle,  on  either  side,  is  an  irregular  ridge  (crista  muscularis), 
in  front  and  behind  which  are  attached  the  rectus  capitis  anticus  major  and  minor 


NOEMA  BASALIS  OF  THE  SKULL.  165 

muscles.  On  either  side  of  the  basi-occipital,  in  front,  there  is  an  irregular  opening 
of  variable  size ;  this  is  placed  between  the  root  of  the  pterygoid  process  anteriorly, 
the  apex  of  the  petrous  portion  of  the  temporal  bone  externally,  and  the  outer 
edge  of  the  basi-occipital  and  basi-sphenoid  internally.  It  is  called  the  foramen 
lacerum  medium.  Opening  into  it  in  front,  just  external  to  the  pterygoid  tubercle, 
is  the  Vidian  canal,  whilst  in  correspondence  with  the  apex  of  the  petrous  temporal 
the  large  orifice  of  the  carotid  canal  may  be  seen  entering  it  behind  and  from  the 
outer  side.  In  the  recent  condition  the  lower  part  of  the  foramen  lacerum  is 
occupied  by  fibro-cartilage,  over  the  upper  surface  of  which  the  internal  carotid 
artery  and  great  superficial  petrosal  nerve  pass  to  reach  their  respective  foramina, 
whilst  a  small  meningeal  branch  of  the  ascending  pharyngeal  occasionally  enters 
the  cranium  through  it.  Leading  outwards  from  the  foramen  lacerum  in  the 
direction  of  the  alar  spine  of  the  sphenoid  is  the  spheno-petrosal  fissure,  which  lies 
at  the  bottom  of  the  sulcus  tubae  auditivse,  and  disappears  from  view  within  the 
bony  Eustachian  canal.  Passing  backwards  from  the  foramen  lacerum  there  is  a 
fissure  between  the  outer  side  of  the  basi-occipital  and  the  posterior  and  inner 
border  of  the  petrous  part  of  the  temporal  bone.  This,  which  is  called  the  petro- 
occipital  fissure  (fissura  petro-occipitalis),  opens  posteriorly  into  the  jugular  foramen. 
In  the  recent  condition  the  fissure  is  filled  up  with  cartilage.  The  under  surface 
of  the  petrous  bone  included  between  these  two  fissures  is  rough  and  irregular,  and 
affords  attachments  near  its  apex  to  two  small  muscles,  the  levator  palati  and  the 
tensor  tympani.  Immediately  behind  the  alar  spine  the  petrous  temporal  is 
pierced  by  a  circular  hole,  the  inferior  opening  of  the  carotid  canal  (canalis  caroticus). 
This  passes  upwards,  and  then  turns  inwards  and  forwards  towards  the  apex  of  the 
bone,  where  it  may  again  be  seen  opening  into  the  outer  and  upper  side  of  the 
foramen  lacerum.  Externally  the  wall  of  the  vertical  part  of  this  canal  which  is 
usually  very  thin,  separates  it  from  the  cavity  of  the  tympanum,  as  may  be  seen  by 
holding  the  skull  up  to  the  light  and  looking  into  the  external  auditory  meatus 
(p.  118).  The  carotid  canal  transmits  the  internal  carotid  artery,  together  with 
the  sympathetic  plexus  around  it.  It  is  noteworthy  that  the  two  carotid  canals 
lie  in  line  with  the  anterior  edges  of  the  two  external  auditory  meatuses. 

The  jugular  foramen  is  an  opening  of  irregular  shape  and  size  placed  between 
the  petrous  temporal  in  front  and  the  jugular  process  of  the  occipital  bone 
behind.  The  former  is  excavated  into  a  hollow  called  the  jugular  fossa,  which  forms 
a  roof  to  the  upper  and  outer  part  of  the  space,  whilst  the  latter,  by  a  curved  edge, 
either  rounded  or  sharp,  constitutes  its  posterior  border.  There  is  often  considerable 
difference  in  the  size  of  the  jugular  foramina  ;  that  on  the  right  side  (with  the  skull 
in  its  normal  position)  is  usually  the  larger.  The  foramen  is  occasionally  sub- 
divided into  two  by  spicules  of  bone  which  bridge  across  it.  Lodged  within  the 
fossa  is  the  sinus  of  the  internal  jugular  vein,  in  front  of  which  the  inferior  petrosal 
sinus  passes  down  to  join  the  internal  jugular  vein  below  the  foramen.  Effect- 
ing an  exit  between  the  two  veins,  in  order  from  before  backwards,  are  the  glosso- 
pharyngeal, pneumogastric,  and  spinal  accessory  nerves.  Small  meningeal  branches 
from  the  ascending  pharyngeal  and  occipital  arteries  also  enter  the  foramen.  The 
two  jugular  foramina  lie  in  line  with  a  line  drawn  through  the  centres  of  the  two 
external  auditory  meatuses.  Following  the  direction  of  a  line  connecting  the  alar 
spine  of  the  sphenoid  and  the  mastoid  process  of  the  temporal,  and  placed  immedi- 
ately external  to  the  apertures  of  the  carotid  canal  and  jugular  foramen,  is  the 
vaginal  process  of  the  tympanic  plate  of  the  temporal  bone,  the  edge  of  whicli  is 
sharp  and  thin,  and  serves  to  separate  the  under  surface  of  the  petrous  temporal 
from  the  non-articular  part  of  the  glenoid  fossa.  Springing  from  this  crest  im- 
mediately external  to  the  jugular  fossa,  and  in  line  with  the  middle  of  the  external 
auditory  meatus,  is  tlie  styloid  process  (processus  styloideum)  of  the  temporal  bone 
(p.  116).  Its  relation  to  th(;  jugular  foramen  is  of  great  importance,  as  the  internal 
jugular  vein  li(;s  immediately  to  its  inner  side. 

Immediately  behind  the  root  of  the  styloid  ])roceHS,  internal  to  and  in  line  with 

t}ie  front  of  the  mastoid  process,  is  the  stylo -mastoid   foramen  (foramen  stylo- 

mastoideum),  the  lower  aperture  of  the  aqua;ductus  Fallopii  through  which  the  facial 

nerve  ]»asHes  out  and  the  stylo-mastoid  branch  of  the  posterior  auricular  artery 

12  & 


166  OSTEOLOGY. 

passes  in.  The  inner  surface  of  the  mastoid  process  is  deeply  grooved  at  its  base 
for  the  origin  of  the  posterior  belly  of  the  digastric  muscle.  Internal  to  this,  and 
running  along,  just  wide  of  the  occipito-mastoid  suture,  is  a  shallow  groove  in  which 
the  occipital  artery  is  lodged.  Immediately  internal  to  the  stylo-mastoid  foramen 
is  the  synchondrosis  between  the  extremity  of  the  jugular  process  (processus 
jugularis)  of  the  occipital  bone  and  the  petrous  temporal.  The  former  is  a  bar  of 
bone  which  limits  the  jugular  fossa  posteriorly  and  abuts  on  the  occipital  condyles 
internally ;  .its  under  surface  is  convex  from  before  1  backwards  and  affords  attachment 
to  the  rectus  lateralis  muscle.  The  occipital  condyles  (condyli  occipitales)  are 
placed  between  the  jugular  processes  and  the  ibramen  magiium.  Limited  in  front 
by  a  rounded  thickening  which  becomes  confluent  with  the  anterior  border  of  the 
foramen  magnum,  they  form  by  their  inner  sides  the  lateral  boundaries  of  that 
aperture  on  its  anterior  half.  Externally  they  are  continuous  with  the  jugular 
processes,  in  front  of  which  they  overhang  a  fossa  which  is  pierced  behind  by  the 
anterior  condylic  foramen  (canalis  hypoglossi),  through  which  passes  the  hypoglossal 
nerve,  together  with  a  small  vein  and  occasionally  a  small  meningeal  Ijranch 
derived  from  the  ascending  pharyngeal  artery. 

The  posterior  condylic  fossae  are  situated  just  behind  the  posterior  extremities  of 
the  condyles.  Not  unfrequently  their  floor  is  pierced  by  the  posterior  condylic 
foramen  (canalis  condyloideus),  through  which  the  posterior  condylic  vein  emerges. 
The  base  of  the  skull  behind  the  jugular  processes  and  condyles  of  the  occipital 
bone  is  formed  by  the  nuchal  surface  (planum  nuchale)  of  the  tal3nlar  plate  of  that 
bone.  Posteriorly  this  surface  is  bounded  by  the  superior  curved  line,  in  the  centre 
of  which  is  placed  the  projecting  external  occipital  protuberance.  Laterally  the 
tabular  plate  is  separated  from  the  mastoid  portion  of  the  temporal  bone  by  the 
occipito-mastoid  suture,  which  curves  backwards  and  outwards,  from  the  extremity 
of  the  jugular  process  in  front,  around  the  base  of  the  mastoid  process  behind.  In 
front  and  in  the  middle  line  this  plate  of  bone  is  pierced  by  the  foramen  magnum, 
the  anterior  half  of  which  has  been  already  seen  to  lie  between  the  occipital 
condyles.  Usually  of  oval  form,  though  in  some  cases  it  tends  to  approach  the 
circular,  the  plane  of  this  opening  is  inclined  downwards  and  slightly  forwards. 
The  extreme  anterior  edge  of  the  foramen  is  sometimes  called  the  basion,  whilst  the 
extreme  posterior  margin  is  termed  the  opisthion.  The  lower  border  of  the  medulla 
oblongata,  where  it  becomes  continuous  with  the  spinal  cord,  is  lodged  within  the 
foramen,  together  with  the  meninges  which  cover  it,  whilst  the  vertebral  arteries 
and  the  spinal  portions  of  the  spinal  accessory  nerves  pass  upwards  through  it. 
The  anterior  and  posterior  spinal  arteries,  some  small  veins,  and  the  roots  of  the 
first  cervical  nerves,  also  traverse  it  from  above  downwards. 

The  student  will,  no  doubt,  experience  considerable  difficulty  in  l)earing  in  mind  the  relative 
positions  of  the  various  foramina  and  j^rocesses  which  he  has  studied  on  the  under  surface  of  the 
base  of  the  skull. 

If  a  line  be  drawn  on  either  side  from  the  anterior  j^alatine  canal  in  front,  through  the  stylo- 
mastoid foramina  posteriorly,  it  will  be  found  to  cut  or  p)ass  near  to  the  following  objects  : — On 
the  hard  j^alate  it  will  lie  close  to  the  posterior  and  accessory  palatine  canals.  It  will  then  pass 
between  the  hanuilar  process  and  the  external  pterygoid  jjlate  overlying  the  foramen  ovale,  the 
foramen  sijinosum,  the  opening  of  the  osseous  Eustachian  canal  and  the  sjsine  of  the  sj^henoid  ; 
behind  this  it  will  cut  through  the  root  of  the  styloid  process  and  define  externally  the  limits  of 
the  jugular  fossa.  After  passing  through  the  stylo-mastoid  foramen,  if  the  line  be  prolonged 
backwards  it  will  usually  be  found  to  jjass  over  the  mastoid  foramen  in  the  occipito-mastoid 
suture.  Another  line  of  nuich  value  is  one  drawn  across  the  base  of  the  skull  from  the  centre 
of  one  external  auditory  meatus  to  the  other.  This  will  be  found  to  j^ass  through  the  root  of 
the  styloid  process,  the  jugular  foramen,  the  anterior  condylic  foramen  ;  it  then  crosses  the  front 
of  the  occipital  condyles,  and  corresponds  with  the  anterior  edge  of  the  foramen  magnum. 

A  line  which  may  be  found  useful  is  one  drawn  from  the  stylo-mastoid  foramen  of  one  side  to 
the  posterior  palatine  canal  of  the  opposite  side.  This  will  be  seen  to  oveilie,  from  behind 
forwards,  the  outer  part  of  the  jugular  foramen  and  the  inferior  opening  of  the  carotid  canal. 
The  line  indicates  the  direction  of  the  carotid  canal,  and  cuts  the  foramen  lacerum  medium 
anteriorly  ;  in  front  of  this  it  usually  corresponds  to  the  position  of  the  j^ostericjr  aperture  of  the 
pterygo-palatine  canal. 

The  examination  of  the  base  of  the  skull  is  incomplete  unless  the  student  examines 
it  with  the  lower  jaw  and  atlas  vertebra  in  position.  The  relation  of  the  ramus  of 
the  lower  jaw  to  the  zygomatic  fossa  has  been  already  sufticiently  studied  (p.  157) ; 


THE  SKULL  IN  SECTION.  167 

one  or  two  points,  however,  may  be  emphasised.  The  alar  spine  of  the  sphenoid 
lies  just  internal  to  the  condyle  of  the  jaw  when  that  structure  is  in  position  in  the 
articular  part  of  the  glenoid  fossa,  and  it  is  noteworthy  that  immediately  to  the 
inner  side  of  the  alar  spine  is  the  commencement  of  the  osseous  Eustachian  tube. 
The  root  of  the  styloid  process  occupies  the  centre  of  the  interval  Letween  the 
mandibular  ramus  and  the  front  of  the  mastoid  process. 

Anteriorly  the  arcade  formed  by  the  body  of  the  lower  jaw  adds  greatly  to  the 
depth  of  the  hard  palate.  In  this  space  are  lodged  the  tongue  and  the  structures 
which  form  the  floor  of  the  mouth.  The  inner  surface  of  each  side  of  the  body  of 
the  mandible  is  traversed  by  the  internal  oblique  line  (linea  mylo-hyoidea),  which 
commences  posteriorly  just  behind  the  root  of  the  last  molar  tooth  and  runs  down- 
wards and  forwards  towards  the  symphysis  in  front. 

When  the  atlas  vertebra  is  in  articulation  with  the  occipital  bone  it  is  well  to 
recognise  the  relation  of  its  transverse  processes  to  the  surrounding  structures.  The 
extremities  of  these  processes  lie  in  line  with  the  ends  of  the  jugular  processes  of 
the  occipital  bone,  and  thus  come  to  be  placed  just  internal  to  and  immediately  below 
and  slightly  in  front  of  the  tips  of  the  mastoid  processes.  They  can  thus  be  easily  felt 
in  the  living.  Anteriorly  they  are  separated  by  a  short  interval  from  the  styloid 
processes,  and  the  stylo -mastoid  foramina  lie  immediately  in  front  and  slightly  to 
the  outer  side  of  their  extremities.  The  student  will  note  that  there  is  no  hole  in 
the  jugular  process  of  the  occipital  bone  corresponding  to  the  arterial  foramen  in 
the  transverse  process  of  the  atlas  through  which  the  vertebral  artery  passes.  The 
course  of  this  vessel  over  the  upper  surface  of  the  posterior  arch  behind  the 
superior  articular  processes  of  the  atlas  will  be  seen  to  coincide  with  the  posterior 
condylic  Ibssse  and  the  margins  of  the  foramen  magnum  immediately  internal 
thereto,  where  a  slight  grooving  of  the  edge  often  indicates  the  course  of  the  artery. 
In  front  the  anterior  tubercle  of  the  atlas  falls  in  line  with  the  pharyngeal  tubercle 
on  the  under  surface  of  the  basi-occipital,  and  the  student  must  not  overlook  the 
fact  that  the  anterior  surface  of  the  cervical  column  does  not  coincide  with  the 
anterior  margin  of  the  foramen  magnum,  but  lies  nearly  half  an  inch  in  front  of 
that,  in  a  coronal  plane  passing  immediately  in  front  of  the  external  auditory 
meatus.  Behind,  the  upper  surface  of  the  posterior  arch  of  the  atlas  overlaps  the 
hinder  margin  of  the  foramen  magnum,  and  it  is  by  the  apposition  of  these  two 
surfaces  that  extension  is  checked  at  the  occipito-atlantal  articulation. 

THE   SKULL   IN    SECTION. 

By  the  removal  of  the  skull-cap  the  interior  of  the  cranial  cavity  is  exposed. 
The  deep  surface  of  the  crauial  vault  is  grooved  mesially  for  the  superior  longitudinal 
sinus,  on  either  side  of  which  are  seen  numerous  depressions  for  the  lodgment  of 
Pacchionian  bodies.  On  holding  the  bone  up  to  the  light,  the  floor  of  these  little 
hollows  is  oftentimes  seen  to  be  very  thin.  A  short  distance  in  front  of  the 
lambda,  and  on  either  side  of  the  saggital  suture,  are  the  internal  openings  of  the 
parietal  foramina.  The  inner  tables  of  the  frontal  and  parietal  bones  are  grooved 
for  the  meningeal  arteries.  The  principal  branch  of  the  middle  meningeal  runs  more 
or  less  yjarallel  to  and  at  a  variable  distance  behind  the  line  of  the  coronal  suture. 
Along  the  bottom  of  thcise  grooves  small  foramina  may  be  seen  for  the  passage  of 
nutrient  arteries  to  the  bone,  and  the  floor  of  the  longitudinal  sinus  is  likewise 
pierced  by  small  apertures  for  the  transmission  of  veins. 

The  Upper  Surface  of  the  Base  of  the  Skull. 

Cranial  Fossae. — The  upper  surface  of  the  base  of  the  skull  is  divided  into 
three  i'ossic,  of  which  tlie  cerebrum  occupies  the  anterior  and  middle,  whilst  in  the 
posterior  is  lodged  tlie  cerebellum. 

'J'hc  anterior  fossa  is  deflned  posteriorly  by  the  sharp,  thin  edge  of  the  lesser 
wings  of  the  Hph(;noid,  which  curve  outwards  and  slightly  upwards  as  well  as  back- 
wards to  reacli  the  region  of  the  pterion  externally.  The  floor  is  formed  from  before 
backwards,  in  the  middle  line,  by  tin;  up])er  surface  of  the  ethmoid  iuid  the  ibre- 
part  of  the  body  of  the  sphenoid;  lat(;rally  it  is  constituted  by  the  orbital  plates 


168 


OSTEOLOGY. 


Fig.  122. 


23  2-2  21 

-Base  of  the  Skull  as  seen  from  Above. 


9. 
10. 
11. 
12. 
13. 
14. 
15. 
16. 
17. 
18. 
19. 
20. 
21. 
22. 
23. 


Frontal  bone. 

Slit  for  nasal  nerve. 

Anterior  ethmoidal  foramen. 

Posterior  ethmoidal  foramen. 

Optic  foramen. 

Foramen   for   internal    carotid  artery  formed  by 

anterior  and  middle  clinoid  process. 
Lesser  wing  of  sphenoid. 
Anterior  clinoid  process,  in  this  case  nnited  on  its 

inner  side  to  the  middle  clinoid  processes. 
Posterior  clinoid  process. 
Foramen  ovale. 

Groove  for  middle  meningeal  artery. 
Foramen  spinosum. 
Hiatus  Fallopii. 
Line  of  petro-sqnamosal  suture. 
Internal  auditory  meatus. 
Groove  for  superior  petrosal  sinus. 
Groove  for  sigmoid  part  of  lateral  sinus. 
Jugular  foramen. 
Anterior  condylic  foramen. 
Groove  for  lateral  sinus. 
Internal  occipital  protuberance. 
Eidge  for  attachment  of  falx  cerebri. 
Fossa  for  the  lodgment  ot  the  occipital  lobes  of 

cerebrum. 


28. 


Ridge  for  the  attachment  of  the  falx  cerebelli. 
Fossa   for   the   lodgment   of  the  left   cerebellar 

hemisphere. 
Foramen  magnum. 
Groove   for  the   sigmoid  sinus  turning   into   the 

jugular  foramen. 
Groove   for  the    inferior   petrosal   sinus  running 

along  the  line  of  suture  betvv^een  the  petrous 

temporal  and  the  basi-occipital. 
Depression  for  the  Gasserian  ganglion. 
Middle   cranial   fossa   for  lodgment  of  temporal 

lobe  of  cerebrum. 
Foramen  lacerum  medium. 
Carotid  groove. 
Dorsum  sellfe  of  sphenoid. 
Leads  into  foi-amen  rotundum. 
Pituitary  fossa. 
Olivary  eminence  of  sphenoid. 
Anterior  cranial  fossa  for  lodgment  of  frontal  lobes 

of  cerebrum. 
Cribriform  plate  of  ethmoid.   ' 
Crista  galli  of  ethmoid. 
Foramen  caecum. 
Crest  for  attachment  of  falx  cerebri. 


THE  UPPER  SURFACE  OF  THE  BASE  OF  THE  SKULL.         169 

of  the  frontal  and  the  lesser  wings  of  the  sphenoid.  On  these  tlie  under  surface 
of  the  frontal  lobes  of  the  cerebrum  rests.  In  front  the  fossa  is  divided  mesially 
by  the  frontal  crest,  to  which  the  falx  cerebri  is  attached.  This  is  confluent  below 
with  the  fore  part  of  the  crista  galli,  from  which,  however,  it  is  separated  by  the 
foramen  csecum,  which  usually  transmits  a  small  vein  from  the  nose.  On  either 
side  of  the  crista  galli  there  are  grooves  which  vary  considerably  in  depth  and 
width :  therein  are  lodged  the  olfactory  lobes.  The  floor  and  sides  of  the  groove 
are  pierced  by  numerous  foramina;  of  these  the  largest  number  transmit  the 
olfactory  nerves  to  the  nasal  fossse.  In  front  an  elongated  slit,  placed  on  either 
side  of  the  crista,  affords  a  passage  to  the  nose  for  the  internal  nasal  nerve  and  a 
small  branch  of  the  anterior  ethmoidal  artery  which  accompanies  it.  To  the  outer 
side  of  the  olfactory  groove  and  the  cribriform  plate,  the  anterior  fossee  communi- 
cate on  either  side  by  means  of  the  two  ethmoidal  foramina  with  the  cavities  of  the 
orbits.  The  anterior  foramen  transmits  the  internal  nasal  nerve  and  the  anterior 
ethmoidal  artery;  the  posterior  affords  passage  to  the  posterior  ethmoidal  artery 
and  the  small  spheno-ethmoidal  nerve  of  Luschka.  External  to  the  olfactory 
groove,  the  floor  of  the  fossa,  which  here  corresponds  to  the  roof  of  the  orbit,  is 
very  thin,  as  may  be  seen  by  holding  the  skull  up  to  the  light ;  it  is  convex  from 
side  to  side,  and  bears  the  impress  of  the  convolutions  of  the  under  surface  of  the 
frontal  lobes  of  the  cerebrum  which  rest  upon  it.  In  front  and  at  the  side  there 
are  a  number  of  vascular  grooves  for  the  branches  of  the  anterior  and  middle 
meningeal  arteries  respectively. 

The  middle  fossa,  which  in  form  may  be  compared  to  the  wings  of  a  bird 
united  by  the  body,  is  bounded  in  front  by  the  curved  thin  posterior  edge  of  the 
lesser  wings  of  the  sphenoid ;  posteriorly,  by  the  line  of  attachment  of  the  tentorium 
cerebelli,  extending  from  the  posterior  clinoid  process  along  the  superior  border  of 
the  petrous  portion  of  the  temporal  bone.  The  median  part  of  the  fossa,  which  is 
narrow,  corresponds  to  the  sella  turcica  and  the  olivary  eminence  of  the  sphenoid. 
It  is  limited  anteriorly  by  a  line  connecting  the  anterior  margins  of  the  two  optic 
foramina,  and  is  overhung  behind  by  the  dorsum  sellae.  In  this  area  are  lodged 
the  structures  which  lie  within  the  interpeduncular  space  on  the  base  of  the  brain. 
The  floor  of  the  lateral  parts  of  the  fossa  on  each  side  is  formed  by  the  great  wing 
of  the  sphenoid  in  front,  the  squamous  part  of  the  temporal  bone  to  the  outer  side, 
and  the  superior  surface  of  the  petrous  temporal  behind.  In  the  hollows  so  formed 
the  temporal  lobes  of  the  cerebrum  are  lodged.  On  either  side  of  the  oUvary 
eminence  are  seen  the  optic  foramina;  these  pass  into  the  orbital  cavities  and 
transmit  the  optic  nerves  and  ophthalmic  arteries.  Immediately  behind  these 
openings  the  anterior  and  middle  clinoid  processes  are  sometimes  united,  so  as  to 
enclose  a  foramen.  Through  this  the  internal  carotid  artery  passes  upwards. 
Leading  backwards  from  this,  along  the  side  of  the  body  of  the  sphenoid,  is  the 
carotid  groove,  which  turns  downwards  near  the  apex  of  the  petrous  temporal,  to 
become  continuous  with  the  carotid  canal,  which  here  opens  on  the  posterior  wall 
of  an  irregular  aperture,  placed  between  the  side  of  the  body  of  the  sphenoid  and 
the  summit  of  the  petrous  temporal,  called  the  foramen  lacerum  medium.  Through 
the  inner  angle  of  this  opening  the  carotid  artery  accompanied  by  its  plexus  of 
veins  and  sympathetic  nerves  passes  upwards.  Running  through  the  fibrous  tissue, 
which  in  life  blocks  up  this  opening,  the  large  superficial  petrosal  nerve  coming 
from  the  hiatus  Fallopii  passes  downwards  and  forwards  to  reach  the  posterior 
orifice  of  the  Vidian  canal,  which  is  placed  on  the  anterior  and  inferior  border  of 
the  foramen  lacerum  medium.  A  small  menino-eal  branch  of  the  ascending 
j)haryngeal  artery  also  passes  upwards  through  this  foramen.  In  front  and  to  the 
outer  side  of  the  foramen  lacerum,  and  separated  from  it  by  a  narrow  bar  of  Ijone, 
is  the  foramen  ovale ;  through  tliis  pass  both  roots  of  the  inferior  maxillary  nerve, 
the  small  meningeal  artery,  and  some  emissary  veins.  A  little  external  and 
posterior  to  this  is  the  foramen  spinosum  for  tlie  transmission  of  the  middle 
meningeal  vessels,  togetlier  with  a  recurrent  branch  from  the  inferior  maxillary 
nerve.  Leading  from  the  external  extremity  of  the  foramen  lacerum  there  is  a 
groove  which  passes  outwards,  backwards,  and  slightly  uy)ward8  on  the  superior 
Hurface  of  the  petrous  temporal  to  end  in  the  hiatus  Fallopii  (a  cleft  opening  into 


170  OSTEOLOGY. 

the  aquseductus  Fallopii),  which  gives  passage  to  the  large  superficial  petrosal  branch 
derived  froin  the  geniculate  ganglion  on  the  seventh  nerve,  together  with  the  small 
petrosal  branch  of  the  middle  meningeal  artery.  Just  external  to  the  hiatus  Fallopii 
there  is  another  small  foramen  for  the  transmission  of  the  lesser  superficial 
petrosal  nerve.  Overhung  by  the  posterior  border  of  the  lesser  wing  of  the  sphenoid 
is  the  sphenoidal  fissure,  the  cleft  which  separates  the  lesser  from  the  great 
sphenoidal  wings,  and  which  opens  anteriorly  into  the  hollow  of  the  orbit ;  through 
this  pass  the  third,  fourth,  ophthalmic  division  of  the  fifth,  and  sixth  nerves, 
together  with  the  ophthalmic  veins  as  well  as  the  sympathetic  filament  to  the 
lenticular  ganglion.  Just  below  its  inner  extremity  is  the  foramen  rotundum  for 
the  passage  of  the  superior  maxillary  nerve  to  the  spheno-maxillary  fossa.  Ijehind 
this,  and  between  it  and  the  foramen  ovale,  the  foramen  Vesalii  may  occasionally 
be  seea,  through  which  a  vein  passes  to  reach  the  pterygoid  plexus. 

The  lateral  parts  of  the  middle  fossa  are  moulded  in  conformity  with  the 
convolutions  of  the  temporal  lobes,  but  towards  their  inner  sides  the  splitting  of 
the  dura  mater  in  the  region  of  the  cavernous  sinus  serves  to  separate  the  cranial 
base  from  the  under  surface  of  the  cerebrum.  As  may  be  seen  by  transmitted  light, 
the  floor  of  the  lateral  parts  of  the  fossa  is  thin  as  it  overlies  the  temporal, 
zygomatic,  and  glenoid  fossae.  The  grooves  for  the  lodgment  of  the  branches  of  the 
middle  meningeal  artery  leading  from  the  foramen  spinosum  are  readily  seen ;  one, 
coursing  backwards  a  little  below  the  line  of  the  squamoso-parietal  suture,  is 
specially  well  marked.  Amongst  other  features  may  be  noticed  the  depression  for 
the  lodgment  of  the  Gasserian  ganglion  overlying  the  summit  of  the  petrous 
temporal ;  behind  and  to  the  outer  side  of  the  hiatus  Fallopii,  the  arcuate 
eminence,  indicating  the  position  of  the  superior  semicircular  canal ;  and  immediately 
anterior  and  slightly  to  the  outer  side  of  this  the  tegmen  tympani,  which  roofs  in 
the  cavity  of  the  tympanum,  the  thinness  of  which  can  readily  be  demonstrated 
if  light  be  allowed  to  fall  through  the  external  auditory  meatus. 

The  posterior  fossa  is  larger  and  deeper  than  the  others.  In  front  it  is  limited 
by  a  line  on  either  side  leading  backwards  and  outwards  from  each  posterior  clinoid 
process  along  the  superior  border  of  the  petrous  part  of  the  temporal  bone,  where 
externally  and  posteriorly  it  becomes  confluent  with  the  superior  lip  of  the 
trans\erse  groove  for  the  lateral  sinus,  ending  posteriorly  in  the  middle  line  at 
the  internal  occipital  protuberance.  Along  the  line  thus  indicated  the  process  of 
dura  mater  called  the  tentorium  cerebelli,  which  roofs  in  the  posterior  fossa,  is 
attached.  The  floor  of  the  fossa,  in  which  the  cerebellar  lobes,  the  pons,  and 
medulla  are  lodged,  is  formed  by  the  petrous  and  mastoid  portions  of  the  temporal 
bone,  with  part  of  the  body  of  the  sphenoid  and  the  basilar  portion  of  the  occipital 
bone  wedged  in  between  them.  Above  the  mastoid  temporal  a  small  part  of  the 
posterior  inferior  angle  of  the  parietal  enters  into  the  constitution  of  the  outer 
wall  of  the  fossa.  Behind  and  within  these  the  lateral  parts  and  lower  portions  of 
the  squamous  occipital  complete  the  floor.  In  the  middle  line  the  floor  of  the  fossa 
is  pierced  by  the  foramen  magnum,  in  which  lies  the  lower  part  of  the  medulla,, 
together  with  its  membranes,  and  through  which  pass  upwards  the  vertebral 
arteries  and  the  spinal  accessory  nerves.  On  either  side  of  the  foramen  magnum, 
and  a  little  in  front  of  a  transverse  line  passing  through  its  centre,  is  the  opening 
of  the  anterior  condylic  foramen  for  the  passage  of  the  hypoglossal  nerve,  a  small 
meningeal  branch  from  the  ascending  pharyngeal  artery  and  an  emissary  vein. 
Overhanging  the  opening  of  the  anterior  condylic  foramen  there  is  a  thickened 
rounded  bridge  of  bone,  to  the  outer  side  of  which  is  placed  the  irregular  opening  of 
the  jugular  foramen  (foramen  lacerum  posterius).  The  size  of  this  is  apt  to  vary  on 
the  two  sides,  and  the  lumen  is  frecjuently  suljdivided  l^y  a  spicule  of  bone  which 
runs  across  it ;  the  posterior  and  external  rounded  part  of  the  foramen  is  occupied 
by  the  lateral  sinus,  which  here  joins  the  internal  jugular  vein.  A  meningeal 
branch  from  the  ascending  pharyngeal  or  occipital  artery  also  enters  the  skull 
through  this  compartment.  The  fore  and  internal  part  of  the  foranien  is  confluent 
with  the  groove  for  the  inferior  petrosal  sinus,  which  turns  downwards  in  front  of 
the  spicule  above  referred  to.  The  interval  between  the  portions  of  the  foramen 
occupied  by  the  two  veins  allow^s  the  transmission  of  the  glosso-pharyngeal,  vagus,. 


MESIAL  SAGITTAL  SECTION  OF  THE  SKULL/  171 

and  spinal  accessory  nerves  in  order  from  before  backwards.  About  a  quarter  of 
an  inch  above  and  to  the  outer  side  of  the  fore  part  of  the  foramen  jugulare  the 
posterior  surface  of  the  petrous  portion  of  the  temporal  bone  is  pierced  by  the 
internal  auditory  meatus,  through  which  the  facial  and  auditory  nerves,  together 
with  the  pars  intermedia  of  Wrisberg,  and  the  auditory  branch  of  the  basilar  artery 
leave  the  cranial  cavity.  Behind  the  jugular  foramen  and  close  to  the  margin  of 
the  foramen  magnum  the  opening  of  the  posterior  condylic  foramen,  when  pre- 
sent, may  be  seen.  This  gives  passage  to  a  vein  which  joins  the  vertebral  vein 
inferiorly.  The  internal  aperture  of  the  mastoid  foramen  is  noticed  opening  into 
the  groove  for  the  lateral  sinus,  a  little  below  the  level  of  the  superior  border  of  the 
petrous  temporal.  Through  it  passes  an  emissary  vein  which  joins  the  occipital 
vein  externally ;  the  mastoid  branch  of  the  occipital  artery  also  enters  the  cranial 
cavity  through  this  foramen. 

The  posterior  fossa  is  divided  into  two  halves  posteriorly  by  the  internal  occipital 
crest,  to  which  the  falx  cerebelli  is  attached,  the  floors  of  the  hollows  on  either  side 
of  which  are  often  exceedingly  thin  and  are  for  the  lodgment  of  the  lateral  lobes  of 
the  cerebellum.  The  grooves  for  the  following  blood  sinuses  are  usually  distinct — 
the  superior  petrosal  running  along  the  superior  border  of  the  petrous  temporal, 
the  inferior  petrosal  lying  along  the  line  of  suture  between  the  petrous  temporal 
and  basilar  process  of  the  occipital  bone ;  the  occipital  sinus  grooving  the  internal 
occipital  crest ;  and  the  lateral  sinus  curving  forwards  and  outwards  from  the 
internal  occipital  protuberance,  across  the  internal  surface  of  the  squamous 
occipital,  to  reach  the  posterior  inferior  angle  of  the  parietal  bone,  in  front  of  which 
it  turns  downwards  and  inwards  to  reach  the  jugular  foramen,  describing  a  sigmoid 
curve,  and  grooving  deeply  the  inner  surface  of  the  mastoid  and  posterior  aspect  of 
the  petrous  portions  of  the  temporal  bone.  Before  it  terminates  at  the  jugular 
foramen  it  again  reaches  the  occipital  bone  and  channels  the  upper  surface  of  the 
jugular  process  of  that  bone.  Slight  grooves  for  meningeal  arteries  are  also  seen — 
some  pass  upwards,  whilst  others  turn  downwards  and  are  occupied  by  branches 
from  the  posterior  offsets  of  the  middle  meningeal  arteries. 

Mesial  Sagittal  Section  of  the  Skull. 

Such  a  section  should  be  made  a  little  to  one  or  other  side  of  the  mesial  plane, 
so  as  to  pass  through  the  nasal  fossae  lateral  to  the  septum ;  one-half  will  then 
display  the  nasal  septum  in  position,  whilst  in  the  other  the  outer  wall  of  the 
nasal  fossa  of  that  side  will  be  exposed. 

The  form  of  the  cranial  cavity  is,  of  course,  subject  to  many  variations  dependent 
on  individual  and  racial  peculiarities.  The  following  details  are,  however,  worthy 
of  note.  The  hinder  border  of  the  foramen  magnum  (opisthion),  and  consequently 
the  floor  of  the  posterior  cranial  fossa,  occupies  the  same  horizontal  plane  as  the 
hard  palate.  The  anterior  border  of  the  foramen  magnum  (basion)  lies  a  little 
higher,  so  that  the  plane  of  the  foramen  is,  in  the  higher  races  at  least,  oblique,  and 
is  directed  downwards  and  slightly  forwards.  From  the  basion  a  line  passing 
upwards  and  forwards  to  reach  the  suture  between  the  sphenoid  and  ethmoid 
passes  through  the  basi-cranial  axis  formed  by  the  basi-occipital,  the  basi-sphenoid, 
and  the  presphenoid.  The  basi-cranial  axis  is  wedge-shaped  on  section  posteriorly, 
whilst  anteriorly  it  is  of  considerable  width,  and  has  within  it  the  large  sphenoidal 
air  sinus,  its  upper  surface  leads  upwards  and  forwards  with  a  varying  degree  of 
obliquity  from  the  basion  to  the  overhanging  edge  of  the  dorsum  sellse,  in  front  of 
which  the  pituitary  fossa,  the  floor  of  which  is  quite  thin,  is  well  seen  in  the 
section. 

From  the  olivary  eminence  the  floor  of  the  anterior  fossa  follows  a  more  or  less 
horizontal  direction,  corresponding  pretty  closely  to  the  level  of  the  axis  of  the  orbital 
cavity.  The  roof  of  the  orbit  is  seen  to  bulge  upwards  to  a  considerable  extent  into  the 
floor  of  the  anterior  fossa  ;  whilst  the  floor  of  the  middle  fossa  sinks  to  a  level  corresponding 
to  that  of  the  under  surface  of  the  basi-cranial  axis,  where  it  forms  the  roof  of  the  posterior 
narcH.  'I'he  maximum  length  of  the  skull  is  measured  from  the  glabella  (a  point  between 
the   superciliary   ridges)   to   the  occipital    point  posteriorly.      It  is  noteworthy  that   the 


172 


OSTEOLOGY. 


maximum  occipital  point  does  not  necessarily  correspond  to  the  external  occipital  pro- 
tuberance (inion).  The  greatest  vertical  height  usually  corresponds  to  the  distance  from 
the  basion  to  the  bregma  (point  of  union  of  the  sagittal  with  the  coronal  suture),  though 
to  this  rule  there  are  many  exceptions.     On  looking  into  the  posterior  fossa  the  anterior 


1. 
2. 
3. 

4. 

5. 

6. 

7. 

8. 

9. 
10. 
11. 
12. 
13. 
14. 
15. 
16. 
17. 
18. 
19. 
20. 
21. 
22. 
23. 


42   41   40  39  38  37  36   35  34  33  32  31  30  29  28   27  26  25   24    23        22       21 

Fig.   123. — Inner  Aspect  of  Left  Half  op  Skull  sagittallt  divided. 


Suture  between  parietal  and  temporal  bones.  24. 

Keniains  of  the  subarcuate  fossa.  25. 
Grooves  for  branches    of  the  middle   meningeal       26. 

artery.  27. 

Dorsum  sellee.  28. 

Pituitary  fossa.  29. 
Anterior  clinoid  fossa. 

Optic  foramen.  30. 

Sphenoidal  sinus.  31. 

Nasal  surface  of  superior  turbinated  bone.  32. 

Cribriform  plate  of  ethmoid.  33. 
Nasal  surface  of  middle  turbinated  bone. 

Frontal  sinus.  34. 

Nasal  spine  of  frontal.  35. 

Nasal  bone.  36. 

Nasal  process  of  superior  maxilla.  87. 
Middle  meatus  of  nose. 

Directed  towards  opening  of  antrum.  38. 

Nasal  surface  of  inferior  turbinated  bone,  39. 

Inferior  meatus  of  nose.  40. 
Anterior  nasal  spine. 

Anterior  palatine  canal.  41. 

Palatal  process  of  superior  maxilla.  42. 
Palatal  process  of  palate  bone. 


Posterior  nasal  spine. 

Hamular  process  of  internal  pterygoid  plate. 

External  pterygoid  plate. 

Superior  meatus  of  nose. 

Spheno-palatine  foramen. 

Pterygo  -  spinous     ligament     almost     completely 

ossified  to  enclose  a  foramen. 
Styloid  process  of  temporal  bone. 
Alar  spine  of  sphenoid. 
Mastoid  process. 
Basion  (mid-point  of  anterior  border  of  foramen 

magnum). 
Internal  auditory  meatus. 
Anterior  condylic  foramen. 
Leading  into  jugular  foramen. 
Opisthion    (mid-point    of    posterior    border    of 

foiumen  magnum). 
Groove  for  sigmoid  sinus. 
Opening  of  mastoid  foramen. 
For    lateral  sinus  and  attachment   of   tentoriuni 

cerebelli. 
Fossa  for  lodgment  of  cerebellar  hemisphere. 
Internal  occipital  protuberance. 


condylic  and  jugular  foramina  and  the  internal  auditory  meatus  are  seen  in  line,  sloping 
from  below  upwards.  The  internal  auditory  meatus  lies  in  a  vertical  plane,  passing 
through  the  basion.  The  grooves  for  the  middle  meningeal  artery  and  its  branches  are 
very  obvious.  The  anterior  groove  curves  forwards  and  outwards,  and  reaching  the  inner 
surface  of  the  pterion,  passes  towards  the  vertex  at  a  variable  distance  behind  and  more 
or  less  parallel  to  the  coronal  suture.     From  this  grooves  pass  forwards  across  the  suture 


THE  NASAL  SEPTUM.  173 

to  reacli  the  frontal  bone.  Another  groove  curves  upwards  and  backwards  a  little  below 
the  line  of  the  parieto-squamosal  suture.  From  this  an  upwardly-dii-ected  branch 
radiates  on  the  inner  surface  of  the  parietal  bone,  in  the  region  of  the  parietal  eminence 
whilst  a  lower  branch  passes  backwards  some  little  distance  above  the  lambdoid  sutui-e, 
and  gives  offsets  which  curve  downwards  and  inwards  over  the  inner  surface  of  the 
squamous  portion  of  the  occipital  bone. 

Nasal  Fossae. — In  the  section  through  the  nasal  fossa  the  structures  which  form 
its  outer  vkiU  can  now  be  studied.     These  are — the  nasal  bone ;  the  nasal  process  of 
the  superior  maxilla  ;  the  lachrymal  bone ;  the  lateral  mass  of  the  ethmoid,  compris- 
ing the  superior  and  middle  turbinated  bones  ;  the  vertical  plate  of  the  palate  bone  ; 
the  inferior  turbinated  bone  ;  and  the  mesial  surface  of  the  internal  pterygoid  plate. 
The  roof  as  seen  in  the  section  is  formed  by  the  nasal  and  frontal  bones,  the  cribri- 
form plate  of  the  ethmoid,  the  body  of  the  sphenoid  and  the  sphenoidal  turbinals, 
the  splienoidal  process  of  the  palate  and  the  ala  of  the  vomer.     The  Jioor,  which  is 
nearly  horizontal  from  before  backwards,  is  formed  by  the  palatal  processes  of  the 
superior  maxilla  and  palate  bones.     On  sagittal  section  the  nasal  fossa  appears 
somewhat  triangular  in  shape  with  the  angles  cut  off;  the  base  corresponds  to  the 
floor;    the  anterior  and  posterior  nares   to  the   truncated  anterior  and  posterior 
angles  respectively  ;  the  superior  angle  is  cut  off  by  the  cribriform  plate  ;  whilst  the 
sides  correspond   to   the  frontal  and  nasal  bones  anteriorly,  and  the  sphenoidal 
turbinals,  sphenoidal  process  of  the  palate,  and  the  ala  of  the  vomer  posteriorly. 
The  cavity  is  therefore  deep  towards  its  middle,  but  gradually  becomes  shallower  in 
front  and  behind  where  the  openings  of  the  nares  are  situated.     The  opening  of 
the  anterior  naris,  which  is  of  half-heart  shape,  is  larger  than  that  of  the  posterior 
naris,  and  is  directed  forwards  and  downwards;  the  opening  of  the  posterior  is 
of  rhomboidal  form,  and  slopes  backwards  and  downwards.     The  inferior  meatus  is 
the  channel  which  is  overhung  by  the  inferior  turbinated  bone,  and  its  floor  is 
formed  by  the  side- to-side  concavity  of   the  upper  surface  of  the  hard  palate. 
Opening  into  it  above,  under  cover  of  the  fore  part  of  the  inferior  turbinated  bone, 
is  the  canal  for  the  nasal  duct ;  whilst  its  floor  is  pierced  in  front  near  the  middle 
line  by  the  anterior  palatine  canal.     The  middle  meatus  is  the  hollow  between  the 
middle  and  inferior  turbinated  bones ;  it  slopes  from  above  downwards  and  back- 
wards, and  is  overhung  by  the  free  curved  edge  of  the  middle  turbinal,  beneath 
which  there  is  a  passage  called  the  infundibulum,  leading  upwards  and  forwards  to 
open  superiorly  into  the  frontal  sinus,  as  well  as  into  some  of  the  anterior  ethmoidal 
cells.     Under  cover  of  the  centre  of  the  middle  turbinated  bone  there  is  an  irregular 
opening   leading   into    the   maxillary    sinus    or    antrum    of   Highmore,  and    there 
are  frequently  independent  openings   for  the  middle   and  some  of  the  anterior 
ethmoidal  cells.     The  superior  meatus,  about  half  the  length  of  the  middle  meatus, 
is  placed  between  the  superior  and  middle  turbinated  bones  in  the  back  and  upper 
part  of  the  fossa ;  it  receives  the  openings  of  the  posterior  ethmoidal  cells.     Near 
its  posterior  extremity  the  spheno -palatine  foramen  pierces  its  outer  wall,  and  brings 
it  in  relation  with  the  spheno-maxillary  fossa.     The  sphenoidal  sinus  opens  on  the 
roof  of  the  nose,  above  the  level  of  the  superior  turbinated  bone,  into  a  depression 
called  the  spheno-ethmoidal  recess. 

Nasal  Septum. — If  the  opposite  half  of  the  section  in  which  the  osseous  nasal 
septum  is  retained  be  now  studied,  it  will  be  seen  to  be  formed  by  the  crests  of  the 
superior  maxillary  and  palate  bones  below,  on  which  rests  the  vomer,  the  posterior 
border  of  which  being  free,  forms  the  posterior  edge  of  the  nasal  septum,  which 
slopes  obliquely  upwards  and  backwards  towards  the  under  surface  of  the  body  of 
the  sphenoid.  Here  tlie  vomer  articulates  with  the  rostrum  of  the  sphenoid.  In 
front  of  this  the  vomer  articulates  with  the  perpendicular  plate  of  the  ethmoid, 
between  which  anteriorly  there  is  an  angular  recess  into  which  the  cartilaginous 
septum  fits.  Superiorly  and  anteriorly  the  osseous  septum  is  completed  by  the 
articulation  of  the  ])eri)endicu1ar  plate  of  the  ethmoid  with  the  nasal  process  of 
the  frontal,  togetlK;r  with  tlio  nasal  crest  formed  by  the  union  of  tlie  nasal  bones; 
whilst  posteriorly  and  su])orior]y  the;  perpendicular  plate  of  the  ethmoid  articulates 
with  tlie  iiKisial  ethjuoiclal  crest  of  the  sphenoid.  In  most  instances  the  osseous 
septum  is  not  perfectly  vertical,  })ut  is  deflected  towards  one  or  other  side. 


174 


OSTEOLOGY. 


1  iDiital   sinus 


Crista  galli  of  etliiuoid 


Perpenflicular, 
plate  of| 
ethuioiil 
Nasal  spine 
of  frontal 


Cribriform  plate  of  ethmoid 
Sphenoidal  sinus 


Pituitary  fossa 

Dorsum  sellte 
\^<*^  I    o(  sphenoid 


Alar  spine 
Vomer 
External  pterygoid  plate 

Hamular  process 


Anterior  palatine  foramen 

Pig.   124. — Nasal  Septum  as  seen  from  the  Left  Side. 


Air-sinuses  in  connexion  with  the  Nasal  Fossae. — Connected  with  the  nasal 
fossae  are   a   number  of  air-sinuses.     These  are  found  within  the  body  of  the 

sphenoid,  the  lateral  mass  of 
the  ethmoid,  the  orbital  pro- 
cess of  the  palate  bone,  the 
body  of  the  superior  maxilla, 
and  the  superciliary  arch  of 
the  frontal  bone. 

The  sphenoidal  sinus,  of 
varialjle  size,  occupies  the 
interior  of  the  body  of  the 
sphenoid.  In  some  cases  it 
extends  towards  the  roots  of 
the  pterygoid  processes.  In 
front  it  is  formed  in  part  by 
the  absorption  of  the  sphen- 
oidal spongy  bones,  and  is 
divided  up  into  two  cavities 
by  a  sagittally-placed  parti- 
tion, which,  however,  is  fre- 
quently displaced  to  one  or 
other  side.  It  opens  an- 
teriorly into  the  roof  of  the 
nose  in  the  region  of  the 
spheno-ethmoidal  recess. 

The  ethmoidal  sinuses  are 
placed  between  the  lateral 
aspects  of  the  upper  part  of 
the  nasal  fossse,  and  the 
cavities  of  the  orbit,  from  which  they  are  separated  by  thin  and  papery  walls. 
These  air  spaces  are  completed  by  the  articulation  of  the  ethmoid  with  the  superior 
maxilla,  lachrymal,  frontal  sphenoid,  and  palate  bones,  and  are  divided  into  three 
groups — an  anterior,  middle,  and  posterior.  The  latter  communicates  with  the 
superior  meatus ;  the  anterior  and  middle  open  either  independently  or  in  conjunc- 
tion with  the  infundibulum  into  the  middle  meatus. 

The  sinus  in  the  orbital  process  of  the  palate  bone  either  communicates  with 
the  sphenoidal  sinus,  or  else  assists  in  closing  in  some  of  the  posterior  ethmoidal 
cells.  Its  communication  with  the  nasal  fossa  is  through  one  or  other  of  these 
spaces. 

The  maxillary  sinus  or  antrum  of  Highmore  lies  to  the  outer  side  of  the  nasal 
fossee,  occupying  the  body  of  the  superior  maxilla.  Its  walls,  which  are  relatively 
thin,  are  directed  upwards  to  the  orbit,  forwards  to  the  face,  backwards  to  the 
zygomatic  and  spheno-maxillary  fossa,  and  inwards  to  the  nose.  In  the  latter 
situation  the  vertical  plate  of  the  palate  bone,  the  uncinate  process  of  the  ethmoid, 
the  maxillary  process  of  the  inferior  turbinated  bone,  and  a  small  part  of  the  lach- 
rymal bone  assist  in  the  formation  of  the  thin  osseous  partition  which  separates  it 
from  the  nasal  fossa.  The  floor  corresponds  to  the  alveolar  border  of  the  jaw,  and 
differs  from  the  other  walls  in  being  stout  and  thick ;  it  is,  however,  deeply  pitted 
inferiorly  by  the  alveoli  for  the  teeth.  The  antrum  opens  by  a  narrow  orifice  into 
the  middle  meatus. 

The  frontal  sinuses  lie,  one  on  either  side,  between  the  inner  and  outer  tables  of 
the  frontal  bone  over  the  root  of  the  nose,  and  extend  outwards  under  the  super- 
ciliary arches.  The  partition  which  separates  them  is  usually  central,  though  it 
may  be  deflected  to  one  or  other  side.  They  communicate  with  the  nose  through 
a  passage  called  the  infundibulum,  which  opens  inferiorly  into  the  fore-part  of  the 
middle  meatus. 

The  fact  should  not  be  overlooked  that  the  air  spaces  within  the  temporal 
bone,  viz.  the  tympanic  cavity  and  the  mastoid  air  cells,  are  brought  into  com- 
munication with  the  naso-pharynx  through  the  Eustachian  tubes.     Eor  further 


COEONAL  SECTIONS  OF  THE  CEANIUM. 


175 


details  regarding  the  air  sinuses  and  the  mode  of  their  growth,  consult  the  descrip- 
tion of  the  individual  bones. 

Coronal  Sections. 

The  relations  of  many  parts  of  the  cranium  are  well  displayed  in  a  series  of  coronal 
sections. 

By  sawing  off  a  thin  slice  from  the  front  of  the  lower  part  of  the  frontal  bone 
above,  and  carrying  the  section  downwards  through  the   inner  wall  of    the    orbit    and 


Fig.  125. — Paet  op  the  Frontal,  Nasal,  and  Superior  Maxillary  Bones  removed  in  order  to 

DISPLAY    THE    RELATION    OF    THE    VARIOUS    CaVITIES    EXPOSED. 


1.  Frontal  sinus. 

2.  Septum  of  frontal  sinus  deflected  towards  the  right. 

3.  Infundibulum  leading  from  sinus  to  middle  meatus. 

4.  Anterior  ethmoidal  air  sinuses. 

5.  Middle  turbinated  bone. 

6.  Red  line  in  upper  part  of  osseous  canal  for  nasal 

duct,  laid  open  throughout  its  entire  length  on 
the  right  side 


7.  Cavity  of  antrum  laid  open. 

8.  Middle  meatus  of  nose. 

9.  Inferior  meatus  of  nose. 

10.  Inferior  turbinated  bone. 

11.  Nasal  septum. 

12.  Canal  for  nasal    duct    laid  open  throughout  its 

entire  length. 

13.  Anterior  nasal  sj)ine. 


the  nasal  process  of  the  superior  maxilla,  into  the  anterior  nares  below,  a  number  of  im- 
portant relations  are  revealed  (see  Fig.  125).  In  the  frontal  region  the  extent  and 
arrangement  of  the  frontal  sinuses  are  displayed.  The  partition  between  the  two  sinuses, 
be  it  noted,  is  usually  complete  and  central  in  position,  though  it  may  occasionally  be 
perforated  or  oblique.  The  sinuses  are  hardly  ever  symmetrical,  the  right  being 
usually  the  srnullor  of  the  two.      (Logan  Turner,  Edin.  Med.  Jour.  ]89(S.) 

'I'ho  infundibulum  on  either  side,  leading  from  the  frontal  sitms  above  to  the  middle 
meatus  below,  is  seen  with  the  middle  turbinated  bone  internal  to  it,  and  the  anterior 
ethmoidal  cells  to  its  outer  side  above.  If  the  section  passes  through  the  canal  for  the 
nasal  duct  the  continuity  of  that  channel   leading  from  the  orbit  above  to  the  inferior 


176 


OSTEOLOGY. 


meatus  of  the  nose  below  is  clearly  shown.  Its  inner  wall  above,  by  which  it  is  separated 
from  the  cavity  of  the  nose,  is  formed  by  the  thin  lachrjnnal  bone ;  below,  it  passes  under 
cover  of  the  inferior  turbinated  bone  to  open  into  the  fore  part  of  the  inferior  meatus.     It 

is  separated  from  the  antrum 
externally  by  a  thin  lamina  of 
bone.  The  cavity  of  the  antrum 
is  seen  to  extend  upwards  and 
forwards  so  as  to  pass  over  the 
outer  side  as  well  as  slightly  in 
fi'ont  of  tlie  canal  for  the  nasal 
duct. 

The  lower  margins  of  the 
middle  turbinated  bones  lie 
pretty  nearly  on  a  level  with 
the  most  dei^endent  parts  of  the 
orbital  margins,  whilst  the  lower 
borders  of  the  inferior  turbinals 
are  placed  a  little  above  the 
lower  margin  of  the  anterior 
nares  on  a  level  with  the  lowest 
point  of  the  malo  -  maxillary 
suture. 

Such  a  section  will  reveal  any 
deflection  of  the  nasal  septum 
should  it  exist,  and  will  also  show 
that  but  a  narrow  cleft  separates 
the  upper  part  of  the  septum, 
on  either  side,  from  the  inner 
surface  of  the  superior  turbinals. 
The  next  section  (Fig.  126) 
passes  through  the  fore  part  of 
the  temjDoral  fossa  just  behind 
the  external  angular  prx)cess  of 
the  frontal  bone  above;  inferiorly 
it  passes  through  the  alveolar 
process  of  the  upper  jaw  in  the 
interval  between  the  first  and 
second  molar  teeth.  The  cranial, 
orbital,  nasal,  and  maxillary 
cavities  are  all  exposed,  together 
with  the  roof  of  the  mouth. 

The  anterior  cranial  fossa 
is  deepest  in  its  centre,  where  its 
floor  is  formed  b}^  the  cribriform 
plate  of  the  ethmoid ;  this  corre- 
sponds to  the  level  of  the  fronto- 
malar  suture  externally.  On 
either  side  the  floor  of  the  fossa 
bulges  upwards,  owing  to  the 
arching  of  the  roof  of  the  orbit. 
Of  the  orbital  walls,  the  external 
is  the  thickest  and  stoutest ;  the 
superior,  internal,  and  inferior 
walls,  which  separate  the  orbit 
from     the     cranial     cavity,     the 


1. 


22  21  20      lit 

riG.  126. — Coronal  Section  passing  inferiorly  through 
Interval  between  First  and  Second  Molar  Teeth. 


Groove    for    superioi' 
tiidiual  sinus. 

2.  Crest  for  attachment  of  falx 

cerebri. 

3.  Crista  galli  of  ethmoid. 

4.  Cribriform  plate  of  ethmoid. 

5.  Perpendicular  plate  of   eth- 

moid, assisting  in  the  forma- 
tion of  nasal  septum. 

6.  Lateral  mass  of  ethmoid  con- 

sisting of  the  ethmoidal  cells. 

7.  Os  planum  of  ethmoid. 

8.  Middle  meatus  of  nose. 

9.  Middle  turbinated  bone. 
0.   Opening  from  middle  meatus 

into  antrum. 
Orbital     plate     of     superior 
maxilla. 


12.  Fronto-nialar  suture. 

13.  Infraorbital  groove. 

14.  Antrum  or  maxillary  sinus. 

15.  Canal  for  the  anterior  dental 

nerve  and  vessels  exposed. 
Inferior  turbinated  bone. 
Inferior  meatiis  of  nose. 
Alveolar  process  of  superior 

maxilla. 
Groove  for  anterior  palatine 

nerve  and  vessels. 
Palatal    process    of   superior 

maxilla. 
Maxillary  crest  forming  part 

of  nasal  septum, 


16. 
17. 

IS. 

19. 
20. 
21. 


ethmoidal  cells,  and  the  antrum, 

22.  Vomer  forming  part  of  nasal    respectively,   are  all  thin.      The 

11.    Orbital     plate     of     superior  septum.  ^^^.^^    ^^     ^^^^    maxillary    SinUS 

lying  to  the  outer  side  of  the  nasal 
fossae  is  well  seen.  Its  roof,  which  separates  it  from  the  orbital  cavity,  is  thin  and 
traversed  by  the  infraorbital  canal.  Its  inner  wall,  wath  which  the  inferior  turbinal 
articulates,  is  very  slender,  and  forms  the  outer  w^alls  of  both  the  middle  and  inferior 
meatuses  of    the  nose.       Its  outer  wall    is  stouter  where    it  arches   up   to   bracket    the 


DIFFEEENCES  DUE  TO  AGE.  177 

zygomatic  or  malar  process.  Its  floor,  which  rests  upon  the  upper  surface  of  the 
alveolar  border  of  the  upi)er  jaw,  sinks  below  the  level  of  the  hard  palate.  The  fangs  of 
the  teeth  sometimes  project  into  the  floor  of  the  cavity. 

The  nasal  fossse  are  narrow  above,  where  they  lie  between  the  orbital  cavities,  from 
which  they  are  separated  by  the  cells  within  the  lateral  mass  of  the  ethmoid.  The  roof 
which  corresponds  to  the  cribriform  plate  is  narrow,  and  lies  between  the  septum  mesially 
and  the  lateral  masses  on  either  side. 

At  the  level  of  the  orbital  floor  the  nasal  fossee  expand  laterally,  the  middle  meatus 
running  longitudinally  in  the  angle  formed  by  the  lateral  mass  of  the  ethmoid  with  the 
body  of  the  superior  maxilla,  overhung  by  the  middle  turbinated  bone.  This  channel  is 
seen  to  have  the  ethmoidal  cells  superior  to  it,  the  orbital  cavity  above  and  to  the  outer 
side,  the  antrum  externally,  whilst  its  floor  is  formed  by  the  upper  surface  of  the  inferior 
turbinated  bone. 

The  inferior  meatus,  much  more  roomy,  runs  along  under  cover  of  the  inferior 
turbinated  bone.  Externally  it  is  related  to  the  antrum,  whilst  its  floor  is  formed  by  the 
concave  superior  surface  of  the  hard  palate. 

The  hard  palate  is  arched  below,  whilst  its  superior  surface  is  concave  upwards  on 
either  side  of  the  median  crest  which  supports  the  nasal  septum.  The  sides  of  the  arch 
below  correspond  to  the  inner  sui^faces  of  the  alveolar  processes  and  fall  in  line  with  the 
outer  walls  of  the  nasal  fossae  supei'iorly.  The  sixmmit  of  the  arch  lies  a  quarter  of  an  inch 
above  the  level  of  the  floor  of  the  antrum. 


SEXUAL  DIFFERENCES  IN  THE  SKULL. 

Whilst  it  is  a  matter  of  difficulty,  in  all  cases,  to  determine  with  certainty  the  sex  of 
a  skull,  the  following  points  of  difi^erence  are  usually  fairly  characteristic.  The  female  skull 
is,  as  a  rule,  smaller  than  the  male.  In  point  of  cranial  capacity  it  averages  about  a  tenth 
less  than  the  male  of  corresponding  race.  It  is  lighter,  smoother  as  regards  the  develop- 
ment of  its  muscular  ridges,  and  possesses  less  prominent  mastoid  processes.  In  the  frontal 
region,  the  superciliary  ridges  are  less  pronounced,  and  this  imparts  a  thinness  and  sharp- 
ness to  the  upper  orbital  margin,  which  is  fairly  characteristic,  and  can  best  be  appre- 
ciated by  running  the  finger  along  that  edge  of  bone.  For  the  same  reason,  the  forehead 
appears  more  vertical  and  the  projections  of  the  frontal  eminences  more  outstanding,  though 
it  is  stated  that  the  frontal  and  occipital  regions  are  less  capacious  proportionately  than  in 
the  male.  The  vertex  in  the  female  is  said  to  be  more  flattened,  and  the  height  of  the  skull 
consequently  somewhat  reduced.  In  man  the  edge  of  the  tympanic  plate  is  generally 
sharp,  and  divides  to  form  the  sheath  of  the  styloid  process,  whilst  in  the  female  the 
corresponding  border  is  described  as  being  rounder  and  more  tubercular. 

Whilst  it  is  true  that  no  one  of  these  differences  is  sufficiently  characteristic  to  enable 
VIS  to  pronounce  with  certainty  on  the  matter  of  sex,  it  is  the  case  that,  taken  together, 
they  usually  justify  us  in  arriving  at  a  conclusion  which,  as  a  rule,  may  be  regarded  as 
fairl}^  accurate.  In  some  instances,  however,  it  is  impossible  to  express  any  definite 
opinion. 

DIFFERENCES  DUE  TO  AGE. 

At  birth  the  face  is  proportionately  small  as  compared  with  the  cranium,  constituting 
about  one-eighth  of  the  bulk  of  the  latter.  In  the  adult  the  face  equals  at  least  half  the 
cranium.  About  the  age  of  puberty  the  development  and  expansion  of  some  of  the  air- 
sinuses,  more  particularly  the  frontal  sinus,  lead  to  characteristic  differences  in  head  and 
face  form. 

The  eruption  of  the  teeth  in  early  life  and  adolescence  enables  us  to  determine  the 
age  with  fair  accuracy.  After  the  completion  of  the  permanent  dentition,  the  wear  of  the 
teeth  may  assist  us  in  hazarding  an  approximate  statement.  The  condition  of  the  sutures, 
too,  may  guide  us,  synostosis  of  the  coronal  and  sagittal  sutures  not  as  a  rule  taking  place 
till  late  in  life.  (Jomplcte  obliteration  of  the  synchondrosis  between  the  occipital  bone 
and  splicnoid  may  be  regarded  as  an  indication  of  maturity.  In  old  age  the  skull 
usually  becomes  lighter  and  the  cranial  bones  thinner.  The  alveolar  borders  of  the 
superior  and  itifcrif)r  iiiaxillfc  become  absorbed  owing  to  the  loss  of  the  teeth.  This  gives 
rise  to  a  flattening  of  the  vault  of  the  hard  palate  and  an  alteration  in  the  form  of  the 
lower  jaw.  whereby  the  rnainlilmhir  angle  l>ecomes  more  obtuse. 

13 


178  OSTEOLOGY. 

CEANIOLOGY. 

The  various  groiq^s  of  mankind  display  in  their  physical  attributes  certain  features  which  are 
more  or  less  characteristic  of  the  stock  to  which  they  belong.  Craniology  deals  with  these 
differences  so  far  as  they  affect  the  skull.  The  method  whereby  these  differences  are  recorded 
involves  the  accurate  measurement  of  the  skull  in  most  of  its  details.  Such  procedure  is  included 
under  the  term  craniometry.  Here  only  the  outlines  of  the  subject  are  briefly  referred  to ; 
for  such  as  desire  fuller  information  on  tlie  subject,  the  works  of  Broca,  Topinard,  Flower,  and 
Turner  may  be  consulted. 

The  races  of  man  display  great  variations  in  regard  to  the  size  of  the  skull.  Apart  altogether 
from  individual  differences  and  the  proportion  of  head-size  to  body -height,  it  may  be  generally 
assumed  that  the  size  of  the  skull  in  the  more  highly  civilised  races  is  much  in  excess  of  that 
displayed  in  lower  tj-pes.  The  size  of  the  head  is  intimately  correlated  with  the  develop- 
ment of  the  brain.  By  measuring  the  capacity  of  that  part  of  the  skull  occupied  by  the 
encephalon,  we  are  enabled  to  form  some  estimate  of  the  size  of  the  brain.  The  cranial  capacity 
is  determined  by  filling  the  cranial  cavity  with  some  suitable  material  and  then  taking  the 
cubage  of  its  contents.  Various  methods  are  employed,  each  of  which  has  its  advantage.  The  use 
of  fluids,  which  of  course  would  be  the  most  accurate,  is  rendered  im^jracti cable,  without  special 
precautions,  owing  to  the  fact  that  the  macerated  skull  is  pierced  by  so  many  foramina.  As  a 
matter  of  j)ractice,  it  is  found  that  leaden  shot,  glass  beads,  or  seeds  of  various  sorts  are  the  most 
serviceable.  The  results  obtained  display  a  considerable  range  of  variation.  For  purposes  of 
classification  and  comparison,  skulls  are  grouped  according  to  their  cranial  capacity  into  the 
following  varieties : — 

Microcephalic  skulls  are  those  with  a  capacity  below  1350  c.c,  and  include  such  well-known 
races  as  Andamanese,  Veddahs,  Australians,  Bushmen,  Tasmanians,  etc. 

Mesoceplialic  skulls  range  from  1350  c.c.  to  1450  c.c,  and  embrace  examples  of  the  following 
varieties  :  American  Indians,  Chinese,  some  African  Negroes. 

Megacephalic  skulls  are  those  with  a  capacity  over  1450  cc,  and  are  most  commonly  met 
with  in  the  more  highly  civilised  races  :  Mixed  Europeans,  Japanese,  Eskimo,  etc. 

Apart  from  its  size,  the  form  of  the  cranium  has  been  regarded  as  an  important  factor  in  the 
classification  of  skulls ;  though  whether  these  differences  in  shape  have  not  been  unduly  em- 
phasised in  the  past  is  open  to  question. 

The  relation  of  the  breadth  to  the  length  of  the  skull  is  expressed  by  means  of  the  cephalic 
index  which  records  the  proportion  of  the  maximum  breadth  to  the  maximum  length  of  the 
skull,  assuming  the  latter  equal  100,  or — 

Max.  breadth  X  100     ~     ,    ,.    .    ■, 

^ — ^^f T Ti      =  Cephalic  index. 

Max.  length 

The  results  are  classified  into  three  groups  : — 

1.  Dolichocephalic,  with  an  index  below  75  :  Australians,  Kaffirs,  Zulus,  Eskimo,  Fijians. 

2.  Mesaticephalic,  ranging  from  75  to  80  :  Europeans  (mixed),  Chinese,  Polynesians  (mixed). 

3.  Brachycephalic,  with  an  index  over  80  :  Malays,  Burmese,  American  Indians,  Anda- 

manese. 

In  order  to  provide  for  uniformity  in  the  results  of  different  observers,  some  system  is  neces- 
sary by  which  the  various  jjoints  from  which  the  measurements  are  taken  must  correspond. 
AVhilst  there  is  much  difference  in  the  value  of  the  measurements  insisted  on  by  indiAddual 
anatomists,  all  agree  in  endeavouring  to  select  such  jDoints  on  the  skull  as  may  be  readily  deter- 
mined, and  which  have  a  fairly  fixed  anatomical  position.  The  more  important  of  these  "  fixed 
points  "  are  included  in  the  subjoined  table  : — 

Nasion. — The  middle  of  the  naso-frontal  suture. 

Glabella. — A  point  midway  between  the  two  superciliary  ridges. 

Ophryon. — The  central  jooint  of  the  narrowest  transverse  diameter  of  the  forehead,  measured 

from  one  temporal  line  to  the  other. 
Inion. — The  external  occipital  protuberance. 
Maximum  Occipital  Point. — The  point  on  the  occipital  squama  in  the  sagittal  plane  most 

distant  from  the  glal;)ella. 
Opisthion. — The  middle  of  the  j^osterior  margin  of  the  foramen  magnum. 
Basion. — The  middle  of  the  anterior  margin  of  the  foramen  magnum. 
Bregma. — The  point  of  junction  of  the  coronal  and  sagittal  sutures. 
Alveolar  Point. — The  centre  of  the  anterior  margin  of  the  ujiper  alveolar  margin. 
Subnasal  Point. — The  middle  of  the  inferior  border  of  the  anterior  nasal  aperture  at  the 

centre  of  the  nasal  spine. 
Vertex. — The  summit  of  the  cranial  vault, 

Obelion. — A  ^^oint  over  the  sagittal  suture,  on  a  line  with  the  parietal  foramina. 
Lambda. — The  meeting-point  of  the  sagittal  and  lambdoid  sutures. 
Pterion. — The  region  of  the  antero -lateral  fontanelle  whei-e  the  angles  of  the  frontal, 

parietal,  squamous  temporal,  and  alisphenoid  lie  in  relation  to  one  another.     As  a 


CRANIOLOGY.  179 

rule,  the  sutures  are  arranged  like  the  letter  H,  the  parietal  and  alisphenoid  separating 

the  frontal  from  the  squamous  temporal.     In  other  cases  the  form  of  the  suture  is  like 

an  X  ;  whilst  in  a  third  variety  the  frontal  and  squamous  temporal  articulate  with 

each  other,  thus  separating  the  alisphenoid  from  the  parietal. 
Asterion  is  the  region  of  the  postero-lateral  fontanelle  where  the  lambdoid,  parieto-mastoid, 

and  occipito-mastoid  sutures  meet. 
Stephanion. — The  point  where  the  coronal  suture  crosses  the  temporal  crest. 
Dacryon. — The  point  where  the  vertical  lachrymo-maxillary  suture  meets  the  fronto-nasal 

suture  at  the  inner  angle  of  the  orbit. 
Jugal  Point. — Corresponds  to  the  angle  between  the  vertical  border  and  the  margin  of  the 

zygomatic  process  of  the  malar  bone. 
Gonion. — The  outer  side  of  the  angle  of  the  inferior  maxilla. 

The  measurements  of  the  length  of  the  skull  may  be  taken  between  a  variety  of  points — the 
nasion,  glabella,  or  ophryon  in  front,  and  the  inion  or  maximum  occipital  point  behind.  Or  the 
maximum  length  alone  may  be  taken  without  reference  to  any  fixed  points.  In  all  cases  it  is 
better  to  state  precisely  where  the  measurement  is  taken.  The  maximum  breadth  of  the  head  is 
very  variable  as  regards  its  position ;  it  is  advisable  to  note  whether  it  occurs  above  or  below  the 
j)arieto-squamosal  suture.  The  inter-relation  of  these  measurements  as  expressed  by  the  cephalic 
index  has  been  already  referred  to.  The  width  of  the  head  may  also  be  measured  from  one  asterion 
to  the  other,  biasterionic  width,  or  by  taking  the  bistephanic  diameter. 

The  height  of  the  cranium  is  usually  ascertained  by  measuring  the  distance  from  the  basion 
to  the  bregma.  The  relation  of  the  height  to  the  length  may  be  expressed  by  the  height  or 
vertical  index,  thus — 

Height  X 100     ,^    ,.     ... 

— $ -, —  =  Vertical  index. 

Length 

Skulls  are  classified  in  accordance  with  the  relations  of  length  and  height  as  follows  : — 

Tapeinocephalic  index  below  72.  Chamaecephalic  index  up  to  70. 

Metriocephalic  index  between  72  and  77.  ,       Orthocephalic  index  from  70-1  to  75. 

Akrocephalic  index  above  77  (Turner).  Hypsicephalic  index  75'1  and  upwards 

(KoUmann,  Eanke,  and  Virchow). 

The  horizontal  circumference  of  the  cranium,  which  ranges  from  450  mm.  to  550  mm.,  is 
measured  around  a  plane  cutting  the  glabella  or  ophryon  anteriorly,  and  the  maximum  occipital 
point  i^osterioiiy.  The  longitudinal  arc  is  measured  from  the  nasion  in  front  to  the  opisthion 
behind ;  if  to  this  be  added  the  basi-nasal  length  and  the  distance  between  the  basion  and  the 
opisthion,  we  have  a  record  of  the  vertico-mesial  circumference  of  the  cranium.  This  may  further 
be  divided  by  measuring  the  lengths  of  the  frontal,  parietal,  and  occipital  jDortions  of  the 
superior  longitudinal  arc.  In  this  way  the  relative  proportions  of  these  bones  may  be 
expressed. 

The  measurements  of  the  skeleton  of  the  face  are  more  complex,  but,  on  the  whole,  of  greater 
value  than  the  measurements  of  the  cranium.  It  is  in  the  face  that  the  characteristic  features  of 
race  are  best  observed,  and  it  is  here  that  osseous  structure  most  accurately  records  the  form  and 
projjortions  of  the  living. 

The  form  of  the  face  varies  like  that  of  the  cranium  in  the  relative  proportions  of  its  length 
and  breadth.  Generally  speaking,  a  dolichocephalic  cranium  is  associated  with  a  long  face,  whilst 
the  brachycephalic  type  of  head  is  correlated  with  a  rounder  and  shorter  face.  This  rule,  how- 
ever, is  not  universal,  and  there  are  many  exceptions  to  it. 

The  determination  of  the  facial  index  varies  according  to  whether  the  measurements  are  made 
with  or  without  the  mandible  in  position.  In  the  former  case  the  length  is  measured  from  the 
ophryon  or  nasion  above  to  the  mental  tubercle  below,  and  compared  with  the  maximum 
bizygomatic  width.  This  is  referred  to  as  the  total  facial  index,  and  is  obtained  by  the 
formula — 

Ophryo-mentallengthxlOO^^^^^^  ^^^.^^  .^^^^ 

iiizygomatic  width 

More  usually,  however,  owing  to  the  loss  of  the  lower  jaw,  the  proportions  of  the  face  are 
expressed  by  the  superior  facial  index.  This  is  determined  by  comparing  the  ophryo-alveolar  or 
naso-alveolar  length  with  the  bizygomatic  width,  thus — 

Ophryo-alveolar  length  x  100     „        .      ~    .  ,  .    , 

— -1.       ^. ?,-r =  Superior  facial  index. 

Jiizygomatic  width 

The  terms  dolichofacial  or  leptoprosope  and  brachyfacial  or  chamoeprosope  have  been 
employed  to  express  the  differences  thus  recorded. 

Uniformity  in  tliese  measurements,  however,  is  far  from  complete  since  many  anthropologists 
compare  the  widtli  witli  the  lengtli  =  100. 

Tlie  jiiojiortiori  of  the  facc-vvidlli  to  tbe  width  of  the  calvaria  is  roughly  expressed  by  the  use  of 
the  t<;rms  cryptozygous  and  phaenozygous  as  applied  to  the  skull.  In  the  former  case  the 
zygomatic  arches  are  concealed,  when  the  .skull  is  viewed  from  above,  by  the  overhanging  and 
13  a 


180  OSTEOLOGY. 

projection  of  the  sides  of  the  cranial  box  ;  in  the  latter  instance,  owing  to  the  narrowness  of  the 

calvaria,  the  zygomatic  arches  are  clearly  visible. 

The  projection  of  the  face,  so  characteristic  of  certain  races  (Negroes  for  example),  may  be 

estimated  on  the  living  by  measuring  the  angle  formed  by  two  straight  lines,  the  one  passing  from 

the  middle  of  the  external  auditory  meatus  to  the  lower  margin  of  the  septum  of  the  nose  ;  the 

other  drawn  from  the  most  prominent  part  of  the  forehead  above  to  touch  the  incisor  teeth 

below.     The  angle  formed  by   the  intersection  of  these  two  lines  is  called  the  facial  angle 

(Camper),  and  ranges  from  62°  to  85°.     The  smaller  angle  is  characteristic  of  a  muzzle-like 

projection  of  tlie  lower  part  of  the  face.     The  larger  angle  is  the  concomitant  of  a  more  vertical 

profile.     The  degree  of  projection  of  the  upjier  jaw  in  the  macerated  cranium  is  most  commonly 

expressed  by  emj)loying  the  gnathic  or  alveolar  index  of  Flower.     This  records  the  relative 

proportions   of  the   basi-alveolar   and    basi-nasal  lengths,  the  latter   being  regarded   as  =  100, 

thus — 

Basi-alveolar  length  x  100     „,,..•, 
^ — ^ p     =  Gnathic  index. 

Uasi-nasal  length 

The  results  are  conveniently  grouped  into  three  classes  : — 

Orthognathous,  index  below  98  :  including  mixed  Europeans,  ancient  Egyptians,  etc. 
Mesognathous,  index  from  98  to  103  :  Chinese,  Japanese,  Eskimo,  Polynesians  (mixed). 
Prognathous,  index  aboA^e  103 :  Tasmanians,  Australians,  Melanesians,  various  African 

Negroes. 

Unfortunately,  however",  little  reliance  can  be  placed  on  the  results  obtained  by  this  method, 
since  it  takes  no  account  of  the  projiortion  of  the  third  or  facial  side  of  the  gnathic  triangle. 
For  a  further  discussion  of  this  matter  see  Thomson  and  Maclver,  Races  of  the  Thebaid  (Oxford  : 
Clarendon  Press,  1905). 

The  form  of  the  nasal  aperture  in  the  macerated  skull  is  of  much  value  from  an  ethnic 
standpoint,  as  it  is  so  intimately  associated  with  the  shape  of  the  nose  in  the  living.  The 
greatest  width  of  the  nasal  aperture  is  compared  with  the  nasal  height  (measured  from  the  nasion 
to  the  lower  border  of  the  nasal  aperture)  and  the  nasal  index  is  thus  determined  : — 

Nasal  width  x  100     „      ,  •    ■■ 
— ^r^^ — ^-T — ^^f- —  =  Nasal  index. 

ISlasal  height 

Skulls  are — 

Leptorhine,  with  a  nasal  index  below  48  :  as  in  mixed  Europeans,  ancient  Egyptians, 

American  Indians,  etc. 
Mesorhine,  with  an  index  ranging  from  48  to  53  :  as  in  Chinese,  Japanese,  Malays,  etc. 
Platyrhine,  with  an  index  above  53  :  as  in  Australians,  Negroes,  Kafi&rs,  Zulus,  etc. 

The  form  of  the  orbit  varies  considerably  in  different  races,  but  is  of  much  less  value  from  the 
standj)oint  of  classification.  The  orbital  index  expresses  the  proportion  of  the  orbital  height  to 
the  orbital  width,  and  is  obtained  by  the  following  formula  : — 

Orbital  height  x  100     «  t,-+  i  •   a 

— 7^; — ^— r- — ^ — •  1  ,^ ^  Uruitai  inctex. 

Orbital  width 

The  orbital  height  is  the  distance  between  the  upper  and  lower  margins  of  the  orbit  at  the 
middle ;  whilst  the  orbital  width  is  measured  from  a  point  where  the  ridge  which  forms  the 
posterior  boundary  of  the  lachrymal  groove  meets  the  fronto  -  lachrymal  suture  (Flower),  or 
from  the  dacrj^on  (Broca)  to  the  most  distant  point  from  these  on  the  anterior  edge  of  the  outer 
border  of  the  orljit. 

The  form  of  the  orbital  aperture  is  referred  to  as — 

Megaseme,  if  the  index  be  over  89  ; 
Mesoseme,  if  the  index  be  between  89  and  84 ; 
Microseme,  if  the  index  be  below  84. 

The  variations  met  with  in  the  form  of  the  palate  and  dentary  arcade  may  be  expressed  by 
the  palato-maxillary  index  of  Flower.  The  length  is  measured  from  the  alveolar  point  to  a 
line  drawn  across  the  hinder  borders  of  the  sujjerior  maxillary  bones,  whilst  the  width  is  taken 
between  the  outer  borders  of  the  alveolar  arch  immediately  above  the  middle  of  the  second 
molar  tooth.     To  obtain  the  index,  the  following  formula  is  employed  : — 

Palato-maxillary  width  x  100     _  ,   .  .„        .    , 

— =,^,  ^ —     .tT       ,       ^,       =  Palato-maxillary  index. 

Palato-maxillary  length 

For  purj)oses  of  classification  Turner  has  introduced  the  following  terms  : — 

Dolichuranic,  index  below  110. 
Mesuranic,  index  between  110  and  115. 
Brachyuranic,  index  above  115. 

As  is  elsewhere  stated  (p.  183),  the  size  of  the  teeth  has  an  important  influence  on  the 
aKihitecture  of  the  skull.     Considered  from  a  racial  standpoint,  the  relative  size  of  the  teeth  to 


DEVELOPMENT  OF  THE  CHONDEO-ORANIUM.  181 

the  length  of  the  cranio-facial  axis  has  been  found  hy  Flower  to  be  a  character  of  much  value. 
The  dental  length  is  taken  by  measuring  the  distance  betweeii  the  anterior  surface  of  the  first  pre- 
molar and  the  posterior  surface  of  tlie  third  molar  of  the  upper  jaw. 
To  obtain  the  dental  index  the  following  formula  is  used  : — 

Dental  length  x  100     ^     .  ,  •    ■, 
-  =R — ; ri n —  =  Dental  index. 

Easi-nasal  length 

Following  the  convenient  method  of  division  adopted  with  other  indices,  the  dental  indices 
may  be  divided  into  three  series,  called  respectively — 

Microdont,  index  below  42  :  including  the  so-called  Caucasian  or  white  races. 
Mesodont,  index  between  42  and  44  :  including  the  Mongolian  or  yellow  races. 
Megadont,  index  above  44  :  comprising  the  black  races,  including  the  Australians. 

Many  complicated  instruments  have  been  devised  to  take  the  various  measurements  required, 
but  for  all  jsractical  purposes  the  calipers  designed  by  Flower  or  the  comjxis  glissih-e  of  Broca  are 
sufficient. 

As  an  aid  to  calculating  the  indices,  the  tables  published  in  the  Osteological  Catalogue  of  the 
Royal  College  of  Surgeons  of  England,  Part  I.,  Man.;  Index- Tahellen  zum  Anthropometrisclien 
Gebrauche,  C.  M.  Furst,  Jena,  1902  ;  or  the  index  calculator  invented  by  Dr.  Waterston  will  be 
found  of  much  service  in  saving  time. 

DEVELOPMENT  OF  THE  CHONDRO-CRANIUM  AND  MORPHOLOGY 

OF  THE  SKULL. 

As  has  been  already  stated  (p.  24),  the  chorda  dorsalis  extends  forwards  to  a  point 
immediately  beneath  the  anterior  end  of  the  mid-brain.  Li  front  of  this  the  head  takes 
a  bend  so  that  the  large  fore-brain  overlaps  the  anterior  extremity  of  the  notochord.  At 
this  stage  of  development  the  cerebral  vesicles  are  enclosed  in  a  membranous  covering 
derived  from  the  mesenchyme  surrounding  the  notochord ;  this  differentiated  mesodermal 
layer  is  called  the  primordial  membranous  cranium.  From  it  the  meninges  which  invest 
the  brain  are  derived.  In  lower  vertebrates  this  membranous  capsule  becomes  converted 
into  a  thick -walled  cartilaginous  envelope,  the  primordial  cartilaginous  cranium.  In 
mammals,  however,  only  the  basal  part  of  this  capsule  becomes  chondrified,  the  roof  and 
part  of  the  sides  remaining  membranous.  In  considering  the  chondrification  of  the  skull 
in  mammals,  it  must  be  noted  that  part  only  of  the  base  is  traversed  by  the  notochord, 
viz.  that  portion  which  extends  from  the  foramen  magnum  to  the  dorsxim  sellse  of  the 
sphenoid.  It  is,  therefore,  conveniently  divided  into  two  parts — one  posterior,  surrounding 
the  notochord,  and  hence  called  chordal,  and  one  in  front,  into  which  the  notochord  does 
not  extend,  and  hence  termed  prechordal.  These  correspond  respectively  to  the  vertebral 
and  evertebral  regions  of  Gegenbauer.  In  the  chordal  region  a  pair  of  elongated  cartilages, 
called  the  parachordal  cartilages,  appear  one  on  either  side  of  the  notochord  ;  these  soon 
all  but  completely  envelop  the  chorda,  and  expand  so  as  to  form  the  basilar  or  occipital 
plate,  which  ossifies  later  to  form  the  basilar  process  of  the  occipital  bone,  and  the  dorsum 
sellee  of  the  sphenoid.  By  backward  extension  from  the  occipital  plate  on  either  side  and 
aromid  the  foramen  magnum  the  cartilaginous  ex-occipitals  and  supra-occipitals  are  also 
formed.  In  the  prechordal  region  two  curved  strips  of  cartilage,  the  trabeculse  cranii  of 
Rathke,  arise  and  pass  forwards  from  the  anterior  extremity  of  the  notochord,  one  on 
either  side  of  the  cranio -pharyngeal  canal.  In  front  these  trabeculse  spread  out  and 
ultimately  fuse  to  form  the  ethmoidal  plate,  which  constitutes  the  fore  part  of  the 
chondro-cranium.  Posteriorly  the  trabeculse  unite  with  the  basilar  plate  and  thus  surround 
the  cranio-pharyngeal  canal,  the  lumen  of  which  is  subsequently  closed  to  foi-m  the  floor 
of  the  pituitary  fossa,  in  which  rests  the  hypophysis  cerebri.  Owing  to  the  presence  of 
the  nasal  capsules,  the  foi-e-part  of  the  ethmoidal  plate  becomes  differentiated  into  an 
ethmo- vomerine  region,  from  which  the  nasal  septum  and  its  associated  cartilages  are 
derived,  whilst  the  remainder  of  the  ethmoidal  plate  by  expansion  and  subsequent  ossifica- 
tion develops  to  form  the  pre-sphenoid,  the  orbito-sphenoids,  and  the  ali-sphenoids,  which 
latter  assist  in  completing  the  orbital  cavity  for  the  lodgment  of  the  eyeball.  The 
membranous  ear  capsules  wliich  lie  lateral  to  the  parachordal  cartilages  become  chondrified 
and  form  the  cartilaginous  ear  capsules.  These  soon  unite  with  the  lateral  aspects  of 
the  basilar  plate,  but  are  separated  in  front  from  the  cartilaginous  alisphenoid  of  the 
ethmoidal  plate  by  a  inembranous  interval,  which  is  subsequently  occupied  by  the 
squamosal,  a  bone  of  dermic  origin.  This  disappearance  of  the  cartilage  under  the  squa- 
mosal was  regarded  by  Parker  as  the  diagnostic  mark  of  the  mammalian  chondro-cranium. 

From  the  ventral  surface  of  this  cartilaginous  platform — formed,  as  described,  by  the 
13  6 


182 


OSTEOLOGY. 


union  of  the  trabeculte,  parachordal  cartilages,  and  cartilaginous  ear  capsules — is  suspended 
the  cartilaginous  framework  of  the  visceral  arches,  which  play  so  important  a  part  in  the 
development  of  the  face,  an  account  of  which  is  elsewhere  given  (p.  36). 

A  consideration  of  the  facts  of  comparative  anatomy  and  embryology  appears  to  justifiy 
the  assumption  that  the  mammalian  skull  is  of  two -fold  origin  —  that,  in  fact,  it  is 
composed  of  two  envelopes,  an  outer  and  an  inner,  primarily  distinct,  but  which  in  the 
process  of  evolution  have  become  intimately  fused  together.  The  inner,  called  the 
primordial  skull,  is  that  which  has  just  been  described,  and  consists  of  the  chondro- 
cranium  and  the  branchial  skeleton.  The  outer,  which  is  of  dermic  origin,  includes  the 
bones  of  the  cranial  vault  and  face  which  are  developed  in  membrane.  This  secondary 
skull,  which  first  appears  in  higher  fishes  as  ossified  dermal  plates  overlying  the  primary 
skull,  acquires  a  great  importance  in  the  mammalia,  as  owing  to  the  expansion  of  the 


Pars  ethmoidali 


Orbito-.sx)henoi 


Sphenoidal  fissure r  j 

Alisplienoid 
Carotid  canal 


Meatus  auditoriu; 
internus 


Floccular  fossa 
Foramen  jugulars 


Canalis  hypoglossi 

Foramen  magnum 


Lamina  ciibrosa 


\  ^  Oibital  portion  of  orbito-sphenoid 


Optic-  foramen 

—  Olivary  process 


Sella  turcica 


^^    ---     T, 

y  ^-  T-' —  Dorsum  sella; 
Pars  petrosa 

111...,        ,^,,"  ' 

Superior  semicircular  canal 


Pars  niastoidea 


Occipital  fontauelle 


Fig.  127. — View  of  the  Chondro- Cranium  of  a  Human  Fcetus  5  cm.  in  length  from  Vertex  to 
Coccyx  (about  the  middle  of  tlie  third  inonth)  ;  the  cartilage  is  coloured  blue.  The  line  to  the  right 
of  the  drawing  shows  the  actual  size. 

brain  and  the  pi-ogressive  reduction  of  the  chondro-cranium,  these  dermal  bones  become 
engrafted  on  and  incorporated  with  the  primordial  skull,  and  act  as  covering  bones  to  the 
cavities  of  the  cranium  and  face;  for  it  may  be  well  to  point  out  that  these  dermal  or 
membrane  bones  are  not  necessarily  external  in  position,  as  over  the  cranial  vault,  but 
also  develop  in  the  tissues  underlying  the  mucous  membrane  of  the  cavities  of  the  face. 

Advantage  is  taken  of  this  difference  in  the  mode  of  development  of  the  bones  of  the 
skull  to  classify  them  according  to  their  origin  into  cartilage  or  primordial  bones,  and 
membrane  or  secondary  bones.  These  differences  in  the  growth  of  the  bone  must  not  be 
too  much  insisted  on  in  determining  the  homologies  of  the  bones  of  the  skull,  as  it  is  now 
generally  recognised  that  all  bone  is  of  membranous  origin,  and  that  whilst  in  some 
cases  cartilage  may  become  calcified,  it  never  undergoes  conversion  into  true  bone,  but  is 
replaced  by  ossific  deposit  derived  from  a  membranous  source.  In  the  subsequent  growth 
of  the  skull  parts  of  the  cartilaginous,  cranium  persist  as  the  septal  and  alar  cartilages  of 
the  nose,  whilst  for  a  considerable  period  the  basi-sphenoid  and  basi-occipital  are  still 
united  by  cai'tilage.  The  cartilage  also  which  blocks  the  foramen  lacerum  medium  may 
be  regarded  as  a  remnant  of  the  chondro-cranium. 

Till   two  years  after  birth   there  are  membranous  intervals  between  the  edges  and 


MORPHOLOGY  OF  THE  SKULL.  183 

angles  of  the  bones  of  the  cranial  vault.  These  are  termed  tlie  fontanelles.  Normally 
they  are  six  in  number,  and  correspond  in  the  adult  to  the  position  of  the  bregma  and 
lambda  in  the  middle  line  and  the  pterion  and  asterion  on  either  side.  The  anterior  or 
bregmatic  fontanelle  is  diamond-shaped,  and  corresponds  to  the  converging  angles  of  the 
parietals  and  two  halves  of  the  frontal  bone.  The  posterior  fontanelle  is  triangular  in 
form,  and  lies  between  the  two  parietals  and  the  summit  of  the  occipital  squama.  The 
antero-lateral  fontanelle  lies  between  the  contiguous  margins  of  the  frontal,  parietal, 
squamous  temporal,  and  great  wing  of  the  sphenoid,  whilst  the  poster o -lateral  fontanelle 
is  situated  between  the  adjacent  borders  of  the  parietal,  occipital,  and  mastoid  portion  of 
the  temporal.  The  term  occipital  fontanelle  is  applied  to  a  membranous  interval  which 
occurs  in  the  foetal  condition  posterior  to  the  foramen  magnum,  and  between  the  lateral 
halves  of  the  cartilaginous  supra- occipital.  Its  persistence  accounts  for  the  occasional 
occurrence  of  a  cerebral  meningocele. ^ 

Whilst  in  many  instances  the  primordial  and  secondary  bones  remain  distinct  in  the 
fully-developed  condition,  they  sometimes  fuse  to  form  complex  bones,  such  as  the  temporal 
and  sphenoid  (see  pp.  120  and  127). 

Various  theories  have  been  advanced  to  account  for  the  mode  of  formation  of  the 
skull.  The  earliest  of  these  was  called  the  vertebrate  theory,  which  assumed  that  the 
cranium  was  built  up  of  a  series  of  modified  vertebrae,  the  centra  of  which  corresponded  to 
the  basi-cranial  axis,  whilst  the  neural  arches  were  represented  by  the  covering  bones  of 
the  cranium.  In  view  of  the  more  recent  researches  regarding  the  composite  origin  of  the 
skull  above  referred  to,  this  theory  was  necessarily  abandoned.  It  gave  way  to  the 
suggestion  of  Gegenbauer  that  the  primordial  cranium  has  arisen  by  the  fusion  of  several 
segments  equivalent  to  vertebrae,  the  number  of  which  he  determined  by  noting  the 
metameric  arrangement  of  the  cranial  nerves,  of  which  he  concluded  there  were  nine  pairs, 
arranged  much  like  spinal  nerves,  both  as  to  their  origin  and  distribution.  The  olfactory 
and  optic  nerves,  though  frequently  referred  to  as  cranial  nerves,  are  excluded,  since  from 
the  nature  of  their  development  they  are  to  be  regarded  as  metamorphosed  parts  of  the 
brain  itself.  Gegenbauer  therefore  assumed  that  that  portion  of  the  cranial  base  which  is 
traversed  by  the  nine  pairs  of  segmentally  arranged  cranial  nerves  must  be  formed  by  the 
fusion  of  nine  vertebral  segments ;  and  as  the  region  where  the  nerves  escape  corresponds 
to  the  part  of  the  chondro-cranium  traversed  by  the  notochord,  he  calls  it  the  vertebral 
portion  of  the  cranial  base,  in  contradistinction  to  the  trabecular  or  non-vertebral  part 
which  lies  in  front.  This  latter  he  regards  as  a  new  formation  adapted  to  receive  the 
greatly-developed  brain  and  afford  protection  to  the  organs  of  sight  and  smell. 

As  has  been  pointed  out  by  Hertwig,  there  is  an  essential  difference  between  the 
development  of  the  axial  cartilaginous  skeleton  of  the  trunk  and  head.  The  former  becomes 
segmented  into  distinct  vertebrae  alternating  with  intervertebral  ligaments ;  whilst  the 
latter,  in  order  to  attain  the  rigidity  necessary  in  this  part  of  the  skeleton,  is  never  so 
divided.  It  follows  from  this  that  the  original  segmentation  of  the  head  is  only  expressed 
in  three  ways,  viz.  in  the  appearance  of  several  primitive  segments  (myotomes),  in  the 
arrangement  of  the  cranial  nerves,  and  in  the  fundament  of  the  visceral  skeleton  (visceral 
arches).  According  to  Froriep  the  mammalian  occipital  corresponds  to  the  fusion  of  four 
vertebrse,  and  there  is  some  reason  for  supposing  that  in  some  classes  of  vertebrates  the 
occipital  region  of  the  primordial  cranium  is  increased  by  fusion  with  the  higher  cervical 
segments. 

The  form  of  skull  characteristic  of  man  is  dependent  on  the  large  proportionate 
development  of  the  cranial  part,  which  contains  the  brain,  and  the  reduction  in  size  of  the 
visceral  part  (face),  which  protects  the  organs  of  special  sense.  This  leads  to  a  decrease 
in  the  mass  and  projection  of  the  jaws,  as  well  as  a  reduction  in  the  size  of  the  teeth. 
Associated  with  the  smaller  mandible  there  is  a  feebler  musculature,  with  a  reduced  area 
of  attachment  to  the  sides  of  the  skull.  In  this  way  the  disappearance  of  the  muscular 
crests  and  fossa3,  so  characteristic  of  lower  forms,  is  accounted  for.  At  the  same  time  the 
fact  that  the  skull  is  poised  on  the  summit  of  a  vertical  column,  leads  to  important 
modifications  in  its  structure.  The  disposition  of  parts  is  such  that  the  occipito-vertebral 
articulation  is  so  placed  that  the  fore  and  hind  parts  of  the  head  nearly  balance  each  other, 
thus  obviating  the  necessity  for  a  powerful  muscular  and  ligamentous  mechanism  to  hold 
the  head  erect. 

Another  noticeable  feature  in  connexion  with  man's  skeleton  is  the  prolonged  period 
during  which  growth  may  occur  before  maturity  is  reached  ;  this  is  associated  with  a  more 
complete  consolidation  of  the  skull,  since  bones,  which  in  lower  forms  remain  throughout 

'  For  furtlier  iiiforniatioii  regfinling  iuiomalous  conditions  of  the  fontanollos  ami  tlie  occurrence  of  Wormian 
or  sutural  osHicles,  Hce  V.  Frassetto,  Aim.  dns  ,Hi:i.  Nat.  ZdoI.  8"  sidv.  xviii.  190:3. 

Vi  c 


184  OSTEOLOGY. 

life  distinct,  are  in  man  fused  witli  each  other,  as  exemplified  in  the  case  of  the  presphenoid 
and  postsphenoid,  the  occipital  and  the  interparietal,  to  mention  one  or  two  instances 
among  many.  It  is  noteworthy,  however,  that  during  ontogeny  the  morphological  signifi- 
cance of  these  bones  is  clearly  demonstrated  by  their  independent  ossification. 

The  points  of  exit  of  the  various  cranial  nerves  remain  remarkably  constant,  and  in 
their  primitive  condition  serve  to  suggest  the  segmental  arrangement  of  the  cartilaginous 
chondro-cranium  already  referred  to.  Owing  to  the  very  great  modifications  which  the 
mammalian  skull  has  undergone  in  the  process  of  its  evolution,  it  may  be  pointed  out  that 
the  passage  of  the  nerves  through  the  dura  mater — a  derivative,  the  readers  may  be 
reminded,  of  the  primordial  membranous  cranium  (see  ante) — alone  represents  the  primitive 
disposition  of  the  nerves.  Their  subsequent  escape  through  the  bony  base  is  a  later  and 
secondary  development.  In  some  cases  the  two,  membranous  or  primary  and  the  osseous 
or  secondary  foramina,  correspond.  In  other  instances  the  exit  of  the  nerves  through  the 
dura  mater  does  not  coincide  with  the  passage  through  the  bone. 

Of  interest  in  this  connexion  it  may  be  pointed  out  that  the  foramina  and  canals 
which  traverse  the  skull  are  either  situated  in  the  line  of  suture  between  adjacent  bones 
or  in  the  line  of  fusion  of  the  constituent  parts  of  which  the  bone  pierced  is  made  up. 
For  example,  the  sphenoidal  fissure  is  situated  between  the  ox'bito  and  alisphenoids ;  the 
anterior  condylic  between  the  basi  and  exoccipitals ;  the  jugular  between  the  petrous, 
basi,  and  exoccipital ;  the  optic  between  the  orbito-sphenoid  and  the  presphenoid  ;  the 
Vidian  between  the  alisphenoid,  internal  pterygoid  plate,  and  the  lingula. 

THE  BONES  OF  THE  UPPEE  EXTEEMITY. 

The  Clavicle. 

The  clavicle  (clavicula),  or  collar  bone,  one  of  the  elements  in  the  formation 
of  the  shoulder  girdle,  consists  of  a  curved  shaft,  the  extremities  of  which  are 
enlarged.  The  inner  end,  since  it  articulates  with  the  sternum,  is  called  the 
sternal  end ;  the  outer  extremity,  from  its  union  with  the  acromion  process  of  the 
scapula,  is  known  as  the  acromial  end. 

The  sternal  end  (extremitas  sternalis)  is  enlarged,  and  rests  upon  the  meniscus 


Fig.  128. — Right  Clavicle  as  seen  from  Above. 

of  fibro-cartilage  which  is  interposed  between  it  and  the  clavicular  facet  on  the 
upper  and  external  angle  of  the  manubrium  sterni.  It  is  also  supported  by  a  small 
part  of  the  inner  end  of  the  cartilage  of  the  first  rib.  Its  articular  surface,  usually 
broader  from  above  downwards  than  from  side  to  side,  displays  an  antero-posterior 
convexity,  whilst  tending  to  be  slightly  concave  in  a  vertical  direction.  The  edge 
around  the  articular  area  which  serves  for  the  attachment  of  the  capsule  of  the 
sterno-clavicular  articulation  is  sharp  and  well  defined,  except  below  where  it  is 
rounded. 

The  shaft  is  so  curved  that  its  anterior  outline  is  convex  in  its  inner  two-thirds, 
whilst  concave  in  the  outer  third  of  its  length.  Eounded  or  prismatic  in  form 
towards  its  sternal  extremity,  the  shaft  becomes  compressed  and  flattened  towards 
its  outer  end.  Its  superior  surface,  which  is  smooth  and  subcutaneous  throughout 
its  whole  length,  is  directed  upwards  and  forwards;  the  inferior  surface  is  inclined 
downwards  and  backwards.  The  anterior  border,  which  separates  the  upper  from 
the  under  surface  in  front,  is  rough  and  tubercular  towards  its  inner  end  for  the 
attachment   of   the  clavicular   fik'es  of  the  pectoralis  major,  whilst  externally 


THE  CLAVICLE. 


185 


where  it  becomes  continuous  with  the  anterior  margin  of  the  acromial  end,  it  is 
better  defined,  and  bears  the  imprint  of  the  origin  of  the  fibres  of  the  deltoid 
muscle ;  here,  not  uncommonly,  a  projecting  spur  of  bone,  called  the  deltoid 
tubercle,  may  be  seen.     The  'posterior  harder  is  broad  internally,  where  it  is  lipped 


Acromial 

FACET 


Rhomboid  impebssios 


Fig.  129. — Right  Clavicle  as  seen  fbom  Below. 

superiorly  to  furnish  an  attachment  for  the  clavicular  fibres  of  the  sterno- 
mastoid  muscle  ;  behind  and  below  this  the  sterno  -  hyoid  and  sterno  -  thyroid 
muscles  are  attached  to  the  bone.  Externally,  the  posterior  border  becomes  more 
rounded,  and  is  confluent  with  the  posterior  edge  of  the  acromial  end  at  a  point 
where  there  is  a  marked  outgrowth  of  bone  from  its  under  surface,  the  conoid 
tubercle  (tuberositas  coracoidea).  Into  the  outer  third  of  this  border  are  inserted 
the  upper  and  anterior  fibres  of  the  trapezius  muscle.  The  inferior  surface  of  the 
shaft  close  to  the  sternal  end  is  marked  by  an  irregular  elongated  impression 
(tuberositas  costalis),  often  deeply  pitted,  for  the  attachment  of  the  rhomboid 
ligament,  which  unites  it  to  the  cartilage  of  the  first  rib.  External  to  this  the 
shaft  is  channelled  by  a  groove  which  terminates  close  to  the  conoid  tubercle ;  into 
this  groove  the  subclavius  muscle  is  inserted. 

The  acromial  end  of  the  bone  is  flattened  and  compressed  from  above  down- 
wards, and  expanded  from  before  backwards ;  its  anterior  edge  is  sharp  and  well 
defined,  and  gives  attachment  to  the  deltoid  muscle,  which  also  spreads  over  part 
of  its  upper  surface.  Its  posterior  margin  is  rougher  and  more  tubercular,  and 
provides  a  surface  for  the  insertion  of  the  trapezius.  The  area  between  these  two 
muscular  attachments  is  smooth  and  subcutaneous.  The  outer  edge  of  this 
forward-turned  part  of  the  bone  is  provided  with  an  oval  facet  (facies  articularis 
acromiaiis)  for  articulation  with  the  acromion  process  of  the  scapula ;  the  margins 
around  this  articular  area  serve  for  the  attachment  of  the  capsule  of  the  joint. 
The  inferior  surface  of  the  acromial  end  of  the  bone  is  traversed  obliquely  from 
behind  forwards  and  outwards  by  a  rough  ridge  or  line  called  the  trapezoid  or 
oblique  ridge.  The  posterior  extremity  of  this  ridge,  as  it  abuts  on  the  posterior 
border  of  the  bone,  forms  a  prominent  process,  the  conoid  tubercle  (tuberositas 
coracoidea) ;  to  each  of  these,  respectively,  are  attached  the  trapezoid  and  conoid 
portions  of  the  coraco-clavicular  ligament. 

Nutrient  Foramina.— The  forainina  for  the  larger  nutrient  vessels,  of  which  there  may  be 
one  or  two  directed  outwards,  are  usually  found  about  the  middle  of  the  posterior  border,  or  it 
may  be  opening  into  the  floor  of  the  groove  for  the  subclavius  muscle. 

Architecture. — The  shaft  consists  of  an  outer  layer  of  compact  bone,  thickest  towards  the 
centre,  Init  gradually  thinning  towards  the  extremities,  the  investing  envelope  of  which  consists 
merely  of  a  thin  shell.  Within  the  shaft  the  cancellous  tissue  displays  a  longitudinal  striation, 
which  internally  assumes  a  more  cellular  appearance.  At  the  acromial  end  the  general  arrange- 
ment of  the  fibres  resembles  the  appearance  of  the  sides  of  a  Gothic  arch.  The  curves  of  the 
Ijone  impart  an  elasticity  to  it,  which  is  of  much  service  in  reducing  the  effects  of  the  shocks  to 
which  it  is- so  frequ(;ntly  subjected. 

Variations.- -The  clavicles  of  women  are  more  slender,  less  curved,  and  shorter  than  those  of 
men.  In  the  latter  the  bone  is  so  inclined  that  its  outer  end  lies  slightly  higher  or  on  the  same 
level  with  tlie  sternal  end.  In  women  the  bone  usually  slopes  a  little  downward  and  outward. 
The  more  i)i'on(junced  cni-ves  of  some  bones  are  probably  associated  with  a  more  powerful 
development  <jf  IIk;  ])ectoral  and  deltoid  muscles,  a  circumstance  which  also  affords  an  explana- 
tion of  the  difrerences  usually  seen  between  the  right  and  left  bomts,  tin;  habitual  use  of  the  right 
\\\)\)(tv  limb  reacting  on  tli(!  form  of  tin;  bone  of  that  side.  The  inlluc.iu;e,  of  muscular  action, 
liowever,  does  not  whfjlly  account  for  the  production  of  the  curves  of  the  bone,  since  the  bone 
lias  been  .shown  to  fJisplay  itH  characteristic  features  in  cases  where  there  has  been  defective 


186 


OSTEOLOGY. 


sternal  epiphysis  ossifies  about 
20tli  year  ;  fiisps  about  -iStli  year 


Primary  centre  appears  about 
Sth  or  6th  month  of  foetal  life 


development  or  absence  of  the  upper  limb  (Reynault).  Partial  or  complete  absence  of  the 
clavicle  has  been  recorded.  W.  S.  Taylor  exhibited  an  interesting  case  of  this  kind  at  the 
Clinical  Society  of  London,  October  25,  1901. 

Ossification. — Phylogenetically  of  dermic  origin,  the  clavicle  in  man  is  remarkable  in 

commencing  to  ossify  before 
any  other  bone  in  the  body  ; 
this  occurs  as  early  as  the 
fifth  or  sixth  week  of  fo3tal 
life.  The  primitive  centre 
from  which  the  sliaft  and 
outer  extremity  are  de  veloped 
appears  prior  to  the  forma- 
tion of  any  cartilaginous 
matrix ;  and  it  is  not  till  a 

later  stage  that  cartilage  plays  a  part  in  the  development  of  the  bone  by  assisting  in  the 

growth  of  its  extremities. 

A  secondary  centre  or  epiphysis  appears  at  the  sternal  end  about  the  age  of  twenty 

or  later,  and  fusion  rapidly  occurring  between  it  and  the  shaft,  ossification  is  completed 

at  the  age  of  twenty-five  or  thereabouts. 


Fig.  130. — Ossification  of  the  Clavicle. 


The  Scapula. 

The  scapula  (scapula),  shoulder  blade  or  blade  bone,  is  of  triangular  shape  and 
flattened  form.  It  has  two  surfaces,  ventral  and  dorsal.  From  the  latter  there 
springs  a  triangular  process  called  the  spine,  v^^hich  ends  externally  in  the  acromion  ; 
whilst  from  its  superior  border  there  arises  a  beak -like  projection  called  the 
coracoid  process. 

The  body  of  the  bone,  which  is  thin  and  translucent,  except  along  its  margins 
and  where  the  spine  springs  from  it,  has  three  borders  and  three  angles.  Of  these 
borders  the  internal  or  vertebral  (margo  vertebralis)  is  the  longest ;  it  stretches 
from  the  superior  angle  above  to  the  inferior  angle  below.  Of  curved  or  somewhat 
irregular  outline,  it  affords  a  narrow  surface  for  the  insertion  of  the  levator  anguli 
scapulpe,  rhomboideus  minor,  and  rhomboideus  major  muscles. 

The  superior  border  (margo  superior),  which  is  thin  and  sharp,  is  the  shortest  of 
the  three.  It  runs  from  the  superior  angle  towards  the  root  of  the  coracoid  process, 
before  reaching  which,  however,  it  is  interrupted  by  the  suprascapular  notcli  (in- 
cisura  scapulse),  which  lies  immediately  to  the  inner  side  of  the  base  of  that  process. 
This  notch,  which  is  converted  into  a  foramen  by  a  ligament,  or  occasionally  by  a 
spicule  of  bone,  transmits  the  suprascapular  nerve.  Attached  to  the  superior 
border,  close  to  the  notch,  is  the  posterior  belly  of  the  omo-hyoid.  The  external  or 
axillary  border  (margo  axillaris),  so  called  from  its  relation  to  the  hollow  of  the 
armpit  (axilla),  is  much  stouter  than  either  of  the  others ;  it  extends  from  the 
external  angle  above  to  the  inferior  angle  below.  The  upper  inch  or  so  of  this 
border,  which  lies  immediately  lielow  the  glenoid  articular  surface,  is  rough  and 
tubercular  (tuberositas  infraglenoidalis),  and  affords  attachment  to  the  long  head 
of  the  triceps.  Below  this  it  is  usually  crossed  by  a  groove  which  marks  the 
position  of  the  dorsal  artery  of  the  scapula.  The  superior  angle  (angulus  medialis) 
is  sharp  and  more  or  less  rectangular ;  the  inferior  angle  (angulus  inferior)  is 
blunter  and  more  acute ;  whilst  the  external  angle  (angulus  lateralis)  corresponds 
to  that  part  of  the  bone  which  is  sometimes  called  the  head,  and  which  supports 
the  glenoid  surface  and  the  coracoid  process. 

The  glenoid  surface  is  a  pyriform  articular  area,  slightly  concave  froni  above  down- 
wards and  from  side  to  side  ;  its  border  is  but  slightly  raised  above  the  general  surface 
and  affords  attachment  in  the  recent  condition  to  the  glenoid  ligament,  which  helps 
to  deepen  the  socket  in  which  the  head  of  the  humerus  rests.  Below,  the  margin 
of  the  glenoid  fossa  is  confluent  with  the  infraglenoid  impression  (tuberositas  infra- 
glenoidalis), whilst  above  it  blends  with  a  tubercle  (tuberositas  supraglenoidalis), 
to  which  the  long  head  of  the  biceps  muscle  is  attached.  Springing  from  the 
upper  part  of  the  head,  in  line  with  the  superior  border,  is  the  coracoid  process 
(processus  coracoideus).     The  base  of  this  is  limited  externally  by  the  glenoid 


THE  8CAPULA. 


187 


edge,  whilst  internally  it  is  separated  from  the  superior  border  by  the  supra- 
scapular notch.  Rising  upwards  for  a  short  space,  it  bends  on  itself  at  nearly  a 
right  angle,  and  ends  in  a  process  which  is  directed  outwards  and  slightly  forwards, 
overhanging  the  glenoid  fossa  above  and  in  front.  Compressed  from  above  down- 
wards, it  has  attached  to  its  upper  surface  near  its  angle  the  conoid  ligament,  wide 
of  which  there  is  a  rough  area  for  the  trapezoid  ligament.  Attached  to  its 
posterior  border  is  the  coraco-acromial  ligament,  whilst  at  its  extremity  and 
towards  the  front  of  its  anterior  border,  is  the  combined  origin  of  the  biceps  and 
coraco-brachialis,  together  with   the  insertion  of  the  pectoralis  minor.     The  neck 

Clavicular  facet 
5      coracoid  process 


Superior  angle 


Supraspinous  fossa 


Vertebral  borde 


Infraspinous  fossa- 


Head  AND  glenoid  fossa 


Neck 
Great  scapular  notch 


Groove  for  dorsal  artery  of  scapula 


AXILI  ARY    BORDER 


Inferior  angle 


Fig.  131. — The  Right  Scapula  as  seen  from  Behind. 

(collum  scapulse)  is  that  somewhat  constricted  part  of  the  bone  which  supports  the 
head  ;  it  corresponds  in  front  and  behind  to  a  line  drawn  from  the  suprascapular 
notch  to  the  infraglenoid  tubercle. 

The  body  of  the  bone  has  two  surfaces,  a  dorsal  (facies  dorsalis)  and  a  ventral 
(facies  costalis).  The  former  is  divided  into  two  fossae  by  an  outstandiug  process 
of  triangular  form,  called  the  spine  (spina  scapulae).  The  attached  border  of  this 
crosses  the  back  of  the  body  obliquely  in  a  direction  outwards  and  slightly 
upwards,  extending  from  the  vertebral  border  near  the  lower  limit  of  its  upper 
fourth  towards  the  centre  of  the  post(;rior  glenoid  edge,  from  which,  however,  it 
is  separated  by  the  great  scapular  notch,  whi(;h  here  corresponds  to  the  posterior 
aspect  of  the  neck.  The  surfaces  of  the  spine,  which  are  directed  upwards  and 
downwards,  are  concave,  the  upper  entering  into  the  formation  of  the  supraspinous 
fossa,  which  lies  above  it,  the  lower  forming  the  upper  wall  of  the  infraspinous  fossa, 


188 


OSTEOLOGY. 


Acromion 


Clavicular  facet 

coracoid  process 


Superior  angle 
/ 


Xeck 


Arterial  foramen 


Subscapular  fossa 


which  hes  below  it.  The  two  fossee  are  in  communication  with  each  other  round 
the  free  external  concave  border  of  the  spine,  where  that  curves  over  the  great 
scapular  notch.  The  posterior  free  border  of  the  spine  is  suljcutaneous  throughout 
its  entire  length.  Its  upper  and  lower  edges  are  strongly  lipped,  and  serve — the 
superior,  for  the  attachment  of  the  trapezius ;  the  inferior,  for  the  origin  of  the 
deltoid.  The  intervening  surface  varies  in  vridth — broad  and  triangular  where  it 
becomes  confluent  with  the  vertebral  border,  it  displays  a  smooth  surface,  over 
which  the  tendinous  fibres  of  the  trapezius  play;  narrowing  rapidly,  it  forms  a 
surface  of  varying  width  which  blends  externally  with  a  flattened  process,  the  two 

forming  a  compressed 
plate  of  bone  which 
arches  across  the 
scapular  notch  above 
and  behind,  and  then 
curves  forwards,  up- 
wards, and  outwards  to 
overhang  the  glenoid 
fospsa.  The  internal 
border  of  this  process 
is  continuous  with  the 
upper  margin  of  the 
spine,  and  is  gently 
curved.  The  external 
border,  more  curved 
than  the  inner,  with 
which  it  is  united  in 
front,  is  confluent  with 
the  inferior  edge  of 
the  spine,  with  which 
it  forms  an  abrupt 
bend,  termed  the 
acromial  angle.  The 
bone  included  between 
these  two  borders  is 
called  the  acromion  pro- 
cess. Of  compressed 
form,  it  much  re- 
sembles the  acromial 
end  of  the  clavicle, 
with  which  it  articu- 
lates by  means  of  a 
facet  (facies  articularis 
acromii)  which  is 
placed  on  its  internal 
border  near  its  anterior 
extremity.  The  su- 
perior surface  of  the 
acromion,  which  is  broad  and  expanded,  is  subcutaneous,  and  is  directed  upwards  and 
backwards,  and  in  the  normal  position  of  the  bone  outwards  as  well.  Its  internal  edge, 
where  not  in  contact  with  the  clavicle,  has  attached  to  it  the  fibres  of  the  trapezius, 
whilst  its  external  margin  affords  origin  to  the  central  part  of  the  deltoid.  At  its 
anterior  extremity  it  is  connected  with  the  coracoid  process  by  means  of  the  coraco- 
acromial  ligament.     Its  under  surface  is  smooth  and  overhangs  the  shoulder  joint. 

The  supraspinous  fossa,  of  much  less  extent  than  the  infraspinous,  is  placed 
above  the  spine,  the  upper  surface  of  which  assists  in  forming  its  curved  floor ;  in 
it  is  lodged  the  supraspinatus  muscle.  The  suprascapular  notch  opens  into  it  above, 
whilst  below  and  externally  it  communicates  with  the  infraspinous  fossa  by  the 
great  scapular  notch,  through  which  the  suprascapular  artery  and  nerve  pass  to 
reach  the  infraspinous  fossa. 


Fig.  132.- 


Inferior  angle 
-The  Right  Scapula  as  seen  from  the  Front. 


THE  SCAPULA.  189 

The  infraspinous  fossa,  overhung  by  the  spine  above,  is  of  triangular  form.  The 
axillary  border  of  the  bone  limits  it  in  front,  whilst  the  vertebral  margin  bounds  it 
behind  ;  the  greater  part  of  this  surface  affords  origin  to  the  infraspinatus  muscle, 
excepting  a  well-defined  area  which  skirts  the  axillary  border  and  inferior  angle  of 
the  bone,  and  which  affords  an  attachment  to  the  fibres  of  origin,  of  the  teres  minor. 
This  muscle  extends  along  the  posterior  surface  of  the  axillary  border  in  its  upper 
two- thirds,  reaching  nearly  as  high  as  the  glenoid  edge  ;  whilst  a  crescentic  surface, 
which  occupies  the  lower  third  of  the  axillary  border  and  curves  backward  round 
the  posterior  aspect  of  the  inferior  angle,  furnishes  an  origin  for  the  teres  major 
muscle.  Here  also,  near  the  inferior  angle,  are  occasionally  attached  some  of  the 
fibres  of  the  latissimus  dorsi  muscle. 

The  ventral  aspect  (facies  costalis)  of  the  body  is  hollow  from  above  downwards 
and  from  side  to  side,  the  greatest  depth  being  in  correspondence  with  the  spring  of  the 
spine  from  the  dorsal  surface.  Its  inner  boundary,  which  is  formed  by  the  anterior 
lipped  edge  of  the  vertebral  border,  affords  attachment  to  the  fibres  of  insertion  of 
the  serratus  magnus  along  the  greater  part  of  its  extent.  The  area  of  insertion  of 
this  muscle  is,  however,  considerably  increased  over  the  anterior  aspects  of  the 
superior  and  inferior  angles  respectively.  Eunning  down  from  the  head  and  neck 
above  to  the  inferior  angle  below,  there  is  a  stout  rounded  ridge  of  bone,  which 
imparts  a  fulness  to  the  anterior  aspect  of  the  axillary  border  and  increases  the 
depth  of  the  ventral  hollow ;  to  this,  as  well  as  to  the  floor  of  the  fossa,  the  sub- 
scapularis  muscle  is  attached.  The  tendinous  intersections  of  this  muscle  leave 
their  imprint  on  this  surface  of  the  bone  in  a  series  of  three  or  four  rough  lines 
which  converge  towards  the  neck. 

Nutrient  Foramina. — Foramina  for  tlie  passage  of  nutrient  vessels  are  seen  in  different  parts 
of  the  bone  ;  the  most  constant  in  position  is  one  whicli  opens  into  tlie  infrasj)inous  fossa,  about  an 
inch,  or  so  from  the  scapular  notch.  Others  are  met  with  on  the  upper  and  under  surfaces  of  the 
spine,  on  the  ventral  aspect  near  its  deepest  part,'  and  also  around  the  glenoid  margin. 

Connexions. — The  scapula  is  not  directly  connected  with  the  trunk,  but  articulates  with  the 
outer  end  of  the  clavicle,  in  union  with  which  it  forms  the  shoulder  girdle  supporting  the 
humerus  on  its  glenoid  surface.  Placed  on  the  upper  and  back  part  of  the  thorax,  it  covers  the 
ribs  from  the  second  to  the  seventh  inclusive.  Possessed  of  a  wide  range  of  movement,  it  alters 
its  position  according  to  the  attitude  of  the  limb,  rising  or  falling,  being  drawn  inwards  or 
outwards,  or  being  rotated  uiDon  itself  according  as  the  arm  is  moved  in  various  directions.  These 
changes  in  position  can  easily  be  determined  by  recognising  the  altered  relations  of  the  subcutaneous 
and  bony  prominences,  more  especially  the  former,  which  include  the  spine,  the  acromion  process, 
and  the  lower  half  of  the  vertebral  border. 

Architecture.— For  so  light  and  thin  a  bone,  the  scapula  possesses  a  remarkable  rigidity.  This 
is  owing  to  the  arrangement  of  its  parts.  Stout  and  thick  where  it  supports  the  glenoid  surface 
and  coracoid  process,  the  rest  of  the  bone  is  thin,  except  along  the  axillary  border ;  but  strength  is 
imparted  to  the  body  by  the  manner  in  which  the  sjDine  is  fused  at  right  angles  to  its  posterior  surface. 

Variations. — The  most  common  variation  met  with  is  a  separated  acromion  process.  In 
these  cases  there  has  been  failure  in  the  ossific  union  between  the  spine  and  acromion,  the 
junction  between  the  two  being  effected  by  a  layer  of  cartilage  or  an  articulation  possessing  a 
joint  cavity.  The  condition  is  usually  symmetrical  on  both  sides,  though  instances  are  recorded 
where  this  arrangement  is  unilateral.  Very  much  rarer  is  the  condition  in  which  the  coracoid 
process  is  separable  from  the  rest  of  the  bone.  The  size  and  form  of  the  suprascapular  notch 
differs.  In  certain  cases  the  superior  border  of  the  bone  describes  a  uniform  curve  reaching  the 
base  of  the  coracoid  without  any  indication  of  a  notch.  In  some  scapulae,  more  joarticularly  in 
those  of  very  old  people,  the  floor  of  the  subscapular  fossa  is  deficient  o"wing  to  the  absorption  of 
the  thin  bone,  the  periosteal  layers  alone  filling  up  the  gaj).  Congenital  elevation  of  the  scapula 
is  due  to  defective  development  of  the  muscles  connected  with  it. 

At  birth  the  vertical  length  of  the  bone  is  less  in  proportion  to  its  width  than  in  the  adult. 

Ossification. — Ossification  begins  in  the  body  of  the  cartilaginous  scapula  about  the 
end  of  the  second  month  of  fcetal  life.  At  birth  the  head,  neck,  body,  spine,  and  base  of 
the  coracoid  process  are  well  defined  ;  the  vertebral  border,  inferior  angle,  glenoid  fossa, 
acromion  and  coracoid  processes,  ai'c  still  cartilaginous.  The  centre  for  the  upper  and 
fore  part  of  the  coracoid  appears  in  the  first  year,  and  fusion  along  an  obliqi;e  line  leading 
from  the  upper  edge  of  the  glenoid  fossa  to  the  conoid  tubercle  is  complete  about  the 
fifteenth  year.  A  separate  centre  (subcoracoid),  which  ultimately  includes  the  upper  part 
of  the  glenoid  fossa  and  external  part  of  the  coracoid  process,  makes  its  appearance  about 
the  tenth  year,  and  fuses  with  the  surrounding  bone  about  sixteen  or  seventeen.  Up  till 
the  age  of  puberty  the  acromion  remains  cartilaginous  ;  centres,  two  or  more  in  number, 


190 


OSTEOLOGY. 


Primary  centre 
appears  about 
2nd  m.  foetal  life. 


Acromial  centres 
appear   15-16   yrs. , 
fuse  about  25  yrs.   \\, 


Secondary  centre  for 
coracoid  appears 
about  end  1st  yr.  ; 
fuses  about  18  yrs. 


Appears  about 

1(3-17  yrs.  ;  fuses 

about  20  yr.s. 


Subcoracoid  centre 
appears  10  yrs.;  fuses 
10-17  yrs. 


then  make  their  appearance,  which  coalesce  and  ultimately  unite  with  the  spine  about 

the  twenty  -  fifth  year. 
Failure  of  union  may, 
however,  persist  through- 
out life  (see  ante,  Varia- 
tions). 

Ossification  com- 
mences in  the  cartilage 
in  the  inferior  angle 
about  puberty,  and  in- 
dependently and  a  little 
later,  along  the  vertebral 
margin,  fusion  with  the 
body  occurring  at  from 
twenty  to  twenty-five 
years. 

Small  scale-like 
epiphyses  make  their 
appearance  on  the  upper 
surface  and  at  the  ex- 
tremity of  the  coracoid, 
and  are  completed  about 
the  twentieth  year.  A 
thin  epiphysial  plate  de- 
velops over  the  lower 
part  of  the  glenoid 
fossa    about    sixteen    or 


Appears  about 

16  or  17  yrs.  : 

fuses  lS-20  yrs. 


Appears  16-17 
vrs. ;  fuses  20- 
25  yrs. 


Appears  16-17  yrs. 
~  fuses  20-25  yrs. 

Scapula  at  end  of  First  Year.  Scapula  about  the  Age  of  Puberty. 

Fig.  133. — Ossification  of  the  Scapula. 


seventeen,  fusion  being  complete  about  eighteen  or  twenty  years  of  age. 


The  Humerus. 

The  humerus,  or  bone  of  the  upper  arm,  articulates  with  the  scapula  above  and 
with  the  bones  of  the  forearm,  the  radius  and  ulna,  below.  Its  upper  end  com- 
prises the  head  and  great  and  small  tuberosities ;  its  shaft,  which  is  longer  than  any 
of  the  other  bones  of  the  upper  extremity,  is  cylindrical  above  and  flattened  below. 
At  the  inferior  extremity,  which  is  expanded  to  form  the  condyles  on  either  side, 
it  supports  the  troclilear  and  capitellar  articular  surfaces  for  the  ulna  and  radius 
respectively. 

The  superior  extremity  is  the  thickest  and  stoutest  part  of  the  bone.  The 
head  (caput  humeri),  which  forms  about  one-third  of  a  spheroid  and  is  covered  by 
articular  cartilage,  is  directed  upwards,  inwards,  and  slightly  backwards,  and  rests  in 
the  glenoid  fossa  of  the  scapula ;  the  convexity  of  its  surface  is  most  pronounced  in 
its  posterior  half.  Separating  the  head  from  the  tuberosities  externally  is  a  shallow 
groove,  which  fades  away  on  the  surface  of  the  bone  which  supports  the  articular 
part  inferiorly.  This  is  named  the  anatomical  neck  (collum  anatomicum)  and 
serves  for  the  attachment  of  the  capsule  of  the  shoulder  joint.  The  articular  edge  of 
the  groove  opposite  the  small  tuberosity  is  usually  notched  for  the  attachment  of  the 
superior  gleno-humeral  ligament.  The  great  tuberosity  (tuberculum  majus)  abuts 
on  the  outer  side  of  the  head  and  becomes  continuous  with  the  shaft  below.  Its 
upper  surface  forms  a  quadrant,  which  is  subdivided  into  three  more  or  less  smooth 
areas  of  unequal  size.  Of  these  the  highest  and  anterior  is  for  the  insertion  of  the 
supraspinatus  muscle,  the  middle  for  the  infraspinatus,  whilst  the  lowest  and 
posterior  serves  for  the  insertion  of  the  teres  minor  muscle.  The  outer  surface  of 
this  tuberosity,  which  bulges  beyond  the  line  of  the  shaft,  is  rough  and  pierced  by 
numerous  foramina.  Anteriorly  the  great  tuberosity  is  separated  from  the  small 
tuberosity  (tuberculum  minus)  by  a  well-defined  farrow,  called  the  bicipital  groove 
(sulcus  intertubercularis),  from  the  circumstance  that  the  tendon  of  origin  of  the 
long  head  of  the  biceps  muscle  is  lodged  within  it.  The  small  tuberosity  lies  in 
front  of  the  outer  half  of  the  head ;  it  forms  a  pronounced  elevation,  which  fades 
into  the  shaft  below.  The  surface  of  this  tuberosity  is  faceted  above  and  in  front 
for  the  insertion   of  the  sub-scapularis   muscle,  whilst  externally  it  forms  the 


THE  HUMERUS. 


191 


"■^-^--^ 


Ml 


Great  tuberosity - 


,  Lesser 
tuberosity 


Bicipital  groove - 


Deltoid  eminence  —  I 


^  •■  A'i 


prominent  inner  lip  of  the  bicipital  groove.  Below  the  head  and  tuherosities  the 
sliaft  of  the  bone  rapidly  contracts,  and  is  here  named  the  surgical  neck  (collum 
chirurgicum)  owing  to  its 
liability  to  fracture  at  this 
spot. 

The  shaft,  or  body  (corpus 
humeri),  is  cylindrical  in  its 
upper  half.  On  it  the  bicipital 
groove  maybe  traced  downwards 
and  slighibly  inwards,  along  its 
anterior  surface.  The  edges  of 
the  groove,  which  are  termed 
its  lips,  are  confluent  above 
with  the  great  and  small 
tuberosities  respectively.  Here 
they  are  prominent,  and  form 
the  crests  of  the  great  and  small 
tuberosities  (cristse  tuberculi 
majoris  et  minoris).  Inferiorly 
the  lips  of  the  bicipital  groove 
gradually  fade  away,  the  inner 
more  rapidly  than  the  outer, 
which  latter  may  usually  be 
traced  down  to  a  rough  eleva- 
tion placed  on  the  outer  side 
of  the  shaft  about  its  middle 
called  the  deltoid  eminence. 
Into  the  outer  lip  of  the 
bicipital  groove  are  inserted 
the  fibres  of  the  pectoralis 
major  muscle ;  hence  it  is  some- 
times described  as  the  pectoral 
ridge.  To  the  floor  of  the  groove 
the  latissimus  dorsi  is  attached  ; 
whilst  the  teres  major  muscle 
is  inserted  into  the  inner  lip. 

The  deltoid  eminence  (tuber- 
ositas deltoidea),  to  which  the 
powerful  deltoid  muscle  is  at- 
tached, is  a  rough,  slightly 
elevated  V  -  shaped  surface, 
placed  on  the  outer  side  of  the 
shaft  about  its  middle.  The 
anterior  limb  of  the  V  is  par- 
allel to  the  axis  of  the 
shaft,  and  is  continuous  with 
the  outer  lip  of  the  bicipital 
groove  above,  whilst  the  pos- 
terior limb  of  the  V  winds  ob- 
liquely round  the  outer  side  of 
the  bone  towards  the  posterior 
surface,  where  it  becomes  con- 
tinuous with  a  slightly  elevated 
and  occasionally  rough  ridge 
which  leads  up  the  back  of 
the  bone  towards  the  gn^at 
tuberosity  superiorly ;  from 
this  latter  ridge  the  outer  head  of  the  trio(!i)s  luiisclc  iii'ises. 

The    iriiKir   surface   of   tin;    shaft  about  its  middle   iiichnes  to   form  a  rounded 


-Arterial  foramen 


External 
epicondylic- 

RIDOn 


_Internal  epicondylic 

RIDGE 


Radial  fossa 


External - 
ki'kjondyle 

CAI'ITELI.UM 


,  CORONOID  FOSSA 


Internal 
■  epicondyle 


Fio.  134. — Antkuioh  Vikvv  ok  thk  Right  Humerus. 


192 


OSTEOLOGY. 


Head- 


Anatomical_ 

NECK 


Great 
tubekositv 


w. 


'SLRQICAL  NECK 


border,  on  which  there  is  often  a  rough  linear  impression  marking  the  insertion  of 
the  coraco-brachialis  muscle.  Below  this  the  shaft  becomes  compressed  and  ex- 
panded laterally,  ending  inferiorly 
on  either  side  in  the  condyles.  Its 
surfaces  are  now  anterior  and  pos- 
terior, being  separated  from  each 
other  by  two  clearly  defined  borders, 
the  epicondylic  ridges.  Of  these,  the 
internal,  margo  medialis,  is  the  more 
curved  and  less  prominent,  and  is 
continuous  above  with  the  surface  to 
which  the  coraco-brachialis  is  at- 
tached, whilst  inferiorly  it  ends  by 
blending  with  the  internal  condyle. 
The  external  epicondylic  ridge,  margo 
lateralis,  is  straighter  and  more  pro- 
jecting ;  its  edge  is  usually  distinctly 
lipped.  Confluent  with  the  external 
condyle  inferiorly,  it  may  be  traced 
upwards  to  near  the  deltoid  emin- 
ence, where  it  turns  backwards  more 
or  less  parallel  to  the  posterior  oblique 
border  of  that  impression,  to  be  lost 
on  the  posterior  surface  of  the  shaft. 
The  interval  between  this  border  and 
the  deltoid  eminence  is  thus  con- 
verted into  a  shallow  oblique  furrow, 
which  winds  round  the  outer  surface 
of  the  bone  just  below  its  middle ; 
this  constitutes  the  musculo -spiral 
groove  (sulcus  radialis)  along  which 
the  musculo  -  spiral  nerve,  together 
with  the  superior  profunda  artery, 
passes  from  the  back  to  reach  the 
front  of  the  arm.  To  the  epicondylic 
ridges  are  attached  the  intermuscular 
septa,  whilst  the  external  in  its  upper 
two-thirds  furnishes  a  surface  for  the 
origin  of  the  brachio-radialis  (supin- 
ator-longus),  and  in  its  lower  third 
for  the  extensor  carpi  radialis  longior 
muscle. 

The  anterior  surface  of  the  lower 
half  of  the  shaft  is  of  elongated 
triangular  form,  the  base  corre- 
sponding to  the  inferior  extremity 
of  the  bone.  Eunning  down  the 
centre  of  this  is  a  broad,  rounded, 
elevated  ridge,  most  pronounced 
above,  where  it  joins  the  deltoid 
eminence,  and  sloping  on  either  side 
towards  the  epicondylic  ridges ;  it  is 
into  the  outer  of  these  slopes  that  the 
musculo  -  spiral  groove  flows.  In- 
feriorly the  elevated  surface  spreads 
out,  and  becomes  confluent  with  the 
condyles,  more  correctly  termed  the 
epicondyles.  The  internal  epicondyle  (epicondylus  medialis)  is  the  more  prominent 
of  the  two,  and  furnishes  a  surface  for  the  origin  of  the  pronator  radii  teres,  and 


.Deltoid  eminence 


-Spiral  groove 


Olecranon 

FOSSA  ~ 


-External 
epicondyle 


Internal 
epicondyle 


Groove  for- 
ulnab.  nerve 


Trochlea 
Fio.  1.3.5. — Posterior  View  of  the  Right  Humerus. 


THE  HUMERUS. 


193 


Lesser  tuberosity 


Head 


Int.  epi- 

CONDYLE" 


rpITAL  GROOVE 


Great 
tdberosity 


Fig. 


the  superficial  flexor  muscles  of  the  forearm.     The  external  epicondyle  (epicondylus 

lateralis),  stunted  and  but  little  projecting,  serves  for  the  attachment  of  the  common 

tendon  of  origin  of  the  extensor 

muscles.     The  brachialis  anticus 

muscle  has  an  extensive  origin 

from  the  anterior  surface  of  the 

lower  half  of  the  shaft,  including 

between  its  upper  slips  the  inser- 
tion of  the  deltoid. 

The  posterior  surface  of  the 

lower  half  of  the  shaft  is  smooth 

and  rounded  from  side  to  side ; 

somewhat  flattened  below,  where 

the  whole  shaft  tends  to  incline 

forwards,  it  becomes  continuous 

on  either  side  with  the  posterior 

surfaces  of  the  epicondyles,  the 

inner  of  which  is  grooved  for  the  passage  of  the  ulnar  nerve,  whilst  the  external 

supplies  an  origin  for  the  anconeus  muscle. 
The  inner  head  of  the  triceps  muscle  has 
an  extensive  origin  from  the  posterior 
surface  of  the  lower  two -thirds  of  the 
shaft,  internal  to  and  below  the  musculo- 
spiral  groove. 

The  lower  extremity  of  the  humerus 
is  furnished  with  two  articular  surfaces 
(the  condyles  proper),  the  outer  of  which, 
called  the  capitellum  (capitulum),  for  ar- 
ticulation with  the  upper  surface  of  the 
head  of  the  radius,  is  a  rounded  eminence, 
lower    border,   but   not    extending    upwards 


136. — The  Head  of  the  PaoHr  Humerus  as  seen  from 
Above  (with  the  outline  of  the  lower  extremity  in  relation 
thereto  shown  in  dotted  line). 


Capitellum 


Olecranon  fossa        Groove  for  ulnar  nerve 


Fig.  137. — The  Lower  Extremity  of  the 
Eight  Humerus  as  seen  from  Below. 


placed  on  the  anterior  surface  and 
on  the  posterior  surface  of  the  inferior  end  of  the 
bone.  Above  it,  in  front,  there  is  a  shallow  de- 
pression (fossa  radialis),  into  which  the  margin  of 
the  head  of  the  radius  sinks  when  the  elbow  is 
strongly  flexed.  A  shallow  groove  separates  the 
capitellum  internally  from  the  trochlea,  which  is  a 
grooved  articular  surface,  with  prominent  edges 
winding  spirally  round  the  lower  extremity  of  the 
shaft.  The  spiral  curves  from  behind  forwards  and 
inwards,  and  its  axis  is  slightly  oblique  to  the  long 
axis  of  the  shaft.  The  inner  lip  is  the  more  salient 
of  the  two,  and  forms  a  sharp  and  well-defined 
margin  to  the  articular  area ;  its  cartilage-covered 
surface  is  slightly  convex.  The  outer  lip,  much 
less  prominent,  is  rounded  off  into  the  articular 
groove  which  separates  it  from  the  capitellum, 
posterior  to  which,  however,  it  is  carried  up  as  a 
more  or  less  definite  crest.  It  is  by  means  of  the 
trochlea  that  the  humerus  articulates  with  the 
great  sigmoid  cavity  of  the  ulna.  On  the  anterior 
surface  of  the  bone,  immediately  above  the  trochlea, 
is  a  depression — the  coronoid  fossa  (fossa  coronoidea), 
into  which  the  coronoid  process  of  the  ulna  slips  in 
flexion  of  the  joint,  whilst  in  a  corresponding  position 
on  the  back  of  the  lower  end  of  the  shaft  there 
is  a  hollow,  called  tlie  olecranon  fossa  fi'ossa  ol(!crani), 
just  above  tlie  trochli^a  ])Ost(;rior]y.  Into  this  the 
olecranon  process  sinks  when  th(!  elljow  is  extended 
14 


FXT.   EPICONDYLIC 
RIl  GE 


KXT.   EPICONDYLE 


Ext.  i.aticral 

1  lOAMENT 


Trochlea 


I'in.  138. — The  Lower  End  of  the 
Right  Humbkus  as  seen  keom 
the  Outeh  Sidk. 


lie 


two  fosste  are  separated 


194  OSTEOLOGY. 

by  a  thin  translucent  layer  of  bone  which  may  be  deficient,  thus  leading  to  the  forma- 
tion of  a  foramen  between  the  two  hollows  in  the  macerated  bone.  The  anterior  part 
of  the  capsule  of  the  elbow-joint  is  attached  to  the  superior  margins  of  the  radial  and 
coronoid  fossse  in  front,  whilst  the  posterior  ligament  is  connected  with  the  upper 
border  and  lateral  edges  of  the  olecranon  fossa  behind.  The  strong  internal  and 
external  lateral  ligaments  are  attached  superiorly  to  the  internal  and  external 
epicondyles  respectively.  The  proportionate  length  of  the  humerus  to  the  body 
height  is  as  1  is  to  4'93-5"25. 

Nutrient  foramina  are  usually  to  be  seen,  one  at  or  near  the  surface  for  the  insertion  of  tlie 
coraco-brachialis,  the  other  usually  close  to  the  hinder  border  of  the  deltoid  eminence ;  both 
have  a  downward  direction.  Numerous  vascular  foramina  are  scattered  along  the  line  of  the 
anatomical  neck,  the  larger  ones  being  situated  near  the  upper  end  of  the  bicipital  groove. 

Connexions. — The  humerus  articulates  with  the  scapula  above,  and  radius  and  ulna  below. 
Embedded  as  the  humerus  is  in  the  substance  of  the  upper  arm,  its  shaft  and  head  are  surrounded 
on  all  sides.  It  is  only  at  its  lower  part  that  it  comes  into  direct  relation  with  the  surface,  the 
internal  epicondyle  forming  a  characteristic  projection  on  the  inner  side  of  the  elbow  ;  whilst  the 
external  ejiicondyle,  less  prominent,  and  the  external  e2)icondylic  ridge  can  best  be  recognised 
when  the  elbow  is  bent. 

Architecture. — The  shaft  consists  of  a  layer  of  compact  bone  surrounding  a  long  medullary 
canal.  The  outer  shell,  thickest  in  the  lower  third  of  the  bone,  gradually  thins  until  it  reaches 
the  superior  epiphysial  line,  where  it  forms  a  layer  no  thicker  than  stout  paper.  Interiorly 
the  external  shell  is  thicker  and  stouter  than  above,  until  it  reaches  the  epicondyles,  below 
which  the  articular  surfaces  are  formed  of  a  layer  of  compact  spongy  bone.  The  upjser  end  of 
the  medullary  canal  is  surrounded  by  loose  spongy  tissue,  the  fibres  of  which  arch  inwards 
from  the  inner  surface  of  the  compact  outer  layer,  whilst  inferiorly  the  cancellous  tissue 
which  springs  from  the  outer  shell  sweeps  downwards  in  a  radiating  fashion  on  either  side 
of  the  olecranon  fossa  towards  the  epicondyles.  Above  the  olecranon  fossa  there  are  a 
number  of  laminse  of  dense  bone  which  arch  across  from  one  side  to  the  other,  the  con- 
vexity of  the  arches  being  directed  downwards.  The  suj)erior  epiphysis,  formed  of  spongy 
bone,  is  united  to  the  shaft  by  a  wavy  line,  concave  externally  and  convex  internally,  leading 
from  the  base  of  the  great  tuberosity  on  the  outer  side  to  the  inferior  articular  edge  on  the  inner 
side.  The  mass  above  this  includes  the  head  and  two  tuberosities.  The  spongy  tissue  of  the 
head  is  fine,  and  is  arranged  generally  in  lines  radial  to  its  surface  ;  that  of  the  great  tuberosity 
is  more  open,  and  often  displays  large  spaces  towards  its  interior,  which  in  old  bones  communi- 
cate freely  with  the  medullary  cavity  of  the  shaft.  The  general  direction  of  the  fibres  is 
parallel  to  the  outer  surface  of  the  tuberosity.  The  lower  articular  end  is  formed  of  fine  spongy 
tissue,  more  compact  towards  the  surface,  and  arranged  in  lines  more  or  less  at  right  angles  to  its 
articular  planes.  In  the  adult  the  principal  nutrient  canal,  viz.  that  which  ojjens  on  the 
surface  near  the  insertion  of  the  coraco-brachialis,  traverses  the  outer  compact  wall  of  the  shaft 
obliquely  downwards  for  a  distance  of  two  and  a  quarter  inches  before  it  opens  into  the 
medullary  cavity. 

Variations. — As  has  been  already  stated,  the  olecranon  and  coronoid  fosste  may  communicate 
with  each  other  in  the  macerated  bone.  The  resulting  supratrochlear  foramen  is  most 
commonly  met  with  in  the  lower  races  of  man,  as  well  as  in  the  anthropoid  apes,  and  in 
some  other  mammals.  The  occurrence  of  a  hook -like  spine,  called  the  epicondylic  process, 
which  projects  in  front  of  the  internal  epicondylic  ridge,  is  not  uncommon.  Its  extremity  is 
connected  with  the  internal  epicondyle  by  means  of  a  fibrous  band,  underneath  which  the  median 
nerve,  accompanied  by  the  brachial  artery,  or  one  of  its  large  branches,  may  pass,  or  in  some 
instances,  the  nerve  alone,  or  the  artery  unaccompanied  by  the  nerve.  This  2>rocess  is  the  honio- 
logue  in  a  rudimentary  form  of  a  canal  present  in  many  animals,  notably  in  the  carnivora  and 
marsupials.  In  addition  to  the  broad  musculo-spiral  groove  already  described,  and  which  is  no 
doubt  produced  by  the  twisting  or  torsion  of  the  shaft,  there  is  occasionally  a  distinct  narrow 
groove  posterior  to  it,  which  marks  precisely  the  course  of  the  musculo-spiral  nerve  as  it  turns 
round  the  outer  side  of  the  shaft  of  the  bone. 

Ossification. — At  birth  the  shaft  of  the  humerus  is  usually  the  only  part  of  the 
bone  ossified,  if  we  except  the  occasional  presence  (22  per  cent)  of  an  ossific  centre  in  the 
head.  (H.  R.  Spencer,  Journ.  Anat.  and  Physiol,  vol.  xxv.  p.  552.)  The  centre  for  the 
shaft  makes  its  appearance  early  in  the  second  month  of  intrauterine  life.  Within  the 
first  six  months  after  birth  a  centre  usually  appears  for  the  head ;  this  is  succeeded  by 
one  for  the  great  tuberosity  during  the  second  or  third  year.  These  soon  coalesce ;  and 
a  thii'd  centre  for  the  small  tuberosity  begins  to  appear  about  the  end  of  the  third  year, 
or  may  be  delayed  till  the  fourth  or  fifth  year.  These  three  centres  are  all  blended  by 
the  seventh  year,  and  form  an  epiphysis,  which  ultimately  unites  with  the  shaft  about 
the  age  of  twenty-five.  It  may  be  noticed  that  the  superior  end  of  the  diaphysis  is 
conical  and  pointed  in  the  centre,  over  which  the  epiphysis  fits  as  a  cap,  an  arrangement 
which  thus  tends  to  prevent  its  displacement  before  union  has  occurred.  The  first  centre 
to  appear   in  the  loiver  extremity  is  that  for  the  capitellum  about  the  second  or  third 


THE  ULNA. 


195 


year.  This  extends  inwards,  and  forms  the  outer  half  of  the  trochlear  surface,  the 
centre  for  the  inner  half  not  making  its  appearance  till  the  eleventh  or  twelfth  year. 
Separate  centres  are  developed  in  connexion  with  the  epicondyles  ;  that  for  the  external 
appears  about  the  twelfth  year,  and  rapidly  coalescing  with  the  centres  for  the  capitellum 
and  trochlea  forms  an  epiphysis,  which  unites  with  the  shaft  about  the  sixteenth  or 
seventeenth  year.  The  centre  for  the  internal  epicondyle  appears  about  the  fifth  year ; 
it  forms  a  separate  epiphysis,  which  unites  with  the  shaft  about  eighteen  or  nineteen. 
These  two  epiphyses  at  the  lower  end  of  the  bone  are  separated  by  a  down-growth  of  the 


At  iDirth.     About  5  years. 


About  12  years. 
Fig.  139. — Ossification  of  the  Humerus. 


About  16  years. 


8.  Centre   for  small  tulDerosity  fuses   with  other  centres 

about  7  years. 

9.  Appears  about  11  or  12  years. 

10.  Inferior  epiphysis  fuses  with  shaft  about  16  to  17  years. 

11.  Superior  epiphysis  fuses  with  shaft  about  25  years. 

12.  Puses  Vith  shaft  about  17  to  18  years. 


1.  Appears  early  in  2nd  month  fojtal  life. 

2.  For  tuberosity,  appears  2  to  3  years. 

3.  For  head,  appears  within  first  6  months. 

4.  For  internal  condyle,  appears  about  5  years. 

5.  For  capitellum,  appears  2  to  3  years. 

6.  Appears  about  12  years. 

7.  Centres  for  head  and  great  tuberosity,  coalesce  about 

5  years. 

shaft,  which  lies  between  the  internal  epicondyle  and  the  trochlea,  and  forms  part  of  the 
base  and  inner  side  of  the  latter  process. 

The  epicondylic  process  when  present  is  developed  from  the  diaphysis,  and  has  been 
observed  to  be  already  well  ossified  by  the  third  year.  ("Proc.  Anat  Soc."  Journ.  Anat. 
and  Physiol.  1898.) 

The  Ulna. 

Of  the  two  bones  of  the  forearm,  the  ulna,  which  is  placed  internally,  is  the 
longer.  It  consists  of  a  large  superior  extremity  supporting  the  olecranon  and 
coronoid  processes ;  a  shaft  tapering  from  above  downwards ;  and  a  small  rounded 
inferior  end  called  the  head. 

Superior  Extremity. — The  olecranon  process  (olecranon)  lies  in  line  with  the 
shaft.  Its  posterior  surface,  more  or  less  triangular  in  form,  is  smooth  and 
subciitaneoiis  and  covered  by  a  bursa.  Its  superior  aspect,  which  forms  with  the 
jjosterior  surface  a  nearly  rectangular  projection — the  tip  of  the  elbow — furnishes 
a  surface  for  the  insertion  of  the  tendon  of  the  triceps  muscle,  together  with  a 
smooth  area  which  is  overlain  by  the  same  tendon,  but  separated  from  it  by  a 
bursal  sac.  To  the  anterior  crescentic  border  of  this  X'rocess  are  attached  the  fibres 
of  the  jxjsterior  part  of  the  capsule  and  portion  of  the  internal  lateral  ligament  of 
tl)e  el  bow- joint.  The  anterior  surface  is  articular,  and  enters  into  the  foruiation  of 
tfie  great  sigmoid  cavity. 


196 


OSTEOLOGY. 


Olecranon  process 


Greai  sigmoid 

CAVITY 


Small  sigmoid 

CAVITY 


Bicipital  hollow 


Posterior  border 


"Interosseous  border 


The  coronoid  process  (processus  coronoideus)  is  a  bracket-like  process,  which  juts 
forwards  from  the  fore  and  upper  part  of  the  shaft,  and  is  fused  with  the  olecranon 

process  superiorly.  By  its  upper  surface  it  enters 
into  the  formation  of  the  great  sigmoid  cavity, 
whilst  its  anterior  aspect,  which  is  separated  from 
its  upper  side  by  a  sharp  irregular  margin,  slopes 
downwards  and  backwards  to  become  confluent 
with  the  anterior  surface  of  the  shaft.  Of  tri- 
angular shape,  this  area,  which  is  rough  and 
-Coronoid  process  tubcrcular,  terminates  inferiorly  in  an  oval  elevated 
tubercle  (tuberositas  ulnae),  into  which  the  tendon 
of  the  brachialis  anticus  muscle  is  inserted.  Of  the 
lateral  margins  of  the  coronoid  process,  the  inner 
is  usually  the  better  defined.  Above,  where  it 
joins  the  sujjerior  border,  there  is  generally  a 
salient  tubercle,  to  which  one  of  the  heads  of 
origin  of  the  flexor  sublimis  digitorum  muscle  is 
attached,  whilst  below  this  point  the  inner  border 
furnishes  origins  for  the  pronator  radii  teres,  and 
occasionally  for  the  flexor  longus  pollicis  muscles, 
from  above  downwards.  The  smooth  inner  surface 
of  the  coronoid  process  merges  with  the  olecranon 
behind,  and  with  the  internal  surface  of  the  shaft 
below. 

The  great  sigmoid  cavity  (incisura  semilunaris), 
for  articulation  with  the  trochlea  of  the  humerus, 
is  a  semicircular  notch,  the  upper  part  of  which 
is  formed  by  the  anterior  surface  of  the  olecranon, 
whilst  below  it  is  completed  by  the  upper  surface 
of  the  coronoid  process.  Constricted  towards  its 
deepest  part  by  the  notching  of  its  lateral  borders, 
the  articular  surface  is  occasionally  crossed  by 
a  narrow  impression  which  serves  to  define  the 
olecranon  process  above  from  the  coronoid  below. 
The  articular  area  is  divided  into  an  inner  portion, 
slightly  concave  transversely,  and  an  outer  part, 
transversely  convex  to  a  slight  degree,  by  a  longi- 
tudinal smooth  ridge  which  extends  from  the  most 
prominent  part  of  the  border  of  the  olecranon 
above  to  the  most  outstanding  point  of  the  coronoid 
process  below.  The  margins  of  the  great  sigmoid 
cavity  are  sharp  and  well  defined,  and  serve,  with 
the  exception  of  the  area  occupied  by  the  small 
sigmoid  cavity,  for  the  attachment  of  the  capsule 
of  the  elbow-joint. 

The  small  sigmoid  cavity,  placed  on  the  outer 
side  of  the  coronoid  process,  is  an  oblong  articular 
surface  for  the  reception  of  the  head  of  the  radius. 
It    encroaches   on  the   lower  and   outer  part  of 
the  great  sigmoid  notch,  so  as  to  narrow  it  con- 
siderably.    Separated   from   it   by  a  rectangular 
curved  edge,  it  displays  a  surface  which  is  plane 
from  above  downwards,  and  concave  from  before 
backwards.       Its  anterior  extremity  is   narrower 
and  more  pointed  than  its  posterior,  and  becomes 
confluent  with  the  anterior  edge '  of  the  coronoid 
process,  at  which  point   the  orbicular  Ugament,  which   retains  the  head   of  the 
radius  in  position,  is  attached  in  front.      Its  posterior   border,  wider   and  more 
outstanding,    hes    in    hne,    and    is    continuous    with    the    interosseous    margin 


ai 


-Head 

Articular  surface 
'for  radius 
^Groove  for  ext.  carpi 

ULNARIS 


Styloid  process 


Fig. 


140. — The  Right  Ulna  as  viewed 
FROM  THE  Outer  Side. 


THE  ULNA.  197 

of    the    shaft.      Behind    this  border,  the    orbicular    ligament    is    attached    pos- 
teriorly. 

The  shaft  of  the  ulna  (corpus  ulnse),  which  is  nearly  straight,  or  but  slightly 
curved;  is  stout  and  thick  above,  gradually  tapering  towards  its  lower  extremity. 
It  may  be  divided  into  two  surfaces,  a  flexor  and  an  extensor,  by  two  well-defined 
borders,  an  external  or  interosseous  (crista  interossea),  and  a  posterior  (margo 
dorsalis),  which  latter  is  subcutaneous  throughout  its  whole  length. 

The  outer,  or  interosseous  border  (crista  interossea),  is  crisp  and  sharp  in  the 
upper  three-fourths  of  the  shaft,  but  becomes  faint  and  ill-defined  in  the  lower 
fourth.  To  this,  with  the  exception  only  of  the  part  which  forms  the  posterior 
boundary  of  the  bicipital  hollow,  is  attached  the  interosseous  membrane  which 
connects  the  two  bones  of  the  forearm.  The  posterior  border  (margo  dorsalis),  of 
sinuous  outline,  curving  outwards  above,  and  slightly  inwards  below,  is  continuous 
superiorly  with  the  triangular  subcutaneous  area  on  the  back  of  the  olecranon, 
being  formed  by  the  confluence  of  the  borders  which  bound  that  surface ;  well 
marked  above,  it  becomes  faint  and  more  rounded  below,  but  may  be  traced  down- 
wards to  the  posterior  surface  of  the  base  of  the  styloid  process.  To  this  border  is 
attached  an  aponeurosis  common  to  the  flexor  carpi  ulnaris,  extensor  carpi  ulnaris, 
and  flexor  profundus  digitorum  muscles.  A  noteworthy  feature  in  connexion  with 
this  part  of  the  shaft  is  the  fact  that  it  is  subcutaneous,  and  can  easily  be  felt 
beneath  the  skin  throughout  its  whole  length. 

The  flexor  surface  corresponds  to  the  front  and  inner  side  of  the  shaft.  It  is 
frequently  described  as  consisting  of  two  surfaces,  an  anterior  and  an  internal, 
which  are  separated  by  a  rounded  anterior  border  (margo  volaris),  which  extends 
from  the  tubercle  above  towards  the  styloid  process  below.  The  prominence  of 
this  ridge  varies  in  different  bones,  being  well  marked  in  bones  of  a  pronounced 
type,  but  corresponding  merely  to  the  rounding  of  the  surfaces  in  poorly  developed 
specimens.  The  flexor  aspect  of  the  bone  affords  an  extensive  origin  to  the  flexor 
profundus  digitorum  muscle,  which  clothes  its  anterior  and  inner  sides  in  its  upper 
three-fourths,  reaching  as  far  back  as  the  posterior  border,  and  extending  upwards 
as  high  as  the  inner  side  of  the  coronoid  process.  Immediately  below  the  small 
sigmoid  cavity  there  is  a  hollow  triangular  area,  limited  behind  by  the  upper  part 
of  the  interosseous  crest,  and  defined  in  front  by  an  oblique  hne  which  extends 
downwards  and  backwards  from  the  outer  margin  of  the  coronoid  process.  In  this 
hollow  the  bicipital  tubercle  of  the  radius  rests  when  the  forearm  is  in  the  prone 
position,  and  to  its  floor  are  attached  the  fibres  of  origin  of  the  supinator  radii  brevis 
muscle.  The  lower  fourth  of  the  shaft  is  crossed  by  the  fibres  of  the  pronator 
quadratus  muscle,  which  derives  its  origin  from  a  more  or  less  weU-defined  crest, 
which  winds  spirally  downwards  and  backwards  towards  the  front  of  the  root  of  the 
styloid  yjrocess,  and  is  continuous  above  with  the  so-called  anterior  border. 

The  extensor  aspect  of  the  shaft  lies  posteriorly  between  the  posterior  border 
and  the  interosseous  crest.  At  its  upper  part  it  is  placed  behind  the  great  and 
small  sigmoid  cavities,  extending  on  to  the  outer  side  of  the  olecranon.  Here  an 
area  corresponding  to  the  upper  third  of  the  length  of  the  bone  is  marked  off" 
inferiorly  by  an  oblique  ridge  which  leaves  the  interosseous  crest  about  an  inch  or 
more  below  the  hinder  edge  of  the  small  sigmoid  cavity.  Into  this  somewhat 
triangular  surface  the  fibres  of  the  anconeus  are  inserted.  Below  this  the 
posterior  surface  is  subdivided  by  a  faint  longitudinal  ridge,  the  bone  between 
which  and  the  interosseous  crest  furnishes  origins  for  the  extensor  ossis  metacarpi 
pollicis,  extensor  longus  pollicis,  and  extensor  indicis  muscles,  in  order  from  above 
downwards.  The  surface  of  bone  between  the  posterior  border  and  the  afore-men- 
tioned longitudinal  line  is  smooth  and  overlain  by  the  extensor  carpi  ulnaris  muscle. 

The  inferior  extremity  of  the  ulna  presents  a  rounded  head  (capitulum  ulnie), 
from  which,  on  its  iiinor  and  ]>osterior  aspect,  there  projects  downwards  a  cylindrical 
pointed  ]jroccss  called  the  styloid  process  f processus  styloideus).  To  the  extremity 
of  this  latter  is  attaclicd  the  internal  lateral  ligament,  whilst  in  front  it  has  con- 
nected with  it  the  antero-internal  y)ortion  of  the  capsule  of  the  wrist-joint.  The 
antero-extcrnal  half  of  the  circumference  of  the  head  is  furnished  with  a  smooth 
narrow  convex  articular  surface,  which  fits  into  the  sigmoid  cavity  of  the  radius. 
Uh 


198 


OSTEOLOGY. 


Dl  ;  (  H  \NON    PROC  LSS 


Great  suimoid  cavity 


Small  sigmoid 

(  AVITV 


—  Bicipital  hollow 


Tm-ebosseods 

U  BDER 


Its  inferior  surface,  fiat  and  semilunar  in  shape,  and  separated  from  the  root  of  the 
styloid  process  by  a  well-marked  groove,  rests  on  the  upper  surface  of  the  triangular 

fibro- cartilage  of  the  wrist,  the 
apex  of  which  is  attached  to  the 
groove  just  mentioned.  The 
margins  of  the  head  in  front  and 
behind  theradialarticular  surface 
have  attached  to  them  the  an- 
terior and  posterior  inferior 
radio  -  ulnar  ligaments.  The 
hinder  and  outer  surface  of  the 
styloid  process  is  channelled  by  a 
groove  which  separates  it  from 
the  posterior  surface  of  the  head, 
and  extends  some  little  way  up 
the  posterior  aspect  of  the  lower 
end  of  the  shaft.  In  this  is  lodged 
the  tendon  of  the  extensor  carpi 
ulnaris  muscle.  The  proportion- 
ate length  of  the  ulna  to  the  body 
height  is  as  1  is  to  6'26-6'66. 

Nutrient  Foramina.  —  A  fora- 
men, liaving  an  upward  direction  for 
the  nutrient  artery  of  the  shaft,  opens 
on  the  anterior  surface  of  the  bone 
from  two  to  three  inches  laelow  the 
tuberosity.  Vascular  canals  of  large 
size  are  seen  above  and  behind  the 
small  sigmoid  cavity,  just  posterior  to 
the  notched  external  border  of  the 
great  sigmoid  cavity.  At  the  lower 
end  of  the  bone  similar  openings  are 
seen  in  the  groove  between  the  styloid 
process  and  the  inferior  articular  sur- 
face of  the  head. 

Connexions. — The  ulna  articu- 
lates above  with  the  trochlea  of  the 
humerus.  On  the  outer  side  it  is  in 
contact  with  the  radius  above  and 
below,  the  suj)erior  radio -ulnar  ar- 
ticulation being  formed  by  the  head 
of  the  radius  and  the  small  sigmoid 
cavity  of  the  ulna,  the  inferior  radio- 
ulnar joint  comjj rising  the  head  of 
the  ulna,  which  hts  into  the  sigmoid 
cavity  of  the  radius.  Between  these 
two  joints  the  shafts  of  the  bones  are 
united  by  the  interosseous  membrane. 
The  inferior  surface  of  the  head  of 
the  ulna  does  not  articulate  with  the 
carjDus,  but  rests  on  the  ujjjjer  surface 
of  the  interposed  triangular  fibro - 
cartilage.  The  ulna  is  sujDcrficial 
throughout  its  entire  extent.  Su- 
jjeriorly  the  olecranon  process  can  be 
readily  recognised,  particularly  when 
the  elbow  is  bent,  as  in  this  jjosition 
the  olecranon  is  withdrawn  from  the 
olecranon  fossa  of  the  humerus  in 
which  it  rests  when  the  joint  is  ex- 
tended. Below  this  the  subcutaneous 
triangular  area  on  the  back  of  the 
olecranon  can  be  easily  determined, 
and  from  it  the  posterior  border  of  the  bone  can  readily  be  traced  along  the  line  of  the  "  ulnar 
furrow  "  to  the  styloid  process  below.  With  the  hand  supine  this  latter  process  can  be  felt  to  the 
inner  side  and  slightly  behind  the  wrist.  When  the  hand  is  pronated,  the  lower  end  of  the 
radius  rolls  round  the  lower  extremity  of  the  ulna,  and  the  antero-external  surface  of  the  head  of 


Interosseous 

BORDER 


Fig.  141.— The  Radius  and  Ulna  as  seen  from  the  Fbont. 


THE  RADIUS. 


]99 


the  latter  hone  now  forms  a  well-marked  projection  on  the  Lack  of  the  wrist  in  line  witli  the 
cleft  between  tlie  little  and  ring  fingers. 

Architecture, — The  weakest  parts  of  the  bone  are  the  constricted  portion  of  the  great 
sigmoid  cavity,  and  the  shaft  in  its  lower  third,  the  bone  being  most  lialjle  to  fracture  at  these 
points.  On  section  the  medullary  cavity  is  seen  to  extend  upwards  as  high  as  the  base  of  the 
coronoid  process ;  inferiorly  it  reaches  as  low  as  the  upper  end  of  the  lower  fifth  of  the  bone.  The 
walls  of  the  shaft,  which  are  formed  of  dense  bone,  are  much  thicker  posteriorly  than  anteriorly. 
Above  they  are  continuous  with  the  front  of  the  coronoid  process  and  the  back  of  the  olecranon, 
where  they  are  composed  of  layers  of  looser  texture,  which,  however,  gradually  become  thinner  as 
the  points  of  these  processes  are  reached.  Inferiorly  they  gradually  taper  until  the  head  and 
styloid  j)rocess  are  reached,  round  which  they  form  a  thin  shell,  considerably  thickened,  however, 
in  the  region  of  the  groove  for  the  extensor  carpi  ulnaris  muscle.  The  bulk  of  the  upper 
extremity  is  formed  of  loose  cellular  bone,  arranged  in  a  series  of  arcades,  stretching  from  the 
anterior  to  the  posterior  wall  over  the  upper  end  of  the  medullary  canal.  Above  the  constricted 
part  of  the  great  sigmoid  cavity  the  bone  displays  a  difl'erent  structure ;  here  it  is  formed  of 
spongy  bone,  of  closer  texture,  arranged  generally  in  lines  radial  to  the  articular  surface.  At  the 
point  of  constriction  of  the  great  sigmoid  cavity  the  layer  immediately  subjacent  is  much  denser 
and  more  compact. 

The  lower  fifth  of  the  bone  is  formed  of  loose  spongy  bone,  the  fibres  of  which  have  a  general 
longitudinal  arrangement ;  towards  its  extremity  the  meshes  become  smaller. 

Variations. — Cases  of  partial  or  complete  absence  of  the  ulna  through  congenital  defect  have 
been  recorded.  Eosenmliller  has  described  a  case  in  which  the  olecranon  was  separated  from  the 
upper  end  of  the  bone,  resembling  thus  in  some  respects  the  patella.  In  powerfully  developed 
bones  there  is  a  tendency  to  the  formation  of  a  sharp  projecting  crest  corresponding  to  the  inser- 
tion of  the  triceps. 

Ossification. — The  ulna  is  ossified  from  one  primary  and  two  or  more  secondary 
centres.      The  centre  for  the  shaft  appears 


Fuses  with  shaft  about  16  years 


Appears  about  10  years 


early  in  the  second  month  of  foetal  life. 
At  birth  the  shaft  and  a  considerable  part 
of  the  upper  extremity,  including  the 
coronoid  process,  are  ossified,  as  well  as  part 
of  the  lower  extremity.  The  olecranon 
process  and  the  inferior  surface  of  the  head 
and  the  styloid  process  are  cartilaginous. 
About  ten  years  of  age  a  secondary  centre 
appears  in  the  cartilage  at  the  upper  end 
of  the  bone,  and  forms  an  epiphysis 
which  unites  with  the  shaft  about  sixteen. 
A  scale-like  centre  appears  in  the  cartilage 
of  the  head  about  the  sixth  year,  from 
which  the  under  surface  of  that  part  of  the 
bone  is  developed,  and  by  the  extension  of 
which  the  styloid  process  is  also  ossified ; 
this  epiphysis  does  not  unite  with  the  shaft 
till  the  twentieth  or  twenty -third  year. 
Independent  centres  for  the  styloid  process 
and  for  the  extreme  edge  of  the  olecranon 
have  also  been  described.  The  student 
may  here  be  warned  that  the  epiphysial 
line  between  the  shaft  and  superior  or 
olecranon  epiphysis  does  not  correspond 
to  the  constricted  part  of  the  great  sigmoid  cavity,  but  lies  considerably  above  it. 


Appears  about  G  years 


Puses  with  shaft  20-23  years 
At  Birth.     About  12  years.       About  16  years. 
Fig.  142. — The  Ossification  op  the  Ulna. 


The  Eadius. 

The  radius,  or  outer  bone  of  the  forearm,  is  shorter  than  the  ulna,  with  which 
it  is  united  on  the  inner  side.  Superiorly  it  articulates  with  the  humerus,  and 
below  suyjports  the  carpus.  It  consists  of  a  head,  a  neck,  a  tubercle,  a  shaft, 
and  an  expanded  lower  extremity.  The  shaft  is  narrow  above,  but  increases  in  all 
its  diameters  below. 

Upper  Extremity. —  The  head  fcapitulum)  is  disc-shaped  and  provided  with 
a  sliallovv  conciavc  surface  ffovea  capital]  radii)  superiorly  for  articulation  with  the 
ca])itelhim  of  the  humerus.  I'he  circumference  of  the  head  (circumfenmtia  articu- 
laris)  is  smooth  and  is  embraced  by  the  orbicular  ligament.  On  the  inner  side  it 
is  usually  much  broader,  and  displays  an  articular  surface,  plane  from  above  down- 
14  c 


200 


OSTEOLOG-Y. 


Subcutaneous 

SURFACE 


Head 


Neck 


INTEEOSSEOUS— 
BORDER 


Post,  oblique 

LINE 


wards,  which  rolls  within  the  small  sigmoid  cavity  of  the  ulna  in  the  movements 
of  pronation  and  supination.  The  character  of  the  outer  half  of  the  circumference 
Olecranon  diffcrs    froui    the   inner  in 

being  narrower,  and  rounded 
from  above  downwards. 

The  neck  (collum  radii) 
is  the  constricted  part  of 
the  shaft  which  supports  the 
head,  the  overhang  of  the 
latter  being  greatest  towards 
the  outer  and  posterior  side. 
Below  the  neck,  on  the  inner 
side,  there  is  an  outstanding 
oval  prominence,  the  bi- 
cipital tuberosity  (tuber- 
ositas radii).  The  posterior 
part  of  this  is  rough  for 
the  insertion  of  the  biceps 
tendon,  whilst  the  anterior 
half  is  smooth  and  covered 
by  a  bursa  which  intervenes 
between  it  and  the  tendon. 
The  shaft  (corpus  radii), 
which  has  an  outward  curve 
and  is  narrow  above  and 
broad  below,  is  wedge-shaped 
on  section.  The  edge  of  the 
wedge  forms  the  sharp  inner 
interosseous  margin  of  the 
bone  (crista  interossea), 
whilst  its  base  corresponds 
to  the  thick  and  rounded 
outer  border  over  which  the 
anterior  or  flexor  surface 
becomes  cohflaent  with  the 
posterior  or  extensor  surface. 
The  internal  or  interos- 
seous border,  faint  above 
where  it  lies  in  line  with 
the  posterior  border  of  the 
bicipital  tubercle,  becomes 
sharp  and  prominent  in  the 
middle  third  of  the  bone. 
Below  this  it  splits  into  two 
faint  lines,  which  lead  to 
either  side  of  the  sigmoid 
cavity  on  the  lower  eud  of 
the  bone,  thus  including 
between  them  a  narrow 
triangular  area  into  which 
the  deeper  fibres  of  the 
pronator  radii  quadratus 
muscle  are  inserted.  To 
this  border,  as  well  as  to 
the    posterior    of    the    two 


Groove  for  ext. 
.  carpi  ulnaris 


Ext.  ossis 
metacarp.  poll. 
Ext.  brevis  poll. 

Ext.  carpi  rad. 
ongior 

Ext,  carpi  rad. 
brevior 


Styloid  pboc. 


Fig.  143. — The  Radius  and  Ulna  as  seen  from  Behind. 


divergent  lilies,  the  interos- 
seous membrane  is  attached. 


The  external  border  (oftentimes  described  as  the  external  surface)  is  thick  and 
rounded  above,  but  becomes  thinner  and  more  prominent  below,  where  it  merges 


THE  EADIUS.  201 

with  the  base  of  the  styloid  process.  About  its  middle  the  anterior  and  posterior 
obli(|ue  Hnes  become  contlueut  with  it,  and  here,  placed  between  them,  is  a  rough 
elongated  impression  which  marks  the  insertion  of  the  pronator  radii  teres  muscle. 
Above  this,  and  on  the  outer  surface  of  the  neck,  the  supinator  radii  brevis  muscle 
is  inserted,  whilst  inferiorly  this  border  is  overlain  by  the  tendons  of  the  brachio- 
radialis  and  the  extensor  carpi  radialis  longior  and  brevior  muscles. 

The  anterior  or  flexor  surface  (facies  volaris)  is  crossed  obliquely  by  a  line  which 
runs  from  the  bicipital  tubercle  above,  downwards,  and  outw^ards  towards  the 
middle  of  the  outer  border  of  the  shaft.  This,  oftentimes  called  the  anterior  oblique 
line,  serves  for  the  attachment  of  the  radial  head  of  origin  of  the  flexor  sublimis 
digitorum  muscle.  Above  it,  the  front  of  the  bone  has  the  fibres  of  the  supinator 
radii  brevis  muscle  inserted  into  it,  whilst  below  and  internal  to  it,  extending 
as  far  down  as  the  inferior  limit  of  the  middle  third  of  the  bone,  is  an  extensive 
surface  for  the  origin  of  the  flexor  longus  poUicis  muscle.  In  the  lower  fourth 
of  the  bone,  where  the  shaft  is  broad  and  flat  in  front,  there  is  a  surface  for  the 
insertion  of  the  pronator  quadratus  muscle  which  also  extends  back  to  tlie  inter- 
osseous ridge. 

The  extensor  or  posterior  surface  (facies  dorsalis)  is  also  crossed  by  an  oblique 
line,  less  distinct  than  the  anterior.  This  serves  to  define  the  superior  limit  of  the 
origin  of  the  extensor  ossis  metacarpi  pollicis  muscle.  Above  this,  the  back  of  the 
neck  and  upper  part  of  the  shaft  is  overlain  by  the  fibres  of  the  supinator  radii  brevis, 
which  become  attached  to  this  surface  of  the  bone  in  its  outer  half.  Below  the 
posterior  oblique  line  the  posterior  surface  in  the  upper  part  of  its  inner  half  gives 
origin  to  the  extensor  ossis  metacarpi  pollicis,  and  the  extensor  brevis  pollicis 
muscles  in  order  from  above  downwards. 

The  lower  extremity,  which  tends  to  be  turned  sKghtly  forward  when  viewed 
from  below,  has  a  somewhat  triangular  form.  Its  inferior  carpal  articular  surface, 
concave  from  before  backwards,  and  slightly  so  from  side  to  side,  is  divided  into  two 
facets  by  a  slight  antero-posterior  ridge,  best  marked  at  its  extremities  where  the 
anterior  and  posterior  margins  are  notched ;  the  external  of  these  areas,  of  tri- 
angular shape,  is  for  articulation  with  the  scaphoid,  whilst  the  inner,  quadrilateral  in 
form,  is  for  the  semilunar  bone.  The  anterior  border,  prominent  and  turned  forward, 
is  rough  at  its  edge,  where  it  serves  for  the  attachment  of  the  anterior  part  of  the 
capsule  of  the  wrist  joint.  The  posterior  border  is  rough,  rounded,  and  tubercular, 
and  is  grooved  by  many  tendons  ;  of  these  grooves  the  best  marked  is  one  which  passes 
obliquely  across  its  posterior  surface.  This  is  for  the  tendon  of  the  extensor  longus 
pollicis  muscle.  The  outer  Up  of  this  groove  is  often  very  prominent,  and  forms 
an  outstanding  tubercle.  To  the  ulnar  side  of  this  oblique  groove  there  is  a  broad 
shallow  furrow  in  which  the  tendons  of  the  extensor  communis  digitorum  and 
extensor  indicis  muscles  are  lodged,  whilst  to  its  outer  side  and  between  it  and  the 
styloid  process,  there  is  another  broad  groove,  subdivided  by  a  faint  ridge  into  two, 
for  the  passage  of  the  tendons  of  the  extensor  carpi  radialis  brevior  and  the  extensor 
carpi  radialis  longior  in  that  order  from  within  outwards.  The  styloid  process  (pro- 
cessus styloideus)  lies  to  the  outer  side  of  the  inferior  extremity ;  broad  at  its  base, 
it  becomes  narrow  and  pointed  below  where  by  its  inner  cartilage-covered  surface 
it  forms  the  summit  of  the  inferior  triangular  articular  area.  The  outer  surface  of 
this  process  is  crossed  obliquely  from  above  downwards  and  forwards  by  a  shallow 
groove,  the  anterior  lip  of  which  is  sharp  and  well  marked,  and  serves  to  separate  it 
from  the  anterior  surface  of  the  bone,  whilst  the  posterior  lip  is  often  emphasised 
by  a  small  tubercle  above.  The  tendon  of  the  brachio-radialis  muscle  is  inserted 
into  the  upper  part  of  either  lip,  and  also  spreads  out  on  to  the  floor  of  the  groove, 
whilst  the  tendons  of  the  extensor  ossis  metacarpi  pollicis  and  the  extensor  brevis 
pollicis  muscles  lie  within  the  groove.  To  the  tip  of  the  styloid  process  is  attached 
the  external  laUsral  ligament  of  the  wrist.  On  the  inner  side  of  the  lower  extremity 
is  yjlaccd  the  sigmoid  cavity  Hncisura  idnaris)  for  the  reception  of  the  head  of  the 
ulna.  Concave  frnm  befcjrc  backwards,  and  yjlane  from  above  downwards,  it  forms 
by  its  inferior  margin  a  rectangular  edge  which  separates  it  from  the  inferior 
carpal  surface.  To  this  edge  the  base  of  the  tri.ingular  fibro-cartilage  is  attached, 
a  structure  which  serves  to  separate  the  inferior  articular  surface  of  the  head  of 


202 


OSTEOLOGY. 


the  ulna  from  the  carpus.     The  anterior  and  posterior  edges  of  the  sigmoid  cavity, 
more  or  less  prominent,  serve  for  the  attachment  of  ligaments. 

The  proportionate   length   of  the   radius   to   the   body   height    is    as    1    is   to 
6-70-7-11. 

Nutrient  Foramina. — Tlie  openings  of  several  small  nutrient  canals  may  be  seen  in  the 
region  of  the  neck.  That  for  the  shaft,  which  has  an  uj^ward  direction,  is  usually  placed  on  the 
front  of  the  l)one,  internal  to  the  anterior  oblique  line,  and  from  an  inch  and  a  half  to  two  inches 
below  the  bicipital  tubercle.  The  back  of  the  lower  e.xtremity  of  the  bone  is  pierced  by  many 
small  foramina. 

Connexions. — The  radius  articulates  with  the  capitellum  of  the  humerus  in  the  flexed 
position  of  the  elbow,  with  the  ulna  to  its  inner  side  by  the  superior  and  inferior  radio-ulnar 
joints,  and  with  the  scaphoid  and  semilunar  ])ones  of  the  carjjus  below.  AboA^e,  the  head  of  the 
bone  can  be  felt  in  the  intermuscular  depression  on  the  outer  side  of  the  back  of  the  elbow  ;  here 
the  bone  is  only  covered  by  the  skin,  superficial  fascia,  and  the  thin  common  tendinous  origin  of 
the  extensor  muscles,  as  well  as  the  ligaments  which  support  it.  Its  jwsition  can  best  be  ascer- 
tained by  pronating  and  supinating  the  bones  of  the  forearm,  when  the  head  will  be  felt  rotating 
beneath  the  finger.  The  lower  end  of  the  bone  is  overlain  in  front  and  behind  by  the  flexor  and 
extensor  tendons,  but  its  general  form  can  be  readily  made  out.  The  styloid  process  lying  to  the 
outer  side  of  the  wrist  in  line  with  the  extended  thumb  can  easily  be  recognised  ;  note  that  it 
reaches  a  lower  level  than  the  corresponding  process  of  the  ulna.  The  outer  border  of  the  lower 
third  of  the  shaft  can  be  distinctly  felt,  as  here  the  bone  is  only  overlain  by  tendons. 

Architecture. — The  neck  is  the  narrowest  part  of  the  bone  ;  here  fracture  may  occur,  though 
not  commonly.  The  point  at  which  the  bone  is  usually  broken  is  about  one  inch  above  the 
lower  extremity.  This  is  accounted  for  by  the  fact  that  the  radius  sujjports  the  hand  at  the 
radio-car j)al  articulation,  and  the  shocks  to  which  the  latter  is  subjected,  as  in  endeavouring  to 
save  oneself  from  falling,  are  naturally  transmitted  to  the  radius.  On  section,  the  medullary 
canal  is  seen  to  extend  as  high  as  the  neck ;  below,  it  reaches  to  the  level  of  the  inferior  fifth  of 
the  bone.  Its  walls  are  thick  as  compared  with  the  diameters  of  the  bone,  particularly  along  the 
interosseous  border,  thus  imparting  rigidity  to  the  curve  of  the  shaft ;  these  walls  thin  out 
above  and  below.  Superiorly,  the  surface  of  the  bicipital  tubercle  is  formed  of  a  thin 
shell  of  bone,  which,  however,  thickens  again  where  it  passes  on  to  the  neck.  The  upper 
extremity  is  formed  of  spongy  bone  arranged  in  the  form  of  arcades,  reaching  below  the  level 
of  the  bicipital  tubercle  internally,  but  not  extending  below  the  level  of  the  neck  ex- 
ternally. Beneath  the  capitellar  articular  surface  there  is  a  dense  layer,  thickest  in  the 
centre,  and  thinning  towards  the  circumference ;  this  is  overlain  by  a  very  thin  layer  of 
less  compact  bone. 

The  inferior   fifth  of    the    shaft  and  lower  extremity   are    formed    of  loose    sjaongy   bone 
^  arranged  more   or   less   longitudinally.      Ini- 

Z  A  i?„  „     -fi    i,„ff  TQ  on  ,<.„      mediately   subjacent    to   the   carpal  articular 

2^  rt  Appears  Fuses  with  shaft  18-20  years  ,.  ,'',,■•'  ■  ^    ,  i     t 

about  5-7  I  suriace  the  tissue  is  more  coinjDact,  and  dis- 

j)lays  a  striation  parallel  to  the  articular  plane. 
The  nutrient  canal  of  the  ^haft  j^ierces  the 
anterior  wall  of  the  upjaer  jDart  of  the  medul- 
lary cavity  obliquely  li'om  below  uj)wards  for 
the  space  of  half  an  inch. 

Variations. — Cases  of  congenital  absence 
of  the  radius  are  recorded  ;  in  these  the  thumb 
is  not  infrequently  wanting  as  well. 

Ossification. — The  centre  for  the  shaft 
makes  its  appearance  early  in  the  second 
month  of  intrauterine  life.  At  birth  the 
shaft  is  well  formed ;  its  upper  and  lower 
extremities  are  capped  with  cartilage,  and 
the  bicipital  tubercle  is  beginning  to  appear. 
A  secondary  centre  appears  in  the  cartilage 
of  the  lower  extremity  about  the  second  or 
third  year ;  this  does  not  unite  with  the 
shaft  until  the  twentieth  or  twenty-fifth 
year,  somewliat  earlier  in  the  female.  From 
this  the  carpal  and  ulnar  articular  surfaces 
are  formed.  The  centre  for  the  head 
appears  from  the  fifth  to  the  seventh  year, 
and  fuses  with  the  neck  about  the  age  of 
eighteen  or  twenty.  It  forms  the  capitellar 
articular  surface  and  combines  with  the  neck  to  form  the  area  for  articulation  with  the 
small  sigmoid  cavity  of  the  ulna.  A  scale-like  epiphysis  capping  the  summit  of  the 
bicipital  tubercle  has  been  described  ;  this  appears  about  the  fourteenth  or  fifteenth  year, 
and  rapidly  fuses  with  that  process. 


Appears  about 
2-3  years 

Unites  witli  shaft 
20-25  years 

At  Birth.         About  12  years.         About  16  years. 

Fig.  144. — The  Ossification  of  the  Kadios. 


THE  BONES  OF  THE  HAND. 


203 


THE   BONES   OF   THE   HAND. 

The  bones  of  the  hand,  twenty-seven  in  number,  may  be  conveniently  divided 
into  three  groups  : — 

(1)  The  bones  of  the  wrist  or  carjjus — eight  in  number. 

(2)  The  bones  of  the  palm  or  metacarpus — five  in  number. 

(3)  The  bones  of  the  fingers  and  thumb  or  ^^Yidl&ngen— fourteen  in  number. 


U^CIIOEM 

Cuneiform 

Pl'^IFOPM 


The  Carpus. 

The  carpal  bones  (ossa  carpi)  are  arranged  in  two  rows :  the  first,  or  proximal 
row,  comprises  from 
without  inwards, 
the  scaphoid  (os 
naviculare),  semi- 
lunar (os  lunatum), 
cuneiform  (os  tri- 
quetrum),  and  pisi- 
form (os  pisiforme) ; 
the  second  or  distal 
row  includes  the 
trapezium  (os  mul- 
tangulum  majus), 
trapezoid  (os  mul- 
tangulum  minus), 
OS  magnum  (os  capi- 
tatum),  and  unciform  sesamoid  bones 
(os  hamatum).  Ir- 
regularly six-sided, 
each  of  these  bones 
possesses  non- ar- 
ticular palmar  and 
dorsal  surfaces.  In 
addition,  the  mar- 
ginal bones  are  non- 
articular  along  their 
ulnar  and  radial 
aspects  according  as 
they  form  the  inner 
or  outer  members 
of  the  series. 


I.  Metacarpal  - 


, —  ^    Metacarpal 


Via.  14.'». — 'J'he  Bones  of  the  Right  Wrist  and  Hand  as  seen  from 
THE  Front. 


Scaphoid  Bone  Tos  naviculare;. — This  is  the  largest  as  well  as  the  outermost 
Ijoric  of  trio  first  row.  Its  'palmar  surface,  rough  for  the  attachment  of  ligaments, 
is  irregularly  triangular.     'I'he    inrcrior  external  angle  forms  a   projection  called 


204 


OSTEOLOG-Y. 


Os  MAGNUM 

Semilunar 


Scaphoid 

Trapezoid 

1r  VPEZIUM 


Cuneiform 
Pisiform  . 


Mft^carpai. 


V.  Metacarpal 


radial 
above 
below. 


the  tuberosity ;  this  can  be  felt  at  the  base  of  the  root  of  the  thumb.  Its  swperior 
surface  is  convex  from  side  to  side  and  before  backwards  for  articulation  with  the 
radius.  This  area  extends  considerably  over  the  posterior  surface  of  the  bone. 
Its  inferior  surface  is  convex  from  before  backwards,  and  extends  on  to  the  dorsal 
aspect  of  the  bone,  slightly  convex  from  side  to  side ;  it  is  divisible  into  two  areas, 
the  outer  for  articulation  with  the  trapezium,  the  inner  for  the  trapezoid.     The 

outer  surface  is  narrow 
and  rounded  and  forms 
a  non  -  articular  border, 
which  extends  from  the 
articular  surface 
to  the  tuberosity 
The  inner  surface 
is  hollowed  out  in  front 
for  articulation  with  the 
head  of  the  os  magnum. 
Above  this  it  displays  a 
small  semilunar  -  shaped 
facet  for  the  semilunar 
bone.  The  dorsal  non- 
artictdar  surface  lies  be- 
tween the  radial  articular 
surface  above  and  the 
surface  for  the  trapezium 
and  trapezoid  below.  It 
is  obliquely  grooved  for 
the  attachment  of  the 
posterior  ligaments  of  the 
wrist.  The  scaphoid  artic- 
ulates with  five  bones — 
the  radius,  the  semilunar, 
the  OS  magnum,  the  trape- 
zoid, and  the  trapezium. 

Semilunar  Bone  (os 
lunatum). — So  called  from 
its  deeply  excavated  form, 
the  semilunar  bone  lies 
between  the  scaphoid  on 
the  outer  side  and  the 
cuneiform  on  the  inner. 
Its  'palmar  surface,  of 
rhombic  form  and  con- 
siderable size,  is  rough  for 
the  attachment  of  liga- 
ments ;  its  superior  sur- 
face, convex  from  side 
to  side  and  from  before 
backwards,  articulates  with  the  radius  and  in  part  with  the  under  surface 
of  the  triangular  fibro-cartilage  of  the  wrist.  Its  inferior  aspect,  deeply  hollowed 
from  before  backwards,  is  divided  into  two  articular  areas,  of  which  the  outer 
is  the  larger ;  this  is  for  the  head  of  the  os  magnum ;  the  inner,  narrow  from 
side  to  side,  articulates  with  the  unciform.  Its  external  surface,  crescentic  in 
shape,  serves  for  articulation  with  the  scaphoid,  and  also  for  the  attachment  of  the 
interosseous  ligaments  which  connect  it  with  that  bone.  Its  inner  surface,  of 
quadrilateral  form,  is  cartilage-covered  for  articulation  with  the  cuneiform,  and 
the  edge  which  separates  this  from  the  superior  surface  has  attached  to  it  the 
interosseous  ligament  which  unites  these  two  bones.  The  rough  dorsal  non- 
articular  surface  is  much  smaller  than  the  palmar ;  by  this  means  the  front 
and  back  of  the    bone   can  readily  be   determined.      The   semilunar  articulates 


Second 

PHALANX 


Third 

PHALANX 


Fig.  146.- 


-The  Bones  of  the  Right  Wrist  and  Hand  as  seen 
FROM  Behind. 


THE  CAEPUS. 


20r 


Trape^iium 


Racliub 


Radius 


Fig.  147. — The  Right  Scaphoid  Bone. 
Note. — The  bone  is  represented  in  the  centre  of  the  figure  in 
the  position  which  it  occupies  in  the  hand  viewed  from 
the  front.  The  views  on  either  side,  and  above  and  below, 
represent  respectively  the  corresponding  surfaces  of  the 
bone  turned  towards  the  spectator. 


with  five  bones — the  scaphoid,  the  radius,  the  cuneiform,  the  unciform,  and  tlie  os 

magnum. 

Cuneiform  or  Pyramidal  Bone 

(os  triquetrum). — This  bone  may 

be   recognised   by  the  small  oval 

or  circular  facet  on    its  anterior 

surface    for    the    pisiform.      This 

is  placed  towards  the  lower  part 

of   the  ])almar   surface,  which   is 

elsewhere     rough    for    ligaments. 

The   bone  is  placed  obliquely,  so 

that   its  surfaces   cannot   be   ac- 
curately   described    as     inferior, 

superior,  etc. ;  but  for  convenience 

of  description,  the  method  already 

adopted  is  adhered  to.  The  sitperior 

surface  has  a  convex  rhombic  sur- 
face for  articulation  with  the  under 

surface   of  the   triangular   fibre - 

cartilage  in  adduction  of  the  hand, 

though  ordinarily  it  does  not  ap- 
pear  to  be  in  contact  with  that 

structure.      To  the  ulnar  side  of 

this   it    is    rough    for    ligaments. 

The  inferior  surface  is  elongated 

and  concavo-convex  from  without 

inwards ;  here  the  bone  articulates  with  the  unciform.     The  external  surface,  broader 

in  front  than  behind,  articulates  with  the  semilunar.     The  inner  surface,  rounded 

and  rough,  is  confluent  above  and  behind  with  the  superior  and  dorsal  aspects  of 

the    bone.     The    dorsal    surface, 

rounded  and  smooth  externally, 

is  ridged  and  grooved  internally 

for  the  attachment  of  ligaments. 

The  cuneiform  articulates  with 

three  bones,  viz.  the  pisiform,  the 

unciform,  and  the  semilunar. 

Pisiform  bone  (os  pisiforme). 

— About  the  size  and  shape  of  a 

large  pea,  the  pisiform  bone  rests 

on  the  anterior  surface  of  the  fore 

end  of  the  cuneiform,  with  which 

it  articulates  by  an  oval  or  circular 

facet  on  its  dorsal  aspect.      The 

rounded  mass  of  the  rest  of  the 

bone  is  non-articular,  and  inclines 

downwards  and  outwards  so  as  to 

overhang  the  articular  facet  in 

front  and  externally.     The  mass 

of  the  bone  is  usually  separated 

^,o     ,„      „        ,.  ,  from  the  articular  surface  by  a 

148.— 'Jhe  Right  Semilunar  Bone.  nii.Ti.-i.  t    , 

small  but  distinct  groove.     Into 

Note.— The  bone  is  represented  in  the  centre  of  the  figure  in  the    the     summit     of     the     bone     the 

f™nl'°"n/f  views  I'TitT  r"«n"  ^'f  V"^"^  ?T/^'  tendon  of  the  flexor  carpi  ulnaris 

iront.       ine   views   on   either  side,    and    above  and    below,  ,      .     .  ,  J^, 

represent  respectively  the  corresponding  surfaces  of  the  bone    lIllJ''^Cle  IS  inserted,  and  here  also 

turned  towards  the  spectator.  the   anterior    annular    ligament 

is  attached. 

Trapezium  ^os  multanguliim  majus).— The  trapezium  is  the  outermost  l)ono  of  the 
secon.J  i-.AV  u\-  the  carpus.  It  may  be  readily  recognised  by  the  oval  saddle-shaped 
facet  on  its  inferior  surface  for  articulation  with  the  metacarpal  bone  of  the  thumb. 


Os  iiia<aium 


206 


OSTEOLOaY. 


Uncifori 


Semilunar 


From  its  palmar  aspect  there  rises  a  prominent  ridge,  within  which  is  a  groove  along 

which  the  tendon  of  the  flexor  carpi 
radialis  muscle  passes.  The  ridge  fur- 
nishes an  attachment  for  the  anterior 
annular  ligament,  as  well  as  for  some 
of  the  short  muscles  of  the  thumb. 
The  superior  surface  has  a  half  oval 
facet  for  the  scaplioid,  external  to  which 
it  is  rough,  and  becomes  continuous 
with  the  non-articular  external  aspect, 
which  serves  for  the  attachment  of 
ligaments.  On  its  inner  surface  there 
are  two  facets;  the  upper  is  a  half 
oval,  concave  from  above  downwards, 
and  very  slightly  convex  from  before 
backwards. 


Triangular 

flbro-cartilage 

of  wrist 


Fig.  149. — The  Right  Cuneiform  Bone. 

Note. — The  bone  is  represented  in  the  centre  of  the 
figui'e  in  the  position  which  it  occupies  in  the 
hand  viewed  from  the  front.  The  views  on  either 
side,  and  above  and  below,  represent  respectively 
the  corresponding  surfaces  of  the  bone  turned 
towards  the  spectator. 


and  is  for 
articulation 
with  the  tra- 
pezoid. The 
lower,  small 
and  circular, 
and  not  al- 
ways pre  - 
sent,  is  for 
articulation 
with      the 


Cuneiform 


Fig.  1.50. — The  Right  Pisiform 
Bone. 

Note. — The  figure  to  the  left  re- 
l^resents  the  palmar  view  of  the 
bone  ;  that  to  the  right  the 
dorsal  view. 


outer 
bone. 


side    of    the 
The    dorsal 


of    the    second 
surface,  of    irregular 


metacarpal 

outline,  is  rough  for  the  attachment 
of  ligaments.  The  trapezium .  articu- 
lates with  four  bones,  the  scaphoid, 
trapezoid,  and  the  first  and  second 
metacarpal  bones. 

Trapezoid  Bone  (os  multangulum 
minus). — With  the  exception  of  the 
pisiform,  this  is  the  smallest  of  the 
carpal  bones.  Its  rough  palmar  sur- 
face is  small  and  pentagonal  in  outline. 
By  a  small  oblong  surface  on  its 
superior  aspect  it  articulates  with  the 
scaphoid.  Inferiorly ,  by  a  somewhat 
saddle -shaped  surface,  it  articulates 
with  the  base  of  the  second  meta- 
carpal. Separated  from  this  by  a 
rough  V-shaped  impression,  is  the 
surface  on  the  outer  side  for  articula- 
tion with  the  trapezium  ;  this  appears 
as  if  obliquely  grooved  from  before 
backwards  and  downwards.  The  in- 
i^  ternal  facet  for  articulation  with  the 

Fig.  151.-THE  Right  Trapezium.  OS    magnum    is    narrow     from    above 

N0TE.-The  bone  is  represented  in  the  centre  of  the  hgure    downwards,    and    deeply    CUrVCd    from 

in  the  position  which  it  occupies  in  the  hand  viewed  before  backwards.    The  dorsal  Surface 

from  the  front.     The  views  on  either  side,  and  above    of   the    boUC,  whicll  is  rOUgll  and  non- 
and  below,  represent  respectively   the   corresponding         ,•    1  •  „v     laro-Pr    than     the 

surfaces  of  the  bone  turned  towards  the  spectator.  arClCUiai,     IS     mucn    Idlger    tnan    tue 

palmar  aspect.  The  mass  ot  the 
bone,  dorsally,  is  directed  downwards  and  towards  the  ulnar  side.  The  trapezoid 
articulates  with  four  bones — the  trapezium,  scaphoid,  os  magnum,  and  the  second 
metacarpal. 


THE  CAEPUS. 


207 


Os  magnuiii 


Its  iialraar 


Metacarpal 


Scaphoid 


Traijezium 


Fig.  152. — The  Kight  Trapezoid. 

Note. — The  bone  is  represented  in  the  centre  of  the  figure  in 
the  position  which  it  occupies  in  the  hand  viewed  from 
the  front.  The  views  on  either  side,  and  above  and  below, 
represent  respectively  the  corresponding  surfaces  of  the 
bone  turned  towards  the  spectator. 


Os  Magnum  (os  capitatum). — This  is  the  largest  of  the  carpal  bones. 
surface  is  rough  and  rounded.  The 
superior  portion  of  the  bone  forms 
the  head,  and  is  furnished  with 
convex  articular  facets  which  fit 
into  the  hollows  on  the  inferior 
surfaces  of  the  scaphoid  and  semi- 
lunar ;  that  for  the  latter  is  in- 
ternal to  and  separated  by  a  slight 
ridge  from  the  scaphoid  articular 
area.  The  inferior  surface,  narrow 
towards  its  palmar  border  and 
broad  dor  sally,  is  subdivided  usu- 
ally into  three  facets  by  two  ridges 
— that  towards  the  radial  side  is 
for  the  base  of  the  second  meta- 
carpal ;  the  middle  facet  is  for  the 
third  metacarpal;  whilst  the  in- 
nermost facet  of  the  three,  not 
always  present,  very  small  and 
placed  near  the  dorsal  side  of  the 
bone,  is  for  the  fourth  metacarpal. 
The  outer  side  of  the  body  has  an 
articular  surface  for  the  trapezoid, 
not  infrequently  separated  from 
the  scaphoid  surface  on  the  head 
by  a   rough   line,   to   which   the   interosseous   ligament   connecting  it  with    the 

scaphoid  is  attached.  The 
inner  side  of  the  body  has 
an  elongated  articular  sur- 
face, usually  deeply  notched 
in  front,  or  it  may  be  di- 
vided anteriorly  into  a  small 
circular  area  near  the  dorsal 
edge  ;  and  a  larger  posterior 
part.  This  latter  articulates 
either  singly  or  doubly  with 
the  unciform,  the  interos- 
seous ligament  which  unites 
the  two  bones  being  attached 
either  to  the  notch  or  to 
the  surface  separating  the 
two  articular  facets.  The 
dorsal  surface  is  rough  for 
ligaments ;  it  is  somewhat 
constricted  below  the  head, 
the  articular  surface  of  which 
sweeps  round  its  upper 
border. 

The  OS  magnum  articu- 
lates with  seven  bones — the 
unciform,  the  semilunar,  the 
scaphoid,  the  trapezoid,  and 
the  second,  third,  and  fourth 
metacarpal  bones ;  occasion- 


Metacarpal 


IV.  Metacarpal 


.  Metacarpal 


Metacarpal 


Semllunai- 


Scaphoid 


Unciform 


Fio.  153. — The  Kjuht  Os  Magnum. 

Note. — The  bone  is   represented   in   the  centre  of  the   figure 
position   which   it  occupies   in   the   hand  viewed    from    tli 

The  views  oij  either  side,  and  above  and  below,  represent  respectively    oily    \V.q    fourth    metlCarD'll 
tlie    (;orrespon<liiig    surfaces    of    the    bone    turned    towards    the    ',    "^  ,         ,.       ,    ,  .j,     ,i' 

8i)ectator. 


in  the 
front. 


Unciform  Bone  (os  hamatum). — Tlu 


does  not  articulate  with  the 
magnum, 
unciform  can  be  readily  distinguished  by 


208 


OSTEOLOGY. 


Metacarpal 


the  hook-like  process  (hamulus)  which  projects  from  the  lower  and  inner  aspect 
of  its  anterior  surface.     To  this  is  attached  the  anterior  annular  ligament  as  well 

as  some  of  the  fibres  of  origin 
of  the  short  muscles  of  the 
little  finger.  The  ulnar  side 
of  the  unciform  process  is 
.  Metacarpal  somctimes  grooved  by  the 
deep  branch  of  the  ulnar 
nerve  (Anderson,  W.,  "  Proc. 
Anat.  Soc."  Journ.  Anat. 
and  Physiol,  vol.  xxviii.  p. 
11).  The  palmar  surface, 
rough  for  ligaments,  is  some- 
what triangular  in  shape. 
Superiorly  and  internally 
there  is  an  elongated  ar- 
ticular surface  for  the  cunei- 
form, convex  above  and 
concave  below.  The  outer 
aspect  of  the  bone  is  pro- 
vided with  a  plane  elongated 
facet,  occasionally  divided 
into  two  (see  above)  for  ar- 
ticulation with  the  OS  mag- 
num. Where  the  superior 
and  external  surfaces  meet, 
the  angle  is  blunt,  and  has 

Note.— The  bone  is  represented  in  the  centre  of  the  figure  in  the  ^.  ^l^^^^'OW  tacct  whlch  ar- 
position  which  it  occupies  in  the  hand  viewed  from  the  front.  tlCulatCS  With  the  Semilunar. 
The  views  on  either  side,  and  above  and  below,  represent  respectively    Infcriorly      there      are      tWO 

!pJctator^'°'"^'"^   '"'^'°''   °^  *'''   ^°'''  *"™''^   *°''''"^'  ^^'  articular  facets  separated  by 

a  ridge ;  these  are  slightly 
concave  from  before  backwards,  and  are  for  articulation,  the  outer  with  the  fourth, 
and  the  inner  with  the  fifth  metacarpal  bone.  The  dorsal  surface,  more  or  less 
triangular  in  shape,  is  rough  for  ligaments. 

The  unciform  articulates  with  five  bones — viz.  the  os  magnum,  semilunar, 
cuneiform,  and  the  fourth  and  fifth  metacarpals. 


/Os  magnum 


Fig.  154. — The  Right  Unciform  Bone. 


The  Carpus  as  a  Whole. 

When  the  carpal  bones  are  articulated  together  they  form  a  bony  mass,  the 
dorsal  surface  of  which  is  convex  from  side  to  side.  Anteriorly  they  present  a 
grooved  appearance,  concave  from  side  to  side.  This  arrangement  is  further 
emphasised  by  the  forward  projection,  on  the  inner  side,  of  the  pisiform  and  hook 
of  the  unciform,  whilst  externally  the  tuberosity  of  the  scaphoid  and  the  ridge  of 
the  trapezium  help  to  deepen  the  furrow  by  their  elevation.  To  these  four  points 
the  anterior  annular  ligament  of  the  wrist  is  attached,  which  stretches  across  from 
side  to  side,  and  thus  converts  the  furrow  into  a  canal  through  which  the  flexor 
tendons  pass  to  reach  the  fingers. 

Architecture. — The  bones  are  formed  of  fairly  compact  spongy  tissue,  surrounded  by  a  thin 
shell  of  denser  bone.  They  are  very  vascular,  and  their  non-articular  surfaces  are  j)ierced  by 
many  foramina. 

Variations. —  Increase  in  the  number  of  the  carpal  elements  is  occasionally  met  with,  and 
these  have  been  ascribed  to  division  of  the  scaj)hoid,  semilunar,  cuneiform,  os  magnum,  trape- 
zoid, and  unciform.  In  the  last-mentioned  case  the  hook-like  process  persists  as  a  sej^arate 
ossicle ;  but  the  researches  of  Thilenius  {Morph.  Arbeiten,  Bd.  v.  Heft  3,  S.  462),  together  with  the 
observations  of  Pfitzner,  prove  that  all  these  supernumerary  bones  are  but  the  persistence  of  inde- 
pendent cartilaginous  elements  which  are  met  with  in  the  hand  of  the  human  embryo  between 
the  second  and  fourth  months,  and  which  either  disapjiear  or  become  fused  with  adjacent 
elements.  Of  these  the  most  interesting  is  the  os  centrale,  first  described  by  Rosenberg,  and 
subsequently  investigated  by  Henke,  Leboucq,  and  others.     This  is  met  with  almost  invariably 


THE  METACARPUS. 


209 


as  an  independent  cartilaginous  element  during  the  earlier  months  of  foetal  life,  and  occasionally 
becomes  developed  into  a  distinct  ossicle  placed  on  the  back  of  the  carpus  between  the  scaphoirl 
and  OS  magnum  and  the  trapezoid.  Its  significance  depends  on  the  fact  that  it  is  an  im- 
portant component  of  the  carpus  in  most  mammals,  and  is  met  with  normally  in  the  orang 
and  most  monkeys.  Ordinarily  in  man,  as  was  pointed  out  by  Leboucq,  it  becomes  fused  with  the 
scaphoid,  where  its  presence  is  often  indicated  by 
a  small  tubercle,  a  condition  which  maintains 
in  the  chimjjanzee,  the  gorilla,  and  the  gibbons. 
D  wight  has  recently  described  a  case  in  which 
there  was  an  os  subcapitulum  in  both  hands. 
The  ossicle  lay  between  the  base  of  the  middle 
metacari^al  bone  and  the  os  magnum  with  the 
trapezoid  to  its  radial  side.  {Anat.  Anz.  vol.  xxiv.) 
Further  addition  to  the  number  of  the  carpal 
elements  may  be  due  to  the  separation  of  the 
styloid  process  of  the  third  metacarpal  bone  and 
its  persistence  as  a  separate  ossicle. 

Eeduction  in  the  number  of  the  carpus  has 
been  met  with,  but  this  is  probably  due  to 
pathological  causes.  Morestin  {Bull.  Soc.  Anat. 
de  Paris,  tome  71,  p.  651),  who  has  investigated 
the  subject,  finds  that  ankylosis  occurs  most  fre- 
quently between  the  bases  of  the  second  and 
third  metacarjDal  bones  and  the  carpus,  seldom 
or  never  between  the  carpus  and  the  first  meta- 
carpal, or  between  the  pisiform  and  cuneiform. 
G.  Elliot  Smith  has  recorded  an  instance  of  com- 
plete fusion  between  the  semilunar  and  cuneiform 
bones  in  both  wrists  of  a  Soudanese  negro.  There 
was  no  evidence  of  any  pathological  change. 
(Anat.  Anz.  vol.  xxiii.  1903.) 


Fig.  155. 


-Radiograph  of  thu  Hand 
AT  Birth. 


Ossification.  —  At  birth  the  carpus  is 
entirely  cartilaginous.  An  exceptional  case 
is  figured  by  Lambertz,  in  which  the  centres 
for  the  OS  magnam  and  unciform  were 
already  present.  The  same  authority  states 
that  it  is  not  uncommon  to  meet  with  these  centres  in  the  second  month  after  birth. 
According  to  Debierre  (Journ.  de  VAnat.  et  de  la  Physiol,  vol.  xxii.  1886,  p.  285), 
ossification  takes  place  approximately  as  follows  : — 


It  will  be  noticed  that  whilst  the  primary 
centres  for  the  metacarpus  and  phalanges 
are    well    ossified,    the    carpus    is    still 
entirely  cartilaginous. 
Compare  this  with  Fig.  197,  in  which  the 
tarsus  is  shown  in  part  already  ossified. 


Os  magnum 
Unciform  . 
Cuneiform  . 
Semilunar  . 
Trapezium  . 
Scaphoid  . 
Trapezoid  . 
Pisiform 


11  to  12  months. 

12  to  14  months. 
3  years. 

5  to  6  years. 

6  years. 
6  years. 

6  to  7  years. 
10  to  12  years. 


The  same  observer  failed  to  note  the  appearance  of  a  separate  centre  for  the  apophysis 
of  the  unciform,  and  records  the  occurrence  of  two  centres  for  the  pisiform. 


The  Metacarpus. 


The  metacarpal  bones  form  tlie  skeleton  of  the  palm,  articulating  proximally 
with  the  corpus,  whilst  by  their  distal  extremities  or  heads  they  su])port  the  hones 
of  the  fingers.  Five  in  number,  one  for  each  digit,  they  lie  side  by  side  and 
slightly  diver<^ent  from  each  otiier,  being  separated  by  intervals,  termed  interosseous 
spaces.  Uistinguished  numerically  from  without  inwards,  they  all  display  certain 
common  cliaracters  ;  each  possesses  a  body  or  sliaft,  a  base  or  carpal  extremity,  and  a 
head  or  phalangeal  end. 

The  shafts,  which  an;  sliglitl}'  curved  towards  tlie  ])almar  aspect,  are  narrowest 
towards  th(nr  middle.     'J'heir  dorsal   surface  is   m.arked   by    two   divero;erit    lines 
15 


210 


OSTEOLOGY. 


Fio.  156.— First  Right 
Metacarpal  Bone. 


Tubercle 


wliich  pass  forward  from  the  back  of  the  base  to  tubercles  on  either  side  of  the 

head.     The  surface  included  between  the  two  lines  is  smooth  and  of  elongated 

triangular  form.      On  either   side  of  these   lines  two  broad 

shallow   grooves   wind   spirally   forward   on   to   the   palmar 

Head       surface,  where  they  are  separated  in  front  by  a  sharp  ridge 

which    is   continuous    with    a    scnnewhat    triangular    surface 

which    corresponds  to  the  palmar  aspect   of  the  base.     The 

grooved  surfaces  on  either  side  of  the  shaft  furnish  origins  for 

the    interossei    muscles.      Close   to   the  palmar  crest  is  the 

Shaft       opening  of  the  nutrient  canal,  which  is  directed  towards  the 

carpal  extremity,  except  in  the  case  of  the  first  metacarpal 

bone. 

The  head    (capitulum)    is    provided   witli    a    surface   for 
articulation  with  the  proximal  phalanx.      This  area  curves 
Base        farther  over  its  palmar  than  its  dorsal  aspect.     Convex  from 
before  backwards  and  from  side  to  side,  it  is  wider  anteriorly 
than  posteriorly ;  notched  on  its  palmar  aspect,  its  edges  form 
two  prominent  tubercles,  which  are  sometimes  grooved  for  the 
small  sesamoid  bones  which  may  occasionally  be  found  on  the 
anterior  surface  of  the  joint.     On  either  side  of  the  head  of  the 
bone  there  is  a  deep  pit,  behind  which  is  a  prominent  tubercle  ; 
to    these    are    at- 
tached   the  lateral 
ligaments    of    the 
metacarpo  -  phalan  - 
geal  joints. 
The  bases    (basis),  all  more   or  less 
wedge-shaped   in  form,   articulate   with 
the  carpus ;  they  differ  in  size  and  shape 
according  to  their  articulation. 

Of  the  five  metacarpal  bones,  the 
first,  viz.  that  of  the  thumb, 
is  the  shortest  and  stoutest, 
the  second  is  the  longest, 
whilst  the  third,  fourth,  and 
fifth  display  a  gradual  reduc- 
tion in  length. 

The  four  inner  bones  ar- 
ticulate by  their  bases  with 
each  other,  and  are  united  at 
their  distal  extremities  by 
ligaments.  They  are  so  ar- 
ranged as  to  conform  to  the 
hollow  of  the  palm,  being  con- 
cave from  side  to  side  an- 
teriorly, and  convex  posteriorly. 
The  first  metacarpal  differs 
from  the  others  in  being  free 
at  its  distal  extremity,  whilst 
its  proximal  end  possesses  only 
a  carpal  articular  facet. 

The  first  metacarpal  bone 
is  the  shortest  and  stoutest  of 
the  series.  Its  shaft  is  com- 
pressed from  before  backwards. 
Its  head,  of  large  size,  is  but 
slightly  convex  from  side  to  side,  and  is  grooved  in  front  for  the  sesamoid  bones. 
The  base  is  provided  with  a  saddle-shaped  surface  for  articulation  with  the  trapezium, 
and  has  no  lateral  facets.     Externally  there  is  a   slight    tubercle    to  which   the 


Trapezoid 


Trapezium 


Fig.  157.- 


Trapezoid 
-Second  Metacarpal  Bone. 


Note. — The  bone  is  represented  in  the  centre  of  the  figure  in  the 
position  which  it  occupies  in  the  hand  viewed  from  the  front. 
The  views  on  either  side,  and  below,  represent  respectively 
the  corresponding  surfaces  of  the  bone  turned  towards  the 
spectator. 


THE  METACAEPUS. 


211 


abductor  longus  pollicis  or  extensor  ossis  rnala- 
carpi  pollicis  muscle  is  attached.  The  canal  for 
the  nutrient  artery  is  directed  towards  the  head  of 
the  bone. 

The  second  metacarpal  bone  is  recognised 
by  its  length  and  its  broad  and  deeply -notched 
base  for  articulation  with  the  trapezoid.     It  has 
a  small  half-oval  facet  for  the  trapezium  on  the 
radial    side    of    its    base, 
whilst  on  its  ulnar  aspect 
it  presents  a  narrow  vertical 
strip  for  the  os  magnum, 
in  front  of  which  there  are 
two  half-oval  surfaces  for 
the  third  metacarpal.     To 
the  dorsal  aspect  of  the  base 
is  attached  the  tendon  of 
the  extensor  carpi  radialis 
longior  muscle,  whilst  the 
flexor  carpi  radialis  is  in- 
serted in  front. 

The  third  metacarpal 
bone  can  usually  be  recog- 
nised by  the  pointed  styloid 
process  which  springs  from 
the  back  of  its  base,  and  is 
directed  radial-wards.  Su- 
periorly there  is  a  facet  on 
the  base  for  the  os  magnum. 


Ulnar 
side 

Insertion 
of  exten- 
sor carpi 
radialis 
brevior 


styloid  process 


II.  Metacarpal 


Fig.  158. — Third  Metacarpal  Boke. 
Note. — The  bone  is  represented  ia  the  centre  of  the  figure  in  the  position 
which  it  occupies  in  the  hand  viewed  from  the  front.     Tlie  views 
on  either  side,  and  IdcIow,  represent  respectively  the  corresponding 
surfaces  of  the  bone  turned  towards  the  spectator. 


V.  Metacarpal    /-, 


Os  magnum 

in.  Metacarpa 
Os  uiagnuni 


IV.  Metacarpal 


Fir;.  ]',<).     FoLitTH  .Mktacaiu'ai,  Bone.  Fig.  160.— Fifth  Metacarpal  Bone. 

NoTK. — Tlie  bone  in  eacli  figure  is  represented  in  the  centre  of  the  figure  in  the  fiosition  which  it  occupies  in  the 
hand  viewed  from  tlie  front.  The  views  on  either  side,  and  below,  represent  respectively  the  corresponding 
surfaces  of  tlie  bone  turned  towards  the  spectator. 

To  the  radial  side  there  are  two  half-oval  facets  ibr  the  second  metacarpal.     To 
the  ulnar  side  there  are  usually  two  small  oval  or  nearly  circular  facets  for  the 


212  OSTEOLOGY. 

fourth  metacarpal.  The  extensor  carpi  radialis  ])revior  muscle  is  inserted  into  the 
back  of  the  base. 

The  fourth  metacarpal  bone  may  l)e  recognised  by  a  method  of  exclusion.  It 
is  unlike  either  the  first,  second,  or  third,  and  differs  from  the  fifth,  which  it 
resembles  in  size,  by  having  articular  surfaces  on  both  sides  of  its  base.  Superiorly 
there  is  a  quadrilateral  surface  on  its  base  for  articulation  with  the  unciform.  On 
its  radial  side  there  are  usually  two  small  oval  facets  for  the  third  metacarpal.  Of 
these  facets  the  dorsal  one  not  infrequently  has  a  narrow  surface  for  articulation 
with  the  OS  magnum.  On  the  ulnar  side  there  is  a  narrow  articular  strip  for  the 
base  of  the  fifth  metacarpal. 

The  fifth  metacarpal  bone  can  be  recognised  by  its  size  and  the  fact  that  it 
has  only  one  lateral  articular  facet  on  its  base,  namely,  that  on  its  radial  side  for 
the  fourth  metacarpal.  The  carpal  articular  surface  is  saddle-shaped,  and  there  is 
a  tubercle  on  the  ulnar  side  of  the  base  for  the  insertion  of  the  extensor  carpi 
ulnaris  muscle. 

As  has  been  already  i3ointed  out,  the  openings  of  the  arterial  canals  are  usually  seen  on  the 
pahnar  surfaces  of  the  nietacarjjals,  those  of  the  four  inner  bones  being  directed  upwards  towards 
the  base  or  carpal  end,  differing  in  this  resjaect  from  that  of  the  first  metacarpal,  which  is  directed 
downwards  towards  the  head  or  phalangeal  extremity.  The  opening  of  the  latter  canal  usually 
lies  to  tlie  ulnar  side  of  the  palmar  aspect  of  the  shaft. 

Architecture. — Similar  in  arrangement  to  that  of  long  bones  generally,  though  it  may  be 
noted  that  the  compact  walls  of  the  shaft  are  thicker  in  proportion  to  the  length  of  the  bone 
than  in  the  other  long  bones  of  the  ujjper  extremity. 

Variations. — As  j^reviously  stated  {ante,  p.  209),  the  styloid  apoj^hysis  of  the  third  meta- 
carjjal  bone  apj^ears  as  a  separate  ossicle  in  about  1"8  jaer  cent  of  cases  examined  ("  Fourth  Annual 
Report  of  the  Committee  of  Collect.  Invest.  Anat.  Soc.  Gt.  Brit,  and  Ireland,"  Journ.  Anat.  and 
Physiol,  vol.  xxviii.  ]).  64).  In  place  of  being  united  to  the  third  raetacarj^al,  the  styloid 
ajjojihysis  may  be  fused  with  either  the  os  magnum  or  the  trapezoid,  under  which  conditions  the 
base  of"  the  third  metacarpal  bone  is  without  this  characteristic  jjrocess. 

Ossification. — Tlie  metacarpal  bones  are  developed  from  primary  and  secondary 
centres  ;  but  there  is  a  remarkable  difference  between  the  mode  of  growth  of  the  first  and 
the  remaining  four  inner  metacarpals,  for  whilst  the  shaft  and  head  of  the  first  metacarpal 
are  developed  from  the  primary  ossific  centre,  and  its  base  from  a  secondary  epiphysis,  in 
the  case  of  the  second,  third,  fourth,  and  fifth  metacarpals,  the  shafts  and  bases  are  de- 
veloped from  the  primary  centres,  the  heads  in  these  instances  being  derived  from  the 
secondary  epiphyses.  In  this  respect,  therefore,  as  will  be  seen  hereafter,  the  metacarpal 
bone  of  the  thumb  resembles  the  phalanges  in  the  manner  of  its  growth,  a  circumstance 
which  has  given  rise  to  considerable  discussion  as  to  whether  the  thumb  is  to  be  regarded 
as  possessing  three  phalanges  and  no  metacarpal,  or  one  metacarpal  and  two  phalanges. 
The  primary  centres  for  the  shafts  and  bases  of  the  second,  third,  fourth,  and  fifth  meta- 
carpals appear  in  that  order  dui'ing  the  ninth  or  tenth  week  of  intrauterine  life,  some 
little  time  after  the  terminal  phalanges  have  begun  to  ossify,  that  for  the  shaft  and  head 
of  the  metacarpal  bone  of  the  thumb  a  little  later.  At  birth  the  shafts  of  the  bones  are 
well  formed.  The  secondar}^  centres  from  which  the  heads  of  the  second,  third,  fourth, 
and  fifth  metacarpals  and  the  base  of  the  first  are  developed,  appear  about  the  third  year, 
and  usually  completely  fuse  with  the  shafts  about  the  age  of  twenty.  There  may  be  an 
independent  centre  for  the  styloid  process  of  the  third  metacarpal,  and  there  is  usually  a 
scale-like  epiphysis  on  the  head  of  the  first  metacarpal  which  makes  its  appearance  about 
eight  or  ten,  and  rapidly  unites  with  the  head. 

The  Phalanges. 

The  phalanges  or  finger  bones  (phalanges  digitorum  manus)  are  fourteen  in 
number — three  for  each  finger,  and  two  for  the  thumb. 

Named  numerically  in  order  from  the  proximal  toward  the  distal  ends  of  the 
fingers,  the  first  phalanx  (phalanx  prima),  the  longest  and  stoutest  of  the  three,  has  a 
semi-cylindrical  shaft  which  is  curved  slightly  forwards.  The  palmar  surface  is  flat, 
and  bounded  on  either  side  by  two  sharp  borders  to  which  the  sheath  of  the  flexor 
tendons  is  attached.  The  dorsal  surface,  convex  from  side  to  side;  is  overlain  by 
the  extensor  tendons.  The  proximal  end,  considerably  enlarged,  has  a  simple  oval 
concave  surface,  which  rests  on  the  head  of  its  corresponding  metacarpal  bone.  On 
either  side  of  this  the  bone  is  tubercular,  and,  affords  attachment  to  the  lateral 


THE  PHALANGES. 


213 


III. 

Phalanx, 
ungual  or 
terminal 


ligaments  of  the  metacarpo-phalangeal  joint,  and  also  to  the  interossei  muscle, 
distal  end  is  much  smaller  than  the  proximal ;  the  convex 
articular  surface  is  divided  into  two  condyles  by  a  central 
groove  running  from  before  backward.  The  second  phalanx 
(phalanx  secunda)  resembles  the  first  in  general  form,  but 
is  of  smaller  size.  It  differs,  however,  in  the  form  of  its 
proximal  articular  surface,  which  is  not  a  simple  oval  con- 
cavity, but  is  an  oval  area  divided  into  two  small,  nearly 
circular  concavities  by  a  central  ridge  passing  from  before 
backwards ;  these  articulate  with  the  condyloid  surfaces  of 
the  proximal  phalanx.  Into  the  margins  of  its  palmar 
surface  near  the  proximal  end  are  inserted  the  split 
portions  of  the  tendon  of  the  flexor  sublimis  digitorum, 
whilst  on  the  dorsal  aspect  of  the  proximal  end  the  central 
slip  of  the  extensor  communis  digitorum  muscle  is  at- 
tached. The  third,  terminal  or  ungual  phalanx  (phalanx 
tertia),  is  the  smallest  of  the  three ;  it  is  easily  recognised 
by  the  spatula-shaped  surface  on  its  distal  extremity  which 
supports  the  nail.  The  articular  surface  on  its  proximal 
end  resembles  that  on  the  proximal  end  of  the  second 
phalanx,  but  is  smaller.  On  the  palmar  aspect  of  this  end 
of  the  bone  there  is  a  rough  surface  for  the  insertion  of 
the  tendon  of  the  flexor  profundus  digitorum  muscle.  The 
dorsal  surface  of  the  same  extremity  has  attached  to  it  the 
terminal  portions  of  the  tendon  of  the  extensor  communis 
digitorum  muscle.  The  phalanges  of  the  thumb  resemble 
in  the  arrangement  of  their  parts  the  first  and  third 
phalanges  of  the  fingers. 


The 


I.  Phalanx 


Hf-ad 


Shaft 


Base 


Metacarpal 
Fig.  161. — The  Phalanges  of 
THE  Fingers  (palmar  aspect). 


The  arterial  canals,  usually  two  in  number,  placed  on  either 
side  of  the  palmar  aspect  and  nearer  the  distal  than  the  proximal 
end  of  the  bone,  are  directed  towards  the  finger-tips. 

Architecture. — Each  phalanx  has  a  medullary  cavity,  the  walls 
of  the  shaft  being  formed  of  dense  compact  bone,  especially  thick 
along  the  dorsal  aspect.     The  extremities  are  made  up  of  spongy  bone  within  a  thin  dense  shell. 

Variations. — Several  instances  have  been  recorded  of  cases  in  which  there  were  three  phalanges 
in  the  thumb.  Bifurcation  of  the  terminal  phalanges  has  occasionally  been  met  with,  and  examples 
of  suppression  of  a  phalangeal  segment  or  its  absorption  by  another  phalanx  have'  also  been  de- 
scribed (Hasselwander,  Zeits.  F.  Morph.  u.  Anthr.,  vol.  vi.  1903). 


B. 


Ossification. — The  phalanges  are  ossified  from  primary  and  secondary  centres.    From 

the  former,  which  appear  as  early  as 
the  ninth  week  of  foetal  life,  the  shaft 
and  distal  extremities  are  developed ; 
whilst  the  latter,  which  begin  to  appear 
about  the  third  year,  form  the  proximal 
epiphyses  whicli  unite  with  the  shafts 
from  eighteen  to  twenty.  Dixey  {Proc. 
Roy.  Soc,  XXX.  and  xxxi.)  has  pointed 
out  that  the  primary  centre  in  the 
ungual  phalanges  commences  to  ossify 

l.halanges  ami  the  four  inner  metacarpal  bones  are  seen.  "J^  ^^^^  '^^^^^l  P^^"^  °f  ^^^  ^""^  rather 
A  little  later.     The  centre  for  the  metacarpal  bone  of  the    ^^an  towards  the  centre  of  the  shaft. 

thumb   is  now  appearing,  and   the  centres  for  the   first    This  observation  has  been  confirmed 

by  Lambertz,  who  further  demon- 
strates the  fact  that  ossification  com- 
mences earlier  in  the  distal  phalanges 
than  in  any  of  the  other  bones  of  the 
hand.  Of  the  other  phalanges,  those 
of  the  first  row,  beginning  with  that 
of  the  third  finger,  next  ossify,  sub- 
shafts  of  the  metacarpal  bones,  whilst 


Fig.  162.  —Radiographs  op  Fcetal  Hands. 
A.  About  10  weeks.      Here  the  ossific  nuclei  of  the  terminal 


phalanges  of  the  index  and  middle  fingers  are  clearly  seen. 

C.  About  the  l)eginning  of  the  third  month.     The  centres  for  all 

the  first  row  of  ph;dang<;s  are  now  distinct,  and  the  centres 
for  the  second  jihalanges  of  tin;  index,  middle,  and  ring  fingers 
have  made  their  appeaiaiicc. 

D.  Between  the  third  and  fourth  month.     The  primary  centres 

for  all  the  phalanges  and  nH;ta(;ai])Us  are  now  well 
developed. 

sequent  to  the  appeanmco  of  ossific  centres  in  the 
15  a 


214  OSTEOLOGY. 

the  second  or  intermediate  row  of  the  phalanges  is  the  hist  to  ossify  about  the  end  of  the 
third  month. 

Sesamoid  Bones. 

Two  little  oval  nodules  (ossa  sesamoidea),  which  play  in  grooves  on  the  palmar 
aspect  of  the  articular  surface  of  the  head  of  the  first  metacarpal  bone,  are  constantly 
met  with  in  the  tendons  and  ligaments  of  that  metacarpo-phalangeal  articulation. 
Similar  nodules,  though  of  smaller  size,  are  sometimes  formed  in  the  corresponding 
joints  of  the  other  fingers,  more  particularly  the  index  and  little  finger ;  as  Thilenius 
has  pointed  out  {3forph.  Arheiten,  vol.  v.),  these  are  but  the  persistence  of  cartilaginous 
elements  which  have  a  phylogenetic  interest. 


THE   LOWEE   LIMB. 

THE  PELVIC  GIRDLE  AND  THE  LOWER  EXTREMITY. 

The  pelvic  girdle  is  formed  by  the  articulation  of  the  two  haunch  bones  with 
the  sacrum  behind,  and  their  union  with  each  other  in  front,  at  the  joint  called  the 
symphysis  pubis. 

The  Innominate  Bone. 

The  innominate  or  haunch  bone  (os  coxee)  is  the  largest  of  the  flat  bones  of  the 
skeleton.  It  consists  of  three  parts — the  ilium,  the  ischium,  and  the  pubis — 
primarily  distinct,  but  fused  together  in  the  process  of  growth  to  form  one  large 
irregular  bone.  The  coalescence  of  these  elements  takes  place  in  and  around  the 
acetabulum,  a  large  circular  articular  hollow  which  is  placed  on  the  outer  side  of  the 
bone.  The  expanded  wing-like  part  above  this  is  the  ilium ;  the  stout  V-shaped 
portion  below  and  behind  it  constitutes  the  ischium ;  while  the  > -shaped  part  to 
the  inner  side,  and  in  front  and  below,  forms  the  pubis.  The  two  latter  portions  of 
the  bone  enclose  between  them  a  large  aperture  of  irregular  outline,  called  the 
thyroid  or  obturator  foramen  (foramen  obturatorum),  which  is  placed  in  front  and 
below,  and  to  the  inner  side  of  the  acetabulum. 

The  ilium,  almost  a  quadrant  in  form,  consists  of  an  expanded  plate  of  bone, 
having  a  curved  superior  border,  the  iliac  crest  (crista  iliaca).  Viewed  from  the 
side,  this  forms  a  curve  corresponding  to  the  circumference  of  the  circle  of  which 
the  bone  is  the  quadrant ;  viewed  from  above,  however,  it  will  be  seen  to  display 
a  double  bend — convex  anteriorly  and  externally,  and  concave  posteriorly  and 
externally.  The  iliac  crest  is  stout  and  thick,  and  for  descriptive  purposes  is 
divided  into  an  outer  lip  (labium  externum),  an  inner  lip  (labium  internum),  and 
an  intermediate  surface  (linea  intermedia)  which  is  broad  behind,  narrowest  about 
its  middle,  and  wider  again  in  front.  About  2|  inches  from  the  anterior  extremity 
of  the  crest  the  outer  lip  is  usually  markedly  prominent  and  forms  a  projecting 
tubercle,  which  can  readily  be  felt  in  the  living.  Attached  to  these  surfaces  and 
lips  anteriorly  are  the  muscles  of  the  flank,  whilst  from  them  posteriorly  the 
latissimus  dorsi,  quadratus  lumborum,  and  erector  spinse  muscles  derive  their 
origins.  The  crest  ends  in  front  in  a  pointed  process,  the  anterior  superior  iliac  spine 
(spina  iliaca  anterior  superior).  To  this  the  outer  extremity  of  Poupart's  ligament 
is  attached,  as  well  as  the  sartorius  muscle,  which  also  arises  from  the  edge  of  bone 
immediately  below  it,  whilst  from  the  same  process  and  from  the  anterior  end  of 
the  outer  lip  of  the  iliac  crest  externally  the  tensor  fasciae  femoris  muscle  takes 
origin. 

The  anterior  border  of  the  ilium  stretches  from  the  anterior  superior  iliac  spine 
to  the  margin  of  the  acetabulum  below.  Above,  it  is  thin  ;  but  below,  it  forms  a 
thick  tubercular  process,  the  anterior  inferior  iliac  spine  (spina  iliaca  anterior  in- 
ferior). From  this  the  rectus  femoris  muscle  arises,  whilst  the  stout  fibres  of  the 
ilio-femoral  ligament  of  the  hip-joint  are  attached  to  it  immediately  above  the 
acetabular  margin.  Posteriorly,  the  crest  terminates  in  the  posterior  superior  iliac 
spine  (spina  iliaca  posterior  superior).  Below  this,  the  posterior  border  of  the  bone 
is  sharp  and  irregularly  notched  terminating  in  a  prominent  angle,  the  posterior 


THE  INNOMINATE  BONE. 


215 


inferior  iliac  spine  (spina  iliaca  posterior  inferior),  in  front  of  which  the  edge  of  the 
bone  becomes  thick  and  rounded,  and  forms  a  wide  notch  which  sweeps  forwards 
and  downwards  to  join  the  mass  of  bone  behind  the  acetabuhim,  where  it  becomes 
fused  with  the  ischium ;  this  is  called  the  ilio-sciatic  or  great  sciatic  notch  (incisura 
ischiadica  major). 

The  ilium  has  two  surfaces,  an  inner  and  an  outer.     The  external  surface  is 


THF,    ILTTIM 


Middle  gluteal  linf 


Posterior 
gluteal  line' 


Posterior 

SUPEllIOR 

spine 


Posterior  inferior  spine 


Groove  for  tendon  of  obturatui 
extern  us- 


Ischial  spine 


Small  sciatic  notlh 


Anterior 

SUPERIOR    spine 


Inferior  gluteal 
line 


Interior  inferior 
spine 


Acetabulum 

Ilio-pectineal  eminence 


[schial  tuberosity 


Superior  ramus 
-of  pubis 
Pubic  spine 

^ Crest  of  pubis 
Body  of  pubis- 


jNtERIOK    RAMUb    OF   PUBIS 


Ramus  of  Ischium 
Fio.  163. — The  RifiHT  Innominate  Bone  as  seen  from  the  Outer  Side. 

divided  into  two  parts,  viz.  a  lower  acetabular,  and  an  upper  gluteal  part.  The 
lower  frjrms  a  little  less  tiian  the  upper  two-fifths  of  the  acetabular  hollow,  and  is 
separated  from  the  larger  gluteal  surface  above  by  the  upper  prominent  margin  of 
the  articular  cavity.  TIk;  gluteal  surface,  broa,d  and  expand(!d,  is  concavo-convex 
from  behind  forward.  It  is  tni,vcrs(!d  hy  three  rough  curved  lines,  well  seen  in 
strongly  develop(;d  hon(;H,  hut  oi'ten  faint  and  indistinct  in  feebly  marked  speci- 
mens. Of  these  the  inferior  curved  line  (linea  glut;ea  inferior)  curves  backwards 
from  a  point  immediately  above  the  anterior  inferior  spine  towards  the  ilio-sciatic 
15  & 


216 


OSTEOLOGY. 


notch  posteriorly ;  the  bone  between  this  and  the  acetabular  margin  is  marked  by 
a  rough  shallow  groove,  from  which  the  reflected  head  of  the  rectus  femoris  muscle 
arises.  The  middle  curved  line  (linea  glutsea  anterior)  commences  at  the  crest  of 
the  ilium,  alxjut  one  inch  and  a  half  behind  the  anterior  superior  iliac  spine,  and 


Crest  of  the  ilium 


For 

posterior 
sacro-iliac 
lioamknt 


Anterior 
superior- 
SPINE 


Small  sciatic  notch 


Symphysis  pubis 


PUBIS 


ISCHIUM 

Ischial  tuberosity 


Inferior  ramus  of  pubis  Ramus  of  Ischium 

Fig.  164. — The  Right  Innominate  Bone  (Inner  Aspect). 

sweeps  backwards  and  downwards  towards  the  upper  and  posterior  part  of  the  ilio- 
sciatic  notch.  The  surface  between  this  line  and  the  preceding  furnishes  an  exten- 
sive origin  for  the  gluteus  minimus  muscle.  The  posterior  or  superior  curved  line 
(linea  glutsea  posterior)  leaves  the  iliac  crest  about  two  and  a  half  inches  in  front 
of  the  posterior  superior  iliac  spine,  and  bends  downwards  and  slightly  forwards  in 
a  direction  anterior  to  the  posterior  inferior  spine.  The  area  between  this  and  the 
middle  curved  line  is  for  the  origin  of  the  gluteus  medius  muscle,  whilst  the  rough 


THE  INNOMINATE  BONE.  217 

surface  immediately  above  and  behind  it  is  for  some  of  the  fibres  of  origin  of  the 
gluteus  maximus  muscle. 

The  inner  surface  of  the  ilium  is  divided  into  two  areas  which  present  very 
characteristic  differences.  The  posterior  or  sacral  part,  which  is  rough,  displays  in 
front  a  somewhat  smooth,  auricular  surface  (facies  auricularis)  which  is  cartilage- 
coated  in  the  recent  condition,  and  articulates  with  the  sacrum.  Above  and  behind 
this  there  is  an  elevated  irregular  area,  the  tuberosity  (tuberositas  iliaca),  which  is 
here  and  there  deeply  pitted  for  the  attachment  of  the  strong  posterior  sacro-iliac 
ligaments.  Above  this  the  bone  becomes  confluent  with  the  inner  lip  of  the  iliac 
crest,  and  here  it  affords  an  origin  to  ^he  erector  spinse  and  multifidus  spinse 
diiuscles.  The  anterior  part  of  the  inner  aspect  of  the  bone  is  smooth  and  exten- 
sive;  it  is  subdivided  by  an  oblique  ridge,  called  the  ilio- pectineal  line  (linea 
arcuata),  which  passes  forwards  and  downwards  from  the  most  prominent  point  of 
the  auricular  surface  towards  the  inner  side  of  the  ilio-pectineal  eminence  which 
is  placed  just  above  and  in  front  of  the  acetabulum,  and  marks  the  fusion  of  the 
ilium  with  the  pubis.  Above  this  the  bone  forms  the  shallow  iliac  fossa  (fossa 
iliaca),  from  the  floor  of  which  the  iliacus  muscle  arises,  whilst  leading  from  the 
fossa,  below  and  in  front,  there  is  a  shallow  furrow,  passing  over  the  superior 
acetabular  margin,  between  the  anterior  inferior  iliac  spine  on  the  outer  side  and 
the  ilio-pectineal  eminence  internally,  for.  the  lodgment  of  the  tendinous  and  fleshy 
part  of  the  ilio-psoas  muscle.  If  held  up  to  the  light  the  floor  of  the  deepest  part 
of  the  iliac  fossa  will  be  seen  to  be  formed  of  but  a  thin  layer  of  bone.  A  nutrient 
foramen  of  large  size  is  seen  piercing  the  bone  towards  the  hinder  part  of  the 
fossa.  Below  and  behind  the  ilio-pectineal  line  the  inner  surface  of  the  ilium 
forms  a  small  portion  of  the  wall  of  the  true  pelvis ;  the  bone  here  is  smooth,  and 
rounded  off  posteriorly  into  the  ilio-sciatic  notch,  where  it  becomes  confluent  with 
the  inner  aspect  of  the  ischium.  Just  anterior  to  the  ilio-sciatic  notch  there  are 
usually  the  openings  of  one  or  two  large  vascular  foramina.  From  this  surface 
arise  some  of  the  posterior  fibres  of  the  obturator  internus  muscle. 

The  ischium  constitutes  the  lower  and  hinder  part  of  the  innominate  bone. 
Superiorly  its  body  (corpus)  forms  somewhat  more  than  the  inferior  two-fifths  of 
the  acetabulum  together  with  the  bone  supporting  it  behind  and  within.  Below 
this,  the  superior  ramus  passes  downwards  and  backwards  as  a  stout  three-sided 
piece  of  bone,  from  the  inferior  extremity  of  which  a  compressed  bar  of  bone,  called 
the  inferior  ramus,  extends  forwards  at  an  acute  angle.  This  latter  unites  in  front 
and  above  with  the  descending  ramus  of  the  pubis,  and  encloses  the  aperture  called 
the  obturator  foramen. 

Superiorly,  and  on  the  outer  aspect  of  the  ischium,  the  acetabular  surface  is 
separated  from  the  bone  below  by  a  sharp  and  prominent  margin,  which  is, 
however,  deficient  in  front,  where  it  corresponds  to  the  cotyloid  notch  (incisura 
acetabuli)  leading  into  the  articular  hollow ;  the  floor  of  this  notch  is  entirely 
formed  by  the  ischium.  Below  the  prominent  acetabular  margin  there  is  a  well- 
marked  groove  in  which  the  tendon  of  the  obturator  externus  lies.  Beneath  this 
tlie  autero-external  surface  of  the  superior  and  inferior  rami  furnish  surfaces  for  the 
attachments  of  the  obturator  externus,  quadratus  femoris,  and  adductor  magnus 
muscles.  The  postero-external  surface  of  the  ischium  forms  the  convex  surface  on 
the  back  of  the  acetabulum.  The  inner  border  of  this  is  sharp  and  well  defined, 
and  is  confluent  above  with  the  border  of  the  ilium,  which  sweeps  round  the  great 
or  ilio-sciatic  notch.  From  this  border,  on  a  level  with  the  lower  edge  of  the 
acetabulum,  there  springs  a  pointed  process,  the  spine  (spina  ischiadica),  to  which  is 
attached  the  lesser  sacro-sciatic  ligament  and  the  superior  gemellus  muscle.  Inferior 
to  this,  the  postero-external  surface  narrows  rapidly,  its  inner  border  just  below  the 
spine  being  hollowed  out  to  form  the  small  sciatic  notch,  (incisura  ischiadica  minor). 
The  lower  part  of  this  surface  and  the  angle  formed  l)y  the  two  rami  are  capped  by 
an  irregularly  rough  pyriform  mass  called  tlu;  tuberosity  (tuber  ischii).  This  is 
divided  by  an  oblique  ridge  into  tw(j  an^as,  the  iqipttr  and  outer  for  the  tendon  of 
origin  of  tlie,  seiuimeinl^raiiosus  muscle,,  the  lower  and  inncsr  i'or  the  conj(jincd  lu^ads 
of  the  biceps  and  semitendinosus  muscles.  Its  prominent  inner  lip  serves  for  the 
attachment  of  the  great  sacro-sciatic  ligament,  whilst  its  outer  edge  furnishes  an 


218  OSTEOLOGY. 

origin  for  the  quadratus  feinoris  muscle ;  in  front  and  below,  the  adductor  magnus 
muscle  is  attached  to  it. 

The  inner  surface  of  the  body  and  superior  ramus  of  the  ischium  form  in  part 
the  wall  of  the  true  pelvis.  Smooth  and  slightly  concave  from  Ijefore  backwards, 
and  nearly  plane  i'rom  above  downwards,  it  is  widest  opposite  the  level  of  the  ischial 
spine.  Below  this,  its  posterior  edge  is  rounded  and  forms  a  groove  leading  to  the 
small  sciatic  notch,  along  and  over  which  the  tendon  of  the  obturator  internus 
passes.  To  part  of  this  surface  the  fibres  of  the  obturator  internus  are  attached, 
whilst  the  inner  aspect  of  the  spine  supplies  points  of  origin  for  the  coccygeus  and 
levator  ani  muscles,  as  well  as  furnishing^fin  attachment  to  the  "  wiiite  line  "  of  the 
pelvic  fascia.  The  inner  surface  of  the  inferior  ramus  of  the  ischium  is  smooth^ 
and  so  rounded  that  its  inferior  edge  tends  to  be  everted.  To  this,  as  well  as  to  its 
margin,  is  attached  the  crus  penis,  together  with  the  ischio-cavernosus,  obturator 
internus,  transversus  perinei,  and  compressor  urethrse  muscles.  In  the  female, 
structures  in  correspondence  with  these  are  also  found. 

The  fore-part  of  the  innominate  bone  is  formed  by  the  pubis ;  it  is  by  means  of 
the  union  of  this  bone  with  its  fellow  of  the  opposite  side  that  the  pelvic  girdle  is 
completed  in  front. 

The  pubis  (os  pubis)  consists  of  two  rami — a  superior,  ascending,  or  horizontal 
(ramus  superior  ossis  pubis),  and  an  inferior  or  descending  (ramus  inferior  ossis  puljis). 
The  broad  part  of  the  bone  formed  by  the  fusion  of  these  two  rami  is  the  body. 

The  body  is  sometimes  described  as  that  part  of  the  bone  which  enters  into  the 
formation  of  tlie  acetabulum,  but  the  English  nomenclature  has  here  been  followed. 

The  body  of  the  pubis  has  two  surfaces.  Of  these  the  inner  or  posterior  is 
smooth,  and  forms  the  fore-part  of  the  wall  of  the  true  pelvis ;  hereto  are  attached 
the  levator  ani  muscle  and  puboprostatic  ligaments.  The  anterior  or  external 
surface  is  rougher,  and  furnishes  origins  for  the  gracilis,  adductor  longus,  adductor 
brevis,  and  some  of  the  fibres  of  the  obturator  externus  muscles.  The  inner  border 
is  provided  with  an  elongated  oval  cartilage -covered  surface  by  means  of 
which  it  is  united  to  its  fellow  of  the  opposite  side,  the  joint  being  called 
the  symphysis  pubis.  The  upper  border,  thick  and  rounded,  projects  somewhat,  so 
as  to  overhang  the  anterior  surface.  It  is  called  the  crest.  Internally  this  forms 
with  the  inner  border  or  symphysis  the  angle,  whilst  externally  it  terminates  in  a 
pointed  process,  the  spine  (tuberculum  pubicum).  From  the  crest  arise  the  rectus 
abdominis  and  pyramidalis  muscles,  and  to  the  spine  is  attached  the  inner  end  of 
Poupart's  ligament.  Passing  upwards  and  outwards  from  the  outer  side  of  the 
body  towards  the  acetabulum,  of  which  it  forms  about  the  anterior  fifth,  is  the 
superior  ramus  (ramus  superior).  This  has  three  surfaces  :  an  antero-superior,  an 
antero- inferior,  and  an  internal  or  posterior.  The  antero-superior  surface  is 
triangular  in  form.  Its  apex  corresponds  to  the  pubic  spine ;  its  anterior  inferior 
border  to  the  obturator  crest  (crista  obturatoria),  leading  from  the  spine  to  the 
upper  border  of  the  cotyloid  notch  ;  whilst  its  sharp  postero-superior  border  trends 
upwards  and  outwards  from  the  spine,  and  is  continuous  with  the  iliac  portion  of 
the  ilio-pectineal  line  just  internal  to  the  ilio-pectineal  eminence,  forming  as  it 
passes  along  the  superior  ramus  the  pubic  portion  of  that  same  line  (pecten  ossis 
pubis).  On  this  line,  just  within  the  ilio-pectineal  eminence,  there  is  often  a  short, 
sharp  crest  which  marks  the  insertion  of  the  psoas  parvus.  The  base  of  the 
triangle  corresponds  to  the  ilio-pectineal  eminence  above  and  the  upper  margin  of 
the  cotyloid  notch  below.  Slightly  hollow  from  side  to  side,  and  convex  from 
before  backwards,  this  surface  provides  an  origin  for,  and  is  in  part  overlain  by,  the 
pectineus  muscle.  The  internal  or  posterior  surface  of  the  superior  ramus  is  smooth, 
concave  from  side  to  side,  and  slightly  rounded  from  above  downwards ;  by  its 
sharp  inferior  curved  border  it  completes  the  thyroid  foramen,  as  seen  from  behind. 
The  antero-inferior  surface  forms  the  roof  of  the  broad  obturator  groove  (sulcus 
obtaratorius)  which  passes  obliquely  downwards  and  forwards  between  the  lower 
margin  of  the  antero-superior  surface  in  front  and  the  inferior  sharp  border  of  the 
internal  surface  behind.  The  inferior  or  descending  ramus  of  the  pubis  (ramus 
inferior)   passes  downwards    and    outwards    from   the   lower   part    of  the   body. 


THE  INNOMINATE  BONE.  219 

Flattened  and  compressed,  it  unites  with  the  inferior  ramus  of  the  ischium,  and 
thus  encloses  the  thyroid  foramen,  whilst  in  correspondence  with  its  fellow  of 
the  opposite  side  it  completes  the  formation  of  the  pubic  arch.  Anteriorly  it 
furnishes  origins  for  the  gracilis,  adductor  brevis,  and  adductor  magnus  muscles, 
as  well  as  some  of  the  fibres  of  the  obturator  externus  muscle.  Its  inner  surface 
is  smooth,  whilst  its  lower  border,  rounded  or  more  or  less  everted,  has  attached  to 
it  the  fore-part  of  the  crus  penis  and  the  subpubic  ligament. 

The  acetabulum  or  cotyloid  cavity  is  the  nearly  circular  hollow  in  which  the 
head  of  the  thigh  bone  fits.  As  has  been  already  stated,  it  is  formed  by  the  fusion 
of  the  ilium  and  ischium  and  pubis  in  the  following  proportions :  the  ilium  a  little 
less  than  two-fifths,  the  ischium  somewhat  more  than  two-fifths,  the  pubis  con- 
stituting the  remaining  one-fifth.  It  is  so  placed  as  to  be  directed  downwards, 
outwards,  and  forwards,  and  is  surrounded  by  a  prominent  margin,  to  which  the 
capsule  and  cotyloid  ligament  of  the  hip  -  joint  are  attached.  Opposite  the 
obturator  foramen  this  margin  is  interrupted  by  the  cotyloid  notch  (incisura 
acetabuli) ;  immediately  external  to  the  ilio- pectineal  eminence  the  margin  is 
slightly  hollowed,  whilst  occasionally  there  is  a  feeble  notching  of  the  border 
above  and  behind.  These  irregularities  in  the  outline  of  the  margin  correspond  to 
the  lines  of  fusion  of  the  ilium  and  pubis,  and  the  ilium  and  ischium  respectively. 
The  floor  of  the  acetabulum  is  furnished  with  a  horseshoe-shaped  articular  surface, 
which  lines  the  circumference  of  the  hollow,  except  in  front,  where  it  is  interrupted 
by  the  cotyloid  notch.  It  is  broad  above ;  narrower  in  front  and  below.  Within 
this  articular  surface  there  is  a  more  or  less  circular  rough  area  (fossa  acetabuli) 
continuous  in  front  and  below  with  the  floor  of  the  cotyloid  notch.  This,  some- 
what depressed  below  the  surface  of  the  articular  area,  lodges  a  quantity  of  fat, 
and  provides  accommodation  for  the  interarticular  ligament  of  the  joint.  As  may 
be  seen  by  holding  the  bone  up  to  the  light,  the  floor  of  this  part  of  the  acetabulum 
is  not  usually  of  great  thickness.  The  major  part  of  the  non-articular  area  is 
formed  by  the  ischium,  which  also  forms  the  floor  of  the  cotyloid  notch.  . 

The  thyroid  or  obturator  foramen  (foramen  obturatum)  Hes  in  front  of, 
below,  and  internal  to  the  acetabulum.  The  margins  of  this  opening,  which  are 
formed  in  front  and  above  by  the  pubis,  and  behind  and  below  by  the  ischium,  are 
sharp  and  thin,  except  above,  where  the  under  surface  of  the  superior  ramus  of  the 
pubis  is  channelled  by  the  obturator  groove.  Below,  and  on  either  side  of  this 
groove,  two  tubercles  can  usually  be  seen.  The  one,  situated  on  the  edge  of  the 
ischium,  just  in  front  of  the  cotyloid  notch,  is  named  the  posterior  obturator 
tubercle  (tuberculum  obturatorium  posterius) ;  the  other,  placed  on  the  lower 
border  of  the  inner  surface  of  the  superior  ramus  of  the  pubis,  is  called  the 
anterior  obturator  tubercle  (tuberculum  obturatorium  anterius).  Between  these 
two  tubercles  there  passes  a  ligamentous  band,  which  converts  the  groove  into  a 
canal  along  which  the  obturator  vessels  and  nerve  pass.  Elsewhere  in  the  fresh 
condition  the  obturator  or  thyroid  membrane  stretches  across  the  opening  from 
margin  to  margin.  The  form  of  the  foramen  varies  much,  being  oval  in  some 
specimens,  in  others  more  nearly  triangular ;  its  relative  width  in  the  female  is 
greater  than  the  male. 

Nutrient  foramina  for  the  ilium  are  seen  on  the  floor  of  the  iliac  fossa,  just  in  front  of  the 
sacro-auricular  surface  ;  on  the  pelvic  aspect  of  the  bone,  close  to  the  great  sciatic  notch  ;  and  on 
the  gluteal  surface  externally,  near  the  centre  of  the  middle  curved  line.  For  the  ischiiim,  on  its 
pelvic  surface,  and  also  externally  on  the  groove  below  the  acetabulum.  For  the  pubis,  on  the 
surface  of  the  body,  and  deeply  also  from  the  acetabular  fossa. 

Connexions. — The  innominate  bone  articulates  with  the  sacrum  Ijehind,  with  the  femur  to 
tlie  outer  side  and  below,  and  with  its  fellow  of  the  opposite  side  internally  and  in  front.  Each 
of  its  thi'ee  parts  comes  into  direct  relation  with  the  surface.  Above,  the  iliac  crest  assists  in 
forming  the  iliac  furrow,  which  serves  to  separate  the  region  of  the  flank  from  that  of  the 
buttock.  In  front,  the  anterior  superior  iliac  spine  forms  a  definite  landmark  ;  whilst  behind, 
the  posterior  superior  iliac  spines  will  be  found  to  correspond  with  dimples  situated  on 
either  side  of  the  middle  line  of  the  root  of  the  back.  The  symphysis,  thcs  crest,  and  spine  of  the 
jjubis  can  all  be  distinguished  in  front,  though  overlain  by  a  considerable  quantity  of  fat, 
whilst  the  position  of  the  tuberosities  of  the;  ischia,  when  uncovei'ed  by  the  great  gluteal 
muscles  in  the  flexed  ]josition  of  the  thigh,  can  readily  be  ascertained.  Tn  the  perineal  region 
the  outline  of  the  pubic  and  ischial  rami  can  easily  be  determined  by  digital  examination. 


220 


OSTEOLOGY. 


Appears  about 
later  end  of  2nd 
m.  o1'  foetal  life 


Architecture.— As  a  flat  bone  tlie  os  innominatitm  consists  of  spongy  tissue  between  two 
compact  external  layers.  These  latter  vary  nuicli  in  thickness,  being  exceptionally  stout  along 
the  ilio-pectinal  line  and  the  floor  of  the  iliac  fossa  innuediately  above  it.  The  gluteal  aspect 
of  the  ilium  is  also  formed  by  a  layer  of  considerable  thickness.  The  spongy  tissue  is  loose  and 
cellular  in  tlie  thick  part  of  the  ilium  and  in  the  body  of  the  ischium  ;  absent  where  the  floor  of 
the  iliac  fossa  is  formed  by  the  coalescence  of  the  thin  dense  confining  layers  ;  fine  grained  and 
more  compact  in  the  tuberosity  of  the  ischium,  the  iliac  crest,  and  the  floor  of  the  acetabulum, 
in  which  latter  situation  it  is  striated  by  fibres  which  are  directed  radially  to  the  surface  of  that 
hollow,  these  again  being  crossed  at  right  angles  by  others  Avhich  are  arranged  circumferentially. 
This  spongy  tissue  forms  a  more  compact  layer  over  the  surface  of  the  upper  and  back  portion  of 
the  acetal)ular  articular  area.  The  bottom  of  the  floor  of  the  acetabulum  varies  in  thickness  ;  in 
most  cases  it  is  thin,  and  in  exceptional  instances  the  bone  is  here  deficient.  The  same  condition 
has  been  met  with  in  the  iliac  fossa,  where  absorption  of  the  thin  bony  plate  has  taken  place. 

Variations.— Some  of  the  anomalies  met  with  in  the  haunch  bone  are  due  to  ossification  of 
the  ligaments  connected  with  it ;  in  other  cases  they  depend  on  errors  of  development.  Failure  of 
union  between  the  pubic  and  ischial  rami  has  also  been  recorded.  Cases  have  occurred  where  the 
obturator  groove  has  been  bridged  across  by  bone,  and  one  case  is  noted  of  absence  of  the  cotyloid 
notch  on  the  acetabular  margin.  In  rare  cases  the  os  acetabuli  (see  Ossification)  remains  as  a 
separate  bone. 

Ossification  commences  in  the  ilium  about  the  ninth  week  of  intrauterine  life; 
about  the  fourth  month  a  centre  appears  below  the  acetabulum  for  the  ischium,  the  pubis 

being   developed   from   a 
Appears  about  15  centre  which  appears  in 

years;  fuses  22-25  ^       i-     ,i  I    i      i 

front  of  the  acetabulum 
about  the  fifth  or  sixth 
month.  At  birth  the 
form  of  the  ilium  is  well 
defined ;  the  body  and 
part  of  the  tuberosity  of 
the  ischium  are  ossified, 
as  well  as  the  horizontal 
ramusand  partof  the  body 
of  the  pubis.  All  three 
parts  enter  into  the  forma- 
tion of  the  sides  of  the 
acetabulum,  and  by  the 
third  year  have  converged 
to  form  the  bottom  of  that 
hollow,  ^  being  separated 
from  each  other  by  a  tri- 
radiate  piece  of  cartilage, 
in  which,  about  the  twelfth 
year,  independent  ossific 
centres  make  their  ap- 
pearance, which  may  or 
may  not  become  fused 
with  the  adjacent  bones.  In  the  latter  case  they  unite  to  form  an  independent  ossicle,  the 
OS  acetabuli,  which  subsequently  fuses  with  and  forms  the  acetabular  part  of  the  pubis. 
By  the  age  of  sixteen  the  ossification  of  the  acetabulum  is  usually  completed,  whilst 
the  rami  of  the  ischium  and  pubis  commonly  unite  about  the  tenth  year.  Secondary 
centres,  six  in  number,  make  their  appearance  about  the  age  of  puberty,  and  are  found  in 
the  following  situations  :  one  for  the  anterior  inferior  iliac  spine,  one  for  the  iliac  crest  and 
the  anterior  and  posterior  superior  iliac  spines,  a  scale-like  epiphysis  over  the  tuberosity  of 
the  ischium,  a  separate  epiphysis  for  the  spine  of  the  ischium,  (?)  a  point  for  the  spine 
and  another  for  the  angle  of  the  pubis.  Fusion  between  these  and  the  primary  centres 
is  usually  complete  between  the  twenty-second  and  twenty-fifth  years. 

Parsons  (Journ.  Anat.  and  Physiol.,  vol.  xxxvii.  p.  315)  regards  the  ischial  epiphysis  as 
the  homologue  of  the  hypo-ischium  in  reptiles,  and  suggests  that  the  epiphysis  over  the 
angle  of  the  pubis  may  represent  the  epipubic  bone  of  marsupials. 


Appears  about 
4th  m.  of  foetal 
life 


Appears  about  15 
years  ;  fuses  22- 
25  years 


years 
Vppears 
bout  18 
%  ears 


Unite  about  10  years 


At  Birth. 


About  12  or  13  years. 


Fig.  165. — Ossification  op  the  Innominate  Bone. 


The  Pelvis. 

The  pelvis  is  formed  by  the  union  of  the  innominate  bones  with  each  other  in 
front,   and   with    the   sacrum    behind.       In  man    the    dwarfed   caudal    vertebrae 


THE  PELVIS. 


221 


(coccygeal)  are  curved  forwards  and  so  encroach  upon  the  limits  of  the  pelvic 
cavity  inferiorly.  The  pelvis  is  divided  into  two  parts  by  the  ilio-pectineal  lines, 
which  curve  forwards  from  the  upper  part  of  the  lateral  masses  of  the  sacrum 
behind,  to  the  roots  of  the  spines  of  the  pubes  in  front.  The  part  above  is  called 
the  false  pelvis  (pelvis  major),  and  serves  by  the  expanded  iliac  fossee  to  support  the 


Fig.  166. — Male  Pelvis  as  seen  from  the  Front. 

abdominal  contents;  the  part  below,  the  true  pelvis  (pelvis  minor)  contains  the 
pelvic  viscera,  and  in  the  female  forms  the  bony  canal  through  which,  at  full  term, 
the  fcetus  is  expelled. 

The  true  pelvis  is  bounded  in  front  by  the  symphysis  pubis  in  the  middle  line, 
and  by  the  body  and  rami  of  the  pubis  on  either  side,  laterally  by  the  smooth  inner 
surfaces  of  the  ischia  and  ischial  rami,  together  with  a  small  part  of  the  ilium 


Female  Pei-vis  as  sh;h:n  from  thk  Front. 


below  the  iliac  ])ortioii  of  the  i]io-])ectincal  lino.  Springing  from  the  posterior 
margin  of  th(;  ischium  are  the  intuiried  ischial  spines.  ]iehind,  the  broad  curved 
anterior  surface  of  the  sacrum,  and  below  it,  the  small  and  irregular  coccyx,  form 
its  posterior  wall.  I'otweeii  tlu;  sides  of  the  sacrum  behind,  and  the  ischium  and 
ilium  in   front  and  above,  t-iien;  is  a  wide  interval,  culled  the  sacro-sciatic  notch, 


222  OSTEOLOaY. 

which  is,  however,  bridged  across  in  tlie  recent  condition  by  the  great  and  small 
sacro-sciatic  hgaments,  which  thus  convert  it  into  two  foramina,  the  larger  above 
the  spine  of  the  ischium — the  great  sacro-sciatic  foramen,  the  lower  and  smaller 
below  the  spine,  called  the  small  sacro-sciatic  foramen. 

The  inlet  (apertura  pelvis  superior)  of  the  pelvis  is  bounded  in  front  by  the 
symphysis  pubis,  witb  the  body  of  the  pubis  on  either  side ;  laterally  by  the  ilio- 
pectineal  lines ;  and  behind  by  the  sacral  prominence.  The  circumference  of  this 
aperture  is  often  called  the  brim  of  the  pelvis ;  in  the  male  its  shape  is  cordate,  in 
the  female  more  oval.  The  aritero-posterior  or  conjugate  diameter  is  measured  from 
the  sacro-  vertebral  angle  to  the  symphysis  pubis ;  the  oblique  diameter  from  the 
sacro-iliac  joint  of  one  side  to  the  ilio-pectineal  eminence  of  the  other ;  whilst  the 
transverse  diameter  is  taken  across  the  point  of  greatest  width. 

The  outlet  (apertura  pelvis  inferior)  is  bounded  anteriorly  by  the  pubic  arch 
(arcus  pubis),  formed  in  front  and  above  by  the  bodies  of  the  puljis,  with  the 
symphysis  between  them,  and  the  inferior  puljic  rami  below  and  on  either  side. 
These  latter  are  continuous  with  the  ischial  rami  which  pass  backwards  and 
outwards  to  the  ischial  tuberosities,  which  are  placed  on  either  side  of  this  aperture. 
In  the  middle  line  and  behind,  the  tip  of  the  coccyx  projects  forward,  and  in  the 
recent  condition  the  interval  between  this  and  the  ischial  tuberosities  is  bridged 
across  by  the  great  sacro-sciatic  ligament,  the  inferior  edge  of  which  necessarily 
assists  in  determining  the  shape  of  the  outlet. 

As  the  anterior  wall  of  the  cavity,  formed  by  the  symphysis  pubis,  measures 
from  IJ  to  2  inches,  whilst  the  posterior  wall,  made  up  of  the  sacrum  and  coccyx,  is 
from  5  to  6  inches  in  length,  it  follows  that  the  planes  of  the  inlet  and  outlet  are 
not  parallel,  but  placed  at  an  angle  to  each  other.  The  term  axis  of  the  pelvis  is 
given  to  lines  drawn  at  right  angles  to  the  centre  of  these  planes.  Thus,  with  the 
pelvis  in  its  true  position,  when  the  figure  is  erect,  the  axis  of  the  inlet  corresponds 
to  a  line  drawn  downwards  and  backwards  from  the  umbilicus  towards  the  tip  of 
the  coccyx  below,  whilst  the  axis  of  the  outlet  is  directed  downwards  and  slightly 
backwards,  or  downwards  and  a  little  forwards,  varying  according  to  the  length  of 
the  coccyx.  Between  these  two  planes  the  axis  of  the  cavity,  as  it  passes  through 
planes  of  varying  degrees  of  obliquity,  describes  a  curve  repeating  pretty  closely  the 
curve  of  the  sacrum  and  coccyx. 

Position  of  the  Pelvis. — The  position  of  the  pelvis  in  the  living  when  the  figure  is 
erect  may  be  approximately  represented  by  placing  it  so  that  the  anterior  superior  iliac 
spines  and  the  sj^mphysis  pubis  lie  in  the  same  vertical  plane.  Under  these  conditions 
the  plane  of  the  inlet  is  oblique,  and  forms  with  a  horizontal  line  an  angle  of  from  50°  to 
60°.  The  position  of  the  pelvis  depends  upon  the  length  of  the  ilio-femoral  ligaments  of 
the  hip-joint,  being  more  oblique  when  these  are  short,  as  usually  happens  in  women  in 
whom  the  anterior  superior  iliac  spines  tend  to  lie  in  a  plane  slightly  in  advance  of  that 
occupied  by  the  symphysis  pubis.  In  cases  where  the  ilio-femoral  ligament  is  long,  a 
greater  amount  of  extension  of  the  hip-joint  is  permitted,  and  this  leads  to  a  lessening  of 
the  obliquity  of  the  pelvis.  This  condition,  Avhicli  is  more  typical  of  men,  I'esults  in  the 
anterior  superior  iliac  spines  lying  in  a  plane  slightly  posterior  to  the  plane  of  the  sym- 
physis, whilst  the  angle  formed  by  the  plane  of  the  inlet  and  the  horizontal  is  theref)y 
reduced.  Bearing  in  mind  the  oblique  position  of  the  pelvis,  it  will  now^  be  seen  that  the 
front  of  the  sacrum  is  directed  downwards  more  than  forwards,  and  that  the  sacral  pro- 
montory is  raised  as  much  as  from  3^  to  4  inches  above  the  upper  border  of  the  symphysis 
pubis,  lying  higher  than  the  level  of  a  line  connecting  the  two  anterior  superior  iliac  spines. 
Fi'om  the  manner  in  which  the  sacrum  articulates  with  the  ilia,  it  will  be  noticed  that  the 
weight  of  the  trunk  is  transmitted  downwards  through  the  thickest  and  strongest  part  of 
the  bone  (see  Architecture)  to  the  upper  part  of  the  acetabula,  where  these  rest  on  the 
heads  of  the  femora. 

Sexual  Differences. — The  female  pelvis  is  lighter  in  its  construction  than  that  of 
the  male  ;  its  surfaces  are  smoother,  and  the  indications  of  muscular  attachments  less 
marked.  Its  height  is  less  and  the  splay  of  its  walls  not  so  pronounced  as  in  the  male, 
so  that  the  female  pelvis  has  been  well  described  as  a  short  segment  of  a  long  cone  as 
contrasted  with  the  male  pelvis,  which  is  a  long  segment  of  a  short  cone.  The  cavity  of 
the  true  pelvis  in  the  female  is  more  roomy,  and  the  ischial  spines  not  so  nmch  inturned. 
The  pubic  arch  is  wide  and  rounded,  and  will  usually  admit  a  right-angled-set  square 


THE  PELVIS. 


223 


being  placed  within,  so  that  the  summit  touches  the  under  surface  of  the  symphysis  pubis, 
whilst  the  sides  lie  in  contact  with  the  ischial  rami.  In  the  male  tlie  arch  is  narrow  and 
angular,  forming  an  angle  of  from  65°  to  70°.  The  sacro-sciatic  notch  in  tiie  female  is 
wide  and  shallow.  The  distance  from  the  postei'ior  edge  of  the  body  of  the  ischium  to  the 
posterior  inferior  iliac  spine  is  longer,  measuring  on  an  average  50  mm.  (2  inches)  in  tlie 
female,  as  contrasted  with  40  mm.  (1-|  inches)  in  the  male. 

The  inlet  in  the  female  is  large  and  oval  or  reniform,  as  compared  with  the  cribbed  and 
heart-shaped  aperture  in  the  male.  The  sacro-vertebral  angle  is  more  pronounced  in  the 
female,  and  the  obliquity  of  the  inlet  greater.  The  sacrum  is  shorter  and  wider.  The 
posterior  superior  iliac  spines  lie  wider  apart ;  the  pubic  crests  are  longer ;  and  the  pubic 
spines  are  separated  by  a  greater  interval  than  in  man.  The  outlet  is  larger ;  the  tubero- 
sities of  the  ischia  ai"e  farther  apart;  and  the  coccyx  does  not  project  forward  so  much. 
The  curve  of  the  sacrum  is  liable  to  veiy  great  individual  variation.  As  a  rule  the  curve 
is  more  uniform  in  the  male,  whilst  in  the  female  it  tends  to  be  flatter  above  and  more 
accentuated  below.  There  is  a  greater  proportionate  width  between  the  acetabular 
hollows  in  the  female  than  in  the  male.  Of  much  importance  from  the  standpoint  of  the 
obstetrician  ai'e  the  various  diameters  of  the  true  pelvis.  In  regard  to  this  it  is  worthy 
of  note  that  the  plane  of  "  greatest  pelvic  expansion  "  extends  from  the  union  between  the 
second  and  third  sacral  vertebrae  behind,  to  the  middle  of  the  symphysis  pubis  in  front, 
its  lateral  boundaries  on  either  side  corresponding  with  the  mid-point  of  the  inner  surface 
of  the  acetabulum  ;  whilst  the  plane  of  "least  pelvic  diameter"  lies  somewhat  lower,  and 
is  defined  by  lines  passing  through  the  sacro-coccygeal  articulation,  the  ischial  spines, 
and  the  lower  third  of  the  symphysis  pubis  (Norris).  Subjoined  is  a  table  showing  the 
principal  average  measurements  in  the  two  sexes  : — 


Males. 

Females. 

Maximum  distance  between  the  iliac  crests 
Distance   between   the   anterior   superior   iliac 

spines 
Distance   between   the   last  lumbar   sj)ine  and 

the  front  of  the  symj)hysis  pubis 

]  1|  in.,  or  282  mm. 
9|  in.,  or  240  mm. 

7  in.,  or  176  mm. 

10|  in.,  or  273  mm. 
9|  in.,  or  250  mm. 

7|  in.,  or  180  mm. 

True  Pelvis. 


Males. 

Females. 

lulet. 

Outlet. 

Inlet. 

Cavity. 

Outlet. 

Greatest.            Least. 

Antero -posterior  (conju- 
gate) diameter 
Oblique  diameter  . 

Transverse  diameter 

4  in.,  or 
101  mm. 

4|    in.,  or 
120  mm. 

5  in.,    or 
127  mm. 

3|  in.,  or 
95  mm. 

3i  in.,  or 
88  mm. 

3^  in.,  or 
88  mm. 

4f  in.,  or 
110  mm. 

5  in.,  or 
125  mm. 

5^  in.,  or 
135  mm. 

5    in.,     or 
127  mm. 

4§  in.,   or 
125  mm. 

4f   in.,  or 
110  mm. 

4|    in.,   or 
110  mm. 

4i  in.,  or 
115  mm. 

4|  in.,  or 
115  mm. 

4§  in.,  or 
110  mm. 

Growth  of  the  Pelvis. — From  the  close  association  of  the  pelvic  girdle  with  the  lower  limb 
we  find  tliat  its  growth  takes  place  concurrently  with  the  develojiment  of  that  member.  At 
birth  the  lower  limits  measure  but  a  fourth  of  the  entire  body  length  ;  consequently  at  that  time 
the  pelvis,  as  compared  with  the  head  and  trunk,  is  relatively  small.  At  this  jDeriod  of  life  the 
bladder  in  both  sexes  is  in  gi'eater  part  an  abdominal  organ,  whilst  in  the  female  the  uterus  has 
not  yet  sunk  into  the  true  pelvic  cavity,  and  the  ovaries  and  Fallopian  tubes  rest  in  the  iliac 
fo88;t.  The  sacro-vertebral  angle,  though  readily  recognised,  is  as  yet  but  faintly  marked. 
Coincident  with  the  remarkaljle  growth  of  the  lower  lindas  and  the  assumjition  of  the  erect 
position  when  the  child  begins  to  walk,  striking  changes  take  place  in  the  form  and  size  of  the 
pelvis.  Tlie.se  consist  in  a  greater  expansion  of  the  iliac  bones  necessai'ily  associated  with  the 
growth  of  the  luusclcs  which  control  the  movements  of  the  hip,  together  with  a  marked  increase 
in  the  sacro-vertel^ral  angle  due  to  the  develojuuent  of  a  forward  lumbar  curve  ;  at  the  same  time, 
the  weight  of  the  trimk  l)(;irig  thrown  on  the  sacrum  causes  the  elements  of  that  bone  to  sink  to 
a  lower  level  h(!twt;eii  the  inuoiiiiriate  bones.  The  cavity  of  the  true  pelvis  increases  in  size 
proportional! J',  and  the  vi.scera  afore-mentioned  now  begin  to  sink  down  and  have  assumed  a 
po.sitiou  within  the  pelviH  by  the  fifth  or  sixth  yeai'.      Tin;  extension  of  the  thighs   in  the 


224 


OSTEOLOGY. 


Head 


Geeat 
trochanter 


Spiral  lisk 


ujj light  position  necessarily  brings  about  a  more  pronounced  pelvic  obliquity,  whilst  the  stoutness 
and  thickness  of  the  ilium  over  the  upper  part  of  the  acetabulum  is  much  increased  to  withstand 

the  pressure  to  which  it  is  obviously  subjected. 
Coincident  with  this  is  the  gradual  development 
of  the  iliac  portion  of  the  ilio-pectineal  line, 
which  serves  in  the  adult  to  separate  sharply 
the  false  from  the  true  pelvis.  This  part  of  the 
bone  is  remarkably  strong,  as  has  been  shown 
(see  Architecture),  and  serves  to  transmit  the 
body  weight  from  the  sacrum  to  the  thigh  bone. 
The  sexual  differences  of  the  pelvis,  so  far  as 
they  refer  to  the  general  configuration  of  this 
I^art  of  the  skeleton,  are  as  jjronounced  at  the 
third  or  fourth  month  of  fostal  life  as  they  are 
in  the  adult  (Fehling,  Ztschr.  f.  Geburtsh.  u. 
Gynaek.  Bd.  ix.  and  x.  ;  A.  Thomson,  Journ. 
Anat.  and  Physiol,  vol.  xxxiii.  p.  359).  The 
rougher  appearance  of  the  male  type  is  cor- 
related with  the  more  powerful  muscular  de- 
velopment. 

The  Femur. 

The  femur  or  thigh  bone  is  remark- 
able for  its  length,  being  the  longest  bone 
in  the  body.  Superiorly  the  femora  are 
separated  by  the  width  of  the  pelvis. 
Inferiorly  they  articulate  with  the  tibia3 
and  patellae.  In  the  military  position 
of  attention,  with  the  knees  close  together, 
the  shafts  of  the  thigh  bones  occupy  an 
oblique  position.  For  descriptive  purposes 
the  bone  is  divided  into  an  upper  ex- 
tremity, comprising  the  head,  neck,  and 
two  trochanters ;  a  shaft ;  and  a  lower 
extremity,  forming  the  expansions  known 
as  the  condyles. 

The  head  (caput  femoris)  is  the  hemi- 
spherical articular  surface  which,  when 
coated  with  cartilage,  fits  into  the  aceta- 
bular hollow.    Its  pole  is  directed  upwards 
and  inwards  and  slightly  forwards.     A 
little  below    the   summit,   and    usually 
somewhat  behind  it,  is  a  hollow  oval  pit 
(fovea  capitis  femoris)  for  the  attachment 
of  the  ligamentum  teres.     The  circum- 
ference of  the  head  forms  a  lip  with  a 
wavy  outline,  more  prominent  above  and 
behind  than  in  front.     The  head  is  sup- 
ported by  a  stout  compressed  bar  of  bone, 
the  neck  (collum  fem- 
oris), which  forms  with 
the   upper  end  of  the 
shaft  an  angle  of  about 
125  degrees,  and  is  di- 
rected upwards,  inwards, 
and   a   little    forwards. 
Its  vertical  width  ex- 
ceeds   its    antero- pos- 
terior thickness.     Con- 
stricted about  its  middle, 
it  expands  internally  to 
support  the  head,  whilst  externally,  where  it  joins  the  shaft,  its  vertical  diameter  is 


External  xuBEROsiTy  — 


Adductoh 
tubercle 


Internal 
tuberosity 


External  condyle 


Patellar 
surface 


Internal  condyle 


Fig.  168. — Right  Femur  as  seen  prom  the  Front. 


THE  FEMUE. 


221 


Digital  fossa 


Great 

trochanter 
1  ubercle  of 
quadratus 
Imertroch- 

AlNTERIC  RIDGE 


Gluteai  ridge 


Apierial  foramen 


much  increased.  Anteriorly  it  is  clearly  defined  from  the  shaft  by  a  rough  ridge 
which  commences  above  on  a  prominence,  sometimes  called  the  tubercle  of  the 
femur,  and  passes  obliquely 
downwards    and    inwards.  head. 

This  constitutes  the  upper  possa  fob  lig.  teres- 
part  of  the  spiral  line  (linea 
inter  -  trochanterica),  and 
serves  for  the  attachment 
of  the  ilio-femoral  ligament 
of  the  hip-joint.  Posteriorly 
where  the  neck  unites  with 
the  shaft,  there  is  a  full 
rounded  ridge  passing  from 
the  trochanter  major  above 
to  the  trochanter  minor 
below  ;  this  is  the  posterior 
intertrochanteric  line  or 
ridge  (crista  intertro- 
chanterica).  A  little  above 
the  middle  of  this  ridge 
there  is  usually  a  fulness 
which  serves  to  indicate 
the  upper  limit  of  attach- 
ment of  the  quadratus  fem- 
oris  muscle,  and  is  called 
the  tubercle  for  the  quad- 
ratus. Externally  the  neck 
is  embedded  in  the  inner 
surface  of  the  trochanter 
major,  by  which,  at  its 
upper  and  back  part,  it  is 
to  some  extent  overhung. 
Here  is  situated  the  digital 
fossa  (fossa  trochanterica), 
into  which  the  tendon  of 
the  obtm^ator  externus  is 
inserted.  Passing  nearly 
horizontally  across  the  back 
of  the  neck  there  is  a  faint 
groove  leading  into  this  de- 
pression ;  in  this  the  tendon 
of  the  obturator  externus 
muscle  lies.  Inferiorly  the 
neck  becomesconfiuent  with 
the  trochanter  minor  be- 
hind, and  is  continuous  with 
the  inner  surface  of  the 
shaft  in  front.  The  neck 
is  pierced  by  many  vascular 
canals,  most  numerous  at 
the  upper  and  back  part. 
Some  are  directed  upwards 
towards  the  head,  whilst 
others  pass  in  the  direction 
of  the  trochanter  major. 

The  trochanter  major 
is  a  larg(;quadi7uigiilur  pi'o- 
cess  which  caps  the  ujii^er  and  outer  part  of  the  shaft,  and  overhiings  the  root  of  the 
neck  above  and  behind.     Its  outer  sv/rface,  of  rounded  irregxilar  form,  slopes  upwards 
16 


Ext.  epicondtlic  line 


Popliteal  surface 


Internal, 

TaiiEKOSITY 

Intrrnal 

condvlk     o 
Surface  for     JL 
attacli  merit 
of  posterior 
crucial  ligaminit 


-External  tuberosity 
—Surface  for  attacliment  of 
.'uit.  crucial  ligament 

RXTEBNAL  condyle 


In  1 1  l.(  ONDYLIC  NOTCH 


Fro.  109. — IlifjitT  Kkmub  as  seen  from  Biciiind. 


226 


OSTEOLOGY. 


Great 
trochanter 


Gluteal  ridge 


and  inwards,  and  is  separated  from  the  external  surface  of  the  shaft  below  by 
a  more  or  less  horizontal  ridge.  Crossing  it  obliquely  from  the  posterior  superior 
to  the  anterior  inferior  angle  is  a  rough  line  which  serves  for  the  insertion  of  the 
gluteus  medius  muscle ;  above  and  below  this  the  surface  of  the  bone  is  smoother 

and  is  overlain  by  bursae.     The 

Hi?  ATI  ^  t/ 

anterior  surf  ace,  somewhat  oblong 
in  shape,  and  inclined  obliquely 
from  ])elow  upwards  and  inwards, 
is  elevated  from  the  general  aspect 
of  the  shaft  below,  from  which  it 
is  separated  in  front  by  an  oblique 
line  leading  upwards  and  inwards 
to  the  tubercle  at  the  upper  end 
of  the  superior  part  of  the  spiral 
line.  This  surface  serves  for  the 
insertion  of  the  gluteus  minimus. 
The  superior  border  is  curved  and 
elevated  ;  into  it  are  inserted  the 
tendons  of  the  obturator  internus 
and  gemelli  muscles  within  and 
in  front,  and  the  pyriformis 
muscle  above  and  behind.  The 
posterior  border  is  thick  and 
rounded,  and  forms  the  upper  part 
of  the  posterior  intertrochanteric 
ridge.  The  angle  formed  by  the 
superior  and  posterior  borders  is 
sharp  and  pointed,  and  forms  the 
tip  of  the  trochanter  overhanging 
the  digital  fossa,  which  lies  im- 
mediately below  and  within  its 
inner  surface. 

The  trochanter  minor  is  an 
elevated  pyramidal  process  situ- 
ated at  the  back  of  the  inner  and 
upper  part  of  the  shaft  where  that 
becomes  continuous  with  the 
lower  and  posterior  part  of  the 
neck.  Confluent  above  with  the  posterior  intertrochanteric  ridge,  it  gradually  fades 
away  into  the  back  of  the  shaft  below.  The  combined  tendon  of  the  ilio-psoas  is 
inserted  into  this  process  and  the  bone  immediately  below^  it. 

The  shaft  (corpus  femoris),  which  is  characterised  by  its  great  length,  is  cylin- 
drical in  form.  As  viewed  from  the  front,  it  is  straight  or  but  slightly  curved ;  as 
seen  in  profile,  it  is  bent  forwards,  the  curve  being  most  pronounced  in  its  upper 
part.  The  shaft  is  thinnest  at  some  little  distance  above  its  middle ;  below  this  it 
gradually  increases  in  width  to  support  the  condyles  inferiorly ;  its  antero-posterior 
diameter,  however,  is  not  much  increased  below.  Its  surfaces  are  generally  smooth 
and  rounded,  except  behind,  where,  running  longitudinally  down  the  centre  of  its 
curved  posterior  aspect,  there  is  a  rough-lipped  ridge,  the  hnea  aspera  (linea  aspera). ' 
Most  s  alient  towards  the  middle  of  the  shaft,  the  linea  aspera  consists  of  an  inner 
lip  (labium  mediale)  and  an  outer  lip  (labium  laterale),  with  a  narrow  intervening 
rough  surface.  Above,  about  2  to  2h  inches  from  the  trochanter  minor,  the  linea 
aspera  is  formed  by  the  convergence  of  three  lines.  Of  these  the  outer  is  a  rough, 
somewhat  elevated,  ridge,  which  commences  above,  on  the  back  of  the  shaft,  external 
to  and  on  a  level  with  the  trochanter  minor,  and  becomes  continuous  below  with 
the  outer  lip  of  the  linea  aspera.  This  serves  for  the  bony  insertion  of  the  gluteus 
maximus,  and  is  occasionally  developed  into  an  outstanding  process  called  the 
trochanter  tertius.  Internally  the  inner  lip  of  the  linea  aspera  is  confluent  above 
with  a  line  which  winds  round  the  shaft  upwards  and  forwards  in  front  of  the 


■Vrterial  foramen 


LiXEA   ASPERA 


Fig.  170.— Back  View  of  Upper  End  of  Eioht  Femdr. 


THE  FEMUE.  227 

trochanter  minor  to  become  continuous  with  the  rough  ridge  which  serves  to  detiue 
the  neck  from  the  shaft  anteriorly  (see  ante).  The  whole  constitutes  what  is  known 
as  the  spiral  line,  and  extends  from  the  fore  and  upper  part  of  the  trochanter  major 
above  to  the  linea  aspera  below.  Intermediate  in  position  between  the  spiral  line 
in  front  and  internally,  and  the  gluteal  ridge  externally,  there  is  a  third  line, 
the  pectineal  line  (linea  pectinea),  which  passes  down  from  the  trochanter  minor 
and  fades  away  interiorly  into  the  surface  between  the  two  lips  of  the  linea  aspera. 
Into  this  the  pectineus  muscle  is  inserted.  About  the  junction  of  the  middle  with 
the  lower  third  of  the  shaft  the  two  lips  of  the  linea  aspera  separate  from  one 
another,  each  passing  in  the  direction  of  the  condyle  of  the  corresponding  side. 
The  lines  so  formed  are  called  the  inner  and  outer  epicondylic  lines  respectively,  and 
enclose  between  them  a  smooth  triangular  area  corresponding  to  the  back  of  the 
lower  third  of  the  shaft ;  this,  called  the  popliteal  surface  (planum  popliteum),  forms 
the  floor  of  the  upper  part  of  the  popliteal  space.  The  continuity  of  the  upper  part 
of  the  internal  epicondylic  line  is  but  faintly  marked,  being  interrupted  by  a  wide 
and  faint  groove  along  which  the  popliteal  artery  passes  to  enter  the  space  of  that 
name.  Below,  where  the  line  ends  on  the  upper  and  inner  surface  of  the  internal 
condyle,  there  is  a  little  spur  of  bone  called  the  adductor  tubercle,  to  which  the 
tendon  of  the  adductor  magnus  is  attached,  and  behind  which  the  inner  head  of 
the  gastrocnemius  muscle  takes  origin. 

The  linea  aspera  affords  extensive  linear  attachments  to  many  of  the  muscles  of  the  thigh. 
The  vastus  internus  arises  from  the  spiral  line  above  and  the  inner  lijD  of  the  linea  aspera  below. 
The  adductor  longus  is  inserted  into  the  inner  lip  about  the  middle  third  of  the  length  of  the  shaft. 
The  adductor  magnus  is  inserted  into  the  intermediate  part  of  the  line,  extending  as  high  as  the 
level  of  the  trochanter  minor,  where  it  lies  internal  to  the  insertion  of  the  gluteus  maximus. 
Below,  its  insertioii  2:)asses  on  the  internal  epicondylic  ridge,  reaching  as  low  as  the  adductor 
tubercle.  The  adductor  brevis  muscle  is  inserted  into  the  linea  aspera  above,  between  the  pec- 
tineus and  adductor  longus  muscles  internally  and  the  adductor  magnus  externally.  Below  the 
insertion  of  the  gluteus  maximus  the  short  head  of  the  biceps  arises  from  tlie  outer  lip  as  well  as 
from  the  external  epicondylic  line  ;  in  front  these  also  serve  for  the  origin  of  the  vastus  externus 
muscle. 

The  canals  for  the  nutrient  arteries  of  the  shaft,  which  have  an  upward  direction,  are  usually 
two  in  number,  and  are  placed  on  or  near  the  linea  aspera — the  upper  one  about  the  level  of  the 
junction  of  the  middle  and  upper  third  of  the  bone,  the  lower  some  three  or  four  inches  below — 
usually  on  the  inner  side  of  the  shaft,  immediately  in  front  of  the  inner  lip  of  the  linea  aspera. 

The  front  and  lateral  aspects  of  the  shaft  are  covered  by,  and  furnish  surfaces 
for,  the  origins  of  the  vasti  and  crureus  muscles. 

The  lower  extremity  of  the  femur  comprises  the  two  condyles.  These  are  two 
recurved  processes  of  bone,  each  provided  with  an  articular  surface,  and  separated 
behind  by  a  deep  intercondylic  notch.  United  in  front,  where  their  combined 
articular  surfaces  form  an  area  on  which  the  patella  rests,  the  two  condyles  differ 
from  each  other  in  the  following  respects  :  If  the  shaft  of  the  bone  be  held  vertically, 
the  internal  condyle  is  seen  to  reach  a  lower  level  than  the  external ;  but,  as  the 
femur  lies  ojjliquely  in  the  thigh,  the  condyles  are  so  placed  that  their  inferior  sur- 
faces lie  in  the  same  horizontal  plane.  Viewed  from  below,  the  internal  condyle  is 
seen  to  be  the  narrower  and  shorter  of  the  two.  The  external  condyle  is  broader, 
and  advances  farther  forward  and  higher  up  on  the  anterior  surface  of  the  shaft. 
The  intercondylic  notch  (fossa  intercondyloidea)  reaches  forwards  as  far  as  a  trans- 
verse line  drawn  through  the  centre  of  the  external  condyle.  Its  sides  are  formed 
by  the  inner  and  outer  surfaces  of  the  outer  and  inner  condyles  respectively,  the 
latter  bfung  more  deeply  excavated,  and  displaying  an  oval  surface  near  its  lower 
and  ant(irior  part  for  the  attachment  of  the  posterior  crucial  ligament  of  the  knee- 
joint.  Placed  high  up,  on  the  posterior  part  of  the  inner  surface  of  the  external 
condyle,  there  is  a  corresponding  surface  for  the  attachment  of  the  anterior  crucial 
ligament.  I'he  floor  of  the  notch,  which  is  pierced  by  numerous  vascular  canals, 
slop(!s  upwards  and  backwards  towards  the  ]joplit(!al  surface  on  the  back  of  the 
shaft,  from  which  it  is  H(']>aiated  by  a  slight  ridge  (linea  intcrcondyloide;!,)  to  which 
the  ])OHterior  jtart  (jf  the  ca])sule  of  the  knee-joint  is  attached. 

'i  lie  cutaneous  asp(!ct  of  each  condyle  {i.e.  the  outer  surface  of  the  external 
condyle  and  the  iriner. surface  of  the  intf^rnal  condyle)  pi'csents  an  elevated  rough 
16a 


228 


OSTEOLOGY. 


surface,  called  the  tuberosity  (epicondylus),  that  of  the  internal  (epicondylus 
medialis)  being  the  more  prouounced  and  outstanding  from  the  line  of  the  shaft ; 
capped  above  by  the  adductor  tubercle,  it  affords  attachment  near  its  most  pro- 
minent point  to  the  fibres  of  tlie  internal  lateral  ligament 
of  the  knee-joint.  The  external  tuberosity  (epicondylus 
lateralis),  less  pronounced  and  lying  more  in  line  with  the 
outer  surface  of  the  shaft,  is  channelled  behind  by  a  curved 
groove,  the  lower  rounded  lip  of  which  serves  to  separate  it 
from  the  inferior  articular  surface.  This  groove  ends  in 
front  in  a  pit  which  is  placed  just  below  the  most  salient 
point  of  the  tuberosity ;  hereto  is  attached  the  tendon  of 
the  popliteus  muscle,  which  overlies  the  lower  lip  of  the 
groove  in  the  extended  position  of  the  joint,  but  slips  into 
and  occupies  the  groove  when  the  joint  is  flexed.  Behind 
the  most  prominent  part  of  the  external 
tuberosity,  and  just  above  the  pit  for 
the  attachment  of  the  popliteus,  the 
external  lateral  Hgament  of  the  knee- 
joint  is  attached,  whilst  superior  to  that 
there  is  a  circumscribed  area  for  the  origin 
of  the  tendinous  part  of  the  outer  head 
of  the  gastrocnemius  muscle. 

The  articular  surface  on  the  lower 
extremity  is  divisible  into  three  parts — 
that  which  corresponds  to  the  inferior  surface  of  the  shaft  and  which  is  formed  by  the 
coalescence  of  the  two  condyles  in  front,  and  those  which  overlie  the  under  and 
hinder  aspects  of  each  of  those  processes.  The  former  is  separated  from  the  latter 
by  two  shallow  oblique  grooves  which  traverse  the  articular  surface  from  before 
backwards,  on  either  side,  in  the  direction  of  the  anterior  part  of  the  intercondylic 
notch.  These  furrows  are  the  impressions  in  which  fit  the  fore-parts  of  the  internal 
and  external  semilunar  cartilages  of  the  knee-joint  respectively,  when  the  knee-joint 
is  extended.  The  anterior  articular  area  or  trochlea  (facies  patellaris)  is  adapted 
for  articulation  with  the  patella.  Convex  from  above  downwards,  it  displays  a 
broad  and  shallow  central  groove,  bounded  on  either  side  by  two  slightly  convex 

surfaces.  Of  the  two  sides, 


Surface  for  the 
attachment  of- 
ext.  lateral  li 

Groove  for 
tendon  of- 
popliteus 


Fig.  171. — LowEE  End  of  Right  Femur  (Outer  Side). 


Patellar  surface 


Impression  of 
internal  semi- 
lunar cartilage 


Impression  of 
external  semi 
lunar  cartilage 

External 
tuberosity 


Semilunar 
patellar  facet 


Internal 
tibial  surface 


External 
tibial  surface 


the  external  is  the  wider 
and  more  prominent,  and 
rises  on  the  front  of  the 
bone  to  a  higher  level  than 
the  internal.  The  con- 
dyloid or  tibial  surfaces  are 
convex  from  side  to  side, 
and  convex  from  before 
backwards.  Sweeping 
round  the  under  surface 
and  posterior  extremities 
of  the  condyles,  they  de- 
scribe a  spiral  curve  more 
open  in  front  than  behind. 
The  inner  condyloid  ar- 
ticular surface  is  narrower  than  the  outer,  and  when  viewed  from  below  is  also  seen 
to  describe  a  curve  around  a  vertical  axis.  The  articular  surface  of  the  external 
condyle  is  inclined  obliquely  from  before  backwards  and  slightly  outwards.  The 
surfaces  of  the  condyles  above  the  articular  area  posteriorly  are  confluent  superiorly 
with  the  popliteal  surface  of  the  shaft ;  from  these  areas  the  heacis  of  the  gastro- 
cnemius muscles  arise.  The  bone  from  which  the  inner  head  of  the  muscle  springs 
is  often  elevated  in  the  form  of  a  tubercle  placed  on  the  lower  part  of  the  popliteal 
surface  of  the  shaft,  just  above  the  internal  condyle.  The  proportionate  length  of 
the  femur  to  the  body  height  is  as  1  is  to  3-53-3'92. 


Ext.  condyle 
Intercondylic  notch 


Int.  condyle 


Surface  of  attachment  of  posterior 
crucial  ligament 


Fig.  172. — Lower  End  of  Right  Femur  as  seen  from  Below. 


THE  FEMUE.  229 

Arterial  Foramina. — Numerous  vascular  canals  are  seen  in  the  region  of  the  neck,  at  the 
bottom  of  the  digital  fossa,  on  the  posterior  intercondylic  ridge  and  on  the  external  surface  of 
the  great  trochanter.  The  nutrient  arteries  for  the  shaft  pierce  the  bone  on  or  near  the  linea 
aspera.  Both  back  and  front  of  the  lower  end  of  the  shaft  display  the  openings  of  numerous 
vascular  canals,  and  the  floor  of  the  intercondylic  notch  is  also  similarly  pierced. 

Connexions. — The  femur  articulates  witli  the  os  innominatum  above  and  the  tibia  and  patella 
below.  The  external  surface  of  the  great  trochanter  determines  the  point  of  greatest  hip  width 
in  the  male,  being  covered  only  by  the  skin  and  sujjerlicial  fascia  and  the  aponeurotic  insertion  of 
the  gluteus  maximus.  In  the  erect  position  the  tijj  of  the  trochanter  corresponds  to  the  level  of 
the  centre  of  the  hip -joint.  When  the  thigh  is  flexed  the  trochanter  major  sinks  under  cover 
of  the  anterior  fibres  of  the  gluteus  maximus.  In  women  the  hip  width  is  usually  greatest  at 
some  little  distance  below  the  trochanter,  due  to  the  accumulation  of  fat  in  this  region.  The 
shaft  of  the  bone  is  surrounded  on  all  sides  by  muscles.  Its  forward  curve,  however,  is  account- 
able to  some  extent  for  the  fulness  of  the  front  of  the  thigh.  The  exposed  surfaces  of  the  condyles 
determine  to  a  large  extent  the  form  of  the  knee.  In  flexion  the  articular  edges  can  easily  be 
recognised  on  either  side  of  and  below  the  patella. 

Architecture. — The  shaft  has  a  medullary  cavity  which  reaches  as  high  as  the  root  of  the 
small  trochanter.  Inferiorly  it  extends  to  within  3^  inches  of  the  lower  articular  surface.  In 
the  upper  half  the  outer  compact  wall  is  very  thick,  but  below  the  middle  of  the  shaft  it 
gradually  thins  until  it  reaches  the  condyles  inferiorly,  over  which  it  passes  as  a  thin,  hardly 
definable  external  layer.  Above,  it  is  especially  thick  along  the  line  of  the  linea  aspera,  and 
here  the  large  nutrient  canal  may  be  seen  passing  obliq^uely  upwards  in  the  substance  of  the 
dense  bone  for  the  space  of  two  inches.  In  the  upper  end  of  the  shaft  the  osseous  lamellae 
springing  from  the  sides  of  the  medullary  cavity  arch  inwards  towards  the  centre,  intersecting 
each  other  in  a  manner  comparable  to  the  tracery  of  a  Gothic  window.  The  lower  wall  of  the 
neck  is  thick  below,  near  the  trochanter  minor,  but  thins  rapidly  before  it  reaches  the  head. 
From  this  aspect  of  the  neck  there  spring  a  series  of  oblique,  lamellae  which  pass  upwards  and 
inwards,  spreading  in  fan-shaped  manner  into  the  under  surface  of  the  head.  These  are 
intersected  above  by  lamellae  which  arch  inwards  from  the  outer  side  of  the  shaft  below  the 
great  trochanter,  as  well  as  from  the  under  surface  of  the  thin  but  compact  outer  shell  of  the 
upper  surface  of  the  neck,  the  whole  forming  a  bracket-like  arrangement  which  assists  materially 
in  adding  to  the  strength  of  the  neck.  Further  support  is  given  by  the  addition  of  a  spur  of 
dense  bone  which  springs  from  the  inner  surface  of  the  under  side  of  the  neck,  just  in  front  of 
and  above  the  trochanter  minor  :  this  is  called  the  calcar  femorale.  From  it  stout  lamellai  having 
a  vertical  direction  arise.  The  spongy  tissue  of  the  head  and  great  trochanter  is  finely 
reticulated,  that  of  the  lower  part  of  the  neck  and  upper  part  of  the  shaft  being  more  open  in  its 
texture.  Passing  vertically  downwards  through  this  tissue  there  is  a  vascular  canal,  the  orifice 
of  which  opens  externally  on  the  floor  of  the  digital  fossa. 

The  spongy  tissue  of  the  lower  part  of  the  shaft  is  more  delicate  and  uniform  in  its 
arrangement,  displaying  a  more  or  less  parallel  striation  in  a  longitudinal  direction.  Subjacent 
to  the  articular  surface  the  tissue  is  rendered  more  compact  by  the  addition  of  lamellae  disposed 
in  curves  in  harmony  with  the  external  aspect  of  the  bone. 

Variations. — Absence  of  the  pit  on  the  head  of  the  femur  for  the  attachment  of  the 
ligamentum  teres  has  been  recorded.  This  corresponds  with  the  condition  met  with  in  the 
orang.  Not  infrequently  there  is  an  extension  of  the  articular  surface  of  the  head  on  to  the  fore 
and  upper  aspect  of  the  neck  ;  this  is  a  "  pressure  facet "  caused  by  the  contact  of  the  iliac  portion 
of  the  acetabular  margin  with  the  neck  of  the  bone,  when  the  limb  is  maintained  for  long  periods 
in  the  flexed  position,  as  in  tailors,  and  also  in  those  races  who  habitually  squat  (Lane,  Journ. 
Anat.  and  Physiol.,  vol.  xxii.  p.  606). 

The  occurrence  of  a  trochanter  tertius  has  been  already  referred  to.  Its  presence  is  not  con- 
fined to  individuals  of  powerful  physique,  but  may  occur  in  those  of  slender  build,  so  far 
suggesting  that  it  is  not  to  be  regarded  merely  as  an  indication  of  excessive  muscular  develop- 
ment. The  observations  of  Dixon  {Journ.  Anat.  and  Physiol.,  vol.  xxx.  p.  502),  who  noted  the 
occurrence  of  a  separate  epiphysis  in  three  cases  in  connexion  with  it,  seem  to  point  to  its 
possessing  some  morphological  significance. 

Occasionally  the  gluteal  ridge  may  be  replaced  by  a  hollow,  the  fossa  hypotrochanterica,  or  in 
some  cases  the  two  may  co-exist. 

The  angle  of  the  neck  is  more  open  in  the  child  than  in  the  adult,  and  tends  to  be  less 
when  the  femoral  length  is  short  and  the  pelvic  width  great — conditions  which  particularly 
appertain  to  the  female.  There  is  no  evidence  to  show  that  after  growth  is  cpmpleted  any 
alteration  takes  place  in  the  angle  with  advancing  years  (Humphry). 

The  curvature  of  the  shaft  may  undergo  considerable  variations,  and  the  appearance  of  the 
posterior  surface  of  the  Vjone  may  )je  modified  by  an  absence  of  the  linea  aspera,  a  condition 
re.seni];ling  that  seen  in  apes ;  or  by  an  unusual  elevation  of  the  bone  which  supjjorts  the  ridge 
(Jemur  a  piluHtre),  produced,  as  Manouvrier  has  suggested,  by  the  excessive  development  of  the 
muscles  here  attached. 

Under  tlie  term  '■^ jilafymerie,"  Manouvrier  descril:)es  an  antero-posterior  compression  of  the 
U2)pei'  part  of  the  shaft,  frequently  met  with  in  the  femora  of  prehistoric  races. 

Ossification. — 'I'lie  sluU't  begins  to  ossify  early  in  the  second  mouth  of  foetal  life,  and  at 

Inrth  disphiys  enlargements  ut  Vjoth  ends,  which  are  capped  with  cartilage.     If  the  inferior 

cartilaginous  end  be  sliced  away,  a  small  ossific  nucleus  for  the  inferior  epiphysis  will  usually 

be  seen.     This,  as  a  rule,  makes  its  appearance  towards  the  latter  end  of  the  ninth  month 

IGi 


230 


OSTEOLOGY. 


of  foetal  life,  and  is  at  service  from  a  medico-legal  standpoint  in  determining  the  age  of  the 
foetus.  According  to  Hartman,  it  is  absent  in  about  12  per  cent  of  children  at  term,  and 
may  appear  as  early  as  the  eighth  month  of  foetal  life  in  about  7  per  cent.     The  superior 

extremity,     entii'ely     carti- 


,„„ „i^„„f     Fuse-)  -with  slialt 

Appears  about      ,      .  ^  ^  .  „ 

early  part  of    *"°'r  ^ 


early  part 
first  year 


Appears  about 
2-3  vpar 


Usually  appears  in 
the  9th  month  of 
foetal  life 


laginous  at  birth,  comprises 
the  head,  neck,  and  tro- 
chanter major.  A  centre 
appeai-s  for  the  head  during 
the  early  part  of  the  first 
year.  That  for  the  tro- 
chanter major  begins  to 
ossify  about  the  second  or 
third  year,  whilst  the  neck 
is  developed  as  an  upward 
extension  of  the  shaft,  which 
is,  however,  not  confined  to 
the  neck  alone,  but  forms  the 
lower  circumference  of  the 
articular  head,  as  may  be 
seen  in  bones  up  to  the  age 
of  twelve  or  sixteen ;  after 
that,  the  separate  epiphysis 
of  the  head  begins  to  over- 
lap it  so  as  to  cover  it  en- 
tirely when  fusion  is  com- 
plete at  the  age  of  eighteen 
or  twenty. 

The  epiphysisof  thegreat 
trochanter  unites  with  the 
shaft  and  neck  about  eigh- 
teen or  nineteen,  whilst  the 
epiphysis  for  the  trochanter  minor,  which  usually  makes  its  appearance  about  the  twelfth 
or  thirteenth  year,  is  usually  completely  fused  with  the  shaft  about  the  age  of  eighteen. 
The  epiphysis  for  the  lower  end,  although  the  first  to  ossify,  is  not  completely  united  to 
the  shaft  until  from  about  the  twentieth  to  the  twenty-second  year.  It  is  worthy  of  note 
that  the  line  of  fusion  of  the  shaft  and  inferior  epiphysis  passes  through  the  adductor 
tubercle,  a  point  which  can  easily  be  determined  in  the  living. 


Usually  appear 
before  birth 


At  birth. 


Fuses  with  shaft  about  20-22  years 
About  12  years.  About  16  years. 

Fig.  173. — Ossification  of  Femue. 


The  Patella. 

The  patella,  the  largest  of  the  sesamoid  bones,  overlies  the  front  of  the  knee- 
joint  in  the  tendon  of  the  quadriceps  extensor.  Of  compressed  form  and  somewhat 
triangular   shape,  its 

1  1  •      4.  Extern  \i    \RTirrLAR  facet 

lower  angle  projects 
downwards  and  forms 
a  peak,  called  the 
apex  (apex  patellse), 
whilst  its  upper  edge, 
or  "base  (basis  patellse), 
broad,  thick,  and 
sloping  forwards  and 
a  little  downwards,  is 
divided  into  two  areas 
by  a  transverse  line 
or  groove ;  the  an- 
terior area  so  defined 
serves  for  the  attach- 
ment of  the  common 
tendon  of  the  quad- 
riceps extensor  muscle,  whilst  the  posterior,  of  compressed  triangular  shape,  is 
covered  by  synovial  membrane.  The  inner  and  outer  borders,  of  curved  outline, 
receive  the  insertions  of  the  vastus  internus  and  externus  muscles  respectively,  the 


Fig. 


a.  Anterior  surface. 


Surface  for  the  liganientum  patellfe 
174, — Eight  Patella. 

B.  Posterior  surface. 


THE  TIBIA. 


231 


attachment  of  the  vastus  internus  being  more  extensive  than  that  of  the  vastus 
externus.  The  anterior  surface  of  the  bone,  slightly  convex  in  both  diameters,  has  a 
fibrous  appearance,  due  to  its  longitudinal  striation,  and  is  pierced  here  and  there 
by  the  openings  of  vascular  canals.  The  posterior  or  femoral  articular  surface  is 
divided  into  two  unequal  parts  (of  which  the  external  is  the  wider)  by  a  vertical 
elevation  which  glides  in  the  furrow  of  the  trochlear  surface  of  the  femur,  and  in 
extreme  flexion  passes  to  occupy  the  intercondylic  notch.  The  outer  of  the  two 
femoral  surfaces  is  slightly  concave  in  both  its  diameters ;  the  inner,  though 
slightly  concave  from  above  downwards,  is  usually  plane,  or  somewhat  convex  trans- 
versely. Occasionally,  in  the  macerated  bone,  indications  of  a  third  vertical  area 
are  to  be  noted  along  the  inner  edge  of  the  internal  aspect.  This  defines  the  X->art 
of  the  articular  surface  which  rests  on  the  border  of  the  internal  condyle  in 
extreme  flexion. 

Below  the  femoral  articular  area  the  deep  surface  of  the  apex  is  rough  and 
irregular ;  the  greater  part  of  this  is  covered  by  synovial  membrane,  the  liga- 
mentum  patellse  being  attached  to  its  summit  and  margins,  reaching  some  little 
distance  round  the  borders  on  to  the  anterior  aspect  of  this  part  of  the  bone. 

Architecture. — The  bone  consists  of  a  tliick  dense  layer  anteriorly,  which,  thins  towards  the 
edges  on  either  side  and  below  ;  above,  it  corresponds  to  the  area  of  insertion  of  the  quadriceps. 
The  femoral  articular  surface  is  composed  of  a  layer  of  compact  bone,  thickest  in  correspondence 
with  the  vertical  elevation.  Sandwiched  between  these  two  layers  is  a  varying  thickness  of 
spongy  tissue  of  fairly  close  grain,  the  striation  of  which  on  cross  section  runs  in  parallel  lines 
from  back  to  front ;  on  vertical  section  the  tissue  appears  to  be  arranged  in  lines  passing  radially 
from  the  deep  surface  of  the  femoral  area  to  the  more  extensive  anterior  dense  plate. 

Variations. — Cases  of  congenital  absence  of  the  patella  have  been  recorded. 

F.  C.  Kempson  {Joum.  Anat.  and  Physiol,  vol.  xxxvi.)  has  recently  drawn  attention  to  the 
condition  described  as  emargination  of  the  patella.  In  specimens  displaying  this  appearance  the 
margin  of  the  bones  is  concave  from  a  point  about  half  an  inch  to  the  outer  side  of  the  middle 
line,  to  a  point  half-way  down  the  outer  margin  of  the  bone,  here  there  is  usually  a  pointed 
spine  directed  upwards  and  outwards.  The  condition  appears  to  be  associated  with  the  insertion 
of  the  tendon  of  the  vastus  externus.  G.  Joachimstal  {Archiv  u.  Atlas  der  nomalen  und  xiatholo- 
gischen  Anatomie  in  typischen  Rontgenbildern,  Bd.  8)  figures  a  case  in  which  on  both  sides  the 
patella  was  double  in  an  adult,  the  lower  and  much  the  smaller  portion  was  embedded  in  the 
ligamentum  patellse. 

Ossification. — The  patella  is  laid  down  in  cartilage  about  the  third  month  of  foetal 
life.  At  birth  it  is  cartilaginous,  and  the  tendon  of  the  quadriceps  is  continuous  with  the 
ligamentum  patellee  over  its  anterior  surface,  and  can  easily  be  dissected  off.  About  the 
third  year  an  ossific  centre  appears  in  it  and  spreads  more  particularly  over  its  deeper 
surface.     Ossification  is  usually  completed  by  the  age  of  puberty. 


The  Tibia 


It  is  much  stouter  and  stronger  than  its 


The  tibia  is  the  inner  bone  of  the  leg. 
neighbour  the  fibula, 
with  which  it  is 
united  above  and  be- 
low. By  its  superior 
expanded  extremity 
it  supports  the  con- 
dyles of  the  femur, 
while  inferiorly  it 
shares  in  the  forma- 
tion of  the  ankle-joint, 
articulating  with  the 
upper  surface  and 
inner  side  of  the  as- 
tragalus. 

The  superior  ex- 
tremity com  firisfis  the 
inner  and  outer  tuberosities,  the  spine,  and  the  tubercle.  Each  tuberosity  is 
provided  on  its  upper  aspect  with  an  articular  surface  (facies  articularis 
superior),  which  supports  the  corresponding  femoral  condyle,  as  well  as  the 
V>c 


Surface  for  attachment  of  anterior 
extremity  of  internal  semilunar  fartilage 
Anterior  crucial  ligament 

Spine 


Internal 
tuberosity 


Synovial  ruRvrn 

SURKAf  1 

Surface  for  attacli   of  post   pxHpmi 
of  internal  semilunar  cartilage 


.'01  I  ITI  Al 
NO  1 1  II 

Post,  crucial  ligament 


Surf  for  attachment 
of  ant  extremity  of 
external  semilunar  cart. 


External 
tuberosity 


iifice  for  attach,  of 
post   (  \tremity  of 
(  \t(  III  il  semilunar 
caitil  i„( 


Fk;.    17.5. — Ul'I'ER    SURKACK    OK    SUPERIOH    EXTREMITY    OK    RKJHT    TIBFA. 


232 


OSTEOLOGY. 


Ilio-tibial  baiifl 


Spine 


External 

tubeeohitv 


Internal 
tuberosity 


Subcutaneous 
internal 

SURFACE 


interposed    semilunar    cartilage.        Of    these    two     condylic    surfaces    the    inner 
is  the  larger;  of  oval  shape,  its  long  axis  is  placed  antero-posteriorly.     Slightly 

concave  from  before  backwards  and 
from  side  to  side,  its  circumference 
rises  in  the  form  of  a  sharp  and 
well-defined  edge.  The  outer  condylic 
surface  is  smaller  and  rounder. 
Slightly  concave  from  side  to  side, 
and  gently  convex  from  before  back- 
wards, its  circumference  is  well  de- 
fined in  front,  but  is  rounded  off 
behind,  thus  markedly  increasing 
the  convexity  of  its  posterior  part. 
Between  the  two  condylic  surfaces 
the  bone  is  raised  in  the  centre  to 
form  the  spine  (eminentia  intercon- 
dyloidea),  the  summit  of  which  is 
grooved  and  capped  on  either  side 
by  tubercles  which  spring  from  and 
are  formed  by  the  upward  extension 
of  the  neighbouring  condylic  areas. 
Of  these  tubercles  the  inner  (tuber- 
culum  intercondyloideum  mediale) 
is  the  higher,  and  longer  in  an 
antero-posterior  direction,  the  outer 
(tuberculum  intercondyloid- 
eum laterale)  being  more  pointed 
and  not  so  elevated.  In  front  and 
behind  the  spine  the  articular  areas 
are  separated  by  two  irregular 
V-shaped  surfaces,  the  intercondylic 
fossse.  The  anterior  fossa  (fossa  inter- 
condyloidea  anterior),  the  larger  and 
wider,  furnishes  areas  for  the  attach- 
ment of  the  semilunar  cartilages  on 
either  side,  and  for  the  anterior 
crucial  ligament  immediately  in  front 
of  the  spine.  The  floor  of  this  space 
is  pierced  by  many  nutrient  foramina. 
The  posterior  intercondylic  fossa 
(fossa  intercondyloidea  posterior)  is 
concave  from  side  to  side,  and  slopes 
downwards  and  backwards.  The 
external  semilunar  cartilage  is  at- 
tached near  its  apex  to  a  surface 
which  rises  on  to  the  back  of  the 
spine  ;  the  internal  semilunar  carti- 
lage is  fixed  to  a  groove  which  runs 
along  its  inner  edge,  and  the  pos- 
terior crucial  ligament  derives  an 
attachment  from  the  smooth  posterior 
rounded  surface. 

The  external  tuberosity  (condylus 
lateralis)  is  the  smaller  of  the  two. 
It  overhangs  the  shaft  to  a  greater 
extent  than  the  internal,  though 
this  is  obscured  in  the  living  by  its 
articulation  ^^•ith  the  fibula.  The  facet  for  the  fibula,  often  small  and  indistinct, 
is  placed  postero-externally  on  the    under   surface  of  its  most  projecting  part. 


Interosseous 

RIDGE 


Surface  foe  ex- 
tensors OF  ANKLE 


Surface  for 
flexors  of  ankle 


Internal 
malleolus 


176. — Right  Tibia  and  Fibula  as  seen  from 
THE  Front. 


THE  TIBIA.  233 

Antero-externally  the  imprint  caused  by  the  attachment  of  the  ilio-tibial  band 
is  often  quite  distinct.  The  circumference  of  the  internal  tuberosity  (condylus 
medialis)  is  grooved  postero-internally  for  tlie  insertion  of  the  tendon  of  the  semi- 
membranosus. 

In  front  of  the  tuberosities,  and  about  an  inch  below  the  level  of  the  condylic  sur- 
faces, there  is  an  oval  elevation  called  the  tubercle  of  the  tibia,.or  the  anterior  tuberosity 
(tuberositas  tibiae).  The  upper  half  of  this  is  smooth  and  covered  by  a  bursa,  while 
the  lower  part  is  rough  and  serves  for  the  attachment  of  the  ligamentum  patellte. 

Considered  in  its  entirety,  the  upper  extremity  of  the  tibia  is  broader  trans- 
versely than  antero-posteriorly,  and  is  inclined  backwards  so  as  to  overhang  the 
shaft  posteriorly. 

The  shaft  (corpus  tibiai)  is  irregularly  three-sided.  It  is  narrowest  about  the 
junction  of  its  middle  and  lower  thirds,  and  expands  above  and  below  to  support 
the  extremities,  liunning  down  the  front  of  the  bone  there  is  a  gently-curved, 
prominent  margin  confluent  above  with  the  tubercle,  but  fading  away  inferiorly  on 
the  anterior  surface  of  the  lower  third  of  the  bone,  where  it  may  be  traced  in  the 
direction  of  the  anterior  border  of  the  internal  malleolus.  This  is  the  crest  or  sMn 
(crista  anterior),  which  is  subcutaneous  throughout  its  entire  length.  To  the 
inner  side  of  this  is  a  smooth,  slightly  convex  surface,  which  reaches  as  high  as  the 
internal  tuberosity  above,  and  inferiorly  becomes  continuous  with  the  inner  surface 
of  the  internal  malleolus.  This  is  the  internal  or  subcutaneous  surface  (facies 
medialis)  of  the  shaft,  which  is  covered  only  by  skin  and  superficial  fascia,  except 
in  its  upper  fourth,  where  the  tendons  of  the  sartorius,  gracilis,  and  semitendinosus 
muscles  overlie  it,  as  they  pass  towards  their  insertions.  This  surface  is  limited 
posteriorly  by  the  internal  border  (margo  medialis)  which  passes  from  the  inner  and 
under  surface  of  the  internal  tuberosity  above  to  the  hinder  border  of  the  internal 
malleolus  below.  This  border  is  rounded  and  indefinite  above  and  below,  beins; 
usually  best  marked  about  its  middle  third.  To  the  outer  side  of  the  tibial  crest  is  the 
external  surface  of  the  bone  (facies  lateralis);  it  is  limited  behind  by  a  straight  vertical 
ridge,  the  crista  interossea,  to  which  the  interosseous  membrane,  which  occupies  the 
interval  between  the  tibia  and  the  fibula,  is  attached.  This  ridge  commences  above, 
near  the  middle  of  the  outer  and  under  surface  of  the  external  tuberosity,  and 
terminates  below  about  two  inches  above  the  lower  extremity  by  dividing  into  two 
lines,  which  separate  and  enclose  between  them  the  surface  for  articulation  with 
the  lower  end  of  the  fibula,  and  the  area  of  attachment  of  the  inferior  interosseous 
ligament,  which  here  unites  the  two  bones.  In  its  upper  two-thirds  the  external 
surface  provides  an  extensive  origin  for  the  tibialis  anticus.  Inferiorly,  where  the 
tibial  crest  is  no  longer  well  defined,  the  external  surface  turns  forward  on  to  the 
front  of  the  shaft,  and  is  limited  inferiorly  by  the  anterior  margin  of  the  inferior 
articular  surface.  Over  this  the  tendon  of  the  tibialis  anticus,  and  the  combined 
fleshy  and  tendinous  parts  of  the  extensor  proprius  hallucis  and  extensor  com- 
munis digitorum  muscles  pass  obliquely  downwards.  The  posterior  surface  (facies 
posterior)  of  the  shaft  lies  between  the  interosseous  ridge  externally  and  the  in- 
ternal border  on  the  inner  side.  Its  contours  are  liable  to  considerable  variation 
according  to  the  degree  of  lateral  compression  of  the  bone.  It  is  usually  fuU  and 
rounded  above,  and  flat  below.  Superiorly  it  is  crossed  by  the  oblique  or  popliteal 
line  (linea  poplitea),  which  runs  downwards  and  inwards,  from  the  fibular  facet 
above,  to  the  internal  border  on  a  level  with  the  junction  of  the  middle  with  the 
upper  third  of  the  shaft.  To  this  line,  as  well  as  to  the  internal  border  for  some 
distance  below  it,  the  soleus  muscle  is  attached.  Into  the  bulk  of  the  triangular 
area  above  it  the  popliteus  muscle  is  inserted.  Arising  from  the  middle  of  the 
popliteal  line  there  is  a  vertical  ridge,  which  passes  downwards  and  divides  the 
posterior  asj^ect  of  the  shaft  into  two  surfaces — an  external  for  the  tibial  origin  of 
the  tibialis  posticus  muscle,  and  an  internal  for  the  flexor  longus  digitorum  muscle. 
The  inferior  third  of  this  surface  of  the  shaft  is  free  I'rom  muscular  attachments, 
but  is  overlain  Ity  the  tendons  of  the  above  muscles,  together  with  that  of  the  Hexor 
longus  hallucis.  A  large  nutrient  canal,  having  a  downward  direction,  opens  on  the 
posterior  surface  of  the  shaft  a  little  })elow  the  ])opliteal  line  and  just  external  to 
the  vertical  ridge  which  springs  from  it. 


234  OSTEOLOGY. 

The  inferior  extremity  of  the  tibia  displays  an  expanded  quadrangular  form. 
It  is  famished  with  a  saddle-shaped  articular  surface  on  its  under  surface  (facias 
articularis  inferior),  which  is  concave  from  before  backwards  and  slightly  convex 
from  side  to  side.  This  rests  upon  the  superior  articular  surface  of  the  body  of  the 
astragalus,  and  is  bounded  in  front  and  behind  by  well-defined  borders.  The 
anterior  border  is  the  rounder  and  thicker,  and  is  oftentimes  channelled  by  a  groove 
for  the  attachment  of  the  anterior  ligament  of  the  joint ;  further,  it  is  occasionally 
provided  with  a  pressure  facet  caused  by  the  locking  of  the  bone  against  the  neck 
of  the  astragalus  in  extreme  flexion.  Externally  the  edge  of  the  articular  urea 
corresponds  to  the  base  of  the  triangle  formed  by  the  splitting  of  the  interosseous 
ridge  into  two  parts.  Where  these  two  lines  join  it,  both  in  front  and  behind,  the 
bone  is  elevated  into  the  form  of  tubercles,  in  the  hollow  between  which"  (iiicisura 
fibularis)  the  lower  end  of  the  fibula  is  lodged,  being  held  in  position  by  powerful 
ligaments.  The  cartilage-covered  surface  occasionally  extends  for  some  little 
distance  above  the  base  of  the  triangle.  Internally  there  is  a  down-projecting 
process,  called  the  internal  malleolus  (malleolus  medialis),  the  inner  aspect  of  which 
is  subcutaneous  and  forms  the  projection  of  the  inner  ankle.  Its  external  surface 
is  furnished  with  a  pyriform  facet  (facies  articularis  malleolaris),  confluent  above 
with  the  cartilage -covered  area  on  the  inferior  extremity  of  the  shaft;  this 
articulates  with  a  corresponding  area  on  the  inner  surface  of  the  body  of  the 
astragalus.  Inferiorly  the  malleolus  is  pointed  in  front,  but  notched  behind  for 
the  attachment  of  the  internal  lateral  ligament  of  the  ankle.  Running  obliquely 
along  the  posterior  surface  of  the  malleolus  there  is  a  broad  groove  (sulcus 
malleolaris)  in  which  the  tendons  of  the  tibialis  posticus  and  flexor  longus 
digitorum  muscles  are  lodged ;  whilst  a  little  to  the  fibular  side  of  this,  and 
running  downwards  over  the  posterior  surface  of  the  lower  extremity  of  the  bone, 
there  is  another  groove,  often  faintly  marked,  for  the  lodgment  of  the  tendon  of 
the  flexor  longus  hallucis  muscle.  The  proportionate  length  of  the  tibia  to  the 
body  height  is  as  1  is  to  4-32-4-80. 

Arterial  Foramina. — Nutrient  canals  are  seen  piercing  tlie  upper  extremity  of  the  bone 
around  its  circumference  and  above  the  tubercle.  The  floors  of  the  intercondylic  fosste  are  also 
similarly  pierced,  and  there  is  usually  a  canal  of  large  size  opening  on  the  summit  of  the  spine. 
Two  or  three  foramina  of  fair  size  are  seen  running  upwards  into  the  substance  of  the  bone  a  little 
below  and  to  the  inner  side  of  the  tubercle,  while  the  principal  vessel  for  the  shaft  passes  down- 
wards into  the  bone  on  its  posterior  surface,  about  the  level  of  the  junction -of  the  iqjper  and 
middle  thirds.  The  inner  surface  of  the  internal  malleoluis,  as  well  as  the  anterior  and  jDosterior 
borders  of  the  inferior  extremity,  are  likewise  pitted  by  the  orifices  of  small  vascular  channels. 

Connexions. — Superiorly  the  tibia  supports  the  condyles  of  the  femur,  and  is  connected  in 
front  with  the  patella  by  means  of  the  patellar  ligament.  Articulating  externally  with  the 
fibula  above  and  below,  it  is  united  to  that  bone  throughout  nearly  its  entire  length  by  the  inter- 
osseous membrane.  The  crest  and  internal  surface  can  be  readily  examined,  as  they  are  sub- 
cutaneous, except  above  where  the  internal  surface  is  overlain  by  the  thin  tendinous  aponeurosis 
of  the  muscles  passing  over  the  inner  side  of  the  knee.  The  form  of  the  lower  part  of  the  knee  in 
front  is  determined  by  the  tuberosities  on  either  side  crossed  mesially  by  the  ligamentum  patellae. 
Inferiorly  the  internal  malleolus  forms  the  jirojection  of  the  inner  ankle,  Avhich  is  wider,  not  so 
low,  less  23ointed,  and  placed  in  advance  of  the  projection  of  the  outer  ankle.  The  front  and 
back  of  the  lower  end  of  the  bone  are  crossed  by  tendons,  which  mask  to  a  certain  extent  its 
form. 

Architecture. — The  shaft  of  the  bone  is  remarkable  for  the  thickness  and  density  of  the 
osseous  tissue  which  underlies  the  crest.  The  posterior  wall  is  stout,  but  the  internal  and 
external  walls  are  thinner.  The  several  walls  are  thickest  oj^j^osite  the  middle  of  the  shaft,  and 
thin  out  above  and  below  where  the  shaft  unites  with  the  epiphyses.  The  medullary  canal, 
narrow  and  circular  in  the  middle  of  the  bone,  increases  in  all  its  diameters  above  and  below, 
and  reaches  to  within  2^  to  3  inches  of  either  extremity.  Superiorly  the  arrangement  of 
the  lamellse  of  the  spongy  tissue  resembles  a  series  of  arches  sjiringing  from  the  dense  outer  walls. 
These  form  a  jalatform  on  which  the  superior  epijjhysis  rests,  tlie  sjjongy  tissue  of  which  disjDlays 
a  more  or  less  vertical  striation.  This  is  much  more  compact  under  the  condylic  surfaces,  the 
superficial  aspect  of  which  is  formed  by  a  thin  layer  of  dense  bone.  The  spine  and  tubercle  are 
also  formed  of  compact  tissue,  whilst  the  circumference  of  the  tuberosities  is  covered  by  a 
thinner  and  less  dense  wall.  In  the  lower  end  of  the  shaft  the  spongy  tissue,  of  a  loose  and 
cellular  character,  is  arranged  in  vertical  fibres,  blending  inferiorly  with  the  closer  tissue  of  the 
inferior  epiphysis,  the  articular  surface  of  which  is  covered  by  a  thin  but  dense  layer. 

In  the  adult  bone  the  nutrient  canal  for  the  shaft  is  embedded  in  the  dense  posterior  wall  for 
the  space  of  two  inches. 

Variations  — The  tibia  is  often  unduly  laterally  conqjressed,  leading  to  an  increase  in  its 


THE  FIBULA. 


Appears 
before  birth 


May  appeal 
independently 
about  11  }  ears 


antero-posterior  diameter  as  compared  with  its  transverse  width.  This  condition  is  more 
commonly  met  with  in  the  bones  of  i^rehistoric  and  savage  races  than  in  modern  Europeans. 
Attention  was  first  directed  to  this  particular  form  by  Busk,  who  named  the  condition 
platycnemia.  The  general  appearance  of  such  tibite  resembles  that  seen  in  the  apes,  and 
depends  on  an  exceptional  development  of  the  tibialis  posticus  muscle,  though,  as  Manouvrier 
has  pointed  out,  in  apes  this  is  associated  with  the  direct  action  of  the  muscle  on  the  foot,  as  in 
climbing,  whereas  in  man,  as  a  consequence  of  the  bipedal  mode  of  progression,  the  muscle  is 
employed  in  an  inverse  sense,  viz.  by  steadying  the  tibia  on  the  foot,  and  thus  providing  a  fixed 
base  on  which  the  femur  can  move.  Such  platycnemic  tibise  are  occasionally  met  with  in  the 
more  highly  civilised  races,  and  are,  according  to  Manouvrier,  associated  with  habits  of  great 
activity  among  the  inhabitants  of  rough  and  mountainous  districts. 

Another  interesting  condition  is  one  in  which  the  upper  extremity  is  more  strongly  recurved 
than  is  usuaL  This  retroversion  of  the  head  of  the  tibia  was  at  one  time  supposed  to  represent 
an  intermediate  condition  in  which  the  knee  could  not  be  fully  extended  so  as  to  bring  the  axis 
of  the  leg  in  line  with  the  thigh  ;  but  such  opinion  has  now  been  upset  by  the  researches  of 
Manouvrier,  who  claims  that  it  is  the  outcome  of  a  habit  not  uncommon  amongst  peasants  and 
countrymen,  viz.  that  of  walking  habitually  with  the  knees  slightly  bent. 

Habitual  posture  also  leaves  its  impi'ess  on  the  form  of  the  tibia,  and  in  races  in  which  the 
use  of  the  chair  is  unknown,  the  extreme  degree  of  flexion  of  the  knee  and  ankle  necessitated  by 
the  adoption  of  the  squatting  position  as  an  attitude  of  habitual  rest  is  associated  with  an  increase 
in  the  convexity  of  the  external  condylic  surface,  and  the  appearance,  not  infrequently,  of  a 
pressure  facet  on  the  anterior  border  of  the  lower  extremity,  which  rests  in  that  position  on  the 
neck  of  the  astragalus.     Cases  of  con-  ^  .^-u  -^  ^^  ^    x  «^  ^- 

.,11  ?  ±1      j_-T  •      ^  1  Fuses  With  shaft  about  20-24  years 

genital  absence  oi  the  tibia  have  been 

frequently  described,  amongst  the  most 

recent  being  those  recorded  by  Glutton, 

Joachimsthal,  Bland  Sutton,  and  Waitz. 

Ossification. — The  shaft  begins  ^ 
to  ossify  early  in  the  second  month  | ; 
of  intrauterine  life.  At  birth  it  is  o 
well  formed,  and  capped  above  and  f 
below  by  pieces  of  cartilage,  in  the 
upper  of  Avhich  the  centre  for  the 
superior  epiphysis  has  already  usually 
made  its  appearance.  From  this  the 
tuberosities  and  tubercle  are  de- 
veloped, though  sometimes  an  inde- 
pendent centre  for  the  latter  appears 
about  the  eleventh  or  twelfth  years, 
rapidly  joining  with  the  already  well- 
developed  mass  of  the  I'est  of  the 
epiphysis.  Complete  fusion  between 
the  superior  epiphysis  and  the  shaft 
doesnot  take  place  until  the  twentieth 
or  the  twenty-fourth  year.  The  centre 
for  the  lower  ai*ticular  surface  and  the 
internal  malleolus  makes  its  appearance  about  the  end  of  the  second  year,  and  union 
with  the  shaft  is  usually  complete  by  the  age  of  eighteen.  Lambertz  notes  the  occasional 
presence  of  an  accessory  nucleus  in  the  malleolus. 


Appears  about  1^  yeais 

Fubes  about  Ibth  yeai 
At  birth.  About  12  years.  About  16  years. 

Fig.  177. — Ossification  op  the  Tibia. 


The  Fibula. 

The  fibula,  or  peroneal  bone,  is  a  slender  bone  with  two  enlarged  ends.  It  lies 
to  the  outer  side  of  the  tibia,  with  which  it  is  firmly  united  by  ligaments,  and  nearly 
equals  that  hone  in  length. 

The  first  difficulty  which  the  student  has  to  overcome  is  to  determine  which  is  the  upper  and 
which  the  lower  extremity  of  the  bone.  This  can  easily  be  done  by  recognising  the  fact  that 
there  is  a  deep  pit  on  the  inner  aspect  of  the  lower  extremity  immediately  behind  the  triangular 
articular  surface.  Holding  the  bone  vertically  with  the  lower  extremity  downwards  and  so 
turned  that  the  triangular  articular  area  lies  in  front  of  the  notch  already  spoken  of,  the 
subcutaneou.s  non-articular  aspect  of  the  inferior  extremity  will  point  to  the  side  to  which  the 
bone  bslongs. 

The  superior  extremity  or  head  of  the  fi})ula  (capitulum  fihiila3),  of  irregular 
rounded  form,  is  bcvolled  on  its  innc^r  surface  so  as  to  adapt  it  to  the  form  of  the 
under  surface  of  tlie  external  tuberosity  ol'  the  tibia.     At  the  border,  where  this 


236 


OSTEOLOGY. 


IXT.    CON'DYLIC 
SURFACF 


oxdylic  surfaci:: 
Popliteal 

NOTCH 


Oblique  li\ 


SUEFACE  FOE  EX- 


surface  becomes  confluent  with  the  outer  aspect  of  the  head,  there  is  a  pointed 

upstanding  eminence  called  the 
styloid  process  (apex  capituli 
fibuhe) ;  to  this  the  short  external 
lateral  ligament  is  attached,  as 
well  as  a  piece  of  the  tendon  of  the 
biceps,  which  is  inserted  into  its 
fore  -  part.  Immediately  to  the 
inner  side  of  this,  and  occupying 
the  summit  of  the  internal  sloping- 
surface,  there  is  an  articular  area 
(facies  articularis  capituli),  of  vari- 
able size  and  more  or  less  triangular 
shape.  This  serves  for  articulation 
with  the  external  tuberosity  of  the 
tibia.  The  long  external  lateral 
ligament,  together  with  the  re- 
mainder of  the  tendon  of  the  biceps 
muscle  which  surrounds  it,  is  at- 
tached to  the  outer  and  upper  side 
of  the  head  in  front  of  the  styloid 
process.  In  front  and  behind  the 
head  there  are  usually  prominent 
tubercles.  The  anterior  of  these 
is  associated  with  the  origin  of 
the  peroneus  longus  muscle ;  the 
TENsoEs  OF  ANKLE  postcrlor,  whllst  fumlshing  an 
origin  for  the  upper  fibres  of  the 
soleus,  serves  to  deepen  the  groove, 
behind  the  superior  tibio- fibular 
articulation,  in  which  the  tendon 
and  fleshy  part  of  the  popliteus 
muscle  play.  The  constricted  por- 
tion of  the  shaft  below  the  head 
is  often  referred  to  as  the  neck ; 
around  the  outer  side  of  this  the 
external  popliteal  nerve  winds. 

The  shaft  of  the  fibula  (corpus 
fibulse)  presents  many  varieties  of 
shape  and  form,  being  ridged  and 
channelled  in  such  a  way  as  greatly 
to  increase  the  difficulties  of  the 
student  in  recognising  the  various 
surfaces  described.  The  most  im- 
portant point  is  first  to  determine 
the  position  of  the  interosseous 
ridge.  Holding  the  bone  in  the 
position  which  it  normally  occupies 
in  the  leg,  it  will  be  noticed  that 
the  external  surface  of  the  lower 
extremity  is  limited  in  front  and 
behind  by  two  lines,  which,  con- 
verging above,  enclose  between 
them  a  triangular  subcutaneous 
area  which  lies  immediately  above 
the  outer  ankle.  From  the  summit 
of  the  triangle  so  formed  a  well- 
defined  ridge  may  be  traced  up  the  front  of  the  shaft  to  reach  the  anterior  aspect 
of  the  head.     This  is  the  anterior  lorder,  and  must  not  be  mistaken  for  the  inter- 


POSTERIOE    &IRF\CE 


Groove  foe/ 
flexor  lonoi7s 
hallucis 


Geoo\-e  for 
tendons  of 
peroneus 
longus  and 

P.REVIS 

External 

malleolus 


Fig.  178.- 


-RiGHT  Tibia  axd  Fibula  as  seen  from 
Behind. 


THE  FIBULA. 


237 


STVr.OID  PROCESS 


Neck- 


Interosseous  ridge  - 


osseous  ridge,  which  is  now  easy  to  find,  for  the  next  ridge  which  lies  immediately 
internal  to  the  anterior  border,  or  towards  the  tibial  side 
on  the  anterior  aspect  of  the  bone,  is  the  line  to  which 
the  interosseous  membrane  is  attached.  As  a  rule  these  ^^^t  for  tibia. 
two  lines  are  separated  by  a  considerable  interval  in  the 
lower  half  of  the  bone,  but  tend  to  run  much  closer 
together  above ;  indeed  it  is  not  uncommon  to  find  that 
they  coalesce  to  form  a  single  crest.  Let  it  therefore  be 
clear  that  the  interosseous  line  is  that  which  lies  im- 
mediately internal  to  the  ridge  which  springs  inferiorly 
from  the  malleolar  subcutaneous  triangular  surface,  not- 
withstanding the  differences  in  width  of  the  surface  which 
separates  the  lines,  or  their  occasional  coalescence  above. 
The  position  of  the  interosseous  ridge  enables  us  at 
once  to  separate  the  flexor  aspect  of  the  bone  from  its 
extensor  surface,  using  these  terms  in  relation  to  the 
movements  of  the  ankle. 

The  use  of  these  terms  is  not,  strictly  speaking,  correct,  and 
they  are  here  used  in  a  physiological  and  not  in  a  morphological 
sense.  The  anterior  surface  of  the  leg  is  the  true  extensor  surface, 
and  is  comparable  with  the  posterior  surface  of  the  forearm,  the 
change  in  position  having  been  brought  about  developmentally  by 
difference  in  the  rotation  of  the  limbs.  Flexion  of  the  ankle,  so 
called,  is  in  reality  an  extensor  movement,  and  corresjDonds  to 
extension  at  the  wrist.  (See  Humphry,  Journ.  Anat.  and  Physiol., 
vol.  xxviii.  p.  15.) 

In  addition,  there  is  the  peroneal  surface,  which 
corresponds  to  the  outer  side  of  the  shaft.  Starting  then 
at  the  interosseous  ridge,  and  passing  forwards  round 
the  outer  side  of  the  shaft,  the  flexor  surface  is  the  first 
met  with ;  this  is  bounded  externally  by  the  anterior 
border,  and,  as  has  been  said,  may  be  either  of  considerable 
width  or  almost  linear.  From  this  arises  the  extensor 
communis  digitorum,  together  with  the  peroneus  tertius 
and  the  extensor  proprius  hallucis  muscles,  which,  though 
extensors  of  the  toes,  are  also  flexors  of  the  ankle. 

The  anterior  border  serves  for  the  attachment  of  the 
intermuscular  septum,  which  separates  the  foregoing 
group  of  muscles  from  that  which  lies  along  the  outer 
side  of  the  shaft,  viz.  the  peroneus  longus  and  brevis 
muscles.  The  surface  from  which  these  arise  is  limited 
behind  by  the  posterior  border,  which  is  usually  sharp 
and  well  defined  below,  where  it  is  continuous  with  the 
bone  immediately  above  the  pit  on  the  inner  surface  of 
the  lower  extremity,  whilst  it  tends  to  be  less  distinct 
and  more  rounded  above  where  it  runs  into  the  base  of 
the  styloid  y^rocess.  In  its  upper  third  or  fourth  this 
border  is  often  rough  and  tubercular  where  it  serves  for 
the  origin  of  the  soleus.  The  outer  or  peroneal  surface 
is  somewhat  twisted,  being  directed  rather  forwards 
above,  but  tending  to  turn  backwards  below  where  it 
Vjecomes  continuous  with  the  groove  which  courses  along 
the  back  of  the  external  malleolus  and  which  lodges  the 
tendons  of  the  peroneus  longus  and  brevis  muscles.  The 
remainder  of  the  shaft,  included  between  the  posterior 
border  behind  and  the  inttsrosseous  ridge  in  front  and 
internally,  is  the  extensor  surface,  for  here  arise  the 
several  muscles  whose  action  in  part  is  to  extend  tlie  ankle.  Tliis  surface  is 
cut  up  by  a  curved  ridge  often  the  most  prominent  and  outstanding  on  the  bone. 


Interosseous_ 

RIDGE 


ffi 


Rough  surface 

for  inter-_ 

osseous" 

ligament 

Facet  for 

astragalus- 

03    OJ    O    S   °    H    H 

m  5  <  o  H  S  !J 


EXTEIINAL 
MALLEOLUS 

Fro.  179.— RioHT  FjiiULA  as 

SKKN    FROM    THU    iNNHIl    SiDK. 


238  OSTEOLOGY. 

aud  hence  frequently  mistaken  by  the  student  Tor  the  interosseous  ridge ;  it  serves 
to  define  the  area  for  the  origin  of  the  tibiahs  posticus,  and  arises  below  from  the 
posterior  border  of  the  interosseous  ridge  at  the  junction  of  the  middle  and  inferior 
thirds  of  the  shaft,  curves  a  little  backwards,  and  passing  upwards  and  oljliquely 
forwards  again  joins  the  interosseous  ridge  once  more  in  the  region  of  the  neck. 
This  is  oftentimes  called  the  internal  border  (crista  mediahs) ;  and  the  surface  so 
mapped  off,  the  internal  surface.  The  ridge  itself  serves  for  the  attachment 
of  the  aponeurosis  which  covers  the  tibialis  posticus  muscle.  The  remainder  of 
the  extensor  aspect  of  the  shaft,  which,  above,  is  directed  backwards,  is  so  twisted 
that  inferiorly  it  is  directed  inwards.  From  this,  in  its  upper  part,  the  soleus 
muscle  arises ;  whilst  lower  down,  the  iiexor  longus  hallucis  muscle  derives  an 
extensive  origin.  Both  of  these  muscles,  together  with  the  tibialis  posticus,  act  as 
extensors  of  the  ankle.  On  this  aspect  of  the  bone,  at  or  near  the  middle  of  the 
shaft,  and  just  behind  the  prominent  tibial  ridge,  is  the  opening  of  the  nutrient 
canal,  which  has  a  downward  direction. 

The  inferior  extremity  of  the  fibula,  or  external  malleolus  (malleolus  lateralis), 
is  of  pyramidal  form.  Its  inner  surface  is  i'urnished  with  a  triangular  articular 
area  (facies  articularis  malleoli),  plane  from  before  backwards,  and  slightly  convex 
from  above  downwards,  which  articulates  with  a  corresponding  surface  on  the  outer 
side  of  the  body  of  the  astragalus.  Behind  this  there  is  a  deep  pit,  to  which  the 
posterior  fasciculus  of  the  external  lateral  ligament  is  attached.  Above  the 
articular  facet  there  is  a  rough  triangular  area  on  the  extensor  surface  of  the  shaft, 
from  the  summit  of  which  the  interosseous  ridge  arises ;  hereto  are  attached  the 
strong  fibres  of  the  inferior  interosseous  ligament  which  binds  together  the  opposed 
surfaces  of  the  tibia  and  fibula.  The  external  surface  of  the  inferior  extremity 
forms  the  elevation  of  the  external  malleolus  which  determines  the  shape  of  the 
projection  of  the  outer  ankle.  Eounded  from  side  to  side  and  from  above  down- 
wards, it  terminates  below  in  a  pointed  process,  which  reaches  a  lower  level  than 
the  corresponding  process  of  the  tibia,  from  which  it  also  differs  in  being  narrower 
and  more  pointed  and  being  placed  in  a  plane  nearer  the  heel.  Superiorly,  tliis 
surface,  which  is  subcutaneous,  is  continuous  with  the  triangular  subcutaneous  area 
so  clearly  defined  by  the  convergence  above  of  the  lines  which  unite  to  form  the 
anterior  border.  The  anterior  border  and  tip  of  the  external  malleolus  furnish 
attachments  to  the  anterior  and  middle  bands  of  the  external  lateral  ligament  of 
the  ankle.  The  posterior  surface  of  the  external  malleolus,  broad  above,  where 
it  is  confiuent  with  the  peroneal  or  external  surface,  is  reduced  in  width  below 
by  the  presence  of  the  pit  which  lies  to  its  inner  side.  This  aspect  of  the 
bone  is  grooved  (sulcus  malleolaris)  by  the  tendons  of  the  peroneus  longus  and 
brevis  muscles,  which  curve  round  the  posterior  and  lower-pointed  aspect  of  the 
malleolus.  The  proportionate  length  of  the  fibula  to  the  body  height  is  as  1  is  to 
4-37-4-82. 

Arterial  Foramina. — Nvimerous  minute  vascular  canals  are  seen  piercing  the  outer  surface  of 
the  head,  and  one  or  two  of  larger  size  are  seen  on  the  inner  surface  immediately  in  front  of  the 
superior  articular  facet.  The  canal  for  the  nutrient  artery  of  the  shaft,  which  has  a  downward 
direction,  is  situated  on  the  back  of  the  bone  about  its  middle.  The  outer  surface  of  the  external 
malleolus  displays  the  openings  of  many  small  canals,  and  one  or  two  larger  openings  are  to  be 
noted  at  the  bottom  of  the  pit  behind  the  inferior  articular  surface. 

Connexions. — The  head  and  external  malleolus,  and  jjart  of  the  shaft  immediately  above  the 
latter,  are  subcutaneous.  The  remainder  of  the  shaft  is  covered  on  all  sides  by  the  muscles  which 
surround  it.  Superiorly  the  bone  plays  no  part  in  the  formation  of  the  knee-joint,  but  inferiorly 
assists  materially  in  strengthening  the  ankle-joint  by  its  union  with  the  tibia  and  its  articulation 
with  the  astragalus.  In  position  the  bone  is  not  parallel  to  the  axis  of  the  tibia,  but  oblique  to 
it,  its  ujjper  extremity  lying  posterior  and  external  to  a  vertical  line  passing  through  the  external 
malleolus. 

Architecture. — A  medullary  canal  luns  throughout  the  length  of  the  shaft,  reaching  as  high 
as  the  neck  above,  and  extending  as  low  as  a  point  about  2^  inches  above  the  inferior  extremity 
of  the  external  malleolus.  The  oiiter  wall  of  the  shaft  is  usually  considerably  thicker  than  the 
inner.  The  head  is  formed  of  loose  cellular  bone,  enclosed  within  a  very  thin  dense  enveloj^e.  The 
spongy  tissue  of  the  lower  extremity  is  more  compact,  and  acquires  considerable  density  on  the 
surfaces  underlying  the  articular  area  and  the  pit  behind  it.  The  canal  for  the  nutrient  artery  of 
the  shaft  ojiens  into  the  medullary  cavity  about  an  inch  below  its  external  aperture. 


THE  ASTEAGALUS. 


239 


Appears  about 
3-4  years 


Fuses  with  shaft 
about  20-24  years 


Ossification. — The  shaft  begins  to  ossify  about  the  middle  of  the  second  month  of 
foetal  life.  At  the  end  of  the  third  month  there  is  but  little  difference  in  size  between  it 
and  the  tibia,  and  at  birth  the  fibula  is  much 
larger  in  projDortion  to  the  size  of  the  tibia  than 
in  the  adult.     Its  extremities  are  cartilaginous, 

the   lower  extremity  not  being  as   long  as  the  <g 

internal  malleolar  cartilage  of  the  tibia.     It  is  in  '^ 

this,  however,  that  an  ossiiic  centre  first  appears  't 

about  the  end  of  the  second  year,  which  increases  'z 

rapidly  in  size,  and  unites  with  the  shaft  about  5 

nineteen   years.      The  centre    for    the   superior  | 

epiphysis  begins    to   ossify  about    the    third  or  -e 

fourth   year,  and   union  with  the    shaft    is  not  Z 

complete    until  a  period    somewhat    later   than  ^ 

that   for  the  inferior    epiphysis.      The  mode  of  1 

ossification  of  the  lower  extremity  is  an  exception  ^ 

to  the  general  rule  that  epiphyses  which  are  the  J 

first  to  ossify  are  the  last  to  unite  with  the  shaft,  t 

In  its  earlier  stages  of  development  it  has  been 
stated,  on  the  authority  of  Leboticq,  Gegenbaur 
and  others,  that  the  fibula  as  well  as  the  tibia  is  in 
contact  with  the  femur.  This  is,  however,  denied  by 
Grunbaum  ("Proc.  Anat.  Soc,"  Journ.  Anat.  and 
Physiol,  vol.  xxvi.  j).  22),  who  states  that  after  the 
sixth  week  the  fibula  is  not  in  contact  with  the 
femur,  and  that  i^rior  to  that  date  it  is  impossible 
to  differentiate  the  tissue  which  is  to  form  femur 
from  that  which  forms  fibula. 

Variations. — The  fibula  may  be  ridged  and 
grooved  in  a  remarkable  manner,  as  is  the  case  in  many  bones  of  prehistoric  races.  This  is 
probably  associated  with  a  greater  or  perhaps  more  active  development  of  the  muscles  attached 
to  it. 

The  superior  articular  facet  varies  much  in  size.  Bennett  {Dublin  Journ.  Med.  Sc,  Aug. 
1891)  records  a  case  in  which  it  was  double,  and  also  notes  the  occurrence  of  specimens  in  which 
it  was  absent  and  in  which  the  head  of  the  bone  did  not  reach  as  high  as  the  tibial  tuberosity. 

Many  instances  of  partial  or  complete  absence  of  the  bone  have  been  published.  (Lefebre, 
Gontribution  a  V^hule  de  l' absence  congenitale  du  peron^,  Lille,  1895.) 


Ajjpears  about 
2nd  year 


At 
birth. 

Fig.  180.- 


Fuses  with  shaft 
about  19  years. 

About 
16  vears. 


Aboiit 
12  years. 

-Ossification  of  Fibula. 


BONES  OF  THE  FOOT. 

The  bones  of  the  foot,  twenty-six  in  number,  are  arranged,  in  three  groups :  the 
tarsal,  seven  in  number  :  the  metatarsal,  five  in  number ;  the  phalanges,  fourteen 
in  number. 

Comparing  the  foot  with  the  hand,  the  student  will  be  struck  with  the  great  pro- 
portionate size  of  the  tarsus  as  compared  with  the  carpus,  and  the  reduction  in  size 
of  the  bones  of  the  toes  as  compared  with  the  fingers.  The  size  of  the  metatarsal 
segment  more  nearly  equals  that  of  the  metacarpus. 

The  Tarsus. 

The  tarsus  fossa  tarsi)  consists  of  seven  bones — the  astragalus,  os  calcis,  navi- 
cular or  scaphoid,  three  cuneiforms,  and  the  cuboid.  Of  irregular  form  and  varying 
size,  thej  may  be  described  as  roughly  cubical,  presenting  for  examination  dorsal 
and  plantar  surfaces  as  well  as  anterior,  posterior,  internal,  and  external  aspects. 


The  Astragalus. 

The  astragalus  Ttalus)  is  the  bone  through  which  the  liody  weight  is  trans- 
mitted from  the  leg  above  to  the  foot  below.  Superiorly  the  tibia  rests  upon  it, 
whilst  on  either  side  it  articulates  with  the  internal  and  external  malleolar  processes 
of  the  tibia  and  fibula  respectively  ;  inferiorly  it  overlies  the  os  calcis,  and  anteriorly 
it  articulates  with  the  navicular.  For  descriptive  purposes  the  bone  is  divisible  into 
two  ]jurts  —  the  body  i^corpus  tali)  blended  in  front  with  tlie  neck  Tcollum  tali), 
which  supports  tlie  head  ('caput  tali;. 


240 


OSTEOLOG-Y. 


Cuboid 


The  %ipx>er  surface  of  the  body  is  provided  with  a  saddle-shaped  articular  surface 
(trochlea  tali),  broader  in  front  than  behind,  for  articulation  with  the  under  surface 
of  the  tibia.  The  inner  edge  of  the  trochlea  is  straight ;  whilst  the  outer  border, 
which  is  sharp  in  front  and  more  rounded  behind,  is  curved  inwards  posteriorly' 

wliere  it  is  Ijevelled  to 
form  a  narrow,  elon- 
gated, triangular  facet, 
which  is  in  contact  with 
the  transverse  or  in- 
ferior tibio-fibular  liga- 
ment during  flexion  of 
the  ankle  (Fawcett,  Ed. 
Med.  Journ.,  1895). 
Over  the  outer  border 
the  cartilage  -  covered 
surface  is  continuous 
externally  with  an  ex- 
tensive area  of  the  form 
of  a  quadrant.  This  is 
concave  from  above 
downwards,  and  articu- 
lates with  the  inner 
surface  of  the  filjular 
malleolus.  The  inferior 
angle  of  this  area  is 
prominent  and  some- 
what everted,  and  some- 
times referred  to  as  the 
external  process  (proces- 
sus lateralis  tali).  The 
inner  aspect  of  the  body 
has  a  comma -shaped 
facet,  confluent  with 
the  superior  articular 
surface,  over  the  inner 
edge  of  the  trochlea ; 
this  articulates  with 
the  outer  surface  of  the 
tibial  malleolus.  In- 
ferior to  this  facet  the 
bone  isroughand  pitted 
hj  numerous  small 
openings,  and  just  below 
the  tail  of  the  comma 
there  is  a  circular  im- 
pression for  the  attach- 
ment of  the  deep  fibres 
of  the  internal  lateral 
ligament.  On  the  in- 
ferior surface  of  the 
body  there  is  a  deep 
concave  facet,  called 
the  posterior  calcanean 
facet  (facies  calcanea 
articularis  posterior),  which  is  of  more  or  less  oval  or  oblong  form  and  is  placed 
obliquely  from  behind  forwards  and  outwards;  this  rests  upon  a  corresponding 
surface  on  the  upper  aspect  of  the  os  calcis.  In  front  of  this,  and  crossing  the 
bone  from  within  outwards  and  forwards,  is  a  deep  furrow  (sulcus  tali),  the  floor  of 
which  is  pierced  by  numerous  large  canals.     It  serves  for  the  attachment  of  the 


V.  Metataesa 


Sesamoid  bone 


First 
phalanx 


Third  or  terminal  phalanx 
Fig.  181. — Bones  of  the  Eight  Foot  as  seen  from  Above. 


THE  ASTRAGALUS. 


241 


OS  CALCIS 


Sustentaculum  tali 


Astragalus 


SCAPHOIlJ 
or  NAVICULAR 


Cuboid 

Middle  cuNEif  gem 
External 
cuneiform 


strong  interosseous  ligament  which  unites  the  astragalus  with  the  os  calcis,  and 
separates  the  facet  already  described  from  a  smaller  oval  articular  area  having  a 
slightly  convex  surface,  which  lies  immediately  in  front  of  it.  This  is  called  the 
middle  calcanean  facet  (facies  articularis  calcanea  media),  and  articulates  with  the 
upper  surface  of  the 
sustentaculum  tali 
of  the  OS  calcis. 
Posteriorly  the  body 
is  provided  with  two 
tubercles,  separated 
by  a  groove ;  the 
external  of  these 
(processus  posterior 
tali)  is  usually  the 
larger,  and  is  occa- 
sionally a  separate 
ossicle  (ostrigonum). 
To  it  is  attached  the 
posterior  fasciculus 
of  the  external 
lateral  ligament  of 
the  ankle-joint.  The 
groove,  which  winds 
obliquely  from  above 
downwards  and  in- 
wards over  the  pos- 
terior surface  of  the 
bone,  lodges  the 
tendon  of  the  flexor 
longus  hallucis 
muscle. 

The  head  (caput 
tali),  of  oval  form,  is 
directed  forwards 
and  inwards.  Its 
anterior  surface  is 
convex  from  side  to 
side  and  from  above 
downwards,  and  ar- 
ticulates with  the 
navicular  bone 
(facies  articularis 
navicularis).  In  - 
feriorly  this  surface 
is  confluent  with  the 
middle  calcanean 
facet,  but  in  well- 
marked  specimens, 
or  when  the  bones 
are  articulated,  it 
will  be  seen  that  a 
small  area  in  front 
of,  and  external  to, 
the  middle  calcanean 

facet  rests  upon  an  articular  surface  on  the  u])per  part  of  the  fore  portion  of  the 
OS  calcis,  and  is  called  the  anterior  calcanean  facet  (facies  articularis  calcanea 
anterior).  To  the  inner  and  under  surface  of  the  head  there  is  a  cartilage-covered 
Hurfac;e  which  does  not  articulate  with  any  bone,  but  rests  on  the  upper  surface 
of    the    inferior    calcaneo- navicular    ligam(3nt,   and    is    supported    on    the    inner 


First  phalanx 


,  I.  Metatarsal 


Sesamoid  bones 


Metatarsal 


Fig.  182.- 


SrcoND 

PHALANX^ 
ThiKD    or   terminal    I'lIALANX 

-Bones  of  the  Right  Foot  as  seen  fkom  Below. 


242 


OSTEOLOGY. 


side  by  the  tendon  of  the    tibialis   posticus  muscle   (Fawcett,  Eil.    Med.    Jonrn. 
1895,  p.  987). 


Fig.  183. — The  Right  Astragalus. 


A.   Upper  Surface. 


B.    Uniler  Surface. 


Groove  for  flex.  long,  hallucis. 

Internal  tubercle. 

Trochlear  surface  fob  tibia. 

Body. 

For  articulation  with  internal 

malleolus. 
Head. 

For  ARTICULATION  with  NAVICULAR. 

Neck. 


9.  For  ARTICULATION  WITH  EXTERNAL 

malleolus. 

10.  Surface     against    which    the 

INFERIOR    TIBIO-riBULAR    LIGA- 
ment rests. 

11.  External  tubercle. 

12.  External  tubercle. 

13.  Posterior,  middle,  and  anterior 

facets  for  OS  CALCIS. 


14.  For   articulation    with    navi- 

cular. 

15.  Surface    resting    on    inferior 

CALCANEO -navicular  LIGA- 

MENT. 

16.  Interosseous  groove. 

17.  Internal  tubercle. 

18.  Groove     for     flexor     longus 

hallucis. 


The  neck  (coUum  tali),  best  seen  above,  passes  from  the  front  of  the  body  and 
inclines  towards  the  inner  side.     It  is  confluent  with  the  inner  surface  in  front  of 


Fig.  184. — The  Eight  Astragalus 


A.  As  seen  from  tlie  Outer  Side. 


External  tubercle. 

Groove  for  flexor  longus 
hallucis. 

Internal  tubercle. 

Surface  against  which  the 
inferior  tibio-fibular  liga- 
ment RESTS. 

Trochlea  for  tibia. 

Fob     articulation     with 

external  malleolus. 
Neck.  S.^  Head. 

For     abticulation     with 

navicular. 


B.  As  seen  from  the  Inner  Side. 


10. 

Interosseous  groove. 

18. 

11. 

Anterior       middle,       and 

posterior     facets      for      OS 

IP. 

CALCIS. 

•20. 

12. 

Body. 

13. 

Surface  resting   on    internal 

21. 

CALCANEO  -  navicular          LIGA- 

22. 

MENT. 

14. 

For     ARTICULATION    WITH     NAVI- 

23. 

CULAR. 

24. 

15. 

Head. 

25. 

l(i. 

Neck. 

17. 

Trochlea  for  tibia. 

For  ABTICUL-iTION  WITH  INTERNAL 

malleolus. 
Body. 

Impression        for         intebn.\l 

lateral  ligament. 
Internal  tubercle. 
GR00^^;     for     flexor    longus 

hallucis. 
B.xternal  tubercle. 
Interosseous  groove. 
Posterior  and  middle    facets 

for  os  calcis. 


the  internal  malleolar  facet,  and  externally  forms  a  wide  groove,  which  becomes 
continuous  inferiorly  with  the  outer  end  of  the  interosseous  groove. 


1 


THE  OS  CALCI8. 


243 


Variations. — The  anterior  is  sometimes  separated  from  tlie  middle  calcaiiean  facet  by  a  non- 
articular  furrow.  The  posterior  external  tubercle,  often  largely  developed,  is  occasionally  (2-6 
per  cent)  a  separate  ossicle  forming  what  is  known  as  the  os  trigonum  (Bardeleben) ;  or  it  may  be 
united  to  the  body  of  the  astragalus  by  a  distinct  synchondrosis.  A  smooth  articular  surface  may 
occasionally  be  found  on  the  outer  side  of  the  upper  surface  of  the  neck.  This  is  a  pressure  facet 
dependent  on  the  frequent  use  of  the  ankle-joint  in  a  condition  of  extreme  flexion,  and  is  caused 
by  the  opposition  of  the  bone  against  the  anterior  edge  of  the  lower  end  of  the  tibia. 

For  a  detailed  study  of  the  varieties  of  this  bone,  see  E.  B.  S.  Sewell  {Journ.  Anat.  and  Phydol, 
vol.  xxxAdii.) 

The  Os  Calcis. 

The  OS  calcis  (calcaneus)  is  the  largest  of  the  tarsal  bones.  It  supports  the 
astragalus  above  and  articulates  with  the  cuboid  in  front.  Inferiorly  and  behind,  its 
posterior  extremity  or  tuberosity  forms  the  heel  on  which  so  large  a  proportion  of 
the  body  weight  rests.  The  long  axis  of  the  bone  inchnes  forwards  and  a  little 
outwards. 

The  iipper  surface  of  the  os  calcis  is  divisible  into  two  parts— a  posterior  non- 


[    Ant. 


<!  \     Mid. 


Sustenta- 
culum 

TALI 


Cuboid 


Surface  for 
attachment 
y/oi  short 
plantar 
ligament 


bOSTENTA- 

CULUM 

TALI 

Groove  fob 

FLEXOR 
LONGUS 
HALLUCIS 

Surface  for 
attachment 
of  long 
plantar  liga- 
ment 

Internal 
tubercle 


Tuberosity 
Fifi.  185. — The  Right  Os  Calcis  as  seen 

FROM    ABOVE. 


Tuberosity 
Fig.   186. — The  Right  Os  Calcis  as  seen 
from  below. 


articular  part  and  an  anterior  articular  portion.  The  length  of  the  former  varies 
according  to  the  projection  of  the  heel ;  rounded  from  side  to  side,  it  is  slightly  con- 
cave from  before  backwards.  In  front  of  this  there  is  a  convex  articular  area  of 
variable  shape  (facies  articularis  posterior),  sometimes  nearly  circular,  at  other  times 
oval  and  occasionally  almost  triangular.  This  is  directed  upwards  and  forwards, 
and  articulates  with  the  posterior  calcanean  facet  on  the  under  surface  of  the  astra- 
galus. Anterior  to  this  facet  the  bone  is  deeply  excavated,  forming  a  fossa  from 
which  a  groove  (sulcus  calcanei)  leads  backwards  and  inwards  around  the  antero- 
internal  border  of  the  articular  surface.  When  the  os  calcis  is  placed  in  contact 
with  the  astragalus,  this  groove  coincides  with  the  sulcus  on  the  under  surface  of 
the  latter  bone,  and  so  forms  a  canal  or  tunnel  (sinus  tarsi)  in  which  the  strong 
interosseous  ligament  which  unites  the  two  bones  is  lodged.  To  the  front  and  inner 
side  of  this  groove  there  is  an  elongated  articular  facet  directed  obliquely  from 
behind  forwards  and  outwards,  and  concave  in  tlie  direction  of  its  long  axis.  This 
is  frequently  divided  into  two  smaller  oval  areas  by  an  intermediate  non-articular 
surface.  Of  these  facets  the  hinder  (facies  articularis  media)  articulates  with  the 
middle  calcanean  facet  on  the  under  surface  of  the  astragalus,  whilst  the  anterior 
(facies  articnlans  anterioi)  supports  the  under  surface  of  the  head  of  the  astragalus 
(facies  articularis  (;alc;ui(;i  ;i,nteriorj.     The  outer  side  of  tlie  upper  surl'ace  of  the 


244 


OSTEOLOGY. 


Facets  for  astragalus 


Interosseous 

GROOVE 


Peroneal  spine 


External  tubercle 


A.  As  seen  from  the  Outer  Side. 


Facets  for  astragalus 


anterior  extremity  of  the  bone  is  rough,  and  hereto  is  attached  the  origin  of  the 
short  extensor  muscle  of  the  toes. 

The  inferior  surface  of  the  bone  is  slightly  concave  from  before  backwards,  and 
convex  from  side  to  side.  The  under  aspect  of  the  tuberosity  is  provided  with  two 
tubercles,  an  inner  (processus  medialis  tuberis  calcanei)  and  an  outer  (processus 
lateralis  tuberis  calcanei),  of  which  the  former  is  the  larger.  From  this  the  short 
flexor  of  the  toes  and  the  abductor  hallucis  muscle  arise,  whilst  from  both  tubercles 
spring  the  fibres  of  origin  of  the  aljductor  minimi  digiti  muscle.  On  the  fore-part 
of  the  under  surface  there  is  an  elevated  elongated  tubercle,  which  terminates 
somewhat  abruptly  just  behind  the  anterior  border  of  this  aspect  of  the  bone, 

giving  rise  at  times  to  a  notch. 
From  the  former  spring  the 
fibres  of  the  long  plantar  liga- 
ment, whilst  the  latter  serves 
for  the  attachment  of  the  deeper 
fibres  of  the  short  plantar  liga- 
ment. The  two  heads  of  origin 
of  the  flexor  accessorius  muscle 
arise  from  the  bone  on  either 
side  of  the  long  plantar  liga- 
ment. The  internal  surface  of 
the  OS  calcis  is  crossed  ob- 
liquely, from  above  downwards 
and  forwards,  by  a  broad  groove 
of  considerable  depth ;  along 
this  pass  many  of  the  structures 
which  enter  the  sole  of  the  foot 
from  the  back  of  the  le^.  The 
groove  is  overhung  in  front  and 
above  by  a  projecting  bracket- 
like process,  called  the  susten- 
taculum tali,  or  lesser  process. 
The  under  surface  of  the  sus- 
tentaculum is  channelled  by  a 
groove,  in  which  is  lodged  the  te  u- 
don  of  the  flexor  longus  hallucis 
muscle  ;  whilst  its  inner  border, 
to  which  is  attached  a  part  of 
the  internal  lateral  ligament  of 
the  ankle,  is  overlain  by  tendon 
of  the  flexor  longus  digitorum. 
To  the  anterior  border  of  the 
sustentaculum  is  attached  the 
inferior  calcaneo-navicular  liga- 
ment, and  placed  on  its  upper 
surface  is  the  articular  facet 
already  alluded  to  (facie  s  articu- 
laris  media).  Posteriorly  the  internal  surface  of  the  bone  is  limited  interiorly  by  the 
projection  of  the  internal  tubercle,  and  above  by  the  internal  lipped  edge  of  the 
tuberosity. 

The  external  surface,  broad  behind  and  narrower  in  front,  is  of  flattened  form. 
Springing  from  it,  just  below  the  outer  end  of  the  sinus  tarsi,  is  the  peroneal  spine 
(processus  trochlearis),  often  indistinctly  marked.  To  this  the  fibres  of  the  external 
annular  ligament  are  attached  ;  whilst  in  grooves,  above  and  below  it,  pass  the 
tendons  of  the  peroneus  brevis  and  longus  muscles  respectively.  To  the  upper 
and  back  part  of  this  surface  are  attached  the  fibres  of  the  middle  fasciculus  of  the 
external  lateral  ligament  of  the  ankle. 

The  anterior  extremity,  sometimes  called  the  greater  process,  is  furnished  with  a 
saddle-sliaped  surface  on  its  anterior  aspect  for  articulation  with  the  cuboid.     This 


Post. 


Sustentaculum 
tali 


Fig, 


Groove  for 

FLEX.  long. 

hallucis 

External  tubercle 
B 

B.  As  seen  from  the  Inner  Side. 
187.— The  Right  Os  Calcis. 


Internal  tubercle 


THE  NAVICULAR  BONE. 


245 


External 
cuveifohm 


Middle  cuneiform 


facet  is  concave  from  above  downwards,  and  slightly  convex  from  side  to  side ;  its 
edges  are  sharply  defined,  except  internally,  and  serve  for  the  attachment  of 
ligaments. 

The  posterior  extremity,  called  the  tuberosity  (tuber  calcanei),  forms  the 
projection  of  the  heel.  Of  oval  form  and  rounded  surface,  it  rests  upon  the  two 
tubercles  inferiorly.  Its  cutaneous  aspect  is  divisible  into  three  areas.  Of  these 
the  highest  is  smooth  and  crescentic,  and  is  covered  by  a  bursa ;  the  intermediate 
is  also  fairly  smooth,  and  is  defined  inferiorly  by  an  irregular  line,  sometimes  a 
definite  ridge,  the  edges  of  which  are  striated.  Into  this  surface  the  tendo  Achillis 
is  inserted.  The  lowest  surface  is  rough  and  striated,  and  is  confluent  below  with 
the  internal  and  external  tubercles ;  this  is  overlain  by  the  dense  layer  of  tissue 
which  forms  the  pad  of  the  heel. 

Variations. — The  peroneal  tubercle  is  occasionally  unduly  proruinent,  constituting  the  sub- 
malleolar  apophysis  of  Hyrtl,  and  cases  are  recorded  of  the  os  calcis  articulating  with  the 
navicular  (Morestin,  H.,  Bull,  de  la  Soc.  Anat.  de  Paris,  1894,  ser.  v.  t.  8,  n.  24,  p.  798  ;  and 
Petrini,  Atti  del  XL  Congr.  Med.  Internaz.  Roma,  1894,  vol.  ii.,  "Anat."  p.  71).  Pfitzner  (Morpho- 
logische  Arbeiten,  vol.  vi.  p.  245)  also  records  the  separation  of  the  sustentaculum  tali  to  form  an 
OS  sustentacula      (See  also  P.  P.  Laidlaw,  Journ.  Anat.  and  Physiol.,  vol.  xxxviii.  p.  133.) 

The  Navicular  Bone. 

The  navicular  or  scaphoid  bone  (os  naviculare  pedis),  of  compressed  pyriform 
shape,  is  placed  on  the  inner  side  of  the  foot,  between  the  head  of  the  astragalus 
posteriorly  and  the  three  cuneiform  bones  anteriorly.  The  bone  derives  its  name 
from  the  oval  or  boat- 
shaped  hollow  on  its 
posterior  surface,  which 
rests  upon  the  head  of 
the  astragalus.  Its 
anterior  aspect  is  fur- 
nished with  a  semilunar 
articular  area,  which  is 
subdivided  by  two  faint 
ridges  into  three  wedge- 
shaped  facets  for  articu- 
lation from  within  out- 
wards with  the  internal, 
middle,  and  external 
cuneiform  bones.  Su- 
periorly the  surface  of  the  bone,  convex  from  side  to  side,  is  rough  fori  the 
attachment  of  the  ligaments  on  the  dorsal  aspect  of  the  foot.  Inferiorly  the 
bone  is  irregularly  concave,  and  marked  by  the  attachment  of  the  plantar  liga- 
ments. The  external  surface  is  narrow  from  before  backwards,  and  rounded  from 
above  downwards.  Usually  devoid  of  any  articular  surface,  it  is  occasionally  x^rovided 
with  a  facet  which  rests  upon  a  corresponding  area  on  the  cuboid.  The  inner  side 
of  the  bone  projects  beyond  the  general  line  of  the  inner  border  of  the  foot,  so  as  to 
form  a  thick  rounded  tubercle  (tuberositas  oss.  navicularis),  the  position  of  which 
can  be  easily  determined  in  the  living.  To  the  inner  and  under  surface  of  this 
process  an  extensive  portion  of  the  tendon  of  the  tibialis  posticus  muscle  is 
inserted. 

Variations.- — Cases  are  recorded  where  the  tubercle  has  formed  an  independent  ossicle. 


Tlberosity      For  head  of  astragalus 


Tuberosity 


B 


A 

Fig.  188. — The  Right  Navicular  Bone. 
A.  As  seen  from  Behind  ;  B.  As  seen  from  the  Front. 


The  Cuneiform  Bones. 

The  cuneiform  bones,  three  in  number,  arc  placed  between  the  navicular 
posteriorly  and  the  bases  of  the  first,  stjcond,  and  tbird  metatarsal  bones  anteriorly, 
for  which  reason  they  are  frequently  named  the  first,  second,  and  third  cuneiforms, 
or,  from  their  position,  internal,  middle,  and  external.  More  or  less  wedge-shaped, 
as  tlieir  name  implies,  the  internal  or  first  is  the  largest,  whilst  the  middle  or 


246 


OSTEOLOGY. 


II.  Metatarsal 


I.  Metatarsal 


in.  Mltatarsal 


Fig.  189. — Anterior  View  of  the  three 
Cuneiform  Bones  of  the  Right  Foot. 


II.  Metatarsal 


Middle  gineijorm 


second  is  the  smallest  of  the  group.     Comljiued,  they  form  a  compact  mass,  the 
proximal  surface  of  which,  fairly  regular  in  (jutline,  rests  on  the  anterior  surface  of 

the  navicular  ;  whilst  anteriorly  they  form  a  base 
of  support  for  the  thr.-e  inner  metatarsals,  the 
outline  of  which  is  irregular,  owing  to  the  base 
of  the  second  metatarsal  bone  Ijeing  recessed 
between  the  inner  and  outer  cuneiforms  as  it 
articulates  with  the  distal  extremity  of  the 
shorter  middle  cuneiform. 

The  internal  cuneiform  bone  (os  cuneiforme 
primum),  the  largest  of  the  three,  lies  on  the  inner 
border  of  the  foot  between  the  base  of  the  meta- 
tarsal bone  of  the  great  toe  in  front,  and  the  fore 
and  inner  part  of  the  navicular  Ijehind.  Its 
upper,  lower,  and  internal  surfaces  are  confluent, 
and  form  a  convexity  from  above  downwards, 
which  is  most  pronounced  inferiorly,  where  it  is 
turned  towards  the  plantar  side  of  the  foot.  On  the  fore-part  of  the  inner  aspect 
of  the  bone  there  is  usually  a  distinct  oval  impression,  which  indicates  the  surface 
of  insertion  of  a  portion  of  the  tendon  of  the  tibialis  anticus  muscle.  Elsewhere 
this  surface  is  rough  for  ligamentous  attachments.  The  external  surface  of  the 
bone,  quadrilateral 
in  shape,  is  directed 
towards  the  middle 
cuneiform ;  but  as 
it  exceeds  it  in 
length,  it  also  comes 
in  contact  with  the 
inner  side  of  the 
base  of  the  second 
metatarsal  bone. 
Running  along  the 
posterior  and  upper 
edges  of  this  area 
is  an  [—-shaped  ar- 
ticular surface,  the  ■.fore  and  upper  part  of  which  is  for  the  base  of  the  second 
metatarsal  bone,  the  remainder  articulating  with  the  inner  side  of  the  middle 
cuneiform.  The  non-articular  part  of  this  aspect  of  the  bone  is  rough  for  the 
attachment  of  the  strong  interosseous  ligaments  which  bind  it  to  the  middle 
cuneiform  and  second  metatarsal  bones  respectively.     The  posterior  or  proximal 

end  of  the  bone  is  provided  with  a  pyri- 
form  facet  which  fits  on  the  inner  articular 
area  of  the  navicular.  Anteriorly  the 
vertical  diameter  of  the  bone  is  much  in- 
y^  \  tiiv  r^^mmf  l  creased,  and  the  facet  for  the  base  of  the 
metatarsal  bone  of  the  great  toe  is  con- 
sequently much  larger  than  that  for  the 
navicular.  The  metatarsal  facet  is  usually 
of  semilunar  form,  but  not  infrequently 
II.  Metatarsal  j^g  niorc  renifomi    in  shape,  and    may  in 

Fig.  19.3.— The  Right   some   cases   display   complete   separation 
Middle  Cuneifohji    •    .      .  i  .  • 

(Outer  Side).  mto  two  oval  portions. 

The  middle  or  second  cuneiform  (os 
cuneiforme  secundum)  is  of  a  typical  wedge  shape ;  shorter  than  the  others  it 
lies  between  them,  articulating  with  the  ba^ee  of  the  second  metatarsal  in  front, 
and  the  middle  facet  on  the  anterior  surface  of  the  navicular  behiiid.  Its  upper 
aspect,  which  corresponds  to  the  base  of  the  wedge,  conforms  to  the  roundness  of 
the  instep,  and  is  slightly  convex  from  side  to  side,  affording  attachments  for  the 
dorsal  ligaments.     Its  under  surface  is  narrow  and  tubercular,  forming  the  edge 


Impression 
for  tendon 
of  tibialis 

ANTItCb 


Fig.  190. — The  Right  Internal 
Cuneiform  (Inner  Side). 


Fig.  191. — The  Right  Internal 
Cuneiform-  (Outer  Side). 


II.  Internal 

Metatarsal  cuneiform 


External  cuneiform 


Fig.  192.— The  Right 
Middle  Cuneiform 
(Inner  Side). 


THE  CUBOID  BONE. 


247 


MiDDLK  CUNEIFORM 


Cuboid        IV.  Metatarsal 


of  the  wedge ;  with  this  the  plantar  ligaments  are  connected.  The  inner  surface, 
quadrilateral  in  outline,  is  furnished  with  an  f-shaped  articular  area  along  its 
posterior  and  superior  borders  in  correspondence  with  the  similar  area  on  the  outer 
side  of  the  internal  cuneiform.  The  rest  of  this  aspect  is  rough  for  ligaments. 
The  outer  side  displays  a  facet  arranged  along  its  posterior  border,  and  usually 
somewhat  constricted  in  the  middle ;  this  is  for  the  external  cuneiform.  In  front 
of  this  the  bone  is  rough  for  the  interosseous  ligaments,  which  bind  the  two  bones 
together.  The  proximal  end  is  provided  with  a  triangular  facet  slightly  concave 
from  above  downwards ;  this  rests  on  the  central  articular  surface  on  the  anterior 
aspect  of  the  navicular.  In  front  the  bone  articulates  by  means  of  a  wedge- 
shaped  facet  with  the  base  of  the  metatarsal  bone  of  the  second  toe. 

The  external  or  third  cuneiform  (os  cuneiforme  tertium)  intermediate  in  size 
between  the  first  and  second,  is  also  of  a  typical  wedge  shape.  Its  superior  surface, 
slightly  convex  from  side  to 
side,  provides  attachments  for 
the  dorsal  ligaments.  Its 
inferior  or  'plantar  aspect  is  ^ 
narrow  and  tubercular,  and  g 
serves  for  the  attachment  of  % 
the  plantar  ligaments.  Its  ^ 
inner  side,  of  quadrilateral  J 
form,  displays  two  narrow 
articular  strips,  placed  along 
its  anterior  and  posterior 
borders  respectively,  each 
somewhat  constricted  in  the  middle.  The  anterior  articulates  with  the  outer 
side  of  the  base  of  the  second  metatarsal  bone,  the  posterior  with  the  outer  side  of 
the  middle  cuneiform.  The  rough  non-articular  surface,  which  separates  the  two 
elongated  facets,  serves  for  the  attachment  of  ligaments.  The  outer  aspect  of  the 
bone  is  characterised  by  a  large  circular  or  oval  facet,  placed  near  its  hinder  border, 
for  articulation  with  the  cuboid ;  in  front  of  this  the  anterior  border  is  lipped  above 
by  a  small  semi-oval  facet  for  articulation  with  the  inner  side  of  the  base  of  the 
fourth  metatarsal.  The  rest  of  the  bone  around  and  between  these  facets  is  rough 
for  ligaments.  Proximally  the  bone  is  furnished  with  a  triangular  facet  for 
articulation  with  the  outer  wedge-shaped  area  on  the  front  of  the  navicular,  whilst 
distally  it  articulates  with  the  base  of  the  third  metatarsal  by  a  surface  of  corre- 
sponding shape. 

Variations. — Numerous  cases  of  division  of  the  internal  cuneiform  l:)one  into  dorsal  and 
plantar  jjarts  have  been  recorded  ;  the  frequent  division  of  its  metatarsal  articular  facet  is  no 
doubt  correlated  with  this  anomalous  condition.  T.  D wight  has  described  {Anat.  Anz.,  vol.  xx. 
p.  465)  in  two  instances  the  occurrence  of  an  Os  Intercuneiforme.  The  ossicle  so  named  lies  on 
the  dorsum  of  the  foot  at  the  proximal  end  of  the  line  of  articulation  between  the  internal  and 
middle  cuneiform  bones. 


Fig.  194. — Right  External 
Cuneiform  (Inner  Side). 


Fig.  195. — Right  External 
Cuneiform  (Outer  Side). 


The  Cuboid  Bone. 

The  cuboid  (os  cuboideum)  lies  on  the  outer  side  of  the  foot,  about  its  middle, 
articulating  with  the  os  calcis  behind  and  the  fourth  and  j&fth  metatarsal  bones  in 
front.  Its  t/.pper  surface,  plane  in  an  antero-posterior  direction,  is  slightly  rounded 
from  side  to  side,  and  provides  attachment  for  ligaments.  Its  plantar  aspect  is 
traversed  obliquely  from  without  inwards  and  forwards  by  a  thick  and  prominent 
ridge,  the  outer  extremity  of  which,  at  the  point  where  it  is  confluent  with  the 
outer  surface,  forms  a  prominent  tubercle  (tuljerositas  oss.  cuboidei),  the  anterior 
and  external  surface  of  which  is  smooth  and  faceted  to  allow  of  the  play  of 
a  sesamoid  bone  which  is  frequently  developed  in  the  tendon  of  the  peroneus 
longus  muscle.  In  front  of  this  ridge  there  is  a  groove  (sulcus  peroniyi)  in 
which  the  tendon  of  the  peroneus  longus  muscle  is  lodged  as  it  passes  across  the 
under  surface  of  the  bone.  Behind  the  ridge  the  bone  is  rough,  and  serves  for 
the  attachment  of  the  short  plantar  ligament,  the  superficial  fibres  of  which  pass 
forwards  and  are  attached  to  the  sumndt  of  the  ridge.     The  outer  aspect  of  the  bone 


248 


OSTEOLOGY. 


Navicular 
External  cuneitorm      (occasional) 


is  short  and  rounded,  and  is  formed  by  the  confluence  of  the  superior  and  inferior 
surfaces ;  it  is  more  or  less  notched  by  the  peroneal  groove  which  turns  round  its 
lower  edge.  The  internal  surface  of  the  bone  is  the  most  extensive ;  it  is  easily 
recognisable  on  account  of  the  presence  of  a  rounded  or  oval  facet  situated  near  its 

middle  and  close 
to  its  upper  border. 
This  is  for  articu- 
lation with  the 
outer  side  of  the 
external  cunei- 
form ;  in  front  and 
behind  this  the 
surface  is  rough 
for  ligaments.  Not 
infrequently  be  - 
hind  the  facet  for 
the  external  cunei- 
form   there    is    a 

small  articular  surface  for  the  navicular,  as  is  the  case  normally  in  the  gorilla,  whilst 
behind  and  below  the  projecting  inferior  angle  is  sometimes  provided  with  a  facet 
on  which  the  head  of  the  astragalus  rests  (Sutton,  "  Proc.  Anat.  Soc,"  Jour.  Anat. 
and  Physiol.,  vol.  xxvi.  p.  18).  The  anterior  surface  is  oval  or  conical  in  outline ; 
sloping  obliquely  from  within  outwards  and  backwards,  it  is  divided  about  its 
middle  by  a  slight  vertical  ridge  into  two  parts,  the  inner  of  which  articulates  with 
the  base  of  the  fourth  metatarsal  bone,  the  outer  with  that  of  the  fifth.  The 
posterior  surface,  also  articular,  has  a  semilunar  outline,  the  convex  margin  of  which 
corresponds  to  the  dorsal  roundness  of  the  bone.  The  inferior  external  angle  corre- 
sponds to  the  tubercle  on  the  outer  border  of  the  bone,  whilst  the  inferior  internal 
angle  forms  a  pointed  projection  which  is  sometimes  called  the  calcanean  process. 
The  posterior  surface  articulates  with  the  os  calcis  by  means  of  a  saddle-shaped 
facet,  which  is  convex  from  side  to  side,  and  concave  from  above  downwards. 


)\  F  FOR  PCRONEUS 
LONQUh 

A 

Fig.  196.- 
Outer  Side. 


Groove  for 
perone0s  lokgus 


-The  Right  Cuboid  Bone. 

B.  Inner  Side. 


'Variations. — Blandin  lias  recorded  a  case  of  division  of  the  cuboid. ' 

'The  tarsus  as  a  whole  may  be  conveniently  described  as  arranged  in  two  columns ;  the 
inner,  corresponding  to  the  inner  border  of  the  foot,  comprising  the  astragalus,  navicular,  and 
three  cuneiforms,  and  forming  a  base  for  the  support  of  the  three  inner  metatarsal  bones  and 
their  j^halanges.  The  outer  column,  formed  by  the  os  calcis  and  cuboid,  supports  the  fourth 
and  fifth  metatarsal  bones  together  with  their  phalanges.  The  superior  surface  of  the  anterior 
portion  of  the  tarsus  determines  the  side-to-side  roundness  of  the  instej),  whilst  its  under  surface 
forms  arches  in  both  a  transverse  and  longitudinal  direction,  in  which  the  softer  tissues  of  the 
sole  are  lodged,  and  so  j)rotected  from  injury. 

Architecture  of  the  Bones  of  the  Foot. — A  longitudinal  section  through  the  articulated 
bones  of  the  foot  reveals  the  fact  that  the  cancellous  structure  of  each  individual  bone  is  determined 
by  the  stress  to  which  it  is  habitually  subjected.  In  this  connexion  it  is  necessary  to  refer  to  the 
arched  arrangement  of  the  bones  of  the  foot,  a  subject  which  is  also  treated  in  the  section  which 
deals  with  the  Joints.  The  summit  of  the  arch  is  formed  by  the  astragalus,  on  which  rests  the  tibia. 
Subjected  as  the  astragalus  is  to  a  crushing  strain,  it  is  obvious  that  this  load  must  be  distributed 
throughout  the  arch,  of  which  the  os  calcis  is  the  posterior  jDillar,  whilst  the  heads  of  the  meta- 
tarsal bones  constitute  the  anterior  pillar.  It  is  found,  consequently,  that  the  lamellae  of  the  can- 
cellous tissue  of  the  astragalus  are  arranged  in  two  directions,  which  intercross  and  terminate 
below  the  sujoerior  articular  surface.  Of  these  fibres,  some  sweep  backwards  and  downwards 
towards  the  posterior  calcanean  facet,  beyond  which  they  are  carried  in  the  substance  of  the  os 
calcis  in  a  curved  and  wavy  manner  in  the  direction  of  the  heel,  wdiere  they  terminate  ;  whilst 
others,  curving  downwards  and  forwards  from  the  trochlea  of  the  astragalus,  pass  through  the 
neck  to  reach  the  articular  surface  of  the  head,  through  which  in  like  manner  they  may  be 
regarded  as  jjassing  onwards  through  the  several  bones  which  constitute  the  anterior  jsart  of  the 
arch,  thus  accounting  for  the  longitudinal  striation  as  displayed  in  the  structure  of  the  navi- 
cular, cuneiform,  and  metatarsal  bones.  In  the  os  calcis,  in  addition  to  the  foregoing  arrange- 
ment, another  set  of  curving  fibres  sweep  from  back  to  front  of  the  bone  beneath  the  more  com- 
pact tissue  which  forms  its  under  shell.  These  are  obviously  of  advantage  to  jjrevent  the  sjDread 
of  the  bone  when  subjected  to  the  crushing  strain.  In  the  sustentaculum  tali  a  bracket-like 
arrangement  of  fibres  is  evident,  and  the  under  surface  of  the  neck  of  the  astragalus  is  further 
strengthened  by  lamellae  arranged  A^ertically. 

In  the  separate  bones  the  investing  envelope  is  thin,  though  under  the  articular  surfaces 
there  is  a  greater  density,  due  to  the  accession  of  lamellse  lying  parallel  to  the  articular  planes. 


THE  METATAKSUS.  249 

The  stoutest  bony  tissue  in  the  astragalus  is  met  with  in  the  region  of  the  under  surface  of  the 
neck,  whilst  in  the  os  calcis  the  greatest  density  occurs  along  the  floor  of  the  sinus  tarsi. 

Numerical  Variation  in  the  Tarsus. — Increase  in  the  number  of  the  tarsal  elements  may 
be  due  to  the  occurrence  of  division  of  either  the  internal  cuneiform  or  the  cuboid  bone,  or  to 
the  occasional  jDresence  of  an  os  trigonum.  Cases  of  separation  of  the  tuberosity  of  the  navicular 
bone  have  been  recorded,  and  instances  of  supernumerary  ossicles  Ijetween  the  internal  cuneiform 
and  second  metatarsal  bone  have  been  noted.  Stieda  mentions  the  occurrence  of  a  small  ossicle 
in  connexion  with  the  articular  surface  on  the  fore  and  upper  part  of  the  os  calcis,  and  Pfitzner 
notes  the  occurrence  of  an  os  sustentacula  For  further  information  on  the  variations  of  the 
skeleton  of  the  foot,  see  Pfitzner  {Morphologische  Arbeiten,  voL  vi.  p.  245). 

The  possibility  of  an  inj  ury  having  been  the  cause  of  the  occurrence  of  some  of  these  so-called 
supernumerary  ossicles  must  not  be  overlooked.  The  use  of  the  Rontgen  rays  has  j^roved  that 
accidents  of  this  kind  are  much  more  frequent  than  was  at  first  supposed. 

The  reduction  in  the  number  of  the  tarsus  is  due  to  the  osseous  union  of  adjacent  bones.  In 
many  instances  this  is  undoubtedly  pathological,  but  cases  have  been  noticed  (Leboucq)  of  fusion 
of  the  cartilaginous  elements  of  the  os  calcis  and  astragalus,  and  the  os  calcis  and  navicular 
in  foetuses  of  the  third  month. 

Ossification. — Unlike  the  carpus,  the  tarsus  is  at  birth  partially  ossified.  At  this 
period  there  is  a  well-marked  osseous  nucleus  within  the  body  and  neck  of  the  astragalus, 
and  the  os  calcis  is  extensively  ossified.  In  the  latter  the  deposition  of  earthy  matter 
appears  as  early  as  the  sixth  month  of  foetal  life,  whilst  in  the  astragalus  the  ossiiic  centre 
makes  its  appearance  in  the  later  weeks  of  gestation.     Shortly  before  or  after  birth  the 


'-mil 


A  B 

Fig.  197. — Radiographs  of  the  Fcetal  Foot. 

A.  Between  the  seveatli  and  eighth  months.     Here  the  ossific  nuclei  of  the  os  calcis  and  astragalus  are  seen. 

B.  At  birth.     The  centres  of  ossification  for  the  os  calcis  and  astragalus  are  well  developed,  the  nucleus  for 

the  cuboid  is  quite  distinct,  and  in  this  instance  the  external  cuneiform  is  already  commencing  to  ossify. 
Compare  this  figure  with  Fig.  155,  in  which  the  carpus  is  shown  as  still  cartilaginous  at  birth. 

cuboid  begins  to  ossify,  succeeded  early  in  the  first  year  by  the  external  cuneiform,  followed 
in  order  by  the  middle  cuneiform,  internal  cuneiform,  and  navicular.  Tlie  ossific  centre 
of  the  latter  appears  at  the  third  year  or  somewhat  later.  An  epiphysis,  which  forms  a 
cap  over  tlic  extremity  of  tlie  great  tuberosity  of  the  os  calcis,  apj)ears  from  the  seventh 
to  the  ninth  year,  and  fusion  is  completed  between  the  ages  of  sixteen  and  twenty. 

The  Metatahsus. 

The  metatarsal  bones,  live  in  number,  in  their  general  configuration  resemble 
the  metaourpuH.     They  are,  however,  Blightly  longer,  their  bases  are  proportionately 


250 


OSTEOLOGY. 


Grooves  for  sesamoid  bones 


Shaft 


larger,  their  shafts  more  slender  and  laterally  compressed,  and  their  heads  propor- 
tionately smaller.  They  are  named  numerically  the  first,  second,  third,  fourth,  and 
fifth  metatarsal  bones,  in  order  from  within  outwards.  The  first  can  be  readily 
recocjnised  on  account  of  its  stoutness ;  it  is  also  the  shortest  of  the  series.     The 

second  is  the  longest  of  the  five,  and  the  fifth  can  easily 
be  distinguished  by  the  projecting  tubercle  at  its  base. 

The  first  metatarsal  or  metatarsal  bone  of  the  great 
toe,  the  shortest  of  the  series,  is  remarkable  for  its 
stoutness.  Its  base,  where  the  bone  is  provided  with  a 
reniform  facet  for  articulation  with  the  internal  cunei- 
form, is  wider  from  before  backwards  than  from  side  to 
side.  As  a  rule  there  are  no  facets  on  the  lateral 
aspects  of  the  base.  The  inferior  angle  projects  backwards 
and  outwards,  and  forms  a  prominent  tuljercle  which  is 
pitted  for  the  insertion  of  the  tendon  of  the  peroueus 
longus  muscle,  whilst  its  internal  margin  is  lipped  by 
a  surface  for  the  attachment  of  part  of  the  tendon  of  the 
tibialis  anticus.  The  shaft,  short,  thick,  and  prismatic  on 
section,  tapers  rapidly  towards  the  head,  the  fore  and  under 
surfaces  of  which  are  articular.  The  former  is  convex  from 
side  to  side,  and  from  above  downwards,  and  supports  the 
proximal  phalanx.  It  is  confluent  below  with  the  inferior 
articular  surface,  which  is  divided  by  a  median  ridge  into 
two  shallow  grooves,  of  which  the  inner  is  the  wider.  In 
these  grooves  are  lodged  the  two  sesamoid  boues  which 
Fig.  198.— The  First  Meta-  ^Q(ierlie  the  metatarso-phalangeal  joint.  On  either  side 
TARSAL  Bone  OF  THE  Right     p   ,  i      i        ■■    ,,       i  ■        -.4.    fn      r-,         .  -i    .        ■,  i- 

Foot  (Piautar  Aspect).  01  the  head  the  Done  IS  pitted  lor  the  strong  lateral  liga- 

ments of  the  joint. 
The  second  metatarsal,  the  longest  of  the  series,  has  a  base  of  wedge-shaped 
form,  the  proximal  aspect  of  which  articulates  with  the  middle  cuneiform.      On  its 


Tuberosity      Tibialis  anticus 


Shai  I 


II.  METATARSAL 

Internal 

i-        ■,^''  "^  J^  EI  FORM 


IV.  IMetatarsal 
IV.  METATARSAL 


External  cuneiform 


III.  Metatarsal 


A.  Inner  sides 


V.  Metatarsal 

B.  Outer  sides 


Fig.   199. — View  of  the  Bases  and  Shafts  of  the  Secoxd,  Third,  and  Fourth  Metatarsal  Bones 

OF  thk  Right  Foot. 

inner  aspect,  near  its  superior  edge,  there  is  a  small  circular  facet  for  the 
internal  cuneiform;  below  and  in  front  of  this  there  is  sometimes  a  tubercle  with 
a  "  pressure "  facet  on  it,  where  the  bone  comes  in  contact  with  the  base  of  the 
first  metatarsal.     On  the  outer  side  of  the  base  there  is  one,  more  usually  two  small 


THE  METATARSUS. 


2r,l 


Cl  BOID 


facets,  each  divided  into  two  parts,  a  posterior  for  articulation  with  the  external 
cuneiform,  and  an  anterior  for  the  base  of  the  third  metatarsal.  The  shafts  of  this 
and  the  three  succeeding  bones  are  slender  and  laterally  compressed.  The  heads 
are  small  and  narrow,  and  display  a  pronounced  side-to-side  and  vertical  convexity. 

The  third  metatarsal  bone  also  jjossesses  a  base  of  wedge-shaped  form,  the 
proximal  surface  of  which  articulates  with  the  external  cuneiform.  On  its  inner 
side  it  is  provided  with  one,  more  usually  two,  small  facets,  for  articulation  with  the 
base  of  the  second  metatarsal.  Externally  the  base  has  a  larger  facet  for  articula- 
tion with  the  base  of  the  fourth  metatarsal,  more  or  less 
conical  in  outline,  and  having  its  lower  edge  sharply  defined 
by  a  narrow  groove  which  underlies  it. 

The  fourth  metatarsal  has  a  base  more  cubical  in  shape. 
Its  proximal  aspect  articulates  with  the  cuboid,  whilst  in- 
ternally an  elongated  oval  facet,  divided  by  a  slight  vertical 
ridge,  provides  surfaces  for  articulation  with  the  third  meta- 
tarsal in  front  and  the  outer  side  of  the  internal  cuneiform 
behind.  On  the  outer  side  there  is  a  demi-oval  facet,  bearing 
a  slightly  saddle-shaped  surface,  for  articulation  with  the  inner 
side  of  the  base  of  the  fifth  metatarsal. 

The  fifth  metatarsal  can  be  readily  recognised  by  the 
peculiar  shape  of  its  base,  from  the  outer  side  of  which  there 
projects  backwards  and  outwards  a  prominent  tubercle 
(tuberositas  oss.  metacarpi  V.)  To  the  hinder  extremity  of 
this  is  attached  the  tendon  of  the  peroneus  brevis  muscle.  To 
its  upper  surface  the  tendon  of  the  peroneus  tertius  is  inserted, 
whilst  its  under  surface  provides  an  origin  for  the  flexor  brevis 
minimi  digiti  muscle.  The  inner  surface  of  the  base  is  pro- 
vided with  a  demi-oval,  slightly  concave  facet,  for  the  outer  side  Fig.  200.— Fifth  Right 
of  the  base  of  the  fourth  metatarsal,  whilst  proximally  it  Metatabsal  Bone 
articulates  with  the  cuboid  by  means  of  a  semicircular  facet. 

Vascular  Foramina. — The  canals  for  tlie  nutrient  vessels  open,  as  a  rule,  on  the  plantar 
aspects  of  the  middle  of  the  shafts.  Those  of  the  outer  metatarsals  are  directed  towards  the  bases 
of  the  bones,  whilst  that  for  the  metatarsal  of  the  great  toe  passes  towards  its  head. 

Architecture. — In  structure  and  the  arrangement  of  their  lamellfe  the  metatarsal  bones 
agree  with  the  metacarpus. 

Variations. — Several  instances  of  separation  of  the  tuberosity  of  the  fifth  metatarsal  (os 
Vesaleanum)  have  been  recorded,  whilst  numerous  examples  of  an  os  intermetatarsum  between 
the  bases  of  the  first  and  second  metatarsal  bones  have  been  recorded  by  Gruber  and  others. 
The  tubercle  on  the  base  of  the  first  metatarsal  for  the  attachment  of  the  peroneus  longus  tendon 
is  occasionally  met  with  as  a  separate  ossicle. 

Ossification. — In  correspondence  with  the  mode  of  ossification  which  maintains  in 
the  metacarpus,  the  primary  centi-es  for  the  metatarsus  appear  as  early  as  the  third 
month  of  foetal  life.  In  the  case  of  the  second,  third,  fourth,  and  fifth,  these  centres 
furnish  the  bases  and  shafts  of  the  bones,  the  heads  being  developed  from  secondary 
centres  which  appear  from  two  to  four  years  after  birth,  fusion  with  the  shaft  being 
usually  completed  about  the  eighteenth  year.  In  striking  contrast  to  this  is  the  mode  of 
ossification  of  the  first  metatarsal.  From  its  primary  centre  the  head  and  sliaft  is 
developed ;  the  secondary  centre  appears  at  its  base  about  the  second  or  third  year,  and 
fuses  with  the  shaft  about  eighteen.  In  this  respect,  therefore,  the  metatarsal  bone  of 
the  great  toe  resembles  in  its  mode  of  development  the  phalanges.  Mayet,  however 
(Bull.  Soc.  Anat.  Paris,  189.o),  describes  the  occurrence  of  two  ossific  centres  in  the 
proximal  epiphysis.  Tliese  fuse  early,  and  he  considers  that  the  one  represents  the 
metatarsal  element,  whilst  the  other  may  be  regarded  as  phalangeal  in  its  origin. 


Peroneus  brevis 


''The  Piialan(;ks. 

The  phalanges  of  the  toes  (phalanges  digitorum  pedis)  differ  from  those  of  the 
fingers  in  ttie  striking  reduction  of  their  size,  and  in  the  case  of  the  bones  of  the 
first  row,  in  the  lateral  compression  of  their  shafts.  Each  toe  is  provided  normally 
witli  throe  plialang(;s,  except  tlie  great  toe,  which  has  only  two.  In  their  general 
configuration  and  in  the  arrangement  of  their  articular  facets  tlu;}'  resemble  the 


252 


OSTEOLOGY. 


III.  Ungual' 

OR  TERMINAL 
I'lIALANX 


II.  Phalanx 


digital  phalanges,  though,  owing  to  the  reduction  in  their  size,  the  shafts,  particu- 
larly those  of  the  second  row,  are  often  so  compressed  longitudinally  as  to  reduce 
the  bone  to  a  mere  nodule.  The  proximal  end  of  each  of 
the  bones  of  the  first  row  is  proportionately  large,  and  is 
provided  with  a  simple  hollow  in  which  the  head  of  the 
metatarsal  bone  rests ;  the  distal  ends  are  furnished  with 
condyloid  surfaces.  The  proximal  extremities  of  the  second 
row  are  each  provided  with  two  small  concavities,  separated 
by  a  slight  ridge  for  articulation  with  the  condyles  of  the 
first  row.  The  joint  between  the  second  and  third  row 
displays  the  same  arrangement — the  third,  terminal  or 
ungual  phalanx,  being  easily  distinguished  by  the  spatula- 
shaped  surface  at  its  extremity  on  which  the  bed  of  the  nail 
is  supported. 

The  phalanges  of  the  great  toe,  two  in  number,  differ 
from  the  others  in  their  size  and  length.  Into  the  base  of 
the  first  phalanx  are  inserted  the  short  muscles  of  the 
great  toe,  whilst  the  second  phalanx  receives  on  its 
plantar  aspect  the  insertion  of  the  fiexor  longus  hallucis 
muscle,  the  tendon  of  the  extensor  longus  hallucis  being 
inserted  into  the  dorsal  aspect. 


I.  Phalanx 


Metatarsal 
Fig.   201.— The   Phalanges 
OF    THE    Toes     (Dorsal 
Aspect). 


^a^-i 


Architecture. — In   their  general   structure   they   resemble    the 
bones  of  the  fingers. 

Variations. — It  is  not  uncommon  to  meet  witli  fusion  of  the 
second  and  third  phalanges,  particularly  in  the  fifth,  less  frequently 
in  the  fourth,  and  occasionally  in  the  second  and  third  toes.  The  union  of  the  phalangeal 
elements  has  been  observed  in  the  foetus  as  well  as  the  adult  (Pfitzner).  The  proportionate 
length  of  the  phalanges  A^aries  much ;  in  some  cases  the  ungual  phalanges  are  of  fair  size,  the 
bones  of  the  second  row  being  mere  nodules,  whilst  in  other  instances  the  reduction  in  size  of  the 
terminal  phalanges  is  most  marked. 

Ossification. — Each  phalanx  is  developed  from  two  centres — one  primary  for  the 
shaft  and  distal  extremity,  the 
other  for  the  epiphysis  on  the 
proximal  end.  The  primary  cen- 
tres for  the  ungual  phalanges  are 
the  first  to  appear,  commencing 
to  ossify  from  the  eleventh  to  the 
twelfth  week  of  foetal  life.  The 
centre  for  the  ungual  phalanx  of 
the  great  toe  makes  its  appearance 
before  that  of  its  corresponding 
metatarsal  bone.  The  primary 
centres  for  the  phalanges  of  the 

first  row  appear  from  the  four-      A  B  C 

teenth    to    the   sixteenth   week.  ^^^-  ^'^^• 

The     primary     centres     for      the  A.   About  the  end  of  the  third  month.     The  primary  centres  of  all 

middle   phalanges   of    the    second  the    metacai-pns    are    shown    as    well    as  the  centres  for  the 

,     ,1  .    T     ,      ®i       .        ,              .™  phalanges  of  the  great  toe  and  the  terminal  phalanx  ot  the 

and   thn-d   toes    begm    to    ossity  ^^j^,^  ^Qg_ 

about  the  sixth  month,  those  for  B.^  A  little  later.     The  centres  for  the  terminal  phalanges  of  the 

the  fourth  and  fifth  toes  not  till  four  inner  toes  are  seen,  as  well  as  the  centres  for  the  first 

later  — the    shaft    of    the    middle  ,,        phalanges  of  the  great  and  second  toe.               ,,    ,.      ,       .     , 

,     ,             J!    .1       i?        iU    •(-        1.   •  ^-   ^^3"^^t    the    fourth    month.     The    centres    for    all    the    terminal 

phalanx  ot   the  tourth   toe    bemg  phalanges  as  well  as  those  of  the  first  row  are  well  ossified, 

frequently  cartilaginous  at  birth,  d.  About   the   fifth    month.     In   this   the   centre   for   the    second 

the  normal  condition   in  the  case  phalanx  of  the  second  toe  has  already  made  its  appearance. 

of  the  fifth  toe  (Lambertz).       The        ^  This  specimen  displays  the  occurrence  of  anomalous  centres  within  the 
1  .    ,  T  '.    1        .        tarsus  the  significance  of  which  is  not  apparent.     The  appearance  is  not  due 

proximal    epiphyses    do  not    begm    to  any  defect  in  the  plate  but  recurred  in  repeated  skiographs. 

to  ossify  until  about  the  fourth 

year,  and  are  usually  fused  with  the  diaphyses  about  the  age  of  sixteen  or  eighteen. 
Union  between  the  shafts  and  epiphyses  of  the  first  row  precedes  that  of  the  second  and 
third  rows. 


MOEPHOLOGY  OF  LIMBS.  253 


Sesamoid  Bones. 


As  in  the  hand,  small  independent  nodules  of  bone,  called  sesamoid  bones,  are  met 
with  in  the  ligaments  and  tendons  of  the  foot.  The  most  constant  of  these  are  found  in 
connexion  with  the  metatarso-phalangeal  articulation  of  the  great  toe,  where  they  lie  in 
grooves  on  the  under  surface  of  the  head  of  the  metatarsal  bone  in  connexion  Avith  the 
tendons  of  the  short  muscles  of  the  great  toe.  Small  osseous  nodules  occupying  a 
corresponding  position  are  occasionally  met  with  in  the  other  toes,  and  instances  have 
been  recorded  of  like  ossicles  occurring  on  the  plantar  aspect  of  the  interphalangeal  joint 
of  the  great  toe. 

An  osseous  nodule  is  not  infrequently  met  with  in  the  tendon  of  the  peroneus  longus 
as  it  turns  roimd  the  outer  border  of  the  foot  to  lie  in  the  groove  on  the  under  surface  of 
the  cuboid. 

MORPHOLOGY  OF  LIMBS. 

Development  and  Moephology  of  the  Appendicular  Skeleton. 

The  paired  limbs  first  appear  in  the  human  embryo  about  the  third  week  as  small  buds  on 
either  side  of  the  cejshalic  and  caudal  ends  of  the  trunk.  That  these  outgrowths  are  derived  from 
a  large  num.ber  of  trunk  segments  is  assumed  on  the  ground  that  they  are  supplied  by  a  corre- 
sjaonding  number  of  segmental  nerves,  and  the  circumstance  that  they  are  more  particularly 
associated  with  the  ventral  offsets  of  these  nerves  would  point  to  the  conclusion  that  they  belong 
rather  to  the  ventral  than  the  dorsal  surface  of  the  body. 

At  first  the  surfaces  of  these  limb  buds  are  so  disposed  as  to  be  directed  ventrally  and  dorsally, 
the  ventral  aspect  corresponding  to  the  future  flexor  surface  of  the  limb,  the  dorsal  to  the  ex- 
tensor side.  At  the  same  time,  the  borders  are  directed  headwards  (pre-axial),  and  tailwards 
(post-axial).  As  the  limbs  grow,  they  soon  display  evidence  of  division  into  segments  correspond- 
ing to  the  hand  and  foot,  forearm  and  leg,  upper  arm  and  thigh.  Coincident  with  this  (about  the 
second  month)  the  cartilaginous  framework  of  the  limb  is  being  differentiated.  The  disposition 
of  these  cartilages  furnishes  a  clue  to  their  homologies.  In  the  fore  limb  the  radius  ancT  thumb 
lie  along  the  pre-axial  borders,  and  correspond  to  the  tibia  and  great  toe,  which  are  similarly  dis- 
posed in  the  hind  limb  ;  whilst  the  ulna  and  fifth  finger  are  homologous  with  the  fibula  and  fifth 
toe,  which  are  in  like  manner  arranged  in  relation  to  the  posterior  (post-axial)  border  of  their 
respective  limbs.  Up  to  this  time  the  limbs  are  directed  obbquely  ventralwards  from  the  head 
towards  the  tail-end  of  the  embryo.  During  the  third  month,  however,  a  change  in  their  posi- 
tion takes  place,  owing  to  their  axes  being  rotated  in  opposite  directions.  The  fore  limb  is 
turned  outwards  and  forwards  to  the  extent  of  90°,  whilst  the  lower  hind  limb  is  twisted  inwards 
and  backwards  to  a  corresponding  degree.  This  gives  rise  to  a  change  in  the  disposition  of  the 
joints  of  the  flexor  and  extensor  surfaces.  The  flexor  surface  of  the  elbow  is  now  directed  for- 
wards, whilst  the  corresponding  aspect  of  the  knee  is  turned  backwards,  and  in  consequence  the 
dorsal  or  extensor  aspect  of  the  fore  limb  is  posterior,  whilst  the  dorsal  or  extensor  aspect  of  the 
hind  limb  has  become  anterior.  Correspondingly,  the  pre-axial  border  of  the  fore  limb  with  the 
thumb  now  lies  external,  whilst  the  pre-axial  border  of  the  hind  limb  with  the  great  toe  has 
become  internaL  A  knowledge  of  these  changes  is  necessary  to  account  for  the  homologies  of  the 
various  structures  within  the  limb.  In  the  axial  mesoderm  of  each  member,  differentiation 
into  cartilaginous  segments  begins  about  the  second  month  ;  each  of  these  cartilages  becomes  in- 
vested by  a  perichondrial  layer  which  stretches  from  segment  to  segment,  and  ultimately  forma 
the  ligaments  surrounding  the  joints,  which  are  subsequently  develoj)ed  between  the  segments. 
Chondrification  first  begins  in  the  basal  part  of  the  limb,  and  extends  towards  the  digits.  In  the 
upper  arm  and  thigh  the  humerus  and  femur  are  homodynamous.  In  the  forearm  and  leg  the 
pre-axial  radius  corresponds  with  the  pre-axial  tibia,  and  the  post-axial  ulna  with  the  post-axial 
fiVjula.  The  homodynamy  of  the  carpal  and  tarsal  elements  may  be  tabular]  y  expressed,  and 
compared  with  the  more  generalised  types  from  which  they  are  evolved. 

Type.  Hand.  Foot. 

Radiale  (Tibiale)  =Scai)hoid  (body)  =  Astragalus. 

Intermedium  =  Semilunar  =  Absent,  or  Os  trigonum  (?) 

Ulnare  (Fibulare)  =  Cuneiform  =0s  Calcis. 

Centrale  =Aljsent,  or  Tubercle  on  Scai)hoid  =  Navicular. 

Carpale  (Tarsale),  i.      =  Trapezium  =  Internal  Cuneiform. 

Carpale  (Tarsale),  ii.     =Ti'apezoid  =  Middle  Cuneiform. 

Carpale  (Tarsale),  iii.   =0h  Magnum  =  External  Cuneiform. 
Carrjale  (Tarsale),  iv.l      tt     ■<•  n  i    -i 

Carpale  (Tarsale)!  v.  /  =  Unciform  =  Cuboid. 

The  pisiform  is  omitted  from  the  above  table,  since  it  is  now  generally  regarded  as  being  a 
vestige  of  an  additional  digit  placed  ]jost-axial  to  the  little  finger  (digitus  post-minimus).  Its 
liomologue  in  the  loot  is  by  .some  considered  as  fused  with  the  os  calcis.  Similarly,  on  the  pre- 
axial  border  of  the  hand  and  foot,  ve.stiges  of  a  suppressed  digit  (prepollex  and  i)rehallux)  may 


254  OSTEOLOGY. 

occasionally  be  met  with.  The  frequent  occurrence  of  an  increase  in  the  numljer  of  digits  seems 
to  indicate  that  jjliylogenetically  the  number  of  digits  was  greater  than  at  present,  and  included  a 
prepoUex  or  preliallux,  and  a  digitus  j'ost-miniuius.  Tlie  correspondence  of  the  metacarpus  witk 
the  metatarsus  and  the  phalanges  of  the  fingers  with  those  of  th.e  toes  is  so  obvious  that  it  is 
sufficient  merely  to  mention  it. 

The  differences  in  size,  form,  and  disposition  of  the  skeletal  elements  of  the  hand  and  foot  is 
easily  accoimted  for  by  a  reference  to  tlie  fuiictions  they  subserve. 

In  the  hand  strengtli  is  sacrificed  to  mobility,  thus  leading  to  a  reduction  in  the  size  of  the 
carpal  elements,  and  a  marked  increase  in  the  length  of  the  digital  phalanges.  The  freedom  of 
movement  of  the  thumb,  and  its  opjaosability  to  the  other  digits,  greatly  enhances  the  value  of 
the  hand  as  a  grasping  organ.  In  the  foot,  where  stability  is  the  main  requirement,  the  tarsus 
is  of  much  greater  proportionate  size,  whilst  tlie  phalanges  are  correspondingly  reduced.  Since 
the  foot  no  longer  serves  as  a  grasping  organ,  the  great  toe  is  not  free  and  opposable  like  the 
thumb. 

Limb  Grirdles. — The  free  limbs  are  linked  to  the  axial  skeleton  by  a  chain  of  bones  which 
constitute  their  girdles.  The  fundamental  form  of  these  limb  girdles  consists  each  of  a  pair  of 
carved  cartilages  placed  at  right  angles  to  the  axis  of  the  trunk  on  either  side,  and  embedded 
within  its  musculature.  Each  cartilage  has  an  articular  surface  externally,  about  the  middle,  for 
the  reception  of  the  cartilage  of  the  first  segment  of  the  free  limb.  In  this  way  each  pectoral 
and  pelvic  cartilage  is  divided  into  an  upper  or  dorsal  half  and  a  lower  or  ventral  half.  The 
dor,sal  halves  constitute  the  sca^Jula  and  ilium  of  the  j^ectoral  and  pelvic  girdles  respectively. 
Witli  regard  to  the  ventral  halves  there  is  more  difficulty  in  establishing  their  homologies.  The 
original  condition  is  best  displayed  in  the  j^elvic  girdle  ;  here  the  ventral  segment  divides  into 
two  branches — one  anterior,  which  represents  the  pubis,  the  other  posterior,  which  ultimately 
forms  the  ischium.  Ventrally,  the  extremities  of  these  cartilages  unite  to  enclose  the  obturator 
foramen.  In  the  pectoral  girdle  the  disposition  of  the  ventral  cartilages  is  not  so  clear,  consisting 
primitively  of  an  anterior  branch  or  precoracoid,  and  a  posterior  portion  or  coracoid ;  these,  in 
higher  forms,  have  undergone  great  modifications  in  adaptation  to  the  requirements  of  the  fore 
limbs.  The  posterior  or  coracoid  element,  the  homologue  of  the  ischial  cartilage  in  the  pelvic 
girdle,  is  but  feebly  represented  in  man  by  the  coracoid  process  and  the  coraco-clavicular  ligament. 
With  regard  to  the  homologue  of  the  pubic  element  in  the  pectoral  girdle,  there  is  much  difference 
of  opinion ;  in  reptiles  and  amphibia  it  corresponds  most  closely  to  the  precoracoid,  but  it  is 
doubtful  what  represents  it  in  mammals.  According  to  Goette  and  Hoff'man,  the  clavicle  is  a 
primordial  bone,  and  not,  as  suggested  by  Gegenbaur,  of  secondary  or  dermic  origin.  If  this  be 
so,  it  corresponds  to  the  ventral  anterior  segment  of  the  pectoral  girdle,  and  is  therefore  homo- 
logous with  the  ventral  anterior  (pubic)  segment  of  the  pelvic  girdle.  On  the  other  hand,  if 
Gegenbaur's  view  he  accef)ted,  the  clavicle  has  no  representative  in  the  pelvic  girdle.  It  must, 
however,  be  borne  in  mind  that  during  its  ossification  it  is  intimately  associated  with  cartilage, 
and  that  that  cartilage  may  represent  the  j)recoracoid  bar ;  nor  must  too  great  stress  be  laid  upon 
the  fact  that  the  clavicle  begins  to  ossify  before  it  is  performed  in  cartilage,  since  that  may  be 
merely  a  modification  in  its  histogenetic  development. 

According  to  another  view  (Sabatier),  the  subcoracoid  centre  (see  Ossification  of  Scapula)  is 
derived  from  the  ^Josterior  ventral  segment,  and  corresponds  to  the  ischium,  whilst  the  coracoid 
process  is  the  remains  of  the  anterior  ventral  segment  (precoracoid),  and  is  homodynamous  with 
•the  pubis. 

In  no  part  of  the  skeleton  does  function  react  so  much  on  structure  as  in  the  arrangement  of 
the  constituent  parts  of  the  pectoral  or  pelvic  girdles.  In  man,  owing  to  the  assumption  of  the 
erect  position  and  the  pij^edal  mode  of  jDrogression,  the  pelvic  girdle  acquires  those  characteristics 
which  are  essentially  human,  viz.  its  great  relative  breadth  and  the  exj^ansion  of  its  iliac 
portions,  which  serve  as  a  support  to  the  abdominal  viscera,  and  also  furnish  an  extensive  origin 
to  the  jiowerful  muscles  which  control  the  movements  of  the  hip-joint.  The  stability  of  the 
pelvic  girdle  is  insured  by  the  nature  of  its  union  with  the  axial  skeleton,  as  well  as  by  the 
osseous  fusion  of  its  several  parts,  and  their  union  in  front  at  the  symj^hysis  pubis. 

In  man,  since  the  erection  of  the  figure  no  longer  necessitates  the  use  of  the  fore  liml)  as  a 
means  of  support,  the  shoulder  girdle  has  become  modified  along  lines  wliich  enhance  its  mobility 
and  determine  its  utility  in  association  with  a  prehensile  limb.  Some  of  its  parts  remain 
independent  (clavicle  and  sca2Dula),  and  are  united  by  diarthrodial  joints,  whilst  others  have 
become  much  reduced  in  size  or  suj^pressed  (coracoid -precoracoid,  see  ante).  The  dorsal  part 
of  the  girdle  (scapula)  is  not  directly  united  with  the  axial  skeleton  as  is  the  ilium,  but  is  only 
indirectly  joined  to  it  through  the  medium  of  the  claAdcle,  which  is  linked  in  front  with  the 
presternum.  The  same  underlying  principles  determine  the  differences  in  mobility  and  strength 
between  the  shoulder,  elbow,  and  wiist,  and  the  hip,  knee,  and  ankle  joints  of  the  fore  and  hind 
limbs  respectively,  whilst  the  utility  of  the  liancl  is  further  enhanced  by  the  movements  of 
pronation  and  sujjination  wliich  occur  between  the  bones  of  the  forearm.  In  the  leg  such 
movements  are  al^sent,  as  they  would  interfere  with  the  stability  of  the  limb. 


THE   ARTICULATIONS   OR  JOINTS. 

ARTHROLOGY. 

By  David  Hepburn. 

Arthrology  is  that  branch  of  human  anatomy  which  treats  of  the  articulations 
or  joints. 

An  articulation  or  joint  constitutes  a  mode  of  union  or  connexion  subsisting 
between  any  two  separate  segments  or  parts  of  the  skeleton,  whether  osseous  or 
cartilaginous,  and  having  for  its  primary  object  either  the  preservation  of  a  more 
or  less  rigid  continuity  of  the  parts  joined  together,  or  else  to  permit  of  a  variable 
degree  of  mobility,  subject  to  the  restraints  of  the  uniting  media. 

Classification  of  Joints. — In  attempting  to  frame  a  classification  of  the 
numerous  joints  in  the  body,  several  considerations  must  be  taken  into  account, 
viz.  the  manner  and  sequence  of  their  appearance  in  the  embryo ;  the  nature  of  the 
uniting  media  in  the  adult,  and  also  the  degree  and  kind  of  movement  permitted 
in  those  joints  where  movement  is  possible. 

In  this  way  we  obtain  two  main  subdivisions  of  joints : — 

(1)  Those  in  which  the  uniting  medium  is  coextensive  with  the  opposed  sur- 
faces of  the  bones  entering  into  the  articulation,  and  in  which  a  direct 
union  of  these  surfaces  is  thereby  effected. 

(2)  Those  in  which  the  uniting  medium  has  undergone  more  or  less  of  interrup- 
tion in  its  structural  continuity,  and  in  which  a  cavity  of  greater  or  less 
extent  is  thus  formed  in  the  interior  of  the  joint. 

To  the  first  group  belong  all  the  immovable  joints,  many  of  which  are  likewise 
of  temporary  duration ;  to  the  second  group  belong  all  joints  which  possess  as  their 
outstanding  features  mobility  and  permanence. 


SYNARTHROSES. 

The  general  characteristics  of  this  group  are  partly  positive  and  partly  nega- 
tive. Thus  there  is  uninterrupted  union  between  the 
opposed  surfaces  of  the  bones  joined  together  at  the  plane 
of  the  articulation,  i.e.  there  is  no  trace  of  a  joint  cavity, 
and  further,  there  is  an  entire  absence  of  movement. 
Develcpmentally,  these  joints  result  from  the  approxi- 
mation of  ossific  processes  which  have  commenced  from 
separate  centres  of  ossification,  and  therefore  the  nature 
of  the  uniting  medium  varies  according  as  the  bones 
thus  joined  together  have  originally  ossified  in  membrane 
or  in  cartilage.  In  the  former  case  union  is  effected  by 
an  interposed  fibrous  membrane  continuous  with  and 
corresponding  to  the  periosteum.  To  such  articulations 
the  term  suture  (Fig.  203)  is  appli(!d.  In  the  latter  case 
the  uniting  medium  is  a  ])late  of  hyaline  cartilage.  Such 
articulations  are  called  synchondroses  fKig.  204).  In  all^the  synclKmdroses,  and  in 
many  of  the  sutures,  th(;   uniting  medium  tends  to  disappear  in   the  progress  of 

255 


203. — Vertical  Skction 
thkouuh  a  sutuuk. 


256 


THE  AETICULATIONS  OE  JOINTS. 


ossification,  and  thus  the  plane  of  articulation  becomes  obliterated,  so  that  direct 
structural  continuity  between  the  osseous  segments  takes  place.  The  primary- 
features  common  to  all  synarthroses  are — {a)  continuous 
and  direct  union  of  the  opposing  surfaces;  (Jb)  no  joint 
cavity  ;  (c)  no  movement. 

Suture. — This  form  of  synarthrosis  is  only  found  in 
connexion  with    the   bones  of   the   skull.     In   a   large 
number  of  cases  the  bones  which  articulate  by  suture 
present   irregular  interlocking  margins,  between  which 
there  is  the  interposed  fibrous  membrane  to  which  refer- 
ence has  already  been  made.     When  these  interlocking 
margins  present  well-defined  projections  they  are  said  to 
form  true  sutures — sutura  vera  ;  on  the  other  hand,  when 
Fig.   204.  — Section  through    the  opposed  surfaces  present  ill-defined  projections,  or 
THE  OccipiTo-spHENoiD  Syn-    gvcn    flat   arcas,  they  are   described  as  false  sutures — 
cHONDRosis.  sutura  notha.     In  each  of  these  subdivisions  the  particular 

characters  of  the  articulating  margins  are  utilised  in  framing  additional  descriptive 
terms.  Thus  true  sutures  may  possess  interlocking  margins  whose  projections  are 
tooth-like  (sutura  dentata),  e.g.  in 'the  interparietal  suture ;  saw-like  (sutura  serrata), 
(Fig.  205)  e.g.  in  the  interfrontal  suture ;  ridge-like,  or  comparable 
to  the  parallel  ridges  on  the  welt  of  a  boot  (sutura  limbosa). 
Similarly  false  sutures  may  articulate  by  margins  which  are  scale- 
like (sutura  squamosa),  e.g.  in  the  squamoso-parietal  suture ;  or  by 
rough  opposed  surfaces  (sutura  harmonia),  e.g.  in  the  suture  between 
the  palate  plates  of  the  superior  maxillary  bones.  There  is  one 
variety  of  synarthrosis  which,  in  the  adult,  can  scarcely  be  called  a 
suture,  although  the  differences  are  of  minor  importance,  viz. 
schindylesis,  which  is  an  articulation  between  the  edge  of  a  plate- 
like bone,  such  as  the  rostrum  of  the  sphenoid,  and  the  cleft  in 
another,  such  as  the  vomer. 

Synchondrosis. — Illustrations  of  this  group  can  only  be  found  ^^^'  gERRAXA'^^^^^ 
in  the  young  growing  individual,  because  as  age  advances  and 
growth  ceases,  the  process  of  ossification  affects  the  hyaline  cartilage  which  con- 
stitutes the  uniting  medium,  and  the  plane  of  articulation  disappears.  Under  this 
heading  we  may  include  the  planes  of  junction  between  all  epiphyses  and  the 
shafts  or  diaphyses  to  which  they  severally  belong.  The  occipito-sphenoid  (Fig. 
204)  and  the  petro-jugular  articulations  in  the  base  of  the  skull  provide  other 
well-marked  examples. 


MOVABLE  JOINTS. 

The  leading  features  of  this  group  are  capability  of  movement  and  permanence. 

In  very  few  instances  do  such  joints  ever  become  obliterated  under  normal  con- 
ditions. Determining  their  permanence,  and  regulating  the  amount  of  possible 
movement,  there  is  always  more  or  less  of  interruption  in  the  continuity  of  the 
structures  which  bind  the  osseous  elements  together.  That  is,  there  is  always  some 
evidence  of  a  joint  cavity,  although  as  a  matter  of  course  such  interruption  can 
never  be  so  extensive  as  to  entirely  disassociate  the  articulating  elements.  There- 
fore in  all  movable  joints  a  new  class  of  structures  is  found,  viz.  the  ligaments,  by 
means  of  which  continuity  is  maintained  even  when  all  the  other  uniting  media 
have  given  place  to  a  joint  cavity.  The  further  subdivision  of  this  group  is  founded 
upon  the  amount  of  movement  permissible,  and  the  extent  to  which  the  joint  cavity 
takes  the  place  of  the  original  continuous  uniting  medium.  Thus  we  obtain  the 
partly  movable  or  ampMarthroses,  and  the  freely  movable  or  diarthroses. 

An  amphiarthrosis  (Fig.  208)  presents  the  following  characteristics :  {a) 
partial  movement ;  (&)  union  by  ligaments  and  by  an  interposed  .plate  or  disc  of 
fibro-cartilage,  in  the  interior  of  which  there  is,  (c)  an  incomplete  or  partial  joint 
cavity  which  may  be  lined  by  a  rudimentary  synovial  membrane  whose  function  it 
is  to  secrete  a  lubricating  fluid,  the  synovia  or  joint-oil ;   {d)  a  plate  of  hyaline 


STRUCTUKE  OF  JOINTS. 


257 


^Articular 
cartilage 


_  Joint 
capsule 

Synovial 
membrane 


cartilage  coating  each  of  the  opposing  surfaces  of  the  Ijones  concerned.  All  tlie 
joints  belonging  to  this  group  occur  in  the  mesial  plane  of  the  body.  It  includes 
the  symphysis  pubis,  the  joints  between  the  Ijodies  of  the  vertebrae,  and  the  joint 
between  the  manubrium  sterni  and  the  gladiolus. 

A  diarthrosis  (Fig.  206)  is  the  most  elaborate  as  well  as  the  most  complete  form 
of  articulation.  It  is  characterised  by  {a)  capability  of  movement  which  is  more  or 
less  free  in  its  range ;  (h)  a  reduction  of  the 
uniting  structures  to  a  series  of  retaining  liga- 
ments; (c)  a  joint  cavity  which  is  only 
limited  by  the  surrounding  ligaments;  {d) 
the  constant  presence  of  synovial  membrane ; 
(e)  hyaline  encrusting  cartilage  which  clothes 
the  opposed  surfaces  of  the  articulating  bones. 
The  majority  of  the  joints  in  the  adult  belongs 
to  this  group.  This  series  of  joints  has  been 
subdivided  into  a  number  of  minor  sections, 
in  order  to  emphasise  the  occurrence  of 
certain  well-marked  structural  features,  or 
because  of  the  particular  nature  of  the  move- 
ment by  which  they  are  characterised. 
Although  in  all  diarthroses  there  is  a  certain 
amount  of  gliding  movement  between  the 
opposed  surfaces  of  the  bones  which  enter  into  their  formation,  yet,  when  this  gliding 
movement  becomes  their  prominent  feature,  as  in  most  of  the  joints  of  the  carpus  and 
tarsus,  they  are  termed  arthroclia.  But  bones  may  be  articulated  together  so  as  to 
permit  of  movement  in  one,  two,  or  more  fixed  axes  of  movement,  or  in  modifications 
of  these  axes.  Thus  in  uniaxial  joints  the  axis  of  movement  may  lie  in  the  longi- 
tudinal axis  of  the  joint,  in  which  case  the  rotatory  form  of  joint  results,  as  in 
the  superior  and  inferior  radio-ulnar  articulations  ;  or  it  may  correspond  with  the 
transverse  axis  of  the  articulation,  as  in  the  elbow-joint  and  knee-joint,  when  the 
ginglymus  or  hinge  variety  results.  If  movement  takes  place  about  two  principal 
axes  situated  at  right  angles  to  each  other,  as  in  the  radio-carpal  joint,  the  terms 
■biaxial  or  condyloid  are  applied.  Movements  occurring  about  three  principal  axes 
placed  at  right  angles  to  each  other,  or  in  modifications  of  these  positions,  con- 
stitute multiaxial  joints,  in  which  the  associated  structural  peculiarities  provide  the 
alternative  terms  of  enarthrodial  or  ball-and-socket  joints. 


Articular 
cartilage 


Fig.  206. 


-Diagram  of 
.Joint. 


DiARTHRODIAL 


STRUCTUEES  WHICH  ENTER  INTO  THE  FORMATION  OF  .JOINTS. 

The  structures  which  enter  into  the  formation  of  joints  vary  with  the  nature 
of  the  articulation.  In  every  instance  there  are  two  or  more  skeletal  elements, 
whether  bones  or  cartilages,  and  in  addition  there  are  the  vmiting  media,  which  are 
either  simple  or  elaborate  according  to  the  provision  made  for  rendering  the  joint 
more  or  less  rigid  or  capable  of  movement.  We  have  already  seen  that  the  uniting 
medium  in  synarthrodia!  joints  is  a  remnant  of  the  common  matrix,  whether  fibro- 
vascular  membrane  or  hyaline  cartilage,  in  which  ossification  has  extended  from 
separate  centres.  Among  the  amphiarthroses  there  is  still  extensive  union  between 
the  opposing  surfaces  of  the  articulating  bones,  but  the  character  of  the  uniting 
medium  has  advanced  from  the  ])rimitive  embryonic  tissue  to  fibrous  and  fibro- 
cartilaginous material,  as  well  as  hyaline  cartilage.  These,  with  very  few  exceptions, 
are  permanent,  non-ossifying  substances,  such  as  may  be  seen  between  the  opposing, 
osseous  surfaces  of  two  vertebral  bodies.  The  joint  cavity,  more  or  less  rudimentary, 
is  confined  to  the  centre  of  the  fibro-cartilaginous  plate,  and  may  result  from  the 
softening  or  imperfect  cleavage  of  tlie  central  tissue.  It  may  also  present  rudiments 
of  a  syuovifil  iiK^jiilji-auc. 

In  the  diarthrodial  group  the  extensive  cavity  has  produced  great  interruption 
in  th(;  continuity  ol'  the  uniting  structures  which  originally  existed  betwcuin  the 
hones  I'orming  such  a  joint.  Jvigamonts  have  therefore  additional  importance  in 
this  grouj),  for  not  only  do  th(;y  constitute  the  uniting  media  which  bind  the 
articulating  bones  together,  but  to  a  large  extent  they  form  the  peripheral 
18 


258 


THE  AETICULATIONS  OR  JOINTS. 


boundary  of  the  joint  cavity,  although  not  equally  developed  in  all  positions. 
Thus  every  diarthrodial  joint  possesses  a  fibrous  or  ligamentous  envelope  or 
capsule  which  is  attached  to  the  adjacent  ends  of  the  articulating  bones.  For 
special  purposes,  particular  parts  of  the  capsule  may  undergo  enlargement  and 
thickening,  and  so  constitute  strong  ligamentous  bands,  although  still  forming  con- 
tinuous constituents  of  the  capsule. 

Within  the  capsule  a  series  of  intracapsular  structures  are  present.  Thus  the 
capsule  itself  is  always  lined  by  a  synovial  membrane,^  which  is  continued  from  the 
inner  surface  of  the  capsule  to  the  surface  of  the  intracapsular  portion  of  each 
articulating  bone.  The  part  of  the  bone  included  within  the  capsule  consists  of  a 
"  non-articular  "  portion  covered  by  synovial  membrane,  and  an  "  articular  "  portion 
covered  by  encrusting  hyaline  cartilage.  The  latter  provides  the  surface  which 
comes  into  apposition  with  the  corresponding  area  of  another  bone.  In  its  general 
disposition  the  synovial  membrane  may  be  likened  to  a  cylindrical  tube  open  at 
each  end.  This  membrane  is  richly  supplied  by  a  close  network  of  vessels  and 
nerves. 

Certain  diarthroses  present  additional  intracapsular  structures  wliich  may  be 
distinguished  as  interarticular  ligaments  and  interarticular  fibro-cartilages. 

Interarticular  ligaments  extend  between  and  are  attached  to  non-articular  areas 
of  the  intracapsular  portions  of  the  articulating  bones.  They  usually  occupy  the 
long  axis  of  the  joint,  and  occasionally  they  widen  sufficiently  to  form  partitions 
which  divide  the  joint-cavity  into  two  compartments,  e.g.  the  costo-central,  and 
certain  of  the  chondro-sternal  joints. 

Interarticular  fibro-cartilages  or  menisci  (Fig.  207)  are  more  or  less  complete 
partitions  situated  between  and  separating  opposing  articular  surfaces,  and  when 
complete  they  divide  the  joint  cavity  into  two  distinct  compartments.     By  its 

periphery,  a  meniscus  is  rather  to  be  associated 
with  the  joint  capsule  than  with  the  articu- 
lating bones,  although  its  attachments  may 
extend  to  non-articular  areas  on  the  latter. 

Both  interarticular  ligaments  and  menisci 
have  their  free  surfaces  covered  by  synovial 
membrane. 

Adipose  tissue  forming  pads  of  varying  size 
is  usually  found  in  certain  localities  within 
the  joint,  between  the  synovial  membrane  and 
the  surfaces  which  it  covers.  These  pads  are 
soft  and  pliable,  and  act  as  packing  material, 
filling  up  gaps  or  intervals  in  the  joint. 
During  movement  they  adapt  themselves  to 

^     „„-     T^  T^  ^     r  T.T..,.  the  changing  conditions  of  the  articulation. 

Fig.  20/. — Diagram  ok  a  Dtarthrodial  Joint    ^'-'■^  ^         o  _  &  ,.  , 

WITH  AN  iNTERARTicuLAK  MENISCUS  DiviD-  lu  additiou  to  mcrcly  biudmg  together  two 
iNG  THE  Joint  -  Cavity  into  two  Com-  or  more  articulating  bones,  ligaments  perform 
PARTMENTs.  ^^^^  importaut  functions  in  connexion  with 

the  different  movements  taking  place  at  a  joint.  They  do  not  appreciably  lengthen 
under  strains,  and  thus  ligaments  may  act  as  inhibitory  structures,  and  by  becom- 
ing tense  may  restrain  or  check  movement  in  certain  directions. 

Synovial  membranes,  in  the  form  of  closed  sacs  termed  synovial  bursse,  are  frequently  found 
in  other  situations  besides  the  interior  of  joints.  Such  bursae  are  developed  for  the  puri^ose  of 
reducing  the  friction,  (a)  between  the  integument  and  certain  prominent  sulacutaneous  bony  pro- 
jections, as,  for  instance,  the  point  of  the  elbow,  or  the  front  surface  of  the  patella  (subcutaneous 
synovial  burste) ;  (6)  between  a  tendon  and  some  surface,  bony  or  cartilaginous,  over  which  it 
plays  (subtendinous  sjTiovial  bursas) ;  (c)  between  a  tendon  or  a  group  of  tendons  and  the  w^alls 
of  osteo-fascial  tunnels,  in  which  they  play  (thecal  synovial  bursse).  Subtendinous  synovial 
bursEe  are  often  placed  in  the  neighbourhood  of  joints,  and  in  such  cases  it  not  infrequently 


Meniscus 

Synovial 

membrane 

Joint 

cavity 

Joint 

capsule 


1  The  term  "  synovial  membrane  "  lias  been  so  long  iu  use  that  one  hesitates  to  discard  it,  even  although  the 
structure  so  described  is  not  in  many  cases  capable  of  being  removed  from  the  objects  of  which  it  forms  a  part. 
A  more  precise  description  in  these'  cases  would  be  "synovial  surface."  There  is  still  considerable  doubt 
whether  the  "synovial  fluid"  is  a  true  secretion  or  merely  a  diluted  friction  product. 


THE  DIFFEEENT  KINDS  OF  MOVEMENT  AT  JOINTS.  259 

happens  that  there  is  a  direct  continuity  between  the  Inirsa  and  the  synovial  iiienil^rane  which 
lines  the  cavity  of  the  joint  through  an  aperture  in  the  jointcapside. 

THE  DIFFERENT  KINDS  OF  MOVEMENT  AT  JOINTS. 

Reference  has  already  been  made  to  the  existence  of  fixed  axes  of  movement  as 
a  basis  for  the  classification  of  certain  forms  of  diarthrodial  joints.  Hence  it  is 
evident  that  the  movements  which  are  possible  at  any  particular  joint  depend  to  a 
large  extent  upon  the  shape  of  its  articular  surfaces  as  well  as  upon  the  nature  of 
its  various  ligaments.  Therefore  the  technical  terms  descriptive  of  movements 
either  indicate  the  directions  in  which  they  occur,  or  else  the  character  of  the  com- 
pleted movement. 

In  the  great  majority  of  articulations  between  short  bones,  the  amount  of  move- 
ment is  so  restricted,  and  the  displacement  of  the  opposing  articular  surfaces  so 
shght,  that  the  term  gliding  sufficiently  expresses  its  character. 

A  gliding  movement  of  an  extensive  kind,  for  example  that  of  the  patella  upon  the  femur,  in 
which  the  movement  largely  resembles  that  of  the  tyre  of  a  wheel  revolving  in  contact  with  the 
ground  so  that  different  parts  are  successively  adapted  to  each  other,  is  called  co-aptation. 

Articulations  between  long  bones,  on  the  other  hand,  are  usually  associated 
with  a  much  freer  range  of  movement,  with  a  corresponding  variety  in  its  character. 
Rotation  is  a  movement  about  an  axis  which  is  longitudinal.  Sometimes  it  is  the 
only  form  of  movement  which  a  joint  possesses ;  at  other  times  it  is  merely  one  of  a 
series  of  movements  capable  of  execution  at  the  same  joint.  Flexion  or  bending  is 
a  movement  in  which  the  formation  of  an  angle  between  two  parts  of  the  body  is 
an  essential  feature.  As  it  is  possible  to  perform  tliis  movement  in  relation  to  two 
axes,  viz.  a  transverse  and  an  antero-posterior  axis,  it  is  necessary  to  introduce 
qualifying  terms.  Thus,  when  two  anterior  or  ventral  surfaces  are  approximated, 
as  at  the  hip-,  elbow-,  or  wrist-joints,  the  movement  is  called  ventral,  anterior,  or 
palmar  flexion ;  but  if  posterior  or  dorsal  surfaces  be  approximated  by  the  process  of 
bending,  then  the  flexion  becomes  posterior  or  dorsi-flexion,  as  at  the  knee-  or  wrist- 
joints.  Further,  at  the  wrist-joint,  the  formation  of  an  angle  between  the  ulnar 
border  of  the  hand  and  the  corresponding  aspect  of  the  forearm,  produces  ulnar 
flexion,  and  similarly  the  bending  of  the  hand  towards  the  radial  border  of  the 
forearm  is  radial  flexion. 

Extension  or  straightening  consists  in  obliterating  the  angle  which  resulted  from 
flexion.  In  the  case  of  certain  joints,  therefore,  such  as  the  elbow,  wrist,  and  knee, 
the  segments  of  the  limb  occupy  a  straight  line  as  regards  each  other  when 
extended. 

At  the  ankle-joint  the  natural  attitude  of  the  foot  to  the  leg  is  flexion  at  a  right  angle.  The 
diminution  of  this  angle  by  approximating  the  dorsum  of  the  foot  towaixls  the  front  of  the  leg 
constitutes  flexion  ;  while  any  effort  at  placing  the  foot  and  leg  m  a  straight  line,  i.  e.  obliteration  of 
the  angle,  as  in  pointing  the  toes  towards  the  ground  and  raising  the  heel,  constitutes  extension. 

Abduction  is  a  term  which  either  expresses  movement  of  an  entire  limb,  in  a 
direction  away  from  the  mesial  plane  of  the  body,  or  of  a  digit,  away  from  the 
plane  of  the  middle  finger  in  the  hand,  or  the  plane  of  the  second  toe  in  the  case 
of  the  foot. 

Adduction  is  the  reverse  of  abduction,  and  signifies  movement  towards  the 
mesial  plane  of  the  body,  or  towards  the  planes  indicated  for  the  digits  of  the  hand 
and  foot. 

Circumduction  is  a  movement  peculiarly  characteristic  of  multiaxial  or  ball- 
and-socket  joints.  It  consists  in  combining  such  angular  movements  as  flexion, 
extension,  abduction,  and  adduction,  so  as  to  continue  the  one  into  the  other, 
whereljy  the  joint  forms  the  apex  of  a  cone  of  movement,  and  the  free  end  of  the 
limb  travels  througli  a  circle  which  describes  the  base  of  this  cone. 

TJIK   DKVELOPMENT  OF  JOINTS. 

Just  as  the  fjucstion  of  structure  determines  to  a  largo  extent  the  presence  or  absence 
of    raovernent   in   joints,    so   in    tracing   their    develofjinent   it   will    Ijo    found    that    the 
18  a 


260  THE  AETICULATIONS  OK  JOINTS. 

manner  of  their  appearance  forecasts  their  nltimate  destination  as  immovable  or  mov- 
able articulations. 

All  joints  arise  in  mesodermic  tissue  which  has  undergone  more  or  less  differentiation. 

When  this  differentiation  has  produced  a  continuous  membranous  layer,  in  which 
ossific  centres  representing  separate  skeletal  segments  make  their  appearance,  we  get  the 
j)rimitive  form  of  suture.  The  plane  of  the  articulation  merely  indicates  the  limit  of 
the  ossific  process  extending  from  different  directions.  If,  again,  the  differentiation  of 
the  mesoblast  has  resulted  in  the  formation  of  a  continuous  cartilaginous  layer,  in  which 
ossification  commences  at  separate  centres,  the  plane  of  the  articulation  is  marked 
out  by  the  unossified  cartilage — in  other  words,  the  articulation  is  a  synchondrosis.  Ulti- 
mately this  disappears  through  the  extension  of  the  process  of  ossification. 

To  some  extent  sutures  also  disappear,  although  their  complete  obliteration  is  not 
usual  even  in  aged  people.  Developmentally,  therefore,  synarthroses  or  immovable 
joints  do  not  present  any  special  structural  element,  and,  speaking  generally,  they  have 
only  a  tempoi'ary  existence. 

The  development  of  all  movable  joints  is  in  marked  contrast  to  that  of  synar- 
throses. Not  only  are  they  permanent  arrangements  so  far  as  concerns  normal  conditions, 
but  they  never  arise  merely  as  planes  which  indicate  the  temporary  phase  of  an  ossific 
process.  From  the  outset  they  present  distinct  skeletal  units,  from  which  the  special 
structures  of  the  joint  are  derived. 

The  primitive  movable  joint  is  first  recognised  as  a  mass  of  undifferentiated  meso- 
dermic cells  situated  between  two  masses,  which  have  differentiated  into  primitive  cartilage. 

The  cell-mass  which  constitutes  the  joint-unit  presents  the  appearance  of  a  thick 
cellular  disc,  the  proximal  and  distal  surfaces  of  which  ai'e  in  accurate  apposition  \vith  the 
primitive  cartilages,  while  its  circumference  is  defined  from  the  surrounding  mesoderm  by 
a  somewhat  closer  aggregation  of  the  cells  of  which  the  disc  is  composed.  From  this 
celhdar  disc  or  joint-unit  all  the  structures  characteristic  of  amphiarthrodial  and  diar- 
throdial  joints  are  ultimately  developed. 

Thus  by  the  transformation  of  the  circumferential  cells  into  fibrous  tissue  the  invest- 
ing ligaments  are  produced.  Within  the  substance  of  the  disc  itself  a  transverse  cleft, 
more  or  less  well-defined  and  complete,  makes  its  appearance.  In  this  manner  the  disc  is 
divided  into  proximal  and  distal  segments,  separated  from  each  other  by  an  interval 
which  is  the  primitive  joint  cavity.  This  cleft,  however,  never  extends  so  far  as  to  inter- 
rupt the  continuity  of  the  circumferential  part  of  the  disc  which  develops  into  the  fibrous 
tissue  of  the  investing  ligaments.  From  the  proximal  and  distal  segments  of  the 
articular  disc  the  various  structures,  distinctive  of  movable  joints,  are  developed. 

Thus,  in  amphiarthrodial  joints  the  cellular  articular  disc  or  primitive  joint-unit  gives 
origin  to  the  following  structures  : — From  its  circumference,  investing  ligaments ;  from 
its  interior,  the  fibro-cartilaginous  plate  or  disc  in  which  an  imperfect  joint  cavity  with 
corresponding  imperfect  synovial  may  be  found. 

In  the  case  of  a  diarthrodial  joint  the  changes  take  place  on  a  more  extended  scale. 
The  joint  cavity  becomes  a  prominent  feature,  in  relation  to  which  the  surrounding 
fibrous  structures  form  an  investing  capsule,  lined  by  a  synovial  membrane. 

When  a  single  cleft  arises,  but  does  not  extend  completely  across  the  longitudinal  axis 
of  the  articular  disc,  the  undivided  portion  develops  into  fibrous  interarticular  ligaments. 
On  tlie  other  hand,  when  two  transverse  clefts  are  formed,  that  portion  of  the  cellular 
disc  which  remains  between  them  becomes  transformed  into  a  fibro-cartilaginous  inter- 
articular disc  or  meniscus,  which  in  its  turn  may  either  be  complete  or  incomplete,  and 
thus  we  may  obtain  two  distinct  synovial  joint  cavities  belonging  to  one  articulation.^ 

In  considering  the  development  of  the  synovial  membrane,  and  the  surfaces  on  which 
it  is  found  in  the  interior  of  a  joint,  it  is  necessary  to  keep  clearly  in  mind  that  a  synovial 
membrane  is  a  special  structure,  whose  function  it  is  to  produce  a  lubricating  fluid  or 
synovia,  and  that,  therefore,  its  position  is  determined  by  the  essential  necessity  of 
proximity  to  a  direct  blood-supply.  In  other  Avords,  this  condition  is  provided  by  all 
parts  of  the  interior  of  a  joint  cavity  except  the  articular  encrusting  cartilage.  Conse- 
quently sjaiovial  membrane  is  only  absent  from  the  free  surface  of  articular  cartilage, 
although  it  forms  a  thicker  layer  upon  the  inner  surface  of  the  joint  capsule  than  upon 
the  free  surfaces  of  interarticular  ligaments  and  menisci. 

^  From  a  series  of  observations  iipon  the  developmeut  of  diarthrorlial  joints,  the  writer  considers  that 
there  is  evidence  to  show  that  the  "cellular  articular  disc "  is  directly  responsible  for  the  production  of 
the  epiphyses  which  adjoin  the  completed  joint  cavity,  and  that,  among  such  amphiarthroses  as  exist 
between  the  bodies  of  vertebrre,  not  only  the  intervertebral  disc,  but  the  proximal  and  distal  epiphyses 
which  ultimately  unite  with  the  vertebral  bodies  have  a  common  origin  in  the  joint-unit. 


LIGAMENTS  OF  THE  VERTEBRAL  COLUMN.  261 

It  is  not  necessary  to  suppose  that  the  synovial  membrane  has  disappeared  from  these 
articular  cartilages  as  the  result  of  friction,  because,  notwithstanding  constant  friction, 
such  parts  as  the  interior  of  capsular  ligaments  or  the  semilunar  cartilages  of  the  knee- 
joint  have  not  been  denuded  of  their  synovial  covering. 

MORPHOLOGY  OF  LIGAMENTS. 

From  what  has  been  said  in  connexion  with  the  development  of  joints,  it  will  be  evident 
that  ligaments  are  essentially  products  derived  from  the  cellular  articular  disc. 

Nevertheless,  in  relation  to  the  fully-formed  joint,  many  structures  are  described  as  ligaments 
which  do  not  take  origin  in  the  manner  just  indicated.  Some  of  these  ligamentous  structures 
remain  fairly  distinct  from  the  capsular  ligaments  with  which  they  are  immediately  associated  ; 
others  become  thoroughly  incorporated  with  the  capsular  ligaments  and  cannot  be  separated 
therefrom,  while  yet  others  may  be  found  situated  within  the  capsule  of  a  joint,  and  thiLs  play 
the  part  of  interarticular  ligaments. 

Instances  of  each  of  these  forms  of  adventitious  ligaments  may  be  readily  given.  For 
examj)le,  we  may  instance  the  expansion  of  the  tendon  of  the  semimembranosus  muscle  to  the 
posterior  ligament  of  the  knee-joint,  and  the  offshoots  from  the  tendon  of  the  tibialis  posticus 
muscle  to  the  plantar  aspects  of  various  tarsal  bones,  as  illustrations  of  structiues  which  play 
an  important  part  as  ligaments,  but  are  not  indelibly  incorporated  with  the  joint  capsule. 

Of  structures  which  have  become  indeKbly  incorporated  -with  the  primitive  capsule,  we  may 
instance  the  broad  tendinous  expansions  of  the  quadriceps  extensor  muscle  around  the  knee-joint. 

The  internal  lateral  ligament  of  the  same  joint  is  regarded  as  a  detached  portion  of  the 
tendon  belonging  to  that  part  of  the  adductor  magnus  muscle  which  takes  origin  from  the 
ischium,  while  the  external  lateral  ligament  of  the  knee  is  considered  by  some  to  be  the  primi- 
tive femoral  origin  of  the  peroneus  longus  muscle.  Another  illustration  of  the  same  condition 
is  found  in  tlie  coraco -humeral  ligament,  which  is  regarded  by  some  as  representing  a  detached 
portion  of  the  pectoralis  minor  muscle. 

Two  illustrations  may  be  given  of  structures  playing  the  part  of  ligaments  within  the 
capsule  of  a  joint,  although  in  the  first  instance  they  are  not  developed  as  ligaments.  It  is 
questionable  if  the  ligamentum  teres  of  the  hij)-joint  is  an  interarticular  ligament  in  the  true 
sense  of  the  term  ;  it  has  been  regarded  as  the  isolated  and  disjjlaced  tendon  of  the  ambiens  muscle 
found  in  birds.  In  the  shoulder-joint,  many  observers  look  upon  the  superior  gleno-humeral 
ligament  as  representative  of  the  ligamentum  teres. 

Such  structures  as  the  stylohyoid  ligament  and  the  internal  lateral  ligament  of  the  temjaoro- 
mandibular  joint,  although  described  as  ligaments,  are  in  reality  skeletal  parts  which  have  not 
attained  their  complete  ossific  development. 

Again,  certain  portions  of  the  deep  or  muscular  fascia  of  the  body  which  become  specialised 
into  restraining  and  supporting  bands  {e.g.  the  ilio-tibial  band  of  the  fascia  lata  ;  the  stylo-mandi- 
bular  ligament ;  the  anterior  and  posterior  annular  ligaments  of  the  wrist-joint ;  the  anterior, 
inner,  and  outer  annular  ligaments  of  the  ankle-joint),  although  called  ligaments,  have  no 
direct  developmental  association  with  articular  ligaments. 

Lastly,  the  ligament  of  Poupart  and  the  ligament  of  Gimbernat,  being  special -developments 
in  connexion  with  an  expanded  tendon  or  aponeurosis,  are  still  further  removed  from  associa- 
tion with  an  articulation. 


LIGAMENTS  OF  THE  VERTEBRAL  COLUMN  AND  SKULL. 

All  vertebrae,  with  the  exception  of  those  which  deviate  from  the  common 
vertebral  type,  present  two  sets  of  articulations  whose  various  parts  are  arranged 
upon  a  uniform  pattern.  Thus  every  pair  of  typical  vertebrae  presents  an  articula- 
tion between  the  centra,  termed  intercentral,  and  a  pair  of  articulations  between 
the  neural  arches,  called  interneural.  With  the  latter  there  are  associated  various 
important  accessory  ligaments  which  bind  together  laminae,  spinous  processes,  and 
transverse  processes. 

Intercentral  Articulations. — These  are  amphiarthrodial  joints.  Singly,  they 
present  only  a  slight  degree  of  mobility,  but  when  this  amount  of  movement  is 
added  to  that  of  the  whole  series,  the  range  of  movement  of  the  spine  becomes 
considerable.  The  articular  surfaces  are  the  flattened  surfaces  of  adjacent  vertebral 
bodies.     Tli(!y  are  bound  together  by  the  following  structures : — 

Intervertebral  Discs  (fibro-cartilagines  intervertebrales,  Fig.  208). — Each  disc 
accommodutes  itself  to  the  space  it  occujnes  between  the  two  vertebral  bodies,  to 
both  of  whicli  it  is  firmly  adherent.  The  discs,  from  dilferent  parts  of  the  spinal 
column,  vary  in  vertical  thickn(;ss,  being  thinnest  from  thi;  third  to  the  seventh  dorsal 
vertebra,  and  thickest  in  the  lumbar  region.  In  the  cervical  and  lumbar  regions 
each  disc  is  thicker  in  front  than  behind,  thereby  assisting  in  the  production  of  the 
18  & 


262 


THE  AETICULATIONS  OK  JOINTS. 


anterior  convexity  which  characterises  the  spinal  column  in  these  two  regions.  In 
the  dorsal  region  the  discs  are  thinnest  on  their  anterior  aspects  in  correspondence 
with  the  anterior  concavity  of  this  section  of  the  spine. 

Each  disc  consists  of  a  circumferential  portion  (annulus  fibrosus),  formed  for 


Vertebral  body 


Intervertebral  disc 


Ligaiiieiituiii  flavuni 
or  subflavuni 


Nucleus  pulposus 


-  Spinous  jirocess 


Fig.  208. — Mesial  Section  through  a  Portion  of  the  Lumbar  Part  of  the  Spine. 

the  most  part  of  oblique  parallel  fibres  running  from  one  vertebra  to  the  other. 
Horizontal  fibres  are  also  found.  The  axial  or  central  part  of  the  disc  is  elastic, 
soft,  and  pulpy  (nucleus  pulposus).'- 

The  upper  and  lower  surfaces  of  the  disc  are  closely  adherent  to  the  adjoining 

Anterior  common  ligament 
Rib 


Anterior  or 
superior  costo- 
transverse 
ligament 


Three  slips  of  the 
stellate  ligament 


Anterior  or 
superior  costo- 
transverse 
ligament 


Fig.  209.— Anterior  Common  Ligament  of  the  Vertebral  Column,  and  the  Costo-vertebral 

Joints  as  seen  from  the  Front. 

epiphyseal  plates  of  the  vertebral  bodies,  and  as  ossification  advances,  the  distinc- 
tion between  epiphyseal  plates  and  vertebral  body  disappears. 

As  a  rule  the  transverse  diameter  of  the  disc  corresponds  to  that  of  the  verte- 
bral bodies  which  it  joins  together ;  but  in  the  cervical  region,  where  the  lower 

1  This  pulpy  substance  does  not  present  a  joint  cavity,  but  in  certain  cases  it  is  more  or  less  divided 
by  fissures  which  occupy  a  transverse  horizontal  direction. 


LIGAMENTS  OF  THE  VERTEBKAL  COLUMN. 


263 


margin  of  the  superimposed  vertebra  is  overlapped  on  each  side  by  the  one  wliich 
bears  it,  the  disc  does  not  extend  to  the  extreme  lateral  margin,  and  in  this  position 
a  small  diarthrosis  may  be  seen  at  each  lateral  margin  of  the  disc. 

The  anterior  common  ligament  (lig.  longitudinale  anterius.  Fig.  209)  consists 
of  a  wide  stratum  of  longitudinal  fibres  which  extends  from  the  front  of  the  axis 
vertebra  to  the  front  of  the  upper  segment  of  the  sacrum,  and  becomes  gradually 
wider  from  above  downwards.  It  Hes  in  front  of  the  intervertebral  discs,  to  which 
it  is  firmly  attached  as  it  passes  from  one  vertebra  to  the  other.  Its  fibres  vary  in 
length.  Some  are  attached  to  contiguous  margins  of  two  adjoining  vertebrae ; 
others  pass  in  front  of  one  vertebra  to  be  attached  to  the  next  below,  and  yet 
others  find  their  lower  attachment  three  or  four  vertebrse  below  the  one  from  which 
they  started.  None  of  the  fibres  are  attached  to  the  transverse  depression  on  the 
front  of  a  vertebral  body. 

The  posterior  common  ligament  (lig.  longitudinale  posterius,  Fig.  210)  is  found 
within  the  spinal  canal  upon  the  posterior  aspect  of  the  vertebral  bodies.  It  con- 
sists of  longitudinal  fibres,  and  it  extends  from 
the  back  of  the  sacrum  to  the  axis  vertebra,  superior 
to  which  it  is  continued  to  the  skull  as  the  posterior 
occipito-axial  ligament.  Opposite  each  interverte- 
bral disc  it  is  attached  to  the  entire  width  of  the 
adjacent  margins  of  the  two  vertebral  bodies,  its 
fibres  being  continued  over  the  posterior  surface  of 
the  disc.  In  the  lumbar  and  dorsal  regions  the 
width  of  the  ligament  is  considerably  reduced 
opposite  the  back  of  each  vertebral  body,  and  thus 
it  forms  a  series  of  dentate  projections  along  both 
of  its  margins ;  but  in  the  cervical  region  the 
width  of  the  ligament  is  more  uniform. 

One  or  two  large  thin-walled  veins  escape  from 
the  body  of  each  vertebra  under  cover  of  this  liga- 
ment. 

Interneural  Articulations. — The  neural  arch 
of  each  typical  vertebra  carries  two  pairs  of 
articular  processes,  by  means  of  which  it  articu- 
lates with  adjacent  neural  arches.  The  articu- 
lations between  these  processes  are  true  diarthroses 
of  the  arthrodial  variety. 

The  distinctive  characters  of  these  articular  sur- 
faces, as  regards  their  shape  and  direction  in  the  different  groups  of  vertebrse,  have 
been  referred  to  in  the  section  on  osteology. 

All  these  articulations  are  provided  with  complete  but  very  thin-walled  cap- 
sules (capsulse  articulares),  which  are  thinnest  and  loosest  in  the  cervical  region, 
where  also  the  movements  are  freest.  Each  capsule  is  lined  by  a  synovial 
membrane. 

Associated  with  these  interneural  joints  are  certain  ligaments  which  are 
accessory  to  the  articulations,  although  they  are  quite  distinct  from  the  capsule. 

The  laminEe  of  adjoining  vertebrse  are  bound  together  by  the  ligamenta  subflava 
(ligamenta  flava  vel  subflava.  Fig.  211),  which  consist  of  yellow  elastic  fibres.  The 
ligamenta  subflava  close  the  spinal  canal  in  the  intervals  between  the  laminge. 
Each  ligament  is  attached  superiorly  to  the  anterior  aspect  of  one  lamina  at  a 
short  distance  above  its  lower  border,  and  inferiorly  it  is  attached  to  the  posterior 
aspect  of  the  subjacent  lamina. 

In  the  dorsal  region,  where  the  im})ncation  of  adjoining  laminae  is  a  prominent 
feature,  these  ligam(!ntH  are  not  so  distinctly  visible  irc^m  behind  as  they  are  in  the 
regions  where  imbrication  of  the  lamintii  is  not  so  marked. 

Laterally  they  extend  as  far  as  the  articular  capsules,  while  mesially  the  margins 
of  th(!  ligaments  of  opposite  sides  meet  under  cover  of  the  root  of  the  spinous  process. 

Contiguous  yjairs  of  spinous  processes  are  also  attached  to  each  other  by  inter- 
spinous  ligaments  (ligamenta  iuterspinalia,  Fig.  208).     These  are  strongest  in  the 


Interverte- 
bral fibro- 
cartilaginous 
disc 


Fig.  210. — Posterior  Common  Ligament 
OP  THE  Vertebral  Column. 


264 


THE  AETIGULATIONS  OE  JOINTS. 


SAWING    THROUfiH    THE 


lumbar,  and  weakest  in  the  dorsal  region.     Each  consists  of  layers  of  obliquely 
interlacing  fibres  which  spring  from  near  the  tips  of  the  two  adjacent  spines  and 

radiate  to  their  opposing 
margins.  In  the  antero- 
posterior direction  they 
extend  from  the  base  to 
the  tip  of  the  spinous 
process. 

The  supraspinous  liga- 
ments (ligg.  supra- 
spinalia,  rig.208)consist 
of  longitudinal  bands  of 
fibres  of  varying  lengths. 
They  extend  from  spine 
to  spine,  being  attached  to 
their  tips,andaresituated 
superficial  to,  although 
in  continuity  with,  the 
interspinous  ligaments. 

In  the  cervical  region 
this  series  of  ligaments 
is  extensively  developed, 
where  they  project  back- 
wards from  the  spinous 
processes  between  the 
muscles  of  the  two  sides 
of  the  neck  in  the  form 
of  an  elastic  partition 
called  the  ligamentum 
nuchse. 
The  antero-posterior  extent  of  the  ligamentum  nuchis  increases  as  it  approaches 
the  occiput,  where  it  is  attached  to  the  occipital  crest  from  the  external  occipital 
protuberance  to  the  posterior  border  of  the  foramen  magnum.  Its  posterior  margin 
is  free,  and  extends  from  the  external  occipital  protuberance  to  the  spine  of  the 
vertebra  prominens. 

Between  the  transverse  processes  there  are  intertransverse  ligaments  (ligg.  inter- 
transversaria),  which  consist  of  vertical  fibres  extending  from  the  postero-inferior 
aspect  of  one  transverse  process  to  the  superior  margin  of  that  next  below.  These 
ligaments  are  generally  absent  from  the  cervical  and  upper  dorsal  regions. 

Sacro-coccygeal  Joint. — The  last  piece  of  the  sacrum  is  joined  to  the  first 
piece  of  the  coccyx  by  an  intervertebral  disc,  and  the  junction  is  rendered 
more  secure  by  the  presence  of  certain  strong  ligaments.  An  anterior  ligament 
(lig.  sacro-coccygeum  anterius),  continuous  with  the  anterior  common  ligament,  is 
placed  in  front.  A  posterior  ligament  (lig.  sacro-coccygeum  posterius),  which 
stretches  downwards  from  the  sharp  border  of  the  lower  opening  of  the  sacral 
canal,  strengthens  the  joint  behind.  A  lateral  ligament  (lig.  sacro-coccygeum 
laterale)  supports  the  joint  on  each  side,  whilst  strong  bands  pass  between  the 
cornua  of  the  two  bones  and  constitute  the  interarticular  ligaments. 

Inter-coccygeal  Joints. — So  long  as  they  remain  separate,  the  different  pieces 
of  the  coccyx  are  joined  by  intervertebral  discs  and  by  anterior  and  posterior  liga- 
ments. 

Movements  of  the  Vertebral  Column. — Althoixgli  the  amount  of  movement  ijermissible 
between  any  two  vertebrie  is  extremely  limited,  yet  the  total  range  of  movement  capable  of 
being  attained  by  the  entire  A'ertebral  column  is  very  considerable. 

Flexion  may  occur  both  forwards  and  backwards  at  the  intercentral  articulations,  but  more 
freely  in  the  lumbar  and  cervical  regions  than  in  the  dorsal  region,  where  the  limited  amount  of 
intervertebral  disc  and  the  imbrication  of  the  iaminse  and  sj^ines  restrict  the  movement.  Back- 
ward flexion  is  most  pronounced  in  the  cervical  region,  and  forward  flexion  in  the  lumbar  region. 
Betw^een  the  articular  surfaces  of  the  interneural  articulations  a  variety  of  movements  are  per- 
mitted, dependent  upon  the  directions  of  these  surfaces.     Thus  lateral  flexion  is  permitted  in 


AETICULATION  OF  ATLAS  WITH  AXIS. 


265 


the  lumbar,  but  not  in  tlie  cervical  or  dorsal  regions.  Again,  in  the  lumlmr  region  rotation 
does  not  occur,  owing  to  the  shape  of  the  articular  processes,  while  it  is  possible  in  the  dorsal 
region.  In  the  cervical  region  the  shape  and  position  of  the  articular  surfaces  prevent  the 
occurrence  both  of  lateral  flexion  and  of  rotation  as  isolated  movements,  but  a  combination  of 
these  two  movements  may  take  place,  whereby  rotatory  movement  in  an  oblique  median  axis 
results.  Finally,  in  the  lumbar  region,  by  combining  the  four  forms  of  flexion,  viz.  forward, 
backward,  and  lateral,  a  certain  amount  of  circumduction  is  possible. 

Articulation  of  Atlas  with  Axis. 

Between  these  two  vertebrse  three  diarthroses  occur.  Two  of  them  are 
situated  laterally  in  relation  to  the  articular  processes,  and  are  called  arthrodial 
diarthroses,  because  of  the  flattened  nature  of  the  articulating  surfaces.  The  third 
articulation  is  mesial  in  position.  It  is  found  between  the  smooth  anterior  surface 
of  the  odontoid  process  of  the  axis  and  the  articular  facet  on  the  posterior  aspect  of 
the  anterior  arch  of  the  atlas.     This  joint  is  a  rotatory  diarthrosis. 

Ligaments. — Each  of  the  joints  is  furnished  with  a  capsular  ligament  whereby 


Membraiia  tectoria 


Basi-ocdipital  bone 


Anterior  occipito-atloid  ligament 
Ligamentum  apicis  rtentis 


Transverse  ligament  of  atlas 


Inferior  eras  of  crucial  ligament 
Riidimentary  intervertebral  disc 


Body 


Synovial  cavity  —    ly       imi 

Odontoid  process     ;  / ,  r'r   I    t  7^\    i 
Anterior  arch  of  atlas    TTT^    // fT'if      ° 


Superior  crus  of  crucial  ligament 
Sa  novial  cavity 

Posterior  occipito-atloid 
ligament 


'— r  Occipital  bone 


Posteriox  common  ligament 
Posterioi  irch  of  atlas 


Spine  of  axis 


Fig.  212. — Mesial  Section  through  the  Occipito-atloid  and  Atlo-axoid  Joints. 


the  joint  cavity  is  circumscribed.  In  the  case  of  the  lateral  articulations,  each 
capsular  ligament  presents  a  distinct  band,  named  the  accessory  ligament,  which  is 
situated  within  the  neural  canal  (Fig.  213),  and  passes  downwards  and  inwards 
from  the  lateral  mass  of  the  atlas  to  the  superior  aspect  of  the  body  of  the  axis. 

The  following  additional  ligaments  constitute  the  leading  bonds  of  union : — 

Tlie  anterior  atlo-axoid  ligament  (Fig.  212)  is  a  membranous  structure  which  is 
thin  laterally,  but  strong  mesially  where  it  is  thickened  by  a  prolongation  of  the 
anterior  common  ligament.  It  extends  from  the  anterior  arch  of  the  atlas  to  the 
front  of  the  body  of  the  axis. 

The  posterior  atlo-axoid  ligament  (Fig.  212)  occupies  the  position  which  is 
elsewhere  taken  by  the  ligamenta  subliava.  It  extends  from  the  posterior  arch 
of  the  atlas  to  the  upper  border  of  the  neural  arch  of  the  axis. 

The  transverse  ligament  of  the  atlas  (lig.  transversum  atlantis,  Figs.  212  and 
213)  is  a  strong  band,  placed  transversely,  which  arches  backwards  behind  the 
neck  of  the  odontoid  process  of  the  axis.  By  its  extremities  it  is  attached  to  the 
tubercle  on  the  inner  aspect  of  each  lateral  mass  of  the  atlas.  A  thin  plate  of 
fibro-f,urti]ag(;  is  develoited  in  its  central  part. 

Synovial  membrane  linos  each  of  the  three  capsular  ligaments,  and  in  addition  a 
synovial  sac  is  developed  between  tlie  odontoid  process  and  the  transverse  ligament. 
This  is  more  extensive  than  the  synovial  cavity  between  the  odontoid  process  and 
the  atlas. 


266 


THE  ARTICULATIONS  OR  JOINTS. 


Articulation  of  Spine  with  Cranium. 

There  are  two  articulations  between  the  atlas  and  the  occiput.  Each  is  a 
diarthrosis  in  which  movement  takes  place  in  relation  to  two  axes,  viz.  the 
transverse  and  the  antero-posterior.  The  condyle  of  the  occiput  being  biconvex, 
fits  into  the  biconcave  superior  articular  surface  of  the  atlas,  while  the  long  axes  of 
the  two  joints  are  directed  horizontally  forwards  and  inwards. 

Ligaments. — Each  articulation  is  provided  with  a  capsular  ligament  which  is 
thin  but  complete.  It  is  attached  to  the  rough  non-articular  surfaces  surrounding 
the  articular  areas  on  the  atlas  and  occiput. 

The  following  supplementary  ligaments  are  the  chief  structures  which  bind  the 
atlas  to  the  occiput : — 

The  anterior  occipito-atloid  ligament  (membrana  atlanto-occipitalis  anterior, 
Fig.  212)  is  a  strong  although  thin  membrane,  attached  inferior ly  to  the  anterior 
arch  of  the  atlas,  and  superiorly  to  the  anterior  half  of  the  circumference  of  the 
foramen  magnum.  Laterally  it  is  in  continuity  with  the  capsular  ligaments,  while 
in  the  mesial  plane,  where  it  extends  from  the  anterior  tubercle  of  the  atlas  to  the 
basi-occiput,  it  presents  a  specially  well-defined  thickened  band  which  might  be 
regarded  as  a  separate  accessory  ligament  or  as  the  beginning  of  the  anterior 
common  ligament  of  the  vertebrfe. 

The  posterior  occipito-atloid  ligament  (membrana  atlanto-occipitalis  posterior, 
Fig.  212)  is  another  distinct  but  still  thin  membrane  which  is  attached  superiorly 
to  the  posterior  half  of  the  circumference  of  the  foramen  magnum,  and  inferiorly  to 
the  upper  border  of  the  posterior  arch  of  the  atlas.  Laterally  it  also  is  continuous 
with  the  capsular  ligaments.  On  each  side  of  the  mesial  plane  its  inferior  border 
is  arched  in  relation  to  the  vertebral  groove,  and  is  therefore  to  some  extent  free, 
in  order  to  permit  the  passage  of  the  posterior  primary  division  of  the  first  cervical 
nerve  and  the  vertebral  artery.  Not  infrequently  this  arched  border  becomes 
ossified,  thus  converting  the  groove  in  the  bone  into  a  foramen. 

Synovial  membrane  lines  each  of  the  capsular  ligaments.  There  is  no  direct 
articulation  between  the  axis  and  the  occiput,  but  union  between  them  is  effected 
by  means  of  the  following  accessory  ligaments : — 

The  posterior  occipito-axoid  ligament  (membrana  tectoria,  Fig,  213)  is  situated 
within  the  neural  canal,  and  is  usually  regarded  as  the  upward  continuation  of  the 
posterior  common  ligament  of  the  vertebral  bodies.     It  extends  from  the  posterior 


Membiana  tectoria 

Ci  us  snpenus 


Occipital  bone- 


Lateral  mass  of  atlas — " 
Atlaiito-a\i 


Luamentum  apicis  dentis 
(iniildle  odontoid) 


Ligameiituni  alare 
or  check  lisanient 


Crns  superius 

Ligamentum  cnicia- 
tuui  atlaiitis 


\, =££\        Accessory  atlaiito- 

:iMal  ligament 


CiUb  infpiius 


Membiana  tectom 


Fig.  213.- 


-DlSSECTION    FROM    BEHIND    OF    THE    LIGAMENTS    CONNECTING    THE    OCCIPITAL    BONE,    THE    ATLAS, 

AND  THE  Axis  with  each  other. 


surface  of  the  body  of  the  axis  to  the  basilar  groove  on  the  upper  surface  of  the 
basi-occipital  bone,  spreading  laterally  on  the  circumference  of  the  foramen 
magnum.  Some  of  its  deepest  fibres  are  attached  to  the  atlas  immediately  above 
the  atlo-axoid  articulation. 


TEMPOEO-MANDIBULAE  JOINT. 


267 


Subjacent  to  the  preceding  ligament  there  is  the  ligamentum  cniciatum  atlantis 
(Fig.  213),  a  structure  which  is  very  closely  associated  with  the  lig.  transversum 
atlantis.  It  consists  of  a  cms  transversum,  formed  by  the  superficial  fibres  of 
the  transverse  ligament  of  the  atlas  ;  a  cms  inferius,  consisting  of  mesial  longi- 
tudinal fibres  which  are  attached  below  to  the  posterior  surface  of  the  body  of  the 
axis,  and  above  to  the  crus  transversum  and  a  cms  superius,  also  mesial  and 
longitudinal,  whose  fibres  extend  from  the  crus  transversum  upwards  to  the 
posterior  surface  of  the  basi-occiput,  immediately  subjacent  to  the  posterior 
occipito-axoid  ligament. 

The  check  ligaments  or  lateral  odontoid  ligaments  (ligamenta  alaria.  Fig.  213)  are 
two  very  powerful,  short,  and  somewhat  rounded  bands.  They  are  attached  mesially 
to  the  sides  of  the  summit  of  the  odontoid  process,  and  laterally  to  the  tubercle 
on  the  inner  aspect  of  the  condylar  portions  of  the  occipital  bone,  viz.  the  ex- 
occipital  bones. 

The  middle  odontoid  ligament  (ligamentum  apicis  dentis,  Fig.  213)  consists  of 
fibres  running  vertically  upwards  from  the  apex  of  the  odontoid  process  to  the 
mesial  part  of  the  anterior  margin  of  the  foramen  magnum.  This  ligament 
to  some  extent  represents  an  intervertebral  disc,  in  the  centre  of  which  remains  of 
the  notochord  may  be  regarded  as  present. 

Even  in  advanced  lil'e  a  small  lenticular  mass  of  cartilage,  completely  sur- 
rounded by  bone,  persists  in  the  plane  of  fusion  between  the  odontoid  process  and 
the  body  of  the  axis. 

Movements  at  these  Joints. — At  the  joints  between  occiput  and  atlas  the  movements  are 
very  simple,  and  consist  essentially  of  movements  whereby  the  head  is  elevated  and  depressed 
upon  the  vertebral  column  (nodding  movements).  In  addition  a  certain  amount  of  oblique 
movement  is  possible,  during  which  great  stability  is  attained  by  resting  the  front  and  hinder 
parts  of  opposite  condyles  upon  corresponding  parts  of  the  atlas. 

The  head  and  the  atlas  rotate  together  upon  the  axis,  the  pivot  of  rotation  being  the  odontoid 
process,  and  the  amount  of  rotation  is  limited  by  the  check  ligaments.  No  rotation  can  occur 
between  the  occiput  and  atlas,  and 

'^J'  . 


stability  between  atlas  and  axis  is 
best  attained  after  a  slight  amount 
of  rotation,  similar  to  the  oblique 
movement  between  occiput  and 
atlas. 


TEMPORO-MANDIBULAR 
JOINT. 


External  lateral  ligament 
(anterior  and  posterior  paits) 


This  joint  is  an  arthrodial 
diarthrosis.  It  occurs  between 
the  articular  part  of  the  glenoid 
fossa  of  the  temporal  bone  and 
the  condylar  head  of  the 
mandible.  These  two  articular 
surfaces  are  markedly  dissimilar 
both  in  size  and  shape.  In  its 
general  outline  the  articular 
surface  of  the  head  of  the 
mandible  is  cylindrical,  having 
its  long  axis  directed  from 
within  outwards  and  forwards. 
On  the  other  hand,  the  articular 
part  of  the  glenoid  fossa  in 
front  of  the  (ilaserian  fissure 
is  concavo-convex  from  beliind 
forwards.  Its  articular  surface  includes  the  emineutia  articularis,  the  eminence  at 
the  base  of  the  anterior  root  of  the  zygoma.  The  articular  surfaces  of  the  bones 
are  clothed  by  hyaline  encrusting  cartilage,  whilst  the  joint  cavity  is  divided  into 
an  uyjper  and  lower  ]«j,rt  by  a  meniscus  of  fibro-cartilagc. 

Ligaments. — The  joint  is  invested  by  a  capsular  ligament  vvhicli  is  quite  com- 


21  4. — TEMl'OUO-MANDIIiUt.AU    JoiNT. 


268 


THE  ARTICULATIONS  OE  JOINTS. 


'S  i?   Eiuinontia  articularis 


Fig.  215. — Section  through  the  Tempoho- 
Mandibulab  Joint. 


plete,  ])ut  is  very  thiu  on  the  inner  side.  The  outer  wall  of  the  capsule — the 
external  lateral  ligament  (lig.  temporo-mandibulare,  Fig.  214) — is  divisible  into 
anterior  and  posterior  portions  which  are  attached  superiorly  to  the  root  tubercle 

and   lower   border    of    the   zygoma,   and 
~      ^  ;|  inferiorly  to  the  outer  side  and  posterior 

border  of  the  neck  of  the  mandible.  The 
direction  of  its  fibres  is  downwards  and 
Ijackwards. 

Within  the  capsule  there  is  an  inter- 
articular  disc  or  meniscus  of  libro-cartilage, 
the  discus  articularis  (Fig.  205),  which  is 
moulded  upon  the  condyle  of  the  mandible 
below,  and  on  the  articular  surface  of  the 
temporal  bone  above.  It  thus  compensates 
for  the  incongruity  between  the  articular 
surfaces  of  the  two  bones.  The  disc  is 
attached  circumferentially  to  the  capsule. 
It  is  widest  in  the  transverse  direction, 
thicker  behind  than  in  front,  and  thinnest 
towards  the  centre,  where  it  may  be  per- 
forated. Its  anterior  margin  is  intimately  associated  with  the  insertion  of  the 
external  pterygoid  muscle. 

A  synovial  membrane  lines  each  of  the  compartments  into  which  the  joint 
cavity  is  divided  by  the  meniscus.  As  a  rule  these  membranes  are  separate  from 
each  other,  but  they  become  continuous  when  the  disc  is  perforated.  The  upper 
synovial  membrane  is  larger  and  more  loosely  disposed  than  the  lower. 

Situated  on  the  mesial  aspect  of  the  joint,  but  at  a  short  distance  from  it,  and 
quite  distinct  from  the  capsule,  there  is  an  accessory  band  called  the  internal 
lateral  ligament  (lig.  spheno-mandi- 
bulare.  Fig.  216).  Superiorly  it  is 
attached  to  the  spinous  process  of  the 
great  wing  of  the  sphenoid  bone,  and   spheno-wandibuiar 

9..-0        ,,        ■,     ^  ,,  .,  or  internal  lateral 

mieriorly  x,o  the  lower  as  well  as  the  ligament 

hinder    border   or    lingula    of     the 

inferior  dental  foramen.    It  is  not  an 

articular  ligament  in  the  true  sense, 

for  instead  of  being  connected  with  the 

joint,  it  is    developed  in  the   tissue 

surrounding  part  of  Meckel's  cartilage. 

Portions  of  the  following  structures  are 
found  in  tlie  interval  between  tlie  splieno- 
luandibular  ligament  and  tlie  ascending 
ramus  of  the  mandible — viz.  the  external 
pterygoid  muscle  ;  internal  maxillary 
vessels  ;  inferior  dental  vessels  and  nerve  ; 
middle  meningeal  vessels ;  auriculo- tem- 
poral nerve  ;  a  deep  portion  of  the  parotid 
gland. 

Movements  of  the  Mandible. — The  nature  of  the  movements  which  the  lower  jaw  can 
perform  is  determined  partly  by  the  character  of  the  articular  surfaces  of  the- temporo-mandibular 
joint,  and  partly  by  the  fact  'that,  while  the  two  joints  always  act  simultaneously,  they  may 
also,  to  some  extent,  perform  the  same  movement  alternately. 

When  movement  takes  place  through  the  long  or  transverse  horizontal  axis  of  each  joint, 
the  mandible  may  be  elevated,  as  in  clenching  the  teeth,  or  it  may  be  depressed,  as  in  gajjing. 
In  the  latter  movement  the  condyle  leaves  the  glenoid  fossa,  and,  along  with  the  meniscus,  it 
moves  forwards  until  they  rest  upon  the  articular  eminence.  Meantime  the  chin  describes  the 
arc  of  a  circle,  of  which  the  centre  or  point  of  least  movement  corresponds  to  the  position  of  the 
inferior  dental  foramen,  and  thus  the  structures  which  enter  at  that  foramen  are  protected 
against  stretching.  Coincidently  with  the  forward  movement  of  the  condyle,  it  glides  in  a 
revolving  manner  upon  the  inferior  asjaect  of  the  meniscus. 

At  any  stage  in  the  movement  of  depressing  the  chin  the  mandible  may  be  protruded,  so 
that  the  inferior  incisor  teeth  are  projected  in  front  of  the  upper  set,  a  movement  which  results 
from  the  condyles  of  the  jaw  being  drawn  forwards  upon  the  articular  eminences.     A  similar 


Ktylo-iuandibular 
liL^ament 


-Internal  Lateral  Ligament  of  the 
Temporo-Maxillary  Joint. 


THE  JOINTS  OF  THE  THORAX.  2G9 

relation  of  the  condyle  to  the  articular  eniinence  occurs  during  the  exaggerated  depression  of 
the  mandible  whicli  results  from  yawning,  in  which  position  the  articulation  is  liable  to  be 
dislocated.  When  the  two  joints  perform  the  same  movement  alternately,  a  certain  amount  of 
lateral  motion  results,  from  the  fact  that  the  long  axis  of  each  joint  presents  a  slight  obliquity 
to  the  transverse  axis  of  the  skull,  and  consequently  a  grinding  or  oblique  movement  in  the 
horizontal  plane  is  jsroduced.  Excessive  depression,  with  the  risk  of  dislocation,  is  resisted  by 
the  fibres  of  the  external  lateral  ligament  which  becomes  tense. 

In  all  movements  of  the  mandible  the  meniscus  conforms  closely  to  the  position  of  the  con- 
dyle, and  they  move  forwards  and  backwards  together,  but  at  the  same  time  the  meniscus  does 
not  restrict  the  movements  of  the  condyle.  Thus  while  the  meniscus,  along  with  the  condyle,  is 
gliding  upon  the  temporal  aspect  of  the  joint,  the  condyle  itself  revolves  upon  the  inferior 
surface  of  the  meniscus. 

Cranial  Ligaments  not  directly  associated  with  Articulations. 

The  stylo-mandibular  ligament  (lig.  stylo-mandibulare,  Figs.  214  and  216)  is  a 
specialised  portion  of  the  deep  cervical  fascia  which  extends  from  the  anterior  aspect 
of  the  tip  of  the  styloid  process  of  the  temporal  bone  to  the  posterior  border  of  the 
angle  of  the  mandilale,  between  the  insertions  of  the  masseter  and  internal  pterygoid 
muscles. 

The  pterygo-spinous  ligament  (lig.  pterygo-spinosum)  is  a  membrane  extending 
from  the  upper  part  of  the  posterior  free  margin  of  the  external  pterygoid  plate, 
backwards  and  slightly  outwards,  to  the  spinous  process  of  the  sphenoid.  An 
interval  is  left  between  its  upper  border  and  the  floor  of  the  skull  for  the  outward 
passage  of  those  branches  of  the  inferior  maxillary  nerve  which  supply  the 
external  pterygoid,  temporal,  and  masseter  muscles.  This  ligament  has  a  tendency 
to  ossify  either  wholly  or  partially. 

The  stylo-hyoid  ligament  (lig.  stylo-hyoideum)  may  be  regarded  as  the  down- 
ward continuation  of  the  styloid  process  of  the  temporal  bone.  Inferiorly  it  is 
attached  to  the  lesser  cornu  of  the  hyoid  bone.  It  is  not  infrequently  ossified,  in 
which  case  it  constitutes  the  epihyal  bone  found  in  many  animals. 


THE   JOINTS   OF   THE   THORAX. 

Costo-vertebral  articulations  (articulationes  costo-vertebrales).  The  typical 
rib  articulates  with  the  vertebral  column  both  by  its  head  and  by  its  tubercle. 
Thus,  two  sets  of  articulations,  with  their  associated  ligaments,  exist  between  the 
ribs  and  the  vertebrae,  but  each  set  is  constructed  upon  a  common  plan,  with  the 
exception  of  certain  joints  situated  at  the  upper  and  lower  ends  of  the  series,  where 
the  ribs  themselves  deviate  from  the  typical  form. 

Costo-Central  Joints. 

The  articulations  of  the  heads  of  the  ribs  with  the  centra  or  bodies  of 
the  vertebrae  (articulationes  capitulorum.  Fig.  209)  are  all  diarthroses,  which,  from 
their  somewhat  hinge-like  action,  may  be  classed  as  ginglymoid. 

The  head  of  every  typical  rib  is  wedge -sha.ped,  and  presents  two  articular 
facets,  an  upper  and  a  lower,  separated  from  each  other  by  an  antero-posterior 
ridge  which  abuts  against  an  intervertebral  disc,  while  the  articular  facets  articu- 
late with  similar  surfaces  on  the  contiguous  margins  of  the  tv^'o  vertebrse  adjoining 
the  disc.  These  surfaces  form  a  wedge-shaped  depression  or  cup,  the  bottom  of 
which  is  more  elastic  than  the  sides,  and  thus  an  arrangement  is  provided  which 
tends  to  reduce  the  shock  of  blows  upon  the  walls  of  the  chest. 

Each  of  these  articulations  is  provided  with  a  capsular  ligament  which 
surrounds  and  encloses  the  joint,  and  is  attached  to  contiguous  non-articular 
margins  on  the  head  of  the  rib  and  the  two  vertebral  bodies.  On  its  anterior  or 
ventral  aspect  the  ca|)Hnle  ])rcsents  throe  radiating  fasciculi  which  collectively  form 
the  stellate  or  anterior  costo-vertebral  ligament  (lig.  capituli  costic  radiatum,  Fig. 
209).  These  fasciculi  radiate  from  a  centre  on  the  front  of  the  head  of  the  rib,  so 
that  the  njiddle  fasciculus    becomes    attached  to  the   intervertebral  disc    while 


270  THE  AKTICULATIONS  OE  JOINTS. 

the  upper  and  lower  fasciculi  proceed  to  the  adjacent  margins  of  the  two  vertebrse 
between  which  the  disc  is  situated,  and  with  which  the  rib  articulates.  To  a  slight 
extent  these  radiating  fasciculi  pass  under  cover  of  the  lateral  margin  of  the  anterior 
common  ligament  of  the  vertebral  bodies.  In  those  joints  in  which  the  head  of 
the  rib  does  not  articulate  with  an  intervertebral  disc  the  central  fasciculus  of 
the  stellate  ligament  is  wanting,  but  the  other  two  retain  the  same  general 
arrangement. 

The  interarticular  ligament  (lig.  capituli  costai  interarticulare)  consists  of  short 
transverse  fibres  within  the  capsule.  These  are  attached,  on  the  one  hand,  to 
the  ridge  which  intervenes  between  the  two  facets  on  the  head  of  the  rib,  and 
on  the  other  to  the  lateral  aspect  of  the  intervertebral  disc.  This  hgameat 
is  not  .a  meniscus,  but  merely  an  interarticular  ligament,  of  width  sufficient 
to  divide  the  joint  cavity  into  an  upper  and  a  lower  compartment.  It  is  absent 
from  those  joints  which  do  not  articulate  with  an  intervertebral  disc,  i.e.  from 
those  ribs  which  only  articulate  with  the  body  of  one  vertebra. 

The  mterarticular  ligament  is  supposed  to  rejjresent  tlie  outer  end  of  a  ligament  wLicli, 
under  the  name  of  the  lig.  conjugale  costarum,  connects  the  heads  of  the  rilDs  of  certain  mammals 
across  the  posterior  aspect  of  the  intervertebral  disc,  and,  in  the  human  subject,  until  the 
seventh  month  of  foetal  life,  connects  the  posterior  aspects  of  the  necks  of  a  pair  of  ribs  with  each 
other  across  the  mesial  plane. 

Synovial  membrane  lines  each  joint  cavity,  and  therefore,  in  all  cases  where  the 
joint  is  divided  into  two  compartments,  each  one  has  its  own  synovial  lining. 

Costo-Transvekse  Joints. 

The  tubercle  of  each  typical  rib  articulates  with  the  transverse  process  of  the 
lower  of  the  two  dorsal  vertebrae  with  which  the  head  of  the  rib  is  associated 
(articulatio  costo-transversaria).  Near  the  tip  of  the  transverse  process  there  is 
an  articular  facet,  on  its  anterior  aspect,  for  articulation  with  the  corresponding 
facet  on  the  mesial  articular  part  of  the  rib  tubercle.  The  joint  so  formed  is  an 
arthrodial  diarthrosis. 

The  joint  cavity  is  surrounded  by  a  comparatively  feeble  capsular  ligament, 
which  is  attached  immediately  beyond  the  margins  of  the  articular  facets,  and  in 
which  no  special  bands  can  be  distinguished. 

A  simple  synovial  membrane  lines  the  capsular  ligament  in  all  cases  where  the 
latter  is  present. 

The  following  accessory  ligaments,  in  connexion  with  this  joint,  strengthen  and 
support  the  articulation  : — 

The  anterior  or  superior  costo-transverse  ligament  (ligamentum  costo-transver- 
sarium  anterius,  Fig.  209)  consists  of  strong  bands  of  fibres  which  are  attached  to 
the  upper  border  of  the  neck  of  the  rib,  extending  from  the  head  outwards  to  the 
non-articular  part  of  the  tubercle.  All  these  fibres  may  be  traced  upwards.  Those 
situated  nearest  to  the  head  of  the  rib  proceed  obliquely  upwards  and  outwards,  to 
be  attached  to  the  transverse  process  immediately  above,  but  with  extensions  to  the 
adjoining  rib  and  its  costo-transverse  capsular  ligament.  Others  proceed  almost 
vertically  upwards  to  the  adjoining  transverse  process,  while  those  which  ascend 
from  the  upper  surface  of  the  tubercle  pass  obliquely  upwards  and  inwards  to  reach 
the  postero-inferior  aspect  of  the  adjoining  transverse  process. 

The  posterior  costo-transverse  ligament  (ligamentum  costo-transversarium  pos- 
terius)  is  a  baud  of  transverse  fibres  applied  to  the  postero-external  aspect  of  the 
capsule.  By  one  end  these  fibres  are  attached  to  the  tip  of  the  transverse  process 
behind  its  articular  facet,  and  by  the  other  to  the  external  rough  surface  of  the 
tubercle  of  the  rib. 

The  middle  costo-transverse  ligament  (lig.  colli  costce)  consists  of  short  fibres 
which  stretch  from  the  posterior  aspect  of  the  neck  of  the  rib,  backwards  and  in- 
wards, to  the  front  of  the  transverse  process,  but,  in  addition,  a  proportion  of  the 
fibres  passes  to  the  posterior  aspect  of  the  inferior  articular  process  of  the  upper  of 
the  two  vertebrae  with  which  the  head  of  the  rib  articulates. 


COSTO-STEENAL  JOINTS.  271 

The  following  exceptions  to  the  general  plan  of  rib-articulation  indicated  above 
must  be  noted  : — 

1.  There  is  no  articulation   between    the  eleventh  and   twelfth  riljs  and  the 

transverse  processes  of  the  corresponding  vertebrse. 

2.  The  superior  costo-transverse  ligament  is  wanting  from  the  first  rib,  and  is 

either  rudimentary  or  wanting  in  the  case  of  the  twelfth  rib. 

3.  The  middle  costo-transverse  ligament  is  rudimentary  in  the  eleventh  and 

twelfth  ribs. 
The  ligamentum  lumbo-costale  extends  from  the  upper  surface  of  the  base  of  the 
transverse  process  of  the  first  lumbar  vertebra  to  the  under  surface  of  the  neck  of 
the  twelfth  rib,  as  well  as  to  the  under  surface  of  the  transverse  process  of  the 
twelfth  dorsal  vertebra. 

Articulations  between  the  Eibs  and  theie  Cartilages. 

Eich  rib  possesses  an  unossified  portion,  termed  its  costal  cartilage.  As  age 
advances,  this  cartilage  may  undergo  a  certain  amount  of  superficial  ossification, 
but  it  never  becomes  entirely  transformed.  The  line  of  demarcation  between 
bone  and  cartilage  is  clear  and  abrupt,  and  usually  the  bone  forms  an  oval  cup,  in 
which  the  end  of  the  cartilage  is  retained  by  means  of  the  continuity  which  exists 
between  the  periosteum  and  the  perichondrium.  There  is  no  articulation  in  the 
proper  sense  between  the  rib  and  its  cartilage,  although  a  synovial  cavity  has 
occasionally  been  found  between  the  first  rib  and  its  cartilage. 

Interchondral  Joints. 

These  articulations  are  arthrodial  diarthroses,  and  they  are  found  between  ad- 
joining margins  of  certain  of  the  costal  cartilages,  viz.  from  the  fifth  to  the  eighth 
or  ninth.  The  cartilages  which  thus  articulate  develop  flattened,  somewhat  conical, 
prolongations  of  their  substance,  and  thereby  the  intercostal  spaces  are  interrupted 
where  these  flat  articular  facets  abut  against  each  other.  Each  joint  is  closed 
by  a  surrounding  capsular  ligament,  the  superficial  and  deep  aspects  of  which  are 
specially  strengthened  by  external  and  internal  interchondral  ligaments.  These 
bands  extend  obliquely  between  adjacent  cartilages. 

A  synovial  membrane  lines  each  joint  capsule. 

Costo-sternal  Joints. 

The  upper  seven  pairs  of  costal  cartilages,  as  a  rule,  extend  to  the  lateral 
margins  of  the  sternum  (articulationes  sternocostales).  Of  these,  the  first  pair  is 
implanted  directly  upon  the  manubrium  sterni.  The  ossific  process  ends  abruptly 
in  connexion  with  the  rib,  and  also  ceases  as  suddenly  in  connexion  with  the 
sternum,  and  hencs  the  cartilage  does  not  normally  present  an  articulation  at 
either  end. 

From  the  second  to  the  seventh  pairs  of  ribs  inclusive,  the  costo-sternal  joints 
are  constructed  upon  the  type  of  arthrodial  diarthroses,  although,  in  the  case  of 
the  sixth  and  seventh  cartilages,  the  joint  cavity  is  always  small,  and  is  frequently 
obliterated. 

The  sternal  end  of  each  of  these  costal  cartilages  presents  a  slight  antero-pos- 
terior  ridge  which  fits  into  a  shallow  V-shaped  depression  upon  the  lateral  margin 
of  the  sternum.  With  the  exception  of  the  sixth  cartilage,  the  others  articulate 
opposite  the  lines  of  union  between  the  primary  segments  of  the  sternum,  whereas 
the  sixth  articulates  upon  the  side  of  the  lowest  segment  of  the  meso-sternum. 

Each  joint  is  enclosed  by  a  capsular  ligament,  composed  of  fibrous  tissue,  attached 
to  the  adjacent  borders  of  the  articulating  elements.  Specially  strong  fibres  dis- 
tinguish the  superficial  and  deep  aspects  of  the  capsule. 

Tfio  anterior  costo-sternal  ligament  flig.  costo-sternalium  radiatum,  Fig.  217)  is 
composed  of  strong  fibres  wliich  radiate  from  the  anterior  surface  of  the  costal 
cartilage,  near  its  sternal  end,  to  the  front  of  the  sternum.  The  ligaments  of 
opyjosile  sides  interlace  with  car;h  other,  and  so  cover  the  front  of  the  sternum  with 
a  felted  membrane — the  membrana  sterni. 


272 


THE  ARTICULATIONS  OR  JOINTS. 


The  posterior  costo-sternal  ligament — also  a  part  of  the  capsule — has  attach- 
ments similar  to  the  foregoing,  Imt  the  arrangement  of  its  fibres  is  not  so  powerful. 

The  ligamentum  costo-xiphoidea  passes  I'rom  the  front  of  the  upper  part  of  the 
xiphoid  cartilage,  o])liquely  upwards  and  outwards  to  the  front  of  the  seventh,  and 
sometimes  to  the  i'ront  of  the  sixth  costal  cartilage. 

Witliin  the  capsules  of  these  joints  interarticular  ligaments  (ligg.  sterno-costalia 
interarticularia,  Fig.  217)  may  be  found.    Their  disposition  is  somewhat  uncertain,  for 


Cj-ito-clavicular  or 
ihoiiiboid  ligaiucnt 


intenoi  stenio-claviiMilar 
li-imPiit 


.Joint  f  ipsu 
Joint  ( avity. 


Interarticular  ligament 

.Toiiit  ca 


Anteiioi  cliondio  sternal  or 
TidntP  ligament 


Fig.  217. — Sterno-clavicular  and  Costo-sternal  Joints. 

whereas,  in  the  case  of  the  second  pair  of  cartilages,  they  invariably  divide  the  joint 
cavity  into  two  distinct  compartments — an  upper  and  a  lower — such  an  arrange- 
ment is  very  uncertain  in  the  other  joints,  and  they  occasionally,  especially  in  the 
cases  of  the  sixth  and  seventh  cartilages,  entirely  obliterate  the  joint  cavity.  These 
ligaments  extend  horizontally  between  the  ends  of  the  costal  cartilages  and  the 
side  of  the  sternum. 

Synovial  membrane  is  found  wherever  a  joint  cavity  is  developed,  and  therefore 
there  may  be  one  or  two  synovial  membranes,  according  to  the  presence  or  absence 
of  a  proper  interarticular  ligament.  When  the  joint  cavity  is  obliterated  by  the 
fibrous  structure  which  represents  the  interarticular  ligament,  a  synovial  membrane 
is  also  absent. 

Sternal  Articulations. 

.  Primarily  the  sternum  consists  of  an  elongated  plate  of  hyaline  cartilage,  which 
becomes  subdivided  into  segments  by  the  process  of  ossification. 

The  four  segments  of  which  the  gladiolus  is  originally  composed  unite  with 
each  other  after  the  manner  of  typical  synchondroses. 

Similarly  the  ensiform  cartilage  and  the  gladiolus  ultimately  l)ecome  united. 
It  is  not  usual  to  find  the  manubrio-gladiolar  joint  obliterated  by  the  ossification  of 
the  two  bony  segments.  Even  in  advanced  life  it  remains  open,  and  the  joint  par- 
takes of  the  nature  of  an  amphiarthrosis  (Fig.  217),  although  a  joint  cavity  is  not 
found  under  any  circumstances  in  the  plate  of  fibro-cartilage  which  intervenes 
between  the  manubrium  and  the  gladiolus. 

The  membrana  sterni,  to  which  reference  has  already  been  made,  assists  in 
strengthening  the  union  between  the  different  segments  of  the  sternum. 

Movements  of  the  Ribs  and  Sternum. — Tliese  movements  may  be  considered  eitlier 
independently  of,  or  as  associated  witli,  respiration. 

In  the  former  condition  tlie  rilis  move  in  connexion  witli  flexion  and  extension  of  the 
vertebral  t'r)himn,  Leiiig  more  or  less  depressed  and  approximated  in  the  former,  and  elevated  or 


STERNO-CLAVICULAE  JOINT.  273 

pulled  apart  in  the  latter  case.  Considered  in  connexion  with  respiration,  it  is  necessary  to 
observe  that,  to  all  intents  and  purposes,  the  vertebi'al  column  and  the  sternum  are  rigid  structures. 
Next  we  must  remember  that  the  heads  of  all  tlxe  ribs  occupy  fixed  positions,  and  siuiilarly 
the  anterior  ends  of  seven  paii'S  of  cartilages  are  fixed  to  the  lateral  margins  of  the  sternum. 
The  ribs  thus  form  arches,  presenting  a  large  amount  of  oljliquity  from  behind  forwards.  There- 
fore, during  inspiration,  when  the  rib  is  elevated,  the  arch  becomes  more  horizontal,  and  the 
transverse  diameter  of  the  chest  is  increased.  At  the  same  time,  the  anterior  ends  of  the  sternal 
ribs  tend  to  thrust  the  sternum  forwards  and  upwards ;  but  the  nature  of  the  attachment  of  the 
first  pair  of  ribs  to  the  sternum,  as  well  as  the  attachment  of  the  diaphragm  to  the  ensiform 
cartilage,  prevents  this  movement  from  becoming  excessive,  and  hence  the  sternum  becomes  a  line 
of  resistance  to  the  forward  thrust  of  the  ribs.  As  a  consequence,  the  ribs  rotate  upon  themselves 
about  an  oblique  axis  which  j)asses  downwards,  outwards,  and  backwards  through  the  capitular 
joint  and  the  neck  of  the  rib  anterior  to  the  costo-transverse  joint. 

In  this  way  increase,  both  of  the  antero-posterior  and  transverse  diameters  of  the  thorax,  is 
provided  for,  although  the  amount  of  increase  is  not  equally  pronounced  in  all  planes.  Thus  at 
the  level  of  the  first  rib  A^ery  little  eversion  is  possible,  because  the  axis  of  rotation  is  nearly 
transverse,  and  therefore  any  increase  in  the  transverse  or  antero-posterior  thoracic  diameters  at 
this  level  may  be  disregarded,  although  a  certain  amount  of  elevation  of  the  manubrium  sterni 
and  anterior  end  of  the  first  rib  is  evident. 

Below  the  level  of  the  sixth  rib  elevation  and  rotation  of  the  rib  during  inspiration  are 
usually  said  to  be  complicated  by  a  certain  amount  of  backward  movement,  due  to  the  character 
of  the  costo-transverse  joint,  until,  in  the  case  of  the  last  two  ribs,  which  are  destitute  of  costo- 
transverse joints,  a  movement  backwards  is  almost  entirely  substituted  for  elevation.  It  is 
probable,  however,  that  the  movements  of  the  asternal  ribs  exactly  correspond  to  those  of  the 
sternal  series,  and  that  by  the  contraction  of  the  costal  digitations  of  the  diaphragm  the 
anterior  ends  of  the  asternal  ribs  are  j)rovided  with  fixed  jDositions  comparable  to  those  supplied 
by  the  sternum  to  the  ribs  of  the  sternal  series. 

We  may  therefore  say  that  during  inspiration  the  ribs  move  upwards  and  outwards  between 
their  fixed  ends,  while  as  a  whole  the  rib  rotates,  and  its  anterior  end  is  thrust  slightly  forwards. 

During  exj^iration  these  movements  are  simply  reversed. 

THE  ARTICULATIONS  OF  THE  SUPERIOR  EXTREMITY. 

The  bony  arch  formed  by  the  clavicle  and  scapula  articulates  directly  with  the 
axial  skeleton  only  at  one  point,  viz.  the  sterno-clavicular  joint. 

AKTICULATIONS  OF  THE  CLAVICLE. 

The  Sterno-clavicular  Joint. 

The  sterno-clavicular  joint  (articulatio  sterno-clavicularis)  is  an  example  of  an 
arthrodial  diarthrosis.  The  articular  surfaces  concerned  in  its  formation  present 
the  following  appearances  : — 

1.  The  sternal  end  of  the  clavicle  is  somewhat  triangular  in  outline,  having  its 
most  prominent  angle  directed  downwards  and  backwards.  The  anterior  and 
posterior  sides  of  the  triangle  are  slightly  roughened  for  the  attachment  of 
ligaments,  while  the  base  or  inferior  side  is  smooth  and  rounded,  owing  to  the 
prolongation  of  the  articular  surface  to  the  inferior  aspect  of  the  bone.  In  the 
antero-posterior  direction  the  articular  surface  tends  to  be  concave,  while  vertically 
it  is  slightly  convex. 

2.  An  articular  facet,  situated  on  the  superior  lateral  angle  of  the  manubrium 
sterni,  but  in  a  plane  slightly  behind  the  supra-sternal  notch,  articulates  with  the 
clavicle.  This  facet  is  considerably  smaller  than  the  clavicular  facet  with  which  it 
articulates. 

'■J.  The  superior  surface  of  the  first  costal  cartilage  close  to  the  sternum  also 
] participates  to  a  small  extent  in  the  articulation. 

It  should  be  noted  that  the  articular  surfaces  of  the  clavicle  and  sternum  are 
covered  mainly  by  fibro-cartilage. 

A  capsular  ligament  is  well  marked  on  all  sides  except  inferiorly,  where  it  is 
very  thin. 

The  anterior  sterno-clavicular  ligament  (Fig.  217)  forms  part  of  the  capsule,  and 
consists  of  shoit  lihics  which  extend  obliijuely  downwards  and  inwards  from  the 
anterior  aspect  of  the  sternal  taid  of  the  clavicle  to  the  adjoining  anterior  surface 
(jf  the  sternum  and  the  anterior  border  of  the  first  costal  cartilage. 

The  posterior  sterno-clavicular  ligament  ;ilso  forms  inirt  of  the  ciipsule,  and 
V.) 


274  THE  ARTICULATIONS  OE  JOINTS. 

consists  of  similarly  disposed,  but  not  so  strong,  oblique   fibres  situated    on    the 
posterior  aspect  of  the  articvilation. 

A  fibro-cartilaginous  meniscus  (discus  articularis,  Tig.  217)  divides  the  joint 
cavity  into  two  compartments.  It  is  nearly  circular  in  shape,  and  adapts  itself  to 
the  articular  surfaces  between  which  it  hes.  It  is  thickest  at  the  circumference  and 
thinnest  at  the  centre,  where  it  occasionally  presents  a  perforation,  thereby 
permitting  the  two  synovial  cavities  to  intercommunicate.  By  its  circumference  it 
is  in  contact  with,  and  adherent  to,  the  surrounding  capsule,  but  its  upper  margin  is 
attached  to  the  apex  of  the  articular  surface  of  the  clavicle,  while  by  its  lower 
margin  it  is  fixed  to  the  sternal  end  of  the  first  costal  cartilage. 

Two  accessory  ligaments  are  associated  with  this  joint,  viz.  the  interclavicular 
and  the  rhomboid. 

The  interclavicular  ligament  (Fig.  217)  is  a  structure  of  considerable  strength, 
forming  a  broad  band  of  fibrous  tissue  which  is  attached  to  the  superior  rounded  angle 
or  apex  of  the  sternal  end  of  the  clavicle  as  well  as  to  the  adjacent  margins  of  the 
articular  surface.  Its  fibres  pass  across  the  interclavicular  notch  to  become  attached 
to  corresponding  parts  of  the  opposite  clavicle,  but  in  their  course  they  dip  down  into 
the  suprasternal  notch,  in  which  many  of  them  are  fixed  to  the  sternum.  In  this 
way  their  presence  neither  bridges  nor  obliterates  the  notch  between  the  two 
clavicles,  and  the  ligament  really  becomes  a  superior  sterno-clavicular  ligament  for 
each  joint. 

The  rhomboid  ligament  (lig.  costo-claviculare,  Fig.  217)  consists  of  short,  strong 
fibres  which  are  attached  inferiorly  to  the  upper  surface  of  the  first  costal  cartilage. 
They  pass  obliquely  upwards  and  outwards  to  a  rough  impression  situated  on  the 
lower  aspect  of  the  sternal  end  of  the  clavicle,  and  are  distinct  from  the  capsular 
ligament.     Occasionally  a  bursa  is  found  in  the  interior  of  this  ligament. 

As  a  rule  there  are  two  synovial  membranes  lining  the  two  joint  cavities  (Fig. 
217),  separated  from  each  other  by  the  interarticular  meniscus.  Sometimes,  however, 
the  two  membranes  establish  continuity  through  a  perforation  in  the  meniscus. 

The  Aceomio- clavicular  or  Scapulo-claviculae  Joint. 

The  acromio  -  clavicular  joint  (articulatio  acromio  -  clavicularis)  is  another 
instance  of  an  arthrodial  diarthrosis.  It  is  situated  between  the  acromial  end  of 
the  clavicle  and  the  inner  aspect  of  the  acromion  process  of  the  scapula.  Each 
articular  surface  is  an  oval,  flattened  facet,  covered  by  fibro-cartilage. 

The  ligaments  which  surround  this  small  joint  form  a  complete  capsule 
(capsula  articularis),  of  which  the  upper  and  lower  parts  are  specially  strong,  and 
are  therefore  named  the  superior  and  inferior  acromio -clavicular  ligaments  (Fig.  219). 
These  consist  of  short  fibres  passing  between  the  adjacent  rough  margins  of  the 
two  bones  in  the  positions  indicated  by  their  names. 

A  meniscus  (discus  articularis),  which  is  nearly  always  incomplete,  and  may 
occasionally  be  wanting,  is  usually  found  within  the  joint  cavity,  where  it  lies 
obliquely,  with  its  upper  margin  farther  from  the  mesial  plane  than  its  lower 
margin,  and  having  its  borders  attached  to  the  surrounding  capsule.  Frequently 
the  meniscus  is  wedge-shaped,  with  its  base  directed  upwards  and  its  apex  free. 

A  synovial  membrane  is  found  forming  either  a  single  or  a  double  sac,  according  to 
the  condition  of  the  meniscus.  Complete  division  of  the  joint  cavity,  however,  is  rare. 

Ligamentum  Coraco-claviculare. — Accessory  to  this  articulation  there  is  the 
strong  coraco-clavicular  ligament  which  binds  the  acromial  end  of  the  clavicle  to 
the  coracoid  process  of  the  scapula.  It  is  readily  divisible  into  two  parts,  viz.  the 
conoid  and  trapezoid  ligaments. 

The  conoid  ligament  (Fig.  219)  is  situated  internal  to  and  slightly  behind  the 
trapezoid.  It  is  narrow  and  pointed  at  its  inferior  end,  by  which  it  is  attached 
to  the  upper  aspect  of  the  coracoid  process,  in  close  proximity  to  the  suprascapular 
notch.  Its  upper  end  widens  out  in  the  manner  expressed  by  its  name,  and  is 
attached  to  the  conoid  tubercle  of  the  clavicle. 

The  trapezoid  ligament  (Fig.  219)  is  attached  inferiorly  to  the  upper  surface  of  the 
posterior  half  of  the  coracoid  process,  external  and  anterior  to  the  attachment  of 


ACROMIO-CLAVICULAK  JOINT.  275 

the  conoid  ligament.  Superiorly  it  is  attached  to  the  trapezoid  ridge  on  the  under 
surface  of  the  acromial  end  of  the  clavicle.  Its  outer  and  inner  borders  are  free. 
Its  anterior  surface  is  principally  directed  upwards,  and  its  posterior  surface,  to  a 
similar  extent,  looks  downwards. 

A  synovial  bursa  usually  occupies  the  re-entrant  angle  between  these  two 
ligaments. 

Movements  at  the  Clavicular  Joints. — The  movements  of  the  inner  end  of  the  clavicle  at 
the  sterno-clavicular  joint  are  limited  in  their  range,  owing  to  the  tension  of  the  ligaments. 
When  the  shoulder  is  raised  or  depressed  the  outer  end  of  the  clavicle  moves  upwards  and 
downwards,  whilst  its  sternal  end  glides  upon  the  surface  of  the  interarticular  meniscus  vsdthin 
the  joint ;  when,  on  the  other  hand,  the  shoulder  is  carried  forwards  or  backwards,  the  inner 
end  of  the  clavicle  along  with  the  interarticular  meniscus  moves  upon  the  sternal  facet.  In 
addition  to  these  movements  of  elevation,  depression,  forward  movement  and  backward  move- 
ment of  the  clavicle,  there  is  also  allowed  at  the  sterno-clavicular  joint  a  certain  amount  of 
circumduction  of  the  clavicle. 

The  part  which  is  played  by  certain  of  the  ligaments  in  restraining  movement  requires 
careful  consideration.  The  rhomboid  ligament  checks  excessive  elevation  of  the  shoulder,  and 
restrains  within  certain  limits  both  backward  and  forward  movement  of  the  clavicle.  When  the 
clavicle  is  depressed,  as  in  cases  where  a  heavy  weight,  such  as  a  bucket  of  water,  is  carried  in  the 
hand,  it  receives  support  by  resting  upon  the  first  rib,  and  the  tendency  for  the  inner  end  of  the 
bone  to  start  up  out  of  its  sternal  socket  is  obviated  by  the  tension  of  the  interarticular 
meniscus,  the  interclavicular  ligament,  and  the  anterior  and  posterior  sterno  -  clavicular 
ligaments. 

The  interarticular  meniscus  not  only  acts  as  a  cushion  which  lessens  the  shock  of  blows 
received  upon  the  shoulder,  but  it  also  acts  as  a  most  important  bond  of  luiion,  and  prevents  the 
inner  end  of  the  clavicle  from  being  driven  upwards  upon  the  top  of  the  sternum  when  force  is 
applied  to  its  outer  end. 

The  movements  at  the  acromio -clavicular  joint  are  of  such  a  kind  as  to  allow  the  inferior 
angle,  and  to  some  extent  the  base  of  the  scapula,  to  remain  more  or  less  closely  applied  to  the 
chest-wall  during  the  various  movements  of  the  shoulder.  The  strong  connexion  between  the 
coracoid  process  and  the  acromial  end  of  the  clavicle,  by  means  of  the  conoid  and  trapezoid 
ligaments,  renders  it  necessary  that  the  scapula  should  follow  the  clavicle  in  its  various 
excursions.  The  presence  of  the  acromio-clavicular  joint,  however,  enables  the  scapula  to  change 
its  position  somewhat  with  reference  to  the  clavicle  as  the  shoulder  is  moved.  Thus,  when  the 
shoulder  is  raised  and  depressed,  a  marked  difference  takes  place  in  the  angle  between  the  two 
bones ;  again,  when  the  shoulder  is  thrown  forwards  or  backwards,  these  movements  can  be 
performed  without  altering  in  a  material  degree  the  direction  of  the  glenoid  cavity  of  the  scapula, 
or  in  other  Avords,  the  socket  of  the  shoulder-joint. 

The  conoid  and  trapezoid  ligaments  set  a  limit  upon  the  movements  of  the  scapula  at  the 
acromio-clavicular  joint.  They  both,  but  more  particularly  the  trapezoid  ligament,  prevent  the 
acromion  process  of  the  scapula  from  being  carried  inward  below  the  outer  end  of  the  clavicle 
when  blows  fall  upon  the  outer  aspect  of  the  shoulder. 

LiGAMENTE  OF  THE  SCAPULA. 

These  ligaments  are  not  directly  connected  with  any  articulation.  The  coraco- 
acromial  ligament  (lig.  coraco-acromiale,  Fig.  219)  completes  the  arch  between  the 
coracoid  and  acromion  processes  of  the  scapula,  and  thus  provides  a  secondary 
socket  for  the  greater  protection  and  security  of  the  shoulder-joint.  It  is  a  flat 
triangular  structure  stretched  tightly  between  its  lines  of  attachment.  By  its  base 
it  is  fixed  to  a  varying  amount  of  the  postero-external  border  of  the  coracoid 
process,  and  by  its  narrower  apical  end  to  the  tip  of  the  acromion  process,  im- 
mediately external  to  the  acromio-clavicular  joint.  Its  surfaces  look  upwards  and 
downwards,  and  its  free  borders  outwards  and  inwards.  It  is  thinnest  in  the 
centre,  where  it  is  sometimes  perforated  by  a  prolongation  of  the  tendon  of  the 
pectoralis  minor  muscle. 

The  suprascapular  ligament  (lig.  transversum  scapulae  superius)  is  a  distinct  but 
short  flat  band  which  bridges  the  notch  of  the  same  name.  It  may  be  continuous 
with  the  conoid  ligament,  and  it  is  frequently  ossified.  As  a  rule  the  foramen 
completed  by  this  ligament  transudts  the  suprascapular  nerve,  while  the  corre- 
sponding vessels  travel  above  the  ligament  to  reach  the  supraspinous  fossa. 

A  small  duplicate  of  tliJs  ligament  may  often  be  found  bridging  the  foramen  on 
its  ventral  aspect,  subjacent  to  which  small  branches  of  the  suprascapular  artery 
return  from  the  supras])irions  to  the  subscapular  fossa. 

The  spino- glenoid  ligament  flig.  transversum  scapulae  inferius)  consists  of 
another  set  of  bridging  fibres  which  are  situated  on  the  posterior  aspect  of  the 


276 


THE  AETICULATIONS  OE  JOINTS. 


neck  of  the  scapula.  By  one  end  they  are  attached  to  the  external  border  of  the 
scapular  spine,  and  by  the  other  to  the  adjacent  part  of  the  posterior  aspect  of 
the  head  of  the  scapula.  The  suprascapular  nerve  and  vessels  pass  subjacent  to 
this  ligament. 

THE  SHOULDER-JOINT. 

The  shoulder-joint  (articulatio  humeri)  is  one  of  the  largest  as  well  as  the  most 
important  of  the  joints  of  the  upper  limb.  It  is  an  example  of  the  enarthrodial, 
i.e.  ball-and-socket  variety  of  a  diarthrosis,  and,  at  the  cost  of  a  certain  amount  of 
security,  it  has  obtained  an  extended  range  of  movement. 

The  bones  which  enter  into  its  formation  are  the  glenoid  fossa  of  the  scapula 
and  the  head  of  the  humerus. 

The  glenoid  fossa  is  a  shallow  pyriform  articular  surface,  having  its  narrow  end 
directed  upwards  and  slightly  forwards.  The  upper  half  of  the  anterior  margin  of 
the  fossa  is  characterised  by  a  shallow  notch  which  accommodates  the  narrow  part 
of  the  subscapularis  muscle  as  it  runs  outwards  to  its  insertion.  At  the  apex  of  the 
fossa  there  is  a  flat  area  for  the  attachment  of  the  long  tendon  of  the  biceps  flexor 
cubiti  muscle.  The  head  of  the  humerus  is  hemispherical  and  articular,  while, 
external  to  its  articular  margin,  there  is  a  slight  constriction  (the  anatomical  or 
true  neck  of  the  humerus),  which  is  most  strongly  marked  in  relation  to  the 
greater  and  lesser  tuberosities  of  the  humerus. 

Under  ordinary  conditions  the  two  articular  surfaces  are  maintained  in 
apposition  by  muscular  action,  aided  by  atmospheric  pressure,  and  thus,  when  the 
muscles  are  removed,  the  bones  fall  asunder  to  the  full  extent  of  the  restraining 
ligaments.  Only  a  small  part  of  the  humeral  head  is  in  contact  with  the  glenoid 
fossa  at  any  particular  moment,  because  the  former  is  much  larger  than  the  latter, 
but,  by  reason  of  the  shallow  character  of  this  fossa,  all  parts  of  the  two  articular 
surfaces  may  successively  be  brought  into  contact  with  each  other. 

In  the  position  of  rest,  as  the  limb  hangs  parallel  to  the  vertical  axis  of  the 
trunk,  the  inferior  aspect  of  the  neck  of  the  humerus  is  brought  into  close  relation 
with  the  lower  part  of  the  glenoid  fossa. 

The  glenoid  ligament  (labrum  glenoidale,  Fig.  219)  deepens  the  glenoid  fossa, 
and  thus  extends  the  articular  surface.     It  is  situated  within  the  joint  capsule,  and 

to  some  sho-ht   ex- 

Acroniion  process  ...  °  , , 

tent  increases  the 
security  of  the  arti- 
culation. It  con- 
sists of  a  strong 
'subbcapiiiaiis  ring  of  dcusc  fibrous 
tissue  attached  to 
the  free  margin  of 
the  glenoid  fossa. 
Many  of  its  fibres 
are  short,  and  pass 
obliquely  from  the 
inner  to  the  outer 
aspect  of  the  ridge, 
so  that  its  attached 
base  is  broader  than 
its  free  edge,  and 
there  fore  in  cross  sec- 
tion it  appears  some- 
what triangular. 
The  long  tendon  of 
the  biceps,  which 
a  considerable  extent  in- 


Coraco-acromial  lioameiit 


Coiaco  huineial 
^anient 


niub(  le 


Coiiimuiiication 

between  subscapular 

bursa  am.l  joint  cavity 


Capsule  of  joint 


biceps 


Fig.  218. — Capsule  of  the  Shoulder-Joint  and  Coraco-acromial  Ligament. 


arises  from  the  apex  of  the  glenoid  fossa,  becomes  to 
corporated  with  this  ligament. 

The  capsular  ligament  (capsula  articularis.  Fig.  218)  presents  the  general  shape 
which  is  characteristic  of  the  corresponding  ligapient  in  other  ball-and-socket  joints, 


THE  SHOULDEE- JOINT. 


277 


viz.  a  hollow  cylinder.  By  its  upper  end  the  capsule  is  attached  to  the  circum- 
ference of  the  glenoid  fossa,  external  to  the  glenoid  ligament,  and  also,  to  a  considei- 
able  extent,  to  the  glenoid  ligament  itself. 

By  its  lower  end  it  is  attached  to  the  neck .  of  the  humerus,  and  therefore 
beyond  the  articular  area  of  the  head.  The  capsule  is  strongest  on  its  superior 
aspect,  while  inferiorly,  where  the  neck  of  the  bone  is  least  defined,  it  extends 
downwards  for  a  short  distance  upon  the  humeral  shaft.  Its  fibres  for  the  most 
part  run  longitudinally,  but  a  certain  number  of  them  pursue  a  circular  direction. 

A  prolongation  of  the  capsule,  the  transverse  humeral  ligament  presenting  both 
longitudinal  and  transverse  fibres,  bridges  that  part  of  the  bicipital  groove  which  is 
situated  between  the  tuberosities  of  the  humerus.  At  this  point  an  interruption 
in  the  capsule,  beneath  the  transverse  humeral  ligament,  permits  the  long  tendon 
of  the  biceps  to  escape  from  its  interior.  In  addition  to  the  opening  just  referred 
to,  there  is  another  very  constant  deficiency  in  the  upper  and  anterior  part  of 
the  capsule,  where  the  narrowing  tendon  of  the  subscapularis  muscle  is  brought 
into  contact  with  a  bursa  formed  by  a  protrusion  of  the  synovial  membrane.  This 
defect  in  the  capsule  has  its  long  axis  in  the  direction  of  the  longitudinal  fibres. 
Occasionally  there  is  a  similar  but  smaller  opening  under  cover  of  the  tendon  of 
the  infraspinatus  muscle.  Through  the  two  latter  openings  the  joint  cavity 
communicates  with  bursse  situated  between  the  capsule  and  the  muscles  re- 
ferred to. 

The  tendons  of  the  subscapularis,  supraspinatus,  and  infraspinatus  muscles 
fuse  with,  and  so  strengthen,  the  capsule  as  they  approach  their  respective 
insertions. 

On  the  superior  aspect  of  the  articulation  the  capsule  is  augmented  by  an 
accessory  structure,  the  ligamentum  coraco-humerale  (Fig.  218).  By  its  inner  end, 
which  is  situated  immediately  above  the  glenoid  fossa,  but  subjacent  to  the  coraco- 
acromial  ligament,  it  is  attached  to  the  external  border  of  the  root  of  the  coracoid 
process,  while  its  outer  end  is  attached  to  the  humeral  neck  close  to  the  great  tuberosity. 
This  ligament  forms  a  flattened  band,  having  its  hinder  and  low^er  border  fused  with 
the  capsule,  but 


its  anterior  and 
upper  margin 
presents  a  free 
edge,  slightly 
raised  above  the 
level  of  the  cap- 
sule. This  struc- 
ture is  believed 
to  represent  that 
portion  of  the 
pectoralis  minor 
to  which  refer- 
ence has  already 
been  made  in  con- 
nexion with  the 
coraco  -  acromial 
ligament  (p.  275). 

Tin;  coraco- 
glenoid  ligament  i.'^ 
anotlifcr  accesHory 
Htnictiire  whicli  L 
not  always  j)r('.s(;nt. 
It  .spring.4  from  the 
coracoid  process 
along       with       the 


clavicular  [Trapezoid 
ligament  J 
Coraco-acromial  ligament 


Coiacoid  proces 


Superior  gleno-humeral, 
li^jament 


Aciomio- 
clavicular 
ligament 


Bursal  perforation  in  capsule" 


Inferior  gleno-liuineral 
ligament 


Glenoi' 


Capsule  of 
slioulder-joint 


\Glen(.i(] 
igauient 


V\(i.  21!). 


-C'AI'SULAIt  LlOAMKNT  OK    SirOIJLDKH-JOLNT  CUT    ACROSS    AND 

Hum  Kites  rkmovkd. 


foniKT  ]ig;i.iiicii1,  ■,i]](]  cxh-iids  to  the  ii]»p(n- and  liindci'  margin  of  the  head  of  the  sca])ula. 

Gleno-humeral  Ligaments  ('h'ig.  ■2\U).—\  f  the  (;aj.Hiilt!  Ix-  opened  from  bc^hind,  and  the  head  of  tiie 
liiinn-rii.s  ill-  n-movi-d,  it  will  Ix:  seen  that  the  Iongitiidiii;il  lil)ivs  of  tin;  anterio)'  part  of  the  capsuh; 
are  special  1  y  develop(;f I  in  the  form  of  thick  flattened  bands  which  extend  from  t  he;  anterioi'  bonh'r 
of  the  glenoid   fossa  to  the  antei'ior  aspect  of  the  neck  of  the   Iiiimenis.     These  gieno-hiiiiici'al 


278 


THE  AETICULATIONS  OE  JOINTS. 


lead  of 
capula 


ligaments  are  three  in  number,  and  occupy  the  following  positions  :  the  superior  is  placed  above  the 
aperture  in  the  front  of  the  capsule  ;  the  middle  and  inferior  on  the  antero-inferior  aspect  of  the 
capsule,  and  heloiv  the  aperture  mentioned. 

Tlie  superior  gleno-liunieral  ligament,  which  some  believe  to  represent  the  ligamentum  teres 
of  tlie  hip-joint,  springs,  along  with  the  middle  gleno-humeral  band,  from  the  upper  part  of  the 
anterior  glenoid  margin.  The  inferior  band  is  the  strongest  of  the  three,  and  springs  from  the 
lower  part  of  the  anterior  glenoid  margin. 

Intra-capsular  Structures. — 1.  The  glenoid  ligament,  already  described.  2. 
The  long  tendon  of  the  biceps  passes  outwards  from  its  attachment  to  the  apex  of 
the  glenoid  fossa  and  the  adjoining  part  of  the  glenoid  ligament,  above  the  head  and 
neck  of  the  humerus,  to  escape  from  the  interior  of  the  capsule  by  the  opening 
between  the  tuberosities  of  the  humerus,  subjacent  to  the  transverse  humeral 
ligament. 

Synovial  membrane  (Fig.  220)  lines  the  capsule  of  the  joint,  and  extends  from 
the  margin  of  the  glenoid  fossa  to  the  humeral  attachments  of  the  capsule,  where  it 

is  reflected  towards  the 
margin  of  the  articular 
cartilage.  It  is  there- 
fore important  to  note 
that  the  inferior  aspect 
of  the  humeral  neck  has 
the  most  extensive 
clothing  of  synovial 
membrane.  Further, 
the  synovial  membrane 
envelops  the  intra-cap- 
sular part  of  the  tendon 
of  the  biceps,  and  al- 
though this  tubular 
sheath  is  prolonged  upon 
the  tendon  into  the 
upper  part  of  the  bi- 
cipital groove,  yet  the 
closed  character  of  the 
synovial  cavity  is  main- 
tained. Thus,  while  the 
tendon  is  within  the 
capsule,  it  is  not  within 
the  synovial  cavity.  The  synovial  membrane  is  continuous  with  those  bursee 
which  communicate  with  the  joint  cavity  through  openings  in  the  ligamentous 
capsule. 

Bursse  (a)  Gommunicating  ivith  the  Joint  Cavity. — Practically  there  is  only  one  bursa  which 
is  constant  in  its  position,  viz.  the  subscapular,  between  the  cajDsule  and  the  tendon  of  the  sub- 
scajjularis  muscle.  It  varies  considerably  in  its  dimensions,  but  its  lining  membrane  is  always 
continuous  with  that  which  lines  the  capsule  (Figs.  217  and  218),  and  therefore  it  may  be 
regarded  merely  as  a  prolongation  of  the  articular  synovial  niembrane.  Occasionally  a  similar 
but  smaller  bursa  occurs  between  the  capsule  and  the  tendon  of  the  infraspinatus  muscle. 

(6)  Not  communicating  ivith  the  Joint  Cavity. — The  sub-deltoid  or  sub-acromial  bursa  is 
situated  between  the  muscles  on  the  suj^erior  aspect  of  the  shoulder-joint  on  the  one  hand  and 
the  deltoid  muscle  on  the  other.  It  is  an  extensive  bursa,  and  is  prolonged  subjacent  to  the 
acromion  jjrocess  and  the  coraco-acromial  ligament.  It  does  not  comnumicate  with  the  shoiilder- 
joint,  but  it  greatly  facilitates  the  movements  of  the  ujjper  end  of  the  humerus  against  the  under 
surface  of  the  coraco-acromial  arch. 

Movements  at  the  Shoulder-Joint. — A  ball-and-socket  joint  permits  of  a  great  variety  of 
movements,  practically  in  all  directions  ;  but  if  these  movements  be  analysed,  it  will  be  seen  that 
they  resolve  themselves  into  movements  about  three  primary  axes  at  right  angles  to  each  other, 
or  about  axes  which  are  the  jjossible  combinations  of  the  primary  ones. 

Thus,  about  a  transverse  axis,  the  limb  may  moA'e  forwards  (flexion)  or  backwards  (extension). 
About  an  antero-posterior  axis  it  m&j  move  outwards,  i.e.  away  from  the  mesial  plane  of  the 
trunk  (abduction),  or  inwards,  i.e.  towards,  and  to  some  extent  up  to,  the  mesial  plane 
(adduction). 

About  a  vertical  axis,  the  humerus  may  rotate  upon  its  axis  in  an  inward  or  outward  direction 
to  the  extent  of  a  quarter  of  a  circle. 


it)  of  joint 


Fig.  220. — Vertical  Section  through  the  Shoulder- Joint. 


THE  ELBOW-JOINT. 


279 


Since  tliese  axes  all  pass  through  the  shoiilder -joint,  and  since  each  may  present  varying 
degrees  of  ol^liquity,  it  follows  that  very  elaborate  combinations  are  possible  until  the  movement 
of  circumduction  is  evolved.  In  this  movement  the  head  of  the  humerus  acts  as  the  apex  of  a 
cone  of  movement  with  the  distal  end  of  the  humerus,  describing  the  base  of  the  cone. 

The  range  of  the  shoulder-joint  movements  is  still  further  increased  from  the  mobility  of 
the  scapula  as  a  whole,  and  from  its  association  with  the  movements  of  the  clavicle  already 
described. 


THE  ELBOW-JOINT. 


This  articulation  (articiilatio  cubiti)  provides  an  instance  of  a  diarthrosis  capable 
of  performing  the  movements  of  flexion  and  extension  about  a  single  axis  placed 
transversely,  i.e.  a  typical  ginglymus  diarthrosis  or  hinge-joint. 

The  bones  which  enter  into  its  formation  are  the  humerus,  ulna,  and  radius. 
The  trochlea  of  the  humerus  articulates  with  the  greater  sigmoid  cavity  of  the 
ulna  (articulatio  humero-ulnaris) ;  the  capitellum  of  the  humerus  articulates  with 
the  shallow  depression  or  cup  on  the  superior  aspect  of  the  head  of  the  radius  (articu- 
latio humero-radialis).  The  articular  cartilage  clothing  the  trochlea  of  the  humerus 
terminates  in  a  sinuous  or  concave  margin  both  anteriorly  and  posteriorly,  so  that 
it  does  not  line  either  the 
coronoid  or  the  olecranon 
fossa.  Internally,  it  merely 
rounds  off  the  inner  margin 
of  the  trochlea,  but  exter- 
nally it  is  continuous  with 
the  encrusting  cartilage 
covering  the  capitellum,  to 
the  margin  of  which  the 
cartilage  extends  in  all 
directions,  and  thus  it  pre- 
sents a  convex  edge  in 
relation  to  the  supra-capi- 
tellar  or  radial  fossa.  The 
cartilage  which  lines  the 
greater  sigmoid  cavity  of 
the  ulna  presents  a  trans- 
verse interruption,  consider- 
ably wider  on  its  inner  as 
compared  with  its  outer 
aspect.  Thereby  the  coro- 
noid and  olecranon  seg- 
ments of  the  fossa  are 
separated  from  each  other. 
The  cartilage  which  clothes 
the  coronoid  segment  is 
continuous  with  that  which 
clothes  the  lesser  sigmoid 
cavity.  'J'lie  shallow  cup- 
shaped  deY)ression  on  the 
head  of  the  radius  is  covered 
by  cartilage  which  rounds 
off  the  margin,  and  is  pro- 
longed without  interruption 
upon  the  vertical  aspect  of  the  head,  descending  to  its  lowest  level  on  that  part 
opposed  to  the  lesser  sigmoid  cavity. 

Ligaments. — Taken  as  a  whole,  the  ligaments  form  a  complete  capsule  (capsula 
articularisy,  which  is  not  defective  at  any  point,  although  it  is  not  of  equal  thick- 
ness throughout,  and  certain  hands  of  fibres  stand  out  distinctly  because  of  their 
greater  strengtl). 

'J'he  anterior  ligament  (Fig.  221)  consists  of  a  layer  wliose  liltres  run  in  several 


Internal  lateral 
ligament , 


Tendon  of  insertion  of 
mnscle 


Oblique  (ulno-radial) 
ligament 


Fio.  221. — Anteetoh  View  of  Elbow-Joint, 


280 


THE  ARTICULATIONS  OR  JOINTS. 


directions — obliquely,  transversely,  and  vertically — and  of  these  the  vertical  fibres 
are  of  most  importance.  It  is  attached  above  to  the  upper  margins  of  the  coronoid 
and  supracapitellar  fosste  ;  below,  to  the  margins  of  the  coronoid  process  and  to  the 
orbicular  ligament  of  the  superior  radio-ulnar  joint,  but  some  loosely  arranged 
fibres  reach  as  far  as  the  neck  of  the  radius.  The  lateral  portions  of  this  ligament, 
which  are  situated  in  front  of  the  capitellum  and  the  inner  margin  of  the  trochlea 
respectively,  are  much  thinner  and  weaker  than  the  central  part.  Fibres  of  origin 
of  the  brachialis  anticus  muscle  are  attached  to  the  front  of  this  ligament. 

The  posterior  ligament  is  an  extremely  thin,  almost  redundant  layer. 
Superiorly  it  is  attached,  in  relation  to  the  margin  of  the  olecranon  fossa,  at  a 
varying  distance  from  the  trochlear  articular  surface,  and  inferiorly  to  the  summit 
and  sides  of  the  lip  of  the  olecranon  process.  Externally  some  of  its  fibres 
pass  from  the  posterior  aspect  of  the  capitellum  to  the  posterior  border  of  the  lesser 
sigmoid  cavity  of  the  ulna.  This  ligament  derives  material  support  from,  and 
participates  in  the  movements  of,  the  triceps  extensor  cubiti  muscle,  since  they  are 
closely  adlierent  to  each  other  in  the  region  of  the  olecranon  process. 

The  internal  lateral  ligament  (lig.  collaterale  ulnare,  Figs.  221  and  222)  is  a  fan- 


InterossRous  membrane 


Interual  coiulj-lp 


VMlMi       Anterior  part  of  internal 
'''Si        lateral  ligament 

PosteFior  part  of 
internal  lateral  ligament 


Transverse  part  of  internal  lateral  ligament 
Fig.  222. — Elbow-Joint  (inner  aspect). 

shaped  structure  of  unequal  thickness,  but  its  margins,  which  are  its  strongest  bands, 
are  continuous  with  the  adjoining  parts  of  the  anterior  and  posterior  ligaments. 
By  its  upper  end  it  is  attached  to  the  anterior,  inferior,  and  posterior  aspects  of  the 
internal  condyle  of  the  humerus.  By  its  broad  lower  end  it  is  attached  to  the 
inner  margin  of  the  greater  sigmoid  cavity,  so  that  the  anterior  land  is  associated 
principally  with  the  inner  margin  of  the  coronoid  process,  and  the  posterior  hand 
with  the  inner  margin  of  the  olecranon  process,  while  the  intermediate  weaker 
portion  sends  its  fibres  downwards  to  join  a  transverse  land,  sometimes  very  strong, 
which  bridges  the  notch  between  the  adjoining  inner  margins  of  the  coronoid  and 
olecranon  processes. 

The  external  lateral  ligament  (lig.  collaterale  radiale,  Fig.  221)  is  a  strong 
flattened  band  attached  superiorly  to  the  lower  and  posterior  aspects  of  the  external 
condyle  of  the  humerus.  It  completes  the  continuity  of  the  capsule  on  the  outer 
side,  and  blends  inferiorly  with  the  orbicular  ligament,  on  the  surface  of  which  its 
fibres  may  be  traced  both  to  the  anterior  and  posterior  ends  of  the  lesser  sigmoid 


THE  EADIO-ULNAR  JOINTS. 


281 


Olecranon  pad  of  fat 


Ulecianon  process 


Fig.  223. — Vertical  Section  through  the  Trochlear  Part  of  the 
Elbow-Joint. 


notch.     Both  of  the  lateral  ligaments  are  mtimately  associated  with  tlie  muscles 
which  take  origin  from  the  inner  and  outer  condyles  of  the  humerus. 

Synovial  Pads  of  Fat  (Fig.  223). — Internal  to  the  capsule,  there  are  several  pads 
of  fat  situated  be- 
tween it  and  the  sy- 
novial membrane. 
Small  pads  are  so 
placed  as  to  lie  im- 
mediately in  front 
of  the  coronoid  and 
supra-capitellar 
fossae.,  but  a  larger 
one  projects  to- 
wards the  olecra- 
non fossa. 

Synovial  mem- 
brane (Fig.  223) 
lines  the  entire 
capsule  and  clothes 
the  pads  of  fat 
above  referred  to, 
as  well  as  those 
portions  of  bone 
enclosed  within  the 
capsule  which  are 
not  covered  by 
articular  cartilage. 
By  its  disposition 
the  elbow  and  the 
superior  radio- 
ulnar joints  possess  a  common  joint  cavity.  It  should  be  specially  noted  that  the 
upper  part  of  the  neck  of  the  radius  is  surrounded  by  this  synovial  membrane. 

Movements  at  the  Elbow-Joint. — The  movements  of  the  radius  and  idna  upon  the  humerus 
have  already  been  referred  to  as  those  characterising  a  uniaxial  joint  constructed  on  the  jjlan  of 
a  hinge.  In  this  case  the  axis  of  the  joint  is  obliquely  transverse,  so  that  in  the  extended 
position  the  humerus  and  ulna  form  an  obtuse  angle  open  towards  the  radius,  whereas  in  the 
flexed  jDOsition  the  hand  is  carried  inwards  in  the  direction  of  the  mouth.  Extreme  flexion  is 
checked  by  the  soft  j)arts  in  front  of  the  arm  and  of  the  fore-arm  coming  into  contact,  and 
extreme  extension  by  the  restraining  eff'ect  of  the  ligaments  and  muscles.  In  each  case  the 
movement  is  checked  before  either  coronoid  or  olecranon  processes  come  into  contact  with  the 
humerus.  The  anterior  and  posterior  bands  of  the  internal  lateral  ligament  are  important  factors 
in  these  results.  Lateral  movement  of  the  ulna  is  not  a  characteristic  movement,  although  it 
may  occur  to  a  slight  extent,  owing  to  a  want  of  complete  adaptation  between  the  trochlear 
surface  of  the  humerus  and  the  sigmoid  cavity  of  the  ulna.  This  incongruence  is  noteworthy 
since  the  inner  lip  of  the  trochlea  is  jjrominent  in  front,  and  the  outer  lip  is  prominent  behind. 
Consequently,  this  latter  part  is  associated  with  a  surface  on  the  outer  side  of  the  olecranon 
which  is  only  utilised  in  complete  extension. 

The  capitellum  and  the  opposing  surface  ujion  the  head  of  the  radius  are  always  in  varying 
degrees  of  contact.  Tlie  lieact  of  the  radius  participates  in  the  movements  of  flexion  and  exten- 
sion, and  is  most  closely  and  completely  in  contact  with  the  humerus  during  the  jDosition  of  semi- 
flexion and  semi-pronation.  In  conqjlete  extension  a  very  considerable  part  of  the  caj^itellum  is 
uncovered  by  the  radius. 

THE  RADIO-ULNAR  JOINTS. 

These  articulations,  which  are  two  in  number,  are  situated  at  the  proximal  and 
distal  ends  of  the  radius  and  ulna.  They  provide  an  adaptation  whereby  the  radius 
rotates  around  a  longitudinal  axis  in  the  movements  of  pronation  and  supination, 
and  heiK'O  this  foiiu  of  uniaxial  diarthrosis  is  termed  lateral  ginglymus. 

Superior  Radio-ulnar  Joint  (articulatio  radio-ulnaris  proximalis). — In  this 
joint  btie  articular  surfacos  which  enter  into  its  formation  are  the  lesser  sigmoid 
cavity  of  tlie  ulna  and  the  lateral  aspect  of  the  head  of  the  radius.  In  each  case 
the  articular  cartilage  is  continuous  with  an  articular  surface  entering  into  the 
formation  of  the  elbow-joint,  consequently  the  joint  cavity  is  continuous  with  that 


282 


THE  AETICULATIONS  OE  JOINTS. 


Olecranon  process 


>rn:il  latrral 
li.naniPiit 


Greater  sigmoirt 
avity 


Orbicular  ligament  Coronoid  process 

Fig.  224. — Orbicular  Ligament  of  the  Radius. 


of  the  elbow-join b,  and  tlierefore,  in  a  sense,  it  lies  mthin  the  cover  of  the  capsule 
of  the  elbow-joint ;  but  its  special  feature  is  the — 

Orbicular  ligament  (lig.  annulare  radii,  Figs.  221  and  224),  which  lias  formerly  been 

mentioned  as  the  inferior  line  of 
attachment  of  the  external  lateral 
ligament  and  the  ligaments  on 
the  front  and  back  of  the  elbow- 
joint. 

It  is  a  strong,well-deJ&ned  struc- 
ture, attached  by  its  extremities 
to  the  anterior  and  posterior 
margins  of  the  lesser  sigmoid 
cavity,  and  thus  it  forms  nearly 
four-fifths  of  an  osseo-tendinous 
circle  or  ring.  This  circle  is  some- 
what wider  at  the  upper  than  at 
the  lower  margin  of  the  orbicular 
ligament,  which,  by  encircling  the 
upper  part  of  the  neck  of  the 
radius,  tends  to  prevent  displace- 
ment of  the  head  of  that  bone  in  a  downward  direction.  The  lower  margin  of 
this  ligament  is  not  directly  attached  to  the  radius. 

The  synovial  membrane  is  continuous  with  that  which  lines  the  elbow-joint.  It 
closes  the  joint  cavity  at  the  inferior  unattached  margin  of  the  orbicular  ligament, 
where  it  is  somewhat  loosely  arranged  in  its  reflexion  from  the  ligament  to  the 
neck  of  the  radius. 

Inferior  Radio-ulnar  Joint  (articulatio  radio-ulnaris  distalis). — This  joint  is 
situated  between  the  sigmoid  cavity  on  the  inner  side  of  the  lower  end  of  the 
radius  and  the  lateral  aspect  of  the  head  of  the  ulna.  In  addition,  it  includes  the 
inferior  surface  of  the  head  of  the  ulna,  which  articulates  with  the  superior 
surface  of  a  triangular  plate  of  fibro-cartilage,  by  means  of  which  the  joint  is 
excluded  from  the  radio-carpal  articulation 

The  triangular  interarticular  fibro-cartilage  (discus  articularis.  Figs.  225  and  227), 
besides  presenting  articular  surfaces  to  two  separate  joints,  is  an  important  ligament 
concerned  in  binding  together  the  lower  ends  of  the  radius  and  ulna..  It  is  attached 
by  its  apex  to  the  de- 
pression at  the  outer 
side  of  the  root  of  the 
styloid  process  of  the 
ulna,  and  by  its  base  to 
the  sharp  line  of  de- 
marcation between  the 
sigmoid  cavity  and  the 
carpal  articular  surface 
of  the  radius. 

The  ligamentous  cap- 
sule is  very  imperfect,  and  consists  of  scattered  fibres,  termed  the  anterior  and 
posterior   radio-ulnar   ligaments  (Fig.   226).      These  ligaments   pass    transversely 
between  adjoining  non-articular  surfaces  on  the  radius  and  ulna,  and  are  of  sufficient 
length  to  permit  of  the  movements  of  the  radius  in  pronation  and  supination. 

The  synovial  membrane  completes  the  closure  of  the  joint  cavity.  It  forms  a 
loose  bulging  projection  (recessus  sacciformis),  passing  vipwards  between  the  lower 
ends  of  the  shafts  of  the  radius  and  ulna,  and  it  also  clothes  the  upper  surface  of 
the  triangular  fibro-cartilage  (Fig.  227).  The  cavity  of  this  joint  is  quite  distinct 
from  that  of  the  radio-carpal  articulation,  except  when  the  triangular  fibro-cartilage 
presents  a  perforation. 

Between  the  foregoing  articulations  there  are  two  accessory  ligaments,  viz.  the 
interosseous  membrane  and  the  oblique  ligament,  which  connect  together  the  shafts 
of  the  radius  and  ulna. 


Su]face 
scaphoid  bon 

Groove  for  temlw 
of  extensor longu 
pollicis 


Styloid  process  of  ulna 


triangular  fibi'o-cartilage 
Ti  langnlar  fibro-cartilage 
Surface  for  semilunar  bone 


Fig 


225. — Carpal  Articular  Surface  of  the  Radius,  and 
Triangular  Fibro-cartilage  of  the  Wrist. 


THE  EADIO-CAEPAL  JOINT.  283 

The  interosseous  membrane  (Fig.  222)  of  the  fore-arm  (memljrana  interossea  inter- 
brachii)  is  a  strong  filn-ous  membrane  which  stretches  across  the  interval  between 
the  radius  and  ulna,  and  is  firmly  attached  to  the  interosseous  border  of  each.  Below 
it  extends  downwards  to  the  lower  limit  of  the  space  between  the  bones,  whilst 
above  it  does  not  reach  higher  than  a  point  about  one  inch  Ijelow  the  tuberosity 
of  the  radius.  A  gap,  called  the  hiatus  interosseus,  is  thus  left  above  its  upper 
margin,  and  through  this  the  posterior  interosseous  vessels  pass  backwards  between 
the  bones  to  reach  the  dorsal  aspect  of  the  fore-arm.  This  gap  is  bounded  above 
by  the  oblique  ligament.  The  fibres  which  compose  the  interosseous  membrane 
run  for  the  most  part  downwards  and  inwards  from  the  radius  to  the  ulna,  although 
on  its  dorsal  aspect  several  bands  may  be  observed  stretching  in  an  opposite  direc- 
tion. The  interosseous  membrane  augments  the  surface  available  for  the  origin  of 
the  muscles  of  the  fore-arm ;  it  braces  the  radius  and  ulna  together ;  and  when 
shocks  are  communicated  from  the  hand  to  the  radius,  owing  to  the  direction  of  its 
fibres,  the  interosseous  membrane  transmits  these,  to  some  slight  extent,  to  the  ulna. 

The  oblique  ligament  (Fig.  222)  is  a  slender  tendinous  band  of  very  varying 
strength  which  springs  from  the  outer  part  of  the  coronoid  process  of  the  ulna,  and 
stretches  obliquely  downwards  and  outwards  to  the  radius  where  it  is  attached 
immediately  below  the  bicipital  tuberosity. 

Movements  of  the  Radius  on  the  Ulna. — The  axis  about  wliicli  the  radius  moves  is  a 
longitudinal  cue,  haviug  one  end  passing  through  the  centre  of  the  head  of  the  radius  and 
the  other  through  the  styloid  process  of  the  rdna  and  the  line  of  the  ring-finger.  In  this  axis 
the  liead  of  the  radius  is  so  secured  that  it  can  only  rotate  upon  the  lesser  sigmoid  cavity 
of  the  ulna  within  the  orbicular  ligament,  and  consequently  the  radial  head  remains  upon  the 
same  j)lane  as  the  ulna ;  but  the  lower  end  of  the  radius  being  merely  restrained  by  the 
triangular  fibro -cartilage,  is  able  to  describe  nearly  a  half-circle,  of  which  the  apex  of  this 
ligament  is  the  centre.  In  this  movement  the  radius  carries  the  hand  from  a  position  in  which 
the  palm  is  directed  forwards,  and  in  which  the  radius  and  ulna  lie  parallel  to  each  other 
(supination),  to  one  in  which  the  palm  is  directed  backwards,  and  the  radius  lies  diagonally  across 
the  front  of  the  ulna  (pronation). 

The  ulna  is  unable  to  rotate  upon  a  long  axis,  but  while  the  radius  is  travelling  through  the 
arc  of  a  circle  from  without  inwards  in  front  of  the  ulna,  it  will  usually  be  seen  that  the  ulna 
appears  to  move  through  the  arc  of  a  smaller  circle  in  the  reverse  direction,  viz.  from  within 
outwards.  If  the  humerus  be  prevented  from  moving  at  the  shoulder-joint,  a  very  large  propor- 
tion, if  not  the  entire  amount,  of  this  apparent  movement  of  the  ulna  will  disappear.  At  the 
same  time  some  observers  maintain  that  it  really  occurs  at  the  elbow-joint,  associated  with  lateral 
moA'ement  during  slight  degrees  of  flexion  and  extension  at  that  joint. 

THE  RADIO-CARPAL  JOINT. 

This  joint  (articulatio  radiocarpea)  is  a  bi-axial  diarthrosis,  frequently  called  a 
condyloid  joint. 

The  articular  elements  which  enter  into  its  formation  are:  on  its 2}roximal  side,  the 
inferior  surface  of  the  lower  end  of  the  radius,  together  with  the  inferior  surface  of 
the  triangular  fibro-cartilage  ;  on  its  distcd  side,  the  superior  articular  surfaces  of  the 
scaphoid,  semilunar,  and  cuneiform  bones.  The  articular  surface  of  the  radius  is 
concave  both  in  its  antero-posterior  and  transverse  diameters,  in  order  to  adapt 
itself  to  the  opposing  surfaces  of  the  scaphoid  and  semilunar,  which  are  convex  in 
the  two  axes  named.  In  the  ordinary  straight  position  of  the  hand  the  triangular 
fibro-cartilage  is  in  contact  with  the  semilunar  bone,  and  the  upper  articular  surface 
of  the  cuneiform  bone  is  in  contact  with  the  capsule  of  the  joint.  When,  however, 
the  hand  is  bent  towards  the  ulna,  the  cuneiform  bone  is  carried  outwards  as  well 
as  the  semilunar  and  scaphoid,  and  the  triangular  fibro-cartilage  comes  into  contact 
■with  the  cuneiform.  The  articular  surface  of  the  radius  is  subdivided  by  an  antero- 
posterior, slightly  elevated  ridge,  into  an  outer  triangular  facet  which  usually  arti- 
culates witli  the  scayjhoid,  and  an  inner  quadrilateral  facet  for  articulation  with  a 
portion  of  LJie  s(;iniluriar  bone. 

In  the  intervals  between  the  scaphoid,  sendlunar,  and  cuneiform  bones,  the  con- 
tinuity of  the  articular  surfaces  is  usually  maintained  by  the  presence  of  interosseous 
h'gamerits  which  are  situated  upon  the  same  level  as  the  articular  cartilage. 

Ligaments. — A  caytsular  ligament  completely  surrounds  the  joint.  It  is  some- 
what loosely  iirranged,  and  injnuits  of  subdivision  into  the  following  portions: — 

"J'he  external  lateral  ligament  TFig.  22G;  is  a  well-defined  band  which  is  attached 


284 


THE  AETICULATIONS  OR  JOINTS. 


Anterior  radio 
ulnar  lijiamenl 


Internal  lateral 
ligament 


Pisiform  bone 


Evternal  lateral 
lU'ament 


Os  magnum,  with 
ligaments  radiat 


Unciform  process 


by  one  end  to  the  tip  of  the  styloid  process  of  the  radius,  and  by  the  other  to  a 

rough  area  at  the  base  of  the  tubercle  of  the  scaphoid  bone,  i.e.  external  to  its 

radial  articular  surface. 

The  internal   lateral  ligament  (Fig.  226)  is  also  a  distinct  rounded  structure, 

having  one  end  attached  to  the  tip  of  the  styloid  process  of  the  ulna,  and  the  other  to 

the  rough  non- articular 
border  of  the  cuneiform 
bone,  some  of  its  fibres 
being  prolonged  to  the 
pisiform  bone. 

The  anterior  ligament 
(Fig.  226)  is  attached 
superiorly  to  the  anterior 
margin  of  the  lower  end 
of  the  radius,  as  well  as 
i  uhercie  of  scaphoid  slightly  to  the  base  of 
the  styloid  process  of  the 

Riilge  on  i  a  i 

trapezium  ulna.  tSomc  transversc 
fibres  may  be  seen,  but 
Trapezium  the  greater  number  pass 
obliquely  downwards  and 
inwards  to  the  palmar 
non-articular  surfaces  of 
the  scaphoid,  semilunar, 
and  cuneiform  bones, 
while  some  of  them  may 
e^'en  be  continued  as  far 
as  the  OS  magnum. 
Those  fibres  from  the 
ulna  run  obliquely  out- 
wards. On  its  deeper 
aspect  this  ligament  is 
closely  adherent  to  the  anterior  border  of  the  triangular  fibro-cartilage  of  the 
inferior  radio-ulnar  articulation. 

The  posterior  ligament  extends  from  the  posterior  margin  of  the  lower  end 
of  the  radius,  obliquely  downwards  and  inwards,  to  the  dorsal  non -articular 
areas  on  the  proximal  row  of  the  carpal  bones.  The  shp  to  the  latter  assists  in 
forming  the  fibrous  sheath  through  which  the  tendon  of  the  extensor  carpi  ulnaris 
muscle  travels  to  its  insertion.  The  principal  bundle  of  fibres  is  connected  with 
the  cuneiform  bone. 

The  synovial  membrane  (Fig.  227)  is  simple,  and  is  confined  to  the  articulation, 
except  in  those  cases  in  which  the  triangular  fibro-cartilage  is  perforated,  or  in  which 
one  of  the  interosseous  ligaments  between  the  carpal  bones  of  the  first  row  is  absent. 

Movements  at  the  Radio-carpal  Joint. — Tke  radio -carpal  jomt  ajffords  an  excellent  example 
(if  a  biaxial  articulation,  in  which  a  long  transverse  axis  of  movement  is  situated  more  or  less  at 
right  angles  to  a  short  axis  placed  in  the  antero-jjosterior  direction.  The  nature  of  the  move- 
ments which  are  possible  about  these  two  axes  is  essentially  the  same  in  both  cases,  viz.  flexion 
and  extension.  The  movements  about  the  longer  transverse  axis  are  anterior  or  jsalmar  flexion, 
extension,  and  its  continuation  into  dorsi-flexion.  About  the  shorter  antero-posterior  axis  we  get 
movements  which  result  from  combined  action  by  certain  flexor  and  extensor  nmscles,  whereby 
the  radial  or  ulnar  borders  of  the  hand  may  be  a^^proximated  towards  the  corresjionding  borders 
of  the  fore-arm.  Lateral  movement  may  also  be  possible  to  a  slight  extent.  The  range  of  move- 
ment iir  connexion  with  either  of  the  principal  axes  is  largely  a  matter  of  individual  peculiarity, 
for,  with  the  excei^tion  of  the  lateral  ligaments,  there  is  no  serious  obstacle  to  the  cultivation  of 
greater  mobility  at  the  radio-carpal  joint. 


Fig.  226.- 


-LlGAMENTS    ON    ANTEHIOE    ASPECT    OF    RaDIO-CARPAL, 

Carpal,  and  Carpo-metacarpal  Joints. 


CARPAL  JOINTS. 

The  articulations  subsisting  between  the  individual  carpal  bones  (articulationes 
intercarpece)  are  all  diarthroses,  and  although  the  total  amount  of  movement 
throughout  the  series  is  considerable,  yet  the  extent  of  movement  which  is  possible 


ARTICULATIONS  OF  THE  OARPU>S.  285 

between  the  two  rows  or  between  any  two  carpal  bones  is  extremely  limited. 
For  this  reason,  as  well  as  because  of  the  nature  of  the  movement,  these  articula- 
tions are  called  gliding  joints  (arthrodia). 

It  is  advisable  to  Gonsider,  first,  the  articulations  between  individual  bones  of 
the  proximal  row ;  second,  the  articulations  between  the  separate  bones  of  the 
distal  row  ;  third,  the  articulation  of  the  proximal  and  distal  rows  with  each  otlier ; 
fourth,  the  pisiform  articulation. 

The  proximal  row  of  carpal  articulations  (Fig.  226)  comprises  the  joints 
between  the  scaphoid,  semilunar,  and  cuneiform  bones.  On  their  adjacent  lateral 
aspects  these  bones  are  partly  articular  and  partly  non-articular. 

Three  sets  of  simple  but  strong,  although  short  ligamentous  bands  bind  these 
three  carpal  bones  together,  and  form  an  investment  for  three  sides  of  their  inter- 
carpal joints.  These  are — (1)  the  anterior  or  palmar  ligaments,  two  in  number,  which 
consist  of  transverse  fibres  passing  between  the  adjacent  rough  palmar  surfaces  of 
the  bones ;  (2)  the  posterior  or  dorsal  ligaments,  also  two  in  number,  and  composed 
of  similar  short  transverse  fibres  passing  between  the  adjacent  dorsal  surfaces ; 
(3)  the  interosseous  ligaments  (Fig.  227),  again  two  in  number,  and  transverse  in 
direction,  situated  on  a  level  with  the  superior  articular  surfaces,  and  extending  from 
the  palmar  to  the  dorsal  aspect  of  the  bones,  while  attached  to  non-articular  areas  of 
the  opposing  surfaces.  The  radio-carpal  joint  is  entirely  shut  off  from  the  inter- 
carpal joints,  and  also  from  the  joint  between  the  two  rows  of  carpal  bones,  except  in 
rare  cases,  when  an  interosseous  ligament  is  wanting. 

The  distal  row  of  carpal  articulations  (Fig.  226)  includes  the  joints  between 
the  trapezium,  trapezoid,  os  magnum,  and  unciform  bones.  Articular  facets  occur 
on  the  opposing  lateral  faces  of  the  individual  bones. 

Associated  with  this  row  there  are  again  simple  bands  of  considerable  strength, 
and  presenting  an  arrangement  similar  to  that  seen  in  the  proximal  row.  As  in 
the  former  case,  they  invest  the  intercarpal  articulations,  except  on  the  superior 
aspect,  where  they  communicate  with  the  transverse  carpal  joint,  and  on  the  inferior 
aspect,  where  they  communicate  with  the  carpo- metacarpal  joint  cavity. 

The  anterior  or  palmar  ligaments  are  three  in  number.  They  extend  in  a  trans- 
verse direction  between  contiguous  portions  of  the  rough  palmar  surfaces  of  the 
bones.  The  posterior  or  dorsal  ligaments,  also  three  in  number,  are  similarly  dis- 
posed on  the  dorsal  aspect.  The  interosseous  ligaments  (Fig.  227)  are  two  or  three 
in  number.  That  which  joins  os  magnum  to  unciform  is  the  strongest ;  that 
between  the  trapezoid  and  os  magnum  is  situated  towards  the  dorsal  parts  of  their 
opposing  surfaces  ;  the  third,  situated  between  contiguous  non-articular  surfaces 
of  the  trapezium  and  trapezoid,  is  always  the  feeblest,  and  is  frequently  absent. 

The  transverse  carpal  articulation  (Fig.  227)  is  situated  between  the  proximal 
and  distal  rows  of  the  carpus.  The  bones  of  the  proximal  row  present  the  following 
characters  on  iheir  inferior  or  distal  aspect.  The  outer  part  of  the  articular  surface 
is  deeply  concave,  both  in  the  antero-posterior  and  in  the  transverse  directions,  but 
the  inner  part  of  the  same  surface  is  concavo-convex,  more  especially  in  the  trans- 
verse direction. 

Superiorly,  the  articular  surfaces  of  the  distal  row  of  carpal  bones  present  an 
irregular  outline.  That  part  pertaining  to  the  trapezium  and  trapezoid  is  concave 
in  the  antero-posterior  and  transverse  directions,  and  lies  at  a  considerably  lower 
level  than  the  yjortion  belonging  to  the  os  magnum  and  unciform,  which  is,  more- 
over, markedly  convex  in  tlie  antero-posterior  and  transverse  directions,  with  the 
exception  of  the  innermost  Y)art  of  the  unciform,  where  it  is  concavo-convex  in 
l)0th  of  these  directions. 

This  articulation  is  invested  by  a  complete  short  capsule  (Fig.  226)  which  binds 
the  two  rows  of  the  carpus  together,  and  sends  ]:)rolongations  to  the  investing 
capsules  of  the  y)ro.ximal  and  distal  articulations.  The  ligament  as  a  whole  is  very 
strong,  and  individual  b;uids  an;  not  n>adily  defined,  althougli  certain  special  bands 
may  Ijc  described.  TIk;  palmar  ligaments  r;i,diate  from  the  os  magnum  to  the  scaphoid, 
cuncdffjrm,  and  ])iHiform.  The  interval  between  the  os  magnum  and  sendlunar  is 
occu])ied  by  oblique  fibres,  some  of  whicli  pass  from  scaphoid  to  cuneiform,  while 
these  are  joined  by  others,  prolonged  o])liquely  downwards  and  inwards,  from  the 


286 


THE  AETICULATIONS  OR  JOINTS. 


radial  end  of  the  anterior  radio-carpal  ligament.     By  these  different  bands  the 
palmar  aspect  of  the  joint  is  completely  closed. 

The  dorsal  ligaments  are  more  feeble  than  the  palmar.  They  form  a  thin,  loosely- 
arranged  stratum,  in  which  the  only  noteworthy  bands  are  one  which  joins  the 
scaphoid  to  os  magnum,  and  another  which  joins  cuneiform  to  unciform. 

The  external  lateral  ligament  (lig.  collaterale  carpi  radiale,  Fig.  227)  extends 
between  contiguous  rough  areas  on  the  radial  aspects  of  the  scaphoid  and 
trapezium.  By  its  margins  it  is  continuous  both  with  the  palmar  and  dorsal 
ligaments. 

The  internal  lateral  ligament  (lig.  collaterale  carpi  ulnare.  Fig.  227)  is  arranged 
like  the  former  in  regard  to  its  margins,  and  by  its  ends  it  is  attached  to  the  con- 
tiguous rough  ulnar  surfaces  of  the  cuneiform  and  unciform  bones. 

Both  of  these  lateral  ligaments  are  directly  continuous  with  the  corresponding 
lateral  ligaments  of  the  radio-carpal  joint. 

An  interosseous  ligament  (Fig.  227)  is  occasionally  found  within  the  capsule, 
extending  across  the  joint  cavity  between  the  os  magnum  and  the  scaphoid. 

The  pisi-cuneiform  articulation  is  an  arthroidal  diarthrosis.  The  mutual 
articular  surfaces  of  the  two  bones  are  flattened  and  circular,  and  only  permit  of  a 
small  amount  of  gliding  movement. 

The  joint  is  provided  with  a  thin  but  complete  capsule  of  fibrous  tissue,  which 
is  specially  strengthened  inferiorly  by  two  strong  bands,  viz.  pisi-unciform  (lig.  piso- 
hamatum)  and  pisi-metacarpal  (lig.  pisometacarpeum.  Fig.  226).  Both  of  these 
bands  extend  from  the  lower  and  inner  aspect  of  the  pisiform  to  adjoining  parts  of 
the  hook  of  the  unciform  and  base  of  the  fifth  metacarpal  bone  respectively.  To  a 
great  extent  these  ligamentous  bands  may  be  regarded  as  extensions  of  the  in- 
sertion of  the  tendon  of  the  flexor  carpi  ulnaris  muscle  which  is  attached  to  the 
upper  part  of  the  pisiform  bone.  Looked  at  as  ligaments,  however,  they  are 
specially  strong  to  prevent  the  displacement  of  the  pisiform  bone  during  contrac- 
tion of  the  muscle  inserted  into  it. 

The  synovial  membranes  (Fig.  227)  of  the  carpal  joints  are  two  in  number.     Of 

these,  one  is  restricted  to 
the  pisi-cuneiform  articula- 
tion, and  is  correspondingly 
simple,  although  occasionally 
the  joint  cavity  may  com- 
municate with  that  of  the 
radio-carpal  joint. 

The  other  synovial  mem- 
brane is  associated  with  the 
transverse  carpal  joint  which 
extends  transversely  be- 
tween the  two  rows  of  carpal 
bones,  with  prolongations 
into  the  vertical  intervals 
between  the  adjoining  bones 
of  each  row,  i.e.  the  inter- 
carpal articulations.  It  is, 
therefore,  an  elaborate  cavity, 
which  may  be  still  further 
extended,  by  the  absence  of 
interosseous  ligaments,  so  as 
to  reach  the  radio-carpal  and 
carpo- metacarpal  series  of 
joints.  The  first  condition 
is  rare,  but  the  second  is  not  uncommon,  and  results  from  the  absence  of  the  inter- 
osseous ligament  between  trapezium  and  trapezoid,  or  of  that  between  trapezoid 
and  OS  mag-num. 


Trajjezoid 


Trapezium 


Fig.  227. — Coronal  Section  through  the  radio-carpal,  carpal,  carpo- 
metacarpal, aud  intermetacarpal  joints,  to  show  joint  cavities  and 
interosseous  ligaments  (diagrammatic). 


CAEPO-METAGAEPAL  JOINTS.  287 

INTERMETACARPAL   JOINTS. 

The  four  inner  metacarpal  bones  articulate  with  each  other  at  their  proximal 
ends  or  bases,  between  the  opposing  surfaces  of  which  joint  cavities  are  found — 
arthrodial  diarthroses.  These  cavities  are  continuous  with  the  carpo-metacarpal 
joint  (not  yet  described),  and  hence  the  ligamentous  arrangements  only  enclose 
three  aspects  of  each  joint. 

Three  strong  transverse  ligaments  (Figs.  226  and  227j  bind  adjacent  palmar, 
dorsal,  and  interosseous  areas  of  the  bases  of  the  metacarpal  bones,  and  hence  they 
are  called  ligamenta  basium  (oss.  metacarp.)  volaria,  dorsalia  et  interossea.  A 
synovial  membrane  is  associated  with  each  of  these  joints,  but  it  may  be  regarded 
as  a  prolongation  from  the  carpo-metacarpal  articulation. 

CARPO-METACARPAL   JOINTS. 

The  articulation  of  the  metacarpal  bone  of  the  thumb  with  the  trapezium 
differs  in  so  many  respects  from  the  articulation  between  the  other  metacarpal 
bones  and  the  carpus,  that  it  must  be  considered  separately. 

(A)  The  articulatio  carpo-metacarpea  pollicis  (Figs.  226  and  227)  is  the  joint 
between  the  infero-external  surface  of  the  trapezium  and  the  superior  surface  of 
the  base  of  the  first  metacarpal  bone.  Both  of  these  surfaces  are  saddle -shaped,  and 
they  articulate  by  mutual  co-aptation. 

The  joint-cavity  is  surrounded  by  a  fibrous  capsule,  in  which  we  may  recognise 
palmar,  dorsal,  external,  and  internal  lateral  bands,  the  last  being  the  strongest  and 
most  important. 

Synovial  membrane  lines  the  capsule,  and  the  joint-cavity  is  isolated  and  quite 
separate  from  the  other  carpal  and  carpo-metacarpal  articulations. 

At  this  joint  movements  occur  about  at  least  three  axes.  Thus,  around  a  more  or  less  trans- 
verse axis,  flexion  and  extension  take  jAsLce  ;  in  an  antero -posterior  axis  abduction  and  adduction 
(movements  which  have  reference  to  the  middle  line  of  the  hand)  are  found  ;  while  a  certain 
amount  of  rotation  is  possible  in  the  longitudinal  axis  of  the  digit.  The  very  characteristic 
movement  of  opposition,  m  which  the  tip  of  the  thumb  may  be  applied  to  the  tips  of  all  the 
fingers,  results  from  a  combination  of  flexion,  adduction,  and  rotation,  and  by  combining  all  the 
movements  possible  at  the  various  axes  a  considerable  degree  of  circumduction  may  be  produced, 
in  spite  of  the  fact  that  this  is  not  a  ball-and-socket  jointi 

(B)  The  articulationes  carpo-metacarpeae  digitorum  are  the  joints  between 
the  bases  of  the  four  inner  metacarpal  bones  and  the  four  bones  of  the  distal  row 
of  the  carpus.  They  are  all  arthrodial  diarthroses,  and  the  opposed  articular 
surfaces  present  alternate  elevations  and  depressions  which  form  a  series  of 
interlocking  joints.  The  joint  cavities  between  the  carpal  bones  of  the  distal 
row,  and  also  the  more  extensive  intermetacarpal  joint  cavities,  open  into  this 
articulation. 

This  series  of  joints  is  invested  by  a  common  capsule  which  is  weakest  on  its 
radial  side,  but  is  otherwise  well  defined.  Its  fibres  arrange  themselves  in  small 
slips,  which  pass  obliquely  in  different  directions,  and  vary  in  number  for  each 
metacarpal  bone.  Thus  the  oblique  palmar  ligaments  (ligamenta  carpo-metacarpea 
volaria,  Pig.  225)  usually  consist  of  one  slip  for  each  metacarpal  bone,  but  there 
may  be  two  slips,  and  the  third  metacarpal  bone  frequently  has  three,  of  which  one 
lies  obliquely  in  front  of  the  tendon  of  the  flexor  carpi  radialis  muscle. 

Tlui  oblique  dorsal  ligaments  (ligamenta  carpo-metacarpea  dorsalia)  are  similar 
short  bands,  of  greater  strength  and  clearer  definition,  by  which  the  index  meta- 
carpal is  bound  to  the  trapezium  and  trapezoid ;  the  middle  metacarpal  to  the  os 
magnum,  and  frequently  to  the  trapezoid ;  the  ring  metacarpal  to  the  os  magnum 
and  unciform,  and  the  metacarpal  of  the  minimus  to  the  unciform. 

Interosseous  ligaments,  one  or  sometimes  two  in  number,  occur  within  the  capsule. 
They  are  usually  situated  in  relation  to  one  or  both  of  the  contiguous  margins  of 
the  bases  of  the  third  and  fourth  metacar[)al  bones,  from  which  they  extend 
upwards  to  adjacent  niargins  of  the  os  magnum  arul  unciform.  Occasionally  they 
are  sulliciently  dev(;lo])(;(l  to  divid<!  the  joint  ca,vity  into  radial  and  ulnar  sections. 


288 


THE  ARTICULATIONS  OE  JOINTS. 


Accessory  pal- 
mar liirainent 


The  synovial  membrane  (Fig.  227)  is  usually  single  and  lines  the  capsule,  but, 
as  already  explained,  it  has  prolongations  into  the  intermetacarpal  and  inter- 
carpal series  of  joints.  In  connexion  with  the  latter,  the  frequent  absence  of 
the  interosseous  ligament  between  the  trapezium  and  trapezoid  permits  the  free 
communication  of  this  joint-cavity  with  that  of  the  transverse  carpal  joint. 

METACARPO-PHALANGEAL  JOINTS. 

In  the  case  of  the  pollex  this  joint  is  constructed  on  the  plan  of  a  ginglymus 
diarthrosis  ;  the  four  corresponding  joints  of  the  fingers  are  also  diarthroses  of  a 
slightly  modified  ball-and-socket  variety.     With  the  exception   of  the  metacarpal 

bone  of  the  pollox,  each  metacarpal  bone  has  a  somewhat 
spherical  head  articulating  with  a  shallow  oval  cup  upon 
the  base  of  the  first  phalanx.  It  is  important  to  note  that 
tlie  articular  surface  upon  the  head  of  each  of  these  meta- 
carpal bones  is  wider  on  the  palmar  aspect  and  narrov/er 
on  the  dorsal  aspect.  The  articulation  in  the  thumb 
presents  features  similar  to  those  of  an  iuter-phalangeal 
joint. 

Each  joint  possesses  an  articular  capsule  (Fig.  228) 

which    presents  very  different  degrees   of  strength   in 

different  aspects  of  the  articulation.     Thus,  on  the  dorsal 

aspect,  it   cannot  be   demonstrated   as   an   independent 

^  structure,  but  the  necessity  for  dorsal  ligaments  is  to  a 

I  large  extent  obviated  by  the  presence  of   the    strong 

|o  flattened  expansions  of  the  extensor  tendons. 

^          The  internal  and  external  lateral  ligaments  (hgamenta 

I  collateralia.  Fig.  228)  are  strong  cord-like  hands  which 

pass  from  the  tubercles  and  adjacent  depressions  on  the 

sides  of  the  heads  of  the  metacarpal  bones  to  the  contiguous 

non-articular  areas  on  the  bases  of  the  proximal  phalanges. 

They  are  intimately  connected  on  their  anterior  aspects 

with  the  palmar  ligaments. 

^         The  palmar  ligaments  consist  of  thick  plates  of  fibro- 

1  cartilage  loosely  connected  to  the  metacarpal  bones,  but 
I"  firmly  adherent  to   the   phalanges.      They   are   placed 

2  between  the  lateral  ligaments,  to  both  of  which  they  are 
I  in  each  case  connected.     Each  plate  is  grooved  on  the 

palmar  surface  for  the  long  flexor  tendons,  whilst  on  its 

reverse  or  joint  surface  it  supports  and  glides  upon  the 

,  ,    , ,.        ^  head  of  the  metacarpal  bone  during  flexion  and  extension 

Lateral  ligament       o      t         •    •  t  i  o      i  i  i        i   •  i 

of  the  joint,     in  the  case  of  the  thumb  this  plate  of 

Fig.   228.— Metacahi-o-phalan-  fibro-cartilage   usually  develops  to  sesamoid  bones,  and 

GEAL  AND  iNTERPHALANGEAL  ^^  j^];^q  g^gc  of  thc  ludcx  fiugcr  One  such  sesamoid  nodule 

is  frequently  found  at  the  radial  side  of  the  plate. 

An  important  accessory  ligament  is  found  in  connexion  with  the   four  inner 

metacarpo-phalangeal  articulations,  viz  : — 

The  Transverse  Metacarpal  Ligament. — This  structure  binds  together  the  distal 
extremities  of  the  four  inner  metacarpal  bones.  The  name  is  applied  to  three  sets 
of  transverse  fibres  of  great  strength  which  are  situated  in  front  of  the  three  inner 
interosseous  spaces.  These  fibres  are  continuous  with  the  palmar  metacarpo- 
phalangeal ligaments  at  their  lateral  margins. 

A  synovial  membrane  lines  the  investing  capsule  of  each  joint. 

INTERPHALANGEAL   JOINTS. 

Of  these  joints  there  are  two  for  each  finger  and  one  for  the  thumb.  They  all 
correspond,  in  being  ginglymus  diarthroses  in  which  the  trochlear  character  of  their 
articular  surfaces  is  associated  with  one  axis  of  movement  directed  transversely. 

In  their  general  arrangement  they  correspond  with  each  other,. and  to  a  large 
extent  with  the  metacarpo-phalangeal  series  already  descril.ied.     Each  is  provided 


Cajisule 


LUMBO-SACEAL  JOINTS.  280 

with  a  definite  capsule  (Fig.  228),  of  which  the  palmar  and  cord-like  lateral  portions 
are  well  marked,  while  on  the  dorsal  aspect  the  extensor  tendons  act  as  the  chief 
support.  The  palmar  ligaments  are  fibrous  plates  of  considerable  thickness,  and 
are  attached  to  the  two  lateral  ligaments  and  to  the  intervening  rough  surface  on 
the  distal  phalanges,  while  their  proximal  margins  are  not  attached  to  bone.  Each 
ligament  has  its  lateral  margins  prolonged  proximally  to  the  adjacent  sharply- 
defined  lateral  ridges  on  the  phalangeal  shafts. 

The  lateral  ligaments  (Fig.  228)  are  strong,  rounded,  short  bands,  continuous  with 
the  preceding,  and  attached  to  adjacent  non-articular  lateral  aspects  of  the  phalanges. 

Each  joint  possesses  a  synovial  membrane  which  lines  its  capsule,  but  its 
arrangement  presents  no  special  peculiarity. 

Movements  of  the  Caepal,  Intermetacakpal,  Metacarpo-phalangeal 
AND  Inteephalangeal  Joints. 

The  amount  of  movement  wliicli  is  possilole  at  individual  joints  of  tlie  intercarpal,  inter- 
metacarpal, and  carpo -metacarpal  series  is  extremely  limited,  both  on  account  of  the  interlocking 
nature  of  the  articular  sm^faces  and  the  restraining  character  of  the  ligamentous  bands.  Taken 
as  a  whole,  however,  the  movements  of  the  carpus  and  metacarpus  enable  the  hand  to  jDerform 
many  varied  and  important  functions.  This  is  largely  due  to  the  greater  mobility  of  those  joints 
on  the  radial  and  ulnar  borders  of  the  hand,  as  well  as  to  the  general  elasticity  of  the  arches 
formed  by  the  carpus  and  metacarjDus.  These  conditions  particularly  favour  the  movements  of 
oppositioii  and  j^reliension.  In  the  ojDiDosite  direction,  i.e.  when  pressure  is  ajjplied  from  the 
palmar  aspect,  the  metacarpal  and  carpal  arches  tend  to  become  flattened,  but  great  elasticity  is 
imparted  by  the  tension  of  the  various  ligaments. 

The  four  inner  metacarpo-phalangeal  joints  are  ball-and-socket  joints,  and  movements  of 
palmar-flexion  and  extension  are  freely  jjerformed  about  a  transverse  axis.  In  exceptional  cases 
a  certain  amount  of  dorsi-flexion  is  jDossible.  About  an  antero-posterior  axis  movements  occur 
which  are  usually  referred  to  tlie  middle  line  of  the  hand,  and  hence  called  abduction  and 
adduction,  but  in  consequence  of  the  difference  in  the  width  of  the  articular  surface  on  the  dorsal 
and  palmar  aspects  of  tlie  heads  of  the  four  inner  metacarpal  bones  it  is  only  possible  to  obtain 
abduction  when  the  joints  are  extended,  while  in  the  flexed  position  the  joints  become  locked  and 
abduction  is  impossible. 

The  movements  of  the  index  finger  are  less  hampered  than  in  the  case  of  the  others,  but 
each  of  them  can  perform  a  modified  kind  of  circumduction. 

The  metacarpo-phalangeal  joint  of  the  thumb  and  all  the  interphalangeal  joints  are  uniaxial 
or  hinge-joints  acting  about  a  transverse  axis,  which  permits  of  palmar-flexion  and  extension 
being  freely  performed,  but  dorsi-flexion  is,  as  a  rule,  entirely  prevented  by  the  palmar  and  lateral 
ligaments. 

ARTICULATIONS   AND   LIGAMENTS   OF   THE   PELVIS. 

Although  we  may  consider  the  pelvis  as  a  separate  part  of  the  skeleton,  yet  it 
is  essential  to  remember  that  the  bones  which  enter  into  its  composition  belong  to 
the  spinal  column  (sacrum,  coccyx)  and  the  lower  limb  (innominate  bone).  Accord- 
ingly, tlie  articulations,  with  their  corresponding  ligaments,  may  be  arranged  as 
follows  :  — 

(a)  Those  by  which  the  segments  of  the  coccyx  are  joined  together  (already 

described,  v.  p.  264) ; 
{h)  That  by  which  the  sacrum    articulates  with    the  coccyx    (already  de- 
scribed, V.  p.  264) ; 
(c)  Those  by  which  the  sacrum  articulates  with  the  last  lumbar  verteljra 

(Lumbo-sacral  joints) ; 
{d)  Those    by   which    the    innominate    bones    are    attached    to    the    spinal 

column  (Sacro-iliac  joints) ; 
{e)  That  by  whicl)  the  innominate  bones  are  attached  to  each  other  fSym- 
physis  pubis). 

L ( ' MBO-SACRAL  JOINTS. 

The    articulation   of   sacrum  witli    the    fifth    lumbar    vertebra  is  constructed 

precisely  on  the  principle  of  the  articulations  between  two  typical  vertebra,  and 

the  usual  ligaments  associated  with  such  joints  an;  repeated.     There  is,  however,  an 

additional  accessory  ligament,  termed  the  lateral  lumbo-sacral  ligament  (Fig.  229). 

20 


290 


THE  ARTICULATIONS  OR  JOINTS. 


This  extends  from  the  front  of  the  inferior  l)order  of  the  transverse  process  of  the 
last  lumbar  vertebra,  downwards  and  slightly  outwards,  to  the  front  of  the  lateral 
aspect  of  the  ala  of  the  sacrum,  close  to  the  sacro-iliac  joint.  Further,  a  variable 
membranous  band  extends  between  the  lateral  aspect  of  the  lower  part  of  the  body 
of  the  last  lumbar  vertebra  and  the  front  of  the  ala  of  the  sacrum.  This  band  lies 
in  front  of  the  anterior  primary  division  of  the  fifth  lumbar  nerve. 


SACRO-ILIAC  JOINT. 

Each  innominate  bone  articulates  with  the  sacral  section  of  the  spinal  column 
on  each  side  through  the  intervention  of  a  diarthrosis,  termed  the  sacro-iliac  joint 
(articulatio  sacro-iliaca). 

This  joint  is  formed  between  the  contiguous  auricular  surfaces  of  the  sacrum 
and  ihum.  Each  of  tliese  surfaces  is  more  or  less  completely  clothed  by  hyaline 
articular  cartilage.  The  joint  cavity,  which  is  little  more  than  a  capilhiry  interval, 
may  be  crossed  by  fibrous  bands. 

The  joint  oavity  is  surrounded  by  ligaments  of  varying  thickness  and  strength, 


Sacrum 


Great  sacro-sciatic 
foraineiK/ 


Small  sacro-sciatic  foramer 


abulum 


Great  sacro- 
sciatic  ligament 


Intel  pubic  flbro-cartilage 


Fic.  229. — Coronal  Section  of  Pelvis. 

which  constitute  its  capsule.  Thus  the  anterior  part  of  the  investing  capsule  is 
thin,  and  consists  of  short  but  strong  fibres  which  pass  between  adjoining  surfaces 
on  the  ala  of  the  sacrum  and  the  iliac  fossa  of  the  innominate  bone ;  they  form  the 
anterior  sacro-iliac  ligament  (lig.  sacro-iliacum  anterius,  Fig.  229).  On  the  posterior 
aspect  there  are  two  ligaments.  The  short  posterior  sacro-iliac  ligament  (lig.  sacro- 
iliacum  posterius  breve,  Fig.  230)  consists  of  numerous  strong  fasciculi,  which  pass 
from  the  rough  area  on  the  inner  aspect  of  the  ilium,  above  and  behind  its 
auricular  surface,  downwards  and  inwards  to  the  transverse  tubercles  and  the 
depressions  behind  the  first  and  second  segments  of  the  sacrum.  This  ligament 
is  of  great  strength,  and  with  its  fellow  it  is  responsible  for 'suspending  the 
sacrum  and  the  weight  of  the  superimposed  trunk  from  the  innominate  bones. 

The    long  or   oblique  posterior  sacro-iliac  ligament    (lig.    sacro-iliacum  posterius 
longum.  Fig  230)  is  a   superficial  thickened  portion    of  the   preceding  ligament. 


SYMPHYSIS  PUBIS. 


29] 


It  cousists  of  a  definite  band  of  fibres  passing  from  the  jjostero-superior  iliac  spine 
to  the  transverse  tubercles  of  the  third  and  fourth  segments  of  the  sacrum. 

The  synovial  cavity  of  this  joint  is  very  imperfect  and  rudimentary. 

Several  accessory  ligaments  are  associated  with  the  articulation  of  the  in- 
nominate bone  to  the  sacral  section  of  the  spinal  column. 

The  ilio-lumbar  lig-ament  (lig.  ilio-lumbale,  Fig.  229),  which  is    merely    the 


lio-lumbar  li''aiMeiit 


ill Posterior  sacro-iliaf 

lic;anient 


^^       l|||     Long  or  obliquR 
^^    "ITT — posterior  sacro-iliae 
ligament 


Reflected  head  of lectus 


Great  sacro-sciatic 

Jl    roi'ameii 


Small  sacro-sciatic 
I  i -lament 


j] Small  sacro-KCiatic 

foramen 


Great  sacro-sciatic 

T]     liijament 


Obturator  membrane 


Fig.  230. — Posterior  View  ov  the  Pelvic  Ligaments  and  of  the  Hip-Joint. 


thickened  anterior  lamina  of  the  fascia  lumborum,  extends  from  the  tip  of  the 
transverse  process  of  the  last  lumbar  vertebra,  almost  horizontally  outwards,  to  the 
inner  lip  of  the  iliac  crest  at  a  point  a  short  distance  behind  its  highest  level. 
A  jjroportion  of  these  fibres  is  attached  to  the  inner  rough  surface  of  the  ilium 
between  the  iliac  crest  and  the  auricular  impression.  To  these  the  name  of  the 
lig.  ilio-lumbale  inferius  is  a  implied. 

.  The  great  or  posterior  sacro-sciatic  ligament  (lig.  sacro-tuberosum,  Fig.  230) 
is  somewhat  triangular  in  <iutline.  It  occupies  tlic  interval  between  the  sacrum 
and  the  innominate  bone,  and  is  attached  mesially  to  the  posterior  inferior  spine 
of  the  ilium;  to  the  posterior  aspect  of  the  transverse  tubercles  and  lateral 
margins  of  the  third,  fourtli,  and  fifth  segments  of  the  sacrum,  as  well  as  to  the 
side  of  the  first  segment  of  the  coccyx.  It  passes  downwards  and  outwards, 
becoming  narrower  as  it  ai)proache8  the  ischium,  near  to  which,  however,  it  ag;iin 
exjiands,  to  be  attached  to  the  inner  side  of  the  ischial  tuberosity,  immediately 
below  tlie  groove  for  th(;  tendon  of  the  obturatoi'  inlemus  muscle,  i.e.  tlie  lesser 
sciatic  notcli.     A  continnaLion  oC  the  inner  bonhii'  of  Uk;  ligament — the  processus 


292  THE  AETICULATIONS  OE  JOIIsTTS. 

falciformis  (Fig.  230) — runs  upwards  aud  forwards  on  the  inner  aspect  of  the 
ramus  of  the  ischium. 

The  great  sacro-sciatic  ligament  is  beheved  by  many  to  represent  the  original 
or  proximal  end  of  the  long  or  ischial  head  of  the  biceps  flexor  cruris  muscle. 

The  small  or  anterior  sacro-sciatic  ligament  (lig.  sacro-spinosum,  Figs.  229  and 
230)  is  situated  in  front,  a,nd  in  a  measure  under  cover  of  the  great  sacro-sciatic 
ligament.  Triangular  in  form,  it  is  attached  ])j  its  base  to  the  last  two  segments  of 
the  sacrum  and  the  first  segment  of  the  coccyx,  and  by  its  pointed  apex  to  the  tip 
and  upper  aspect  of  the  ischial  spine.  This  ligament  is  intimately  associated 
with  the  coccygeus  muscle,  and  by  some  it  is  regarded  as  being  derived  from  it  by 
fibrous  transformation  of  the  muscle  fasciculi. 

By  the  great  and  small  sacro-sciatic  ligaments  the  two  sciatic  notches  of  the 
innominate  bone  are  converted  into  foramina.  Thus  the  small  sacro-sciatic  liga- 
ment completes  the  boundaries  of  the  great  sciatic  foramen  (foramen  ischiadicum 
majus) ;  while  the  great  sacro-sciatic  ligament,  assisted  by  the  small  sacro-sciatic 
ligament,  closes  the  small  sciatic  foramen  (foramen  ischiadicum  minus). 

SYMPHYSIS  PUBIS. 

The  anterior  wall  of  the  osseous  pelvis  is  completed  by  the  articulation  of  the 
bodies  of  the  two  pubic  bones  constituting  the  symphysis  pubis.  This  joint  con- 
forms in  its  construction  to  the  general  plan  of  an  amphiarthrosis.  Thus  it  is 
mesial  in  position ;  each  pubic  bone  is  covered  by  a  layer  of  hyaline  cartilage, 
which  closely  adapts  itself  to  the  rough  tuberculated  surface  of  the  pubic  bone ; 
while  between  these  two  hyaline  plates  there  is  an  interposed  fibro-cartilage 
(lamina  fibro-cartilaginea  interpubica),  in  the  interior  of  which  there  is  usually 
a  vertical  antero-posterior  cleft.  This  cavity,  which  is  placed  nearer  the  posterior 
than  the  anterior  aspect  of  the  joint,  does  not  appear  until  between  the  seventh 
and  tenth  years,  and  as  it  is  not  lined  by  a  synovial  membrane,  it  is  supposed  to 
result  from  the  breaking  down  of  the  interpubic  lamina. 

The  anterior  puhic  ligament  (lig.  pubicum  anterius.  Fig.  229)  is  a  structure  of 
considerable  thickness  and  strength.  Its  superficial  fibres,  which  are  derived  very 
largely  from  the  tendons  and  aponeuroses  of  adjoining  muscles,  are  oblique,  and 
form  an  interlaced  decussation.  The  deeper  fibres  are  short,  and  extend  trans- 
versely from  one  pubic  bone  to  the  other. 

The  posterior  pubic  ligament  (lig.  pubicum  posterius,  Fig.  230)  is  very  weak, 
and  consists  of  scattered  fibres  which  extend  transversely  between  contiguous 
pubic  surfaces  posterior  to  the  articulation. 

The  superior  pubic  ligament  (hg.  pubicum  superius,  Fig.  229)  is  likewise  w^eak, 
and  consists  of  transverse  filjres  passing  between  the  two  pubic  crests. 

The  inferior  or  subpubic  ligament  (lig.  pubicum  inferius  vel  lig.  arcuatum  pubis. 
Fig.  230)  occupies  the  arch  of  the  pubis,  and  is  of  considerable  strength.  It  gives 
roundness  to  the  pubic  arch  and  forms  part  of  the  pelvic  outlet.  It  has  con- 
siderable vertical  thickness  immediately  below  the  interpubic  disc  to  which  it  is 
attached.  Laterally  it  is  attached  to  adjacent  sides  of  the  descending  rami  of  the 
pubis.  Its  lower  border  is  free,  and  separated  from  the  triangular  hgament  of 
the  perineum  by  a  transverse  oval  interval  through  which  the  dorsal  vein  of  the 
penis  passes  backwards  to  the  interior  of  the  pelvis. 

The  Triangulae  Ligament  of  the  Perineum. 

The  triangular  ligament  of  the  perineum  is  a  membranous  structure  which 
occupies  the  pubic  arch  below  and  distinct  from  the  subpubic  ligament.  It  assists 
in  completing  the  pelvic  walls  anteriorly  in  the  same  manner  that  the  obturator 
membrane  does  laterally.  Indeed,  these  two  structures  occupy  the  same  mor- 
phological plane.  The  triangular  ligament  presents  two  surfaces — one  superficial 
or  perineal ;  the  other  deep,  or  pelvic,  and  both  of  these  surfaces  are  associated 
with  muscles.  Its  lateral  borders  are  attached  to  the  sides  of  the  pubic  arch, 
while  its  base  is  somewhat  ill-defined,  by  reason  of  its  fusion  with  the  fascia  of 
Colles  in  the  urethral  region  of  the  perineum. 


HIP-JOINT.  293 

The  apex  of  the  triangular  Hgameat  is  truncated,  free,  and  well  defined,  constitut- 
ing the  transverse  perineal  ligament,  above  which  there  is  the  interval  for  the  dorsal 
vein  of  the  penis.  It  is  pierced  by  a  number  of  vessels  and  nerves,  but  the 
principal  opening  is  situated  mesially  one  inch  below  the  pubic  arch,  and  transmits 
the  urethra. 

The  Obtueatok  Membrane. 

The  obturator  membrane  (membrana  obturatoria,  Fig.  232)  occupies  the 
obturator  or  thyroid  foramen.  It  is  attached  to  the  pelvic  aspect  of  the 
circumference  of  this  foramen.  It  consists  of  fibres  irregularly  arranged  and  of 
varying  strength,  so  that  sometimes  it  almost  appears  fenestrated.  At  the  highest 
part  of  the  foramen  it  is  incomplete  and  foiins  a  U-shaped  border,  between  which 
and  the  bony  circumference  of  the  foramen,  the  obturator  canal  (canalis  obtura- 
torius)  is  formed.  In  this  position  the  inembrane  is  continuous  with  the  parietal 
pelvic  fascia  which  clothes  the  inner  side  of  the  obturator  internus  muscle,  above 
the  upper  free  margin,  of  the  muscle.  From  the  outer  or  crural  aspect  of  the 
membrane  some  of  its  fibres  are  prolonged  to  the  antero-inferior  aspect  of  the 
capsule  of  the  hip-joint. 

Mechanism  and  Movements  of  the  Pelvis. — Tlie  liuman  jjelvis  j^resents  a  mechanism  the 
principal  requirement  of  which  is  stability  and  not  movement,  for,  through  the  pelvis,  the  weight 
of  the  trunk,  superimposed  upon  the  sacrum,  is  transmitted  to  the  lower  limbs.  Moreover,  its 
stability  is  largely  concerned  in  the  maintenance  of  the  erect  attitude.  The  movements  of  its 
various  parts  are  therefore  merely  such  as  are  consistent  with  stability,  without  producing  absolute 
rigidity. 

The  two  innominate  bones,  being  bound  together  by  powerful  Kgaments  at  the  joubic  articula- 
tion, constitute  an  inverted  arch,  of  which  the  convexity  is  directed  downwards  and  forwards, 
while  its  piers  are  turned  ujjwards  and  backwards,  and  considerably  expanded  in  relation  to  the 
hinder  parts  of  the  iliac  bones.  Between  the  jjiers  of  this  inverted  arch  the  sacrum  is  situated. 
This  bone  is  in  no  sense  a  key -stone  to  an  arch,  because,  as  may  readily  be  seen  in  antero -posterior 
transverse  section,  the  sacrum  is  wider  in  front  than  behind,  and  the  superposed  weight  naturally 
tends  to  make  the  sacrum  fall  towards  the  pelvic  cavity,  and  so  fit  less  closely  between  the 
innominate  bones.  The  sacrum  is  in  reality  an  oblique  platform,  in  contact  with  each  innominate 
bone  through  its  articular  auricular  surfaces,  and  in  this  position  it  is  suspended  by  the  posterior 
sacro-iliac  ligaments,  and  kept  securely  in  place  by  the  "  grip  "  due  to  the  irregularity  of  the 
opposed  surfaces  of  the  two  sacro-iliac  articulations.  Since  the  weight  of  the  trunk  is  trans- 
mitted to  the  anterior  and  upjjer  end  of  this  sacral  platform,  there  is  a  natural  tendency  for  the 
sacrum  to  revolve  upon  the  transverse  axis  which  jjasses  through  its  sacro-iliac  joints.  If  this 
were  permitted,  the  jjromontory  of  the  sacrum  would  rotate  downwards  and  forwards  towards 
the  pelvic  cavity,  as  really  does  occur  in  certain  deformities.  This  revolution  or  tilting  down- 
wards of  the  forej)art  of  the  sacrum  is  prevented  by  the  action  of  the  great  and  small  sacro- 
sciatic  ligaments,  extending  from  the  ischial  tuberosity  to  the  hinder  and  lower  end  of  the 
suspended  platform  of  the  sacrum.  Not  only  so,  but  these  ligaments,  acting  on  a  rigid  sacrum, 
tend  to  hold  up  the  weight  upon  the  sacral  promontory. 

The  various  ligaments  passing  between  the  last  lumbar  vertebra  and  the  sacrum  and  ilium 
retain  the  weight  of  the  trunk  in  position  ujDon  the  anterior  end  of  the  sacrum,  and  resist  its 
tendency  to  slip  forwards  and  downwards  towards  the  pelvic  cavity.  The  entire  weight  of  the 
trunk  and  pelvis  is  transmitted  to  the  heads  of  the  thigh  bones  in  the  most  advantageous 
position,  Ijotli  for  effectiveness  and  the  strengthening  of  the  inverted  innominate  arch,  for  it  will 
be  evident  tliat  the  heads  of  the  femora  thrust  inwards  upon  the  convex  side  of  the  arch,  very 
much  at  the  place  where  the  arches  are  weakest,  viz.  at  the  springing  of  the  arcli  from  its  j^iers. 
The  forces  which  tend  to  cause  movement  of  the  pelvic  bones  during  parturition  act  from  within 
the  pelvis,  and  have  for  their  object  tlie  increase  of  the  various  pelvic  diameters,  in  order  that 
the  foetal  head  n^ay  more  readily  be  transmitted.  For  this  purjjose  the  wedge-like  dorsal  surface 
of  the  sacrum  is  driven  backwards,  and  a  certain  amount  of  extra  space  may  thereby  be  obtained. 
An  important  factor,  however,  in  the  increase  of  the  pelvic  caj^acity  at  this  period  is  found  in 
the  relaxation  of  its  various  liifanients. 


THE   ARTICULATIONS   OF   THE   LOWER   EXTREMITY. 

TM  K    HIP-JOIN'I'. 

Th(;  fiuman  body  pjovidcs  no  more  perfect  exaun)le  of  an  enarthrodial  diarthrosis 
than  the  hip-joint  (articulatio  coxie).  Combined  with  all  that  variety  of  movement 
which  characterises  a  multi-axial  joint,  it  neveith(!less  ])rusents  great  stability,  wliicli 
has  been  rjbtained  by  sinijjle  arrangcni(^nts,  for  restricting  the  range  of  its  natural 


294 


THE  AETICULATIONS  OR  JOINTS. 


Ischial  spii 


movements.  This  stability  is  of  paramount  importance  for  tlie  maintenance  of  the 
erect  attitude,  and  the  mechanical  adaptations  whereby  this  result  is  obtained  are 
such  that  the  erect  attitude  may  be  preserved  without  any  great  degree  of  sustained 
muscular  effort. 

Articular  Surfaces. — The  head  of  the  femur  is  globular  in  shape,  and  consider- 
ably exceeds  a  hemisphere.     It  is  clothed  by  hyaline  articular  cartilage  on  those 

parts  which  come  into  direct 
contact  with  the  acetabulum. 
There  is  frequently  more  or 
less  of  extension  of  tlie 
articular  cartilage  from  the 
head  to  the  adjoining  anterior 
part  of  the  neck,  an  extension 
which  is  accounted  for  by  the 
close  and  constant  apposition 
of  this  portion  of  the  neck 
with  the  hinder  aspect  of 
the  ilio  -  femoral  ligament. 
The  limit  of  the  articular 
cartilage  covering  the  head 
is  indicated  by  a  sinuous 
border.  Further,  there  is  an 
absence  of  articular  cartilage 
from  the  pit  or  depression 
on  the  head  of  the  femur. 

The  acetabulum  is  a  deep 
cup-shaped  cavity  which  pre- 
sents an  interruption  or  notch 
on  its  antero-inferior  margin. 
The  interior  of  the,  cup  is 
lined  by  a  ribbon -like  band 
of  articular  cartilage  which 
extends  to  the  brim  of  the 
cavity,  but  does  not  cover  the 
floor  of  the  cup.  This  ar- 
ticular ribbon  -  shaped  band 
narrowest  at  the  anterior  margin  of 


DlSSECTIUN    OF    THE    HiP-JOINT. 


Bottom  of  the  acetalralum  removed,  and  capsule  of  the  joint  thrown 
outwards  towards  the  trochanters. 


is  widest  on  its  supero-posterior  aspect,  and 
the  notch. 

The  transverse  ligament  (lig.  transversum  acetabuli,  Fig.  231)  bridges  the  ace- 
tabular notch,  and  consists  of  strong  transverse  fibres  which  are  attached  to  both 
of  its  margins,  but  more  extensively  to  the  postero-inferior.  This  ligament  does 
not  entirely  fill  the  notch,  but  leaves  an  open  interval  between  its  lower  border  and 
the  bottom  of  the  notch  through  which  vessels  and  nerves  enter  the  cup.  The 
acetabular  aspect  of  this  ligament  constitutes  an  articular  surface. 

The  acetabulum  is  deepened  by  the  cotyloid  ligament  (labrum  glenoidale,  Figs. 
231  and  232),  which  consists  pf  a  strong  ring  of  fibro-cartilaginous  tissue  attached 
to  the  entire  rim  of  the  cup.  The  attached  surface  of  the  ring  is  broader  than  its 
free  edge,  and,  moreover,  the  latter  is  somewhat  contracted,  so  that  the  ligament 
grasps  the  head  of  the  femur  which  it  encircles.  Its  fibres  are  partly  oblique  and 
partly  circular  in  their  direction.  By  the  former  it  is  firmly  implanted  on  the  rim 
of  the  acetabulum  and  the  transverse  ligament  of  the  notch ;  by  the  latter  the 
depth  of  the  cup  is  increased  through  the  elevation  of  its  edge,  and  its  mouth 
slightly  narrowed.     By  one  surface  this  ligament  is  also  articular. 

A  capsule  (capsula  articularis.  Figs.  230  and  232)  completely  invests  the  joint 
cavity.  This  is  a  fibrous  membrane  of  great  strength,  although  it  is  not  of  equal 
thickness  throughout,  being  considerably  thicker  on  the  supero-anterior  aspect  than 
at  any  other  part.  Unlike  the  corresponding  structure  of  the  shoulder-joint,  it  does 
not  permit  of  the  withdrawal  of  the  head  of  the  femur  from  contact  with  the  aceta- 
bular articular  surfaces,  except  to  a  very  limited  extent.     Its  fibres  are  arranged 


HIP- JOINT.  295 

both  in  the  circular  and  in  the  longitudinal  direction,  the  former,  known  as  the 
zona  orbicularis,  beiug  best  marked  posteriorly,  while  the  longitudinal  fibres  stand 
out  more  distinctly  in  front,  where  they  constitute  special  ligaments.  Looked  at 
as  a  whole,  the  capsule  has  the  following  attachments :  swperiorly  it  surrounds 
the  acetabulum,  on  the  upper  and  hinder  aspects  of  which  it  is  attached  directly 
to  the  innominate  bone,  while  on  the  front  and  lower  aspects  it  is  attached  to  the 
non- articular  surfaces  of  the  cotyloid  and  transverse  ligaments;  inferiorly  it 
encircles  the  neck  of  the  femur,  where  it  is  attached  in  front  to  the  anterior  inter- 
trochanteric line ;  above,  to  the  inner  aspect  of  the  root  of  the  great  trochanter ; 
below,  to  the  lower  part  of  the  neck  of  the  femur,  in  close  proximity  to  the  small 
trochanter ;  behind,  to  the  line  of  junction  of  the  outer  and  middle  thirds  of  the 
neck  of  the  femur.  It  is  a  matter  of  some  importance  to  note  that  only  part 
of  the  posterior  surface  of  the  neck  of  the  femur  is  enclosed  within  the  capsule. 
The  femoral  attachments  of  the  capsule  vary  considerably  in  their  strength,  being 
particularly  firm  above  and  in  front,  but  much  weaker  below  and  behind,  where 
the  orbicular  fibres  are  well  seen.  Many  fibres  of  the  capsule  are  reflected  from 
its  deep  aspect  upwards  upon  the  neck  of  the  femur,  where  they  form  ridges,  and 
to  these  the  term  rectinacula  (Fig.  231)  is  applied. 

The  longitudinal  fibres  of  the  capsule  are  arranged  so  as  to  form  certain  definite 
bands,  viz : — 

(1)  The  ilio-femoral  ligament  (lig.  ilio-femorale.  Fig.  232)  consists  of  a  triangular 
set  of  fibres  attached  above,  by  their  apex,  to  the  lower  part  of  the  anterior  inferior 
iliac  spine  and  the  immediately  adjoining  part  of  the  rim  of  the  acetabulum,  and 
below,  by  their  base,  to  the  anterior  intertrochanteric  line  of  the  femur.  This 
ligament  is  the  thickest  part  of  the  capsule,  but  its  sides  are  more  pronounced  than 
its  centre,  especially  towards  its  base.  Consequently  the  ilio-femoral  band  presents 
some  resemblance  to  an  inverted  Y  (A),  and  therefore  it  is  very  generally  known 
as  the  Y-shaped  ligament  of  Bigelow. 

The  outer  or  upper  limb  of  tlie  ilio-femoral  ligament  may  be  somewhat  extended  by  the 
inclusion  of  additional  longitudinal  fibres,  and  described  as  the  ilio-trochanteric  ligament  (lig. 
iho-trochantericum).  This  band  arises  from  the  anterior  part  of  the  dorsum  of  the  acetabulum, 
and  extends  to  the  femoral  neck,  close  to  the  anterior  end  of  the  inner  surface  of  the  great 
trochanter. 

(2)  The  pubo-femoral  or  pubo-capsular  ligament  (lig.  pubo-femorale  v.  pubo- 
capsulare.  Fig.  232)  is  composed  of  some  bands  of  fibres  of  no  great  strength, 
which  extend  from  the  outer  end  of  the  horizontal  ramus  of  the  pubis,  the  ilio- 
pectineal  eminence,  the  obturator  crest  and  the  obturator  membrane,  to  lose  them- 
selves for  the  most  part  in  the  capsule,  although  a  certain  proportion  of  them  may 
be  traced  to  the  inferior  aspect  of  the  femoral  neck,  where  they  adjoin  the  lower 
attachment  of  the  Y-shaped  ligament. 

(3)  The  ischio-capsular  ligament  (lig.  ischio-capsulare,  Fig.  230)  consists  of  a  broad 
band  of  short,  fairly  strong  longitudinal  fibres,  which,  by  their  upper  ends,  are 
attached  to  the  ischium  between  the  small  sciatic  notch  and  the  obturator  foramen, 
while  their  lower  ends  become  merged  in  the  zona  orbicularis  of  the  general  capsule. 

Within  the  capsule,  and  quite  distinct  from  it,  there  are  the  ligamentum  teres 
and  the  Haversian  gland. 

The  interarticular  ligament  (lig.  teres  femoris,  Fig.  231)  is  a  strong,  somewhat 
flattened  band  of  fibrous  tissue,  attached  by  one  end  to  the  upper  half  of  the  pit 
or  depression  on  the  head  of  the  femur.  By  its  inner  end  it  is  attached  to  the 
lower  edge  of  the  articular  surface  of  the  transverse  ligament,  with  extensions  to 
the  opposite  borders  of  the  acetabular  notch,  but  chiefiy  to  the  hinder  or  ischial 
border.  This  ligament  varies  very  greatly  in  its  strength  and  development  in 
different  subjects,  and  in  certain  rare  cases  it  is  absent. 

The  so-called  Haversian  gland  occupies  the  bottom  or  non-articular  area  of  the 
acetabulum.  It  consists  of  a  mass  of  fat  covered  by  synovial  membrane.  This 
pad  of  fat  is  continuous  witli  th(i  extra-capsular  fat  through  the  passage  subjacent 
to  the  transverse  ligament  of  the  notch. 

A  synovial  membrane  lines  the  capsule  from  which  it  is  reflected  to  the  neck  of 
the    iemur   along    a    line  which  corresponds  to  the   femoral  attachments   of   the 


296 


THE  AETICULATIONS  OE  JOINTS. 


Anterior  inferior 
iliac  spine 


Cotyloid  ligament 


capsule.     Thus  the  synovial  memljrane  clothes  more  of  the  femoral  neck  anteriorly 
than  in  any  other  position.     Posteriorly,  where  the  capsule  is  feebly  attached  to 

the  neck  of  the  femur, 
the   synovial   mem- 
brane may  be  seen 
from  the  outside  of 
the     capsule.      The 
synovial    membrane 
extends  close  up  to 
the  articular  margin 
of  the  head  of  the 
femur,  and    on    the 
upper  and  lower  as- 
pects of  the  neck  it 
in  gathered  into  loose 
folds   upon    the   re- 
tinacula.  These  folds 
or  plications  are  best 
marked    along    the 
line  of  synovial  re- 
%    flection,  and  do  not 
M   reach  as  far  as  the 
£   femoral  head.   At  its 
■5   acetabular   end   the 
I   synovial    membrane 
I   is  prolonged  from  the 
inside  of  the  capsule 
to   the    outer   non- 
articular   surface  of 
the   cotyloid   and 
transverse      liga- 
acetabular  or  articular 
at    the  bottom  of  the 


Fig.  232.  ^Dissection  op  the  Hip- Joint  from  the  front. 


ments,  upon  which  it  is  continued  as  a  lining  for  their 
surfaces,  and  further,  it  provides  a  covering  for  the  fat 
acetabular  fossa,  as  well  as  a  complete  tubular  investment  for  the  ligamentum  teres. 
Occasionally  the  synovial  bursa,  which  is  subjacent  to  the  tendon  of  the  ilio- 
psoas muscle,  communicates  with  the  interior  of  the  hip-joint  through  an  opening 
in  the  anterior  wall  of  the  capsule  (Fig.  232),  situated  between  the  pubo-femoral 
ligament  and  the  inner  or  lower  limb  of  the  ilio-femoral  ligament. 

Movements  at  the  Hip-Joint. — The  movements  which  occur  at  the  hip-joint  are  those  of 
a  multiaxial  joint.     These  are  flexion,  extension,  abduction,  adduction,  rotation,  and  circumduction. 

The  range  of  each  of  these  movements  is  less  extensive  than  in  the  case  of  the  shoulder-joint,  be- 
cause, at  the  hip,  the  freedom  of  movement  is  subordinated  to  that  stability  ^yhioh  is  essential  alike 
for  the  maintenance  of  the  erect  attitude  and  for  locomotion.  When  standing  at  rest  in  the  erect 
attitude  the  hip-joint  occupies  the  position  of  extension,  and  as  the  weight  of  the  trunk  is  trans- 
mitted in  a  perpendicular  which  falls  behind  the  centres  of  the  hip-joints,  both  the  erect  attitude 
and  the  extended  position  are  maintained  to  a  large  extent  mechanically,  without  sustained  mus- 
cular action,  by  means  of  the  tension  of  the  ilio-femoral  ligament.  Moreover,  the  tension  of  this 
ligament  is  sustained  by  the  pressure  of  the  front  of  the  head  and  neck  of  the  femur  against  its 
synovial  surface.  In  this  association  of  parts  it  is  important  to  note  that  the  articular  cartilage 
of  the  femoral  head  may  be,  and  in  certain  races  is,  prolonged  to  the  front  of  the  femoral  neck  ; 
and  further,  that  the  constant  friction  does  not  destroy  tlie  synovial  lining  of  the  capsule. 
Again,  the  same  mechanism  which  preserves  the  erect  attitude  prevents  an  excessive  degree  of 
extension  or  dorsiflexion.  In  movement  forwards,  i.e.  ventral  flexion,  the  front  of  the  thigh 
is  approximated  to  the  anterior  abdominal  wall.  The  amount  of  this  movement  depends  upon 
the  position  of  the  knee-joint,  because  when  the  latter  is  flexed  tlie  thigh  may  be  brought  into 
contact  with  the  abdominal  wall,  whereas  when  the  knee-joint  is  straightened  {i.e.  extended) 
the  tension  of  the  hamstring  muscles  greatly  restricts  the  amount  of  flexion  at  the  liip-joint. 
Abduction  and  adduction  are  likewise  much  more  restricted  than  at  the  shoulder-joint.  Abduc- 
tion is  brought  to  a  close  by  the  tension  of  the  pulio-femoral  band  and  the  lower  part  of  the 
capsule,  and,  in  addition,  the  upper  aspect  of  the  neck  of  the  femur  locks  against  the  margin 
of  the  acetabulum.  Excessive  adduction  is  prevented  by  the  tension  of  the  upper  band  of  the 
ilio-femoral  ligament  and  the  upper  part  of  the  capsule.  Eotation  or  movement  in  a  longi- 
tudinal axis  may  be  either  inwards,  i.e.  towards  the  front,  or  outwards,  i.e.  toward  the  back. 


THE  KNEE-JOINT.  297 

111  tlie  former  the  movement  is  brought  to  a  close  by  the  tension  of  tlie  ischiu-cfqwular  ligament 
and  back  part  of  the  capsule,  aided  by  the  muscles  on  the  back  of  the  joint ;  in  tlie  Jatter — 
rotation  outwards — the  chief  restraining  factor  is  the  outer  or  upper  limb  of  tlie  ilio-femoral 
ligament.     The  total  amount  of  rotation  is  probably  less  than  &f. 

Circumduction  is  only  slightly  less  free  than  at  the  shoulder,  but  it  is  complicated  by  the 
jjreservation  of  the  balance  upon  one  foot. 

The  value  and  influence  of  the  ligamentum  teres  are  not  easily  estimated,  because  it  may  be 
absent  without  causing  any  known  interference  with  the  usefulness  of  the  joint.  In  the  erect  attitude 
this  ligament  lies  lax  between  the  lower  part  of  the  femoral  head  and  the  acetabular  fat.  In  the 
act  of  walking  it  is  rendered  tense  at  the  moment  when  the  pehds  is  balanced  on  the  summit  of  tlie 
sui^porting  femur.  Analysis  of  this  position  shows  the  femur  to  be  adducted,  with  probably,  in 
addition,  a  small  amount  of  flexion  (i.e.  bending  forwards)  and  internal  rotation.  Again,  this 
ligament  is  said  to  be  tense  when  the  thigh  is  rotated  outwards.  The  equivalent  of  this 
movement  is  doubtless  found  in  the  rotation  of  the  jjelvis,  which  occurs  in  the  act  of  walking 
at  the  moment  of  transition  from  the  toe  of  the  supj)orting  foot  to  the  heel  of  the  advancing 
foot.  The  interest  connected  with  this  ligament  is  perhaps  morj)hological  rather  than  j)hysio- 
logical.  It  is  believed  by  some  to  represent  the  tendon  of  a  muscle  which  in  birds  occupies  a 
j)osition  external  to  the  joint  capsule. 

THE  KNEE-JOINT. 

The  knee-joint  (articulatio  genu)  is  the  largest  articulation  in  the  body,  and 
its  structure  is  of  a  very  elaborate  nature.  The  part  it  plays  in  maintaining  the 
erect  attitude  materially  influences  its  construction,  and  special  arrangements  are 
provided  for  the  mechanical  retention  of  the  joint  in  the  extended  position,  in  view 
of  the  fact  that  the  line  of  gravity  falls  in  Iront  of  the  centre  of  the  articulation. 
Its  principal  axis  of  movement  is  in  the  transverse  direction,  consequently  it  belongs 
to  the  ginglymus  or  hinge  variety  of  the  diarthroses.  At  the  same  time  a  slight 
amount  of  rotation  of  the  tibia  in  its  long  axis  is  permitted  during  extreme  flexion  ; 
but  while  this  fact  is  of  considerable  importance  in  the  study  of  certain  accidents 
to  which  the  joint  is  liable,  as  well  as  in  the  study  of  its  comparative  morphology,  it 
is  not  sufflciently  pronounced  to  interfere  with  its  classiflcation  as  a  hinge-joint. 

Articular  surfaces  pertaining  to  the  femur,  tibia,  and  patella,  enter  into  the 
formation  of  the  knee-joint.  The  articular  surface  of  the  femur  extends  over  a 
large  part  of  both  condyles,  and  may  be  divided  into  patellar  and  tibial  portions 
by  faintly -marked,  almost  transverse  grooves,  which  pass  across  the  articular 
surface  immediately  in  front  of  the  intercondylar  notch.  As  a  rule  marginal 
indentations  of  the  articular  surface  render  the  positions  of  tliese  transverse 
grooves  more  distinct. 

The  patellar  portion  (Fig.  233)  is  situated  anteriorly,  and  is  common  to  both 
condyles,  although  developed  to  a  larger  extent  in  association  with  the  outer  condyle, 
on  which  it  ascends  to  a  higher  level  than  on  the  inner  condyle.  This  surface  is 
trochlear,  and  forms  a  vertical  groove  bordered  by  prominent  lateral  borders. 

The  tibial  portion  of  the  articular  surface  of  the  femur  is  divided  into  two 
articular  areas,  in  relation  to  the  inferior  aspects  of  the  two  condyles,  by  the  wide 
non- articular  intercondyloid  notch.  These  two  surfaces  are  for  the  most  part 
parallel,  but  in  front  the  internal  tibial  surface  turns  obliquely  outwards  as  it 
passes  into  continuity  with  the  patellar  trochlea,  while  posteriorly,  under  certain 
circumstances,  e.g.  the  squatting  posture,  the  articular  surface  of  the  inner  condyle 
may  extend  to  the  adjoiniug  portion  of  the  popliteal  area  of  the  bone. 

When  tlie  joint  is  in  the  position  of  extreme  flexion,  the  patella  is  brought  into 
direct  contact  with  that  part  of  the  articular  surlace  on  the  inner  condyle  which 
bounds  the  intercondyloicl  notch  upon  its  inner  and  anterior  aspects.  This  relation- 
ship is  indicated  by  the  presence  of  a  distinct  semilunar  facet  on  the  cartilage  in 
that  situation  (Fig.  233).  The  articular  surface  of  the  femur  may  therefore  be 
regarded  as  pntsenting  femoro- patellar  and  femoro-tibial  areas. 

The  patella  ])rcsontK  on  its  posterior  asjiect  a  transversely  -  elongated  oval 
articular  facet  and  an  inferior  rough,  triangular,  non-articular  area.  The  articmlar 
facet  is  divided  into  two  p)'incij)al  lateral  portions  liy  a  ])romineut  rounded  vertical 
ridge.  Of  these  th<!  outer  is  the  wid(;i-.  A  loss  pronounced  and  nearly  vertical 
ridge  marks  off  an  additional  lacet  called  the  internal  ]jerpendicular  facet,  close  to 
the  inner  margin  of  the  articular  surface.     Two  faint  transverse  ridges  cut  ofl' 


298 


THE  AETICULATIONS  OR  JOINTS. 


narrow  upper  and  lower  facets  from  the  general  articular  surface  without  encroach- 
ing on  the  narrow  innermost  vertical  facet  (Goodsir)  (Fig.  233). 

The  head  of  the  tibia  presents  on  its  superior  aspect  two  condylar  articular 
surfaces,  separated  from  each  other  by  a  non-articular  antero-posterior  area,  which 
is  wider  in  front  and  behind  than  in  the  middle,  where  it  is  elevated  to  form  a 
bifid  tibial  spine. 

The  external  condylar  facet  is  slightly  concavo-convex  1'rom  before  Ijackwards, 
and  slightly  concave  transversely.-  This  surface  is  almost  circular,  and  extends 
to  the  free  external  ])order  of  the  tibial  head,  where  it  is  somewhat  flattened. 
Posteriorly  the  articular  surface  is  prolonged  downwards  on  the  tuberosity  in 
relation  to  the  position  occupied  by  the  tendon  of  the  popliteus  muscle.      The 


/^"^y^ 


Impression  of  external  semi- 
lunar cartilage 


External  tibial  surface  of 
femur 


External  lateral  lijrament 


Cut  tendon  of  biceps  flexor 
cruris  muscle 


Anterior  superior  tibio-fibular        \  L 
ligament  — ~-\i\ 

External  lateral  ligament  .l_  \   '^~~y. 


Opening  in  interosseous 

membrane  for  anterior  tibial 

vessels 


Patellar  surface  of  femur 


beiiiiluiiar  facet  for  patella 


Internal  tibial  surface  of 
lemur 


Posterior  crucial  lisament 


Anterior  crucial  ligament 


Transverse  ligament 
_'//         Internal  semilunar  tibro- 
jr  cartilage 


Internal  lateral  ligament 


Ligamentum  patellar 


Inner  perpendicular  facet  on 
patella 


Fig.  233. — Dissectiojs:  of  the  Knee-Joint  from  the  front  :  Patella  thrown  down. 

internal  condylar  facet  is  oval  in  outline,  and  distinctly  concave  both  in  its  antero- 
posterior and  transverse  diameters. 

Ligaments. — Like  all  diarthroses,  this  joint  is  invested  by  an  envelope  or 
capsule  (capsula  articularis),  which  does  not,  however,  entirely  surround  the  joint 
cavity,  for  it  is  absent  as  a  fibrous  membrane  above  the  joint  cavity,  subjacent  to 
the  tendon  of  the  quadriceps  extensor  muscle.  Its  specially  named  bands  are  not 
of  themselves  sufficient  to  form  a  complete  investment,  and  a  capsular  membrane, 
which  largely  consists  of  augmentations  from  the  fascia  lata  and  the  tendons  of 
surrounding  muscles,  supplies  the  defective  areas.  Thus,  anteriorly,  on  each  side 
of  the  patella  and  the  ligamentum  patella,  expansions  of  the  vasti  tendons  and 
fascia  lata,  constituting  lateral  patellar  ligaments,  are  evident.  On  the  outer  side  of 
the  joint  the  external  lateral  ligament  is  hidden  within  a  covering  derived  from 
the  ilio-tibial  band  of  the  fascia  lata.  On  the  inner  side  expansions  from  the 
tendons  of  the  sartorins  and  semi-membranosus  muscles  augment  the  capsule,  which 
here  becomes  continuous  with  the  internal  lateral  ligament.  Posteriorly  the  capsule 
also  receives  augmentation  from  the  tendon  of  the  semi-membranosus  muscle,  but 
it  is  very  thin  subjacent  to  the  origins  of  the  gastrocnemius  muscle,' where  it  covers 
the  hinder  parts  of  the  condyles.  Not  unfrequently  the  capsule  presents  an 
opening  of  communication  between  the  interior  of  the  joint  cavity  and  a  bursa 
which  lies  under  cover  of  the  inner  head  of  the  gastrocnemius  muscle. 


THE  KNEE-JOINT. 


299 


The  anterior  ligament  (lig.  patellae,  Fig.  233),  also  called  the  ligamentuni 
patellae,  is  a  powerful  flattened  band,  attached  superiorly  to  the  apex  and  adjoining 
margins  of  the  patella,  and  inferiorly  to  the  rough  anterior  tuberosity  at  the  upper 
end  of  the  shaft  of  the  tibia.  This  ligament  also  serves  as  a  tendon  of  insertion  for 
the  quadriceps  extensor  muscle,  and  a  certain  number  of  the  fibres  of  the  tendon 
may  be  observed  to  descend  as  a  thin  fibrous  covering  for  the  anterior  surface  of 
the  patella.  The  deep  surface  of  the  tendon  is  separated  from  the  front  of  the  head 
of  the  tibia  by  a  synovial  bursa,  and  above  this  it  rests  upon  the  infrapatellar  pad 
of  fat,  which  is  placed  between  the  tendon  and  the  synovial  membrane  of  the  joint. 

The  posterior  ligament  (Fig.  234)  is  a  compound  structure  of  unequal  strength, 


Tendon  of  adductor  magnus  muscle  (cut) 


Inner  head  of  gastrocnemius  (cut) 


Posterior  ligament  or  ligament 
of  Win'ilo\\ 


Bursa  beneath  tendon  o 
semi-mem  branosu- 


Popliteal  surface  of  femur 


Plantaiis  muSLle  (cut) 


Tendon  ofsemi-membranosub 
muscle  (cut) 


Posterior  ligament 

(oblique  slip) 

Internal  lateral  ligament 


Outer  head  of  gastro- 
emius  muscle  (cut) 


r  ong  evternal  lateral 
ligament 


Short  external  lateral 
ligament 

Popliteus  muscle  (cut) 


Biceps  flexor 
'cruris  muscle  (cut) 


Popliteal  fascia' 


Popliteus  muscle  (cut) 


Head  of  hbula 


Popliteal  surface  of  tibia 


Fk;.  234. — The  Knee-Joint.     Posteeioe  View. 

and  those  portions  by  which  it  establishes  continuity  with  the  lateral  parts  of  the 
capsule  are  remarkably  thin.  It  is  attached  superiorly  to  the  popliteal  surface  of 
the  femur,  close  to  the  intercondyloid  notcli,  with  lateral  extensions  to  the  non- 
articular  areas  immediately  above  the  posterior  articular  margins  of  the  two  con- 
dyles, where  it  is  closely  associated  with  the  origins  of  the  gastrocnemius  muscle. 

Interiorly  it  is  attached  to  the  rough  non-articular  posterior  border  of  the  head 
of  the  tibia,  where,  to  its  fibular  side,  it  i)resents  an  opening  of  exit  for  the  tendon 
of  the  ])Oj>liteus  muscle  (Fig.  234). 

The  tendon  of  insertion  of  the  semi  -  )ueml)ranosus  muscle  contril)utes  an 
important  expansion  which  augments  the  ])osteri<)r  ligament  on  its  superficial 
aHi)ect.  This  <;xpausion — ligamentum  posticum  Winslowii — passes  obliquely  upwards 
and  outwards  to  lose  itself  in  the  general  ligauienl,  but  it  is  most  distinct  in  the 
region  between  the  femoral  condyles,  where  it  may  present  upper  and  lower  arcuate 


300  THE  ARTICULATIONS  OR  JOINTS. 

borders.  A  number  of  vessels  aud  nerves  perforate  this  ligament,  and  hence  it 
presents  a  number  of  apertures. 

The  internal  lateral  ligament  (lig.  collaterale  tibiale,  Figs.  233  and  235)  is  a  well- 
defined,  strong,  fiat  band  which  is  applied  to  the  inner  side  of  the  knee-joint,  and  is 
rather  wider  in  the  middle  than  at  either  end.  It  is  frequently  regarded  as  consisting 
of  two  portions — an  anterior  or  long  portion,  and  a  posterior  or  short  one.  The  two 
parts  arise  close  together  from  the  non-articular  inner  surface  of  the  inner  condyle, 
immediately  lielow  the  adductor  tubercle.  The  short  or  posterior  portion  descends 
slightly  backwards,  to  be  attaclied  to  the  postero-internal  aspect  of  tlie  inner  part  of 
the  tibia  above  the  groove  for  the  semi-membranosus  tendon.  The  long  or  anterior 
portion  inclines  somewhat  forwards,  and  descending  superficially  to  the  tendon  of 
the  semi-membranosus,  it  is  continued  downwards,  to  be  attached  to  the  upper  part  of 
the  inner  surface  of  the  shaft  of  the  tibia  below  the  level  of  the  anterior  tuberosity. 

On  its  superficial  aspect  the  internal  lateral  ligament  is  augmented  by  prolonga- 
tions from  the  tendons  of  the  semi-membranosus  and  sartorius  muscles,  but  is 
separated  by  a  bursa  from  the  tendons  of  adductor-gracilis,  semi-tendinosus,  and 
sartorius.  Its  deep  surface  is  adherent  to  the  convex  edge  of  the  internal  semilunar 
cartilage,  but  lower  down  the  inferior  internal  articular  vessels  intervene  between 
the  ligament  and  the  shaft  of  the  tibia. 

The  external  lateral  ligament  (lig.  collaterale  fibulare,Figs.  233  and  235),  sometimes 
called  the  ligamentum  laterale  externum  longum,  is  a  distinct  rounded  band  which 
is  under  cover  of  the  ordinary  capsule,  and  yet  well  separated  from  the  joint  cavity  by 
intervening  objects.  It  is  attached  superiorly  to  a  tubercle  on  the  outer  surface  of 
the  external  condyle,  immediately  above  the  groove  occupied  by  the  tendon  of  the 
popliteus  muscle,  superficial  to  which  the  ligament  descends.  By  its  lower  end  it  is 
attached  to  the  outer  side  of  the  head  of  the  fibula,  in  front  of  the  styloid  process. 
In  its  course  vertically  downwards  it  splits  the  tendon  of  insertion  of  the  biceps 
flexor  cruris  (Fig.  233),  the  portions  of  which  are  fixed  to  the  head  of  the  fibula  on 
either  side  of  the  ligament,  and  a  bursa  may  intervene  between  the  tendon  and  the 
ligament.  The  inferior  external  articular  vessels  pass  forwards  subjacent  to  this 
ligament  and  above  the  head  of  the  fibula.  Unlike  the  internal  ligament,  it  is  not 
attached  to  the  corresponding  semilunar  cartilage. 

The  ligamentum  laterale  externum  breve  seu  posticum  (Fig.  234)  is  an  iuconstant  structure 
wliicli  is  attached  by  its  upper  end  immediately  behind  the  preceding,  and  subjacent  to  the 
outer  head  of  the  gastrocnemius  muscle.  It  likewise  descends  superficial  to  the  popliteal  tendon, 
and  is  affixed  inferiorly  into  the  styloid  process  of  the  fibula. 

The  intra-articular  structures  of  the  knee-joint  are  more  important  and  more 
numerous  than  in  any  other  joint  of  the  body. 

The  crucial  ligaments  (ligamenta  cruciata  genu)  are  two  strong,  rounded,  tendinous 
bands,  which  extend  from  the  non-articular  area  on  the  upper  surface  of  the  head 
of  the  tibia  to  the  non-articular  sides  of  the  intercondyloid  notch  of  the  femur. 
These  interarticular  ligaments  are  distinguished  from  each  other  as  the  anterior  or 
external  and  the  posterior  or  internal.  They  cross  each  other  like  the  limbs  of 
an  X,  yet  they  remain  distinct  throughout,  and  each  has  its  own  partial  synovial 
covering.  They  lie  within  the  capsule  of  the  joint,  and  extend  between  non- 
articular  surfaces  in  relation  to  the  longitudinal  axis  of  the  limb. 

The  ligamentum  cruciatum  anterius  (Figs.  233,  235,  and  236)  is  attached  inferiorly 
to  the  inner  part  of  the  rough,  depressed  area  in  front  of  and  close  to  the  spine  of 
the  tibia.  It  passes  obliquely  upwards,  outwards,  and  backwards  to  the  inner 
non-articular  surface  of  the  external  condyle,  where  it  finds  attachment  far  back  in 
the  posterior  part  of  the  intercondyloid  notch.  This  ligament  is  tense  in  the  position 
of  extension,  and  therefore  it  assists  in  maintaining  the  erect  attitude. 

The  ligamentum  cruciatum  posterius  (Figs.  233,  235,  and  236)  is  somewhat  shorter 
than  the  preceding.  It  is  attached  inferiorly  to  the  hinder  part  of  the  depressed 
surface  behind  the  spine  of  the  tibia  and  close  to  the  popliteal  notch.  Its  fibres 
pass  obliquely  upwards,  forwards,  and  inwards,  to  be  inserted  into  the  outer  non- 
articular  surface  of  the  inner  condyle,  far  forwards  towards  the  anterior  margin  of 
the  intercondyloid  notch.     It  is  rendered  tense  in  the  position  of  flexion. 


THE  KNEE-JOINT. 


501 


The  semilunar  interarticular  fibro-cartilages  are  two  in  number — an  inner  and  an 
outer— placed  horizontally  Ijetween  the  articular  surfaces  of  the  femur  and  tibia. 
In  general  outline  they  correspond  to  the  circumferential  portions  of  the  tibial 
i'acets  upon  which  they  rest.  Each  has  a  thick,  convex,  fixed  border  in  relation  to 
the  periphery  of  the  joint,  and  a  thin,  concave,  free  border  directed  towards  the 
interior  of  the  joint.  Neither  of  them  is  sufficiently  large  to  cover  the  whole  of  the 
tibial  articular  surface  upon  which  it  rests.  The  upper  and  lower  surfaces  of  each 
semilune  are  smooth  and  free,  and  each  cartilage  terminates  in  an  anterior  and  a 
posterior  fibrous  horn  or  coriiu. 

The  internal  semilunar  fibro  -  cartilage  Cmeniscus  medialis.  Figs.  2-35  and  236) 


Tendon  of  insertion  ot 
adductor  niagnn 
muscle  (cut) 


Popliteal  surface  of  femur 


Anterior  crucial  ligament 


Tendon  of  popliteus  muscle 
cut) 


Accessoryattaclimeiit    y  r  , 
of  external  semilun  n      J  \j 
cartiku      Hi" 


Internal  semilunar 
caitilascp 


External  semilunar 
cartilage 


Posterior  crucial 
ligament 


Tendon  of  semi-memhianus' 
mus(  le  (cu  , 
Internal  lateial  ligament 


Popliteal  surface  of  tibia 


Groove  on  tibia  for  tendon 
of  popliteus  muscle 
Superior  portion  of  cap- 
.sule  of  superior  tibio- 
fibular articulation 
.External  lateral  ligament 
of  knee-joint 


Posterior  superior  tibio- 
fibular ligament 


"•Head  of  fibula 


Fig.  23.5. — The  Knee-Joint  opened  kkom  Behind  by  the  Removal  of  the  Posterior  Ligament. 


forms  very  nearly  a  semicircle.  It  is  attached  by  its  anterior  horn  to  the  non- 
articular  surface  on  the  head  of  the  tibia,  in  front  of  the  tibial  attachment  of  the 
anterior  crucial  ligament,  and  by  its  posterior  horn  to  the  non-articular  surface 
immediately  in  front  of  the  tibial  attachment  of  the  posterior  crucial  ligament. 
The  deep  or  hinder  part  of  the  internal  lateral  ligament  is  attached  to  its  |)eriphery. 
The  external  semilunar  fibro-cartilage  (meniscus  later.ilis,  Figs.  235  and  236)  is 
attached  by  its  anterior  hf)rn  to  the  non-articular  surface  of  the  tibia  in  front  of 
the  tiftial  S])ine,  whore  it  is  yilaced  to  the  out(!r  side,  and  ])artly  under  cover  of  the 
tibial  end  of  the  anterior  crucial  ligament.  By  its  ])OSterior  horn  it'  is  attached  to  the 
interval  between  the  two  tubercles  which  surmount  the  tibial  spine,  i.e.  in  front  of 
the  attachment  of  the  posterior  horn  of  the  internal  semilunar  cartilage.  1'his  fibro- 
cartilagfi,  with  its  two  horns,  therefore  forms  almost  a  comijlete  circle.  Posteriorly 
it  is  attached  ])y  its  yjerijihery  to  the  jiosterior  ligament,  1)ut  on  the  outer  side  it 


502 


THE  AETICULATIONS  OE  JOINTS. 


Transverse  lip;rirneiit 
Anterior  cornu  of  internal 
semilunar  cartila 


Anterior  cornn  of  external 
seniihiiiar  cartilage 


Internal 
semilunar^^v    |S 
fibro-      1  ^ 
cartilage        \ 

Posterior  cornu 
of  internal  semi- 
lunar cartilaKB 


Posterior  crucial  lit^ament 


Posterior  cornu  of  exter- 
semilunar  cartilage 
Fasciculus  from  external  semilunar 
cartilage  to  posterior  crucial  ligament 


i'lG.  236. — Upper  E^'D■OF  Tibta  with  Semilunar  Cartilages  and  Attached 
Portions  of  Crucial  Ligaments. 


is  separated  from  the  external  lateral  ligaineut  by  the  tendon  of  the  popliteus 
muscle,  and  on  this  aspect  its  periphery  is  free. 

The  two  horns  of  the  external  semilune  are  endjraced  by  the  two  horns  of  the 
internal  one,  and,  while  the  anterior  crucial  ligament  has  its  tibial  attachment  almost 
between  the  anterior  horns  of  the  two  semilunes,  the  tibial  attachment  of  the 
posterior  crucial  ligament  is  situated  behind  the  posterior  horns  of  the  two 
semilunes. 

Both  semilunes  possess  certain  accessory  attachments.  Thus  the  external  semi- 
lune sends  a  large  bundle  of  fibres  from  its  convex  posterior  border  to  augment  the 

posterioraspect 
of  the  posterior 
crucial  liga- 
ment, by  which 
these  fibres  are 
conducted  to 
the  f  e  in  u  r. 
Again,  the  con- 
vex or  periph- 
eral margins  of 
each  semilune 
possess  certain 
attachments  to 
the  deep  surface 
of  the  capsule 
on  its  inner  and 
posterior  as- 
pects, as  has 
already  been 
explained,  but, 
in     addition, 

they  are  attached  to  the  non-articular  circumference  of  the  tibial  head  by  short 
fibrous  bands  known  as  the  ligamenta  coronaria.  Lastly,  a  rounded  band  which 
varies  in  strength,  the  transverse  ligament  (lig.  transversum  genu.  Figs.  233  and 
236),  stretches  between  the  anterior  convex  margins  of  the  two  semilunes,  crossing 
the  front  part  of  the  non-articular  area  on  the  tibial  head  in  its  course. 

The  synovial  membrane  of  the  knee-joint  is  not  only  the  largest,  but  the  most 
elaborately  arranged  of  its  kind  in  the  body.  It  not  only  lines  the  capsule,  but  it 
forms  a  more  or  less  extensive  covering  for  the  intracapsular  ligaments  and  the 
free  surface  of  the  infra-patellar  pad  of  fat.  This  pad  acts  as  a  wedge  which  fits 
into  the  interval  lietween  the  patella,  tibia,  and  femoral  condyles,  and  the  synovial 
membrane  upon  its  surface  forms  a  band  or  fold  which  extends  from  below  the 
level  of  the  patellar  articular  surface  to  the  anterior  part  of  the  intercondyloid 
notch.  This  is  in  no  sense  a  ligament,  although  it  is  named  the  ligramentum 
mucosum,  or  plica  syno\'ialispatellaris.  At  its  femoral  eud  it  is  narrow  and  attenu- 
ated, but  at  its  patellar  end  it  expands  laterally  to  form  wing-like  fringes  or  mem- 
branes— the  alar  ligaments  fplicse  alares) — wdiich  are  often  distinguished  from  each 
other  as  the  inner  (plica  aliformis  medialis)  and  the  outer  (plica  aliformis  lateralis). 
These  folds  are  more  or  less  loaded  with  fat. 

Apart  from  these  special  foldings,  the  synovial  membrane  lines  the  deep  surface 
of  the  common  extensor  tendon,  and  extends  upwards  for  a  variable  distance  above 
the  patella.  This  extension  of  the  joint  cavity  almost  ahvays  communicates  with 
a  large  bursa  situated  still  higher  on  the  front  of  the  femur.  Tracing  the  synovial 
membrane  downwards,  it  wall  be  found  to  cover  both  surfaces  of  the  semilunar  fibro- 
cartilages.  The  peripheral  or  convex  margins  of  these  cartilages  are  only  covered 
by  this  membrane  where  they  are  unattached  to  the  capsule.  A  prolongation 
invests  the  intracapsular  portion  of  the  tendon  of  the  popliteus  muscle,  and 
separates  this  tendon  from  the  back  part  of  the  tibial  head,  besides  intervening 
between  the  external  semilune  and  the  head  of  the  til)ia. 

From  the  back  part  of  the  joint  cavity  the  synovial  membrane  extends  forwards, 


THE  KNEE- JOINT.  803 

and  provides  a  partial  covering  for  the  crucial  ligaments  Ijetween  which  a  bursa  may 
be  found. 

This  somewhat  complicated  arrangement  of  the  synovial  membrane  may  be 
readily  comprehended  if  it  be  borne  in  mind  that  it  really  represents  the  fusion  of 
three  separate  synovial  cavities,  which  in  some  animals  are  permanently  distinct. 
These  are  indicated  in  the  two  femoro-tibial  and  the  single  femoro-patellar  parts  of 
the  articulation. 

The  joint  cavity  may  communicate  with  bursas  situated  in  relation  to  the  inner 
head  of  the  gastrocnemius  muscle  and  the  tendon  of  the  semi-membranosus  muscle, 
besides  the  large  supra-patellar  bursa  already  described.  Lastly,  there  may  be 
intercommunication  between  this  joint  cavity  and  that  of  the  superior  tibio-fibular 
articulation. 

Movements  at  the  Knee- Joint. — In  studying  the  movements  whicli  may  occur  at  the 
human  knee-joint,  it  is  necessary  to  bear  in  mind  that  the  lower  limb  of  man  is  primarily  required 
for  purposes  of  support  and  locomotion.  The  principal  requirement  of  the  former  function  is 
stability  accompanied  by  rigidity,  whereas  in  the  latter  function  the  special  desideratum  is  regu- 
lated and  controlled  mobility.  Thus,  in  the  same  joint,  two  entirely  oi:)posite  conditions  have 
to  be  provided.  The  stable  conditions  of  support  are  chiefly  concerned  in  the  maintenance 
of  the  erect  attitude,  and  the  mechanism  associated  therewith  does  not  call  for  the  exertion  of  a 
large  degree  of  sustained  muscular  effort. 

In  standing  erect  the  attitude  of  the  limb  is  that  of  extension,  which  mainly  concerns  the 
femoro-tibial  parts  of  the  joint.  In  this  position  the  force  of  gravity  acts  along  a  vertical  line 
which  falls  in  front  of  the  transverse  axis  of  the  joint,  and  therefore  any  tendency  to  flexion,  i.e. 
bending  backwards,  is  mechanically  counteracted  by  the  application  of  a  force  which  tends  to 
j^roduce  bending  forwards  (so-called  over-extension).  This,  however,  is  absolutely  prohibited  in 
normal  states  of  the  joint,  by  the  tension  of  the  posterior  and  lateral  ligaments  aided  by  the 
anterior  crucial  ligament.  The  value  of  this  fact  may  be  seen  by  observing  the  eftect  produced  by 
giving  the  joint  a  sudden  push  from  behind,  which  causes  an  immediate  reversal  of  the  positions  of 
the  transverse  and  vertical  axes,  whereby  the  body  weight  at  once  produces  flexion  of  the  joint. 

The  semilunar  cartilages  and  the  infra-patellar  pad  of  fat  also  assist  in  maintaining  extension, 
by  reason  of  their  close  adaptation  to,  and  packing  round  the  condyles  as  these  rest  upon  the  tibia. 
The  anterior  margin  of  the  intercondyloid  fossa  is  also  brought  into  contact  with  the  front  of 
the  anterior  crucial  ligament. 

In  the  position  of  extension  the  patella  is  retained  at  a  high  level  in  relation  to  the  trochlear  sur- 
face of  the  femur,  so  that  the  lower  articular  facets  of  the  patella  are  in  contact  with  the  trochlea. 

During  locomotion  the  movements  of  the  knee-joint  are  somewhat  intricate,  for  both  the 
femoro-tibial  and  the  femoro-patellar  sections  of  the  joint  are  brought  into  action.  The  principal 
movement  which  results  is  flexion,  with  which  there  is  associated,  both  at  its  beginning  and 
ending,  a  certain  amount  of  screw  movement  or  rotation.  Flexion  and  rotation  occur  at  the 
femoro-tibial  sections  of  the  joint,  whereas  the  movement  at  the  femoro-patellar  portion  produces 
a  regulating  and  controlling  influence  uj)on  flexion. 

Taking  these  factors  separately,  we  observe  that  each  condyle  adapts  itself  to  a  shallow  cup 
formed  by  the  head  of  the  tibia  and  the  corresponding  semilunar  cartilage,  and  as  the  two 
condyles  move  simultaneously  and  parallel  to  each  other,  there  is  more  than  the  characteristic 
hinge-joint  action,  for  each  condyle  glides  and  rolls  in  its  cup  "  like  a  wheel  restrained  by  a 
drag  "  (Goodsir)  when  the  movement  of  bending  occurs.  Thus  the  different  parts  of  the  condyles 
are  successively  brought  into  relation  with  the  transverse  axis  of  the  joint  while  it  passes  from 
extension  to  flexion  and  vice  versa.  From  the  fact  that  the  internal  condyle  is  longer  than  the 
external,  it  is  believed  that  extension  is  completed  by  a  movement  of  rotation  whereby  the  joint 
becomes  locked,  and  the  anterior  crucial,  the  posterior  and  the  lateral  ligaments,  become  tense.  A 
sinular  rotation  initiates  the  movement  of  flexion,  and  unlocks  the  joint  by  relaxing  the  liga- 
ments just  mentioned. 

Since  the  tibia  and  foot  are  fixed  in  the  act  of  walking,  it  is  the  femur  which  rotates  upon 
the  tibia  in  passing  from  extension  to  flexion  and  vice  versa  ;  and  as  relaxation  of  the  ilio-femoral 
ligament  is  essential  for  this  rotation,  some  observers  are  of  opinion  that  the  body  weight  falls 
beliind  the  transverse  axis  of  the  knee-joint,  as  in  the  case  of  the  Lip-joint,  and  consequently  that 
extension  of  the  knee-joint  is  maintained  l)y  the  ilio-femoral  ligament,  as  it  is  not  possible  to 
bend  the  knee  witljout  first  having  bent  the  hip-joint. 

During  flexion  and  extension  the  semilunar  cartilages  g]id(;  along  with  the  condyles,  so  as  to 
maintain  their  close  adaptation  anrl  preserve  tlieir  value  as  packing  agents.  When  the  movement 
of  flexion  is  completed,  the  condyles  are  r(;tain(;d  upon  the  tibia,  and  prevented  from  slipj)ing  off 
by  the  tt;nsion  of  tin;  posterior  crucial  ligament.  In  this  position  a  small  degree  of  rotation  of 
the  tibia,  both  inwanls  and  outwards,  is  also  permissible. 

TIk!  i-egulafing  and  controlling  in(luenc(!  of  the  femoro-patellar  portion  of  tlu;  articulation  is 
brought  into  j»lay  during  the  movements  of  fl(r.\iou  and  extension.  In  the  latter  position  the 
infi^rior  pair  of  patellar  facets  is  in  aj)position  with  the  upper  part  of  the  femoral  trochlea.  As 
(I'-xion  advance.^,  the  niiddie  ])air  of  facets  adapt  thciniselves  to  a  deeper  area  of  the  trochlea,  into 
which  the  jiafellar  keel  fits.  When  flexion  is  still  further  advanced,  the  upper  pair  of  patellar 
facets  will   he  found  fitting  into  that  j)art  of  tlie  trochlea  adjoining  the  intercondyloid  notch  ; 


304  THE  AETICULATIONS  OR  JOINTS. 

and  finally,  when  flexion  is  complete,  the  i)atel]a  lies  op])Osite  the  intercondyloid  notch,  while 
the  forward  thrust  of  the  longer  internal  condyle  brings  its  semilunar  facet  (Groodsir)  into 
ajiposition  witli  the  somewhat  vertical  facet  at  the  inner  border  of  the  j)atella.  The  wedge-like 
inliuence  of  the  patella  is  most  marked,  for  it  is  only  in  the  position  of  extension  that  it  can  be 
moved  from  side  to  side.  The  movements  of  the  patella  may  be  described  as  gliding  and 
co-aptation,  as  it  slips  or  rocks  from  one  pair  of  facets  to  another  in  its  progress  along  the  trough 
of  the  femoral  trochlea. 

THE   TIBIO-FIBULAR   JOINTS. 

The  upper  and  lower  ends  of  the  fibula  articulate  with  the  tibia.  Primarily, 
the  fibula  is  required  to  form  a  strong  lateral  support  for  the  ankle-joint,  and 
therefore  its  articulations  are  so  arranged  as  to  provide  a  certain  amount  of 
elasticity  without  any  sacrifice  of  the  rigidity  necessary  for  security.  Hence  the 
amount  of  movement  is  very  small,  but  what  there  is  enables  these  joints  to  be 
classified  as  arthrodial  diarthroses. 

The  superior  tibio-fibular  joint  (articulatio  tibio-fibularis)  is  formed,  on  tlie 
one  hand,  by  a  flat  oval  or  circular  facet  which  is  situated  upon  the  postero-external 
aspect  of  the  outer  tuberosity  of  the  head  of  the  tibia,  and  is  directed  downwards 
and  backwards ;  on  the  other,  by  a  similar  facet  on  the  upper  surface  of  the  head 
of  the  fibula  in  front  of  the  styloid  process. 

A  fibrous  capsule  (capsula  articularis,  Tig.  234)  invests  the  joint,  and  it  may 
be  regarded  as  holding  the  articular  surfaces  in  apposition,  although  certain 
special  bands  receive  separate  designations.  Occasionally  there  is  an  opening  in  the 
capsule  by  which  communication  is  established  between  the  joint  cavity  and  the 
knee-joint  through  the  intermediation  of  the  synovial  prolongation,  subjacent  to  the 
tendon  of  the  popliteus  muscle. 

The  anterior  superior  tibio-fibular  ligament  (lig.  capituli  fibul?e  anterius.  Fig.  233) 
is  a  strong  flat  band  whose  fibres  extend  from  the  anterior  aspect  of  the  fibular 
head,  upwards  and  inwards,  to  the  adjoining  part  of  the  tuberosity  of  the  tibia. 

The  posterior  superior  tibio-fibular  ligament  (lig.  capituli  filjulte  anterius. 
Fig.  234)  is  a  similar,  but  weaker  band,  passing  upwards  and  inwards  from  the 
posterior  aspect  of  the  fibular  head  to  the  posterior  aspect  of  the  outer  tuberosity 
of  the  tibia,  where  they  are  attached  immediately  below  the  opening  in  the 
capsule  of  the  knee-joint,  from  which  the  tendon  of  the  popliteus  muscle  escapes. 

Equally  strong  but  much  shorter  bands  are  found  on  the  superior  and  inferior 
aspects  of  the  joint.  The  former  is  intimately  associated  with  the  tendon  of  the 
biceps  flexor  cruris  muscle  which  strengthens  the  upper  aspect  of  the  joint,  and 
here  also  is  found  the  occasional  opening  by  which  it  communicates  with  the  knee- 
joint. 

The  synovial  membrane  is  in  certain  cases  continuous  with  that  of  the  knee- 
joint  in  the  manner  already  described. 

The  interosseous  membrane  (membrana  interossea  cruris,  Figs.  234  and  237) 
plays  the  part  of  an  accessory  ligament  both  for  the  upper  and  the  lower  tibio-fibular 
joint.  It  is  attached  to  the  interosseous  borders  on  the  shafts  of  the  tibia  and 
fibula,  and  binds  them  together.  The  general  direction  of  its  fibres  is  from  the 
tibia  downwards  and  outwards  to  the  fibula,  but  many  fibres  pass  in  the  opposite 
direction.  The  membrane  may  extend  upwards  until  it  comes  into  contact  with 
the  ligaments  of  the  superior  tibio-fibular  joint,  but  there  is  always  a  vertical  oval 
aperture  in  its  upper  part  for  the  forward  passage  of  the  anterior  tibial  vessels. 
This  aperture  (Fig.  234),  which  is  about  one  inch  long,  adjoins  the  shaft  of  the 
fibula  at  a  point  rather  less  than  one  inch  below  its  head.  Towards  the  lower  end 
of  the  leg  the  distance  between  the  tibia  and  the  fibula  rapidly  diminishes,  and 
consequently  the  width  of  the  interosseous  membrane  is  correspondingly  reduced, 
so  that  it  is  tense  throughout  its  entire  length.  In  the  lower  part  of  the  membrane 
there  is  a  small  opening  ibr  the  passage  of  the  anterior  perforating  vessels.  There 
is  no  sharply-marked  demarcation  between  the  interosseous  membrane  and  the 
interosseous  ligament  which  connects  the  lower  ends  of  the  tibia  and  fibula — the 
one,  indeed,  may  be  said  to  run  into  the  other. 

The  inferior  tibio-fibular  joint  (syndesmosis  tibio-fibulare)  is  not  on  all 
occasions  pro^'ided  with  articular  cartilage,  so  that  it  may  either  be  a  separate  articu- 


THE  TIBIO-FIBULAK  JOINTS. 


505 


lation,  or  it  may  merely  preseut  a  series  of  ligaments  which  are  accessory  to  the  uukle- 
ioint,  because  it  is  clear  that,  under  any  circumstances,  the  object  aimed  at  in  this 
articulation  is  to  obtain  additional  security  for  the  ankle-joint.  The  articular  surface 
on  the  tibia,  when  present,  constitutes  a  narrow  articular  strip  on  the  outer  side  of 
the  lower  end  of  the  bone,  and  the  joint-cavity  is  practically  an  upward  extension 
of  the  ankle-joint.  The  corresponding  fibular  facet  is  continuous  with  the  ex- 
tensive articular  area,  by  means  of  which  the  fibula  articulates  with  the  astragalus. 
By  far  the  greater  part  of  the  opposing  surfaces  of  tibia  and  fibula  are,  however, 
non-articular  and  rough. 

The  supporting  ligaments  are  of  great  strength. 


Lower  end  of  shaft  uf  tibi 


Groove  on  internal  malleolui 
for  tendon  of  tibialis  posticus— nr-r 
tendon    "'    ' 

Trochlear  surface  of 
astragalus 


Internal  lateral  ligament 

Fibrous  sheath  for  tendon  of  flexoi 
longus  hallucis 

Sustentaculum  tab 

Flexor  longus  hallucis  tendon  (cut) 

Posterior  caleaneo-astragaloid  ligament 


1_-  Tibio-fibular  interosseous  meiiiVjrane 
Tjower  end  of  shaft  of  libula 


Posterior  inferior  tibio- 
tibular  ligament 

Transverse  inferior  tibio- 
fibular ligament 

Facet  on  astragalus  for 
transverse  inferior  tibio- 
iiliular  ligament 

Posterior  talo-iibular  ligament 
(posterior  fasciculus  of  external 
lateral  ligament) 


Calcaneo-ftbuiar  ligament 
(middle  fasciculus  of  external 
lateral  ligament) 


Tuberosity  of  os  calcis 


Fig.  237. — Ankle-Joint  Dissected  vhou  Behind  with  Part  ok  the  Capsular  Ligament  Removed. 

The  anterior  inferior  tibio-fibular  ligament  (lig.  malleoli  lateralis  anterius.  Fig. 
240)  consists  of  strong  fibres  which  pass  obliquely  downwards  and  outwards  from 
the  front  of  the  lower  end  of  the  tibia  to  the  front  of  the  external  malleolus. 

The  posterior  inferior  tibio-fibular  ligament  (lig.  malleoli  lateralis  posterius,  Figs. 
237  and  2.':i8;  is  equally  strong,  and  passes  in  a  similar  direction  between  corre- 
sponding posterior  surfaces. 

A  transverse  inferior  tibio-fibular  ligament  (Figs.  237  and  238)  stretches,  in  the 
direction  indicated  by  its  name,  between  the  posterior  inferior  border  of  the  tibia 
and  the  upper  end  of  the  pit  on  tlie  inner  and  posterior  aspect  of  the  external 
malleolus. 

An  interosseous  ligament,  jxnverful  and  somewhat  extensive,  connects  the  con- 
tiguous rough  ntjii-artioular  surfaces.  Sujjeriorly,  as  already  mentioned,  it  is  con- 
tinuous with  the  intercsseous  membrane.  Anteriorly  and  postericjrly  it  comes 
into  contact  with  the  more  superficial  ligaments.  Inferiorly  it  descends  until  it 
comes  into  intimate  asHOciation  with  the  joint-cavity. 
21 


306 


THE  AETICULATIONS  OE  JOINTS. 


A  synovial  membrane  is  found  lining  the  small  joint-cavity,  but  it  is  always  a 
direct  prolongation  from  that  which  lines  the  ankle-joint. 

JOINTS    OF   THE   FOOT. 


THE   ANKLE-JOINT. 

The  ankle-joint  (articulatio  talo-cruralis)  is  a  ginglymus  variety  of  a  diarthrosis. 
The  bones  which  enter  into  its  formation  are  the  lower  ends  of  the  tibia  and  fibula, 
with  the  articular  areas  on  the  upper,  lateral,  and  mesial  surfaces  of  the  astragalus. 
The  tibia  and  fibula,  aided  by  the  transverse  inferior  tibio-fibular  ligament,  form  a 
three-sided  socket  within  which  the  astragalus  is  accommodated.  The  roof  or 
highest  part  of  the  socket,  which  is  wider  in  front  than  behind,  is  formed  chiefly  by 
the  quadrilateral  articular  surface  which  characterises  the  lower  end  of  the  tibia, 
but  towards  its  postero-external  margin  the  transverse  inferior  tibio-fibular  liga- 
ment assists  in  its  formation.  Here  also  the  tibial  articular  surface  is  continuous 
with  the  narrow  articidar  facet  already  described  as  forming  part  of  the  inferior 
tibio-fibular  joint.  The  inner  wall  of  the  socket  is  formed  by  the  articular  facet  on 
the  outer  side  of  the  internal  malleolus,  and  there  is  no  interruption  of  the  articular 
cartilage  between  the  roof  and  inner  wall.  The  outer  wall  of  the  socket  is  quite 
separate  from  the  foregoing  parts,  and  consists  of  a  large  triangular  facet  upon  the 
inner  side  of  the  external  malleolus.  This  facet  is  situated  immediately  in  front  of 
the  deep  pit  which  characterises  the  posterior  part  of  this  surface  of  the  fibula. 

A  small  lunated  facet  is  frequently  found  upon  the  anterior  surface  of  tlie  lower  end  of  the 
tibia,  particularly  among  those  races  characterised  by  the  adoption  of  the  "  squatting '"  posture. 
When  this  facet  exists  it  is  continuous  with  the  anterior  margin  of  the  roof  of  the  socket,  and  it 
articulates  with  a  similar  facet  upon  the  upper  surface  of  the  neck  of  the  astragalus  in  the 
extreme  flexion  of  the  ankle-joint  which  "squatting"  entails. 

The  articular  surface  upon  the  body  of  the  astragalus  adapts  itself  to  the  tibio- 
fibular socket,  and  presents  articular  facets  corresponding  to  the  roof  and  sides  of 
the  socket.  Thus  the  superior  surface  of  the  astragalus  possesses  a  quadrilateral 
articular  area,  wider  in  front  than  behind,  distinctly  convex  in  the  antero-posterior 
direction,  and  slightly  concave  transversely.  In  addition,  towards  its  postero- 
external margin,  there  is  also  a  narrow  antero-posterior  facet  corresponding  to  the 
transverse  inferior  tibio-fibular  ligament.  The  articular  cartilage  of  this  upper 
surface  is  continued  without  interruption  to  the  tibial  and  fibular  sides  of  the  bone, 
although  the  margins  of  the  superior  area  are  sharply  defined  from  the  lateral 
facets,  the  outer  of  which  is  triangular  in  outline,  while  the  inner  is  pyriform,  but 
in  each  case  the  surface  is  vertical. 

Ligaments. — The  ligaments  form  a  complete  investment  for  the  joint,  i.e.  a 
capsule  in  which  the  individual  parts  vary  considerably  in  strength,  and  are 
described  under  separate  names. 

The  anterior  ligament  is  an  extremely  thin  membrane,  containing  very  few 
longitudinal    fibres.       It   extends   from    the   lower   border    of    the    tibia   to   the 

upper  border  of  the  head  of 

the    astragalus,    passing    in 

lateral  or     fj^-Qnt  of  a  pad  of  fat  which 

deltoid  Tin 

ligament  of  fills  up  the  liollow  abovc  the 

aiikle-ioint  i        n  ,-\      ,    i 

neck  01  that  bone. 

The  posterior  ligament 
is  attached  to  contigu- 
ous non- articular  borders 
of  the  tibia  and  astragalus. 
Many  of  its  fibres  radiate 
inwards  from  the  external 
malleolus.  This  aspect  of  the 
joint  is  strengthened  by  the 
strong,  well-defined,  trans- 
verse ligament  already  described  in  connexion  with  the  inferior  tibio-fibular  joint. 


All  tenor  talo 
fibular  lij;amei 
Articular  facet  on 
external  malleoU 


Anteiioi  mfeiior  tibio  fibular  ligament 
Internal 


Calcaneo-fibular 
ligament' 

Posterior  inferioi 

tibio-fibnlai 

ligament 

Posterior  talo-fibular 

ligament 

-Articular  Surfaces  of  Tibia  and  Fibula  which 
are  opposed  to  the  astragalus. 


Transverse  inferior 
tibio-fibular  ligament 


Synovial  pad  of  fat 


Fig.  238. 


THE  ANKLE-JOINT. 


307 


The  external  lateral  ligament  (Figs.  237,  238,  and  240)  is  very  powerful,  and  is 
divisible  into  three  fasciculi,  which  are  distinguished  from  each  other  by  names 
descriptive  of  their  chief  points  of  attachment. 

The  anterior  fasciculus  (lig.  talo-fibulare  anterius)  is  the  shortest.  It  extends 
from  the  anterior  border  of  the  external  malleolus  to  the  astragalus  immediately  in 
front  of  its  external  articular  surface. 

The  middle  fasciculus  (lig.  calcaneo-fibulare)  is  a  strong  and  rounded  cord.  It 
is  attached  by  one  end  to  the  front  of  the  tip  of  the  external  malleolus,  and  by 
the  other  to  the  outer  side  of  the  os  calcis,  immediately  above  the  groove  for  the 
peroneal  tendons. 

The  2^osterior  fasciculus  (lig.  talo-fibulare  posterius)  is  the  strongest.  It  runs 
transversely  between  the  lower  part  of  the  fibular  or  digital  fossa  on  the  inner 
aspect  of  the  malleolus  and  the  posterior  surface  of  the  astragalus,  where  it  is  attached 


Internal  malleolus 


Internal  lateral  or  deltoid 
lijjanient  of  the  ankle 

Tiochlear  surface  of  astragalus 

Groove  for  tendon  of  tibialis 
]josticus  muscle  on  inferior 
'  ilcaiieo-scaphoid  ligament 
/  Groove  and  tunnel  for  the 
tendon  of  flexor  longus 
hallucis  muscle 
Inner  tarso-  ^    ^^^^^^     -  -.x.         - .».,        .    -      .  -...>^ ,..-.         _/0s  calcis 

metatarsal  .joint 
(opened) 


Long  plantar  ligament 

Tendon  of  tibialis  posticus  muscle  (cut) 

Sustentaculum  tali 

Fig.  239. — Ankle  and  Tarsal-Joints  from  the  Tibial  Aspect. 

to  the  external  tubercle  and  the  adjoining  rough  surface.     Sometimes  this  tubercle 
is  detached  from  the  astragalus,  and  represents  a  separate  bone — the  os  trigonum. 

^^The  internal  lateral  ligament  (lig.  deltoideum,  Figs.  238  and  239)  has  the  general 
shape  of  a  delta,and  is  even  stronger  than  the  external  ligament.  It  is  attached  above 
to  a  m-irked  impression  on  the  lower  part  of  the  internal  malleolus,  and  below,  in  a 
continuous  layer,  to  the  scaphoid,  astragalus,  and  os  calcis.  In  it  we  may  recog- 
nise the  following  special  bands — {a)  the  lig.  talo-tihicde  anterius,  which  extends 
from  the  front  of  the  inner  malleolus  to  the  neck  of  the  astragalus ;  (&)  the  lig. 
talo-tihiale  'posterius,  stretching  between  the  back  of  the  inner  malleolus  and  the 
postero-internal  rough  surface  of  the  astragalus  ;  (c)  the  lig.  tihio -navicular e,  which 
extends  from  the  tiyj  of  the  inner  malleolus  to  the  inner  side  of  the  scaphoid ;  {d) 
the  lig.  calcaneo-tihicde,  which  extends  between  the  tip  of  the  inner  malleolus  and 
the  inner  side  of  the  Hiistentaculum  tali;  (e)  lig.  talo-tihiale  profundum,  which 
consists  of  deeyxjr  fibres  exttiuding  I'roiii  the  tip  of  the  internal  malleolus  ti3  the 
inner  side  of  the  ;istragaluH. 

Synovial  membrane  lines  tbe  capsular  ligament,  and,  as  already  described,  the 
joint-cavity  communicateB  directly  with  the  inferior  tibio-fibular  joint.  Both  at 
the  front  and  \y,)Mk  of  the  ankle-joint,  as  well  as  superiorly  in  the  angle  formed  })y 
the  three  bones,  the  synovial  membrane  covers  pads  of  fat. 


308 


THE  ARTICULATIONS  OR  JOINTS. 


Movements  at  the  Ankle-Joint. — In  the  erect  attitude  the  foot  is  placed  at  right  angles  to 
the  leg;  in  other  words,  tlic  ncniiiul  position  of  the  ankle-joint  is  flexion.  Those  movements 
which  tend  to  diminish  the  angle  so  formed  by  the  dorsum  of  the  foot  and  the  front  of  the 
leg  are  called  dorsiflexion,  while  those  which  tend  to  increase  the  angle,  i.e.  to  straighten  the 
foot  upon  the  leg,  are  called  extension.  As  a  matter  of  fact  neither  dorsiflexion  nor  extension 
is  ever  completcdy  carried  out,  and  the  range  of  movement  of  which  the  foot  is  capable  is  limited 
to  about  90".  These  movements  occur  about  an  oljliquely  transverse  axis,  as  is  indicated  by  the 
natural  outward  pointing  of  the  toes.  The  weight  of  the  body  falls  slightly  anterior  to  the  ankle- 
joint,  so  that  a  certain  amount  of  muscular  action  is  necessitated  in  order  to  maintain  the  foot  at 
right  angles  to  the  leg  ;  but  additional  stability  is  olitained  fi'om  the  obliquity  above  mentioned. 

When  the  foot  is  raised  from  the  ground,  muscular  action  tends  naturally  to  produce  a  certain 
amount  of  extension.  When  the  foot  is  extended,  as  in  standing  on  the  toes,  the  hinder  narrow 
part  of  the  astragalus  moves  forM'ards  into  the  wider  part  of  the  interval  ljet\\een  the  tibia  and 
tibula,  whereas  in  dorsiflexion,  as  in  raising  the  fore  part  of  the  foot  from  the  ground,  the  widest 
part  of  the  astragalus  is  forced  back  between  the  tibia  and  fibula  ;  but  notwithstanding  the  dif- 
ference between  these  two  movements,  the  fibula  remains  in  close  contact  with  the  astragalus  by 
reason  of  the  action  of  the  transverse  inferior  tibio-fibular  ligament  and  the  posterior  talo-fibular 
ligament,  so  that  lateral  movement  is  ^u'evented. 

It  is  doubtful  whether  lateral  movement  at  the  ankle-joint  can  be  obtained  by  any  natural 
movement  of  the  foot,  although  it  is  generally  believed  that  in  the  position  of  jiartial  extension 
a  small  amount  of  lateral  movement  may  be  produced  by  the  application  of  external  force. 
"  This  apparent  play  "  of  the  ankle-joint  cluring  extension  "  is  really  due  to  oscillation  of  the 
small  bones  of  the  foot  on  each  other,  largely  of  the  scaphoid  on  the  astragalus,  but  also  of  the 
cuboid  on  the  calcaneum.  Excessive  mobility  of  these  latter  is  restrained  by  an  important 
function  of  the  posterior  tubercle  of  the  cuboid  which  locks  into  a  notch  in  the  os  calcis" 
(Blake). 

INTERTARSAL  JOINTS. 

These  joints  (articulationes  intertarsese)  are  all  diarthroses  in  which  the  gliding 
movement  is  characteristic,  as  in  the  carpus.     With  the  view  of  obtaining  a  proper  con- 


Posterior  infpii 
tibio-fibular  h^aim 


Articwlav  surface  of  astnr,alu 
Posterior  fasciculus  of  extern  i 
lateral  ligainoiit  of  ankle 


Anteiioi  lufeii   i  tibio-libuhir  ligament 


Aiticul  u  -^urt  ice  of  astragalus 

■Vnterior  fasciculus  of  external  lateral  ligament 
ot  lukle 

1  01  sal  astiagalo  navicular  ligauiont 
y_         \stia^  ilo  na\iculai  joint 
^:^  Evt   L  ill  aneo  navicalar  ligament 


Middle  fasciculus  of  external 
lateral  ligament  of  ankle^ 
Posterior  talo-calcaneal 
ligament 
Os  calcis 


I)  isil  scapho-cuneiform 
qilio-cuboid  ligaments 
Ml  Idle  cuneiform 


1  xternal  cuneiform 


Cuboid 


iJorsal  calcaiieo-cuboiil  ligament 
L  ikaueo-cuboid  joint 
lendon  of  peroneus  longus 
'  Interosseous  tilo  calcaneU  ligament 

Tilo  calcineal  joint 
External  tilo  cakaueil  ligament 


Fig.  240.— Ligaments  on  the  Outkr  Asi'ect  of  the  Ankle-Joixt  and  on  the  Dorsum  of  the  Tarsus. 


ception  of  the  many  beautiful  mechanical  principles  involved  in  the  construction  of  the 
foot,  it  is  necessary  to  study  these  articulations  with  considerable  attention  to  detail. 

Articulatio  Talo-calcanea. — The  astragalus  and  os  calcis  articulate  with  each 
other  in  the  articulatio  talo-calcanea  or  calcaneo-astragaloid  joint. 

This  joint  is  situated  between  the  inferior  facet  on  the  body  of  the  astragalus 


INTEETAESAL  JOINTS. 


309 


Scaplioid  bom 


Inferior  calcaneo- 
scaphoid  ligament 
Internal  calcaneo- 
scaphoid  ligament 

Tendon  of  tibialis 

posticus  muscl 

(cut) 


Sustentaculum  tali ;  articular 
surface  for  astragalus 


Articular  surface  on 
scaphoid  for  head  of 
astragalus 

Inner  surface  of  external 
calcaneo-scaphoid  ligament 
External  calcaneo-scaphoid 


Interosseous  cal- 
caneo-astragaloid 
ligament 

Articular  surface 
on  OS  calcis  for 
body  of  astragalus 


Os  calcis 


and  a  corresponding  facet  on  the  upper  aspect  of  the  hinder  part  of  the  os  calcis. 
On  each  bone  the  articulation  is  limited  in  front  by  a  wide,  deep  groove  which 
runs  obliquely  across  each  bone  from  within  outwards  and  forwards. 

The  supporting  and  investing  ligaments  form  a  capsule,  consisting  for  the  most 
part  of  short  fibres,  but  the  joint  derives  additional  strength  from  the  external  and 
internal  lateral  ligaments  of  the  ankle-joint.  The  capsule  is  subdivided  into  the 
following  astragalo-calcaneal  or  talo-calcaneal  bands  : — 

The  anterior  talo-calcaneal  ligament  consists  of  a  band  of  short  fibres 
placed  immediately  in  relation  to  the  anterior  end  of  the  deep  groove  which 
bounds  the  articular  facets. 
They  are  attached  to  the 
antero  -  external  aspect  of 
the  neck  of  the  astragalus, 
from  which  they  extend 
downwards  to  the  adjacent 
superior  surface  of  the  os 
calcis. 

The  external  talo-cal- 
caneal ligament  (Fig.  240) 
is  in  continuity  with  the 
hinder  border  of  the  pre- 
ceding ligament,  and  it  is 
placed  parallel  to,  but  on 
a  deeper  plane  than,  the 
middle  fasciculus  of  the 
external  lateral  ligament 
of  the  ankle-joint.  It  con- 
sists of  short  fibres  passing 
between  the  adjacent  rough 
outer  margins  of  the  two 
bones. 

The  posterior  talo-cal- 
caneal ligament  (Fig.  240) 
closes  the  joint-cavity  on  its 
posterior  aspect.  It  consists  of  fibres  which  radiate  from  the  posterior  aspect  of 
the  external  tubercle  of  the  astragalus  to  the  upper  surface  of  the  os  calcis, 
immediately  behind  the  articular  facet. 

The  internal  talo-calcaneal  ligament  lies  oldiquely  on  the  inner  side  of  the  joint, 
and  consists  of  fibres  which  extend  from  the  inner  posterior  tubercle  of  the 
astragalus  to  the  hinder  roughened  border  of  the  sustentaculum  tali.  Some  of  its 
fibres  become  continuous  with  the  internal  calcaneo-scaphoid  ligament. 

The  interosseous  talo-calcaneal  ligament  (Fig.  240)  closes  the  antero-internal 
iispect  of  the  joint.  It  is  the  strongest  of  the  series  of  ligaments  entering  into  the 
capsule.  Compared  with  it  the  other  bands  are,  comparatively  speaking,  insigni- 
ficant. Its  attachments  are  to  the  bottom  of  each  groove,  so  that  it  occupies  the 
tarsal  canal  formed  by  these  opposing  grooves. 

A  synovial  membrane  lines  the  capsule,  and  it  is  distinct  from  other  tarsal 
synovial  inem l)ranes. 

Articulatio  Talo-calcaneo-navicularis. — This  is  one  of  the  most  important  of 
the  joints  of  the  foot,  not  only  because  the  astragalus  is  here  situated  in  relation 
to  the  summit  of  the  antero-posterior  arch  of  the  foot,  but  because  the  head  of 
the  astragalus  is  received  into  a  composite  socket  made  up  of  sustentaculum  tali, 
scaphoid,  and  the  inferior  or  internal  calcaneo-scaphoid  ligament. 

The  articular  suri'ace  on  the  head  of  the  astragalus  presents  anteriorly  a 
convex  rounded  facet  for  articulation  with  the  scaphoid,  inferiorly  a  convex  facet 
which  rests  upon  the  sustentaculum  tali,  and  intermediate  between  these  two  there 
is  a  triangular  facet  which  articulates  with  the  inferior  calcaneo-scaphoid  ligament. 
All  the.se  facets  are  in  continuity  with  each  other,  and  are  in  front  of  the  tarsal 
groove  on  the  under  surface  of  the  astragalus.     Occasionally  a  fourth  narrow  I'acet  is 


Fig.  241. — The  Composite  Articular  Socket  for  the  Head  oi-- 
THE  Astragalus. 


310 


THE  AETICULATIONS  OK  JOINTS. 


found  along  the  outer  and  hinder  part  of  the  articular  surface  of  the  head  of  the 
astragalus,  whereby  it  articulates  with  superior  or  external  calcaneo-scaphoid  ligament. 

The  scaphoid  or  navicular  bone  presents  a  shallow,  cup-shaped,  articular  cavity 
towards  the  head  of  the  astragalus. 

The  articular  surface  of  the  sustentaculum  tali  is  concave,  and  is  usually  marked 
off  into  two  fleets. 

Two  ligaments  play  an  iniY)ortant  part  in  binding  together  the  os  calcis  and 
the  scaplioid,  although  these  bones  do  not  directly  articulate ;  and  further,  these 
ligaments  provide  additional  articular  surfaces  for  the  head  of  the  astragalus. 
These  are  the  two  following : — 

(a)  The  inferior  or  internal  calcaneo-scaphoid  ligament  (Figs.  239  and  242)  is  an 


Tendon  of  insortion  of 
pproneus  longus  muscle 


Hasp  of  metatarsal  bone  of 

A  I      Inllux 


Plantar  Inter-metatarsal 
ligaments 


Plantar  cuboid  iid 


Plantar  cubo-cuneifonn  ligament 

■"' "1 

Tendon  of  peroneus  longus  musclt— 
Long  plantai  ligament 


Tendon  of  insertion  of 
tibialis  aiiticus  muscle 


Internal  cuneiform  bone 

Plantar  scaplio-cuneifonn 
ligament 


X  \    Tendon  of  tibialis  posticus 
^'     muscle 

dnove  for  tendon  of  tibialis 
"y    posticus  muscle 

Inferior  calcaneo-scaphoid 
li 'anient- 


''    ^s^j^^Intprnal  lateral  or  deltoid 
isanient  of  ankle 


Internal  malleolus 


Groove  for  tendon  of  flexor  longus 
hallucis  muscle 
Os  calcis 


Fig.  242. — Plantaij  Aspect  of  Tarsal  amd  Tarso-metataesal  Joints. 

extremely  powerful  fibro-cartilaginous  tie-band.  It  extends  between  the  anterior 
margin  of  the  sustentaculum  tali  and  the  inferior  surface  of  thescaphoid  bone.  Certain 
of  its  upper  fibres  radiate  upwards  on  the  inner  surface  of  the  scaphoid,  and  become 
continuous  with  the  tibio-navicular  portion  of  the  deltoid  ligament  of  the  ankle- 
joint.  The  plantar  aspect  of  this  ligament  is  in  contact  with  the  tendon  of  the 
tibialis  posticus  muscle,  through  which  the  head  of  the  talus  receives  great  support. 
Superiorly  it  contributes  an  articular  surface  which  forms  a  triangular  portion  of 
the  floor  of  the  composite  socket  in  which  the  head  of  the  talus  is  received. 

(6)  The  superior  or  external  calcaneo-scaphoid  ligament  (Fig.  241)  lies  deeply 
in  the  front  part  of  the  sinus  tarsi,  i.e.  the  interval  between  the  astragalus  and  os 
calcis.  Its  fibres  are  short,  and  extend  from  the  dorsal  surface  of  the  front  part  of 
the  OS  calcis,  immediately  to  the  outer  side  of  the  sustentacular  facet,  forwards  to 
the  outer  side  of  the  scaphoid  bone.     Frequently  the  ligament  presents  a  surface 


INTEETARSAL  JOIiNTS.  311 

which  articulates  with  the  head  of  the  astragalus,  and  in  these  cases  it  forms  a  part 
of  the  composite  socket. 

The  cavity  of  the  talo-calcaneo-navicular  joint  is  closed  posteriorly  by  the 
interosseous  talo-calcaneal  ligament  already  described.  On  its  inner  and  outer 
inferior  aspects  it  is  closed  by  the  calcaneo-scaphoid  ligaments. 

The  superior  and  lateral  aspects  are  covered  by  an  astragalo-scaphoid  membrane 
or  ligament.  This  ligament  is  thin,  and  extends  from  the  upper  non-articular  area 
on  the  head  of  the  astragalus  to  the  dorsal  surface  of  the  scaphoid  bone.  It  may 
be  subdivided  into  dorsal  (superiorj,  lateral  (external),  and  medial  (internal), 
astragalo-scaphoid  ligaments  (Fig.  239),  which,  with  the  calcaneo-scaphoid  and 
interosseous  talo-calcaneal  ligaments,  complete  the  capsular  investment  of  the  joint. 

A  distinct  synovial  membrane  lines  all  parts  of  the  capsule  of  the  joint. 

Articulatio  Calcaneo-cuboidea. — This  is  situated  between  the  anterior  concavo- 
convex  surface  of  the  os  calcis  and  the  posterior  similar  surface  of  the  cuboid. 

The  ligaments  which  invest  this  joint  constitute  a  calcaneo-cuboid  capsule,  whose 
parts  are  arranged  in  relation  to  the  four  non-articular  sides  of  the  cuboid  bone, 
and  are  especially  strong  upon  the  plantar  aspect,  in  relation  to  their  great  import- 
ance in  resisting  strains. 

The  internal  calcaneo-cuboid  ligament  occupies  part  of  the  interval  between 
the  astragalus  and  os  calcis — sinus  tarsi.  It  is  sometimes  called  the  interosseous 
calcaneo-cuboid  ligament,  and,  in  conjunction  with  the  superior  or  external 
calcaneo-scaphoid  ligament,  it  forms  a  V-shaped  structure,  of  which  the  single  end 
is  attached  to  the  os  calcis,  and  the  double  ends  separate  to  reach  contiguous 
areas  on  the  scaphoid  and  cuboid  respectively. 

The  dorsal  calcaneo-cuboid  ligament  (Fig.  240)  is  a  broad  portion  of  the  capsule 
extending  between  the  dorsal  surfaces  of  the  two  bones. 

The  external  calcaneo-cuboid  ligament  is  another  but  narrower  part  of  the 
capsule  which  extends  from  the  outer  aspect  of  the  os  calcis  to  the  outer  side  of 
the  cuboid,  immediately  behind  the  facet  on  the  tuberosity. 

The  inferior  calcaneo-cuboid  ligaments  are  two  in  number — a  superficial  and  a 
deep.  The  superficial  series  of  fibres,  the  long  plantar  ligament  (Fig.  "242),  is 
attached  to  the  under  surface  of  the  os  calcis  in  front  of  its  tuberosities.  It  forms 
a  long  powerful  structure  which  runs  forwards  to  be  fixed  to  the  under  surface  of  the 
cuboid  ridge,  but  many  of  its  fibres  pass  superficial  to  the  tendon  of  the  peroneus 
longus,  and  extend  to  the  bases  of  the  third,  fourth,  and  fifth  metatarsal  bones. 

The  deep  series  of  fibres,  the  short  plantar  ligament  (Fig.  242), is  distinctly  separated 
from  the  former  by  a  layer  of  areolar  tissue.  It  forms  a  broad  t)ut  short  band  of  great 
strength,  which  is  attached  to  the  under  surface  of  the  front  end  of  the  os  calcis, 
and  extends  to  the  under  surface  of  the  cuboid  just  behind  the  ridge.  Both  of 
these  ligaments  are  of  great  importance  in  maintaining  the  longitudinal  arch  of  the 
foot,  and  in  this  respect  are  only  second  to  the  inferior  calcaneo-scaphoid  ligaments. 

A  synovial  membrane  lines  the  capsule. 

Transverse  Tarsal  Articulation. — This  is  a  term  sometimes  applied  to  the 
astragalo-scaphoid  and  calcaneo-cuboid  joints.  These  articulations  do  not  com- 
municate with  each  other ;  and  although  there  is  an  occasional  direct  articula- 
tion between  the  scaphoid  and  cuboid,  it  does  not  constitute  an  extension  of  the 
transverse  tarsal  joint,  but  is  a  prolongation  from  the  series  of  scapho-cuneiform 
and  cuneo-cuboid  articulations. 

Nevertheless  there  is  always  a  eet  of  ligaments  which  bind  the  scaphoid  and 
cuboid  bones  together,  and  these  may  be  regarded  as  accessory  to  the  various 
transverse  tarsal  joints. 

The  dorsal  scapho-cuboid  ligament  (Fig.  240)  consists  of  short  oblique  fibres  which 
attach  tbe  contiguous  dorsal  surfaces  of  the  cuboid  and  scaphoid  bones. 

The  plantar  scapho-cuboid  ligament  is  transverse  in  direction,  and  extends 
between  adjaccMiL  ]»laiila,r  an;a,s  oi'  the  culioid  and  scaphoid  bones. 

The  interosseous  scapho-cuboid  ligament  int(!rvorieH  between  contiguous  surfaces 
of  t  lie  same  bones.  When  there  is  an  extension  of  the  scapho-cuneiform  joint  back- 
wards l>etweeri  the  scaphoid  and  cuboid,  it  is  situated  in  front  of  the  last-men- 
tioned ligament,  and  is  called  tlie  articulatio  scapho-cuboidea.     Around  this  joint 


312  THE  AKTICULATIONS  OE  JOINTS. 

the  preceding  ligaments  are  grouped.  Since,  however,  the  joint  is  inconstant  while 
the  ligaments  are  always  present,  it  is  preferable  to  consider  them  as  above  indicated. 

Scapho-cuneiform  Articulation  (articulatio  cuneo-navicularis). — This  joint  is 
situated  between  the  scaplioid  and  the  three  cuneiform  Ijones.  The  anterior  surface 
of  the  scaphoid  presents  facets  for  each  of  the  cuneiform  bones,  but  its  articular  surface 
is  not  interrupted.  These  facets  form  a  somewhat  convex  anterior  surface  which  fits 
into  the  shallow  articular  concavity  presented  by  the  proximal  ends  of  the  three 
cuneiform  bones.  This  joint  may  be  extended  by  the  occasioual  scapho-cuboid 
articulation  already  referred  to. 

The  capsule  is  composed  of  short,  strong  bands  which  are  distinctly  visible 
on  all  sides  except  towards  the  cuboid  bone,  where  the  joint  may  connnunicate 
with  the  cuneo-cuboid  and  scapho-cuboid  joints.  Anteriorly  the  joint  communi- 
cates with  the  intercuneiform  articulations.  The  dorsal  parts  of  the  capsule  are 
short  longitudinal  bands  termed  dorsal  scapho-cuneiform  ligaments  (Figs.  239  and 
240).  These  extend  without  interruption  to  the  inuer  aspect  of  the  joint. 
Interiorly  there  are  similar  bands,  known  as  plantar  scapho-cuneiform  ligaments, 
also  longitudinal  in  direction,  but  intimately  associated  with  offsets  Irom  the 
tendon  of  the  tibialis  posticus  muscle. 

The  synovial  membrane  which  lines  the  capsule  sends  prolongations  forwards  on 
each  side  of  the  middle  cuneiform  bone,  and  in  addition  it  often  communicates 
witii  the  cuneo-cuboid  joint  cavity,  and  it  always  communicates  with  the  scapho- 
cuboid  cavity  when  that  joint  exists. 

Intercuneiform  Articulations. — These  are  two  in  number,  and  exist  between 
adjacent  contiguous  surfaces  of  the  three  cuneiform  bones.  These  surfaces  are  partly 
articular  and  partly  non-articular.  The  small  size  of  the  middle  cuneiform  bone 
allows  the  internal  cuneiform  as  well  as  the  external  cuneiform  to  project  forwards 
beyond  it  on  both  sides,  and  therefore  the  articular  surfaces  turned  towards  the  middle 
cuneiform  are  not  entirely  occupied  by  that  bone.  They  form  a  recess  towards 
the  metatarsus,  into  which  the  base  of  the  second  metatarsal  bone  is  thrust. 

Dorsal  intercuneiform  ligaments  constitute  fairly  strong  transverse  '  bands 
which  extend  between  adjacent  dorsal  surfaces  and  invest  the  joint  cavities  in  this 
direction. 

The  plantar  or  interosseous  intercuneiform  ligaments  are  two  strong  bands 
which  pass  from  the  rough  non-articular  areas  on  opposite  sides  of  the  middle 
cuneiform  to  the  opposing  surfaces  of  the  inner  and  outer  cuneiform  bones.  These 
ligaments  shut  in  the  joint  cavities  inferiorly,  and  also  anteriorly  in  the  case  of  the 
outer  of  the  two  joints. 

The  synovial  membrane  is  an  extension  of  that  which  lines  the  scapho-cuneiform 
joint ;  but  while  it  is  restricted  to  the  outer  of  the  two  joints,  in  the  case  of  the 
inner  one  it  is  prolonged  still  farther  forward  to  the  tarso-metatarsal  series  of  joints. 

Cubo-cuneiform  Articulation. — This  occurs  between  the  rounded  or  oval  facets 
on  the  opposing  surfaces  of  tlie  cuboid  and  external  cuneiform. 

The  dorsal  cubo-cuneiform  ligament  is  a  flat,  somewhat  transverse  band  which 
closes  the  joint  on  its  superior  aspect,  and  extends  between  the  dorsal  surfaces  of 
the  two  bones. 

The  plantar  cubo-cuneiform  ligament  is  diificult  to  determine.  It  is  situated 
subjacent  to  the  long  plantar  ligament,  and  extends  between  adjacent  rough  svirfaces 
of  the  two  bones. 

The  interosseous  cubo-cuneiform  ligament  is  the  strongest.  It  closes  the  joint 
cavity  anteriorly,  and  is  attached  to  the  contiguous  non-articular  surfaces  of  the 
two  bones. 

The  synovial  membrane  is  frequently  distinct,  but  at  other  times  the  joint  cavity 
communicates  with  those  of  the  scapho-cuneiform  and  scapho-cuboid  articulations. 

Synovial  Membranes  of  the  Intertarsal  Joints. — Four  and  sometimes  five 
distinct  and  separate  synovial  membranes  may  thus  be  enumerated  in  connexion 
with  the  tarsal  articulations,  viz. :  (1)  talo-calcaneal;  (2)  talo-calcaneo-navicularis ; 
(3)  calcaneo-cuboid ;  (4)  ^  scapho-cuneiform  and  its  extensions ;  (5)  occasionally 
cubo-cuneiform. 


TAESO-METATARSAL  JOINTS.  313 


TARSO-METATARSAL  JOINTS. 

The  tarso-metatarsal  joints  are  found  between  certain  articular  facets  on  the 
cuboid  and  three  cuneiform  bones  on  the  one  hand,  and  others  on  the  bases  of  the 
five  metatarsal  bones.  These  articulations  are  associated  with  three  distinct 
synovial  cavities — namely,  an  inner,  middle,  and  outer. 

(1)  The  inner  tarso-metatarsal  articulation  occurs  between  the  distal  convex 
reuiform  surface  of  the  internal  cuneiform  bone  and  the  concavo-reniform  surface 
on  the  proximal  aspect  of  the  base  of  the  first  metatarsal  bone. 

Ligaments  which  form  a  capsule  surround  the  articulation.  In  the  capsule  the 
dorsal  and  plantar  tarso-metatarsal  bands  are  its  strongest  parts,  but  it  is  not 
deficient  either  on  the  inuer  or  on  the  outer  aspects. 

A  separate  synovial  membrane  lines  the  capsule. 

(2)  The  middle  tarso-metatarsal  articulation  is  an  elaborate  joint.  It 
involves  the  three  cuneiform  bones  and  the  bases  of  the  second,  third,  and  part  of 
the  fourth  metatarsal  bones. 

The  articulation  presents  the  outline  of  an  indented  parapet  both  on  its  tarsal 
and  its  metatarsal  aspects.  Thus,  on  its  tarsal  side,  the  inner  and  the  outer  cunei- 
form bones  project  in  front  of  the  middle  cuneiform,  so  that  the  latter  only  presents 
a  distal  surface  to  the  articulation ;  while  the  internal  cuneiform  presents  a  portion 
of  its  external  surface,  and  the  external  cuneiform  presents  ?joth  its  distal  and 
portions  of  its  outer  and  inner  surfaces,  since  it  projects  in  front  of  the  cuboid 
bone.  On  its  metatarsal  side  the  base  of  the  second  metatarsal  bone  fits  into  the 
indentation  between  the  outer  and  inner  cuneiforms,  to  which  it  presents  external 
and  internal  articular  facets,  but  its  proximal  facet  rests  upon  the  distal  facet  of  the 
middle  cuneiform.  The  base  of  the  third  metatarsal  bone  rests  its  proximal  facet 
upon  the  outer  cuneiform.  The  fourth  metatarsal  base  presents  part  of  its  internal 
facet  to  the  external  side  of  the  outer  cuneiform.  In  this  way  the  indentations 
alternate  on  the  two  sides  of  the  articulation,  and  an  extremely  powerful  interlock- 
ing of  parts  is  provided,  which  places  any  marked  independent  movement  of  these 
metatarsal  iDones  entirely  out  of  the  question. 

The  dorsal  tarso-metatarsal  ligaments  are  broad,  flat  bands  which  represent  the 
most  distinct  part  of  an  investing  capsule.  They  pass  from  behind  forwards,  and 
while  the  second  metatarsal  bone  receives  three,  i.e.  one  from  each  cuneiform,  the 
third  metatarsal  only  receives  one — from  the  external  cuneiform. 

The  plantar  tarso-metatarsal  ligaments  correspond  with  the  foregoing  in  their 
general  arrangement,  but  they  are  weaker.  That  for  the  second  metatarsal  is  the 
strongest.  Oblique  bands  extend  from  the  inner  cuneiform  bone  to  the  second 
and  third  metatarsals. 

The  interosseous  cuneo-metatarsal  ligaments  are  three  in  number.  The  inner 
connects  the  outer  side  of  the  internal  cuneiform  with  the  inner  side  of  the  base  of 
the  second  metatarsal  bone.  The  middle  connects  the  inner  side  of  the  external 
cuneiform  with  the  outer  side  of  the  base  of  the  second  metatarsal.  The  outer 
connects  the  adjacent  outer  sides  of  the  external  cuneiform  and  third  metatarsal. 

The  synovial  membrane,  which  lines  this  articulation,  sends  a  prolongation  back- 
wards between  the  inner  and  middle  cuneiform  bones,  where  it  opens  into  the 
scayjho-cuneiform  joint.  It  is  likewise  prolonged  forwards  upon  both  sides  of  each 
of  the  bases  of  the  second  and  third  metatarsal  bones. 

(3)  The  external  tarso-metatarsal  articulation  is  found  between  the  proximal 
surfaces  of  the  bases  of  the  fourth  and  fifth  metatarsal  bones  and  the  distal  surface 
of  the  cuboid. 

The  investing  capsule  may  bo  resolved  into  the  following  ligaments : — 
The  dorsal  tarso -metatarsal  ligaments   rcsein))le  those  already  descriljed.     The 
base  of  the  fourth  metatarsal  receives  one  froin  tlie  external  cuneiform  and  one 
from  the  cuboid.     The  base  of  the  fifth  metatarsal  receives  one  from  the  cuboid. 

The   plantar   tarso-metatarsal   ligaments  are  the  wealcest  bands  of  the  series, 
and    corisiHt   of   scattered    filjrcs   ])aHsing    from   the  cuboid    to    the    bases   of   the 
two   metatarsals.     Some    fibres,   which   are   almost   transverse,  extend   from    the 
22 


314  THE  ARTICULATIONS  OE  JOINTS. 

external  cuneiform  to  the  fifth  metatarsal,  and  additional  filjres  reach  the  meta- 
tarsals in  question  from  the  long  plantar  ligament  (calcaneo-cuboid). 

Occasionally  the  tarsal  end  of  the  external  interosseous  (cuneo-metatarsal)  liga- 
ment is  attached  to  the  inner  margin  of  the  culjoid. 

The  synovial  membrane  is  restricted  to  this  articulation,  and  merely  sends  a 
prolongation  forwards  between  the  opposing  articulate  aspects  of  the  fourth  and 
fifth  metatarsal  bases. 

INTERMETATARSAL  JOINTS. 

The  intermetatarsal  articulations  are  found  between  adjacent  lateral  aspects  of 
the  bases  of  the  four  outer  metatarsal  bones.  The  articular  facets  are  small,  oval, 
or  rounded  surfaces  which  occupy  only  a  limited  portion  of  the  flattened  contiguous 
surfaces  of  the  bones.  Each  joint  is  provided  with  a  capsule,  which,  however,  is  not 
a  complete  investment,  because  the  three  joint  cavities  are  in  free  communication 
on  their  proximal  aspects  with  the  tarso-metatarsal  joint  cavities — one  with  the 
outer  and  two  with  the  middle.  The  definite  fibres  of  each  capsule  are  situated 
chiefly  in  the  transverse  direction. 

The  dorsal  ligaments  are  short  bands  which  extend  from  one  base  to  the  other. 

The  plantar  and  interosseous  ligaments  are  similarly  arranged,  but  the  latter  are 
the  strongest  and  most  important  members  of  this  series. 

The  synovial  membranes  are  extensions  from  those  which  line  the  outer  and 
middle  tarso-metatarsal  joint  cavities. 

Frequently  a  bursa  is  found  between  the  bases  of  the  first  and  second  metatarsal  bones.  It 
produces  an  apj^earance  of  indistinct  facetting  upon  these  bones,  and  it  may  communicate  with 
the  inner  tarso-metatarsal  (cuneo-metatarsal)  joint. 

The  transverse  metatarsal  ligament  lies  upon,  and  is  attached  to,  the  non- 
articular  plantar  aspects  of  the  heads  of  all  the  metatarsal  bones.  It  differs 
from  the  corresponding  ligament  in  the  palm  in  the  fact  that  it  binds  all  the 
metatarsal  bones  together,  whereas  in  the  palm  the  thumb  is  left  free.  It  is 
closely  associated  with  the  plantar  fibrous  plates  of  the  metatarso-phalangeal  joints, 
to  the  plantar  surfaces  of  which  it  contributes  prolongations  termed  ligamenta 
accessoria  plantaria. 

METATARSO-PHALANGEAL  JOINTS. 

Each  of  these  joints  is  a  modified  ball-and-socket  in  which  a  shallow  cup  upon  the 
bases  of  the  first  phalanges  receives  the  somewhat  globular  head  of  a  metatarsal  bone. 

Each  joint  retains  a  modified  capsule  which  invests  the  joint.  Its  only  distinct 
bands  are  the  ligamenta  collateralia.  These  are  strong  cord-like  bands  which  are 
situated  on  the  inner  and  outer  sides  of  each  joint,  where  they  extend  between 
adjacent  rough  surfaces. 

On  the  dorsal  aspect  ligaments  distinct  from  the  dorsal  expansion  of  the  ex- 
tensor tendons  can  hardly  be  said  to  exist.  The  plantar  aspect  of  the  capsule 
consists  of  a  thick  fibrous  plate,  which  in  the  case  of  the  great  toe  presents 
developed  within  it  two  large  sesamoid  bones.  In  the  other  toes  this  plate  remains 
fibrous  throughout,  and  is  grooved  on  its  plantar  aspect  for  the  accommodation  of 
the  long  flexor  tendons.  It  will  thus  be  seen  that  the  metatarso-phalangeal  joints  are 
constructed  upon  a  plan  very  similar  to  that  of  the  corresponding  joints  in  the  hand. 

A  synovial  membrane  lines  the  capsule  of  each  articulation. 

INTERPHALANGEAL  JOINTS. 

Each  toe  possesses  two  interphalangeal  joints  except  the  great  toe,  which  has 
only  one.  Not  unfrequently  in  the  little  toe  the  distal  joint  is  obliterated  through 
ankylosis.  All  the  joints  of  this  series  are  uniaxial  or  hinge  joints.  The  nature 
of  the  articular  surfaces  closely  resembles  the  corresponding  joints  in  the  fingers. 

Each  joint  possesses  a  capsule  which  is  either  very  thin  or  limited  to  synovial 
membrane  on  the  dorsal  aspect.     The  plantar  surface  of  the  capsule  is  strength- 


INTERPHALANGEAL  JOINTS.  315 

ened  by  a  fibrous  plate.  The  lateral  ligaments  (ligamenta  collateralia)  are  well- 
defined  bands  similar  to  those  already  described  in  connexion  with  the  metatarso- 
phalangeal joints. 

A  synovial  membrane  lines  each  capsule  in  the  series. 

Mechanism  of  the  Foot. — The  bones  of  tbe  foot  are  arranged  in  the  form  of  a  longitudinal 
and  a  transverse  arch.  The  longitudinal  arch  is  built  on  a  very  remarkable  plan.  Posteriorly 
the  mass  of  the  os  calcis  constitutes  a  rigid  and  stable  pier  of  support,  while  anterioi'ly,  by  increasing 
the  number  of  component  parts,  the  anterior  pier  acquires  great  flexibility  and  elasticity  without 
sacrificing  strength  or  stability.  The  summit  of  the  arch  is  formed  by  the  astragalus,  which 
receives  the  weight  of  the  body  from  the  tibia,  and  the  resilience  of  the  arch  is  assured  by  the 
calcaneo-scaphoid  and  calcaneo-cuboid  ligaments,  together  with  the  plantar  fascia,  which  act  as 
powerful  braces  or  tie  bands,  preventing  undue  separation  of  the  piers  of  the  arch,  and  consequent 
flattening  of  the  foot.  The  weight  of  the  body  is  distributed  over  all  the  five  digits,  owing  to 
the  arrangement  of  the  bones  of  the  foot  in  two  parallel  columns,  an  inner  and  an  outer.  The 
former,  consisting  of  the  astragalus,  scaphoid,  and  the  three  cuneiforms,  with  the  three  inner 
metatarsal  bones,  distributes  weight  through  the  talo-scaphoid  joint,  while  the  latter  {i.e.  the 
outer  column),  comprising  the  calcaneum,  cuboid,  and  the  two  outer  metatarsal  bones,  acts  in  a 
similar  manner  through  the  talo-calcanean  joint.  The  main  line  of  immobility  of  this  arch 
passes  from  the  heel  forwards  through  the  middle  toe,  but  its  anterior  section,  which  is  slender, 
is  supported  on  either  side  by  two  metatarsal  bones,  with  their  proximal  tarsal  associations,  in 
all  of  which  greater  freedom  of  movement  is  found.  The  transverse  arch  is  most  marked  at  the 
level  of  tarso-metatarsal  articulations.  The  intersection  of  these  two  arches  at  right  angles  to 
each  other  introduces  an  architectural  feature  of  great  importance  in  connexion  with  the 
support  of  heavy  weights.  These  longitudinal  and  transverse  arches  of  the  foot  are  in  effect 
"  vaults  "  intersecting  each  other  at  right  angles,  and  in  relation  to  the  area  which  is  common  to 
both  "  vaults "  the  body  weight  is  superposed  exactly  as  the  dome  of  a  cathedral  is  carried 
upon  two  intersecting  vaults. 

Movements  at  the  Joints  of  Tarsus,  Metatarsus,  and  Phalanges. — Considered  in  detail, 
the  amount  of  movement  which  takes  place  between  any  two  of  these  bones  is  extremely  small, 
and,  so  far  as  the  tarsus  and  metatarsus  are  concerned,  it  is  mostly  of  the  nature  of  a  gliding 
motion. 

At  the  metatarso -phalangeal  and  interphalangeal  joints  movement  is  much  more  free,  and 
is  of  the  nature  of  flexion  (bending  of  the  toes  towards  the  sole  of  the  foot,  i.e.  plantar  flexion) 
and  extension.  The  latter  movement  when  continued  so  as  to  raise  the  toes  from  the  ground, 
and  bend  or  approximate  them  towards  the  front  of  the  leg,  is  termed  dorsiflexion.  Coincident 
with  dorsiflexion  there  is  always  associated  a  certain  amount  of  spreading  of  the  toes,  which  is 
called  abduction,  and  similarly  with  prolonged  flexion  there  follows  a  diminution  or  narrowing 
of  the  transverse  diameter  of  the  front  part  of  the  foot  by  drawing  the  toes  together — a  move- 
ment termed  adduction.  In  the  foot  the  movements  of  abduction  and  adduction  take  place  in 
regard  to  a  plane  which  bisects  the  foot  antero-posteriorly  through  the  second  toe,  for  this  toe 
carries  the  first  and  second  dorsal  interosseous  muscles. 

Notwithstanding  the  small  amount  of  possible  movement  in  connexion  with  individual 
tarsal  and  metatarsal  joints,  yet  the  sum  total  of  these  movements  is  considerable  as  regards  the 
entire  foot.  In  this  way  the  movements  of  inversion  and  eversion  of  the  foot  result.  By 
inversion  we  mean  the  raising  of  the  inner  border  of  the  foot  so  that  the  sole  looks  inwards, 
while  the  toes  are  depressed  towards  the  ground,  and  the  outer  border  of  the  foot  remains  down- 
wards. This  takes  place  chiefly  at  the  talo-calcanean  joint,  but  the  transverse  tarsal  joints  also 
participate. 

Eversion  is  chiefly  the  opposite  of  inversion,  and  the  return  of  the  foot  to  the  normal  position 
of  the  erect  attitude ;  but  under  certain  conditions  it  may  be  carried  further,  so  that  the  outer 
border  of  the  foot  is  raised  from  the  ground,  while  the  inner  border  is  depressed.  In  both  of  these 
movements  thei-e  is  rotation  between  the  astragalus  and  os  calcis  about  an  oblique  axis  which 
passes  from  the  inner  side  of  the  neck  of  the  astragalus  to  the  outer  and  lower  part  of  the  os 
calcis. 

Of  course  all  the  movements  of  the  foot  are  subordinated  to  its  primary  functions  as  an  organ 
of  support  and  progression.  For  these  purposes  its  longitudinal  and  transverse  arches  are  of 
extreme  importance.  The  longitudinal  arch  resting  on  the  os  calcis  behind  and  the  heads  of 
the  metatarsal  bones  in  front  receives  the  weight  of  the  body,  as  already  exjalained,  on  the  summit 
of  the  astragalus  in  the  line  of  the  third  toe.  Hence  it  is  that  the  inner  malleolus  ajii^ears  to  be 
unduly  proMiinent  on  the  inner  side  of  the  ankle.  The  transverse  arch  buttresses  the  longitudinal 
one,  and  tlierefore,  whetlier  the  body  weight  fall  to  the  outer  or  tlie  inner  side  of  the  longitudinal 
arch,  it  is  supported  Ijy  a  mechanism  at  once  stable,  flexible,  and  elastic,  or  resilient,  and  capable 
of  reducing  to  a  minimum  all  jars  that  may  be  received  by  the  fore-part  of  the  foot.  As  the  heel 
is  raised  in  the  act  of  walking,  the  weight  is  gradually  transferred  from  the  outer  to  the  inner 
side  of  the  foot,  until  the  foot  finally  leaves  the  ground  with  a  propulsive  movement,  which 
results  froiri  flexion  of  the  phalanges  of  the  great  toe.  In  this  connexion  it  is  worthy  of  note 
that  the  longitudinal  line  of  greatest  strength  is  on  the  inner  side  of  the  longitudinal  arch,  i.e. 
in  I'elution  to  the  great  toe. 
22  a 


THE   MUSCULAR   SYSTEM. 

MYOLOGY. 

By  A.  M.  Paterson. 

The  movements  of  the  various  parts  and  organs  of  the  body  are  brought  about  by 
the  agency  of  muscle-cells,  which  are  characterised  by  a  special  histological  structure 
and  by  the  special  function  of  contracting  in  length  under  the  influence  of  a  proper 
stimulus. 

There  are  three  classes  of  muscle-cells  :  (1)  the  striated,  and  usually  voluntary 
muscle-cells,  out  of  which  the  skeletal  muscular  system  is  constructed  ;  (2)  the  non- 
striated,  involuntary  muscle-cells,  occurring  in  the  walls  of  vessels  and  hollow 
viscera,  etc. ;  and  (3)  the  cardial  muscle-cells,  striated  but  involuntary,  of  which  the 
substance  of  the  heart  is  composed. 

The  following  section  deals  solely  with  the  skeletal  muscles,  the  structure, 
arrangement,  and  mechanical  action  of  which  are  based  upon  a  common  plan. 

The  cells  of  which  the  skeletal  muscles  are  composed  are  long,  narrow,  and 
characterised  by  a  peculiar  striation,  which  is  different  from  the  striation  of 
the  muscle-cells  of  the  heart ;  they  also  differ  both  in  structure  and  function 
from  the  non-striated  muscle-cells  which  occur  in  viscera  and  vessels. 

A  typical  skeletal  muscle  consists  of  a  fleshy  mass  enveloped  in  a  membranous 
aponeurosis  or  fascia,  and  provided  at  its  extremities  or  borders  with  membranous 
or  tendinous  attachments  to  bone,  cartilage,  or  fascia. 

Each  muscle  is  made  up  of  a  number  of  fasciculi  or  bundles,  arranged  together 
in  different  muscles  in  different  ways,  so  as  to  give  rise  to  the  particular  form  of 
the  muscle  in  question.  These  fasciculi  are  connected  together  by  a  dehcate 
connective  tissue,  the  perimysium  externum,  continuous  externally  with  the 
aponeurosis  enclosing  the  muscle. 

Each  muscular  bundle  or  fasciculus  is  composed  of  a  number  of  narrow,  elon- 
gated muscle-cells  or  fibres,  held  together  by  a  still  more  delicate  connective  tissue, 
the  perimysium  internum.  This  tissue  is  connected  on  the  one  hand  with  the  sarco- 
lemma  or  cell-wall  of  the  muscle-cell^  and  on  the  other  hand  with  the  coarser 
tissue  of  the  perimysium  externum  enclosing  the  muscular  bundles. 

By  means  of  these  connective  tissue  envelopes  the  muscle-cells,  the  essential 
agents  of  motor  activity,  are  brought  into  firm  and  intimate  relation  with  the 
osseous  or  other  attachments  of  the  muscle.  Through  the  agency  of  sarcolemma, 
perimysium  internum,  perimysium  externum,  aponeurosis,  and  tendon,  the  muscle- 
cell  when  it  contracts  can  produce  a  precise  and  definite  effect  upon  the  weight  to 
be  moved. 

Each  muscle  is  supplied  by  one  or  more  nerves,  which,  in  their  course 
through  the  muscle,  separate  into  smaller  and  smaller  branches,  ultimately,  by 
their  terminal  filaments  (axons),  forming  special  end-organs  in  relation  to  each 
muscle-cell. 

While  a  muscle  may  thus  be  looked  upon  as  an  organ  endowed  with  particular 
properties,  and  executing  a  definite  movement  in  response  to  a  stimulus  by  the 
simultaneous  contraction  of  its  constituent  cells,  the  various  muscles  may  further 
be  considered  in  groups,  associated  together  by  mode  of  development,  nerve-supply, 
and  co-ordination  of  action.     For  example,  we  speak  of  the  hamstring  muscles  of 

316 


MYOLOGY.  317 

the  thigh,  the  muscles  of  the  back,  and  the  pr&evertebral  muscles — groups  iu  which 
separate  muscles  are  associated  together  by  development,  nerve-supply,  and  action. 
In  their  development  the  separate  muscles  arise  from  the  subdivision  of  a  larger 
stratum,  as  in  the  limbs,  or  from  the  fusion  of  segmental  elements  (myotomes),  as  in 
the  case  of  the  axial  muscles ;  the  peripheral  nerves  supplying  skeletal  muscles  are 
distributed,  through  the  plexuses  or  directly,  so  as  to  associate  particular  muscles 
morphologically  and  physiologically,  and  to  secure  a  co-ordinated  movement  by  the 
simultaneous  contraction  of  several  muscles  together. 

FASCI.E. 

Beneath  the  skin  there  are  two  (or  in  some  regions  three)  layers  of  tissue  which 
require  consideration :  the  superficial  fascia  (panniculus  adiposus),  the  deep  fascia 
(fascia  lata),  and,  in  animals,  the  panniculus  carnosus  (rudimentary  in  man,  and 
represented  chiefly  by  the  platysma  myoides  in  the  neck). 

Superficial  Fascia. — The  superficial  fascia  is  a  continuous  sheet  of  areolar 
tissue  which  underlies  the  skin  of  the  whole  body.  It  is  closely  adherent  to  the 
cutis  vera,  and  is  sometimes  termed  panniculus  adiposus,  from  the  fact  that,  except 
beneath  the  skin  of  the  eyelids,  penis,  and  scrotum,  it  is  always  more  or  less 
impregnated  with  fat.  It  is  traversed  by  the  cutaneous  vessels  and  nerves ;  and 
its  deep  surface,  membranous  in  character,  is  in  loose  connexion  with  the  subjacent 
deep  fascia.     It  is  in  this  layer  that  dropsical  effusions  chiefly  occur. 

Deep  Fascia. — Underneath  the  skin  and  superficial  fascia  is  a  fibrous 
membrane,  bluish  white  in  colour,  devoid  of  fat,  and  in  closest  relation  to  skeleton, 
ligaments,  and  muscles.  This  is  the  deep  fascia.  It  covers,  invests,  and  in  some 
cases  forms  the  means  of  attachment  of  the  various  muscles.  It  has  a  special 
tendency  to  become  attached  to  all  subcutaneous  bony  prominences,  and  to  be 
continuous  with  the  connecting  ligaments.  It  forms  septal  processes,  which 
separate  groups  of  muscles  and  individual  muscles ;  enclose  glands  and  viscera ; 
and  form  sheaths  for  vessels  and  nerves.  Around  joints  it  gives  rise  to  bands 
which  strengthen  the  capsule  or  limit  the  mobility  of  the  joint,  or,  as  in  the  case 
of  annular  ligaments,  bind  down  the  tendons  passing  over  the  joint.  It  not  only 
ensheathes  vessels  and  nerves,  but  is  perforated  by  those  which  pass  between  super- 
ficial and  deeper  parts. 

The  term  aponeurosis  is  used  in  relation  to  muscles.  It  is  synonymous  with  deep 
fascia,  either  as  an  investing  fascia,  or  as  a  membranous  layer  which  {e.g.  vertebral 
aponeurosis)  performs  at  one  and  the  same  time  the  purpose  of  a  deep  fascia  and 
the  expanded  membranous  attachment  of  a  muscle. 

The  panniculus  carnosus  is  a  thin  muscular  layer  enveloping  the  trunk  of 
animals  with  a  hairy  or  furry  coat.  It  is  strongly  developed  in  the  hedgehog.  In 
man  it  is  represented  mainly  in  the  (rudimentary)  platysma  myoides.  It  is  placed 
between  the  superficial  and  the  deep  fascia. 

Bursae. — ^Where  a  tendon  passes  over  a  bony  surface,  or  where  the  superficial 
fascia  and  skin  cover  a  bony  prominence,  there  is  generally  formed  a  synovial 
sac,  or  bursa,  containing  fluid,  for  the  purpose  of  lubricating  the  surface  over 
which  the  tendon  or  fascia  glides.  Allied  to  these  are  the  synovial  sheaths 
which  envelop  tendons  beneath  the  annular  ligaments  in  relation  to  the  several 
joints. 

Description  of  Muscles. — In  studying  the  muscular  system  it  is  necessary  to 
note  the  following  characters  in  reference  to  each  individual  muscle  :  (1)  The  shape 
of  the  muscle — flat,  cylindrical,  triangular,  rhomboidal,  etc. — and  the  character  of 
its  extremities — membranous,  tendinous,  or  fleshy.  (2)  The  attachments  of  the 
muscle.  The  orir/in  is  the  more  fixed  or  central  attachment :  the  insertion  is  the 
more  movaljle  or  peri])])oral  attachment.  (3)  The  relations  of  the  surfaces  and 
borders  of  the  musch;  to  bones,  joints,  other  muscles,  and  other  important  structures. 
(4)  Its  vascular  iiud  nervous  supply ;  and  (5)  its  action.  It  must  be  borne  in  mind 
that  hardly  any  single  muscle  acts  alone.  Each  muscle,  as  a  rule,  forms  one 
of  a  group  acting  more  or  less  in  harmony  with,  and  antagonised  by,  other  and 
opposite  groups. 
22  & 


318  THE  MUSCULAE  SYSTEM. 

DESCRIPTION  OF  THE  MUSCLES. 

The  skeletal  muscles  may  be  divided  into  two  series  :  axial  and  appendicular. 
The  axial  muscles  comprise  the  muscles  of  the  trunk,  head,  and  face,  including 
the  panniculus  carnosus  (platysma  myoides).  These  muscles  are  more  or  less 
segmental  in  arrangement,  grouped  around  the  axial  skeleton.  The  appendicular 
muscles,  the  muscles  of  the  limbs,  are  grouped  around  the  appendicular  skeleton. 
They  are  not  segmental  in  arrangement,  they  are  clearly  separate  from  the 
axial  muscles,  and  they  are  arranged  in  definite  strata  in  relation  to  the  bones  of 
the  limbs. 

APPENDICULAR  MUSCLES. 

THE  UPPER  LIMB. 
FASCIA  AND  SUPERFICIAL  MUSCLES  OF  THE  BACK. 

Fascia. 

The  superficial  fascia  of  the  back  presents  no  peculiarity.  It  is  usually 
of  considerable  thickness,  and  contains  a  quantity  of  fat. 

The  deep  fascia  closely  invests  the  muscles.  It  is  attached  in  the  middle  line 
of  the  back  to  the  ligamentum  nuchse,  supraspinous  ligaments,  and  vertebral  spines  ; 
laterally  it  is  attached  to  the  spine  of  the  scapula  and  the  clavicle,  and  is  continued 
over  the  deltoid  region  to  the  arm.  In  the  neck  it  is  attached  above  to  the 
superior  curved  line  of  the  occipital  bone,  and  is  continuous  laterally  with  the  deep 
cervical  fascia.  Below  the  level  of  the  arm  it  is  continuous  round  the  border  of  the 
latissimus  dorsi  muscle,  with  the  fascia  of  the  axilla  and  of  the  abdominal  wall. 
In  the  back  and  loin  it  constitutes  the  vertebral  aponeurosis  or  aponeurosis  of  the 
latissimus  dorsi.  It  conceals  the  erector  spiufe  muscle,  forming  the  posterior  layer  of 
the  lumbar  fascia,  and  it  is  attached  internally  to  the  vertebral  spines,  and  externally 
to  the  angles  of  the  ribs,  to  the  lumbar  fascia,  and  to  the  iliac  crest. 

The  Superficial  Muscles  of  the  Back. 

The  muscles  of  the  back  are  arranged  in  four  series  according  to  their  attach- 
ments: (1)  vertebro-scapularand  vertebro-humeral;  (2)  vertebro-costal;  (3)vertebro- 
cranial ;  and  (4)  vertebral.  The  first  of  this  series  consists  of  the  posterior  muscles 
connecting  the  upper  limb  to  the  trunk,  and  comprises  the  first  two  layers  of  the 
muscles  of  the  back — (1)  trapezius  and  latissimus  dorsi,  and  (2)  levator  anguli 
scapuhe  and  rhomboidei  (major  and  minor).  The  deeper  (axial)  muscles  of  the  back 
are  dealt  with  later. 

The  trapezius  (m.  trapezius,  cucullaris)  is  a  large  triangular  muscle  occupying  the 
upper  part  of  the  back.  It  arises  from  the  superior  curved  line  of  the  occipital  bone 
in  its  inner  third,  from  the  external  occipital  protuberance  (Fig.  312,  p.  397),  from 
the  ligamentum  nuchse,  from  the  spines  of  the  seventh  cervical  and  all  the  thoracic 
vertebrae,  and  the  corresponding  supra-spinous  ligaments.  The  origin  is  by  direct 
fleshy  attachment,  except  in  relation  to  the  occipital  bone,  the  lower  part  of  the 
neck,  and  the  lower  thoracic  vertebrse,  in  which  places  the  origins  are  tendinous. 
From  their  origin  the  muscular  fibres  converge  towards  the  bones  of  the  shoulder, 
to  be  inserted  conti-nously  from  before  backwards  as  follows:  (1)  The  occipital 
and  upper  cervical  fibres — into  the  posterior  surface  of  the  clavicle  in  its  outer 
third  (Figs.  243,  p.  319,  and  248,  p.  324);  (2)  the  lower  cervical  and  upper 
thoracic  fibres— into  the  inner  border  of  the  acromion  process,  and  the  upper 
border  of  the  spine  of  the  scapula ;  and  (3)  the  lower  thoracic  fibres,  by  a 
triangular  flat  tendon,  beneath  which  a  bursa  is  placed — into  a  rough  tuberosity 
at  the  base  of  the  spine  of  the  scapula  (Fig.  299,  p.  383).  The  fibres  inserted 
into  the  clavicle,  acromion,  and  the  upper  border  of  the  spine  of  the  scapula,  spread 
over  the  adjacent  subcvitaneous  surfaces  of  these  bones  for  a  variable  distance. 


FASCIA  AND  SUPEIiFICIAL  MUSCLES  OF  THE  BACK.         319 

The  occipital  portion  of  tlie  muscle  may  be  in  the  form  of  a  separate  slip,  or  may 
be  entirely  absent. 

The  trapezius  is  superficial  in  its  whole  extent.  Its  upper  lateral  border  forms 
the  posterior  limit  of  the  posterior  triangle  of  the  neck.  The  lower  lateral  border, 
passing  over  the  upper  edge  of  the  latissimus  dorsi  and  the  vertebral  border  of  the 
scapula,  forms  a  boundary  of  the  so-called  triangle  of  auscultation  completed  below 
by  the  latissimus  dorsi,  and  externally  by  the  vertebral  border  of  the  scapula.  This 
space  is  partly  filled  up  by  the  rhomboideus  major.  The  deep  surface  of  the  muscle 
is  in  contact  with  the  complexus,  splenius  capitis,  omohyoid,  supraspinatus,  levator 
anguli  scapulae,  rhomboidei,  serratus  posticus  superior,  erector  spinse,  and 
latissimus  dorsi  muscles.  The  spinal  accessory  nerve,  branches  of  the  cervical 
plexus  (C.  3.  4.),  and  of  the  superficial  cervical  and  posterior  scapular  arteries,  are 
situated  beneath  the  muscle. 

The  latissimus  dorsi  is  a  large  triangular  muscle  occupying  the  lower  part  of 
the  back.     It  has  a  triple  origin.     The  greater  part  of  the  muscle  arises — (1)  from 


Pectoralis  major  (origin) 


Trapezius  (insertion), 
Fig.  243. — Muscle- Attachments  to  the  Clavicle  (Upper  Surface). 

the  vertehral  aponewosis  (posterior  layer  of  the  lumbar  fascia  or  aponeurosis  of  the 
latissimus  dorsi).  This  is  a  thick  membrane  which  conceals  the  erector  spinee  in 
the  lower  part  of  the  back.  Through  it  the  latissimus  dorsi  gains  attachment  to 
the  spines  of  the  lower  six  thoracic  vertebrae,  the  spines  of  the  lumbar  vertebrae, 
and  the  tendon  of  the  erector  spinse  with  which  the  aponeurosis  blends  below.  It 
also  arises  more  externally  by  fleshy  fibres  from  the  posterior  part  of  the  iliac  crest 
From  this  origin  the  muscle  is  directed  upwards  and  outwards,  its  fibres  converging 
to  the  lower  angle  of  the  scapula.  In  relation  to  its  upper  and  outer  borders 
additional  fibres  arise.  (2)  Along  the  outer  harder  muscular  slips  arise  from  the 
lower  three  or  four  ribs,  inter-digitating  with  the  origins  of  the  obliquus  externus 
abdominis.  (3)  As  the  upper  border  of  the  muscle  passes  horizontally  over  the 
lower  angle  of  the  scapula,  an  additional  fleshy  slip  usually  takes  origin  from  this 
part  of  the  bone  to  join  the  muscle  on  its  deep  surface  (Fig.  245,  p.  321). 

Beyond  the  lower  angle  of  the  scapula  the  latissimus  dorsi,  greatly  narrowed, 
curves  spirally  round  the  teres  major  muscle,  and  forms  the  prominence  of  the 
posterior  axillary  fold.  It  ends  in  a  ribbon-like  tendon,  closely  adherent  at  first  to 
the  teres  major,  which  is  inserted  into  the  floor  of  the  bicipital  groove  of  the 
humerus,  extending  for  about  three  inches  below  the  lower  and  outer  part  of  the 
lesser  tuberosity  (Fig.  253,  p.  329).  It  is  placed,  behind  the  coraco-brachialis  and 
biceps,  and  the  axillary  vessels  and  nerves,  and  in  front  of  the  insertion  of  the  teres 
major,  from  which  it  is  separated  by  a  bursa. 

In  the  back  the  latissimus  dorsi  is  superficial,  except  in  its  upper  part,  which  is 
concealed  by  the  trapezius.  It  lies  upon  the  lumbar  fascia,  serratus  posticus 
inferior,  the  ribs,  and  lower  angle  of  the  scapula,  and  at  its  borders  two  triangular 
spaces  are  formed  ;  at  the  upper  border  is  the  so-called  triangle  of  auscultation ;  at 
the  outer  border  is  the  triangle  of  Petit,  a  small  space  bounded  by  the  iliac  crest, 
the  latissimus  dorsi,  and  the  obliquus  externus  abdominis.  This  is  the  site  of  an 
occasiona]  luml^ar  licrnia. 

Th(;  levator  anguli  scapulae  (levator  scapulae)  is  a  strap-like  muscle,  arising 
by  tendinous  sli|:)S  from  the  posterior  tubercles  of  the  transverse  processes  of  the 
first  three  or  four  cervical  vertebrae,  between  the  attachments  of  the  scalenus 
medius  in  front  and  the  splenius  colli  behind.     It  is  directed  downwards  along  the 


320 


THE  MUSCULAE  SYSTEM. 


side  of  the  neck,  to  be  inserted  into  the  vertebral  border  of  the  scapula  in  its  upper 
fourth,  from  the  superior  angle  to  the  spine  (Fig.  245,  p.  321).  It  is  concealed  in 
its  upper  third  by  the  sterno-mastoid  and  deep  muscles  of  the  neck.  In  its  middle 
third  it  occupies  the  floor  of  the  posterior  triangle.     In  its  lower  third  it  is  again 


complexus 

Stebn'o-mastoid- 

Splenios  capitis 

SpLENIUS  COLLI' 

Serratus  posticus  superior 
Levator  anguli  scAPUL,y- 

Rhomboxdeus  minor 


Rhomboideus 

MAJOR 


■Sterno-mastoid 


Deltoid 


Rhomboideus 


Teres  major' 

Vertebral 
aponeurosis 


Mfp- Teres  major 


Latissimus  dorsi 


Serratus  posticus 
inferior 


Obliquus  externus 
abdominis 


Obliquus  internus 


Fascia  over  gluteus 
ina\imus 


Latissimus 

DORSI 


Fascia  over  gluteus 
maximui.  (cut  along  upper 


m     border  of  the  muscle) 


Gluteus  maximus 


Fig.  244. — Superficial  Muscles  of  the  Back. 

hidden  from  view  by  the  trapezius.     It  conceals  the  splenius  colli  and  cerAdcalis 
asceudens  muscles. 

The  rhomboideus  minor  may  be  regarded  as  a  separated  slip  of  the  rhom- 
boideus major,  with  which  it  is  often  continuous.  It  arises  from  the  ligamentum 
nuchce  and  the  spines  of  the  seventh  cervical  and  first  thoracic  vertebra.  Passing 
obliquely  downwards  and  outwards,  it  is  inserted  into  the  vertebral  border  of  the 


FASCIiE  AND  MUSCLES  OF  THE  PECTOKAL  REGION. 


521 


Deltoid  (origin) 


Triceps  (origin  of 
long  head) 


Teres  minor  (origin)  with 
gap  for  dorsal  scapular 
artery 


scapula  below  the  levator  anguli  scapulae  muscle,  and  opposite  to  the  base  of  the 
spine  (Fig.  245,  p.  321). 

The  rhomboideus 
major  arises  from  the 
spinous  processes  of  the 
thoracic  vertebrse  from 
the  second  to  the  fifth 
inclusive,  and  from  the 
corresponding  supra- 
spinous ligaments.  Pass- 
ing downwards  and  out- 
wards, it  is  inserted  below 
the  rhomboideus  minor 
into  the  vertebral  border 
of  the  scapula,  between 
the  spine  and  the  lower 
angle  (Fig.  245,  p.  321). 
The  muscle  is  only  in- 
serted directly  into  the 
scapula  by  means  of  its 
lower  fibres.  Its  upper 
part  is  attached  to  a 
membranous  band,  which, 
connected  for  the  most 
part  by  loose  areolar 
tissue  to  the  vertebral 
border  of  the  scapula,  is 
fixed  to  the  bone  at  its 
extremities,  above  near 
the  base  of  the  spine,  and 
below  at  the  inferior 
angle. 

The  rhomboid  muscles  are  concealed  for  the  most  part  by  the  trapezius.  The 
lower  part  of  the  rhomboideus  major  is  superficial  in  the  triangle  of  auscultation. 
The  muscles  cover  the  serratus  posticus  superior  and  vertebral  aponeurosis. 


Teres  major  (origin) 


Latib.simus  dorsi  (oi  igin) 


Pig.  245. — Muscle-Attachments  to  the  Scapula  (Posterior  Surface). 


THE  FASCIA  AND  MUSCLES  OF  THE  PECTOEAL  EEGION. 

FASCIiE. 


The  superficial  fascia  of  the  chest  usually  contains  a  quantity  of  fat,  in  which 
the  mamma  is  embedded.  The  origin  of  the  platysma  myoides  muscle  lies  beneath 
its  upper  part. 

The  deep  fascia  is  attached  above  to  the  clavicle,  and  internally  to  the 
sternum.  Below  it  is  continuous  with  the  fascia  of  the  abdominal  wall.  It  gives 
origin  to  the  platysma  myoides,  and  invests  the  pectoralis  major.  At  the  outer 
border  of  the  great  pectoral  muscle  it  is  thickened,  and  forms  the  floor  of  the 
axillary  sjjace  (axillary  fascia),  continued  posteriorly  on  to  the  posterior  fold  of  the 
axilla  (teres  major  and  latissmus  dorsi),  and  externally  into  connexion  with  the 
deep  fascia  of  the  arm. 

Costo-Coracoid  Membrane. — Beneath  the  pectoralis  major  a  deeper  stratum  of 
fascia  invests  the  pectoralis  minor  muscle.  At  the  up])er  border  of  this  muscle  it 
forms  the  costo-coracoid  membrane,  which  passes  upwards  to  the  lower  border  of  the 
subclaviijs  muscle,  where  it  splits  into  two  layers,  attached  in  front  of  and  behind 
that  muscle  to  the  borders  of  the  under  surface  of  the  clavicle.  The  membrane 
traced  inwards  along  the  subclavius  muscle  is  attached  to  the  first  costal  cartilage ; 
yjassing  outwards  along  the  upp(;r  border  of  the  pectoralis  minor  it  roaches  the 
coracoid  j)rocess.     The  part  of  the  membrane  extending  directly  between  the  first 


322 


THE  MUSCULAE  SYSTEM. 


costal  cartilage  and  the  coracoid  process  is  thickened  and  forms  the  costo-coracoid 
ligament.  The  costo-coracoid  memljrane  is  otherwise  thin  and  of  com]^>aratively 
small  importance.  It  is  pierced  by  the  cephalic  vein,  thoracic  axis  artery  and 
vein,  and  branches  of  the  external  anterior  thoracic  nerve.  By  its  deep  surface  it  is 
connected  to  the  sheath  of  the  axillary  vessels. 

At  the  lower  border  of  the  pectoralis  minor  there  is  a  further  extension  of  the 
deep  fascia  beneath  the  pectoralis  major.  It  passes  downwards  to  join  the  fascia 
forming  the  floor  of  the  axilla,  and  is  continued  externally  into  the  fascia  covering 
the  biceps  and  coraco-brachialis  muscles. 


MUSCLES  OF  THE  PECTORAL  REGION. 


The  anterior  muscles  connecting  the  upper  limb  to  the  axial  skeleton  comprise 
the  pectoralis  major,  pectoralis  minor,  subclavius,  serratus  magnus,  and  sterno- 
cleido-mastoid.     The  last  is  described  in  a  later  section. 

The  pectoralis  major  is  a  large  fan-shaped  muscle  arising  in  three  parts :  (1) 
a  clavicular  "portion  arising  from  the  front  of  the  clavicle  in  its  inner  half  or  two- 
thirds  (Figs.  248,  p.  324,  and  243,  p.  319) ;  (2)  a  costo-sternal  portion,  the  largest 
sterno-cieido-mastoicKorigin)  P^^t  of  the  muscle,  arising  from  the  anterior 
surface  of  the  pre-sternum  and  meso-sternum 
by  tendinous  fibres  decussating  with  those  of 
the  opposite  muscle  (Fig.  246,  p.  322) ;  and 
more  deeply  from  the  cartilages  of  the  iirst  six 
ribs;  (3)  an  ahdominal  portion,  a  small  and 
separate  slip,  arising  from  the  aponeurosis  of 
the  obliquus  externus  muscle.  The  abdominal 
slip,  at  first  separate,  soon  merges  with  the 
costo-sternal  portion,  but  a  distinct  interval 
usually  remains  between  the  two  first -named 
parts  of  the  muscle.  The  fibres  converge  towards 
the  upper  part  of  the  arm,  and  are  inseparably 
blended  at  a  point  half  an  inch  from  their  in- 
sertion into  the  humerus.  The  muscle  is  inserted 
into  (1)  the  outer  border  of  the  bicipital 
groove  of  the  humerus,  extending  upwards  to 
the  great  tuberosity,  and  blending  externally 
with  the  insertion  of  the  deltoid,  internally 
with  the  insertion  of  the  latissimus  dorsi  (Fig. 
253,  p.  329) ;  (2)  from  the  upper  border  of  the 
insertion  a  membranous  band  extends  upwards 
to  the  capsule  of  the  shoulder -joint,  enveloping 
at  the  same  time  the  tendon  of  the  biceps ;  and 
(3)  from  the  lower  border  a  band  of  fascia  passes 
downwards  to  join  the  fascia  of  the  arm. 

The  arrangement  of  the  fibres  of  the  muscle 
at  its  insertion  is  peculiar.  The  muscle  is  twisted 
on  itself,  so  that  the  lower  (costo-sternal)  fibres 
are  directed  upwards  and  outwards  behind  the 
upper  (clavicular)  part  of  the  muscle  ;  in  conse- 
quence the  clavicular  part  is  attached  to  the 
humerus  lower  down  than  the  costo-sternal 
portion,  and  is  inserted  also  into  the  fascia  of  the 
arm.  The  twisting  of  the  fibres  is  specially  found  in  the  lower  costo-sternal  fibres 
of  the  muscle  and  the  abdominal  fibres.  These  curve  upwards  behind  the  upper 
costo-sternal  fibres,  and  are  inserted  highest  to  the  shaft  of  the  humerus,  helping  to 
form  the  fascial  expansion  which  extends  upwards  over  the  biceps  tendon  to  the 
capsule  of  the  shoulder-joint.     In  this  way  a  bilaminar  tendon  is  produced  united 


Rectus  abdominis 
(insertion) 


Fig.  246. — Muscle- Attach jient.s  to  the 
Front  of  the  Sternum. 


MUSCLES  OF  THE  PECTORAL  KEGION. 


323 


alono-  its  lower  border ;  and  consisting  of  a  superficial  lamina  formed  by  the  upper 
Gosto-sternal  fibres,  blending  for  the  most  part  with  the  tendon  of  the  clavicular 
portion ;  and  a  deep  lamina,  composed  of  the  twisted  lower  costo-sternal  and 
abdominal  fibres.     The  disposition  of  the  muscular  fibres  at  their  insertions  is  the 


Sterno-mastoid' 
Trapezius 


SUBf  LAVirS 


Coracoid 
process 

Pectoralis 
MAJOR  (divided) 

Pectoralis 

MINOR 

Pectoralis 
MAJOR  (divided) 


Serratus 

\\  \    J  MAGNUS 


LmecC  transversse 


Obliquus  externus 
abdominis 


Lmea  spmilunaris 
Lmea  alba 


Pvramidalis  abdominis 

Poupart  s  hgaiaeiit 
External  abdominal  nng- 

TrianKiilai  fa->cia 


Fio.  247. — Anterior  Muscles  of  the  Trunk. 

reason  for  tlie  application  of  the  terms  ijortio  attollens  to  the  clavicular  portion, 
and  'portio  deprimens  to  the  costo-sternal  and  abdominal  portions  of  the  muscle. 

I 'laced  superficially  on  the  chest  wall,  the  pectoralis  major  forms  the  front 
wall  of  the  axilla,  and  by  its  lower  or  outer  border,  the  anterior  fold  of  the  space. 
Its  upper  border  is  sei>arated  from  the  edge  of  the  deltoid  muscle  by  an  interval 
in  which  lie  the  cephalic  vein  and  humeral  artery.  Its  deep  surface  is  in 
relation  nvith  the  ribs  and  intercostal  muscles,  the  costo-coracoid  membrane  and 


324 


THE  MUSCULAE  SYSTEM. 


the  structures  piercing  it,  the  pectoralis  minor,  the  axillary  vessels,  and  the  nerves 
of  the  brachial  plexus. 

Sternalis  muscle. — The  sternalis  is  an  occasional  muscle  placed,  wlien  present,  parallel  to 
the  sternum  upon  the  sterno-costal  origin  of  the  pectoralis  major.  It  has  attachments  which 
are  very  variable  both  above  and  below,  to  the  costal  cartilages,  sternum,  rectus  sheath,  sterno- 
mastoid,  and  pectoralis  major.  Its  nerve-supply  is  from  one  or  both  of  the  anterior  thoracic 
nerves.  In  certain  rare  cases  it  has  been  said  to  be  innervated  by  intercostal  nerves.  It  is 
present  in  4'4  cases  out  of  100,  and  it  is  slightly  more  frequent  in  the  male  than  in  the  female. 
It  has  been  regarded  by  different  observers  as  (1)  a  vestige  of  the  panuiculus  carnosus,  (2)  a 
homologue  of  the  sterno-mastoid,  or  (3)  a  displaced  slip  of  the  pectoralis  major. 

Chondro-epitrochlearis,  dorso-epitrochlearis,  axillary  arches,  costo-coracoideus. — One 
or  other  of  tlie  above-iiauied  slips  is  occasionally  j^resent,  crossing  the  floor  (jf  the  axilla  in  the 
interval  between  the  latissimus  dorsi  and  the  j^ectoralis  major.  They  take  origin  from  the  costal 
cartilages,  ribs,  or  borders  of  the  pectoralis  major  {chondro-epitroddearis,  axillary  arches,  costo- 
coracoicleas),  or  from  the  border  of  the  latissimus  dorsi  {dorso-ejntrochlearis,  axillary  arches,  costo- 
coracoideus).  Their  insertion  is  variable.  The  chondro-epitrochlearis  and  dorso-epitrochlearis  are 
inserted  into  the  fascia  of  the  arm  on  the  inner  side,  the  internal  intermuscular  septum,  or  the 
internal  condyle  of  the  humerus.  The  axillary  arches  are  inserted  into  the  border  of  the  pectoralis 
major,  the  fascia  of  the  arm,  or  the  coraco-brachialis  or  biceps  muscle.  The  costo-coracoideus, 
arising  from  the  ribs  or  the  aponeurosis  of  the  obliquus  externus,  or  detaching  itself  from  the 
border  of  the  pectoralis  major  or  latissimus  dorsi,  is  attached  to  the  coracoid  process,  alone  or 
along  with  one  of  the  muscles  attached  to  that  bone.  These  variable  slips  of  muscle  are  supplied 
by  the  internal  anterior  thoracic  nerve,  the  lesser  internal  cutaneous  nerve,  or  the  intercosto- 
humeral. 

The  pectoralis  minor  is  a  narrow,  flat,  triangular  muscle.  It  arises  from  (1) 
the  outer  surfaces  and  upper  borders  of  the  third,  fourth,  and  fifth  ribs  near  their 
anterior  ends,  and  (2)  from  the  fascia  covering  the  third  and  fourth  intercostal 
spaces  between  these  ribs.  It  may  have  an  additional  origin  from  the  second  rib 
(Fig.  830,  p.  420) ;  and  that  from  the  fifth  rib  is  often  absent.  Directed  obliquely 
outwards  and  upwards,  it  is  inserted  by  a  short,  fiat  tendon  into  the  outer  half  of 
the  anterior  (inner)  border  and  upper  surface  of  the  coracoid  process  (Fig.  250, 
p.  325),  and  usually  also  into  the  conjoint  origin  of  the  biceps  and  coraco-brachialis. 
It  is  wholly  concealed  by  the  pectoralis  major,  except  when  the  arm  is  raised, 
when  the  outer  border  of  the  muscle  becomes  superficial.  It  enters  into  the 
formation  of  the  front  wall  of  the  axilla,  and  gives  attachment  along  its  upper 
border  to  the  costo-coracoid  membrane.  It  crosses  the  axillary  vessels  and  the 
cords  of  the  brachial  plexus,  and  is  pierced  by  branches  of  the  anterior  thoracic 
nerves. 

Either  in  part  or  wholly  the  jDectoralis  minor  may  pass  over  the  coracoid  process  of  the 
scapula,  sejDarated  from  it  by  a  bursa,  to  be  inserted  into  the  coraco-acromial  ligament,  or  the 
acromion  process ;  or  piercing  the  coraco-acromial  ligament,  it  may  be  attached  to  the  capsule  of 
the  shoulder-joint  (coraco-humeral  ligament). 

Pectoralis  minimus. — This  is  a  slender  slip,  rarely  present,  which  extends  between  the  first 
costal  cartilage  and  the  coracoid  j^rocess. 

The  subclavius  muscle  arises  from  the  upper  surface  of  the  first  costal  cartilage 
in  front  of  the    costo  -  clavicular  ligament,  and  from  the  upper  surface   of  the 


Pectoralis  major  (origin) 


Trapezius 
(insertion) 


Subt;lavius  (insertion) 
Fig.  248. — Muscle-Attachments  to  the  Clavicle  (Under  Surface). 


distal  end  of  the  first  rib  (Fig.  330,  p.  420).  It  is  inserted  into  a  groove  in  the 
middle  third  of  the  under  surface  of  the  clavicle  (Fig.  248,  p.  324).  The  muscle 
is  invested  by  the  fascia  which  forms  the  costo-coracoid  membrane,  and  is  concealed 
by  the  clavicle  and  the  clavicular  origin  of  the  pectoralis  major. 


MUSCLES  OF  THE  PECTOKAL  EEGION. 


325 


The  sterno-clavicularis  is  a  small  separate 
slip,  rarely  j^resent,  extending  beneath  the  pector- 
alis  major  from  the  upper  j^art  of  the  sternum  to 
the  clavicle. 

The  serratus  magnus  (m.  serratus 
anterior)  is  a  large  curved  quadrilateral 
muscle  occupying  the  side  of  the  chest 
and  inner  wall  of  the  axilla.  It  arises  by 
fleshy  slips  from  the  external  aspect  of 
the  upper  eight  and  occasionally  (as  in 
the  figure)  from  nine  ribs.  The  first  slip 
is  a  double  one,  arising  from  the  first  two 
ribs  and  the  fascia  covering  the  inter- 
vening space  (Fig.  330,  p.  420).  The 
insertion  of  the  muscle  is  threefold.  (1)  }s 
The  first  portion  of  the  muscle  (from  the 
first  and  second  ribs)  is  directed  back- 
wards to  be  inserted  into  the  ventral 
aspect  of  the  upper  angle  of  the  scapula. 
(2)  The  next  three  slips  of  the  muscle 
(from  the  second,  third,  and  fourth  ribs) 
are  inserted  into  the  vertebral  border  of 
the  scapula.  (3)  The  last  four  slips 
(from  the  fifth,  sixth,  seventh,  and  eighth 
ribs)  are  directed  obliquely  upwards  and 
backwards,  to  be  inserted   on  the  ventral 


Deltoid  (origin) 

Biceps  and  coraco  biachialis  (origin) 
I  Ppctoialis  ramor  (insertion) 

Omohyoid  (origin) 


Triceps  (origin  ot 
long  head) 


Fio.  250.- 


-Ml'scle-Attach.mk.n'I'.s  to  'I'he  Scapula 
(Anterior  Aspect). 


Fig.  249.— The  Serratus  Magnus  Muscle. 

aspect  of  the  lower  angle  of  the 
scapula  (Fig.  250,  p.  325). 

The  external  surface  of  the 
muscle  is  partly  superficial  below 
the  axillary  space,  on  the  side 
wall  of  the  chest,  where  its 
slips  of  origin  are  seen  inter - 
digitating  with  those  of  the 
obliquus  externus  abdominis. 
Higher  up  it  forms  .  the  inner 
wall  of  the  axilla,  and  is  in 
contact  with  the  pectoral  muscles 
in  front  and  the  subscapularis 
behind.  Its  upper  border  ap- 
pears in  the  floor  of  the  pos- 
terior triangle,  and  over  it  the 
axillary  artery  and  the  cords 
of  the  brachial  plexus  pass  in 
their  course  through  the  aimpit. 
The  lower  border  is  oblique, 
and  is  in  contact  with  the 
latissimus  dorsi  muscle.  The 
deep  surface  of  the  muscle  is 
in  contact  with  the  chest  wall, 
so  that  the  serratus  magnus 
along  with  the  sul)scapularis 
muHcL^  separates  the  scapula 
from  the  ribs.  The  muscle  may 
extend  higher  than  usual,  so 
as  to  be  continuous  in  the  neck 
with  th(;  levfitor  angiili  scapulae. 


326 


THE  MUSCULAE  SYSTEM. 


Nerve-Supply. 

The  nerves  supplying  the  muscles  connecting  the  upper  limb  to  tlie  trunk  are  given  in  the 
following  table  :■ — 


Muscles. 


Trapezius 

Latissimus  dorsi 

Levator  scapulae 

Rhomboidei 

Pectorales 

Subclavius 
Serratus  magnus 


Nerves. 


(Spinal  accessory  nerve 
I  Cervical  plexus 

Long  subscapular 
/  Cervical  plexus 
I  Posterior  scapular 

Posterior  scapular 
/  External  anterior  thoracic 
llnternal         „  „ 

Brachial  plexus 

Posterior  thoracic 


Origin. 


Spinal 

Cord 

C.     3. 

4. 

C.     6. 

7.     8. 

C.     3. 

4. 

C.     5. 

C.     5. 

C.     5. 

6.     7 

C.     8. 

T.    1 

C.     5. 

6. 

C.     5. 

6.     7 

Actions. 

The  muscles  of  this  group  (together  with  the  sterno-cleido-mastoid  and  omohyoid  muscles)  act 
for  the  most  part  in  the  movements  of  the  shoulder  girdle  at  the  sterno-clavicular  and  acromio- 
clavicular joints.  At  the  former  joint  they  jsroduce  the  various  moA^ements  of  the  clavicle  on  the 
sternum,  and  cause  the  shoulder  to  move  in  an  arc  the  centre  of  which  is  the  sterno-clavicular  joint. 
At  the  acromio-clavicular  articulation  they  produce  a  rotation  of  the  scapula  on  the  clavicle,  and  a 
consequent  alteration  in  the  direction  of  the  glenoid  fossa.  At  the  same  time  the  several  muscles 
are  agents  in  other  equally  important  movements,  when  the  shoulder  girdle  is  fixed  ;  movements 
of  the  head  and  neck  ;  movements  of  the  trunk  and  ribs ;  and,  in  addition  in  the  case  of  the 
pectoralis  major  and  latissimus  dorsi,  important  movements  of  the  arm  at  the  shoulder-joint. 

1.  Movements  of  the  Shoulder  Girdle, — The  action  of  this  group  of  muscles  on  the  shoulder 
girdle  (mainly  corresponding  to  movements  at  the  sterno-clavicular  joint)  may  be  expressed  in 
the  following  table  : — 


a.  Movement  in  a  Vertical  Plane. 

b.  Movement  in  a  Horizontal  Plane. 

Elevation.                         Depression. 

Forwards. 

Backwards. 

Trapezius     (upper         Trapezius      (lower 

fibres)                                fibres) 
Levator  scapulae         j     Subclavius 
Rhomboidei                 I     Pectoralis  minor 
Sterno-mastoid           ,     Latissimus  dorsi 
Omohyoid                    '     Pectoralis       major 
(lower  fibres) 

Serratus  magnus 
Pectoralis  major 
Pectoralis  minor 

Trapezius 
Rhomboidei 
Latissimus  dorsi 

j           c.  Rotation — a  combination  of  these 
muscles. 

2.  Movements  of  the  scapula  on  the  clavicle  produce  an  alteration  of  the  direction  of  the 
glenoid  fossa  of  the  scaj)ula,  and  are  accompanied  by  movements,  inwards  or  outwards,  forwards 
or  backwards,  of  the  inferior  angle  of  the  scapula.  By  the  combined  action  of  the  muscles 
acting  upon  the  shoulder  girdle  a  rotatory  movement  of  the  scapula  at  the  acromio-clavicular 
joint  is  effected,  by  which  the  relation  of  the  glenoid  fossa  to  the  head  of  the  humerus  is  preserved 
in  movements  of  the  arm. 

3.  In  forced  inspiration,  the  sterno-mastoid,  trapezius,  levator  scapulae,  rhomboidei,  sub- 
clavius, omohyoid,  serratus  magnus,  pectoral  muscles,  and  latissimus  dorsi,  acting  together,  raise 
and  fix  the  shoulder  girdle  ;  while  those  of  them  which  have  costal  attachments — subclavius, 
pectoral  muscles,  serratus  magnus,  and  latissimus  dorsi,  simultaneously  elevate  the  ribs  and 
expand  the  thorax. 

4.  Lateral  flexion  and  rotation  of  the  spine  in  the  neck  is  effected  partly  by  the  action  of 
the  trajsezius,  levator  scapula,  and  rhomboid  muscles  (with  the  shoulder  fixed).  The  latissimus 
dorsi  and  pectoralis  major  act  in  climbing  in  a  similar  way,  raising  up  the  trunk  towards  the 
shoulder. 

5.  Action  on  the  Upper  Limb. — By  reason  of  their  insertion  into  the  humerus  the  pectoralis 
major  and  latissimus  dorsi  muscles  assist  the  movements  of  the  upper  limb.  Acting  together,  the 
two  muscles  depress  the  shoulder,  and  draw  the  arm  to  the  side  of  the  body,  at  the  same  time 
rotating  the  humerus  inwards.  The  two  parts  of  the  pectoralis  major  have  slightly  different 
actions  on  the  humerus.  The  clavicular  part  of  the  muscle  {portio  attollens)  draws  the  arm  in- 
wards and  upwards  ;  the  costo-sternal  part  of  the  muscle  (j)ortio  cUprimens)  draws  it  inwards  and 
downwards.  The  latissimus  dorsi  acting  alone,  besides  rotating  the  limb,  draws  it  inwards  and 
backwards,  as  in  the  act  of  swimming. 


FASCIiE  AND  MUSCLES  OF  THE  SHOULDER. 


327 


FASCIA  AND  MUSCLES  OF   THE  SHOULDER. 

The  deep  fascia  covering  the  scapular  muscles  presents  no  feature  of  special 
importance.  Attached  to  the  clavicle,  acromion,  and  scapular  spine,  it  is  thin  over 
the  deltoid  muscle.  Belovs^  the  deltoid  it  is  thicker ;  it  encases  and  gives  origin  to 
the  infraspinatus  muscle,  and  is  continuous  with  the  fasciae  of  the  axilla  and  the 

back. 

Muscles. 

The  muscles  proper  to  the  shoulder  comprise  the  deltoid,  supraspinatus,  infra- 


IjEvator  anguli  scapula.. 


SOPR^SPINATUS 

Scapular  spine  (cut) 

Infraspinatus 

' __Teres  minor 


Dorsal  scapular 
artery  (branch  of)' 


Latissimus  dorsi 


^  ^head) 

<i^a^  Triceps  (long  head) 
■Musculo-spiral  nerve 


.Nerve  to  teres  minor 
Circumflex  nerve  and 
aitery 

Deltoid  (reflected) 


Cutaneous  branch 
of  circumflex 
.Triceps  (outer 


Triceps  (outer  head) 
.Bkachialis  anticus 

.Triceps  (Inner  head) 

External  intermuscular 

septum 

\  External  cutaneous  branches 

/  of  musculo-spiral  nerve 


Flexor 
carpi- 

ulnaris 


Brachio-radialis 


Extensor  carpi  radialis 

LONGIOR 


Extensor  muscles  of  fore- 
arm (common  tendon) 


spmatus,  teres  minor,  teres  major, 
and  subscapularis.  They  sur- 
round, and  along  with  other 
muscles,  act  on  the  shoulder- 
joint. 

The  deltoid,  a  coarsely  fasci- 
culated, multipennate  muscle, 
has  an  extensive  origin  from 
(1)  the  front  of  the  clavicle  in 
its  outer  third  (Figs.  248,  p. 
324,  and  24.3,  p.  319) ;  (2)  the 
outer  border  of  the  acromion 
process;  (3)  the  lower  edge  of 
the  free  border  of  the  spine  of 
the  scapula  fFigs.  254,  p.  330,  and  250,  p.  325) ;  and  (4)  from  the  deep  fascia  cover- 
ing the  infrasy)inatus  muscle.  Its  origin  erni)races  the  insertion  of  the  trapezius. 
The  fi})res  of  the  muscle  converge  to  the  outer  side  of  the  sliaft  of  the  humerus,  to 
be  inserted  into  a  well-marked  V-shaped  impression  above  the  spiral  groove  (Figs. 
257  and  258,  p.  335).  The  insertion  is  x^artly  united  with  the  tendon  of  the 
pectoralis  major.    The  deltoid  is  superficial  in  its  whole  extent,  and  forms  theprom- 


Fio.  251. — Deltoid  Region  and  Back  of  the  Ahm. 


328 


THE  MUSCULAK  SYSTEM. 


inence  of  the  shoulder.  Its  anterior  border  is  separated  from  the  pectoralis  major 
by  a  narrow  interval,  in  which  the  cephalic  vein  and  humeral  artery  are  placed.  The 
deep  surface  of  the  muscle  is  separated  by  a  bursa  from  the  capsule  of  the  shoulder- 


Trapfziits 

Cla\  icIp  (cut) 
Coraco-claviciilar  ligaments. 
Feci  ORALIS  minor 
Coracoid  process 
Coraco-acroTTiial  litjament 
Circumflev  artery 

Circumflex  nerve 

Deltoid 

Long  head 
of  biceps 


Pectoralis  major 

CoRAco     :=; 
brachialis 


_ Suprascapulai  nene 


Postenoi  cord  of  brachial 

plexus 

Short  subscapular  nerve 

Long  subscapular  nerve 
Lower  subscapular  nerve 


,^  SeRRATUS  MAGNUS 

^^L^    Dorsal  scapular  arteiy 
^^Sl  Subscapularis 


Teres  major 


'  Short  head 
.  Long  head' 


Musculo-cutaneous. 
nerve 


3RACHIALIS  ANTICUS- 


Musculo-spiral  nerve 


Brachio-radialis 

Biceps  (cut) 

Extensor  carpi 

RADIALIS  LONGIOR 


Posterior  interosseous 

nerve 

Radial  nerve 

Supinator  radii  brevis 


Latissimus  dorsi 


Internal 

cutaneous  branch 
^   of  musculo-spiral 
nerve 


Teiceps  (long  head) 

Ner\e  to  inner  head  ot 
triceps  (ulnar  collateral) 

joint  and  the  tendons  inserted 
into  the  tuberosities  of  the 
humerus.  It  is  related  to  (1)  the 
coracoid  process,  associated  with 
which  are  the  coraco  -  acromial 
lio-ament,  and  the  attachments  of 
the  pectoralis  minor,  the  coraco- 
brachialis  and  the  short  head  of 
the  biceps ;  (2)  with  the  capsule 
of  the  shoulder-joint  covering  the 
head  of  the  humerus,  associated 
with  which  are  the  long  head  of  the 
biceps,  and  the  attachments  of  the 
subscapularis,  supraspinatus,  infra- 
spinatus, and  teres  minor  ;  and  (3) 
with  the  upper  part  of  tlie  external 
surface  of  the  shaft  of  the  humerus, 
associated  with  which  are  the  cir- 
cumflex vessels  and  nerve.  The 
most  anterior  part  of  the  deltoid 
muscle  is  formed  of  parallel  fibres, 
not  uncommonly  separate  from  the 
rest  of  the  muscle  at  their  origin 
from  the  clavicle.  These  fibres  may 
be  continuous  with  the  trapezius 
over  the  clavicle.  The  most  posterior  part  arises  by  a  fascial  origin  from  the  spine 
of  the  scapula  and  the  fascia  over  the  infraspinatus  muscle.  These  portions  are 
attached  respectively  to  the  front  and  back  of  the  main  tendon  of  insertion.  The 
intermediate  fibres  are  multipennate,  attached  above  and  below  to  three  or  four 


Fig. 


252. — The  Posterior  Wall  of  the  Axilla  and  the 
Front  of  the  Arm  (the  biceps  being  divided). 


MUSCLES  OF  THE  SHOULDER. 


329 


Supraspinatus 
(insertion) 


septal  tendons,  which  extend  for  a  variable  distance  from  the  origin  and  insertion 
of  the  muscle. 

The  supraspinatus  arises  by  fleshy  fibres  from  the  sujjrasxjinous  fossa  (except 
near  the  neck  of  the  bone)  and  from  the  deep  fascia  over  it  (Fig.  254,  p.  330). 
It  is  directed  outwards  under  the  acromion  process  and  coraco-acromial  ligament 
to  be  inserted  by  a  broad  thick  tendon  into  the  uppermost  facet  on  the  great 
tuberosity  of  the  humerus,  and 
into  the  capsule  of  the  shoulder- 
joint  (Fig.  253,  p.  329). 

The  muscle  is  entirely  con- 
cealed from  view  by  the  trapezius, 
the  acromion  process,  and  the 
deltoid  muscle.  It  covers  the 
neck  of  the  scapula,  the  supra- 
scapular vessels  and  nerves,  and 
the  upper  surface  of  the  capsule 
of  the  shoulder-joint. 

The  infraspinatus  arises  from 
the  infraspinous  fossa  of  the 
scapula  (excepting  near  the  neck 
of  the  bone  and  the  flat  surface 
along  the  axillary  border)  and 
from  the  thick  fascia  over  it 
(Fig.  254,  p.  330).  The  fibres  of 
the  muscle  converge  to  the  neck 
of  the  scapula ;  and  are  inserted 
by  tendon  into  the  middle  facet 
on  the  great  tuberosity  of  the 
humerus,  and  into  the  capsule 
of  the  shoulder-joint  (Fig.  258, 
p.  335).  A  bursa  separates  the 
muscle  from  the  neck  of  the 
scapula,  and  in  a  minority  of 
cases  communicates  with  the 
synovial  cavity  of  the  shoulder- 
joint. 

The  upper  part  of  the  muscle 
is  hidden  from  view  by  the  del- 
toid. Its  lower  part  is  super- 
ficial, and  its  outer  border  is  in 
contact  with  the  teres  minor. 
Near  its  insertion  it  crosses  the 
neck  of  the  scapula  and  the 
back  of  the  capsule  of  the 
shoulder-joint. 

The  teres  minor  is  a  small 
muscle,  arising  by  fleshy  fibres 
from  the  upper  two-thirds  of  the 
flat  surface  on  the  dorsal  aspect 
of  the  axillary  border  of  the 
scapula,  and  from  fascial  septa 

separating  it  from  the  infraspinatus  and  teres  major  muscles  (Fig.  254,  p.  330). 
Lying  alongside  the  outer  border  of  the  infraspinatus,  it  is  inserted  under  cover 
of  the  deltoid  by  a  thick  flat  tendon  into  the  lowest  of  the  three  facets  on  the 
great  tuberosity  of  the  humerus  and  into  the  capsule  of  the  shoulder-joint,  and 
by  fleshy  fibres  into  the  posterior  aspect  of  the  surgical  neck  and  shaft  of  the 
humerus,  below  the  tuberosity  for  about  an  inch  (Fig.  258,  p.  335),  It  is 
separated  from  the  teres  major  by  the  scapular  head  of  the  triceps,  and  by  the 
posterior  circumflex  vessels  and  the  circumflex  nerve.  Its  origin  is  pierced  by 
23 


Extensor  carpi 
radialis  longior 
origin) 

Common  tendon 
for  origin  of 
pronator  radii 
teres  and  flexor 
muscles  of 
forearm 


Common  tendon  fo}-  origin  of 
extensor  muscles  of  forearm 


Fig.  253. — Muscle-Attachments  to  the  Front  of  the 

HUiMERUS. 


330 


THE  MUSCULAE  SYSTEM. 


Deltoid  (origin) 


fncpps  (origin  of 
loiio  liPad) 


TerPs  minor  (origin)  with 
^ap  for  dorsal  scapular 
artery 


the  dorsal  scapular  artery.     The  muscle  is  invested  by  the  deep  fascia  enclosing  the 
infras[)inatus,  and  is  sometimes  inseparable  from  that  muscle. 

The  teres  major  is  much  larger  than  the  preceding  muscle.  It  arises  by  fleshy 
fibres  from  the  lower  tliird  of  the  flat  surface  on  the  dorsum  of  the  scapula  along  its 
axillary  border  (except  for  a  small  area  at  the  lower  angle;,  and  from  fascial  septa, 
which  separate  it  on  the  one  side  from  the  subscapularis,  and  on  the  other  from  the 
infraspinatus  and  teres  minor  (Fig.  254,  p.  330).  The  muscle  is  directed  along 
the  axillary  border  of  the  scapula  to  the  front  of  the  shaft  of  the  humerus,  where 
it  is  inserted  by  a  broad  flat  tendon  into  the  inner  border  of  the  bicipital  groove 
internal  to  the  latissimus  dorsi  muscle  (Fig.  257,  p.  335).  Just  before  its  insertion 
it  is  closely  adherent  to  the  tendon  of  the  latissimus  dorsi. 

The  teres  major  helps  to  form  the  posterior  wall  of  the  axilla.  It  lies  below 
the  subscapularis,  and  is  in  close  relation  with  the  latissimus  dorsi  muscle,  which 

conceals  its  origin  pos- 
teriorly, winds  round  its 
outer  border,  and  partially 
separates  its  anterior  sur- 
face from  the  axillary 
vessels  and  nerves.  The 
muscle  forms  the  lower 
boundary  of  a  large  tri- 
angular interval,  bounded 
externally  on  the  posterior 
wall  of  the  axilla  by  the 
surgical  neck  of  the 
humerus,  and  above  by 
the  borders  of  the  sub- 
scapularis and  teres  minor 
muscles.  The  long  head 
of  the  tricepspasses  behind 
the  teres  major  and  sub- 
divides this  space  into 
two,  a  quadrilateral  space 
limited  by  the  triceps  and 
surgical  neck  of  the 
humerus  for  the  passage 
of  the  circumflex  nerve 
and  posterior  circumflex 
vessels,  and  a  smaller  tri- 
angular space  bounded  by 
the  triceps,  subscapularis, 
and  teres  major,  for  the 
dorsal  scapular  artery. 
The  subscapularis 
is  a  large  triangular  muscle  occupying  the  venter  of  the  scapula.  It  arises 
by  fleshy  fibres  from  the  whole  of  the  subscapular  fossa  and  the  groove  along 
the  axillary  border,  excepting  the  surfaces  at  the  angles  of  the  bone  (Fig.  250, 
p.  325).  Springing  from  several  ridges  in  the  fossa  are  septa  projecting  into 
the  substance  of  the  muscle,  which  increase  the  extent  of  its  attachment.  Con- 
verging to  the  head  of  the  humerus,  the  muscular  fibres  are  inserted  by  a  broad,  thick 
tendon  into  the  lesser  tuberosity  of  the  humerus  and  into  the  capsule  of  the  shoulder- 
joint,  and  by  fleshy  fibres  into  the  surgical  neck  and  the  shaft  of  the  humerus 
below  the  tuberosity  for  about  an  inch,  under  cover  of  the  coraco-brachialis  and 
short  head  of  the  biceps  (Fig.  257,  p.  335).  This  muscle  forms  the  greater  part  of 
the  posterior  wall  of  the  axilla.  Its  inner  or  anterior  surface  is  in  contact  with  the 
serratus  magnus  and  the  axillary  vessels  and  nerves.  Its  deep  surface  is  separated 
from  the  neck  of  the  scapula  by  a  bursa,  which  is  in  direct  communication  with  the 
synovial  cavity  of  the  shoulder-joint.  Its  upper  border  passes  beneath  the  coracoid 
process ;  its  outer  border  is  separated  from  the  teres  major  by  the  posterior  cireum- 


Teres  major  (origin) 


L  itissimns  dorsi  (origin) 


Fig.  254. — Muscle-Attachmexts  to  the  Scapula  (Posterior  Surface). 


MUSCLES  OF  THE  SHOULDEli. 


331 


flex  vessels  and  the  circumflex  nerve,  the  long  head  of  the  triceps  muscle,  and  the 
dorsal  scapular  artery. 

The  subscapularis  minor  is  an  occasional  muscle  situated  below  the  cajisule  of  the  shoulder- 
joint.  It  arises  from  the  axillary  border  of  the  scapula  below  tlie  subscapularis,  and  is  inserted 
into  the  capsule  of  the  joint  or  the  upper  part  of  the  sliaft  of  the  humerus. 


Nerve -Supply. 

The  muscles  of  this  group  are  all  supplied  by  the  fifth  and  sixth  cervical  nerves,  through 
nerves  arising  from  posterior  trunks  of  the  brachial  plexus. 


Muscles. 

Nerves. 

Origin. 

Deltoid            'I 
Teres  minor    } 
Supraspinatus) 
Infraspinatus  / 
Teres  major 
Subscapularis 

Circumflex 

Suprascapular 

Lower  subscapular 

Lower  and  upper  subscapular 

-  C.  5.  6. 

Actions. 

The  principal  action  of  this  groups  of  muscles  is  on  the  shoulder-joint.      They  have  also 
secondary  actions  in  relation  to  movements  of  the  trunk  and  limbs. 


1.  Movements  at  the  Shoulder -Joint. 


a.  Abduction. 

Adduction. 

b.  Flexion  (Forwards). 

Extension  (Backwards). 

Deltoid 
Supraspinatus 

Teres  major 
Teres  minor 
Pectoralis  major 
Latissimus  dorsi 
Coraco-brachialis 
Biceps  (short  head) 
Triceps  (long  head) 
(Weight  of  limb) 

Deltoid  (anterior  fibres) 
Subscapularis 
Pectoralis  major 
Coraco-brachialis 
Biceps 

Deltoid  (posterior  fibres) 
Teres  major 
Infraspinatus 
Latissimus  dorsi 
Triceps 

c.  Rotation  Outwards. 

Rotation  Inwards. 

Deltoid  (posterior  fibres) 

Infraspinatus 

Teres  minor 

Deltoid  (anterior  fibres)" 
Teres  major  -. 
Pectoralis  major 
Latissimus  clorsi 

d.  Circumduction— combination  of  previous  muscles. 

The  various  movements  at  the  shoulder-joint  are  greatly  aided  by  tlie  nuiscles  acting  on  the 
shoulder  girdle.  In  raising  the  arm  above  the  head,  for  instance,  the  humerus  is  brought  to  the 
horizontal  ])osition  Ijy  the  dfdtoid  and  su])r'aspinatus,  and  tlie  movement  is  continued  by  the 
elevators  of  the  shoulder  girdle.  Again,  in  forward  and  backward  movements  at  the  shoulder- 
joint,  great  asHistaiice  is  derived  fi'om  muscles  acting  dii'cctly  on  the  shoulder  girdle — i)ectoralis 
ininoi-  and  serratus  niagnns  ;  trapc^zius  and  rhoinboidei.  _ 

■2.  In  relation  to  the  trunk  and  limbs,  the  shoulder  muscles,  by  fixing  the  humerus,  have 
auxiliaiy  iiowi-i'  on  the  one  liiui'l  in  niovcnii-nts  of  the  trunk,  such  as  forcc^d  insjiiration  ;  on  the 
other   hand,  acting  along  with   muscles  fixing  the  elbow-joint,  they  stid'cn   the   lind)  so  as  to 
jK'rniit  of  the  more  refined  movements  of  the  wrist  and  fingers. 
2?ja 


332  THE  MUSCULAR  SYSTEM. 

EASCIiE  AND  MUSCLES  OF  THE  AEM. 

FASCIA. 

The  superficial  fascia  presents  no  features  of  iiaportance.  There  is  a  bursa 
beneath  it  over  the  olecranon  process,  and  occasionally  another  over  the  inner 
condyle  of  the  humerus. 

The  deep  fascia  forms  a  strong  tubular  investment  for  the  muscles  on  the  front 
and  back  of  the  humerus.  It  is  continuous  above  with  the  deep  fascia  of  the 
shoulder  and  axilla,  and  is  further  strengthened  by  fibres  derived  from  the  insertions 
of  muscles  attached  to  the  upper  part  of  the  humerus,  viz.,  from  the  pectoral! s  major, 
latissimus  dorsi,  and  deltoid.  At  the  elbow  it  becomes  continuous  with  the  deep 
fascia  of  the  forearm,  and  gains  attachment  to  the  condyles  of  the  humerus  and 
the  olecranon  process  of  the  ulna ;  it  is  strengthened  also  by  important  bands 
associated  with  the  insertions  of  the  biceps  in  front  and  the  triceps  behind,  to  which 
reference  will  be  made  in  the  account  of  these  muscles. 

About  the  middle  of  the  upper  arm  in  front  of  the  inner  border,  the  deep  fascia 
is  perforated  for  the  passage  of  the  basilic  vein  and  the  internal  cutaneous  nerve. 

The  intermuscular  septa  are  processes  of  the  deep  fascia  attached  to  the 
supracondyloid  or  epicondylic  ridges,  of  the  humerus.  The  internal  and  stronger 
septum  is  placed  between  the  brachialis  anticus  in  front  and  the  inner  head  of  the 
triceps  behind,  and  gives  origin  to  both.  It  extends  upwards  to  the  insertion  of 
the  coraco-brachialis  (which  is  often  continued  into  it),  and  the  ulnar  nerve  and 
inferior  profunda  vessels  pass  down  over  its  inner  edge.  The  external  septum  is 
thinner.  It  separates  the  brachialis  anticus  and  brachio-radialis  in  front  from 
the  inner  and  outer  heads  of  the  triceps  behind,  and  gives  origin  to  these  muscles. 
It  extends  upwards  to  the  insertion  of  the  deltoid,  and  is  pierced  by  the  musculo- 
spiral  nerve  and  superior  profunda  vessels. 

MUSCLES. 

The  coraco-brachialis  is  a  rudimentary  muscle  placed  on  the  front  and  inner 
aspect  of  the  arm.  It  arises  in  common  with  the  short  head  of  the  biceps  from 
the  tip  of  the  coracoid  process  of  the  scapula  (Fig.  250,  p.  325),  and  is  commonly 
connected  at  its  origin  with  the  insertion  of  the  pectoralis  minor  The  origin  of 
the  muscle  is  by  fleshy  fibres  attached  (1)  to  the  tip  of  the  coracoid  process  below 
and  internal  to  the  biceps  tendon,  and  (2)  to  the  tendon  of  the  biceps  itself.  The 
muscle  is  partially  subdivided  into  two  parts  by  the  musculo-cutaneous  nerve,  and 
ends  in  a  flat  tendon  inserted  into  a  faint  linear  impression  about  an  inch  in  length 
on  the  middle  of  the  inner  border  of  the  shaft  of  the  humerus  (Fig.  257,  p.  335). 
It  is  often  continued  into  the  internal  intermuscular  septum. 

The  muscle  lies  on  the  inner  side  of  the  biceps,  and  is  concealed  at  first  by  the 
deltoid  and  pectoralis  major.  In  the  lower  part  of  its  extent  it  is  superficial,  and 
forms  a  swelling  beneath  the  skin  on  the  inner  side  of  the  arm  which  serves  as  a 
guide  to  the  axillary  and  brachial  arteries. 

The  coraco-brachialis  is  the  remains  of  a  threefold  muscle,  of  which  only  two  elements  are 
usually  j^resent  in  man,  but  of  which  in  anomalous  cases  all  the  jjarts  may  be  more  or  less  fully 
develoijed.  The  jaassage  of  the  musculo-cutaneous  nerve  through  the  muscle  is  an  indication  of 
its  natural  sejaaration  into  two  parts,  which  rej^resent  the  persistent  middle  and  inferior  elements. 
The  commonest  variety  is  one  in  which  tlie  more  sui^erficial  (inferior)  jiart  of  the  muscle  extends 
farther  down  the  arm  than  usual,  so  as  to  be  inserted  into  the  internal  intermuscular  septum,  or  even 
into  tlie  internal  condyle  of  the  humerus.  A  third  slijj  (coraco-brachialis  superior  or  brevis, 
rotator  humeri)  may  more  rarely  be  jiresent,  forming  a  short  muscle  arising  from  the  root  of  the 
coracoid  process,  and  inserted  into  the  inner  side  of  the  humerus  just  below  the  cajisule  of  the 
shoulder-joint. 

The  biceps  (m.  biceps  brachii)  is  the  large  superficial  muscle  which  lies  on  the 
front  of  the  upper  arm.  It  arises  by  two  tendinous  heads.  (1)  The  short  head  (caput 
breve)  is  attached  in  common  with  the  coraco-l)rachialis  to  the  tip  of  the  coracoid 
process  of  the  scapula  (Fig.  250,  p.  325).  Tendinous  at  first,  this  head  forms  a  separ- 
ate fleshy  belly,  which  is  united  to  the  long  head  by  an  investment  of  the  deep  fascia. 


MUSCLES  OF  THE  AKM. 


Insertion  of  .^^^ 
pectoralis 

MAJOR 

coraco-bracdialis 

Short  head  of  biceps 
Long  head  of  biceps  - 


Brachialis  anticus 


Insertion  ok 
pectoralis 

MINOR 


.._     Axillary  artery 

Musculo- 

cutaneous  nerve 
Median  nerve 

(outer  head) 

— Median  nerve 

\     (inner  head) 

'~~  Ulnar  nerve 


Triceps  (inner  head) 


Musculo-cutaneous  ner\e 


Musculo-spiral  nerve- 


Brachio-radialis 


EXTENSORCARPI  RADIALIS 
LONGIOR 


Radial  artery  (out)  - 


(2)  The  long  head  (caput  longuin)  arises  by  a  round  tendon  from  the  supra-glenoid 
impression  at  the  root  of  the  coracoid  process  and  irom  the  glenoid  ligament  on 
either  side.  Its  tendon 
traverses  the  cavity  of  the 
shoulder-joint,  and  emerging 
from  the  capsule  beneath 
the  transverse  ligament  (in- 
vested by  a  prolongation  of 
the  synovial  membrane),  it 
occupies  the  bicipital  groove 
of  the  humerus,  covered  by 
a  fascial  prolongation  of  the 

tendon  of  the  pectoralis  '^''''' mTjor  ''  \'^^'f  |{r  i 
major.  In  the  upper  arm 
it  forms  a  fleshy  belly  united 
to  that  derived  from  the 
short  head  by  an  envelope 
of  deep  fascia. 

The  insertion  of  the  muscle 
is  likewise  twofold.  (1)  The 
two  bellies  become  connected 
with  a  strong  tendon,  at- 
tached deeply  in  the  hollow 
of  the  elbow  to  the  rough 
posterior  portion  of  the 
bicipital  tubercle  of  the 
radius  (Figs.  264,  p.  343, 
and  271,  p.  351).  A  bursa 
separates  the  tendon  from 
the  anterior  portion  of  the 
tubercle.  (2)  From  the  inner 
and  anterior  part  of  the 
tendon,  and  partly  in  con- 
tinuity with  the  fleshy  fibres 
of  the  muscle,  a  strong  mem- 
branous hand  (the  semilunar 
or  bicipital  fascia)  extends 
downwards  and  inwards  over 
the  hollow  of  the  elbow  to  join 
the  deep  fascia  covering  the 
origins  of  the  flexor  and  pro- 
nator muscles  of  the  forearm. 
Its  upper  part  is  thickened 
and  can  be  felt  subcutaneously 
as  a  crescentic  border. 

Except  at  its  origin  and 
insertion  the  biceps  muscle 
is  placed  superficially  on  the 
front  of  the  arm,  concealing 
the  brachialis  anticus  muscle 
and  the  musculo-cutaneous 
nerve.  The  brachial  artery 
and  median  nerve  lie  along 
its  inner  border.  The  origin 
of  the  muscle  is  deeply  jtlaced 
under  cover  of  the  deltoid 
and  pectoralis  major.  The  tendon  of  insertion  in  the,  liolhnv  of  the  elbow  lies 
beneath  the  end  of  tlie  brachial  and  the  beginning  of  the  radial  artery.  The 
bicipital  fascia  separates  the  brachial  artery  from  the  median  basilic  vein. 


Extensor  ossis 

metacarpi  pollicis 

Radial  artery  (cut) 

Anterior  annular 
ligament 


-Semilunar  fascia  of  biceps 

-Pronator  radii  teres 
^Deep  fascia  of  forearm 

Flexor  carpi  radialis 

Palmaris  longus 
■  Flexor  carpi  ulnaris 
;, Flexor  sublimis  digitorum 

, Flexor  longus  pollicis 

-Pronator  quadratus 
-Ulnar  artery 

-Ulnar  nerve 


Fl(i.    2.0.5. — SUPKHI'IC'IAL 


Muscles  on  the  Fkont  ok  'I'me  Arm 
AND  Forearm. 


su 


THE  MUSCULAE  SYSTEM. 


Tlie  biceps  is  an  extremely  variable  muscle.     lis  cliief  anomalies  are  due  to  an  increase  or 
fliminution  in  the  number  of  origins.     A  third  head  of  origin  is  common  (10  jjer  cent),   and 

nsually  arises  from  the  humerus,  between  the 

__.   .  insertions  of  the  deltoid  and  coraco-brachialis. 

\i^\\}\\' tHI//4/^^  _     '-Trapezius  Two  or  even  three   additional    heads  may  be 

l^resent  at  the  same  time.  The  long  head  of 
the  muscle  may  be  absent,  or  may  take  origin 
from  the  bicipital  groove.  The  muscle  may 
have  an  additional  insertion  into  the  internal 
condyle  of  the  humei'us,  or  into  the  fascia  of 
the  foreai'm. 


Infraspinatus 


Teres  major 


LATISSIiMUS 
DO  RSI 


Tlie  brachialis  anticus  (m.  brachi- 
alis)  is  a  large  muscle  arising  from 
the  lower  two- thirds  of  the  front  of 
the  shaft  of  the  humerus,  ynd  from 
the  inter -muscular  septum  on  each 
side  (Figs.  257  and  258,  p.  335). 
Clasping  the  insertion  of  the  deltoid 
above,  it  ends  below  in  a  strong  tendon 
inserted  into  the  rough  inferior  surl'ace 
of  the  coronoid  process  of  the  ulna  and 
into  the  anterior  surface  of  the  shaft  of 
the  bone  immediately  below  (Fig.  264, 
p.  343).  A  few  of  the  deep  fibres  are 
inserted  into  the  anterior  ligament  of 
the  elbow-joint.  The  outer  part  of  the 
muscle  arising  from  the  external  epi- 
condylic  ridge  and  external  intermus- 
cular septum  forms  a  slip  more  or  less 
separate,  which  may  be  partially  fused 
with  the  brachio-radialis  muscle. 

The  brachialis  anticus  is  almost 
wholly  concealed  from  view  by  the 
biceps  in  front,  the  brachio-radialis 
externally,  and  the  brachial  vessels  in- 
ternally. It  covers  the  elbow-joint,  and 
forms  part  of  the  floor  of  the  hollow 
of  the  elbow.  It  is  separated  from  the 
brachio-radialis  and  extensor  muscles 
of  the  carpus  by  the  musculo  -  spiral 
nerve. 

The  triceps  (m.  triceps  brachii)  is 
the  only  muscle  on  the  back  of  the 
arm.  It  arises  by  three  heads:  an  outer 
and  an  inner  head,  from  the  humerus, 
and  a  middle  or  long  head  from  the 
scapula.  (1)  The  middle,  long  or  scapular 
head  (caput  lougum)  begins  as  a  strong 
tendon  attached  to  a  rough  triangular 
surface  on  the  axillary  border  of  the 
scapula  just  below  the  glenoid  fossa 
(Figs.  254,  p.  330,  and  250,  p.  325). 
This  gives  rise  to  a  fleshy  belly  which 
occupies  the  middle  of  the  back  of  the 
arm.  (2)  The  outer  head  (caput  laterale) 
is  attached  by  fibres,  partly  tendinous 
and  partly  fleshy,  to'  the  curved  outer 
border  of  the  humerus  from  the  insertion  of  the  teres  minor  above  to  the  musculo- 
spiral  groove  below,  and  receives  additional  fibres  from  the  back  of  the  external 
intermuscular  septum  (Fig.  258,  p.  335).     This  origin  is  thick  above  and  becomes 


i   RACHIALIS  ANTICUS 


__  Cxteiinl  iiiteriiinscular  septum 


Brachio  radialis 


Ulnar  ner^e 


EXTFNSOR  CARPI  RADIALIS 
lON&IOR 


KXTENSOR  CARPI  RADIALTS 
BUEVIOR 

Deep  fascia  of  forearm 

Extensor  communis  digitorum 

Extensor  carpi  ulnaris 

Extensor  ossis  metacarpi 
pollicis 

Extensor  brkvis  pollicis 

Extensor  minimi  digiti 
1'endons  oe  Extensors  of 

"C'AHPUS 

Posterior  annular  li>,'ament 
-  Extensor  i.ongus  pollicis 
Extensor  indicis 


Fig.  256. 


-The  ^Muscles  on  the  Back  ok 
Arm,  Forearm,  and  Hand. 


MUSCLES  OF  THE  AEM.  ^35 

linear  below.  Its  fibres  are  directed  downwards  and  inwards  over  the  musculo-spiral 
groo\»e  and  the  inner  head  of  the  muscle  to  the  tendon  of  insertion  (3)  The  inner 
head  (caput  mediale)  arises  by  fleshy  fibres  from  an  elongated  triangular  area  on  the 
back  of  the  humerus,  extending  upwards  to  the  level  of  the  insertion  of  the  teres 
major  on  the  inner  side,  and  downwards  nearly  to  the  margin  of  the  olecranon  fossa. 
(Fig.  258,  p.  335).     Externally  it  is  limited  above  by  the  musculo-spiral  groove  ; 


I'ere.s  minor  (in.sertioii 


riceps  :  outer  head 
(origin) 


Deltoid  (insertion) 


Fig.  257.- 


Extensor  carpi 
radiaiis  longior 
origin) 

Common  tendon 
for  origin  of 
pronator  radii 
teres  and  flexor 
muscles  of 
forearm 

Common  tendon  for  origin  of 
extensor  muscles  of  forearm 

-Mu.scle-Attachments  to  the  Front  of 
THE  Humerus. 


Common  tendon  for 
origin  of  extensor 
muscles  of  forearm 

Anconeus  (origin) 


Fig.  258. — Muscle-Attachments  to  , the  Back 
OF  THE  Humerus. 


and  below  it  extends  downwards  on  either  side  of  the  olecranon  fossa  almost  to 
the  condyles  of  the  humerus.  It  also  arises  on  each  side  from  the  intermuscular 
septa, — from  the  whole  length  of  the  internal  septum,  and  from  the  part  of  the 
external  septum  which  is  below  the  passage  of  the  musculo-spiral  nerve. 

The  three  heads  of  origin  are  inserted  by  a  common  tendon,  broad  and  membranous, 

into  an  imjmjssion  occu])ying  the  posterior  part  of  the  upper  end  of  the  olecranon 

process  of  the  ulna  CFig.  271,  ]).  351),  and  into  the  deep  fascia  of  the  forearm 

on  either  side  of  it.     Tlu^  long  and  outer  heads  join  the  borders  of  the  tendon  of 

23  h 


336 


THE  MUSCULAE  SYSTEM. 


insertion,  and  the  inner  head  is  attached  to  its  deep  surface.  A  small  thick-walled 
bursa  separates  the  tendon  of  the  triceps  from  the  posterior  ligament  of  the  elbow- 
joint  and  the  anterior  part  of  the  upper  end  of  the  olecranon  process. 

The  long  head  of  the  triceps  is  concealed  at  first  by  the  teres  major  and  teres 
minor,  and  by  the  deltoid  muscle.  Along  with  the  outer  head  it  conceals  the  musculo- 
spiral  nerve  and  superior  profunda  artery,  and  covers  the  inner  head  of  the  muscle. 
The  inner  is  the  deep  head,  and  is  only  visible  at  the  lateral  borders  of  the  muscle. 

Tlie  subanconeus  i«  a  small  muscle  occasionally  present,  whicli  consists  of  scattered  fibres 
arising  from  the  lower  end  of  tlie  humerus  beneath  the  triceps,  and  inserted  into  the  posterior 
ligament  of  the  elbow-joint. 

Nerve-Supply. 
The  following  nerves  sujaply  the  muscles  of  the  arm  : — 


Muscles. 

Nerves. 

Origin. 

Coraco-brachialis  \ 

BicejDS 

Bi-acliialis  anticusj 

Bracliialis  anticus                 -^ 

Triceps 

Outer  head 

Middle  and  inner  heads  j 

Musculo-cutaneous 
Musculo-spiral 

rC.    7. 

-  C.    5.    6. 
[C.     5.     6. 

rC.    (5)     6. 

-  C.    (6)     7.     8. 
1 C.     7.     8. 

Actions. 


(1)  The  chief  action  of  these  muscles  (excepting  the  coraco-brachialis)  is  on  the  elbow -joint, 
producing  along  with  other  muscles  flexion  and  extension.  The  flexor  muscles  are  nuich  more 
powerful  than  tlie  extensors. 

Table  of  Muscles  acting  on  the  Elbow-Joint. 


Flexors. 

1 
Extensors. 

Biceps 

Bracliialis  anticus 

Brachio-radialis 

Pronator  radii  teres 

Flexors  of  wrist  and  fingers 

Extensors  of  wrist  (in  pronation) 

Triceps 

Anconeus 

Extensors  of  wrist  and  fingers  (in  supination)    i 

(2)  The  coraco-brachialis  muscle  acts  only  on  the  shoulder-joint,  assisting  the  biceps  as  an 
adductor  and  flexor  of  the  humerus. 

(3)  Subordinate  and  accessory  movements  are  performed  by  all  the  muscles  of  this  group 
except  the  bracliialis  anticus.  The  biceps  supinates  the  forearm,  flexes  the  elbow,  and  witli  the 
aid  of  the  coraco-bracliialis  adducts  and  flexes  the  humerus  at  the  shoulder-joint.  The  triceps 
through  its  scajiular  head  adducts  and  extends  the  humerus,  besides  extending  the  ell^ow-joint. 


FASCIA   AND    MUSCLES   OF   THE   FOEEAEM   AND   HAND. 


FASCI.E. 

The  superficial  fascia  in  the  forearm  presents  no  exceptional  features.  On 
the  dorsum  of  the  hand  it  is  loose  and  thin;  in  the  palm  it  is  generally  well 
furnished  with  fat,  forming  pads  for  the  protection  of  the  vessels  and  nerves.  It  is 
closely  adherent  to  the  palmar  fascia  and  to  the  skin,  especially  along  the  lines  of 
flexure. 

The  palmaris  brevis  is  a  quadrilateral  subcutaneous  muscle  occupying  the 
inner  side  of  the  hand  under  the  superficial  fascia.  It  arises  from  the  inner  border 
of  the  thick  central  portion  of  the  palmar  fascia  and  from  the  front. of  the  anterior 
annular  ligament  of  the  wrist,  and  is  inserted  into  the  skin  of  the  inner  border  of 
the  hand  for  a  variable  distance.  It  covers  the  ulnar  artery  and  nerve,  branches 
of  which  supply  it.     Its  action  is  to  wrinkle  the  skin  of  the  inner  border  of  the 


MUSCLES  OF  THE  EOKEAEM  AiS'D  HAND. 


ulnar  nerve 


First  dorsal  iNrtR 

OSSEOUS  MU'tiCLh 

AriDL'CTOR  TRANS 

VERSUS  POLLICIS 

Digital  biancliKs 
(median  ner\e) 


Abductor  polliois 


Opponens  pollicis 

Superficial  volar  artery 
Palmaeis  longus  tendon 


hand,  and  by  raising  up  the  skin  and  superficial  fascia,  to  deepen  tlx;  hollow  of 
the  hand. 

The  deep  fascia  of  the  forearm  and  hand  is  continuous  above  with  the  deep 
fascia  of  the  arm.  At  the  upper  part  of  the  forearm  it  is  strengthened  by  additional 
fibres  around  the  elbow;  in  front  by  fibres  from  the  semilunar  fascia  of  the 
biceps,  behind  by  the  fascial  insertions  of  the  triceps,  and  laterally  Ijy  fibres  derived 
from  the  humeral 

T     1         ■  ^  '  Collateral  digital  branches      Collatei'al  digital 

COnClyieS   in   rela-  of  the  mediau  nerve        branches  of  the 

tion  to  the  com- 
mon tendons  of 
origin  of  the 
fiexor  and  ex- 
tensor muscles  of 
the  forearm.  It 
closely  invests 
and  gives  origin 
to  these  muscles. 
It  is  attached  to 
the  posterior 
border  of  the  ulna 
in  the  whole 
length  of  the  fore- 
arm, and  aftbrds 
increased  attach- 
ment to  the  flexor 
and  extensor 
carpi  ulnaris  and 
the  flexor  pro- 
fundus digitorum 
muscles.     Above 

the    wrist     the  Fig.  259.— The  Palm  op  the  Hand  (Superficial  Dissection). 

fascia  is   pierced 

anteriorly  by  the  tendon  of  the  palmaris  longus,  and  by  the  ulnar  artery  and  nerve. 
At  the  wrist  it  gains  attachment  to  the  bones  of  the  forearm  and  carpus,  is  greatly 
strengthened  by  addition  of  transverse  fibres,  and  constitutes  the  annular  ligaments. 

The  anterior  annular  ligament  of  the  wrist  is  a  band  about  an  inch  and  a 
half  in  depth,  continuous  above  and  below  with  the  deep  fascia  of  the  forearm  and 
the  palm  of  the  hand.  It  is  attached  to  the  scaphoid  and  trapezium  externally : 
to  the  pisiform  and  unciform  bones  internally ;  and  it  forms  a  membranous  arch 
binding  down  in  the  hollow  of  the  carpus  the  flexor  tendons  of  the  fingers  and  the 
median  nerve.  It  is  divided  into  hoo  compartments,  the  larger  accommodating  the 
tendons  of  the  flexors  of  the  digits  and  the  median  nerve,  the  smaller  (placed 
externally)  containing  the  tendon  of  the  flexor  carpi  radialis.  There  are  tho^ee 
synovial  membranes  in  these  compartments :  one  for  the  flexor  carpi  radialis 
tendon,  and  two  others,  which  often  communicate  together,  enveloping  the  tendon 
of  the  flexor  longus  pollicis  and  the  flexor  tendons  of  the  fingers  respectively. 
The  surface  of  the  ligament  is  crossed  by  the  palmar  branches  of  the  median  and 
ulnar  nerves ;  by  the  tendon  of  the  palmaris  longus  muscle,  which  is  attached  to 
its  surface ;  and  by  the  ulnar  artery  and  nerve,  which  are  again  bridged  over  and 
protected  by  a  band  of  fibrous  tissue  passing  from  the  pisiform  bone  and  the 
superficial  fascia  to  the  surface  of  the  ligament.  To  the  lower  border  of  the 
ligament  arc  attached  the  palmar  fascia  in  the  centre,  and  the  superficial  muscles 
of  tlie  thumb  and  the  muscles  of  the  little  finger  on  each  side. 

'J'lie  posterior  annular  ligament  of  the  wrist  is  placed  at  a  higher  level 
than  the  previous  ligament.  It  consists  of  an  oblique  band  of  fibres  about  an 
inch  broad,  continuous  above  and  below  with  the  deep  fascia  of  the  forearm  and 
hand.  It  is  attached  externally  to  the  outer  side  of  the  lower  end  of  the  radius, 
and  internally  to  the  lower  end  of  the  ulna  (styloid  process),  the  carpus,  and  the 
internal  lateral  ligament  of  the  wrist.     It  is  covered  by  veins,  Ity  the  radial  nerve, 


338 


THE  MUSCULAE  SYSTEM. 


and  by  the  dorsal  branch  of  the  uhiar  nerve.  Six  compartments  are  formed 
beneath  it  by  the  attachment  of  septal  bands  to  the  lower  ends  of  the  radius 
and  ulna.  Each  compartment  is  provided  with  a  synovial  mem,brane,  and  they 
serve  to  transmit  the  extensor  tendons  of  the  wrist  and  fingers  in  the  following 
order  from  without  inwards : — 

1.  Extensor  ossis  metacarpi  pollicis  and  extensor  breads  pollicis. 

2.  Extensores  carpi  radiales,  longior  and  brevior. 

3.  Extensor  longus  pollicis. 

4.  Extensor  communis  digitorum  and  extensor  indicis. 

5.  Extensor  minimi  digiti. 

6.  Extensor  carpi  ulnaris. 


Flexor  profundus-^^ 
digitorum 


Flexor  sublimis__ 
digitorum 


lumbricales' 

Flexor  profundus 

DIGITORUM  tendons 

Flexor  sublimis 

DIGITORUM  tendons 

OpPONENS  MINIMI 

DIGITI 

Flexor  brevis  minimi  digiii 


Abductor  minimi  digiti 

Origin  of  palmar  fascia  (cut) 
Anterior  annular  ligament 

Palmaris  longuv 

Flexor  carpi  ulnari; 

fr.exor  sublimi'5  digitorum 


Tendon  of  flexor 
longus  pollicis 

dductor  transverstjs 

IMiLLICIS 

—  Adductor  obliquus  po'llicis 
Flexor  brevis  pollicis 
^ Abductor  pollicis 


xtensor  ossis  metacarpi  pollicis 


—  J Flexor  carpi  radialis 

Posterior  annular  ligament 


Fig.  260. — The  Muscles  and  Tendons  in  the  Palm  of  the  Hand. 

The  thin  deep  fascia  of  the  dorsum  of  the  hand  is  lost  over  the  expansions  of 
the  extensor  tendons  on  the  fingers.  Between  the  metacarpal  bones  a  strong  layer 
of  fascia  covers  and  gives  attachment  to  the  interossei  muscles. 

The  palmar  fascia  is  of  considerable  importance.  In  the  centre  of  the  palm 
it  forms  a  thick  triangular  membrane,  the  apex  of  which  joins  the  lov.^er  edge  of 
the  anterior  annular  ligament,  and  receives  the  insertion  of  the  tendon  of  the 
palmaris  longus  muscle.  The  fascia  separates  below  into  four  slips,  one  for  each 
finger,  connected  together  by  transverse  fibres,  forming  beneath  the  webs  of  the 
fingers  the  superficial  transverse  metacarpal  ligament.  Beyond  this  each  slip 
separates  into  two  parts,  to  be  connected  to  the  sides  of  the  metacarpo-phalangeal 
joints  and  the  first  phalanx  of  the  inner  four  digits.  In  the  cleft  between  the  two 
halves  of  each  slip  the  digital  sheath  is  attached  and  extends  downwards  on  to  the 
finger.     The  lateral  borders  of  this  triangular  central  portion  of  the  palmar  fascia 


MUSCLES  OF  THE  FOKEAKM  AND  HAND.  339 

are  continuous  with  thin  layers  of  deep  fascia,  which  cover  and  envelop  the  inusfjles 
of  the  thenar  and  hypothenar  eminences.  The  inner  border  gives  origin  to  the 
palmaris  hrevis  muscle. 

The  digital  sheaths  are  tubular  envelopes  extending  along  the  anterior  aspect 
of  the  digits  and  enclosing  the  flexor  tendons.  Each  consists  of  a  fibrous  sheath 
attached  to  the  lateral  borders  of  the  phalanges  and  inter-phalangeal  joints,  and 
continuous  above  with  the  palmar  fascia.  Opposite  each  inter-phalangeal 
articulation  the  digital  sheath  is  loose  and  thin ;  opposite  the  first  two  phalanges 
(the  first  only  in  the  case  of  the  thumb)  it  becomes  extremely  thick,  and  gives 
rise  to  the  ligamenta  vaginalia,  which  serve  to  keep  the  tendons  closely  applied 
to  the  bones  during  flexion  of  the  fingers.  Within  each  digital  sheath  are  the  flexor 
tendons,  enveloped  in  a  synovial  membrane  which  not  only  envelops  the  tendon, 
but  also  lines  the  interior  of  the  sheath.  The  synovial  membranes  of  the  digital 
sheaths  extend  a  short  distance  upwards  in  the  palm,  and  in  some  cases  com- 
municate with  the  large  synovial  membranes  lining  the  flexor  tendons  beneath 
the  annular  ligament.  There  may  be  a  separate  distinct  synovial  membrane  for 
each  digit ;  but  most  commonly  only  the  sheaths  for  the  three  middle  digits  have 
separate  synovial  membranes ;  those  for  the  flexor  longus  poUicis  and  for  the 
flexor  tendons  of  the  little  finger  communicate  usually  with  the  synovial  mem- 
branes placed  beneath  the  anterior  annular  ligament. 

THE  MUSCLES  ON  THE  FRONT  AND  INNER  ASPECT  OF 
THE  FOREARM. 

The  pronator  and  flexor  muscles  which  lie  on  the  front  of  the  forearm  occupy 
different  levels,  and  are  divisible  into  two  main  groups,  superficial  and  deep. 

SuPEEFiciAL  Muscles. 

The  superficial  niuscles  form  the  prominence  on  the  front  and  inner  side  of 
the  forearm,  and  all  take  origin  in  whole  or  part  by  means  of  a  common  tendon 
from  the  internal  condyle  of  the  humerus.  The  group  comprises  five  muscles — 
pronator  radii  teres,  flexor  carpi  radialis,  palmaris  longus,  flexor  carpi  ulnaris,  and 
flexor  sublimis  digitorum. 

The  pronator  radii  teres  (m.  pronator  teres)  is  the  most  external  and  shortest 
muscle  of  this  group.  It  has  a  double  origin:  (1)  a  super/lcial  head,  the  main  origin, 
partly  fleshy,  partly  tendinous,  from  the  lowest  part  of  the  internal  supracondyloid 
ridge  of  the  humerus  and  from  the  internal  intermuscular  septum,  from  the  internal 
condyle  of  the  humerus,  from  the  fascia  over  it,  and  from  an  intermuscular  septum 
between  it  and  the  flexor  carpi  radialis  (Fig.  257,  p.  335) ;  (2)  a  dee]3  head,  a 
slender  tendinous  slip  from  the  inner  side  of  the  coronoid  process  of  the  ulna, 
which  joins  the  superficial  origin  of  the  muscle  on  its  deep  surface  (Fig.  264, 
p.  343).  The  median  nerve  separates  the  two  heads  from  one  another.  The  muscle 
is  directed  downwards  and  outwards  to  be  inserted  by  tendon  into  an  oval 
impression  on  the  middle  of  the  outer  surface  of  the  shaft  of  the  radius  (Figs. 
264,  p.  343,  and  271,  p.  351).  The  fibres  of  the  muscle  are  twisted  on  themselves, 
so  that  the  highest  humeral  fibres  form  the  lowest  fibres  of  the  tendon  of 
insertion,  and  the  lowest  humeral  fibres  and  those  arising  from  the  coronoid 
process  are  highest  at  the  insertion  of  the  muscle. 

The  muscle  forms  the  inner  boundary  of  the  hollow  of  the  elbow.  It  is  super- 
ficially placed,  except  near  its  insertion,  where  it  is  covered  by  the  brachio-radialis 
muscle  and  by  the  radial  vessels  and  nerve.  The  flexor  carpi  radialis  is  on  its  inner 
side.  The  muscle  conceals  the  ulnar  and  radial  origins  of  the  flexor  sublimis 
digitorum,  and  the  median  nerve  and  ulnar  artery,  which  are  separated  from  one 
another  by  tlie  di'(;])  head  of  origin. 

The  flexor  carpi  radialis  muscle  takes  its  origin  from  the  c'unmon  tendon  J'rom 
the  int(;rnal  condyle  of  the  humerus,  from  the  fascia  over  it,  and  from  the  inter- 
muscular septa  on  either  side.  Its  fleshy  belly  gives  place  to  a  strong  round 
tendon  in  the  lower  half  of  the  forearm,  which,  at  the  wrist,  enters  the  hand  in  a 


340 


THE  MUSCULAE  SYSTEM. 


A, 


special  compartment  beneath  the  anterior  annular  ligament,  and  after  occupying 
the  groove  on  the  trapezium,  is  inserted  into  the  upper  ends  of  the  second  and 
third  metacarpal  bones  on  their  anterior  surfaces.     The  chief  tendon  is  that  to  the 

second  metacarpal  bone,  which 
gives  off  a  small  slip  on  its 
inner  side  to  be  attached  to 
the  third  metacarpal  bone. 
Each  is  inserted  about  a 
quarter  of  an  inch  below  the 
carpo- metacarpal  joint  (Fig. 
267,  p.  346). 

The  flexor  carpi  radialis  is 
superficial  except  near  its  in- 
sertion. Its  fleshy  belly  in  the 
upper  half  of  the  forearm  lies 
between  the  pronator  radii 
teres  and  the  palmaris  longus, 
and  conceals  the  flexor  sub- 
limis  digitorum.  Its  tendon 
in  the  lower  half  of  the  fore- 
arm is  subcutaneous,  on  the 
outer  side  of  the  palmaris  longus 
tendon.  It  is  an  important 
guide  to  the  radial  vessels 
which  are  placed  in  the  hollow 
external  to  it.  Just  above  the 
wrist  it  crosses  obliquely  the 
tendon  of  the  flexor  longus 
pollicis.  After  passing  beneath 
the  anterior  annular  ligament 
the  tendon  is  concealed  by  the 
origins  of  the  short  muscles  of  the  thumb,  and  is  crossed  from  witliin  outwards  by 
the  tendon  of  the  flexor  longus  pollicis.  Besides  the  synovial  bursa  enveloping 
the  tendon  beneath  the  annular  ligament,  another  is  found  beneath  the  tendons 
at  their  insertion. 

The  palmaris  longus  arises  also  from  the  common  flexor  tendon,  from  the 
internal  condyle  of  the  humerus,  from  the  fascia  over  it,  and  from  intermuscular 
septa  on  either  side.  It  forms  a  short  fusiform  muscle,  which  ends  in  the  middle 
of  the  forearm  in  a  long  flat  tendon.  This  pierces  the  deep  fascia  above  the  wrist, 
and  passing  over  the  anterior  annular  ligament,  is  inserted  (1)  into  the  surface  of 
the  anterior  annular  ligament,  and  (2)  into  the  apex  of  the  thick  central  portion  of 
the  palmar  fascia.  A  tendinous  slip  is  frequently  sent  to  the  short  muscles  of  the 
thumb  and  the  fascia  covering  them. 

The  pahnaris  longus  is  the  smallest  muscle  of  the  forearm.  It  is  placed  between 
the  flexor  carpi  radiahs  and  the  flexor  carpi  ulnaris,  and  upon  the  flexor  sublimis 
digitorum.  In  the  lower  third  of  the  forearm  its  tendon  is  placed  directly  over  the 
median  nerve,  along  the  outer  border  of  the  tendons  of  the  flexor  sublimis  digitorum. 

The  palmaris  longus  is  the  most  variable  muscle  in  the  body,  and  is  often  absent  (10  per  cent). 

The  flexor  carpi  ulnaris  muscle  has  a  double  origin,  from  the  humerus  and  from 
the  ulna.  (1)  It  arises  from  the  common  tendon  attached  to  the  inner  condyle  of  the 
humerus,  from  the  fascia  over  it,  and  from  an  intermuscular  septum  externally.  (2) 
By  means  of  the  deep  fascia  of  the  forearm  it  obtains  an  attachment  to  the  inner 
border  of  the  olecranon  process  and  the  posterior  border  of  the  ulna  in  its  upper 
three-fifths.  The  fleshy  fibres  join  a  tendon  which  lies  on  the  anterior  border  of  the 
muscle  and  is  inserted  into  the  pisiform  bone.  From  the  pisiform  bone  the  fibres 
are  continued  in  the  form  of  two  ligamentous  bands  (pisi-unciform  and  pisi-meta- 
carpal)  to  be  attached  to  the  upper  margin  of  the  hook  of  the  unciform  bone,  and 
the  palmar  surface  of  the  upper  end  of  the  fifth  metacarpal  bone  (Fig.  267,  p.  346). 


Fig.  261.  — Section  across  the  Forearm  in  the  Middle 

Third. 
Pronator  radii  teres  (insertion) ;  B,  Flexor  carpi  radialis  ;  C, 
Flexor  sublimis  digitorum  ;  D,  Palmaris  lonous  ;  E,  Flexor  carpi 
ulnaris  ;  F,  Flexor  profundus  digitorum  ;  G,  Extensor  carpi 
ulnaris  ;  H,  Extensor  longus  pollicis  ;  I,  Extensor  communis 
digitorum  and  extensor  minimi  diqiti  ;  J,  Extensor  ossis  metacarpi 
pollicis  ;  K,  Extensor  carpi  radialis  brevior  ;  I;,  Extensor  carpi 
radialis  longior  ;  M,  Brachio-radialis.  a,  Radius  ;  6,  Interosseous 
membrane  ;  c,  Ulna.  1,  Radial  nerve  ;  2,  Radial  Artery ;  3,  Anterior 
interosseous  artery  ;  4,  Anterior  interosseous  nerve  (underneath  flexor 
longus  pollicis) ;  5,  Median  nerve  ;  6,  Ulnar  artery  7,  Ulnar  nerve  ;  8, 
Posterior  interosseous  artery  ;  9,  Posterior  interosseous  nerve. 


MUSCLES  ON  FEONT  AND  INNER  ASPECT  OF  FOREARM.       841 


\](iH 


Biacliial  aitery 


Meilian  iieive 


Ulnar  nerve 


Musculo-spiral 
nerve 

Brachio 
radialis 

extfnsor 

CARPI  RADIALIi 
LONOIOl 

Posterior  interosseous 

neive 

Supinator  radii 

BREVIS 

Radial  nervi 


Semilunar  fascia 
(reflecteil) 


Origins  of 
superficial  muscles 


FlE\0E  carpi  ULNARIS 


The  muscle  is  superficially  placed  along  the  inner  border  of  the  forearm.  It 
internal  to  the  palmaris 
longus  and  flexor  sublimis 
digitorum,  and  conceals  the 
flexor  profundus  digitorum 
muscle.  The  ulnar  nerve 
(which  enters  the  forearm 
between  the  two  heads  of 
origin  of  the  muscle)  is 
concealed  by  it  in  its  whole 
length.  The  ulnar  artery 
lies  undercover  of  the  muscle 
in  its  lower  two  -  thirds. 
The  tendon  of  the  muscle 
serves  as  a  guide  to  the 
artery  in  the  lower  half 
of  the  forearm. 

The  flexor  sublimis 
digitorum  occupies  a  deeper 
plane  than  the  four  previous 
muscles.  It  has  a  threefold 
origin,  from  the  humerus, 
radius,  and  ulna.  (1)  The 
chief  or  humeral  origin  is 
from  the  internal  condyle 
of  the  humerus  by  the 
common  tendon,  from  the 
internal  lateral  ligament  of 
the  elbow,  and  from  ad- 
jacent inter-muscular  septa. 

(2)  The  ulnar  origin  is 
by  a  slender  fasciculus  from 
the  inner  border  of  the  cor- 
onoid  process  of  the  ulna, 
above  and  internal  to  the 
origin  of  the  pronator  radii 
teres    (Fig.    264,    p.    343). 

(3)  The  radial  origin  is 
from  the  oblique  line  and 
middle  third  of  the  anterior 
border  of  the  radius  by  a 
thin  fibro-muscular  attach- 
ment (Fig.  264,  p.  343). 

The  muscle  divides  in 
the  lower  third  of  the  fore- 
arm into  four  parts,  each 
provided  with  a  separate 
tendon  which  passes  be- 
neath the  anterior  annular 
ligament,  traverses  the  palm 
of  the  hand,  and  enters  the 
corresponding  digital  sheath. 
Within  the  digital  sheath 
each  tendon  is  split  into 
two  parts  by  the  tendon  of 
the  flexor  profundus  digi- 
torum ;  after  surrounding 
that  tendon  the  two  parts  are  ])artially  re-united  on  its  (he\)  surface,  find  are  inserted, 
after  partial  decussation,  in  two  portions  into  the  sides  of  the  second  ])liahuix. 


Brachio-radialis 

Extensor  carpi 
radialis  loxgior 

Extensor  carpi 
radialis  brevior 

Plexor  longus 
pollicis 


Extensor  ossis 

METACARPI  POLLICIS 

Radial  artery 

Plexor  carpi 

RADIALIS  (tendon) 

Muscular  branch 
of  median  ner\  e 


Flexor  longus 
pollicis 


Ulnar  arteiy 

Dn  ision  of  ulnar  nerve 


OpPONENS  POLLICIS 

Abductor  pollicis 
Flexor  brevis  pollicis 

\  Tendons  of  flexor 
/sublimis  digitorum 


"\  Tendons  of 
v  flexor  pro- 
j  fundus  digitorum 


Fig.  262.— The  Musoi,es  and  Nerves  on  the  Front  of  the 

FOHBARM    AND    HaND. 


'J'lic  pronator  radii  teres,  flexor  carj)i  radiiili.s, 
have  Ijeeii  removed. 


iiid  palmaris  longus 


342 


THE  MUSCULAE  SYSTEM. 


Ligain 


The  vincula  accessoria  tendinum  form  additional  insertions  of  the  muscle. 
They  consist  of  delicate  hands  of  connective  tissue  enveloped  in  synovial  membrane, 
and  are  known  as  the  ligamenta  longa  and  brevia.  Tlie  ligamentum  breve  is  a 
triangular  band  of  fibres  containing  yellow  elastic  tissue  (ligamentum  sub- 
flavum),  occupying  the  interval  between  the  tendon  and  the  digit  for  a  short  distance 

close  to  the  insertion.  It  is  attached 
to  the  front  of  the  inter-phalangeal 
articulation  and  the  head  of  the  first 
phalanx.  The  ligamentum  longum  is 
a  long  narrow  band  extending  from  the 
back  of  the  tendon  to  the  upper  part 
of  the  anterior  surface  of  the  first 
phalanx. 

The  flexor  sublimisdigitorum  muscle 
is  partially  concealed  in  the  forearm  by 
the  pronator  radii  teres,  flexor  carpi 
radialis,  and  palmaris  longus  muscles, 
and  by  the  radial  vessels  and  nerve. 
It  conceals  the  flexor  profundus  digi- 
torum  and  flexor  longus  pollicis  muscles, 
the  median  nerve,  and  the  ulnar  artery. 
Its  inner  border  is  in  contact  with  the 
flexor  carpi  ulnaris,  and  in  the  lower 
half  of  the  forearm  with  the  ulnar 
vessels  and  nerve.  The  median  nerve 
emerges  at  its  outer  border  above  the 
wrist,  and  separates  the  muscle  from 
the  tendon  of  the  flexor  carpi  radialis. 
At  the  wrist  the  four  tendons  are 
arranged  in  pairs,  those  for  the  middle 
and  ring  fingers  in  front,  those  for  the 
fore  and  little  fingers  behind,  and  are  enveloped  in  a  synovial  sheath  (along  with 
the  tendons  of  the  flexor  profundus  digitorum)  beneath  the  anterior  annular 
ligament.  In  the  palm  the  tendons  separate,  and  lying  beneath  the  superficial 
palmar  arch  conceal  the  tendons  of  the  deep  flexor  and  the  lumbrical  muscles. 
Within  the  digital  sheaths  on  the  fingers  the  tendons  at  first  conceal  those  of  the 
deep  flexor ;  after  being  pierced  by  them,  they  are  in  turn  concealed  by  these 
tendons  at  their  insertion. 


Ligamentum  breve 
Flexor  sitblimis  diqitorum 

Expansion  of  extensor  tendon 
Flexor  profundus 
digitorum 


First  lumbrical  muscle 


First  dorsal  inter- 
osseous MUSCLE 


Extensor  indicis  tendon 


Extensor  communis 
digitorum  tendon 


Fig.  263. — The  Tendons  attachkd  to  the  Index 

FiNGEE. 


Deep  Muscles. 


The  deep  muscles  on  the  front  of  the  forearm  are  three  in  number  :  flexor 
profundus  digitorum,  flexor  longus  pollicis,  and  pronator  quadratus. 

The  flexor  profundus  digitorum  is  a  large  muscle  arising  from  the  ulna,  the 
interosseous  membrane,  and  the  deep  fascia  of  the  forearm.  Its  ulnar  origin  is 
from  the  anterior  and  inner  surfaces  of  the  bone  in  its  upper  two-thirds,  extending 
up  so  as  to  include  the  inner  side  of  the  olecranon  process,  and  to  embrace  the 
insertion  of  the  brachialis  anticus  into  the  coronoid  process.  It  arises  externally 
from  the  inner  half  of  the  interosseous  membrane  in  its  middle  third  (Figs.  264, 
p.  343,  and  271,  p.  351),  and  internally  from  the  deep  fascia  of  the  forearm  behind 
the  origin  of  the  flexor  carpi  ulnaris. 

The  muscle  forms  a  broad  thick  tendon  which  passes  beneath  the  anterior 
annular  ligament,  and  divides  in  the  palm  into  four  tendons  for  insertion  into  the 
terminal  phalanges  of  the  fingers.  The  tendon  associated  with  the  forefinger  is 
usually  separate  from  the  rest  of  the  tendons  in  its  whole  length.  Each  tendon  enters 
a  dio-ital  sheath  beneath  the  tendon  of  the  flexor  sublimis  digitorum,  which  it 
pierces  opposite  the  first  phalanx,  and  is  finally  inserted  into  the  base  of  the 
terminal  phalanx.      Like  the  tendons  of  the  flexor  sublimis,  those  of  the  deep 


MUSCLES  ON  FRONT  AND  INNER  ASPECT  OF  FOREARM.     343 


Brachialis  anticus  (insertion)  i 
Supinator  radii  bre\'is 
(ulnar  origin) 


Supinator  radii 
brevis(insertion) 


Flexor  sublimis 

digitoruni  (radial 

origin) 


Pronator  radii 
teres  (insertion) 


Flexor  longus 
pollicis  (origin) 


Flexor  sublimis  digi- 
toruni (ulnar  origin) 
Pronator  radii  teres 
(ulnar  origin) 
Flexor  longus  pollicis 
(occasional  origin) 


Bicejjs  (insertion) 


flexor  are  provided  with  vincula  accessoria,  viz.  ligamenta  brevia  attached  to  the 
capsule  of  the  second  iuter-phalangeal  articulation,  and  ligamenta  longa,  which 
are  in  this  case  connected  to  the  tendons  of  the  subjacent  flexor  sublimis 
dig'itorum. 

Lunibricales. — Four  small  cylindrical  muscles  are  associated  with  the  tendons 
of  the  flexor  profundus  digitoruin  m  the  palm  of  the  hand.  The  tvjo  outermost 
muscles  arise  each  by  a  single  head  from  the  radial  sides  of  the  tendons  of  the 
flexor  profundus  digitorum  destined 
respectively  for  the  fore  and  middle 
fingers.  The  two  innermost  muscles 
arise,  each  by  two  heads,  from  the 
adjacent  sides  of  the  second  and 
third,  and  third  and  fourth  tendons. 
From  these  origins  the  muscles  are 
directed  downwards  to  the  radial 
side  of  each  of  the  metacarpo- 
phalangeal joints,  to  be  inserted  into 
the  capsules  of  these  articulations, 
the  outer  border  of  the  first  phalanx, 
and  chiefly  into  the  outer  side  of 
the  extensor  tendon  on  the  dorsum 
of  the  phalanx.  The  lumbricales 
vary  considerably  in  number,  and 
may  be  increased  to  six  or  di- 
minished to  two. 

In  the  forearm  the  flexor  pro- 
fundus digitorum  is  concealed  by 
the  flexor  sublimis  digitorum  and 
flexor  carpi  ulnaris  muscles,  and 
by  the  ulnar  nerve  and  artery. 
Under  the  anterior  annular  liga- 
ment the  muscle  is  placed  beneath 
the  tendons  of  the  flexor  subhmis 
digitorum,  and  is  enveloped  in  the 
common  bursal  sac.  In  the  palm 
the  tendons,  along  with  the  lum- 
brical  muscles,  cover  the  deep  palmar 
arch  and  the  interossei  muscles, 
and  are  concealed  by  the  tendons 
of  the  flexor  sublimis  digitorum. 
On  the  finger  each  tendon  is  placed  p^^^^^^^  ^^,,^^. 
at  first  beneath,  and  afterwards  ratus  (insertion) 
pierces,  the  tendon  of  the  flexor 
sublimis  digitorum  in  its  passage 


Brachio-radialis 
(insertion) 


Flexor  XJi'ofundus 
digitorum  (origin) 


I'ronator  quadratus 
(origin) 


Fig.  264. — Muscle-Attachments  to  the  Kadius  and  Ulna 
(Anterior  Aspects). 


through  the  digital  sheath.  The 
lumbrical  muscles  passing  down- 
wards on  the  radial  side  of  the 
deep  flexor  tendons  lie  beneath  the 
digital  vessels  and  nerves  on  their 
way  to  their  insertion. 

The  flexor  longus  pollicis  arises  by  fleshy  fibres  from  the  anterior  surface  of 
the  shaft  of  the  radius  in  its  middle  two-fourths,  and  from  a  corresponding  portion 
of  the  interosseous  membrane.  It  has  an  additional  origin  occasionally  from  the 
inner  border  of  the  coronoid  process  of  the  ulna  (Fig.  2G4,  p.  343).  Its  radial 
origin  is  limited  above  by  the  oblique  line  and  the  origin  of  the  flexor  sublimis 
digitorum,  and  below  by  the  insertion  of  the  pronator  quadratus  iftuscle.  The 
muscle  ends  above  the  wrist  in  a  tendon,  which  passes  into  the  liand  beneath  the 
anterior  annular  ligament,  enveloped  in  a  special  synovial  sheath.  In  front  of  the 
carjjus  it  crosses  over  the  tendon  of  the  flexor  carpi  radialis.     In  tiie  palm  the 


344 


THE  MUSCULAE  SYSTEM. 


Internal  iiitermusculai 


Common  ORiorN  op  pronaior  and 
fij:xor  MU'^rLE'i 

Brachialis  ANiicns 


Termination  of  musculo  spiral 
nprve 

Biceps  ilndon 

Ulnai  nene 
Supinator  radii  brevis — 
Median  nerve- 
Ulnar  origin  of  flexor  lonous  poi  i  icis 

Flexor  carpi  ulnaris 
Badial  origin  of  flexor 

SUKLIMIS  DIGirORUM 


Flexor  profundus  dicitorum 


Kadtat,  origin  of  flexor 
lonous  poliicis 


tendon  is  directed  downwards  along  the  inner  side  of  the  thenar  eminence,  between 

the  flexor  brevis  and  adductor 
muscles  of  the  thumb,  to 
be  inserted  into  the  base  of 
the  terminal  phalanx  of 
the  thumb  on  its  anterior 
surface. 

In  the  forearm  the  muscle 
is  deeply  placed  beneath 
the  flexor  sublimis  digjit- 
orum  and  flexor  carpi  radialis 
muscles.  The  radial  artery 
lies  upon  it,  and  the  an- 
terior interosseous  artery  and 
nerve  intervene  between  it 
and  the  flexor  profundus 
digitorum.  It  crosses  over 
the  insertion  of  the  pro- 
nator quadratus  near  the 
wrist. 

The  pronator  quadratus 
is  a  quadrilateral  fleshy 
muscle,  occupying  the  lower 
fourth  of  the  forearm.  It 
arises  from  the  lower  fourth 
of  the  anterior  border  and 
surface  of  the  ulna  and 
frequently  from  the  adjoin- 
ing part  of  the  inner  surface 
(Fig.  271,  p.  351),  and  is 
directed  transversely  out- 
wards to  be  inserted  into 
the  lower  fourth  of  the  an- 
terior surface  of  the  radius, 
and  into  the  narrow  tri- 
angular area  on  its  inner 
side  in  front  of  the  attach- 
ment of  the  interosseous 
membrane  (Fig.  264,  page 
343). 

The  muscle  is  deeply 
placed  beneath  the  flexor 
tendons,  the  radial  and 
ulnar  arteries,  and  the  ulnar 
and  median  nerves.  It  con- 
ceals the  lower  part  of  the 
interosseous  membrane,  the 
radius  and  ulna,  and  the 
anterior  interosseous  artery 
and  nerve,  which  pass  be- 
hind i^s  upper  border.  The 
pronator  quadratus  is  sub- 
ject to  considerable  varia- 
tions. It  may  even  be  absent ; 
or  it  may  have  an  origin 
from  radius  or  ulna,  or  from  both  bones,  and  an  insertion  into  the  carpus. 


Extensor  ossis  metacarpi/ 
poLLiois  (double)  ^ 


Extensor  brevis  pollicis 
Pronator  Quadratus. 

Flexor  carpi  radialis 

Abductor,  pollicis  (cu 
Opponbns  pollicis 
Flexor  brevis  pollicis 


Tendon  of  flexor  lonous 

pollicis 

Adductor  transversus 

pollicis 

lumbricales 


Fig.  265. —Deep  Muscles  on  the  Front  of  the  Forearm 
AND  Hand. 


SHORT  MUSCLES  OF  THE  HAND. 


345 


SHORT  MUSCLES  OF  THE  HAND. 

Muscles  of  the  Thumb. 

The  short  muscles  of  the  thumb  are  six  in  number,  abductor,  opponens,  and 
flexor  brevis  (with  its  deep  portion,  interosseus  primus  volaris),  and  two  adductor 
muscles,  adductor  obliquus,  and  adductor  transversus  pollicis. 

The  abductor  pollicis  (m.  abductor  pollicis  brevis)  arises  by  fleshy  fibres  from 
the  tubercle  of  the  scaphoid,  the  upper  part  of  the  outer  surface  of  the  ridge  of  the 
trapezium,  the  upper  part  of  the  anterior  surface  of  the  anterior  annular  ligament 
at  its  outer  end,  and  from  tendinous  slips  derived  from  the  insertions  of  the  palmaris 


Transverse  metacarpal, 
ligament 

Interosseous  muscle 


Abductoe,  and  flexor 

BEEVIS  MINIMI  DIGITI  (cut)' 

Interosseous  muscle 
Interosseous  muscle 


Deep  palmar  arch  (along  with  deep 
branch  of  ulnar  nerve) 


Opponens  minimi  digiti 


First  dorsal 
interosseous  muscle 

LFlexor  longus  pollicis 

TENDON 

Adductor  transversus 
pollicis 

—t'-j- Abductor  pollicis  (cut) 

— Flexor  brevis  pollicis 

Adductor  obliquus  pollicis 
Flexor  brevis  pollicis 

Opponens  pollicis 


Flexor  carpi  ulnaris-L—  V\\ 


Ulnar  nei  ve, 


'^^^-—r-  'itdian  nerve  (muscular  branches) 
~~^      '"     Abductor  pollicis  (cut) 


Extensor  ossis  metacarpi  pollicis 


Flexor  carpi  radialis  tendon 


Fig.  266. — Short  Muscles  of  the  Hand. 

longus  and  extensor  ossis  metacarpi  pollicis  muscles  (Fig.  267,  p.  346).  Strap- 
like  in  form,  it  is  inserted  by  a  short  tendon  into  the  outer  side  of  the  first  phalanx 
of  the  thumb  at  its  upper  end,  and  into  the  capsule  of  the  metacarpo-phalangeal 
joint. 

It  is  the  most  superficial  muscle  of  the  thenar  eminence,  and  conceals  partially 
the  opponens  and  the  superficial  portion  of  the  flexor  brevis  pollicis. 

The  opponens  pollicis  arises  beneath  the  preceding  muscle  by  fleshy  and 
tendinous  fibres  from  the  lower  and  outer  part  of  the  anterior  surface  of  the 
anterior  annular  ligament  and  from  the  outer  surface  of  the  ridge  on  the  trapezium. 
Extending  downwards  and  outwards,  it  is  inserted  into  the  whole  length  of  the  outer 
border  and  the  radial  half  of  the  palmar  surface  of  the  first  metacarpal  bone  (Fig. 
267,  p.  346).  The  muscle  is  superficial  along  the  outer  border  of  the  abductor 
pollicis. 

The  flexor  brevis  pollicis  consists  of  two  parts,  a.  The  superficial  -part  of  the^ 
muscle  arises  by  fleshy  and  tendinous  fibres  from  the  outer  half  or  two-thirds  ot 
the  lower  border  of  the  anterior  annular  ligament,  and  sometimes  from  the  ridge  of 
the  trapezium,  and  is  inserted  into  the  outer  side  of  the  base  of  the  first  phalanx  of 
the  thumb,  a  sesamoid  bone  being  present  in  the  tendon  of  insertion.  This  part  of 
the  muscle,  partly  concealed  by  the  abductor  pollicis,  is  superficial  in  the  interval 
between  that  muscle  and  the  tendon  of  the  flexor  longus  pollicis. 

h.  The  deej)  'part  of  the  muscle  (interosseus  primus  volaris)  arises  from  the 
ulnar  side  of  the  base  of  the  first  metacarpal  bone,  and  is  inserted  into  the  inner 
side  of  the  base  of  the  first  phalanx  of  the  thumb  along  with  the  adductor 
obliquus  pollicis.  This  little  muscle  is  deeply  situated  in  the  first  interosseous 
space,  in  the  interval  between  the  adductor  obliquus  pollicis  and  the  first  dorsal 
interos.seous  muscle.  It  may  be  regarded  as  homologous  with  the  palmar  interossei 
muscle.s,  with  which  it  is  in  series. 
24 


346 


THE  MUSCULAK  SYSTEM. 


The  adductor  obliquus  pollicis  arises  l)y  fleshy  fibres  from  the  anterior  surfaces 
of  the  trapezium,  trapezoid,  and  os  magnum,  from  the  sheatli  of  the  tendon  of  the 
flexor  carpi  radialis,  from  the  basis  of  the  second,  third,  and  fourth  metacarpal  bones, 
and  from  the  palmar  ligaments  connecting  these  bones  together  (Fig.  267,  p.  346). 
It  is  inserted  by  a  tendon,  in  which  a  sesamoid  bone  is  developed,  into  the  inner 
side  of  the  base  of  the  first  phalanx  of  the  thumb.  At  its  outer  border  a  slender 
slij)  separates  from  the  rest  of  the  muscle,  and  passing  obliquely  beneath  the  tendon 
of  the  flexor  longus  pollicis,  is  inserted  into  the  outer  side  of  the  base  of  the  first 
phalanx  along  with  the  superficial  part  of  the  fiexor  brevis  pollicis. 

The  adductor  obliquus  pollicis  lies  on  the  ulnar  side  of  the  tendon  of  the  flexor 
longus  pollicis,  internal  to  the  thenar  eminence.  It  is  covered  by  the  flexor  tendons 
of  the  thumb  and  fingers,  and  conceals  the  radial  artery  and  the  deep  part  of  the 
flexor  brevis  pollicis.  At  its  inner  border  the  radial  artery  (deep  palmar  arch) 
appears  between  it  and  the  adductor  transversus  pollicis. 

The  adductor  transversus  pollicis  arises  by  fleshy  fibres  from  the  median  ridge 


Os  masnuni 


Scaphoid  bone 
Abductor  pollicis  (oiinin). 

Opponens  pollicis  (oi  i 

Trapezmni, 
Extensor  ossis  metaearpi 
pollicis  (insertion) 


Opponens  pollicis  (insertion) 

Flexor  carpi  ladialis  ^/_j 
(inseition)' 


Semilunar  bone 
Unciform 


Adductor  obliquus 
pollicis  (origin)' 


First  dorsal  interosseous  muscle 
(one  origin) 


First  palmar  interosseous  mnscl 
(origin)' 


Second  dorsal  interosseous 
muscle  (one  origin) 


Adductor  transversus 
pollicis  (origin)l 


pifoim  bone 
iloim  bone 

Abductor  minimi  digiti  (origin) 


Flexor  carpi  nlnaris  (insertion) 

Flexor  brevis  minimi  digiti 
(oiigin) 

Flexor  carpi  ulnaris  (insertion) 


lens  minimi  digiti 
and  insertion) 


Third  palmar  inter- 
osseous muscle 
(origin) 


i<  ourth  dorsal  interosseous 
muscle  (one  origin) 

•second  palmar  interosseous 

muscle  (origin) 


Third  dorsal  interosseous 
muscle  (one  origin) 


Fig.  267. — Muscle- Attachments  to  the  Palmar  Aspect  of  the  Carpus  and  Metacarpus. 


on  the  front  of  the  shaft  of  the  third  metacarpal  bone,  in  its  lower  two-thirds 
(Fig.  267,.  p.  346),  and  from  the  fascia  covering  the  interosseous  muscles  in  the 
second  and  third  spaces.  Triangular  in  form,  it  is  directed  outwards,  to  be 
inserted  by  tendon  into  the  inner  side  of  the  base  of  the  first  phalanx  of  the 
thumb  along  with  the  adductor  obliquus.  Lying  deeply  in  the  palm  beneath  the 
flexor  tendons,  this  muscle  conceals  the  interossei  muscles  of  the  first  two  spaces 
and  the  radialis  indicis  and  princeps  pollicis  arteries.  Its  upper  border  is 
separated  from  the  adductor  obliquus  pollicis  by  the  radial  artery  (deep 
palmar  arch). 


Muscles  of  the  Little  Finger. 

The  short  muscles  of  the  little  finger  are  three  in  number 
and  flexor  brevis  minimi  digiti. 


abductor,  opponens. 


SHORT  MUSCLES  OF  THE  HAND. 


'A1 


The  abductor  minimi  digiti  (m.  abductor  digiti  quiuti)  arises  from  the  front 
and  inner  side  of  the  pisiform  Ijone  and  from  the  tendon  of  the  flexor  carpi  ulnaris 
and  its  ligamentous  continuations  (Fig.  267,  p.  346j,  and  is  inserted  by  tendon  into 
the  inner  side  of  tlie  base  of  the  first  phalanx  of  the  little  finger.  It  lies 
superficially  upon  the  opponens  and  flexor  brevis  minimi  digiti. 

The  opponens  minimi  digiti  (m.  opponens  digiti  quinti)  arises  by  tendinous 
fibres  from  the  lower  part  of  the  anterior  surface  and  from  the  lower  border  of  the 
anterior  annular  ligament  at  its  inner  end,  and  from  the  lower  border  and  inner  side 
of  the  hook  of  the  unciform  bone,  and  is  inserted  into  the  inner  margin  and 
ulnar  half  of  the  palmar  surface  of  the  fifth  metacarpal  bone  in  its  lower 
three-fourths  (Fig.  267,  p.  346). 

It  is  concealed  by  the  previous  muscle,  and  may  be  pierced  near  its  origin  for 
the  passage  of  the  deep  branches  of  the  ulnar  artery  and  nerve. 

The  flexor  brevis  minimi  digiti  (m.  flexor  digiti  quinti  brevis)  arises  by 
tendinous  fibres  from  the  inner  part  of  the  anterior  surface  of  the  anterior  annular 
ligament  and  from  the  inner  side  of  the  hook  of  the  unciform  bone  (Fig.  267, 
p.  346),  and  is  inserted  along  with  the  abductor  into  the  inner  side  of  the  first 
phalanx  of  the  little  finger. 

This  muscle  is  placed  external  to  the  opponens  and  abductor,  and  is  separated 
from  the  latter  by  the  deep  branches  of  the  ulnar  artery  and  nerve.  It  may  be 
reduced  in  size,  absent  altogether,  or  incorporated  with  either  the  opponens  or 
abductor  minimi  digiti. 

The  Intekosseous  Muscles. 


The  interosseous  muscles  of  the  hand  are  arranged  in  two  sets,  palmar  and 
dorsal. 

The  palmar  interossei  (m.  interossei  volares)  are  three  in  number,  occupying 
the  three  inner  interosseous  spaces. 
Each  arises  by  a  single  head ;  the 
first  from  the  ulnar  side  of  the  shaft 
of  the  second  metacarpal  bone ;  the 
second  and  third  from  the  radial 
sides  of  the  shafts  of  the  fourth  and 
fifth  metacarpal  bones  respectively 
(Fig.  267,  p.  346).  Each  ends  in  a 
tendon  which  is  directed  downwards 
behind  the  deep  transverse  meta- 
carpal ligament,  to  be  inserted  into 
the  dorsal  expansion  of  the  extensor 
tendon,  the  capsule  of  the  meta- 
carpo  -  phalangeal  articulation,  and 
the  side  of  the  first  phalanx  of  the 
finger ;  the  'first  is  inserted  into  the 
ulnar  side  of  the  second  finger ;  the 
second  and  third  into  the  radial  sides 
of  the  fourth  and  fifth  fingers.  The 
deep     part    of     the    flexor     brevis 

pollicis   (interosseus  primus  volaris)         ^     „.„     ^      t, 

f    ,      ,      ^  T    T         ,11  1  Fig.  268. — The  Palmar  Interosseous  Muscles. 

IS  to  be  regarded  as  the  homologous 

_         1  V      i.\.         c     i-       •    I.  P  )  fir''^t  ;  P  ,  second ;  and  P'>,  third  palmar    interosseons 

muscle    of     the     first     mterosseous  muscles. 

space. 

The  dorsal  interossei  arc  four  in  number.  Each  arises  by  two  heads  from  the 
sides  of  the  metacarpal  bones  bounding  each  interosseous  space  (Figs.  267,  p.  346, 
and  269,  j;.  348).  Each  forms  a  fleshy  mass,  ending  in  a  membranous  tendon, 
which,  paHsing  downwards  behind  the  deej)  transverse  metacarpal  ligament,  is 
inserted  exactly  like  tfie  palmar  muscles  into  the  dorsal  aspect  of  each  of  the  four 
fingerH.  Th(;  insertion  of  the  fi/rst  dorsal  interosseous  muscle  is  into  the  radial 
side  of  ti.'o  index  finger;  the  second  muscle  is  attached  to  the  radial  side  of  the 


348 


THE  MUSCULAE  SYSTEM. 


middle  finger ;  the  third  muscle  to  the  ulnar  side  of  the  same  finger ;  and  the  fourth 
muscle  to  the  ulnar  side  of  the  ring  finger. 

These  muscles  fill  up  the  interosseous  spaces ;  the  dorsal  interossei  are  visible 


Extensor  carpi  ulnaris  (insertion) 


Fourth  dorsal  interosseous 
muscle  (ori: 


Third  dorsal  inter- 
osseous muscle 
(origin) 


Extensor  carpi  radialis 
brevior  (insertion) 

Extensor  carpi  radialis 
ongior  (insertion) 

First  dorsal  inter- 
osseous muscle 
(origin) 


Second  dorsal  interosseous 
muscle  (origin) 


Fig.  269. — Muscle-Attachments  to  the  Dorsal  Aspect  of  the  Metacarpus. 

on  the  back  of  the  hand  when  the  extensor  tendons  are  removed ;  in  the  palm  the 
muscles  are  concealed  by  the  flexor  tendons  and  the  muscles  of  the  thumb  and 
little  finger,  and  are  crossed  by  the  deep  palmar  arch  and  the  deep  branch  of  the 


Abductor  pollicis  :  origin  (ciit). 
Insertion  of  flexor  carpi  radialis 

Insertion  of  opponens  pollicis 
Interosseoqs  primus  volaris 


Abductor  pollicis  :  insertion  (cut). 
Adductor  obliquus  (insertion). 
Adductor  transveesus  (insertion)_. 

First  dorsal  interosseous  muscle, 
Second  dorsal  interosseous  muscle^-'' 

Third  dorsal  interosseous  musclk 
Fourth  dorsal  interosseous  muscle 


Insertion  of  flexor 
carpi  ulnaris 


Orioins  of 

PALMAR  inter- 
osseous muscles 
Insertion  of 
opponens  minimi 
digiti 


Insertion  of 
abductor  minimi 
digiti 


Fig.  270. — Dorsal  Interosseous  Muscles  of  the  Hand  (seen  from  the  Palmar  Aspect). 


ulnar  nerve.  Between  the  two  heads  of  the  first  dorsal  muscle  the  radial  artery 
enters  the  palm,  and  the  perforating  arteries  pass  between  the  heads  of  the  other 
dorsal  muscles. 

The  interossei  muscles  of  the  hand  in  some  cases  have  a  disposition  similar  to 
that  of  the  corresponding  muscles  of  the  foot. 


MUSCLES  ON  THE  BACK  OF  THE  FOKEAKM.  349 

THE  MUSCLES  ON  THE  BACK  OF  THE  FOREARM. 

The  group  of  muscles  occupying  the  outer  side  of  the  elbow  and  the  back  of  the 
forearm  and  hand  include  the  supinator  muscles  of  the  forearm  and  the  extensors 
of  the  wrist  and  digits.     They  are  divisible  into  a  superficial  and  a  deep  layer. 

Superficial  Muscles. 

The  superficial  layer  comprises  seven  muscles,  viz.  from  without  inwards,  the 
brachio- radial  is,  the  two  radial  extensors  of  the  carpus,  the  extensor  communis 
digitorum  and  extensor  minimi  digiti,  the  extensor  capri  ulnaris,  and  the  anconeus. 

The  brachio-radialis  (supinator  radii  longus)  arises  by  fleshy  fibres  from  the 
anterior  aspect  of  the  upper  two-thirds  of  the  external  supra  condyloid  ridge  of 
the  humerus,  and  from  the  front  of  the  external  intermuscular  septum  (Fig.  257, 
p.  335).  Occupying  the  outer  side  of  the  hollow  of  the  elbow,  the  muscle  descends 
along  the  outer  border  of  the  forearm,  and  ends  about  the  middle  in  a  narrow  flat 
tendon  which  is  inserted  under  cover  of  the  tendons  of  the  extensor  ossis  metacarpi 
pollicis  and  extensor  brevis  poUicis,  by  a  transverse  linear  attachment,  into  the 
upper  limit  of  the  groove  for  the  above-named  muscles  on  the  outer  side  of  the 
lower  extremity  of  the  radius.  Some  of  its  fibres  gain  an  attachment  to  the  ridge 
in  front  of  the  groove,  and  others  spread  over  the  surface  of  the  groove  for  a 
variable  distance  (Figs.  271,  p.  351,  and  264,  p.  343). 

The  muscle  is  superficial  in  its  whole  length.  Near  its  origin  it  is  separated 
from  the  brachialis  anticus  by  the  musculo-spiral  nerve.  It  forms  the  outer 
boundary  of  the  hollow  of  the  elbow,  and  conceals  the  radial  extensors  of  the  carpus, 
and,  in  the  upper  two-thirds  of  the  forearm,  the  radial  artery  and  nerve. 

The  extensor  carpi  radialis  longior  (m.  ext.  carp.  rad.  longus)  arises  by  fleshy 
fibres  from  the  lower  third  of  the  external  supracondyloid  ridge  of  the  humerus 
on  its  anterior  aspect,  from  the  front  of  the  external  intermuscular  septum,  and 
from  the  common  tendon  of  origin  of  succeeding  muscles,  which  is  attached  to  an 
impression  on  the  antero-external  surface  of  the  external  condyle  (Figs.  257, 
and  258,  p.  335).  It  ends  in  a  tendon  in  the  lower  half  of  the  forearm,  which 
passes  beneath  the  posterior  annular  ligament,  to  be  inserted  into  the  back  of  the 
base  of  the  second  metacarpal  bone  on  its  radial  side  (Fig.  269,  p.  348). 

The  upper  part  of  the  muscle  is  concealed  by  the  brachio-radialis,  and  the  lower 
part  is  crossed  by  the  extensors  of  the  thumb.  It  covers  the  supinator  radii  brevis 
and  extensor  carpi  radialis  brevior  above,  and  the  back  of  the  radius  and  the  carpus 
below. 

The  extensor  carpi  radialis  brevior  (m.  ext.  carp.  rad.  brevis)  arises  from  the 
common  tendon,  from  the  external  lateral  ligament  of  the  elbow,  from  the  fascia 
over  it,  and  i'rom  intermuscular  septa  on  each  side.  It  passes  down  the  back  of 
the  forearm  and  under  the  posterior  annular  ligament  in  close  relation  to  the 
previous  muscle,  to  be  inserted  by- a  tendon  into  the  back  of  the  base  of  the  third 
metacarpal  bone  below  the  styloid  process  on  its  radial  side.  It  usually  has 
an  additional  insertion  into  the  back  of  the  base  of  the  second  metacarpal  bone 
(Fig.  269,  p.  348).  A  bursa  is  placed  beneath  the  two  radial  extensor  tendons 
close  to  their  insertion. 

Partially  concealed  by  the  extensor  carpi  radialis  longior  and  the  extensor 
muscles  of  the  thumb,  and  having  the  extensor  communis  digitorum  on  its  inner 
side,  the  muscle  covers  the  supinator  brevis,  the  lower  part  of  the  radius,  and  the 
back  of  the  carpus. 

The  extensor  communis  digitorum  arises  from  the  common  tendon,  Irom  the 
external  condyle,  from  the  fascia  over  it,  and  from  intermuscular  septa  on  each  side. 
Extending  down  the  back  of  the  ibrearm  it  ends  aljove  the  wrist  in  four  tendons,  of 
which  the  outf-rmost  ol'ten  has  a  separate  fleshy  belly.  After  passing  l)eneath  the 
posterior  annular  ligament  in  a  compartment  along  with  the  extensor  indicis,  the 
tendons  separate  on  the  back  of  the  hand,  where  the  three  innermost  tendons  are 
joined  together  by  two  obli(|uely-placed  bands.  One  pusses  downwards  and  out- 
wards, and  connects  together  th(3  third  and  second  tendons ;  the  other  is  a  broader 


350  THE  MUSCULAK  SYSTEM. 

and  shorter  ?jand,  which  passes  also  downwards  and  outwards,  and  joins  the  fourth 
to  the  third  tendon.  In  some  cases  (Eig.  257)  a  third  band  is  present,  wliich  passes 
downwards  and  inwards  Iroui  the  first  to  the  second  tendon ;  and  frequently  the 
tendon  for  the  little  finger  is  joined  to  the  tendon  for  the  ring  finger,  and  separates 
from  it  only  a  short  distance  above  the  lower  end  of  the  metacarpal  bone. 

The  tendons  are  inserted  in  the  following  manner :  On  the  finger  each  tendon 
spreads  out  so  as  to  form  a  membranous  expansion  over  the  knuckle  and  on  the 
back  of  the  first  phalanx.  The  border  of  the  tendon  is  indefinite  over  the  meta- 
carpo-phalangeal  articulation,  of  which  it  forms  the  posterior  liga.ment.  On  the 
back  of  the  first  phalanx  the  tendon  receives  laterally  the  insertions  of  the  interossei 
and  lumbrical  muscles.  At  the  lower  end  of  the  first  phalanx  the  tendon  splits 
into  ill -defined  median  and  lateral  slips,  proceeding  over  the  back  of  the  first 
inter-phalangeal  articulation,  of  which  they  form  the  posterior  ligament.  The 
median  slip  is  inserted  into  the  back  of  the  base  of  the  second  phalanx,  while  the 
two  lateral  pieces  become  united  to  form  a  membranous  tendon  on  the  back  of 
the  second  phalanx,  which,  after  passing  over  the  second  inter-phalangeal  articula- 
tion, is  inserted  into  the  base  of  the  terminal  phalanx. 

The  extensor  communis  digitorum  is  superficial  in  its  whole  length,  and  lies  in 
the  upper  part  of  the  forearm  between  the  radial  extensors  of  the  carpus  externally 
and  the  extensor  minimi  digiti  internally.  It  conceals  the  supinator  brevis  and 
other  deep  muscles  of  the  forearm,  as  well  as  the  posterior  interosseous  vessels  and 
nerves.  The  extensors  of  the  thumb  become  superficial  along  its  outer  border  in 
the  lower  third  of  tbe  forearm. 

The  extensor  minimi  digiti  (m.  extensor  digiti  quinti  proprius)  has  an  origin 
similar  to  and  closely  connected  with  that  of  the  preceding  muscle,  from  the 
common  tendon,  the  fascia  over  it,  and  lateral  intermuscular  septa.  Passing  down 
the  back  of  the  forearm  as  a  narrow  fleshy  slip,  between  the  extensor  communis 
digitorum  and  the  extensor  carpi  ulnaris,  it  ends  in  a  tendon  which  occupies  a 
groove  between  the  radius  and  ulna  in  a  special  compartment  of  the  posterior 
annular  ligament.  On  the  back  of  the  hand  the  tendon,  usually  split  into  two  parts, 
lies  internal  to  the  tendons  of  the  extensor  communis  digitorum,  and  is  finally 
inserted  into  the  expansion  of  the  extensor  tendon  on  the  dorsum  of  the  first 
phalanx  of  the  little  finger. 

The  extensor  carpi  ulnaris  has  a  double  origin :  (1)  from  the  common  tendon 
from  the  external  condyle  of  the  humerus,  from  the  fascia  over  it,  and  from  the 
intermuscular  septa;  and  (2)  through  the  medium  of  the  deep  fascia,  from  the 
posterior  border  of  the  ulna  in  its  middle  two -fourths.  The  muscle  ends  in  a 
tendon  in  the  lower  third  of  the  forearm,  which  occupies  a  groove  on  the  back  of 
the  ulna  in  a  special  compartment  of  the  posterior  annular  ligament,  and  is  inserted 
into  the  ulnar  side  of  the  base  of  the  fifth  metacarpal  bone  (Eig.  269,  p.  348). 

The  muscle  is  superficially  placed  between  the  extensor  minimi  digiti  and  the 
anconeus,  external  to  the  posterior  border  of  the  ulna.  lb  conceals  the  supinator 
radii  brevis  and  the  posterior  interosseous  vessels  and  nerve  above,  and  in  the  lower 
two-thirds  of  the  forearm  it  lies  upon  the  posterior  surface  of  the  ulna. 

The  anconeus  is  a  small  triangular  muscle  arising  by  a  separate  tendon  from 
the  lower  part  of  the  back  of  the  external  condyle  of  the  humerus  (Eig.  258, 
p.  335),  and  from  the  posterior  ligament  of  the  elbow-joint.  Spreading  out  over 
the  ulna,  it  is  inserted  by  fleshy  fibres  into  a  triangular  surface  on  the  outer  side 
of  the  olecranon  process  and  back  of  the  ulna,  as  low  down  as  the  oblique  line 
(Fig.  271,  p.  351).     It  is  also  inserted  into  the  fascia  which  covers  it. 

It  is  covered  by  the  thickened  fascia  of  the  forearm  giving  insertion  to  the 
triceps  muscle.  It  conceals  the  back  of  the  elbow-joint  and  part  of  the  origin  of 
the  supinator  brevis  muscle. 

The  epitrochleo-anconeus  is  an  occasional  small  muscle  arising  from  tlie  back  of  tlie  internal 
condyle  of  the  humerus,  and  inserted  into  the  inner  side  of  the  olecranon  process.  It  covers  the 
ulnar  nerve  in  its  passage  to  the  forearm. 

Deep  Muscles. 
The  deep  muscles  on  the  back  of  the  forearm  comprise  five  muscles,  of  which 


MUSCLES  ON  THE  BACK  OF  THE  FOEEARM. 


351 


Anconeus  (insertion 


Supinator  radii  brev 
(ulnar  origin 


Plexor  profundus 
digitoruni  (origin) 


Biceps  (insertion) 

Supinator  radii  brevis 
(insertion) 


Extensor  ossis  metacarpi 
pollicis  (origin) 


Pronator  radii  teres 
(insertion) 


one,  the  supinator  radii  Lrevis,  extends  between  the  ulna  and  radius ;  the  others 
are  extensors  of  the  thumb  and  forefinger:  the  extensor  ossis  metacarpi  pollicis, 
extensor  brevis  and  extensor  longus  pollicis,  and  extensor  indicis. 

The  supinator  radii  brevis  (m.  supinator)  muscle  has  a  complex  origin.  It 
arises  by  fleshy  and  tendinous  fibres  :  (1)  from  the  external  condyle  of  the  humerus  ; 
(2)  from  the  external  lateral  and  orbicular  ligaments  of  the  elbow-joint ;  (3)  from 
the  triangular  surface  on  the  shaft  of  the  ulna  just  below  the  lesser  sigmoid  cavity; 
and  (4)  from  the  fascia  over 

it.         From     this      origin      the  ^P^^fe^Trlceps  (insertion) 

muscle  spreads  outwards  and 
downwards,  enveloping  the 
upper  part  of  the  radius,  and 
is  inserted  into  the  anterior 
and  outer  surfaces  of  the  bone, 
as  far  forwards  as  the  bicipital 
tubercle,  as  far  upwards  as 
the  neck,  and  as  far  down- 
wards as  the  oblique  line  and 
the  insertion  of  the  pronator 
radii  teres.  The  insertion  of 
the  muscle  in  some  cases  en- 
croaches for  a  variable  dis- 
tance on  to  the  posterior 
surface  of  the  shaft  of  the 
radius  above  the  origin  of  the 
extensor  ossis  metacarpi  pol- 
licis ;  but  the  neck  and  the 
inner  half  of  the  posterior 
surface  of  the  shaft  are  left 
without  muscular  attachment 
(Figs.  271,  p.  351,  and  264, 
p.  343). 

The  supinator  brevis  is 
deeply  placed,  and  is  un- 
covered only  anteriorly  in 
the  hollow  of  the  elbow.  It 
is  covered  by  all  the  super- 
ficial muscles  on  the  back  of 
the  forearm.  It  conceals  the 
back  of  the  elbow-joint  and 
the  upper  part  of  the  radius. 
At  its  lower  border  is  the 
extensor  ossis  metacarpi  pol- 
licis, separated  from  it  by  the 
posterior  interosseous  artery. 
The  muscle  is  divisible  into 
sv/perfieial  and  deejp  parts 
with  humeral  and  ulnar 
origins,  between  which  the 
posterior  interosseous  nerve 
passes  in  its  course  to  the 
back  of  the  forearm. 

The  extensor  ossis  metacarpi  pollicis  (m.  abductor  pollicis  longus)  arises  by 
fleshy  fibr(!S  below  the  sujiinator  brevis  iVom  the  posterior  or  extensor  surfaces  of 
the  shafts  of  the  radius  and  ulna ;  from  the  uppermost  of  the  narrow  impressions  on 
the  outer  lialf  of  the  posterior  surface  of  tlie  ulna;  i'rom  tlie  middle  third  of 
the  postfirior  surface  of  the  radius ;  and  from  the  intervening  portion  of  the 
interosseous  membrane  (Fig.  271,  p.  351).  Becoming  superficial  in  the  lower  part 
of  the  forearm  along  with  the  extensor  brevis  pollicis,  its  tendon  passes  with  that 


Extensor  longus  pollicis 
(origin) 


Extensor  indicis. 
(origin) 


Pronator  quadratns 
(origin)' 


Groove  for  extensor 
carpi  ulnaris 


Extensor  brevis  pollicis 
(origin) 


Brachio-radialis 
(insertion)' 

Groove  for  tendons  of 

radial  extensors  of 

carpus 

Gi'oove  for  extensor 

longus  pollicis 


Groove, for  extensor 


Fl(!, 


digitorum  and  extensor  indicis 

271. — Muscle- Attachments  to  the  Radius  and  Ulna 
(Posterior  Aspects). 


352 


THE  MUSCULAE  SYSTEM. 


External  condyle, 
of  hixmeru.s 


Insertion  of 

TRICEPS 


Extensor  muscles 
(origin) 


Supinator  radii 

BRE\  IS 

Flexor  carpi 

TTLN\RIS 


Extensor  carpi 

ULNARIS 


muscle  beneath  the  posterior  annular  ligament,  to  be  inserted  into  the  outer  side  of 
the  base  of  the  first  metacarpal  bone  (Fig.  267,  p.  346).     From  the  tendon  close  to 

its  insertion  a  tendinous 
slip  passes  to  the  ab- 
ductor pollicis  and  the 
fascia  over  the  thenar 
eminence,  and  another  is 
frequently  attached  to 
the  trapezium. 

At  its  origin  the 
muscle  is  deeply  placed 
beneath  the  superficial 
extensor  muscles  and  the 
posterior  interosse- 
ous vessels  and  nerve. 
Above  is  the  supinator 
brevis ;  below  and  inter- 
nally, the  long  and  short 
extensors  of  the  thumb. 
In  the  lower  third  of  the 
forearm  it  becomes  super- 
ficial along  with  the  ex- 
tensor brevis  pollicis, 
between  the  extensor 
communis  digitorum  and 
the  radial  extensors  of 
the  carpus.  It  covers  the 
last-named  muscles  in  its 
further  course  in  the  fore- 
arm, and  at  the  outer 
side  of  the  carpus  it 
crosses  the  radial  artery. 
The  extensor  brevis 
pollicis  (extensor  primi 
intern  odii  pollicis),  an 
essentially  human  muscle, 
is  a  specialised  portion  of 
the  previous  muscle.  It 
arises  from  a  rhomboid 
impression  on  the  pos- 
terior surface  of  the 
radius,  extending  from 
the  middle  of  the  bone 
to  within  an  inch  and  a 
half  of  the  lower  end, 
and  from  the  interosseous 
membrane,  below  the  ex- 
tensor ossis  metacarpi 
pollicis  (Fig.  271,  page 
351).  It  is  closely  ad- 
herent to  that  muscle, 
and  accompanies  it  be- 
neath the  posterior 
annular  ligament  and 
over  the  radial  artery  to 
the  thumb.    Its  tendon  is 


Extensor  longi 

POLLItl 


Extensor  indicia 


Dorsal  branch  of  ulnar 

neive 

Extensor  minimi 

DiGiTi  (tendon) 

Extensor  communis 

DIGITORUM  (tendons) 


Extensor  indicis 


Trkieps  (long  head) 
Trk;eps  (outer  head) 


Brachio-radialis 


Brachialis  anticus 


Triceps  (inner  head) 


Extensor  carpi  radialis 
LONGIOR  (origin) 

Extensor  carpi  radialis 
brevior  (origin) 

Musculo-spiral  nerve 


Posterior  interosseous  nerve 


E>^tensor  ossis  metacarpi 
pollicis 

Extensor  carpi  radialis 

LONGIOR 

Extensor  carpi  radialis 
brevior 

Extensor  brevis  pollicis 


Extensor  carpi  radialis 

LONGIOR 

Extensor  ossis  metacarpi 

pollicis 

Extensor  carpi  radialis 

BREVIOR 

Extensor  brevis  pollicis 

Extensor  longus 
pollicis 
First  dorsal 
interosseous 
muscle 


Fig.  272.- 


-The  Muscles  op  the  Back  of  the  Forearm 
suiierticial  muscles  being  reflected). 


(the 


then  continued  along  the  back  of  the  first  metacarpal  bone,  and  the  metacarpo- 
phalangeal articulation,  to  be  inserted  into  the  back  of  the  base  of  the  first  phalanx 
of  the  thumb.     Before  reaching  its  insertion  the  tendon  helps  to  form  the  capsule 


m 


MUSCLES  ON  THE  BACK  OF  THE  FOEEAKM. 


553 


of  the  metacarpo-phalangeal  joint.  In  the  forearm  the  muscle  is  deeply  placed 
beneath  the  superficial  extensors,  and  is  separated  from  the  extensor  longus  pollicis 
by  the  posterior  interosseous  nerve. 

The  extensor  longus  pollicis  (extensor  secundi  internodii  pollicis)  arises  from 
the  intermediate  impression  occupying  the  outer  part  of  the  posterior  or  extensor 
surface  of  the  ulna  in  its  middle  third,  and  from  the  interosseous  membrane,  below 
the  extensor  ossis  metacarpi  pollicis  (Fig.  271,  p.  351).  Its  tendon  grooves  the 
back  of  the  radius,  and  occupies  a  special  compartment  beneath  the  posterior 
annular  ligament.  Extending  obliquely  across  the  back  of  the  hand,  it  is  inserted 
into  the  dorsal  surface  of  the  base  of  the  second  phalanx  of  the  thumb. 

The  muscle  is  deeply  placed  beneath  the  superficial  extensors  of  the  forearm, 
and  lies  between  the  extensor  brevis  pollicis  and  the  extensor  indicis.  It  separates 
the  posterior  interosseous  artery  from  the  nerve,  the  latter  passing  beneath  it.  On 
the  back  of  the  hand  the  tendon  crosses  the  radial  artery,  and  helps  to  form  the 
capsule  of  the  first  metacarpo-phalangeal  articulation. 

At  the  wrist  the  tendons  of  the  muscles  of  the  thumb,  the  extensor  ossis  meta- 
carpi pollicis  and  extensor  brevis  pollicis  externally,  and  the  extensor  longus 
pollicis  internally,  bound  a  hollow  (the  "anatomical  snuff-box")  best  seen  in 
extension  and  abduction  of  the  thumb,  which  corresponds  to  the  position  of  the 
radial  artery  as  it  winds  round  the  wrist  to  reach  the  palm  of  the  hand. 

The  extensor  indicis  (m.  extensor  indicis  proprius)  arises  by  fleshy  fibres  below 
the  extensor  longus  pollicis  from  the  lowest  impression  on  the  back  of  the  ulna, 
extending  down  from  the  middle  of  the  shaft  to  within  two  inches  of  its  lower  end, 
and  sometimes  also  from  the  interosseous  membrane  (Fig.  271,  ]3.  351).  Its  tendon 
passes  through  a  compartment  of  the  posterior  annular  ligament  along  with  the 
tendons  of  the  extensor  communis  digitorum,  and  is  inserted  into  the  forefinger 
joining  the  membranous  expansion  of  the  tendon  of  the  extensor  communis 
digitorum  on  the  dorsum  of  the  first  phalanx. 

Lying  deeply  in  the  forearm,  the  muscle  is  placed  internal  to  the  extensor 
longus  pollicis,  and  covers  the  posterior  interosseous  nerve.  On  the  back  of  the 
hand  its  tendon  lies  on  the  inner  side  of  the  tendon  of  the  common  extensor 
destined  for  the  forefinger. 

Nerve-Supply. 

Four  nerves  are  engaged  in  supplying  the  muscles  of  the  forearm  and  hand — the  median  and 
ulnar  on  the  front,  the  musculo -spiral  and  posterior  interosseous  nerves  on  the  back  of  the 
limb. 


Muscles. 

Nerves. 

Origin. 

A.  Anterior  Muscles  of  the  Forearm. 

Pronator  radii  teres               "i 
Flexor  carpi  radialis              | 
Pal  maris  longus                      f 
Flexor  sublimis  digitorum   ; 

Median  .... 

C.  6. 

Flexor  carpi  ulnaris    .... 

Ulnar     .... 

C.  8.  T.  1. 

Flexor  profundus  digitorum 

/Ulnar  and  Anterior  in- 
l     terosseous  (median) 

C.  8.  T.  1. 

C.  7.  8.  T.  1. 

Flexor  longus  pollicusl 

Pronator  qiiadi-atus      /       '         '         ' 

Anterior  interosseous     . 

C.  7.  8.  T.  1. 

B.  Muscles  of  the  Hand. 

Abductor  pollicis                               \ 

OjJiJonens  pollicis                              j-     . 

Median  .... 

C.  6.  7. 

Flexor  brevis  pollicis  (superficial).) 

Flexor  brevis  pollicis  (deep)    "j 
Adductor  obliij^uus  pollicis       -    . 
Adductor  transversiis  pollicis  j 

Ulnar     .... 

C.  8.  (T.  1). 

IjUiiibricales  Ist  and  2iid 

Median   .... 

C.  6.  7. 

Liiinliricales  3rd  and  4tli 

Iiiti'.rossei 

Flexor  l^revis  iiiininii  digiti 

Ulnar     .... 

C.  8.  (T.  1). 

(Jpponeiis  iiiiniiiii  riigiti 

AI)diictor  iiiiiiiiiii  digiU         j 

25 


554 


THE  MUSCULAE  SYSTEM. 


Muscles. 

Nerves. 

Origin. 

C.  Posterior  Muscles  of  the  Forearm. 

Bracliio-radialis                             \ 
Extensor  carpi  radialis  longior   j 
Extensor  carpi  radialis  l)revior            ^ 
Extensor  communis  digitorum              1 
Extensor  minimi  digiti                          j 
Extensor  carpi  iilnaris                          ; 

Anconeus 

Supinator  radii  Ijrevis                   A 
Extensor  ossis  metacarpi  pollicis 
Extensor  brevis  pollicis                 r 
Extensor  longus  pollicis 
Extensor  indicis                             J 
■ 

Musculo-spiral 

Posterior  interosseous     ) 
(musculo-spiral)          / 

Musculo-spiral 
Posterior  interosseous     . 

C.  5.  6. 
C.  6.  7. 
C.  6.  7. 

C.  6.  7.  8. 

C.  7.  8. 
C.  6. 

C.  6.  7.  8. 

Action  of  the  Muscles  of  the  Forearm  and  Hand. 

The  muscles  of  the  forearm  and  hand  are  concerned  in  the  movements  of  the  elbow,  wrist,  and 
fingers. 

In  the  majority  of  cases  the  muscles  act  upon  more  than  one  joint. 

1.  Action  on  the  Elbow- Joint. — It  has  been  shown  already  that  flexion  and  extension 
of  the  elljow  are  assisted  by  certain  of  these  muscles.  The  flexor  muscles  are  the  jironator 
radii  teres,  and  the  flexor  muscles  of  the  wrist  and  fingers.  In  the  position  of  pronation,  the 
movement  of  flexion  is  aided  by  the  brachio-radialis  and  extensors  of  the  wrist  and  fingers.  The 
extensors  are  the  sujjinator  brevis  and  anconeus,  and  the  extensor  muscles  of  the  wrist  and  fingers. 

2.  Pronation  and  supination  of  the  hand  are  j^erformed  by  special  muscles,  aided  by  muscles 
which  act  also  upon  other  joints.  The  brachio-radialis  assists  in  flexion  and  pronation  on  the  one 
hand,  and  in  extension  and  supination  on  the  other  hand.  In  the  supine  j^osition  it  assists 
jjrouation,  and  in  the  prone  position  it  assists  supination,  in  each  case  bringing  the  hand  into 
the  position  intermediate  between  pronation  and  supination. 


Pronation. 

Supination. 

Pronator  radii  teres 
Pronator  quadratus 
Brachio-radialis 
Flexor  carpi  radialis 
Weight  of  the  limb 

Supinator  radii  brevis 

Biceps 

Brachio-radialis 

Extensors  of  thumb  and  fingers 

"Weight  of  the  limb 

3.  Action  on  the  Wrist- Joint. — The  movements  at  the  wrist-joint  are  flexion  and  extension, 
abduction  and  adduction.  Flexion  and  adduction  are  much  more  extensive  movements  than 
extension  and  abduction,  on  account  of  the  form  of  the  wrist-joint.  The  following  muscles  pro- 
duce these  movements : — 


Flexion. 

Extension. 

Adduction. 

1 
Abduction.            ' 

Flexor  carpi  radialis 
Palmaris  longus 
Flexor  carjji  ulnaris 
Long   flexors   of 
thumb  and  fingers 

Extensors  of  the  wrist 
Extensors    of    thumb 
and  fingers 

Flexor  carpi  ulnaris 
Extensor  carpi  ulnaris 

Flexor  carpi  radialis  1 
Extensors  of  wrist 
Extensors  of  thumb 

4.  Movements  of  the  Fingers. — Two  separate  series  of  movements  occur  in  relation  to  the 

articulations  of  the  fingers :  flexion  and  extension  (at  the  metacar230-phalangeal  and  inter- 
phalangeal  joints),  and  aljduction  and  adduction  (only  at  the  metacar]3o-plialangeal  joints).  The 
movements  and  the  muscles  concerned  are  given  in  the  following  tables  : — 


Flexion. 

Extension. 

Flexor  sublimis  digitorum 
Flexor  profundus  digitorum 
Lumbricales    "^  {acting  on    the   metacarpo- 
Interossei        1  fhalangeal  articulations) 
Flexor  brevis  minimi  digiti 

Extensor  communis  digitorum 

Extensor  indicis 

Extensor  minimi  digiti 

Lumbricales  ^  {acting  on  the   inter -phal- 

Interossei        /  angeal  articulations) 

FASCIA  AND  MUSCLES  OF  THE  THIGH  AND  BUTTOCK. 


Abduction. 

Adduction. 

Lumbricales           •"! 

Flexor  brevis  and  1  (from  the  inner  side 
Oj)ponens  minimi  f     of  the  hand) 
digiti                   J 

^(from      the      middle 
Dorsal  interossei  <      line  of  the  middle 

[     finger) 

{ (to  the  middle  line 
Palmar  interossei]      of    the     middle 
[     finger) 

Flexion  is  more  powerful  and  complete  than  extension  of  the  fingers.  The  flexor  profundus 
digitorum  alone  acts  on  the  terminal  phalanges  ;  the  flexor  sublimis  and  flexor  profundus  together 
flex  the  proximal  inter-j)halangeal  joint ;  and  flexion  of  the  metacarpo-phalangeal  articulation  is 
effected  by  these  muscles,  assisted  by  the  interossei,  lumbricales,  and  flexor  brevis  minimi  digiti. 
Extension  of  the  phalanges  is  eft'ected  by  the  united  action  of  the  extensors  of  the  digits,  the 
interossei  and  lumbricales  ;  extension  of  the  fingers  at  the  metacarpo-phalangeal  joints  is  produced 
solely  by  the  long  extensor  muscles.  Separate  extension  of  the  index  finger  only  is  possible  ;  the 
three  inner  fingers  can  only  be  flexed  and  extended  together,  on  account  of  the  connecting  bands 
joining  the  extensor  tendons  together  on  the  back  of  the  hand. 

5.  Movements  of  the  Thumb. — The  movements  of  which  the  thumb  is  capable  are  flexion 
and  extension  (occurring  at  the  cariao-metacarpal,  metacarpo-phalangeal,  and  inter-phalangeal 
joints) ;  abduction  and  adduction,  together  with  circumduction  (occurring  at  the  carpo-metacarpal 
joint). 

The  muscles  and  their  respective  actions  are  given  in  the  following  table  : — 


Flexion. 

Extension. 

Opponens  poUicis  {  (car£-metacarpal 

Flexor  brevis  1  (carpo-metacarpal  and 
Adductors       r     metacarpo-phalangeal 
Abductor        J     joint) 
Flexor  longus  poUicis  (all  joints) 

Extensor  ossis  meta-  f  (carpo-metacarpal 
carpi  23ollicis           \     joint) 

Extensor  brevis/ ^•^^^P^r^^^^^^'^^Pf  f^^ 
in-  •                j       metacarpo  -  phalan- 

Extensor  longus  pollicis  (all  joints) 

Adduction. 

Abduction. 

Adductors  of  the  thumb 
Flexor  brevis ^     it  . 
Opponens       jPoUi'^is 
First  dorsal  interosseous 

Abductor  pollicis 
Extensors  of  the  thumb 

Circumduction — a  combination  of  the  above  muscles. 

The  characteristic  features  of  the  movements  of  the  upper  limb  are  their  range  and 
refinement.  The  hand,  in  addition  to  its  intrinsic  powers,  can  be  moved  through  a 
wide  range  and  in  several  planes  by  the  muscles  acting  on  the  wrist  and  radio-ulnar 
joints ;  this  range  is  increased  by  the  fore  and  aft  movements  at  the  elbow-joint,  and  the 
extensive  movements  of  which  the  shoulder  and  clavicular  joints  are  capable.  The 
result  is  that  the  hand  can  be  brought  into  a  position  to  cover  and  guard  any  portion 
of  the  body.  The  precision  and  refinement  of  movement  is  made  possible  by  the  co- 
oi'dinate  movements  of  the  various  muscles  acting  upon  the  several  joints,  so  that 
actions  can  be  performed  (as  raising  the  food  to  the  mouth)  in  which  all  the  articulations  of 
the  limb  are  brought  into  play ;  while  others  (such  as  writing)  are  possible  by  movements 
at  the  joints  of  the  wrist  and  fingers  along  with  fixation  of  the  elbow-joint. 


THE  LOWER  LIMB. 
FASCIiE  AND  MUSCLES  OF  THE  THIGH  AND  BUTTOCK. 


FASCIA. 

Til';  superficial  fascia  of  tho  thigh  and  biiiLock  jh  coiilinuous  aJ)()V(!  witli  the 
f'aHcia  of  t}i<;  ubdoiiicn  and  back,  iiiLernally  with  that  of  tlio  ])oriiu!uni,  and  below 
with  tfiat  of  th(!  log.     It  ])r(;H(!nts  noticeable  features  in  the  buttock  and  groin. 


356 


THE  MUSCULAE  SYSTEM. 


In  the  buttock  the  superficial  fascia  is  of  considerable  thickness,  and  is  usually 
loaded  with  fat,  whereby  it  assists  in  forming  the  contour  of  the  Ijuttock  and  the 
fold  of  the  nates. 

In  the  groin  it  is  divisilde  into  two  layers :  a  superficial  fatty  layer,  continuous 
with  a  similar  layer  on  the  front  of  the  abdominal  wall  above,  and  over  the 
perineum  internally,  and  a  deeper  membranous  layer,  which  is  attached  above  to 
the  inner  half  of  Poupart's  ligament,  and  to  the  deep  fascia  of  the  thigh  just  below 
the  outer  half  of  that  ligament.  Internally  it  is  attached  to  the  pubic  arch,  and 
below  the  level  of  Scarpa's  triangle  it  blends  inseparably  with  the  superficial  fatty 

layer.  The  separa- 
tion of  these  two 
layers  of  the  super- 
ficial fascia  is  oc- 
casioned by  the 
presence  between 
them  of  the  femoral 
and  inguinal  lym- 
phatic glands,  the 
internal  sa}'henous 
vein  and  its  tribu- 
taries, and  some 
small  arteries.  The 
attachment  of  the 
deeper  layer  of  the 
fascia  to  the  pubic 
arch  and  Poupart's 
ligament  cuts  oft' 
the  superficial 
tissues  of  the  thigh 
from  the  perineum 
and  the  anterior 
abdominal  wall, 
and  prevents  the 
passage  down  the 
fascia^  of   the  anterior 


Superflcial  layer  of 
superficial  fascia 


Superficial  circumflex  iliac  vessels 
Inguinal  lymphatic  glands 

Deep  layer  of  superficial  fascia 
Femoral  lymphatic  glands 

Genito-crural  nerve 

Superficial  layer  of 

superficial  fascia 

Internal  saphenous  vein 


Deep  layer  of 
superficial  fascia 
Superficial 
epigastric  vessels 
Su]ierficial  layer  of 
superficial  fascia 

Superior  external 
l)udic  vessels 

Ilio-inguinal  nerve 
Spermatic  cord 


Fig.  273.— The  Groin. 


STRtJCTaRES    BETWEEN    THE 

Superficial  Fascia. 


I 


Layers  of  the 


thigh   of  fiaid  collected  in  the   perineum  or   beneath  the 
abdominal  wall. 

The  deep  fascia  or  fascia  lata  forms  a  tubular  investment  for  the  muscles  and 
vessels  of  the  thigh  and  buttock.  Tt  is  firmly  attached  above  to  the  iliac  crest,  the 
great  sacro-sciatic  ligament,  the  ischium,  the  pubic  arch,  the  pubic  symphysis  and 
crest,  and  Poupart's  ligament.  Below,  in  relation  to  the  knee,  it  is  continuous 
with  the  deep  fascia  of  the  leg,  gains  attachment  to  the  patella,  the  tuberosities  of 
the  tibia  and  the  head  of  the  fibula,  and  forms  the  lateral  ligaments  of  the  patella. 

On  the  front  of  the  thigh  the  deep  fascia  is  thick  and  strong.  It  is  pierced 
by  numerous  openings  for  vessels  and  nerves,  the  most  important  of  which  is 
the  saphenous  opening  for  the  internal  saphenous  vein.  A  femoral  hernia  passes 
through  this  opening  to  reach  the  front  aspect  of  the  anterior  abdominal  wall.  It 
is  an  oval  opening  of  variable  size  situated  just  below  the  inner  half  of  Poupart's 
ligament,  and  immediately  in  front  of  the  femoral  vessels.  It  is  covered  by 
the  superficial  i'ascia,  and  by  a  special  layer  of  fascia,  the  cribriform  fascia,  a 
thin  perforated  lamina,  attached  to  the  margins  of  the  opening.  The  outer  edge 
of  the  opening  is  formed  by  the  margin  of  the  iliac  2Mrtion  of  the  fascia  lata, 
which  is  attached  above  to  the  iliac  crest  and  Poupart's  ligament ;  the  inner 
edge  is  formed  by  the  2^ulic  portion  of  the  fascia  lata,  which  is  continued  upwards 
behind  the  femoral  sheath,  over  the  adductor  longus  and  pectineus  muscles  to 
the  ilio-pectineal  line  and  the  capsule  of  the  hip-joint.  These  two  layers  of  the 
fascia  lata  are  continuous  at  the  lower  concave  margin  of  the  saphenous  opening, 
forming  its  inferior  cornu.  As  they  pass  upwards  towards  the  pelvis  they  occupy 
different  planes,  the  iliac  portion  being  in  front  of  the  femoral  sheath,  while  the 
pubic  portion  of  the  fascia  is  behind  it.     The  superior  cornu  of  the  saphenous  opening. 


FASCIiE  AND  MUSCLES  OF  THE  THIGH  AND  BUTTOCK. 


n 


placed  in  front  of  the  sheath,  is  derived  solely  from  the  iliac  portion  of  the  fascia  lata. 
It  forms  a  strong  triangular  band  of  fascia  attached  above  to  the  inner  half  of 
Poupart's  ligament,  and  is  known  as  tlie  falciform  ligament.  It  has  an  important 
share  in  directing  the  course  of  a  femoral  hernia  upwards  on  to  the  abdominal 

wall. 

Internally  in  relation  to  the  adductor  muscles  of  the  thigh  the  fascia  lata 
becomes  much  thinner.  At  the  knee  it  is  associated  with  the  tendons  of  the  vasti 
muscles,  and  forms  the  lateral  ligaments  of  the  patella,  attached  Lo  the  borders  of 
the  patella  and  to  the  tuberosities  of  the  tibia.     Externally  it  gives  rise  to  the 


Obliquus  externus  muscle 

Aponeurosis  of  obliquus  externus 

Intercolumnar  fibres 

Poupart's  ligament 

Iliac  portion  of  fascia  lata. 

External  cutaneous  nerve 

Falciform  ligament 
Crural  sheath  _ 
Femoral  veui  J' 
Femoral  artery __j 
Genito-crural  nei\e 
Inferior  coruu  of  saphenous 
opening 
Femoral  lymphatic  gland 

Internal  saphenous  vein 


Eleventh  thoracic  nerve 
Twelfth  thoracic  nerve 


Tlio-hypogastric  nerve 

Ex^terna.1  \  ^^^y[s,vs  of  external  abdominal  ring 

Internal  /  '- 

External  abdominal  ring  and  spermatic  cord 

Suspensory  ligament  of  penis 
Ilio-inguinal  nerve 


Body  of  penis 

Dartos  muscle  of  scrotum 


Middle  cutxneous  nerve 

Middle  cutaneous  nerve  Pubic  portion  of  fascia  lata 

Fig.  274. — The  Groin — the  Structures  seen  on  removal  of  the  Superficial  Fascia. 


ilio-tibial  band— a  broad  thick  layer  of  fascia  which  is  attached  .above  to  the  iliac 
crest,  and  receives  the  insertions  of  two  muscles  in  the  upper  part  of  the  thigh — • 
the  tensor  fasciae  femoris,  and  part  of  the  gluteus  maximus ;  it  is  attached  below 
to  the  capsule  of  the  knee-joint  and  the  outer  tuberosity  of  the  tibia.  The  fascia 
beneath  the  tensor  fasciae  femoris  muscle,  continued  upwards  from  the  ilio-tibial 
band,  sends  a  strong  band  inwards  which  joins  the  origin  of  the  rectus  femoris  and 
the  capsule  of  the  hip-joint. 

On  either  side  of  the  thigh  above  the  knee  an  intermuscular  septum  is  formed ; 
the  external  intermuscular  septum  extends  inwards  from  the  ilio-tibial  band  to  the 
external  supra-condyloid  ridge  and  linea  aspera  of  the  femur,  and  gives  attachment 
to  the  vastus  externus  and  crureus  in  front,  and  the  short  head  of  the  biceps  behind. 
The  internal  intermuscular  septum  is  more  complex.  It  is  represented  by  a  layer  of 
fascia  which  forms  separate  envelopes  for  the  gracilis  and  sartorius  muscles,  and 
in  the  upper  and  middle  thirds  of  the  thigh  encloses  the  adductor  muscles.  In  the 
middle  third  of  the  thigh  the  fascia  is  specially  thickened  by  transverse  fibres 
connecting  together  the  adductor  muscles  and  the  vastus  internus.  This  sheet  of 
fascia  forms  a  special  aponeurosis  lieneath  the  sartorius,  which  roofs  over  the 
femoral  artery  in  Hunter's  canal.  In  the  lower  third  of  the  thigh  the  intermuscular 
septum  is  cliwoly  associated  with,  and  is  to  a  large  extent  represented  by,  the 
tendon  of  the  adductor  magnus  muscle. 

Tlie  fascia  lata  of  the  buttock  is  thick  anteriorly  where  it  covers  and  gives  origin 
to  the  ghiteu's  medius,  tliinner  jjosteriorly  over  the  gluteus  maximus,  at  the  upper 
border  of  which  it  splits  to  enclose  the  muscle.     It  is  greatly  thickened  over  the 


358 


THE  MUSCULAR  SYSTEM. 


region  of  the  great  trochanter,  where  it  forms  the  insertion  of  the  greater  part  of 
the  same  muscle. 

On  the  back  of  the  thigh  and  over  the  popliteal  space  the  fascia  is  strengthened 
by   transverse   fibres  derived   from   the  hamstring  muscles.     The  popliteal  fascia 


complexus 
Sterno-mastoid 

Splenius  capitis 
Splenius  colli 

Serratus  posticus  superior 
Levator  anguli  st  apui  e 
Bromboideus  minor 


Rhomboideus 
major 


Stfrno-mastoid 


Trapezius 


Teres  major  - 


Vertebral 
aponeurosis   (iiA  \ 


^ homboideus 

Teres  major 


Latissimus  dorsi 


Serratus  posticus 
inferior 


Obliquus  externus 
abdominis 


Obliquus  internus 


Fascia  over  gluten 

maxiiiins      / 


Latispimus 

DORSI 


Obliquus  externus 
abdominis 


Obliquus  internus 


Fascia  over  gluteus 


Gluteus  maximus 


Fig.  275. — Superficjal  Muscles  of  the  Back. 

forming  the  roof  of  the  popliteal  space  is  specially  thick,  and  is  usually  pierced 
by  the  external  saphenous  vein. 

A  femoral  hernia  appears  in  the  thigh  through  tlie  saphenous  opening,  thereafter 
passing  upwards  over  Poupart's  hgament  to  the  anterior  abdominal  wall. 

Femoral  Sheath. —  This  is  a  conical  membranous  investment  for  the  femoral 
vessels,   prolonged   into    Scarpa's  triangle  beneath  Poupart's   ligament,  and  con- 


THE  MUSCJLES  ON  THE  FRONT  OF  TJIE  Til  I  OH.  359 

tinuous  above  with  the  internal  fascial  lining  of  tlie  abdominal  wall,  formed  by 
the  fascia  transversalis  in  front  and  the  fascia  iliaca  behind.  The  sheath  is 
divided  into  three  compartments — an  external  space  for  the  artery,  an  inter- 
mediate space  for  the  vein,  and  an  internal  channel  containing  lympliatics,  and 
named  the  crural  canal.  The  wall  of  this  is  known  as  the  crural  sheath.  This 
canal  is  the  passage  through  which  a  femoral  hernia  enters  the  thigh.  Its  upper 
limit  is  the  crural  ring,  placed  behind  Poupart's  ligament  in  front  of  the  origin  of 
the  pectineus  muscle  from  the  pulus  ;  it  is  bounded  internally  1-jy  Gimbernat's 
ligament,  and  externally  by  the  femoral  vein.  In  front  of  it  the  fascia  trans- 
versalis  forming  the  sheath  is  thickened  to  form  the  deep  crural  arch.  The  part  of 
Poupart's  ligament  in  front  of  the  ring  is  called  the  superficial  crural  arch.  The 
deep  epigastric  artery  separates  the  crural  ring  from  the  internal  abdominal  ring. 
The  crural  canal  ordinarily  contains  fat  which  is  continuous  above  with  the  extra- 
peritoneal tissue.  The  crural  ring  is  filled  by  a  plug  of  fat  or  a  lymphatic  gland, 
constituting  the  crural  septum. 

The  crural  canal  ends  behind  the  saphenous  opening,  covered  by  the  cribriform 
fascia ;  the  falciform  ligament  crosses  over  it  and  conceals  its  upper  portion.  The 
course  of  a  femoral  hernia  is  determined  by  this  band  of  the  fascia  lata.  The  hernia 
descends  through  the  crural  ring,  pushing  the  crural  septum  before  it ;  it  traverses 
the  crural  canal,  and  is  directed  forwards  through  the  saphenous  opening.  The 
anterior  part  of  the  hernia  being  pressed  upon  and  retarded  by  the  crural  arches 
and  by  the  falciform  ligament,  the  posterior  part  pushes  onwards,  hooks  round  the 
falciform  ligament,  and  is  directed  upwards  over  Poupart's  ligament.  The  cover- 
ings of  a  femoral  hernia,  in  addition  to  peritoneum  and  extra-peritoneal  tissue 
(crural  septum),  are  crural  sheath,  cribriform  fascia,  superficial  fascia,  and  skin. 

THE  MUSCLES  ON  THE  FRONT  OF  THE  THIGH. 

The  muscles  on  the  front  of  the  thigh  include  the  sartorius,  quadriceps  extensor, 
ilio-psoas,  and  pectineus  muscles. 

The  sartorius,  a  long  strap-like  muscle  stretching  obliquely  across  the  thigh, 
arises  by  short  tendinous  fibres  from  the  anterior  superior  spine  of  the  ilium  and 
half  of  the  notch  below  it  (Fig.  285,  p.  369).  It  passes  down  the  thigh  to  the 
inner  side  of  the  knee,  where  it  is  inserted  by  aponeurotic  fibres  into  the  inner 
surface  of  the  shaft  of  the  tibia  just  below  the  inner  tuberosity,  and  by  its  borders 
into  fascial  expansions  which  join  the  capsule  of  the  knee-joint  and  the  fascia 
lata  of  the  leg  (Fig.  279,  p.  363).  An  expansion  from  the  upper  part  of  the 
tendon  of  insertion  is  attached  along  an  oblique  line,  which  is  directed  downwards 
and  backwards,  above  the  attachment  of  the  gracilis,  to  the  internal  lateral  ligament 
of  the  knee-joint,  with  which  it  is  connected. 

The  sartorius  is  superficial  in  its  whole  extent.  It  is  so  twisted  on  itself  that 
in  the  upper  third  of  its  length  its  superficial  surface  looks  forwards,  in  the  lower 
third  inwards,  at  the  side  of  the  knee.  It  passes  diagonally  down  the  thigh,  separat- 
ing the  quadriceps  extensor  externally  from  the  adductor  muscles  internally.  Its 
upper  third  forms  the  outer  boundary  of  Scarpa's  triangle  ;  its  middle  third  forms 
the  roof  of  Hunter's  canal ;  and  its  lower  third,  in  contact  with  the  inner  side  of  the 
knee,  is  separated  from  the  tendon  of  the  gracilis  muscle  by  the  long  saphenous 
nerve  and  a  branch  of  the  anastomotic  artery.  A  bursa  lies  beneath  the  tendon  at 
its  insertion.  Tlie  sartorius  coiiC(;als  in  its  upper  third  the  external  circumflex 
vessels  and  branches  of  tlie  anterior  crural  nerve,  and  it  covers  the  femoral  vessels 
in  Hunter's  canal. 

The  quadriceps  extensor  fm.  quadriceps  femorisj  lies  between  the  sartorius 
on  the  oufj  hand  and  the  tensor  fasciai  femoris  and  ilio-tibial  Ijand  on  the  other; 
it  is  com))osed  of  four  muscles — the  rectus  femoris,  vastvis  externus,  crureus,  and 
vastus  internus. 

The  rectus  femoris  has  ;i  doulile  tondinous  origin.  (1;  The  draiglU  head 
arises  from  the  anterior  inferior  spine  ol'  th(!  ilium  fFig.  2(S2,  p.  366);  (2)  the 
reJUcted  head  springs  froni  a  niugh  groove  on  tlie  dorsum  ilii  just  above  the 
highest  part  of   the  acetabulum  (Fig.  285,  p.  369;.       A  bursa  lies  beneath  this 


360 


THE  MUSCULAK  SYSTEM. 


head  of  origin.  The  two  heads,  bound  together  and  connected  to  the  capsule  of 
the  hip-joint  by  a  band  of  fascia  derived  from  the  under  surface  of  the  tensor 
fascife  femoris  (ilio-tibial  band),  give  rise  to  a  single  tendon  which  extends  for 


Gluteus  mediu 
Iliacu 

Tensor  fasci.b  femori 


•Adductor  longus 


Fascia  lata  and  ilio-tibial 
band" 

Nerve  and  artery  to 
vastus  externus 


Crubeus 


Fascia  lata  and  ilio-tibial 
band 


Vastus  externus 


Tendon  of  quadriceps  extensor  _j^ 


.Poupart's  ligament 
Anterior  crural  nerve  (with 
branch  to  pectineus) 


Tendon  of  psoas  muscle 
Adductor  bbevis 
.Pectineus 


•Vastus  internus 


Lateral  ligament  of  patella- 

Lioamentum  patfll* 


Lateral  ligament  of  patella 


Insertion  of  sartorius 


Fig.  276.— The  Muscles  OiN  the  Front  of  the  Thigh. 

some  distance  on  the  front  of  the  muscle,  and  from  which  the  muscular  fibres  arise. 
The  muscular  fibres  springing  from  this  tendon,  and  also  from  a  median  septal 
tendon,  present  a  bipennate  arrangement,  and  end  below  in  a  broad  tendon  which 
passes  upwards  for  some  distance  along  the  posterior  surface  of  the  muscle.     This 


THE  MUSCLES  ON  THE  EEONT  OF  THE  THIGH. 


361 


glutei 


Pynfonnis  (insertion) 


Gluteus  medius 
(insertion) 


Gluteus  niimmu 
(insertion) 


Vastus  mternus 
(origin) 


Vastus  externus  (origin) 


tendon  gradually  narrows  towards  the  knee,  and  spreading  out  again,  is  inserted 
into  the  upper  border  of  the  patella.  It  receives  laterally  parts  of  the  insertions 
of  the  vasti  muscles,  and  on  its  deep  surface  is  joined  by  the  tendinous  insertion 
of  the  crureus. 

The  rectus  femoris  is  superficial  except  at  its  origin,  which  is  covered  by  the 
tensor  fascise  femoris,  and  sartorius  muscles.  On  its  inner  side  lie  the 
iliacus,  sartorius,  and  vastus  internus  ;  on  its  outer  side  are  the  tensor  fasciae  femoris 
and  vastus  externus.  It  conceals  the  crureus  muscle  and  branches  of  the  external 
circumflex  artery  and  anterior  crural  nerve.  A  bursa,  which  communicates  with 
the  synovial  membrane  of  the  knee-joint,  lies  beneath  its  tendon  in  front  of  the 
lower  end  of  the  shaft  of  the  femur. 

The  vastus  externus  (m.  vastus  lateralis)  has  an  origin,  partly  fleshy,  partly 
membranous,  (1)  (slightly)  from  the  ca^Dsule  of  the ,  hip-joint,  (2)  from  the  tubercle 
of   the  femur,  (3)   from   a   concave  ^=««5.<^w 

surface  on  the  front  of  the  shaft 
of  the  bone  internal  to  the  great 
trochanter,  (4)  from  the  lower  border 
of  the  great  trochanter,  (5)  from  the 
outer  margin  of  the  gluteal  ridge 
of  the  femur  and  the  tendon  of  the 
gluteus  maximus,  (6)  from  the  upper 
half  of  the  linea  aspera,  and  (7)  from 
the  fascia  lata  and  external  inter- 
muscular septum  (Fig.  277,  p.  361). 

It  forms  a  thick,  broad  muscle 
directed  downwards  and  forwards, 
and  is  inserted  by  a  broad  mem- 
branous tendon  into  (1)  the  outer 
border  of  the  tendon  of  the  rectus 
femoris,  (2)  the  upper  and  outer 
border  of  the  patella,  and  (3)  the 
capsule  of  the  knee-joint,  and  the 
external  lateral  ligament  of  the 
patella.  The  vastus  externus  is 
covered  superficially  by  the  fascia 
lata  and  the  ilio- tibial  band.  A 
bursa  intervenes  between  it  and  the 
membranous  insertion  of  the  gluteus 
maximus  :  at  its  inner  border  is  the 
rectus  femoris ;  and  under  cover  of 
it,  on  a  deeper  plane,  is  the  crureus,  which  is  also  to  a  large  extent  concealed  by 
the  muscle.  Between  the  vastus  externus  and  crureus  is  the  descending  branch  of 
the  external  circumflex  artery. 

The  vastus  internus  (m.  vastus  medialis)  is  larger  than  the  vastus  externus 
and  has  a  more  extensive  origin,  from  (1)  the  shaft  of  the  femur — from  the  lower 
two-thirds  or  more  of  the  spiral  line,  the  linea  aspera,  and  the  upper  two-thirds 
of  the  line  leading  from  the  linea  aspera  to  the  internal  condyle  of  the  femur ; 
(2)  the  membranous  expansion  of  the  fascia  lata  which  lies  beneath  the  sartorius 
and  forms  tlie  roof  of  Hunter  s  canal ;  and  (3)  the  internal  intermuscular  septum 
and  the  tendon  of  the  adductor  magnus  (Figs.  277,  p.  361,  and  281,  p.  365). 

From  its  origin  the  muscle  is  directed  downwards  and  outwards  towards  the 
knee ;  it  is  inserted  by  a  strong  aponeurotic  tendon  into  (1)  the  inner  border  of  the 
rectus  tendon  ;  (2)  the  upper  and  inner  border  of  the  patella;  and  (3)  the  capsule  of 
the  knee-joint  and  the  internal  lateral  ligament  of  the  patella.  The  vastus 
internus  is  superficial  except  at  its  origin,  which  is  concealed  by  the  sartorius 
rnuscle  and  femoral  vessels.  Along  its  outer  side  are  the  rectus  and  crureus ; 
the  muscle  conceals  the  inner  side  of  the  shaft  of  the  femur  and  tlie  crureus, 
with  which  it  is  closely  incorporated  in  its  lower  two-thirds. 

The  crureus  muscle  (\n.  vastus  iiit(irmedius)  arises  by  fleshy  fibres  (1)  from  the 
26 


Crureus  (origin) 


Fig.    277. — Muscle-Attachments   to  the   Anterior 
Surface  of  the  upper  part  op  the  Femur. 


562 


THE  MUSCULAE  SYSTEM. 


upper  two-thirds  of  the  shaft  of  the  femur  on  the  anterior  and  external  surfaces, 
(2)  from  the  lower  half  of  the  outer  lip  of  the  linea  aspera  and  the  upper  part 
of  the  line  leading  therefrom  to  the  external  condyle,  as  well  as  (3)  from  a 
corresponding  portion  of  the  external  intermuscular  septum  (Fig.  277,  p.  361). 

For  the  most  part  deeply  placed,  the  muscle  is  directed  downwards  to  an 
insertion  into  the  deep  surface  of  the  tendons  of  the  rectus  and  vasti  muscles  by 
means  of  fibres  which  join  a  membranous  expansion  on  its  surface. 

The  crureus  is  concealed  by  the  rectus  and  vasti  muscles,  and  externally,  in 
the  lower  half  of  the  thigh,  by  the  ilio-tibial  band.  It  is  closely  adherent  to  the 
vastus  externus  muscle  in  the  middle  third  of  the  thigh ;  it  is  inseparable  from 
the  vastus  iuternus  below  the  upper  third.      Beneath  the  crureus  is  the  femur ; 


Vastus  internds 


Rectus  femoris 


Internal  saphenous  nerve 
Femoral  vessels 
Sartorius 


Adductor  longus' 


Adductor  magnue- 
Gracilii 


Biceps  (short  head) 


Semimembranosus''  ^  .^^^^^^^^^^^^^^ 

vV  7^^5^5H5^^^^.-^>^^    Biceps  (long  head) 
Semitendinosus 

Great  sciatic  nerve 
Fig.  278. — Transverse  Section  of  the  Thigh  (Hunter's  Canal). 

and  in  the  lower  third  of  the  thigh  it  conceals  the  subcrureus  muscle,  a  bursa,  and 
the  upward  prolongation  of  the  synovial  membrane  of  the  knee-joint. 

The  subcrureus  consists  of  a  number  of  separate  bundles  of  muscular  fibres 
arising  beneath  the  crureus  from  the  lower  fourth  of  the  front  of  the  femur,  and 
inserted  into  the  synovial  membrane  of  the  knee-joint  beneath  the  tendon  of  the 
rectus  femoris. 

The  four  elements  composing  the  quadriceps  extensor  muscle  have  been  traced 
in  their  convergence  to  the  patella  and  the  lateral  ligaments  of  the  patella.  Their 
ultimate  insertion  is  into  the  tibia  (Fig.  279,  p.  363),  by  means  of  the  ligamentum 
patellae  and  the  lateral  ligaments  of  the  patella.  The  patella,  indeed,  is  in  one  sense 
a  sesamoid  bone  formed  in  the  tendon  of  the  muscle,  the  ligamentum  patellae  being 
the  real  tendon  of  insertion,  and  the  lateral  ligaments  fascial  expansions  from 
its  borders.  The  insertion  of  the  muscle  forms  the  front  of  the  capsule  of  the 
knee-joint. 

The  ilio-psoas  muscle  is  a  compound  muscle,  consisting  of  one  or  sometimes 
two  elements, — psoas  (magnus  and  parvus),  connecting  the  femur  and  pelvic  girdle  to 
the  axial  skeleton;  and  another  element,  the  iliacus,  extending  between  the 
innominate  bone  and  the  femur.  The  muscles  chiefly  occupy  the  posterior  wall  of 
the  abdomen  and  false  pelvis,  their  insertions  only  appearing  in  the  thigh  below 
Poupart's  ligament. 

The  psoas  magnus  (m.  psoas  major)  is  a  large  pyriform  muscle,  which  has  an 
extensive  origin  by  fleshy  fibres  from  the  vertebral  column  in  the  lumbar  region. 
It  arises  (1)  from  the  intervertebral  discs  above  each  lumbar  vertebra,  and  from  the 


THE  MUSCLES  ON  THE  FRONT  OF  THE  THIGH. 


363 


Semi-niembranosus 

(insertion) 
Ligamentum  jjatellse 
(nibertion) 


Attachment  of  internal 
lateral  ligament  of  the  knee 

Gracilis  (insertion) 


Semi-tendinosus  (insertion) 


adjacent  margins  of  the  vertebrte — from  the  lower  border  of  the  12th  thoracic 
to  the  upper  border  of  the  5th  lumbar  vertebra;  (2)  it  arises  also  from  four 
aponeurotic  arches  which  pass  over  the  sides  of  the  bodies  of  the  first  four 
lumbar  vertebrae ;  and  (3)  it  has  an  additional  origin  posteriorly  from  the  transverse 
processes  of  all  the  lumbar  vertebrae.  The  fibres  form  a  fusiform  muscle  directed 
downwards  over  the  pelvic  brim  and  beneath  Poupart's  ligament,  ending  in  a 
tendon  which  is  inserted  into  the  apex  of  the  lesser  trochanter  of  the  femur  (Fig. 
281,  p.  365). 

The  psoas  muscle  occupies  the  posterior  abdominal  wall,  the  false  pelvis,  and 
the  thigh.  In  the  abdomen  it  lies  in  the  groove  alongside  the  bodies  of  the  lumbar 
vertebrse,  in  front  of  the  transverse  pro- 
cesses, and  is  enveloped  by  a  fascia 
derived  from  the  lumbar  aponeurosis. 
The  abdominal  viscera  in  contact  with 
it  are :  the  kidney  and  colon  on  both 
sides,  with  the  duodenum  on  the  right, 
and  the  pancreas  on  the  left  side.  The 
ureter  is  in  front  of  it,  along  with  the 
spermatic  or  ovarian,  the  renal  and  colic 
vessels.  The  inferior  vena  cava  is  in 
front  of  the  right  muscle ;  the  inferior 
mesenteric  vein  is  in  front  of  that  of  the 
left  side.  The  lumbar  plexus  is  em- 
bedded in  its  substance,  and  the  nerves 
of  distribution  emerge  from  its  surface 
and  borders.  In  the  false  pelvis  the 
psoas  covers  the  pelvic  brim,  and  is 
covered  by  the  ureter,  the  iliac  vessels, 
the  ileum  on  the  right  side,  and  the 
iliac  colon  on  the  left  side.  The  vas 
deferens  and  spermatic  vessels  cross  over 
it  just  above  Poupart's  ligament.  In 
Scarpa's  triangle  the  tendon  is  behind 
the  femoral  vessels,  between  the  iliacus 
and  pectineus,  and  in  front  of  the 
obturator  externus  muscle  and  the  hip- 
joint.  A  bursa,  which  may  be  con- 
tinuous with  the  synovial  cavity  of  the 
hip-join  b,  separates  the  tendon  from  the 
pubis  and  the  capsule  of  the  hip-joint. 

The  psoas  parvus  (m.  psoas  minor)  is  often  absent  (40  per  cent).  It  arises  by 
fleshy  fibres  from  the  intervertebral  disc  between  the  last  thoracic  and  first  lumbar 
vertebrae,  and  from  the  contiguous  margins  of  these  vertebrae.  The  muscle  is 
closely  apposed  to  the  anterior  surface  of  the  psoas  magnus.  It  forms  a  slender 
fleshy  belly,  and  is  inserted  by  a  narrow  tendon  into  the  middle  of  the  ilio-pectineal 
line  and  the  ilio-pectineal  eminence,  its  margins  blending  with  the  fascia  covering 
the  psoas  magnus. 

The  iliacus  muscle  arises  by  fleshy  fibres,  mainly  from  a  horseshoe- shaped 
origin  around  tlie  margin  of  the  iliac  fossa ;  it  has  additional  origins  also  from 
the  ala  of  the  sacrum,  the  anterior  sacro-iliac,  lumbo-sacral,  and  ilio-lumbar 
ligaments,  and  outside  the  pelvis,  from  the  upper  part  of  the  ilio-femoral  band. 
It  is  a  fan-shaped  muscle,  its  fibres  passing  downwards  over  the  hip-joint  towards 
the  small  trochanter  of  the  femur.  It  is  inserted  by  fleshy  fibres  (1)  into  the 
outer  side  of  the  tendon  of  the  psoas  magnus ;  (2)  into  the  concave  anterior  and 
upper  surfaces  of  the  small  trochanter  ;  and  (3)  into  the  shaft  of  the  femur  below 
the  small  trochanter  for  about  an  inch  (Fig.  281,  p.  365) ;  and  (4)  by  its  most 
external  fibres  into  the  capsule  of  the  hip-joint.  These  fibres  are  often  separate, 
forming  the  iliacus  minor,  or  ilio-capsularis. 

The  muscle  occupies  the  false  pelvis  and  Scarpa's  triangle.     It  forms  the  back 


Fig. 


279. — Muscle-Attachments  to  the  inner  side 
OF  the  upper  part  of  the  Tibia. 


364 


THE  MUSGULAE  SYSTEM. 


wall  of  the  false  pelvis  and  is  covered  anteriorly  by  the  iliac  fascia.  It  is_  in 
contact  with  the  cfficum  on  the  right  side  and  the  iliac  colon  on  the  left  side. 
The  psoas  muscle  lies  along  its  inner  border,  with  the  anterior  crural  nerve  in  the 
interval  between  them.  After  passing  beneath  Poupart's  ligament,  and  over  the 
capsule  of  the  hip-joint,  the  muscle  occupies  the  outer  part  of  the  floor  of  Scarpa's 
triangle  internal  to  the  sartorius  and  rectus  femoris  muscles. 


Vena  caval  openins     (Esophagpal  opening;  Oeiitial  tendon  (middle  part) 


Central  tendon  (right  pari). 
Diaphragm,  costal  fibrf 
Internal  arcuate  ligament 

External  arcuate  ligament 

End  of  last  nb 

Last  thoracic  ner\  e 

Ant.  layer  of  lumbar  fascia 

Lumbar  fascia 

Ilio-hypogastric  nerve 

Lumbar  vessels  and  symjia 

thetic  communicating  ner\e'. 

Ilio-inguinal 

QuADRATUR  LUMBORl  >I 


External  cutaneous  ner^e 

Psoas  magnl"- 

Iliacls- 

Lumbo-sacral  cord 


Genito-crural  nerve 
Anterior  crural  ner\ 
Obturator  ner\ 


Great  sciatic  ner\  t  — 


Diaphragm,  right  crus 

Middle  arcuate  ligament 
Aortic  opening 


Central  tendon 
(left  part) 
Uiaphraom,  left 

CRUS 


Last  thoracic  nerve 
End  of  last  rib 
Lumbar  nerve  I. 
[lio-hypogastric 
Lumbar  nerve  II. 

Ilio-inguinal  nerve 
Ql'adeatus 
ll'mborum 
Lumbar  nerve  III. 

Genito-crural  nerve*. 
Lumbar  nerve  IV. 


Lumbo-sacral  cord 


External  cutaneous  nerve 
—Anterior  crural  nerve 
Obturator  nerve 
Great  sciatic  nerve 


Fig.  280. — View  of  the 


Gracilis  (origin) 
Adductor  magnus  (origin) 
Pectin  Eus  (cut) 
Superficial  branch  of  obturator  nerve 
beep  .branch  of  obturator  nerve 
Obturator  exteknus 

Posterior  Abdominal  Wall,  to  show  the  Muscles  and  the  Nerves  of 
THE  Lumbo-Sacral  Plexcs. 


The  pectineus  muscle  arises  by  fleshy  fibres  from  the  sharp  anterior  portion 
of  the  ilio-pectineal  line  of  the  pubis,  and  from  the  triangular  surface  of  the 
pubic  bone  in  front  of  this  (Fig.  282,  p.  366).  It  also  arises  from  the  femoral 
surface  of  Gimbernat's  ligament,  and  from  the  pubic  portion  of  the  fascia  lata  which 
covers  it.  Forming  a  broad  muscular  band,  it  is  directed  obliquely  downwards, 
backwards,  and  outwards,  to  be  inserted  by  a  thin  fiat  tendon  about  two  inches 
in  length  into  the  upper  half  of  the  pectineal  line  leading  from  the  back  of  the 


THE  MUSCLES  ON  THE  INNER  SIDE  OF  THE  THIGH. 


]6i 


(iri'^prtioii) 


small  trochanter  of  the  femur  towards  the  linea  aspera ;    its  lower  attachment 

being    placed    in    front    of    the 

insertion  of  the  adductor  brevis 

muscle  (Fig.  281,  p.  365).  ^VertZ) 

The  pectineus  forms  a  part  oiutpus  medms 
of  the  floor  of  Scarpa's  triangle. 
Covered  by  the  pubic  portion  of 
the  fascia  lata,  it  is  partially 
concealed  by  the  femoral  vessels 
and  the  insertion  of  the  ilio- 
psoas. It  lies  in  i'ront  of  the 
pubic  bone,  the  obturator  ex- 
ternus  and  adductor  brevis 
muscles,  and  the  superficial  part 
of  the  obturator  nerve.  Its 
outer  border  is  separated  from 
the  psoas  by  the  internal  cir- 
cumflex vessels.  Its  inner  border 
is  in  contact  above  with  the 
adductor  longus,  but  is  separated 
from  it  below  by  the  deep 
femoral  vessels.  The  muscle 
may  be  occasionally  divided 
into  inner  and  outer  parts,  the 
former  innervated  by  the  ob- 
turator, the  latter  by  the  anterior 
crural  nerve. 


THE  MUSCLES  ON  THE  INNEli 
SIDE  OF  THE  THIGH. 


Oh)turator  interims  and 
gfmelli  (insertion; 
Obturator  externus 
(insertion) 

Quadratus  femoris 
(insertion) 


^B     Ilio-psoas  (insertion) 


Gluteus  maximus 
(insertion) 

Adductor  niagnus 
(insertion) 

Adductor  brevis 
(insertion) 


Pectineus  (insertion) 


Vastus  externus  (origin) 


281. — Muscle-Attachments  to  the  Posterior  Aspect 
01'  THE  Upper  Part  of  the  Femur. 


brevis,   and   adductor 


The  muscles  on  the  inner  side    ^^'^• 
of    the    thigh    include    the    ad- 
ductors  of    the    femur — the    adductor    longus,   adductor 
magnus ;  the  gracilis,  and  the  obturator  externus. 

The  gracilis  muscle  is  a  long  flat  band  placed  on  the  inner  side  of  the  thigh 
and  knee.  It  arises  by  a  thin  aponeurotic  tendon  from  the  lower  half  of  the  edge 
of  the  symphysis  pubis,  and  for  a  similar  distance  from  the  border  of  the  adjoining 
part  of  the  pubic  arch  (Fig.  282,  p.  366).  Its  flattened  fleshy  belly  passes  down 
on  the  inner  side  of  the  thigh  to  the  knee,  where  it  ends  in  a  tendon,  which  expands 
to  be  inserted  into  the  inner  side  of  the  shaft  of  the  tibia  just  below  the  inner 
tuberosity,  behind  the  sartorius  and  above  and  in  front  of  the  semitendinosus 
(Fig.  279,  p.  363).  It  is  separated  from  the  sartorius  tendon  by  a  bursa,  and 
beneath  its  tendon  is  another  bursa  common  to  it  and  the  semitendinosus. 

The  gracilis  is  superficial  in  its  whole  extent,  except  at  its  insertion  which  is 
concealed  by  the  insertion  of  the  sartorius  muscle.  Its  deep  surface  covers  the 
borders  of  the  adductor  longus  and  adductor  magnus  muscles,  as  well  as  the  super- 
ficial part  of  the  obturator  nerve.  At  the  inner  side  of  the  knee  it  lies  between 
the  sartorius  and  semitendinosus. 

The  adductor  longus  is  a  triangular  muscle  arising  by  a  rounded  tendon  from 
the  arit(;rior  surface  of  the  body  of  the  pubis  in  the  angle  between  the  crest  and 
symphysis  CFig.  282,  \).  366).  Extending  downwards  and  outwards,  it  is  inserted 
into  tlie  middle  two-fourths  of  the  inner  lip  of  the  linea  aspera  in  front  of  the 
adductor  niagnus.  Lying  in  the  same  plane  as  the  pectineus,  the  adductor  longus  is 
in  contact  with  that  muscle  near  its  origin,  l)ut  is  separated  from  it  below  })y  an 
interval  tlirough  wliich  t}ie  deep  femoral  vessels  pass.  Its  inner  border  is  in  contact 
with  the  gracilis  and  s;i,rtorius  muscles.  Its  anterior  siirlace  i'orms  part  of  the  floor 
of  Scarpa's  triangle  above,  part  of  the  floor  of  Hunter's  canal  below.  It  is  cov(!red 
near  its  insertion  by  the  sartorius  and  the  femoral  vessels,  and  it  is  connected  to 


366 


THE  MUSCULAE  SYSTEM. 


the  origin  of  the  vastus  interims  by  an  aponeurotic  expansion  of  fascia  beneath 
the  sartorius,  forming  the  roof  of  Hunter's  canal.  Its  posterior  surface  is  in 
relation  with  the  adductor  bre\is  and  the  adductor  magnus  muscles,  the  deep 
femoral  vessels,  and  the  superficial  part  of  the  ol)turator  nerve.  The  adductor 
longus  may  he  doulile,  or  more  or  less  fused  with  the  pectineus. 

The  adductor  brevis  is  a  large  muscle  which  arises  by  fleshy  and  short 
tendinous  fibres  from  an  elongated  oval  surface  on  the  front  of  the  body  and 
upper  part  of  the  descending  ramus  of  the  pubis,  surrounded  by  the  other  muscles 
of  this  group  (Fig.  282,  p.  366).  Directed  downwards  and  outwards,  the  muscle 
expands,  to  be  inserted  by  a  short  aponeurotic  tendon,  behind  the  insertion  of  the 
pectineus,  into  the  lower  two-thirds  of  the  line  leading  from  the  small  trochanter  of 


-Rectus  fenioris  (straight  head  of  origin) 

.Rectus  femoris  (reflected  head  of  origin) 
,  Attachment  of  ilio-feiuoral  band 


Pyramidalis  abdominis  (origin 
Rectus  abdominis  (origin) 


Gracilis  (origin) 

Adductor  brevis 
(origin) 


Semi-membranosus 
(origin) 

Quadratns  femoiis 
(origin) 


Biceps  and  semi-tendin 
osus  (origin) 


Fig.  282. — Muscle- Attachments  to  the  outer  surface  of  the  Pubis  and  Ischiuje. 

the  femur  to  the  linea  aspera,  and  to  the  upper  fourth  of  the  linea  aspera  itself 
(Eig.  286,  p.  370). 

The  adductor  brevis  is  the  central  muscle  of  the  adductor  group.  It  is  almost 
wholly  concealed  by  the  pectineus  and  adductor  longus.  It  rests  upon  the 
adductor  magnus;  at  its  upper  border  is  the  obturator  externus,  separated  from 
it  by  the  internal  circumflex  vessels ;  at  its  lower  border  is  the  adductor  longus, 
separated  by  the  deep  femoral  vessels.  It  separates  the  superficial  and  deep  parts 
of  the  obturator  nerve  in  their  course  down  the  thigh. 

The  adductor  magnus,  the  largest  of  the  adductor  group,  is  a  roughly  tri- 
angular muscle  arising  mainly  by  fleshy  fibres  by  a  curved  origin  from  the  lower 
part  of  the  outer  border  and  a  large  portion  of  the  adjoining  inferior  surface  of  the 
ischial  tuberosity,  from  the  edge  of  the  ischial  ramus,  and  from  the  anterior  surface 
of  the  descending  ramus  of  the  pubis,  its  most  anterior  fibres  arising  between  the 
obturator  externus   and   adductor   brevis  (Figs.   282,  p.    366,  and   285,  p.   369). 


THE  MUSCLES  ON  THE  INNEE  SIDE  OF  THE  THIGH.         367 


Its  upper  fibres  are  directed  horizontally  outwards  from  the  pubis  towards  the 
upper  part  of  the  femur ;  the  lowest  fibres  are  directed  downwards  from  the  ischial 
tuberosity  to  the  internal  condyle  of  the  femur ;  while  the  '  intermediate  fibres 
radiate  obliquely  outwards  and  downwards.  The  muscle  is  inserted  by  tendinous 
fibres  (1)  into  the  space  below  the  insertion  of  the  quadratus  femoris,  above  the 
linea  aspera ;  (2)  into  the  whole  length  of  the  linea  aspera ;  (3)  into  the  internal 
supracondyloid  ridge  of  the  femur;  (4)  into  the  adductor  tubercle  on  the 
internal  condyle  of  the  femur;  and  (5)  into  the  internal  intermuscular  septum 
(Fig.  286,  p.  370).  The  part  of  the  muscle  attached  to  the  space  above  the  linea 
aspera  is  often  separated  from  the  rest  as  the  adductor  minimus.  The  attachment 
of  the  muscle  into  the  supracondyloid  ridge  is  interrupted  for  the  passage  of  the 


Obturator  nerve. 


Psoas  magnus 

Branch  to  liip-jomt. 
Deep  branch 

Superficial  brancli 1 

Descending  muscular  branches' 

Pectineus' 

Ascending  branch  to  obturator 

extern  us 

Internal  circumflex  arteiy 


Adductob  long  us, 
Adductor  bbevis 


Bi-ancli  to  knee-joint 


Cutaneous  branch 


Branch  to  femoral  artery  Gracilis 

Fig.  283.— Scheme  of  the  Course  and  Distribution  of  the  Obturator  Nerve. 

femoral  vessels  to  the  popliteal  space.  The  attachment  to  the  internal  condyle 
is  by  means  of  a  strong  tendon  which  receives  the  fibres  arising  from  the  ischium 
(the  part  of  the  muscle  associated  with  the  hamstring  group).  This  tendon  is  closely 
connected  with  the  internal  lateral  ligament  of  the  knee-joint. 

The  adductor  magnus  intervenes  between  the  other  adductor  muscles  in  front 
and  the  hamstring  muscles  behind.  It  is  concealed  anteriorly  by  the  pectineus, 
adductor  brevis,  adductor  longus,  and  sartorius.  The  deep  femoral  artery  lies  on 
it  above.  It  forms  the  floor  of  Hunter's  canal  below,  where  the  femoral  vessels  lie 
upon  it.  The  hamstring  muscles  and  great  sciatic  nerve  are  behind  the  adductor 
magnus ;  the  obturator  externus  and  quadratus  femoris  are  at  its  upper  border ;  and 
along  its  inner  border  are  the  gracilis  and  sartorius  muscles. 

The  obturator  externus  is  placed  deeply  under  cover  of  the  previous  muscles. 
It  is  a  fau-Hha]jed  muscle  lying  horizontally  in  the  angle  between  the  hip  boneand 
the  neck  of  the  femur.  It  arises  from  the  outer  surface  of  the  pubis  and  ischium, 
which  form  the  inferior  half  of  the  margin  of  the  thyroid  foramen,  and  from  the 
corresponding  portion  of  the  outer  surface  of  the  obturator  membrane  (Figs.  282, 
p.  366,  and  285,  p.  369).     Its  fibres  converge  towards  the  great  trochanter,  and 


368 


THE  MUSCULAE  SYSTEM. 


end  in  a  stout  tendon  which,  after  passing  below  and 


Origin  of  HAMsxRiNf 

MU.Sf  I  I 


Adductor  maoni 


Popliteal  vessels 


Semitendinosus. 

Semimembranosus 
(insertion) 

Gracilis, 


Sartorius 


P\R1F0RMIS 


Obturator  intebnus 
and  oemelij 

Obturator  externus 
Quadratus  femoris 


Gluteus  maximus 
(insertion) 


Biceps  (short  head) 


Biceps  (long  head) 


jehind  the  hip-joint,  is  inserted 
into  the  digital  fossa  of 
the  great  trochanter  (Figs. 
286,p.  370,and289,p.37l). 
The  inferior  surface  of 
the  muscle  is  in  contact 
with  the  pectineus,  ad- 
ductor brevis,  and  ad- 
ductor magnus  muscles, 
separated  from  them  by 
the  internal  circumflex 
vessels.  The  superior  sur- 
face is  in  relation  to 
the  obturator  membrane 
and  the  neck  of  the 
femur.  The  tendon  lies 
below  and  behind  the 
capsule  of  the  hip-joint, 
and  near  its  insertion 
appears  in  the  buttock 
(under  cover  of  the 
gluteus  maximus)  be  - 
tween  the  inferior  gemel- 
lus and  quadratus  femoris 
muscles. 

THE  MUSCLES  OF    THE 
BUTTOCK. 

This 


Gastrocnemius  (outer 
■'lead) 


group  includes 
the  three  glutei  muscles, 
the  tensor  fascite  femoris, 
pyriformis,  obturator  in- 
ternus  and  gemelli,  and 
quadratus  femoris. 

The  gluteus  maximus 
is  a  large  quadrilateral 
muscle,  with  a  crescentic 
origin,  from  (1)  a  portion  of 
the  area  on  the  dorsum  ilii 
above  the  superior  curved 
line  (Fig.  285,  p.  369) ;  (2) 
the  tendon  of  the  erector 
spinas ;  (3)  the  posterior 
surface  of  the  sacrum  and 
coccyx  (Fig.  311,  p. 
396);  and  (4)  the  posterior  surface  of  the  great  sacro-sciatic  ligament.  The 
fibres  which  form  its  upper  and  outer  border  take  origin  directly  from  the 
fascia  lata  which  envelopes  the  muscle.  The  muscle  forms  a  large  fleshy 
mass,  whose  fibres  are  directed  obliquely  outwards  over  the  buttock,  invested 
by  the  fascia  lata,  and  are  inserted  by  short  tendinous  fibres,  partly  into  the  fascia 
lata  over  the  great  trochanter  of  the  femur  (joining  the  ilio-tibial  band),  and 
partly  into  the  gluteal  ridge  (Fig.  286,  p.  370).  The  fascia  lata  receives  the 
insertion  of  the  whole  of  the  superficial  fibres  of  the  muscle  and  the  upper  half 
of  the  deep  fibres.  The  lower  half  of  the  deep  portion  of  the  muscle  is  inserted  for 
the  most  part  into  the  gluteal  ridge ;  but  the  lowest  fibres  of  all '  are  inserted  into 
fascia  lata,  and  are  thereby  connected  with  the  external  intermuscular  septum  and 
the  origin  of  the  short  head  of  the  biceps. 

The  gluteus  maximus  is  the  coarsest  and  heaviest  muscle  in  the  body.     By  its 


Fig.  284. 


-The  Posterioe  Surface  of  the  Thigh  (superficial 
muscles  removed). 


THE  MUSCLES  OF  THE  BUTTOCK. 


;69 


weight  it  helps  to  form  the  fold  of  the  nates.  It  is  superficial  in  its  whole  extent. 
The  gluteus  medius  is  visible  at  its  upper  border,  covered  by  the  fascia  lata ;  at  its 
lower  border  the  hamstring  muscles  and  great  sciatic  nerve  appear  on  their  way- 
down  the  thigh.  The  muscle  conceals  the  bones  from  which  it  arises,  along  with 
the  great  sciatic  ligament,  the  ischial  tuberosity,  and  the  great  trochanter  of  the 
femur.  It  also  conceals  the  gluteus  medius  and  pyriformis,  with  a  branch  of  the 
gluteal  artery  between  them  ;  the  obturator  intern  us  and  gemelli,  with  the  sciatic 
vessels  and  nerves,  the  pudic  vessels  and  nerve,  and  the  muscular  branches  of  the 
sacral  plexus  above  them,  and  the  obturator  externus  and  a  branch  of  the  internal 
circumflex  artery  below  them  ;  the  quadratus  femoris  and  upper  part  of  the 
adductor  magnus  muscles,  with  the  internal  circumflex  vessels  between  them.  It 
covers  the  origins  of  the  hamstring  muscles,  and  by  its  insertion  into  the  fascia  lata. 


Obliquus  externus  abdoiriinis 
insertion) 


Tensor  fascice 
femoris  (origin) 


Gluteus  maximus 
(origin) 


Rectus  femoris  (reflected 
head  of  origin) 


Gemellus  superior  (origin) 

Gemellus  inferior  (origin). 

Semimembranosus  (origin) 

Biceps  and  semitendinosus  (origin)' 


Quadratus  femoris  (origin) 

Obturator  externus  (origin) 
Adductor  magnus  (origin) 


Adductor  magnus  (origin)' 
Fig.  285. — Muscle-Attachments  to  the  Doesum  Ilii  and  Tubek  Ischii. 

the  vastus  externus.  The  first  perforating  artery  pierces  the  attachment  of  the 
muscle  to  the  gluteal  ridge.  Three  bursse  are  beneath  it :  one  (not  always  present) 
over  the  tuberosity  of  the  ischium,  a  second  over  the  outer  side  of  the  great 
trochanter,  and  a  third  over  the  vastus  externus.  The  fibres  of  the  gluteus 
maximus  arising  from  the  coccyx  may  form  a  separate  muscle  (agitator  caudse). 

The  tensor  fasciae  femoris  (m.  tensor  fascise  latse),  lying  on  the  same  plane  as 
the  gluteus  maximus,  arises  from  the  iliac  crest  and  the  dorsum  ilii  just  external  to 
the  anterior  superior  spine,  and  from  the  fascia  covering  its  outer  surface  (Fig. 
285,  p.  369).  Invested  like  tlie  gluteus  maximus  by  the  fascia  lata,  it  is  inserted 
about  the  lev(d  of  the  great  trochanter  of  the  femur  into  the  fascia,  which  forms  the 
ilio-tibial  band  (p.  357). 

The  tensor  fasciae  femoris  muscle  is  superficially  placed,  and  is  enclosed  in  a 
strong  investment  of  the  fascia  lata,  the  deeper  layer  of  which  is  prolonged  up  to  join 
the  tendon  of  the  rectus  femoris  and  the  capsule  of  the  hip-joint.  The  muscle  is 
placed  along  the  anterior  borders  ol'  th(!  gluteus  medius  and  gluteus  minimus,  and 
conceals  branch(;H  of  the  ghiteal  and  (!xt(;rna]  circumllex  vcissels  and  the  termination 
of  tlie  Huuerior  gluteal  nerve.  Tlie  sartoriiis  iimscle  is  adjacent  to  it  anteriorly  at 
27 


370 


THE  MUSCULAR  SYSTEM. 


Pyrifonuis  (insertion) 

Gluteus  niedius 
(in.spi'tiiin) 


its  origin,  and  is  separated  from  it 
below  by  the  rectus  femoris. 

The  gluteus  medius  arises 
by  fleshy  and  tendinous  fibres 
(1)  from  the  dorsum  ilii,  between 
the  iliac  crest  and  the  superior 
curved  line  above  and  the  middle 
curved  line  below  (Fig.  285, 
p.  369),  and  (2)  from  the  strong 
fascia  lata  covering  its  surface 
anteriorly.  It  is  a  fan -shaped 
muscle,  its  fibres  converging  to 
the  great  trochanter,  to  be  in- 
serted by  a  strong,  short  tendon 
into  the  postero- superior  angle 
of  the  trochanter,  and  into  a  well- 
marked  diagonal  line  on  its  outer 
surface  (Figs.  286,  p.  370,  277, 
p.  361,  and  289,  p.  371). 

The  muscle  is  covered  along 
its  anterior  border  by  the  tensor 
fasciae    femoris.     Its    surface    is 
covered   over  by  the   fascia  lata 
and   the   gluteus   maximus.     Its 
inferior  border  is  separated  from  the  pyriformis 
muscle  by  the  superficial  branch  of  the  gluteal 
artery.      Its   deep    surface    is    in    contact   with 
the    gluteus    minimus,   the    gluteal   vessels,   the 
superior  gluteal  nerve,  and  the  insertion  of  the 
pyriformis   muscle.     A   bursa  is  placed  beneath 


Obturator  internus  and 
genielli  (insertion) 

Obturator  externus 

(infteition) 

Quadratus  femoris 
(insertion) 


Ilio-psoas  (insertion) 


Gluteus  niaxinui 
(insertion) 

Adductor  magnus 
(insertion)' 


Adductor  bre\  i 
(insertion) 


(■tineusiT<insertion) 


internus  (origin) 


Fig.  286. — Muscle  -  Attachments  to 
THE  Posterior  Aspect  of  the 
Upper  Part  of  the  Femur. 


.The  tbiangle 
OF  Petit 


Fascia  lata 


Gluteus  maximus 


Adductor  ma&nuis 


Semimembranosus 


Semitendinosus 


Gieat  sciatic 
nerve 

Biceps  (long 
head) 


Fig.  287.— The  Gluteus  Maximus  Muscle. 


the  tendon  at  its  insertion. 
The  gluteus  minimus 
arises  by  fleshy  fibres  from 
the  dorsum  ilii  between 
the  middle  and  inferior 
curved  lines  (Fig.  285, 
p.  369).  This  muscle  is 
fan-shaped  and  its  fibres 
converge  to  the  antero- 
superior  angle  of  the 
great  trochanter,  to  be 
inserted  into  the  anterior 
surface  of  the  trochanter, 
and  sometimes  also  into 
the  front  part  of  the 
upper  border  (Figs.  277, 
p.  361,  and  289,  p.  371). 
It  is  also  inserted  into  the 
capsule  of  the  hip-joint. 
The  muscle  is  concealed 
by  the  tensor  fasciae 
femoris  and  gluteus 
medius.  •  The  pyriformis 
is  in  contact  with  its  in- 
ferior border,  and  beneath 
it  are  the  capsule  of  the 


THE  MUSCLES  OF  THE  BUTTOCK. 


371 


Internal  inidic  nei\e 

Nerve  to  obtiiratoi 

intern us 


Gracilis_]_ 


Adductor  magni 


Hamstring  musglfn 
(bioepb) 


Superior  gluteal  nerve 

Gloteus  medius  (cut) 
Inferior  gluteal  nerve 

\RIFORMIS 


Obturator  internus 
and  gemelli 
Obturator  externus 

quadratus  femoris 

Great  sciatic  nerve 
(and  subdivisions) 

■Small  sciatic  nerve 


Gluteus  maximus 
(insertion) 


Adductor  magnus 


hip-joint  and    the   reflected   tendon    of   the  rectus   lemoris   muscle.      A   bursa  is 
placed  beneatli  tlie  tendon  in  front  of  the  great  trochanter. 

The  pyriformis  is  one  of  the  few  muscles  connecting  the  lower  limb  to  the 
axial  skeleton.  It 
arises  (1)  within  the 
pelvis  from  the 
pedicles  of  the  second, 
third,  and  fourth 
sacral  vertebrae,  and 
from  the  adjacent 
part  of  the  bone  ex- 
ternal to  the  anterior 
sacral  foramina;  pass- 
ing outwards  through 
the  great  sacro-sciatic 
foramen,  it  receives 
an  origin  (2)  from 
the  upper  margin  of 
the  great  sciatic 
notch  of  the  ilium, 
and  (3)  from  the 
pelvic  surface  of  the 
great  sacro  -  sciatic 
ligament.  In  the 
buttock  it  forms  a 
rounded  tendon, 
which  is  inserted  into 
a  facet  on  the  upper 
border  and  inner 
aspect  of  the  great 
trochanter  of  the 
femur,  partly  sur- 
rounding the  inser- 
tion of  the  obturator  internus  (Figs.  286,  p.  370,  277,  p.  361,  and  289,  p.  371). 

The  pyriformis,  besides  appearing  in  the  buttock,  lines  the  posterior  wall  of  the 
pelvis.  In  the  pelvis  it  lies  behind  the  rectum,  covered  by  a  thin  layer  of  the 
parietal  pelvic  fascia.     In  the  buttock  it  is  covered  by  the  gluteus  maximus,  and 

at  its  insertion  by  the 

Obturator  internus  and  gemelli  (insertion)  ..rf-tfJlSSS^^S^^i.  glutCUS      mediuS,      and 

it  lies  upon  the  ilium 
and  the  capsule  of 
the  hip-joint.  At  its 
upper  border  are  the 
gluteus  medius  and 
gluteus  minimus,  sepa- 
rated by  the  superior 
gluteal  nerve  and  the 
gluteal  artery ;  its 
lower  border  is  separ- 
ated from  the  gemelli 
and  obturator  internus 
by  an  interval  in  which 
the  sciatic  and  pudic 
The  anterior  fibres  of  the 


The 


Fig.  288. — The  Muscles  and  Nerves  of  the  Buttock. 

gluteus  maximus  is  reflected  ;  and  the  gluteus  medius  is  cut  in  part  to  show 
the  a;lateus  minimus.  j      \ 


'Gluteus  minimus 
(insertion 
Pyriformis 
<insertion) 


Obturator  externus 
(insertion) 

Fig.  289. — Muscle -Attachments   to   the    Ui'per  Aspect   of  the   Great 
Trochanter  of  the  Femur. 


vessels  and  tiie  nerves  of  the  sacral  plexus  appear. 
muscle  may  be  sey)arate. 

The  obturator  internus  arises  by  fleshy  flbres  on  the  pelvic  aspect  of  the  hip 
bone,  (1)  from  the  whole  of  the  margin  of  the  thyroid  foramen  (except  tlie  obturator 
notch,  and  a  portion  posteriorly  opposite  the  small  sciatic  notch) ;  (2)  from  the 
surface  of  the  obturator  membrane ;  (3)  from  the  whole  of  the  pelvic  surface  of 


372  THE  MUSCULAE  SYSTEM. 

the  hip  bone  behind  and  above  the  thyroid  foramen ;  and  (4)  slightly  from  the 
parietal  pelvic  fascia  covering  it  internally.  It  is  a  fan-shaped  muscle,  and  its 
fibres  converging  to  the  lesser  sacro-sciatic  foramen,  give  rise  to  several  tendons 
which  hook  round  the  margin  of  the  foramen  (a  bursa  intervening),  and  after 
traversing  the  buttock,  unite  together  to  be  inserted  into  a  facet  on  the  inner 
surface  of  the  great  trochanter  of  the  femur  above  the  digital  fossa  (Tigs.  286,  p. 
370,  and  289,  p.  371). 

In  the  pelvis  the  muscle  occupies  the  lateral  wall,  covered  by  the  parietal 
(obturator)  layer  of  pelvic  fascia,  which  separates  it  from  the  pelvic  cavity  above 
and  the  ischio-rectal  fossa  below.  It  is  separated  from  tbe  contents  of  the  pelvis, 
above  by  the  peritoneum  and  extra-peritoneal  fat,  below  by  the  fat  in  the  ischio- 
rectal fossa.  Tbe  internal  pudic  vessels  and  nerve  cross  it  in  the  outer  wall  of  the 
fossa  in  a  special  sheath  of  the  fascia.  In  the  buttock  the  tendon  is  embraced  by 
the  gemelli  muscles  which  are  attached  to  its  upper  and  lower  margins.  The  tendon 
is  crossed  by  the  sciatic  vessels  and  nerves,  and  lies  against  the  upper  and  back  part 
of  the  capsule  of  the  hip-joint. 

The  gemelli  muscles  form  accessory  portions  of  the  obturator  internus.  They 
are  two  in  number,  superior  and  inferior,  and  are  wholly  composed  of  fleshy  fibres. 

The  superior  gemellus  arises  from  the  gluteal  surface  of  the  ischial  spine  and 
from  the  upper  part  of  the  margin  of  the  lesser  sciatic  notch  (Fig.  285,  p.  369). 
It  is  inserted  into  the  upper  margin  and  superficial  surface  of  the  tendon  of  the 
obturator  internus  muscle. 

The  gemellus  inferior  arises  from  the  upper  part  of  the  gluteal  surface  of  the 
ischial  tuberosity  and  the  lower  part  of  the  m.argin  of  the  lesser  sciatic  notch 
(Fig.  285,  p.  369).  It  is  inserted  into  the  lower  margin  and  superficial  aspect 
of  the  tendon  of  the  obturator  internus. 

The  quadratus  femoris  arises  from  the  outer  margin  of  the  ischial  tuberosity 
(Figs.  282,  p.  366,  and  285,  p.  369),  and  is  inserted  into  the  quadrate  tubercle 
and  quadrate  line  of  the  femur  (Fig.  286,  p.  370).  The  muscle  is  placed  beneath 
the  gluteus  maximus,  and  is  crossed  by  the  sciatic  vessels  and  nerves.  Its  origin 
is  concealed  by  the  hamstring  muscles.  Its  deep  surface  is  in  contact  with  the 
obturator  externus  muscle  and  the  small  trochanter  of  the  femur,  a  bursa  inter- 
vening. Its  upper  border  is  separated  from  the  inferior  gemellus  by  an  interval, 
containing  the  tendon  of  the  obturator  externus  and  the  ascending  branch  of  the 
internal  circumflex  artery.  Its  lower  border  is  separated  from  the  upper  margin 
of  the  adductor  magnus  by  the  internal  circumflex  vessels.  The  muscle  is  not 
infrequently  fused  with  the  adductor  magnus. 


THE  MUSCLES  ON   THE  BACK  OF  THE  THIGH. 

The  Hamstring  Muscles. 

The  muscles  comprised  in  this  series  include  the  biceps,  semitendinosus  and 
semimembranosus.  A  part  of  the  adductor  magnus,  already  described,  also  belongs 
morphologically  to  this  group. 

The  biceps  flexor  cruris  (m.  biceps  femoris)  has  a  double  origin.  (1)  Its  long 
head  arises  by  means  of  a  tendon,  in  common  with  the  semitendinosus,  from  the 
lower  and  inner  facet  upon  the  tuberosity  of  the  ischium  (Figs.  282,  p.  366,  and 
285,  p.  369)  and  from  the  great  sacro-sciatic  ligament.  This  head,  united  for  a 
distance  of  two  to  three  inches  with  the  semitendinosus,  forms  a  separate  fleshy 
mass,  which  extends  to  the  lower  third  of  the  thigh,  to  end  in  a  tendon  joined  by 
the  short  head  of  the  muscle.  (2)  The  short  head  arises  separately  by  fleshy. and 
tendinous  fibres  (1)  from  the  whole  length  of  the  outer  lip  of  the  Imea  aspera  and 
the  upper  two-thirds  of  the  external  supra-condyloid  ridge  of  the  femur,  and  (2) 
from  the  external  intermuscular  septum  for  a  corresponding  ext6nt.  The  upper 
limit  of  its  origin  is  sometimes  blended  with  the  insertion  of  the  lowest  fibres  of 
the  gluteus  maximus.  The  fibres  of  the  short  head,  directed  downwards,  join  the 
tendon  of  the  long  head,  and  the  muscle  is  inserted  (1)  into  the  head  of  the 


THE  MUSCLES  ON  THE  BACK  OF  THE  THIGH. 


m 


fibula  by  a  strong  tendon,  which  is  split  into  two  parts  by  the  long  external  lateral 
ligament  of  the  knee-joint;  (2)  by  a  slip  attached  to  the  outer  tuberosity  of  the 
tibia ;  and  (3)  along  its  posterior  border  by  a  fascial  expansion  which  connects  the 
tendon  with  the  popliteal  fascia. 

The  long  head  of  the  biceps  is  concealed  at  its  origin  by  the  gluteus  maximus 
muscle.  In  the  lower  two-thirds  of  the  thigh  it  is  superficially  jjlaced,  with  the 
semitendinosus  and  semimembranosus  on  its  inner  side.  It  conceals  the  great 
sciatic  nerve,  the  origins  of  the  semimembranosus  and  quadratus  femoris,  the 
adductor  magnus,  and  the  short  head  of  the  muscle.     The  united  heads  assist  in 


Gluteus  maximus 
(origin)' 


Obliquus  extenius  abdominis 
(insertion) 


Tensor  fasciae  femoris 
(origin) 


Sartorius  (origin) 


Rectus  femoris  (reflected  head 
of  origin) 


Gemellus  superior  (origin) 

Gemellus  inferior  (origin). 

Semimembranosus  (oriffin) 

Biceps  and  semitendinosus  (origin). 


Adductor  magnus  (origin) 


Quadratus  femoris  (origin) 
Obturator  externus  (origin) 
Adductor  magnus  (origin) 


Fig.  290. — Muscle-Attachments  to  the  Dorsum  Ilii  and  Tubee  Ischii. 

forming  the  outer  boundary  of  the  popliteal  space,  and  partially  conceal  the  outer 
head  of  the  gastrocnemius. 

The  short  head  may  be  absent :  there  may  be  an  additional  origin  from  the 
ischium  or  femur ;  and  the  long  head  may  send  a  slip  to  the  gastrocnemius  or 
tendo  Achillis  (tensor  fasciae  suralis). 

The  semitendinosus  arises,  in  common  with  the  long  head  of  the  biceps,  from 
the  lower  and  inner  facet  upon  the  ischial  tuberosity  (Fig.  285,  p.  369).  Separat- 
ing from  the  common  tendon  after  a  course  of  two  or  three  inches,  the  muscle 
forms  a  long,  narrow  band  which  becomes  tendinous  in  the  middle  third  of  the 
thigh.  Passing  over  the  inner  side  of  the  knee  it  spreads  out  and  becomes 
membranous,  and  is  inserted  (1)  into  the  inner  side  of  the  shaft  of  the  tibia  just 
below  the  internal  tuberosity,  below  the  gracilis  and  behind  the  sartorius  (Fig. 
292,  p.  374),  and  (2)  into  the  fascia  lata  of  the  leg.  A  bursa  separates  it  from 
the  sartorius  in  front,  and  another,  common  to  it  and  the  gracilis,  lies  beneath  its 
insertion. 

The  origin  of  the  muscle  is  concealed  })y  the  gluteus  maximus.  In  the  back 
of  the  thigh  it  is  superficial  to  the  semimembranosus ;  and  at  the  inner  side  of  the 
knee  the  tendon  li('s  behind  tliat  of  the  gracilis,  and  also  behind  the  sartorius.  It 
forms  one  of  the  inner  boundaries  of  the  ])0pliteal  space.  The  belly  of  the  muscle 
is  marked  by  an  oblique  septal  tendinous  intersection  about  its  middle. 
27  a 


374 


THE  MUSCULAE  SYSTEM. 


The  semimembranosus  arises  by  a  tendon  from  the  upper  and  outer  facet  on 
the  ischial  tuberosity  (Figs.  282,  p.  366,  and  2(85,  p.  369).      In  the  upper  third 

of  the  thigh  the  tendon  gives  place 
to  a  rounded  fleshy  belly,  which, 
becoming  tendinous  at  the  back  of 
the  knee,  is  inserted  mainly  into 
the  horizontal  groove  on  the  back 
of  the  inner  tuberosity  of  the 
tibia,  and  into  a  triangular  area 
below  the  hinder  end  of  the  groove, 
and  above  the  insertion  of '  the 
popliteus  (Figs.  292,  p.  374,  and 
299,  p.  383).  A  bursa  lies  beneath 
the  tendon  at  its  insertion.  It  has 
three  additional  membranous  in- 
sertions :  (1)  a  fascial  band  extends 
downwards  and  inwards  to  join  the 
posterior  border  of  the  internal 
lateral  ligament  of  the  knee-joint ; 
(2)  another  fascial  band  extends 
downwards  and  outwards,  form's 
the    fascia  covering    the  popliteus 


Gra<. 


Adductor  magnis- 


Semitendinosi  ' 


SEMIMEJIBRANOS.L  S  = 


Saktorius  TENDON- 


,PyRll'ORMIS 

Obtlrator 
'intehnus  and 

OEMELLI 

^Obturator 

"externus 

_Gluteus 
"maximus 

^(jUADRATUS 
'l  TMOKIS 

_&reat  sciatic 
nerve 


■  iDDLCTOR 

MAGNUS 


L  EPS  (long 

Wl) 


Biceps  (short 
'head) 


■  Tibial  nerve 

Biceps  tendon 
"(ilong  with 

peroneal  nerve) 
"Plantaris 


iiiiiiieinbran- 
o'iUs  (insertion) 
gamentum 
patellse  (insertion) 


•Vttaclinient  of  in- 
__teinal  lateral  ligament 
of  the  knee 
Giacilis  (insertion) 


Gastro- 

"CNEMIUS 


Seniitendinosus 
(insertion) 


Fio.  291. — Thk  Muscles  on  the  Back  of  the  Thigh. 


Fig.   292. — Muscle- Attachments  to  the  Inner 
Side  of  the  Upper  Part  of  the  Tibia. 


muscle  (popliteus  fascia),  and  is  attached  to  the  oblique  line  of  the  tibia;  and 
(3)  a  third  strong  band  extends  upwards  and  outwards  to  the  back  of  the  external 
condyle  of  the  femur,  forming  the  posterior  ligament  of  the  knee-joint. 

The  tendon  of  origin  of  the  semimembranosus  is  concealed  by  the  gluteus 
maximus,  and  immediately  beyond  the  ischium  ib  is  grooved  by  the  common  origin 
of  the  long  head  of  the  biceps  and  semitendinosus.     In  the  back  of  the  thigh  it  is 


THE  MUSCLES  ON  THE  BACK  OF  THE  THIGH. 


375 


covered  by  the  semi  ten  dinosus,  and  lies  upon  the  adductor  magnus  and  great 
sciatic  nerve.  It  forms  part  of  the  inner  boundary  of  the  popliteal  space,  and 
conceals  the  popliteal  vessels.  Its  tendon  passes  over  the  inner  head  of  the 
gastrocnemius  on  its  way  to  its  insertion. 


Nerve-Supply  of  the  Muscles  of  the  Thigh  and  Buttock. 
The  innervation  of  the  muscles  described  aljove  is  given  in  the  following  tahle  : — 


Muscles. 

Nerves. 

Origin. 

Pectineus 

. 

L.  2.  3. 

Sartorius .... 

L.  2.  3.                 ' 

Iliacus      .... 

L.  2.  3.  4. 

Psoas        .... 

L.  2.  3.  4. 

Quadriceps  extensor 

I  Anterior  crural 

L.  3.  4. 

Vastus  externus 

-L.  3.  4. 

Rectus  femoris . 

Crureus    . 

Vastus  internus 

J                                                         ^ 

Tensor  fasciae  femoris 

] 

Gluteus  minimus     . 

rSuperior  gluteal 

L.  4.  5.  S.  1. 

Gluteus  medius 

Gluteus  maximus 

Inferior  gluteal 

L.  5.  S.  1.  2. 

Biceps  (short  head)  . 

Peroneal          .... 

L.  5.  S.  1.  2. 

Pyriformis 

Sacral  plexus 

S.  1.  2. 

Adductor  longus 

-Obturator        .         .         .         -! 

L.  2.  3. 

Gracilis    . 
Adductor  brevis 

L.  2.  3.  4. 
L.  3.  4. 

Obturator  externus  . 

L.  3.  4. 

Adductor  magnus    . 

(Obturator        .... 
\  Nerve  to  hamstrings 

L.  3.  4. 

L.  4.  5.  S.  1. 

Semimembranosus  . 

-Nerve  to  hamstrings 

L.  4.  5.  S.  1. 

Semitendinosus 

L.  .5.  S.  1.  2. 

Biceps  (long  head)    . 

J                                                       i 

S.  1.  2.  3. 

Quadratus     femoris     and     inferior 

,' Sacral  plexus 

-      L.  4.  .5.  S.  1. 

gemellus 
Superior  gemellus    and   obturator 

S.  1.  2.  3. 

internus 

Action  of  the  Muscles  of  the  Thigh  and  Buttock. 

Most  of  the  alxjve  muscles  act  on  the  pelvis  and  on  the  hip-  and  knee-joints.  The  psoas 
muscle  in  additirm  assists  in  tlie  movements  of  the  vertebral  column  (p.  398). 

1.  Movements  at  the  Hip- Joint- — The  movements  of  the  thigh  at  the  hip-joint  are  flexion 
and  extension,  adduction  and  abduction,  internal  and  external  rotation.  The  following  table 
gives  the  muscles  producing  these  movements  : — 


11.  Flexion 


Extension. 


Sartorius 

Iliacus 

Psoas 

Pectus  femoris 

Pectineu.s 

Ai\(\\\i:\.()Y  longus 

Gr/icilis 

Obturator  externus 


21  h 


Gluteus  maximus 
„         medius 
„         minimus 
Bicejis 

Semitendinosus 
Seniimeml)raiiosns 
Adductor  ma'nius 


376 


THE  MUSCULAR  SYSTEM. 


b.  Adduction      and      Abduction. 

1 

Pectineus 

Tensor  fasciae  femoris  -• 

Adductor  longus 

Gluteus  medius 

„         brevis 

Gluteus  minimus 

„         inagnus 

Obturator  externus 

Gracilis 

Pyriformis 

Quadratus  femoris 

Obturator  intern  us 

Gluteus  maxim  us 

Gem  ell  i 

during 

(lower  iibi'es) 

Sartorius 
Gluteus  maximus 

flexion 

(uijper  fibres) 

c.  Internal  Rotation      ami      External  Rotation. 

Tensor  fascia;  femoris 

Obturator  externus  . 

Gluteus  medius  (anterior  fibres) 

Gluteus  maximus  (lower  fibres) 

„         minimus       „           ,, 

Quadratus  femoris 

Gluteus  medius       )  (posterior 

„        minimus   J  fibres) 

Pyriforniis                  ]  ^^^^^.. 
GemeUi'*'           ''''  /extension 

Sartorius 

Ilio-psoas 

Pectineus 

Adductor  longus 

„         brevis 

„         magnus 

Biceps  flexor  cruris 

2.  Movements  of  the  Pelvis  on  the  Thigh. — It  is  to  be  noted  that  the  several  movements 
tabulated  above  refer  to  the  movements  of  the  femur  at  the  hip-joint.  The  contraction  of  the 
same  groups  of  muscles  produces  similar  movements  of  the  pelvis  on  the  femur,  exemplified  in 
the  various  changes  in  the  attitude  of  the  pelvis  in  relation  to  the  thigh  and  the  vertebral 
column,  which  occur  in  locomotion. 

3.  Movements  at  the  Knee-Joint. — The  movements  at  the  knee-joint  are  mainly  flexion 
and  extension.  Flexion  is  much  more  powerful  than  extension.  There  is  also  a  limited  amount 
of  rotation  of  the  tibia.  The  movements  are  produced  by  certain  of  the  muscles  described  above, 
associated  with  certain  of  the  muscles  of  the  leg. 


a.  Flexion      and      Extension. 

b.  Rotation  inwards  and  Rotation  outwards. 

Sartorius 

Gracilis 

Semiteiidinosus 

Semimembranosus 

Biceps 

Gastrocnemius 

Plantaris 

Pojjliteus 

Quadriceps  extensor 

Sartorius 

Gracilis 

Semiteiidinosus 

Semimembranosus 

Popliteus 

Biceps  flexor  cruris 

THE  FASCIyE  AND  MUSCLES  OF  THE  LEG  AND  FOOT. 

FASCLE. 

The  superficial  fascia  of  the  leg  presents  no  special  features  except  iu  the 
sole,  where  it  is  greatly  thickened  by  pads  of  fat,  particularly  under  tlie  tuberosity 
of  the  OS  calcis,  and  under  the  balls  of  the  toes.  It  is  closely  adherent  to  the 
plantar  fascia,  especially  at  the  roots  of  the  toes. 

The  deep  fascia  has  numerous  important  attachments  about  the  knee. 
Posteriorly  it  forms  the  popliteal  fascia,  and  is  joined  by  expansions  from  the 
tendons  of  the  sartorius,  gracilis,  semitendinosus,  and  biceps  muscles.  In  front  of 
the  knee  it  is  attached  to  the  patella,  the  ligamentum  patellae,  and  the  tubercle  of 


•THE  FASOIrE  AND  MUSCLES  OF  THE  LEG  AND  FOOT. 


377 


Extensor  pboprius  h\lluci=;. 

Anterior  tibial  nerve  and      y^ 
dorsalis  pedi'i  arter-s  '~/~pr- 

Peroneus  TEBTIUS- 


Extensor  longus  digitorum. 


Fibula' 


Interosseous  calcaneo 
astra£;aloid  ligament 


Calcaneum 


Peroneus  brevis 


External  annular  ligament 


Peroneds  longds 


AbDDCTOB  minimi  DIGITI 

Plantar  fascia 


Anterior  annular  1 
Tibialis  anticds 


Astragalus 


the  tibia;  laterally  it  is  connected  to  the  tuberosities  of  the  tibia  ard  the  head  of 
the  fibula,  and  forms  the  lateral  patellar  ligaments,  broad  fascial  Ijands  which  pass 
obliquely  from  the  sides  of  the  patella  to  the  tuberosities  of  the  tibia,  and  arc  joined 
by  fibres  of  the  vasti  muscles.  Passing  down  the  leg,  the  fascia  blends  over  the 
inner  surface  of  the  tibia  with  the  periosteum  of  the  bone.  It  extends  round 
the  outer  side  of  the  leg  from  the  anterior  to  the  internal  border  of  the  tibia, 
binding  together  and  giving  origin  to  the  muscles,  and  gaining  an  attachment  to 
the  lower  part  of  the  shaft  of  the  fibula.  Two  septa  pass  from  its  deep  surface ; 
one  septum,  attached  to  the  anterior  border  of  the  fibula,  encloses  the  musculo- 
cutaneous nerve,  and  separates  the  extensor  from  the  peronei  muscles.  The  other 
septum  is  attached  to  the  posterior  border  of  the  fibula,  and  separates  the  peronei 
from  the  flexor  muscles.  From  the  last-named  septum  another  extends  across  the 
back  of  the  leg,  forms  a  partition  between  the  superficial  and  deep  flexor  muscles, 
and  encloses  the  posterior  tibial  vessels  and  nerves.  It  gives  rise  to  a  subordinate 
septum  attached  to  the  vertical  line  of  the  tibia  and  the  oblique  line  of  the  fibula, 
which  separate  the 
tibialis  posticus 
muscle  from  the 
flexors  of  the  toes 
on  either  side. 

At  the  ankle 
the  deep  fascia  is 
strengthened  by 
additional  trans- 
verse fibres ;  it  is 
attached  to  the 
malleoli  and  the  os 
calcis,  and  gives 
rise  to  the  annular 
ligaments. 

The  internal 
annular  ligament 
stretches  between 
the  internal  mal- 
leolus and  the 
tuberosity  of  the 
OS  calcis.  While 
it  is  continuous  at 

its  upper  border  with  the  general  investment  of  the  deep  fascia  of  the  leg,  it  is 
chiefly  formed  by  the  septal  layer  covering  the  deep  muscles  on  the  back  of  the 
leg.  It  sometimes  gives  insertion  to  the  plantaris  muscle.  It  is  continuous  below 
with  the  plantar  fascia,  and  gives  origin  to  the  abductor  hallucis  muscle.  It  is 
pierced  by  the  calcanean  vessels  and  nerve.  Along  with  the  posterior  tibial  vessels 
and  nerve,  the  tendons  of  the  tibialis  posticus,  flexor  longus  digitorum,  and  flexor 
longus  hallucis,  pass  beneath  it,  each  enclosed  in  a  separate  synovial  sheath. 

The  external  annular  ligament,  much  smaller,  is  a  thickened  band  of  the 
deep  fascia  stretching  between  the  external  malleolus  and  the  os  calcis.  It  binds 
down  the  tendons  of  the  peronei,  which  occupy  a  space  beneath  the  ligament,  lined 
by  a  single  synovial  membrane. 

The  anterior  annular  ligament  is  in  two  parts.  An  upper  band,  broad  and 
undefined  at  its  upper  and  lower  borders,  stretches  across  the  front  of  the  ankle 
between  the  two  malleoli.  This  band  binds  down  to  the  lower  end  of  the  tibia 
the  tendons  of  the  tibialis  anticus  and  extensor  muscles  of  the  toes.  One  synovial 
sheath  is  found  beneath  it,  surrounding  the  tendon  of  the  tibialis  anticus. 

On  the  dorsuni  of  tlic  i'oot,  where  the  general  covering  of  deep  fascia  is  much 
thinner,  a  s]X!(;ial  well-defined  band  stretches  over  the  extensor  tendons.  Tiiis 
lower  band  of  the  anterior  annular  ligament  (fundiform  or  lambdoid  ligament)  has 
au  attachiiient  externally  to  the  outer  border  of  the  greater  process  of  the  os  calcis. 
It  divides  into  two  bands  as  it  passes  inwiirds  over   the  dorsum  ^f  the  foot — an 


Tibialis  postigds 


Internal  annular 
ligament 

Flexor  longus 
digitorum 

Internal  plantar  artery- 
Internal  plantar  nerve 
Flexor  longus  hallucis 

\bductor  hallucis 

External  plantar  nerve 
External  plantar  artery 
Flexor  brevis  digitorum 


Fig.  293. 


ACCESSOBIUS 

-Coronal  Section  through  the  left  Ankle-.Joint,  Astragalus, 
AND  Calcaneum. 


378 


THE  MUSCULAE  SYSTEM. 


Jlii^oli     Connective  tissue  and 

;\~  fat  in  the  web  of  the 

toes 


Superficial  transverse 
metatarsal  ligament 


tipper  part,  which  joins  the  upper  ligament  and  is  attached  to  the  internal  malleolus, 
and  a  loiver  part,  which  passes  across  the  dorsum  of  the  foot,  and  jcjins  the  fascia  of 
the  sole  at  its  inner  border.  Beneath  this  ligament  are  three  special  compartments 
with  separate  synovial  sacs,  one  for  the  tibialis  anticus  tendon,  a  second  for  that 
of  the  extensor  proprius  hallucis,  and  a  third  for  the  extensor  longus  digitorum 
and  peroneus  tertius  tendons.  There  are  occasionally  other  additional  bands  of 
the  deep  fascia  passing  like  the  straps  of  a  sandal  across  the  dorsum  of  the  foot. 

The  plantar  fascia  is  of  great  importance.  In  the  centre  of  the  sole  it  forms 
a  thick  triangular  band,  attached  posteriorly  to  the  tuberosity  of  the  os  calcis.  It 
spreads  out  anteriorly  and  separates  into  five  slips,  which  are  directed  forwards  to 
the  bases  of  the  toes.  These  slips  as  they  separate  are  joined  together  by  ill-defined 
bands  of  transverse  fibres,  which  constitute  the  superficial  transverse  metatarsal 
ligament.      The  slip  for  each  toe  joins  the  tissue  of  the  web  of  the  toe  and  is 

continuous  with  the  digital 
sheath.  It  splits  to  form  a 
band  of  fibres  directed  forwards 
on  each  side  of  the  toe  to  be 
attached  to  the  sides  of  the 
metatarso-phalangeal  articula- 
tion and  the  base  of  the  first 
phalanx. 

This  central  portion  of  the 
plantar  fascia  assists  in  pre- 
serving the  arch  of  the  foot,  by 

\  Branches  of  external     drawing    the     tOCS    and     tllC     OS 

calcis  together. 

On  each  side  it  is  continuous 
with  a  much  thinner  layer 
which  covers  the  lateral  muscles 
of  the  sole,  and  joins  the  fascia 
of  the  dorsum  of  the  foot  at 
each  border.  It  also  gives  rise 
to  intermuscular  septa,  which 
pass  upwards  on  each  side  of 
the  flexor  brevis  digitorum, 
enclosing  that  muscle  in  a 
separate  sheath,  and  giving 
investments  on  either  side  to 
the  abductor  muscles  of  the 
great  and  little  toes.     At  the 

outer  border  of  the  foot  the  calcaneo-metatarsal  ligament,  a  thickened  band  of  the 

fascia,  connects  the  tuberosity  of  the  os  calcis  with  the  base  of  the  fifth  metatarsal 

bone. 

The  digital  sheaths,  though  smaller,  are  the  same  in  arrangement  as  those  of 

the  fingers.      Vaginal  ligaments  are  present  in  relation  to  the   first  and  second 

phalanges. 

THE   MUSCLES   OF   THE   LEG   AND    FOOT. 

The  muscles  of  the  leg  and  foot  are  divisible  into  three  series :  (1)  the  extensor 
muscles  on  the  front  of  the  leg  and  dorsum  of  the  foot ;  (2)  the  perouei  on  the 
outer  side  of  the  leg ;  and  (3)  the  flexor  muscles  on  the  back  of  the  leg  and  in  the 
sole  of  the  foot. 


Branches  of  internal 
plantar  nerve 


Inner  portion  of 
plantar  fascia 

Thick  central  portion 

of  plantar  fascia 

Inner  portion  of 

plantar  fascia 


(  plantar  nerve 


Outer  portion  of 
plantar  fascia 

Branches  of  external 
plantar  nerve 


Outer  portion  of  plantar 
fascia 

Calcaneo-metatarsal 
ligament 


Fig.  294. — The  Plantar  Fascia  and  Plantar  Cutaneous 
Nerves. 


The  Muscles  on  the  Front  of  the  Leg  and  Dorsum  of  the  Foot. 

The  muscles  on  the  front  of  the  leg  and  dorsum  of  the  foot  include  two  groups : 
(1)  on  the  front  of  the  leg,  the  tibialis  anticus,  long  extensors  of  the  toes  and 
peroneus  tertius ;  and  (2)  on  the  dorsum  of  the  foot,  the  extensor  brevis  digitorum. 

The  tibialis  anticus  (m.  tibialis  anterior)  arises  by  fleshy  fibres  from  the  outer 


THE  MUSCLES  OF  THE  LEG  AND  FOOT. 


579 


tuberosity  and  the  upper  two-thirds  of  the  outer  surface  of  the  shaft  of  the  tibia, 
from  the  interosseous  membrane,  from  the  fascia  over  it,  and  from  an  inter- 
muscular septum  externally.  The  muscle  ends  in  a  strong  tendon  which  passes 
over  the  dorsum  of  the  foot,  to  be  inserted  into  a  facet  on  the  anterior  and  inferior 
part  of  tlie  inner  surface  of  the  internal  cuneiform  and  the  adjacent  inner  side  of 
the  base  of  the  first  metatarsal  bone  (Fig.  295,  p.  379). 

The  muscle  is  superficially  placed  along  the  outer  side  and  front  of  the  tibia, 


Abductor  minimi  digiti 
(origin) 


Accessorius  (origin)' 

Long  and  short  plantaif 
ligaments  1 


Tibialis  posticus  (part  ot 
insertion)! 


Peroneus  brevis 
(insertion) 


Flexor  brevis  minimi 
digiti  (origin) 


Adductor  obliquus 
liallucis  (origin) 


Fle\oi  brevis  digitornm  (origin) 
Abductor  liallucis  (origin) 


Attachments  of 
inferior  calcaneo- 
navicular ligament 


Plexor  brevishallucis 
(origin) 


Tibialis  posticus  (part 
of  insertion) 


Peroneus  longus 
(insertion) 


Tibialis  anticus 
(insertion) 


Fig.  29.5. — Moscle- Attachments  to  Tarsus  and  Metatarsus  (Plantar  Aspect). 

internal  to  the  louo;  extensors  of  the  toes  and  the  anterior  tibial  vessels  and  nerve. 
Its  tendon  occupies  special  compartments  beneath  both  upper  and  lower  parts  of 
the  anterior  annular  ligament,  enclosed  in  a  separate,  single,  synovial  sac. 

Tlj(i  tibio-fascialis  anticus  is  a  separated  portion  of  the  muscle  occasionally  present,  inserted 
into  tin;  fascia  on  tliedorsuiu  of  the  foot. 

The  extensor  longus  digitorum  arises  by  fleshy  fibres  from  the  outer  side  of 
the  external  tubiMosity  of  tlic  tilua,,  from  the  upper  two-thirds  or  more  of  the 
anterior  surface  of  the  shaft  of  the  fibula,  from  the  fascia  over  it,  and  from  inter- 
muscular septa  on  either  side,  it  gives  rise  to  a  tendon  which  passes  beneath  the 
anterior  annular  ligament,  and  in  front  of  tlie  ankle  subdivides  into  four  tendons, 
inserted  into  the  four  outer  toes,  exactly  in  the  same  way  as  the  corresponding 
tendons   in   the  hand   (see  p.  347>     They    form  membranous   expansions  on  the 


380 


THE  MUSCULAR  SYSTEM. 


SOLEUS, 

EXTENSOK 
LONG  US 

digitobum 
Peroneus 

LONOUS 


dorsum  of  the  first  phalanx,  joined  hj  tlie  tendons  of  the  extensor  brevis  digitorum, 

lumbricales,  and  interossei,  wliich  separate  into  one  central  and  two  lateral  slips, 

attached  respectively  to  the  middle  and  terminal  phalanges. 

The  muscle   is   superficial,  and  is  placed  external  to  the  tibialis  anticus  and 

extensor  proprius  hallucis,  and  internal  to  the  peronei  muscles.  The  musculo- 
cutaneous nerve  is  on  its  outer  side.  It  con- 
ceals the  anterior  tibial  vessels  and  nerve. 
The  tendon  occupies  a  separate  compartment 
along  with  the  peroneus  tertius  Ijcneath  the 
lower  part  of  the  anterior  annular  ligament, 
invested  by  a  special  synovial  membrane. 

The  peroneus  tertius  is  a  separated 
portion  of  the  extensor  longus  digitorum. 
It  is  an  essentially  human  muscle.  It  arises 
(inseparably  from  the  extensor  longus  digi- 
torum) from  the  lower  part  of  the  anterior 
surface  of  the  fibula,  from  the  interosseous 
membrane,  and  from  the  intermuscular  septum 
external  to  it.  The  tendon  of  the  muscle  is 
inserted  into  the  dorsal  aspect  of  the  base  of 
the  fifth  metatarsal  bone.  It  accompanies 
the  extensor  longus  digitorum  beneath  the 
anterior  annular  ligament,  and  lies  external 
to  the  tendons  of  that  muscle  on  the  dorsum 
of  the  foot. 

The  extensor  proprius  hallucis  muscle 
(m.  extensor  hallucis  longus)  arises  by  fleshy 
fibres  from  the  front  of  the  fibula  in  its 
middle  three-fifths,  internal  to  the  origin  of 
the  extensor  longus  digitorum,  and  for  a 
corresponding  extent  from  the  interosseous 
membrane.  Its  tendon  passes  over  the  dorsum 
of  the  foot,  to  be  inserted  into  the  base  of 
the  terminal  phalanx  of  the  great  toe.  In 
the  leg  the  muscle  is  deeply  placed  between 
the  tibialis  anticus  and  extensor  longus  digi- 
torum. It  conceals  the  anterior  tibial  vessels 
and  nerve,  and  crosses  the  termination  of  the 
anterior  tibial  artery  in  front  of  the  ankle- 
joint.  It  is  invested  by  a  special  synovial 
sac  as  it  lies  beneath  the  lower  part  of  the 
anterior  annular  ligament.  On  the  dorsum  of 
the  foot  the  tendon  is  placed  on  the  inner  side 
of  the  dorsalis  pedis  artery. 

The  extensor  longus  primi  internodii  and 
extensor  ossis  metatarsi  hallucis  are  occasional 
separate  slij^s  of  tliis  muscle  inserted  into  the  bones 
of  the  great  toe. 

The  extensor  brevis  digitorum  arises  on 

the  dorsum   of  the  foot   by  short    tendinous 
Fm.  296. -Muscles  OF  the  Front  of  the  :^  ggg|      g^^-^^^g  ^^,^^^   ^  special  impression  on 

Right  Leg  and  Dorsum  of  the  Foot.  .  -^        ,,  p  ,  i  .  j?  4.1 

the  upper  surface  of  the  greater  process  of  the 

OS  calcis,  and  from  the  deep  surface  of  the  lower  band  of  the  anterior  annular 
ligament. 

It  usually  gives  rise  to  four  fleshy  bellies,  from  which  narrow  tendons  are 
directed  forwards  and  inwards,  to  be  inserted  into  the  four  inner  toes.  The  three 
outer  tendons  join  those  of  the  long  extensor  muscle  to  form  the  membranous 
expansions  on  the  dorsum  of  the  toes.  The  innermost  tendon  is  inserted  separately 
into  the  base  of  the  first  phalanx  of  the  great  toe. 


Perokeus  brevis 


Lower  portion  of 

anterior  annular 

ligament 

Tendon  of  peroneus 

-    TERTIUS  —f. 

Innermost  slip  01  A 
extensor  bre\  is  /'// 
digitorum 


THE  MUSCLES  ON  THE  FEONT  OF  THE  LEG  AND  FOOT. 


581 


Abductor  obi,iquus  hallucis 


The  muscle  is  covered  by  the  lower  band  of  the  anterior  annular  ligament,  and 
by  the  tendons  of  the  extensor  longus  digitorum  and  peroneus  tertius ;  the  slip 
of  the  muscle  passing  to  the  great  toe  crosses  over  the  dorsalis  pedis  artery. 

The  Muscles  on  the  Outer  Side  of  the  Leg. 

The  muscles  on  the  outer  side  of  the  leg  comprise  the  peronei — longus 
and  brevis. 

The  peroneus  longus  arises  by  fleshy  fibres  from  the  head  and  the  upper 
two-thirds  of  the  outer  surface  of  the  shaft  of  the  fibula,  from  intermuscular  septa 
on  either  side,  and  from  the  fascia  over  it.  It  forms  a  stout  tendon,  which  hooks 
round  the  external  malleolus,  crosses  the  outer  side  of  the  os  calcis,  and  passing 
through  the  groove  on  the  cuboid  bone,  is  directed  across  the  sole  of  the  foot  to  be 
inserted  into  the  outer  sides  of  the  internal  cuneiform  and  the  base  of  the  first  meta- 
tarsal bones  (Fig.  295,  p.  379).  The  muscle  is  placed  superficially  in  the  leg,  and 
is  separated  by  intermuscular  septa  from  the 
extensor  longus  digitorum  and  peroneus  brevis 
in  front,  and  the  soleus  and  flexor  longus 
hallucis  behind.  It  partially  conceals  the 
peroneus  brevis,  along  with  which  it  passes 
beneath  the  external  annular  ligament,  in- 
vested by  a  common  synovial  sheath.  As  it 
enters  the  sole  of  the  foot  a  fibro-cartilage 
is  formed  in  the  tendon,  which  plays  over  a 
smooth  tubercle  on  the  cuboid  bone,  a  bursa 
intervening.  In  its  passage  across  the  foot 
the  tendon  is  enclosed  in  a  fibrous  sheath 
derived  from  the  inferior  calcaneo-cuboid 
ligaments  and  the  tibialis  posticus  tendon, 
and  is  concealed  by  the  first  three  layers  of 
the  muscles  of  the  sole. 

The  peroneus  brevis  arises  by  fleshy  fibres 
from  the  lower  two-thirds  of  the  outer  surface 
of  the  shaft  of  the  fibula,  and  from  an  inter- 
muscular septum  along  its  anterior  border. 
Its  tendon  passes  over  the  back  of  the  ex- 
ternal malleolus  and  the  outer  side  of  the  os 
calcis,  to  be  inserted  into  the  tubercle  and 
dorsal  surface  of  the  base  of  the  fifth  meta- 
tarsal bone.  In  the  leg  the  peroneus  brevis 
lies  behind  the  extensor  longus  digitorum  and 

peroneus  tertius,  and  in  front  of  the  peroneus  longus,  which  partially  overlaps  it. 
The  tendon  lies  directly  behind  the  external  malleolus  beneath  the  external  annular 
ligament,  invested  by  a  synovial  sheath  common  to  it  and  the  peroneus  longus. 

The  peroneus  longus  and  brevis  may  be  fused  together,  or  additional  slips  may  be  present,  as 
peroneus  accessorius,  peroneus  quinti  digiti,  peroneo-calcaneus  externus,  and  peroneo-cuboideus. 


Insertion  of 
peroneds 

LONGUS 


Insertion  of 

tibialis 

posticus 

Flexor  longus 
digitorum 

Flexor  longus 
hallucis 


Fig.  297. — The  Insertions  of  the  Peroneus 
Longus  and  Tibialis  Posticus  Muscles 
IN  THE  Sole  of  the  Right  Foot. 


The  Muscles  on  the  Back  of  the  Leg. 

The  muscles  on  the  back  of  the  leg  are  divisible  into  two  layers :  (1)  a 
superficial  set,  consisting  of  the  gastrocnemius  and  soleus  (the  so-called  triceps 
muscle  of  the  leg),  and  the  plantaris  ;  and  (2)  a  deep  set,  consisting  of  the  popliteus, 
flexor  longus  digitorum,  tibialis  posticus,  and  flexor  longus  hallucis. 

The  gastrocnemius  arises  by  htu)  Ihejtds,  inner  and  outer,  by  means  of  strong 
tendons  which  are  prolonged  over  the  surface  of  the  muscle.  The  outer  head  arises 
from  an  impression  on  the  upper  and  ])osterior  part  of  the  outer  surface  of  the 
external  condyle,  and  from  the  lower  end  of  the  external  supra-condyloid  ridge  ; 
while  the  inner  head  arises  from  a  y)romineut  rough  mark  on  the  popliteal  space  of 
the  femur  above  the  internal  condyle  and  from  the  surface  between  that  and  the 


382 


THE  MUSCULAE  SYSTEM. 


Semimembranosus 
TENDON  (cut)' 


Tibial  nerve  und 
popliteal  vessels 


Plantaris  tendon 
(cut) 


adductor  tubercle.  Each  head  has  an  additional  origin  from  the  back  of  the 
capsule  of  the  knee-joint.  A  bursa  lies  beneath  each  tendon  of  origin.  Each  fleshy 
belly  of  the  muscle  is  inserted  into  a  broad  membranous  tendon,  prolonged  upwards 
on  its  deep  surface  for  some  distance.     The  inner  head  is  the  larger. 

The  tendo  Achillis  is  formed  by  the  union  of  the  two  membranous  insertions 
of  the  bellies  of  the  gastrocnemius.  Prolonged  upwards  beneath  the  separate 
bellies,  the  tendon  forms  a  broad  membranous  band  connecting  together  the  lower 

parts  of  the  two  bellies.  Narrowing 
gradually,  and  becoming  thicker  in 
the  lower  half  of  the  leg,  the  tendon 
is  finally  inserted  into  the  intermediate 
surface  on  the  posterior  aspect  of  the 
OS  calcis.  A  bursa  lies  beneath  the 
tendon  at  its  insertion.  The  tendo 
Achillis  also  affords  insertion  to  the 
soleus  and  (sometimes)  the  plantaris 
muscles. 

The  gastrocnemius  is  superficial 
except  at  its  origin.  The  inner  head 
is  concealed  by  the  semitendinosus 
and  semimembranosus  muscles,  and 
partially  covers  the  popliteal  vessels 
and  the  tibial  nerve  in  the  lower  part 
of  their  course.  It  forms  part  of  the 
inner  boundary  of  the  popliteal  space. 
The  outer  head  is  concealed  partially 
by  the  biceps  tendon  and  the  peroneal 
nerve,  and  covers  the  plantaris  muscle, 
the  popliteal  vessels,  and  the  tibial 
nerve.  It  forms  part  of  the  outer 
boundary  of  the  popliteal  space.  The 
two  bellies  are  for  the  most  part  in 
close  contact,  the  external  saphenous 
vein  occupying  the  interval  between 
them.  The  tendo  Achillis  in  the 
lower  half  of  the  leg  partially  conceals 
the  soleus  and  the  deeper  muscles. 
The  plantaris  tendon  lies  along  its 
inner  border. 

The  plantaris  arises  by  fleshy 
fibres  from  the  external  supra -con- 
dyloid ridge  of  the  femur  for  about  an 
inch  at  its  lower  end,  from  the  adjacent 
part  of  the  popliteal  space  of  the  femur, 
and  from  the  posterior  ligament  of  the 
knee-joint.  It  forms  a  narrow  fleshy 
slip  which  ends  in  a  tendon  extending 
down  the  back  of  the  leg,  to  be  inserted 
into  the  inner  side  of  the  tuberosity 
of  the  OS  calcis,  or  the  tendo  Achillis, 
or  the  internal  annular  ligament.  The  tendon  of  the  muscle  is  capable  of  con- 
siderable lateral  extension.  The  plantaris  lies  between  the  outer  head  of  the 
gastrocnemius  and  the  soleus,  and  crosses  the  pophteal  vessels  and  the  tibial 
nerve.  In  the  lower  half  of  the  leg  its  tendon  lies  along  the  inner  border  of  the 
tendo  Achillis.     The  muscle  is  not  always  present. 

The  soleus  has  a  triple  origin  by  means  of  short  tendinous  and  fleshy  fibres : 
(1)  from  the  posterior  surface  of  the  head  and  the  shaft  of  the  fibula  in  its  upper 
third ;  (2)  from  a  fibrous  arch  stretching  over  the  popliteal  vessels  and  tibial  nerve 
between  the  tibia  and  fibula ;  and  (3)  from  the  oblique  line  and  middle  third  of 


Tendo  Achillis 


Internal  annular 
ligament- 


FiG.  2£ 


Peroneus  longus 


External  annular 
igaiuent 


-The  Soleus  Muscle 


THE  MUSCLES  ON  THE  BACK  OF  THE  LEG. 


the  inner  border  of  the  tibia  (Fig.  299,  i).  383).  Fvom  this  origin  the  upper 
muscular  fibres  are  directed  downwards  to  join  a  tendon  placed  on  the  superficial 
aspect  of  the  muscle,  which  is  inserted  into  the  tendo  Achillis ;  the  lower  fibres 
are  inserted  directly  into  the  tendo  Achillis  to  within  one  or  two  inches  of  the  os 

calcis. 

The  muscle  is  concealed  by  the  gastro- 
cnemius, plantaris,  and  tendo  Achillis  in 
nearly  its  whole  extent.  It  is  partially 
superficial  on  each  side  of  the  gastrocnemius 

Semimembranosus 
(insertion) 


Popliteus/ 
(insertion) 


Soleus  (origin )- 


jH  Tibialis  posticus 
(origin) 


Flexor  longus 


I     digitorum  (origin) 


Fig.  299. — Mcscle- Attachments  to  the 
PosTEKioii  Surface  of  the  Tibia. 


iSEMIMEMBEANOST/S 
TENDON  (cut) 


Popliteus  fascia 
(cut) 

Popliteus  muscle 


ObIQINS  OF  SOLEUS 


Flexor  lonous 

DIf  ITORUM 

Tibialis  posticus 

FlEXOPv  LONGUS 
HALLUCIS 


Posterior  tibial 
artery  and  nerve 


Fio.  300. — The  Deep  Muscles  on  the  Back  of 
the  Left  Leg. 


and  tendo  Achillis.     The  muscle  covers  the  tibialis  posticus  and  the  flexor  muscles 
of  the  toes  as  well  as  the  posterior  tibial  vessels  and  nerve. 

The  deep  muscles  of  the  back  of  the  leg  comprise  the  popliteus,  the  long  flexors 
of  the  toes,  and  the  tibialis  posticus. 

The  popliteus  is  deeply  placed  behind  the  knee.  It  arises  by  a  stout  tendon 
from  a  rough  impression  in  front  of  a  groove  on  the  outer  aspect  of  the  external 


384 


THE  MUSCULAE  SYSTEM. 


condyle  of  the  femur.  This  tendon  passes  between  the  external  semilunar  cartilage 
and  the  capsule  of  the  knee-joint,  and  pierces  the  posterior  ligament,  from  which 
it  takes  an  additional  fleshy  origin.  A  bursa  is  placed  beneath  the  tendon,  which 
communicates  usually  with  the  synovial  cavity  of  the  knee-joint.  The  muscle  is 
inserted  by  fleshy  fibres  (1)  into  a  triangular  surface  on  the  back  of  the  tibia  above 
the  oblique  line  (except  a  small  area  below  the  fibular  facet)  (Fig.  299,  p.  383),  and 
(2)  into  the  fascia  over  it  (the  popliteus  fascia,  derived  from  the  tendon  of  the  semi- 
membranosus muscle).  The  popliteus  is  covered  at  its  origin  by  the  capsule  of  the 
knee-joint.  Posteriorly  it  is  concealed  by  the  gastrocnemius  and  plantaris  muscles, 
and  by  the  popliteal  vessels  and  the  tibial  nerve.  Its  lower  border  corresponds  to 
the  point  of  bifurcation  of  the  popliteal  artery  and  the  origin  of  the  soieus  muscle. 
The  popliteus  minor  is  a  small  occasional  muscle  attached  to  the  2:)opliteal  space  of  the  femur 
and  the  jjosterior  ligament  of  the  knee-joint. 

The  flexor  longus  digitorum  occupies  both  the  back  of  the  leg  and  the  sole  of 
the  foot.  Its  origin  is  by  fleshy  fibres  from  the  posterior  surface  of  the  shaft  of  the 
tibia  in  its  middle  three-fifths,  below  the  oblique  line,  and  internal  to  the  vertical 

line  and  the  origin  of  the  tibialis 
posticus,  from  the  fascia  over  it, 
and  from  an  intermuscular  septum 
on  each  side  (Fig.  299,  p.  383). 
Its  tendon,  after  passing  beneath 
the  internal  annular  ligament, 
enters  the  sole  of  the  foot,  and 
divides  into  four  subordinate  ten- 
dons, which  are  inserted  into  the 
four  outer  toes  in  precisely  the 
same  manner  as  the  flexor  pro- 
fundus digitorum  is  inserted  in 
the  hand.  Each  tendon  enters 
the  digital  sheath  of  the  toe,  per- 
forates the  tendon  of  the  flexor 
lore  vis  digitorum,  and  is  inserted 
into  the  base  of  the  terminal 
phalanx.  Ligamenta  accessoria 
(longa  and  brevia)  are  present  as 
in  the  hand.  Associated  with 
this  muscle  in  the  sole  of  the  foot 
are  the  lumbricales  and  acces- 
sorius  muscles. 

The  lumbricales  are  four  small 
muscles  arising  in  association  with 
the  tendons  of  the  flexor  profundus 
digitorum  in  the  sole.  The  first 
muscle  arises  by  a  single  origin  from 
the  tibial  side  of  the  tendon  of 
the  flexor  longus  digitorum  for 
the  second  toe ;  the  other  three 
arise  by  two  heads  from  the 
adjacent  sides  of  all  four  tendons. 
Each  muscle  is  inserted  into  the 


Lumbricales 


Flexor 
brevis  minimi  — 

DIGITI 


ACCESSORIl  S 


Abductor  minimi 

DIGIH 


Fig.  301. — The  Muscles  of  the  Right  Foot  (after 
removal  of  the  first  layer). 


dorsal  expansion  of  the  extensor  tendon,  the  metatarso-phalangeal  capsule,  and 
the  base  of  the  first  phalanx,  precisely  as  in  the  case  of  the  lumbrical  muscles 
of  the  hand.  Each  muscle  passes  forwards  on  the  tibial  side  of  the  corresponding 
toe,  superficial  to  the  transverse  metatarsal  ligament. 

The  flexor  accessorius  muscle  (m.  quadratus  plantse)  arises  by  two  heads :  (1) 
the  outer  tendinous  head  springs  from  the  outer  border  of  the  inferior  surface  of 
the  OS  calcis  and  from  the  outer  border  of  the  long  plantar  ligament ;  (2)  the  inner 
head,  which  is  fleshy,  arises  from  the  concave  inner  surface  of  the  os  calcis  in  its 
whole  extent,  and  from  the  inner  border  of  the  long  plantar  ligament  (Fig.  295, 


THE  MUSCLES  IN  THE  SOLE  OF  THE  FOOT.  385 

p.  379).  The  long  plantar  ligament  separates  the  two  origins.  The  two  heads 
unite  to  form  a  flattened  band,  whicli  is  inserted  into  the  upper  aspect  of  the 
tendons  of  the  flexor  longus  digitorum,  and  usually  into  those  destmed  for  the 
second,  third,  and  fourth  toes. 

In  the  leg  the  flexor  longus  digitorum  lies  at  first  internal  to  the  tibialis 
posticus,  and  is  partially  concealed  by  the  soleus  and  tendo  Achillis.  Its  tendon 
crosses  over  the  tibialis  posticus  above  the  ankle-joint,  passes  beneath  the  internal 
annular  ligament,  invested  by  a  special  synovial  sheath,  and  below  the  ligament 
crosses  the  plantar  or  superficial  surface  of  the  tendon  of  the  flexor  longus  hallucis. 
As  it  passes  over  this  tendon  it  receives  from  it  a  special  band  of  fibres,  usually 
associated  with  the  tendons  for  the  second  and  third  toes. 

In  the  sole  of  the  foot  the  tendons  of  the  flexor  longus  digitorum,  along  with  the 
lumbricales  and  accessorius,  and  the  flexor  longus  hallucis  muscles,  constitute  the 
second  layer  of  muscles  of  the  sole.  They  are  placed  between  the  abductors  of  the 
great  and  little  toes  and  the  flexor  brevis  digitorum  on  the  one  hand,  and  the  flexor 
brevis  and  adductors  of  the  great  toe  on  the  other. 

The  flexor  longus  hallucis  arises  by  fleshy  fibres  on  the  back  of  the  leg  from 
the  lower  two-thirds  of  the  posterior  surface  of  the  shaft  of  the  fibula,  from  the 
fascia  over  it,  and  from  intermuscular  septa  on  either  side.  Its  tendon  passes 
beneath  the  internal  annular  ligament  enclosed  in  a  special  synovial  sheath,  and 
after  grooving  the  back  of  the  lower  end  of  the  tibia,  the  astragalus,  and  the  under 
surface  of  the  sustentaculum  tali  of  the  os  calcis,  it  is  directed  forwards  in  the 
sole  of  the  foot,  to  be  inserted  into  the  base  of  the  terminal  phalanx  of  the  great  toe. 

The  muscle  is  partially  concealed  in  the  leg  by  the  soleus  and  tendo  Achillis. 
It  lies  at  its  origin  between  the  tibialis  posticus  and  the  peronei  muscles,  separated 
from  the  former  by  the  peroneal  artery.  In  the  foot,  concealed  by  the  abductor 
hallucis,  it  crosses  over  the  deep  aspect  of  the  tendon  of  the  flexor  longus  digitorum, 
to  which  it  is  connected  by  a  strong  fibrous  band  destined  for  the  tendons  for  the 
second  and  third  toes.  At  the  root  of  the  great  toe  the  tendon  occupies  the 
interval  between  the  insertions  of  the  flexor  brevis  hallucis. 

The  tibialis  posticus  muscle  (m.  tibialis  posterior)  has  a  fourfold  fleshy  origin 
in  the  leg.  It  arises  (1)  from  the  upper  four  -  fifths  of  the  shaft  of  the  fibula 
between  the  oblique  line  and  the  interosseous  border ;  (2)  from  the  lower  part  of 
the  outer  tuberosity  of  the  tibia  and  from  the  upper  two-thirds  of  the  shaft  of  the 
bone  below  the  oblique  line  and  between  the  vertical  line  and  the  interosseous 
border  (Fig.  299,  p.  383) ;  (3)  from  the  interosseous  membrane ;  and  (4)  from  the 
fascia  over  it  and  the  septa  on  either  side.  The  muscle  gives  rise  to  a  strong 
tendon  which  passes  beneath  the  internal  annular  ligament,  invested  by  a  special 
synovial  sheath,  and  grooves  the  back  of  the  internal  malleolus,  on  its  way  to  the 
inner  border  of  the  foot.  The  tendon  then  spreads  out  and  is  inserted  by  three 
bands  into  (1)  the  tubercle  of  the  navicular  bone  and  the  plantar  surfaces  of  the 
internal  and  middle  cuneiform  bones,  (2)  the  plantar  aspects  of  the  second, 
third,  fourth,  and  sometimes  the  fifth  metatarsal  bones,  the  middle  and  external 
cuneiform  bones,  and  the  groove  on  the  cuboid,  and  (3)  by  a  recurrent  slip 
into  the  inner  border  of  the  sustentaculum  tali  of  the  os  calcis  from  which  a 
fibrous  expansion  passes  outwards  to  join  the  inner  border  of  the  short  plantar 
ligament  (Fig.  302,  p.  386). 

In  the  leg  the  tibialis  posticus  is  concealed,  as  it  lies  on  the  interosseous  mem- 
brane between  the  tibia  and  fibula,  by  the  superficial  muscles  and  the  posterior 
tibial  vessels  and  nerve.  It  lies  between  the  flexor  longus  hallucis  and  flexor 
longus  digitorum,  and  is  crossed  by  the  tendon  of  the  latter  muscle  just  above  the 
ankle.  Just  below  the  knee  between  its  tibial  and  fibular  origins  is  an  anyular 
sjjace  through  which  the  anterior  tibial  vessels  pass.  In  the  foot  its  tendon  is 
covered  by  the  long  flexor  tendons  and  by  the  short  flexor  muscles  of  the  great  toe. 
The  tendon  is  in  contact  with  the  inferior  calcaneo-navicular  ligament  in  the 
interval  between  the  sustentaculum  tali  and  the  navicular  bone. 

The  peroneo-calcaneus  uui.sclc,  wlicu  iiresciiL,  arises  from  the  iibula,  and  i.s  inserted  hito  the 
08  calciH. 

28 


386 


THE  MUSCULAE  SYSTEM. 


The  Muscles  ix  the  Sole  of  the  Foot. 

The  muscles  in  the  sole  of  the  foot  are  divisiljle  into  four  layers  placed  beneath 
the  plantar  fascia. 

First  layer :  Abductor  hallucis,  flexor  brevis  digitorum,  abductor  minimi  digiti. 

Second  layer :  Lumbricales  and  accessorius,  together  with  the  tendons  of  the 
flexor  longus  hallucis  and  flexor  longus  digitorum. 


Abductor  niiuimi  digiti 
(origin) 


Accessorius  (origin) 

Long  and  short  plantar  f 
ligaments  I 


Tibialis  posticus  (part  of^ 
insertion)' 


Peroneus  brevis 
(insertion)' 

Flexor  brevis  minimi 
digiti  (origin)' 


Adductor  obliquus 
hallucis  (origin) 


Flexor  brevis  digitornm  (origin) 
Abductoi  hallucis  (origin) 


Attachments  of 
inferior  calcaneo- 
navicular ligament 


Flexor  brevis  hallu  cis 
(origin) 


Tibialis  posticus  (part 
of  insertion) 

Peroneus  longus 
(insertion) 


Tibialis  anticus 
(insertion) 


Fig.  302. — Muscle- Attachments  to  Tarsus  and  Metatarsus  (Plantar  Aspect). 


Third  layer :  Flexor  brevis  hallucis,  adductors  of  the  great  toe,  and  flexor  brevis 
minimi  digiti. 

Fourth  layer :  Interossei  (plantar  and  dorsal). 

The  abductor  hallucis  has  a  double  origin,  (1)  by  a  short  tendon  from  the  inner 
side  of  the  greater  tubercle  on  the  tuberosity  of  the  os  calcis  (Fig.  302,  p.  386), 
and  (2)  by  fleshy  fibres  from  the  internal  annular  ligament,  the  plantar  fascia 
which  covers  it,  and  the  intermuscular  septum  between  it  and  the  flexor  brevis 
digitorum.  Lying  superficially  along  the  inner  border  of  the  sole,  its  tendon  is 
inserted,  along  with  part  of  the  flexor  brevis  hallucis,  into  the  inner  side  of  the 
posterior  end  of  the  first  phalanx  of  the  great  toe.  The  muscle  lies  beneath  the 
plantar  fascia,  internal  to  the  flexor  brevis  digitorum,  and  conceals  the  plantar 
vessels  and  nerves,  and  near  its  origin  the  long  flexor  tendons. 

The  flexor  brevis  digitorum  has  likewise  a  double  origin :   (1)  by  a  short 


THE  MUSCLES  IN  THE  SOLE  OF  THE  FOOT. 


387 


tendon  from  the  fore-part  of  the  greater 
tubercle  of  the  tuberosity  of  the  os  calcis 
(Fig.  302,  p.  386),  and  (2)  by  fleshy 
fibres  from  the  thick  central  part  of  the 
plantar  fascia  which  covers  it,  and  from 
the  intermuscular  septa  on  either  side. 
Passing  forwards,  it  gives  rise  to  four 
slender  tendons,  which  are  inserted  into 
the  second  phalanges  of  the  four  outer  toes, 
after  having  been  perforated,  just  as  in  the 
case  of  the  tendons  of  the  flexor  sublimis 
digitorum  of  the  hand,  by  the  long  flexor 
tendons.  Placed  in  the  centre  of  the  sole 
beneath  the  plantar  fascia,  and  between 
the  abductor  hallucis  and  abductor  minimi 
digiti  mviscles,  the  muscle  conceals  the 
second  layer  of  muscles  and  the  external 
plantar  vessels  and  nerve. 

The  abductor  minimi  digiti  (m.  ab- 
ductor digiti  quinti)  has  also  a  double 
origin :  (1)  by  fleshy  and  tendinous  fibres 
from  the  fore-part  of  both  tubercles  on 
the  tuberosity  of  the  os  calcis,  partly 
concealed  by  the  flexor  brevis  digitorum 
(Fig.  302,  p.  386),  and  (2)  by  fleshy  fibres 
from    the    outer   portion    of    the    plantar 


Adductor 

TEAl^SVERSUS. 


Inteeossei. 

Flexor 

bkevis  minimi. 

DIGITI 


Abductor 

MINIMI 
DIGITI 


Fig. 


303. — The  Muscles  of  the  Right  Foot 
(after  removal  of  the  plantar  fascia). 


Adductor  obliquus 
hallucis 


ACCESSORIUS 


Fio. 


304. — The  Muscles  of  tiiij   I^ioht  Foot  (after  removal  of  the 
second  layer). 


fascia  and  the  calcaneo- metatarsal  -liga- 
ment, and  from  the  intermuscular  septum 
between  it  and  the  flexor  brevis  digitorum. 
Its  tendon  lies  along  the  fifth  metatarsal 
bone,  and  is  inserted  by  a  tendon  into  the  outer 
side  of  the  posterior  end  of 
the  first  phalanx  of  the  little 
toe.  The  outermost  fibres 
usually  obtain  an  additional 
insertion  into  the  outer  side 
of  the  plantar  surface  of  the 
fifth  metatarsal  bone.  It  lies 
on  the  outer  side  of  the  flexor 
brevis  digitorum,  and  parti- 
ally conceals  the  flexor  brevis 
minimi  digiti. 

The  tendons  of  the  long 
flexors  of  the  toes,  the  lumbri- 
cales  and  accessorius  muscles, 
constituting  the  second  layer 
of  muscles,  have  already  been 
(l(!.scril)ed.  Lying  Ijeneath 
the  abductor  hallucis  and  the 
Hexor  brevis  digitorum,  and 
separated  from  them  by  the 


LL  L  Flexor  brevis  hallucis 


Tibialis  posticus 

Pi  exor  longus  hallucis 

Flexor  longus  dioitorui 


388 


THE  MUSCULAE  SYSTEM. 


plantar  vessels  and  ner^'es,  they  occupy  the  hollow  of  the  tarsus  and  the  space 
between  the  first  and  fifth  metatarsal  bones;  their  deep  surfaces  are  in  contact 
with  the  adductors  of  the  great  toe  and  the  interossei  muscles. 

The  flexor  brevis  hallucis  arises  by  tendinous  fibres  (1)  from  the  inner  part  of 
the  under  surface  of  the  cuboid  bone  (Fig.  302,  p.  386),  and  (2)  from  the  tendon 
of  the  tibiahs  posticus.  Directed  forwards  over  the  first  metatarsal  bone,  the 
muscle  separates  into  two  parts,  between  which  is  the  tendon  of  the  flexor  longus 
hallucis.  Each  portion  gives  rise  to  a  tendon  which  is  inserted  into  the  corre- 
sponding side  of  the  base  of  the  first  phalanx  of  the  great  toe ;  in  each  tendon, 
under  the  metatarso-phalangeal  articulation,  a  sesamoid  bone  is  developed.  The 
inner  tendon  is  united  with  the  insertion  of  the  abductor,  the  outer  tendon  with 
the  insertions  of  the  adductor  muscles  of  the  great  toe. 

The  adductor obliquus  hallucis  arises  by fleshyandshort  tendinous  fibres  (1)  from 
the  sheath  of  the  peroneus  longus,  and  (2)  from  the  plantar  surfaces  of  the  posterior 
extremities  of  the  second,  third,  and  fourth  metatarsal  bones  (Fig.  302,  p.  386). 
Occupying  the  hollow  of  the  foot,  on  a  deeper  plane  than  the  long  flexor  tendons 
and  lumbricales,  and  separated  from  the  interossei  by  the  plantar  arch,  it  is  placed 

on  the  outer  side  of  the 
flexor  brevis  hallucis,  and 
is  directed  obliquely  in- 
wards and  forwards,  to 
be  inserted  on  the  outer 
side  of  the  base  of  the 
first  phalanx  of  the  great 
toe  between  and  along 
with  the  flexor  brevis  and 
adductor  transversus 
hallucis.  The  muscle 
forms  one  side  of  a  tri- 
angular space  in  the  sole 
through  which  the  ex- ' 
ternal  plantar  vessels 
and  nerve  pass. 

The  adductor  trans- 
versus hallucis  arises 
from  (1)  the  capsules  of 
the  outer  four  metatarso- 
phalangeal articulations 
and  (2)  the  transverse 
metatarsal  hgament.  Directed  transversely  inwards,  under  cover  of  the  flexor 
tendons  and  lumbricales,  the  muscle  is  inserted,  along  with  the  adductor 
obliquus  (from  which  it  is  separated  by  an  angular  interval),  into  the  outer 
side  of  the  base  of  the  first  phalanx  of  the  great  toe. 

The  flexor  brevis  minimi  digiti  (m.  flexor  brevis  digiti  quinti)  arises 
from  (1)  the  sheath  of  the  peroneus  longus,  and  (2)  the  base  of  the  fifth 
metatarsal  bone  (Fig.  302,  p.  386).  Partially  concealed  by  the  abductor  minimi 
digiti,  the  muscle  passes  along  the  fifth  metatarsal  bone,  to  be  inserted,  in  common 
with  that  muscle,  into  the  outer  side  of  the  base  of  the  first  phalanx  of  the  little  toe. 
The  interossei  muscles  of  the  foot  resemble  those  of  the  hand  except  in  one 
respect.  In  the  hand  the  line  of  action  of  the  muscles  is  the  middle  line  of  the 
middle  finger.  In  the  foot  the  second  toe  is  the  digit  round  which  the  muscles  are 
grouped,  and  their  attachments  and  their  actions  differ  accordingly. 

There  are  four  dorsal  and  three  plantar  muscles,  which  occupy  together  the  four 
interosseous  spaces,  and  project  into  the  hollow  of  the  foot. 

The  four  dorsal  muscles,  one  in  each  interosseous  space,  arise  by  two  heads  each 
from  the  shafts  of  the  metatarsal  bones.  Each  gives  rise  to  a  tendon,  which,  after 
passing  dorsal  to  the  transverse  metatarsal  ligament,  is  inserted  on  the  dorsum  of  the 
foot  into  the  side  of  the  first  phalanx,  the  metatarso-phalangeal  capsule,  and  the 
dorsal  expansion  of  the  extensor  tendon.     The  first  and  second  muscles  are  inserted 


305. — Interosseous  Muscles  of  the  Foot. 
A,  Dorsal  muscles  (plantar  aspect)  ;  B,  Plantar  muscles  of  the  right  foot. 


THE  MUSCLP:S  in  ^JlIE  SOLE  OF  THE  FOOT. 


389 


into  the  second  toe  on  the  tibial  and  fibular  Bides  respectively.     The  th/lrd  and 
fourth  muscles  are  inserted  into  the  third  and  fourth  toes  on  their  fibular  sides. 

I'lie  three  plantar  muscles  occupy  the  three  outer  interosseous  sjjaces.  Each 
arises  by  a  single  head  from  the  tibial  side  of  the  third,  fourth,  and  fifth  metatarsal 
bones  respectively.  Each  ends  in  a  tendon  which  passes  dorsal  to  the  transverse 
metatarsal  ligament,  and  is  inserted,  in  the  same  manner  as  the  dorsal  muscles,  into 
the  third,  fourth,  and  fifth  toes  on  their  tibial  side. 


Nerve-Supply  of  the  Muscles  of  the  Leg  and  Foot. 


Muscles. 


Tibialis  anticus  .  .  .  . 
Extensor  proprius  liallucis 
Extensor  longus  digitorum  . 
Peroneus  tertius  .  .  .  . 
Peroneus  longus  .  .  .  . 
Peroneus  brevis  .  .  .  . 
Extensor  brevis  digitorum 

Plantaris 

Popliteus         .         .         .         .         . 
Gastrocnemius        .         .         .         . 

Soleus 

Soleus 

Flexor  longus  digitorum 

Tibialis  posticus     .         .         .         . 

Flexor  longus  hallucis    . 
Abductor  liallucis  .         .         .         . 

Flexor  brevis  digitorum 
Flexor  brevis  hallucis     . 
First  lumbricalis    .         .         .         . 

Second,  third,  and  fourth  lumbri- 
cales    ...... 

Flexor  accessorius  .         .         .         . 

Adductores  hallucis 

Interossei        .         .         .         .         . 

Flexor  brevis  minimi  digiti  . 
Abductor  minimi  digiti 


Nerves. 


Origin. 


I  anterior  tibial    . 

■  musculo-cutaneous 
anterior  tibial    . 

y tibial . 


Uwsterior  tibial  . 


^internal  plantar 


external  plantar 


L.  4.  5.  S.  1. 


}l.  4. 

J.S.  1. 

L.  5. 
L.  5. 
L.  5. 
L.  5. 


5.  S.  1. 


S.  1.  2. 
S.  1. 
S.  1. 
S.  1.  2. 


L.  4.  5.  S.  1. 


S.  1.  2. 


Action  of  the  Muscles  of  the  Leg  and  Foot. 

The  muscles  of  the  leg  and  foot  act  chiefly  in  the  movements  of  the  ankle-joint  (assisted  by 
movements  of  the  inter-tarsal  joints) ;  of  the  metatarso -phalangeal  joints  (assisted  by  movements 
of  the  tarso-metatarsal  and  inter-metatarsal  joints) ;  and  of  the  inter-phalangeal  joints  of  the 
several  toes. 

I.  Tibio-Fibular  Articulations- — The  upper  tibio-fibular  articulation  is  only  capable  of 
slight  gliding  movement,  occasioned  Ijy  the  action  of  the  biceps  and  popliteus  and  the  muscles 
arising  from  tlie  hljula. 

II.  Movements  at  tlie  Ankle-Joint. — The  movements  at  the  ankle-joint  are  movements  of 
flexion  and  extension  of  tlie  loot  on  the  leg,  along  with  inversion  and  eversion  (only  during 
extension).  These  movements  are  produced  at  the  ankle,  aided  by  movements  in  the  inter-tarsal 
joints,  and  are  occasioned  by  the  following  muscles : — 


L''^'^" 

n     jr*^ 

\  ; 

r 

a.  Flexion. 
Tibialis  anticus 

Extension. 

h.  Inversion. 
Tibialis  anticus 

Eversion. 

Gastrocnemius 

Peroneus  tei-tius 

Extensor  communis  digitorum 

Plantaris 

Peroneus longus 

Exten.sor  jiropiiiis  lialluci.s 

Soleus 

Tibialis  ])osticus 

Peroneus  brevis 

Peroneus  tei-tius 

Tibialis  posticus 
Peroneus longus 
PcroiH'US  brevis 
FI(!Xor  longus  digitorum 

Flexor  longus  liallucis 

28  « 


390 


THE  MUSCULAR  SYSTEM. 


III.  Movements  of  the  Toes. — A.  At  the  Metatarso-Phalangeal  Joints  (assisted  by  move- 
ments at  the  tarso-inetatarsal  and  inter-metatarsal  joints). — Tliese  movements  are  flexion  and 
extension,  abduction  and  adduction  (in  a  line  corresjjonding  to  the  axis  of  the  second  toe). 


a.  Flexion. 

Extension. 

Flexor  longus  digitorum 
Accessoi'ius           ;v  { \,iy^'>  '■'^ 
Lumbricales 
Flexor  longus  hallucis 
Flexor  brevis  hallucis 
Flexor  l)revis  digitorum 
Flexor  brevis  minimi  digiti 
Interossei 

Extensor  longus  digitorum 
Extensor  brevis  digitorum 
Extensor  proprius  hallucis 

b.  Abduction. 


Adduction. 


(From  and  to  the  middle  line  of  the  second  toe.) 


Abductor  hallucis 
Dorsal  interossei 
Abductor  minimi  digiti 


Adductores  hallucis 
Plantar  interossei 


-B.  At  the  inter-phalangeal  joints  the  movements  are  limited  to  flexion  and  extension. 


Flexion. 

Extension. 

Flexor  brevis  digitorum  (acting  on  the  first 

Extensor  longus  digitorum    ^ 

joint) 
Flexor   longus    digitorum    (acting    on   both 

Extensor  brevis  digitorum 

(acting  on  both 

joints) 
Flexor  longus  hallucis  (acting  on  the  hallux) 

Interossei 

Lumbricales 

Extensor  proprius  hallucis 

joints) 

Movements  op  the  Lower  Limb  generally. 

The  characteristic  features  of  the  lower  limb  are  stability  and  strength,  and  its  muscles  and 
joints  are  both  subservient  to  the  functions  of  transmission  of  weight  and  of  locomotion.  In  the 
standing  position  the  centre  of  gravity  of  the  trunk  falls  between  the  heads  of  the  femora, 
and  is  located  about  the  middle  of  the  body  of  the  last  lumbar  vertebra.  It  is  transmitted 
through  the  bones  of  the  lower  limb  to  the  arch  of  the  foot,  where  the  astragalus-  distributes  it 
backwards  through  the  os  calcis  to  the  heel,  and  forwards  through  the  tarsus  and  metatarsus  to 
the  balls  of  the  toes. 

Locomotion. — The  three  chief  means  of  progression  are  walking,  running,  and  leaping.  In 
"walking,  the  body  and  its  centre  of  gravity  are  inclined  forwards,  the  trunk  oscillates  from  side 
to  side  as  it  is  supported  alternately  by  each  foot,  the  arms  swing  alternately  with  the  correspond- 
ing leg,  and  one  foot  is  always  on  the  ground.  The  act  of  progression  is  performed  by  the  leg, 
aided  in  two  Avays  by  gravity.  The  movements  of  the  leg  are  as  follows  :  At  the  beginning  of 
a  step,  one  leg,  so  to  speak,  "  shoves  off ; "  the  heel  is  raised  and  the  limb  is  extended.  By  the 
action  of  the  muscles  flexing  the  hip  and  knee-joint,  and  extending  the  ankle-joint  and  toes,  this 
limb  is  raised  from  the  ground  sufiiciently  to  clear  it,  and  passes  forwards  by  the  action  of 
gravity,  aided  by  the  force  given  to  the  movement  by  the  extensor  muscles.  After  passing  the 
line  of  the  centre  of  gravity  the  flexion  of  the  joints  ceases,  the  muscles  relax,  and  the  limb 
gradually  retui-ns  to  the  ground.  The  other  limb  then  passes  through  the  same  cycle,  the  weight 
of  the  body  now  resting  on  the  limb  which  is  in  contact  with  the  ground.  As  the  foot  reaches 
the  ground  it,  as  it  were,  rolls  over  it ;  the  heel  touches  it  first,  then  the  sole,  and  lastly,  as  the 
foot  leaves  the  ground  again,  only  the  toes.  In  running,  the  jjrevious  events  are  all  exaggerated. 
The  time  of  the  event  is  diminished,  while  the  force  and  distance  are  increased.  Both  feet  are  oft' 
the  ground  at  one  time  ;  the  action  of  flexors  and  extensors  alternately  is  much  more  powerful,  so 
that  on  the  one  hand  the  knees  are  drawn  U23wards  to  a  greater  extent  in  the  forward  movement, 
and  not  the  whole  foot,  but  only  the  toes  reach  the  ground  in  the  extension  of  the  limb.  The 
attempt  is  made  to  bring  the  foot  to  the  ground  in  front  of  the  line  of  the  centre  of  gravity.  At 
the  same  time  the  trunk  is  slojjed  forwards  much  more  than  in  Avalking.  In  leaping,  the  actions 
of  the  limbs  are  still  more  exaggerated.  The  movements  of  flexion  of  the  limb  are  still  more 
marked,  and  the  foot  reaches  the  ground  still  farther  in  front  of  the  line  of  the  centre  of  gravity. 


AXIAL  MUSCLES. 


391 


AXIAL   MUSCLES. 

THE  FASCIA  AND  MUSCLES  OF  THE  BACK. 


THE  FASCIA  OF  THE  BACK. 

The  general  fascial  investments  of  the  back  have  been  described  along  with  the 
superficial  muscles  associated  with  the  shoulder -girdle  (p.  318).  The  latissimus 
dorsi  muscle  has  been  described  as  arising  in  large  part  from  the  vertebral  apo- 
neurosis. This  is  a  strong  fibrous  lamina  which  conceals  the  erector  spinas  muscle. 
In  the  loin  it  extends  from  the  spines  of  the  lumbar  vertebrte  outwards  to  the 
interval  between  the  last  rib  and  the  iliac  crest,  where  it  is  concerned  in  forming 
the  lumbar  fascia.  Below  the  loin  the  vertebral  aponeurosis  is  attached  to  the  ihac 
crest,  and  more  internally  blends  with  the  subjacent  tendinous  origin  of  the  erector 
spinas.    The  fascia 

can    be    followed  rectus  abdominis 

upwards  over  the 
erector  spinse  in 
the  region  of  the 
thorax,  where  it  is 
attached  exter- 
nally to  the  ribs 
and  is  continuous 
with  the  inter- 
costal aponeur- 
oses. In  the  lower 
part  of  the  thorax 
it  is  replaced  by 
muscular  slips — 
the  serratus  posti- 
cus inferior ;  in 
the  upper  part  of 
the  thorax  it 
passes  beneath  the 
serratus  posticus 
superior  and 
blends  with  the 
deep  cervical 
fascia. 

The  lumbar 
fascia  is  a  narrow 
ligamentous  band 
which  connects 

the  last  rib  to  the  iliac  crest  between  the  muscles  of  the  back  on  the  one  hand  and 
those  of  the  abdominal  wall  on  the  other.  It  is  formed  by  the  union  of  three  fascial 
strata,  called  respectively  the  vertebral  aponeurosis  or  posterior  layer,  just  described ; 
the  middle,  and  tlie  anterior  layers.  The  middle  layer  is  a  fascia  which  stretches 
outwards  from  the  ends  of  the  transverse  processes  of  the  lumbar  vertebrfe,  between 
the  erector  spinjc  behind  and  the  quadratus  lumborum  muscle  in  front.  The  anterior 
layer  is  attached  to  the  lum})ar  vertebrai  near  the  bases  of  their  transverse  processes. 
It  covers  the  front  of  the  quadratus  lumborum  muscle,  and  separates  it  from  the 
psoas.  The  psoas  fascia  is  continuous  at  the  outer  border  of  the  psoas  muscle  with 
the  anterior  lay(;r  of  the  lumbar  iascia.  At  the  outer  borders  of  the  quadratus 
Juiiiljoriim  and  erector  Hpina;  muscles  the  three  layers  are  blended  together  to  form 
the  luml^ar  fascia,  \vhif;h  in  turn  gives  partial  origin  to  tlie  obliquus  internus  and 
transversalis  abdominis  muscles. 


Obliquus  exteknus 

Obliquus  internu'^ 
Transversalis 
abdominis 
Fascia  transversalis 

Peritoneum 


Colon 


Extraperitoneal 

tissue  \  V      >{ 

Kidnej  Vr' 


Lumbar  fascia 


Latissimus  dorsi 


Quadratus  lumborum 


Psoas  fascia 


Second  lumbar 
■\'ertebra 


Anterior  layer  of 
lumbar  fascia 


Multifidus 

SPIN/E 

^emispinalis 
dorsi 


Fig. 


Middle  layer  of  lumbar  fascia 

Ilio  costalis 
Vertebral  aponeurosis  Longissimus  dorsi 

306.— Transverse  Section  through  the  Abdomen,  opposite  the 
Second  Lumbar  Vertebra. 


392 


THE  MUSCULAE  SYSTEM. 


THE  MUSCLES  OF  THE  BACK. 

The  muscles  of  the  back  are  arranged  in  four  series  according  to  their  attach- 
ments:  (1)  vertebro- scapular  and  vertebro- humeral,  (2)  vertebro- costal,  (3) 
vertebro- cranial,    and    (4)    vertebral.       They    are    in    irregular    strata,    the    most 

superficial    muscles    having    the    most 
widely  spread  attachments. 

The  first  series  of  muscles  of  the 
back,  connecting  the  axial  skeleton  to 
the  upper  limb,  have  already  been 
described.  They  are  arranged  in  two 
layers :  (1)  trapezius  and  latissimus 
dorsi  superficially ;  (2)  levator  anguli 
scapuhe,  and  rhomboidei,  beneath  the 

u.s       , 

trapezius. 

The  remaining  muscles  are  almost 
entirely  axial,  and  may  be  divided, 
according  to  position,  into  four  groups  : 
(1)  serrati  postici,  superior  and  inferior, 
splenius  capitis  and  splenius  colli ;  (2) 
erector  spinee  and  complexus;  (3)  trans- 
verso-spinales  (semispinalis  and  multi- 
fidus  spinse) ;  and  (4)  the  small  deep 
muscles  (rotatores,  interspinales,  inter- 
transversales,  and  suboccipital  muscles). 


Trachelo-mastoid 


Tbansversalis 
cervicis 


ACCESSORIUS 


Ilio-costalis 


FiPvST  Group. 

The   serratus    posticus    superior 

LoNGissiMus  ]2as  a  membranous  origin  from  the  liga- 
mentum  nuchse  and  the  spines  of  the 
last  cervical  and  upper  three  or  four 
thoracic  vertebra.  It  is  directed  ob- 
liquely downwards  and  outwards,  to  be 
inserted  by  separate  slips  into  the  second, 
third,  fourth,  and  fifth  ribs.  The  muscle 
is  concealed  by  the  vertebro -scapular 
muscles,  and  crosses  obliquely  the 
splenius,  erector  spin?e,  and  complexus. 
It  lies  superficial  to  the  vertebral 
aponeurosis. 

The  serratus  posticus  inferior  has 
a  membranous  origin  through  the 
medium  of  the  vertebral  aponeurosis 
from  the  last  two  thoracic  and  first  two 
lumbar  spinous  processes.  It  forms  four 
muscular  bands  which  pass  almost 
horizontally  outwards  to  an  insertion 
into  the  last  four  ribs.  The  muscular 
slips  overlap  one  another  from  below 
upwards.  The  muscle  is  on  the  same 
plane  as  the  vertebral  aponeurosis,  and 
is  concealed  by  the  latissimus  dorsi. 
The  splenius  muscle  is  a  broad,  flattened  band  which  occupies  the  back  of  the 
neck  and  the  upper  part  of  the  thoracic  region.  It  arises  from  the  ligamentum  nuchse 
(from  the  level  of  the  fourth  cervical  vertebra  downwards)  and  from  the  spinous 
processes  of  the  last  cervical  and  higher  (four  to  six)  thoracic  vertebrie.  Its  fibres 
extend  upwards  and  outwards  into  the  neck,  separating  in  their  course  into  an 
upper  and  a  lower  part.  The  upper  part  forms  the  splenius  capitis,  which  is 
inserted  into  the  mastoid  process  and  the  outer  part  of  the  superior  curved  line  of 


Fig.  307.- 


— ScHEJiATic  Representation  of  the  Parts 
OF  THE  Erector  SpiNiE  Muscle. 


THE  MUSCLES  OF  THE  BACK. 


303 


the  occipital  bone  (Fig.  312,  p.  397).  The  lower  part  forms  the  splenius  colli 
or  cervicis,  which  is  inserted  into  the  posterior  tubercles  of  the  transverse  processes 
of  the  upper  three  or  four  cervical  vertebrse,  behind  the  origin  of  the  levator 
anguli  scapulae.  The  muscle  is  partially  concealed  by  the  trapezius  and  sterno- 
mastoid,  and  appears  between  them  in  the  floor  of  the  posterior  triangle  of  the 
neck  (splenius  capitis).  It  is  covered  by  the  rhomboid  muscles,  levator  anguli 
scapuhe,  and  serratus  posticus  superior.  It  conceals  the  transversalis  cervicis, 
trachelo-mastoid,  and  complexus  muscles. 

Second  Group. 


The  erector  spinse  (m.  sacro-spinalis)  possesses  vertebral,  vertebro-cranial,  and 
vertebro-costal  attachments.  It  consists  of  an  elongated  mass  composed  of  separated 
slips  extending  from  the  sacrum  to  the  skull.  Simple  at  its  origin,  it  becomes 
more  and  more  complex  as  it  is  traced  upwards  towards  the  head.  It  arises  (1)  by 
fleshy  fibres  from  the  iliac  crest ;  (2)  from  the  posterior  sacro-iliac  ligament ;  and 
(3)  by  tendinous  fibres  continuous  with  the  former  from  the  iliac  crest,  the  back  of 
the  sacrum,  and  the  spines  of  the  upper  sacral  and  all  the  lumbar  vertebrae.  Its 
fibres  extend  upwards  through  the  loin,  enclosed  between  the  posterior  and  middle 
layers  of  the  lumbar  fascia,  and  separate  into  two  columns — an  outer  portion 
derived  from  the  external  fleshy  origin,  the  ilio-costalis,  and  an  inner  portion  com- 
prising the  remaining  larger  part  of  the  muscle,  the  longissimus  dorsi. 

The  ilio-costalis  (m.  ilio-costalis  lumborum)  is  inserted  by  six  slender  slips  into 
the  lower  six  ribs. 

Internal  to  the  insertion  of  each  is  the  origin  of  a  slip  of  the  accessorius  muscle 


Posterior 

tubercles  of 

transverse 

processes 


Articular  processes- 


scalenus  medius 

Levator  anguli  scapula 

Splenius  colli 


Scalenus  posticus 

Cervicalis  ascendens 

Transversalis  cervicis 


Trachelo-mastoid 

Complexus 

Semispinalis  colli 

multifidus  spin^ 


tBectus  capitis 
anticus  major 


nCONGUS  COLLI 


Anterior 
tubercles  of 
transverse 
processes 


FfG.  308. — Scheme  of  Muse u'lar- Attachments  to  the  Transverse  Processes  of  the 

Cervical  Vertebrte. 

(m.  ilio-costalis  dorsi),  which,  arising  from  the  lower  six  ribs  internal  to  the  ilio- 
costalis,  is  inserted  in  line  with  it  by  similar  slips  into  the  upper  six  ribs. 

Tfie  cervicalis  ascendens  (m.  ilio-costalis  cervicis)  arises  in  the  same  way  by 
six  slips  i'rom  the  upper  six  ribs,  internal  to  the  insertions  of  the  accessorius.  It 
forms  a  narrow  band,  which,  extending  into  the  neck,  is  inserted  into  the  posterior 
tubercles  of  the  transverse  processes  of  the  fourth,  fifth,  and  sixth  cervical  vertebrae, 
behind  the  scalenus  posticus.  The  ilio-costalis,  accessorius,  and  cervicalis  ascendens 
form  together  a  continuous  muscular  column,  and  constitute  the  outermost  group 
of  the  cornponeul  el(;iri(!nts  of  the  erector  spirue. 

The  longissimus  dorsi  is  the  largest  element  in  the  erector  spinse  muscle. 


394 


THE  MUSCULAE  SYSTEM. 


With  its  cervical  prolongations — the  transversalis  cervicis  and  trachelo-mastoid — 
it  forms  tlie  middle  column  of  the  erector  spinae.  Mostly  tendinous  on  the  surface 
at  its  origin,  it  becomes  fleshy  in  the  upper  part  of  the  loin.  It  is  thickest  in  the 
loin,  and  becomes  thinner  as  it  passes  upwards  in  the  back  Ijetween  the  column 
formed  by  the  iUo-costalis,  etc.,  externally,  and  the  spinalis  dorsi  internally.  It 
is  inserted  by  two  series  of  slips,  inner  and  outer,  externally  into  nearly  all  the 


Obliquus  suplkicii 

Rectus  capitis  posticus  major 

Obliquus  invlrior 

Sterno-mastoid 

gomplexus  muscle 


Trachplo-mastoid 
scaleni,  siedius  and  posticus 


Semispinalis  colli 


Levatores  costarum 


Semispinalis  dorsi 


Middle  layer  of  lumbar  fascia- 
Vertebral  aponeurosis  (cnt)- 

Obliquus  internus  abdominis 
Origin  of  erector  spin^. 


Vertelwal  aponeurosis  (cut^jiv. 


COMPLEXUS  muscle 

Sterno-mastoid 


Splenius  capitis 


Splenius  colli 
Levator  anguli  scapula; 
Transversalis  colli 

tERVICALIS  ASCENDENS 


Complexus  muscle 


Longissimus  dorsi 


accessorius 
Semispinalis  dorsi 


Spinalis  dorsi 


Ilio-costalis 


Vertebral  aponeurosis  (cut) 

Lumbar  fascia 

Obliquus  internus  abdominis 

Obliquus  externus  abdominis 


Origin  of  gluteus  maxim  us 


Fig.   309. — Deeper  Muscles  of  the  Back. 

ribs,  and  internally  into  the  transverse  processes  of  the  thoracic  and  the  accessory 
processes  of  the  upper  lumbar  vertebrse.  It  is  prolonged  upwards  into  the  neck 
by  its  association  with  the  common  origin  of  two  muscles,  the  transversalis  cervicis 
and  the  trachelo-mastoid. 

The  transversalis  cervicis  (m.  longissimus  cervicis)  has  an  origin  from  the 
transverse  processes  of  the  upper  six  thoracic  vertebrte,  internal  to  the  insertions 
of  the  longissimus  dorsi.     Extending  upwards  into  the  neck,  it  is  inserted  into  the 


THE  MUSCLES  OF  THE  JUCK.  395 

posterior  tubercles  of  the  transverse  processes  of  the  second,  third,  fourth,  fifth, 
and  sixth  cervical  vertebrae.  It  lies  in  the  neck,  underneath  the  cervicalis  ascendens 
and  splenius  colli  muscles. 

The  trachelo- mastoid  (m.  longissimus  capitis)  arises,  partly  by  an  origin 
common  to  it  and  the  previous  muscle,  from  the  transverse  processes  of  the  upper 
six  thoracic  vertebr£e,  and  partly  by  an  additional  origin  from  the  articular  pro- 
cesses of  the  lower  four  cervical  vertebrae.  Separating  from  the  transversalis 
cervicis,  the  muscle  ascends  through  the  neck  as  a  narrow  band  which  is  inserted 
into  the  mastoid  process  beneath  the  splenius  capitis  muscle.  In  the  neck  the 
muscle  is  placed  between  the  splenius  capitis  and  complexus. 

The  spinalis  dorsi  forms  the  innermost  column  of  the  erector  spinse.  It 
occupies  the  thoracic  portion  of  the  back,  and  arises  by  tendinous  fibres  from  the 
lower  two  thoracic  and  upper  two  lumbar  spinous  processes,  and  also  directly  from 
the  tendon  of  the  longissimus  dorsi.  It  is  a  narrow  muscle  which,  lying  close  to 
the  thoracic  spinous  processes  internal  to  the  longissimus  dorsi  and  complexus,  is 
inserted  into  the  upper  (four  to  eight)  thoracic  spines.  This  muscle  is  not  prolonged 
into  the  neck.     It  partially  covers  the  semispinalis,  dorsi,  and  colli. 

The  erector  spinge  muscle  is  bound  down  by  the  vertebral  aponeurosis,  and 
is  concealed  by  the  more  superficial  muscles  (sterno  -  mastoid,  trapezius,  levator 
anguli  scapulse,  rhomboids,  splenius,  serrati  postici).  It  covers  the  ribs  posteriorly, 
and  partially  conceals  the  semispinales  and  complexus  muscles. 

The  complexus  muscle  (m.  semispinalis  capitis)  closely  resembles  in  position 
and  attachments  the  trachelo-mastoid.  It  takes  origin  by  tendinous  slips  from  the 
transverse  processes  of  the  upper  six  thoracic  and  the  articular  processes  of  the 
lower  four  cervical  vertebrse,  internal  to  the  transversalis  cervicis  and  trachelo- 
mastoid.  It  has  an  additional  origin  also  from  the  spinous  process  of  the  last 
cervical  vertebra.  It  forms  a  broad  muscular  sheet  which  extends  upwards  in  the 
neck,  to  be  inserted  by  fleshy  and  short  tendinous  fibres  into  the  inner  impression 
between  the  superior  and  inferior  curved  lines  of  the  occipital  bone  (Fig.  312, 
p.  397).  The  inner  portion  of  the  muscle  is  separate,  and  forms  the  biventer 
cervicis,  consisting  of  two  fleshy  bellies  with  an  intervening  tendon,  placed  vertically 
in  contact  with  the  ligamentum  nuchse.  The  insertion  of  the  muscle  is  crossed  by 
the  occipital  artery.  The  complexus  is  covered  mainly  by  the  splenius  and 
trachelo-mastoid  muscles.  It  conceals  the  semispinalis  colli  and  the  muscles  of 
the  suboccipital  triangle,  along  with  the  accompanying  vessels  and  nerves. 

Thikd  Geoup. 

This  group  comprises  the  semispinales  and  multifidus  spinse. 

These  muscles  are  only  incompletely  separate  from  one  another.  The  semi- 
spinales, dorsi,  and  colli,  form  a  superficial  stratum,  the  multifidus  spinse  being  more 
deeply  placed.  The  more  superficial  muscles  have  the  longer  fibres  ;  the  fibres  of  the 
multifidus  spinse  pass  over  fewer  vertebrse.  Both  muscles  extend  obliquely  upwards 
from  transverse  to  spinous  processes. 

The  semispinalis  muscle  extends  from  the  loin  to  the  axis  vertebra.  Its 
fibres  are  artificially  separated  into  an  inferior  part,  the  semispinalis  dorsi,  and 
a  superior  part,  the  semispinalis  colli. 

The  semispinalis  dorsi  arises  from  the  transverse  processes  of  the  lower  six 
thoracic  vertebrai.  It  is  inserted  into  the  spinous  processes  of  the  last  two  cervical 
and  first  four  thoracic  vertebrse. 

The  semispinalis  colli  or  cervicis  arises  from  the  transverse  processes  of  the 
upper  six  thoracic  vertebrai  and  the  articular  processes  of  the  lower  four  cervical 
vertebrai.  It  is  inserted  into  the  spines  of  the  cervical  vertebrte  from  the  second  to 
the  fifth.  The  sendspinalis  muscle  occupies  the  vertebral  furrow,  and  is  concealed 
by  the  erector  spime  and  complexus;  it  covers  the  multifidus  spinse  muscle.  It  is 
on  the  same  ])lane  as  the  muscles  of  the  suboccipital  triangle. 

The  multifidus  spinae  differs  from  the  xjrevious  muscle  in  extending  from  the 
sacrum  to  th(;  axis,  and  in  the  shortness  of  its  fasciculi,  which  pass  over  fewer 
vertebra;  to  reach  their  insertion,     it  arises  from  the  sacrum,  from  the  posterior 


596 


THE  MUSCULAK  SYSTEM. 


INSKRTION  OF  STERNO- 
MASTOIU' 

.Splenius  capitis. 
Trachelo-mastoid 


Com  PLEXUS  thrown 

OUTWARDS 

Ijeast  occiijital  nerve 


SpLENHTS  CAPITIS 


Trachelo-mastoid, 


Trapezius 
Com  PLEXUS 
fiieat  or.cipilal  nerve 

(jBLlyUUS  SUPERIOR 

Rectus  capitis  posticus  major 

RECTI'S  capitis  posticus  MINOR 

Vertebral  artery 
Suboccipital  nerve 
Posterior  arch  of  atlas 

ObIIQUUS  INFERIOR 

Posterior  primary  division  of  second 
ceiMcal  nerve 


Posterior  primary  division  of  tliird 
cei  vical  nerve 

Deep  cervical  artery 

Posterior  ]iriniary  division  of  fourth 

cerMcal  nerve 


.Semispinalis  colli 


Fig.   310. — The  Suboccipital  Triangle. 
sacro-iliac   ligament  (Fig.   311,  p.  396),  from  the   mammillary  processes    of   the 


Atlachment  of 
posterior  sacio- 
iliac  ligaments 


Gluteus  maxmms  (origin) 
Fig.  311. — Muscle-Attachments  to  the  SACKUii  (Posterior  Aspect). 


THE  MUSCLES  OF  THE  BACK. 


397 


lumbar  vertebrae,  from  the  transverse  processes  of  the  thoracic  vertebra,  and  from 
the  articular  processes  of  the  lower  four  cervical  vertebrae.  It  is  inserted  into  the 
spines  of  the  vertebrae  up  to  and  including  the  axis.  Lying  in  contact  with  the 
vertebral  laminse,  the  muscle  is  covered  in  the  back  and  neck  by  the  semispinalis, 
and  in  the  loin  by  the  erector  spinse  muscle. 


Fourth  Group. 

This  group  includes  several  sets  of  small  muscles,  which  are  vertebro-cranial  or 
inter- vertebral  in  their  attachments. 

The  muscles  bounding  the  suboccipital  triangle  are  four  in  number — obliquus 
inferior,  obliquus  superior,  rectus  capitis  posticus  major,  and  rectus  capitis  posticus 
minor. 

These  muscles  are  concealed  by  the  complexus  and  splenius  capitis  ;  they  enclose 
a  triangular  space  (the  suboccipital  triangle)  in  which  the  vertebral  artery, 
the  posterior  primary  division  of  the  suboccipital  nerve,  and  the  posterior  arch  of 


Complexus  (insertion) 

Kectus  capitis  posticus  minor 
(insertion) 

\ 

Rectus  capitis  posticus  major 
(insertion) 


Trapezius  (origin) 


Sterno-cleido-inastoid 
(insertion) 

Splenius  capitis 
^/(insertion) 


Obliquus  superior  (insertion)  \W| 


Rectus  capitis  lateralis  (mseitioii) 

Rectus  capitis  anticus  niinoi  (insertion) 

Rectus  capitis  anticus  major  (insertion) 


Superior  constrictor  of  x^liarynx  (insertion) 


Fia.  312. — Muscle- Attachments  to  Occipital  Bone  (Inferior  Surface). 

the  atlas  are  contained.  The  obliquus  inferior  is  separated  from  the  semispinalis 
muscle  by  the  great  occipital  (second  cervical)  nerve. 

The  obliquus  inferior  arises  from  the  spine  of  the  axis,  and  is  inserted  into  the 
transverse  process  of  the  atlas. 

The  obliquus  superior  arises  from  the  transverse  process  of  the  atlas,  and  is 
inserted  into  the  occipital  bone  beneath  and  external  to  the  complexus  and  above 
the  inferior  curved  line  (Fig.  312,  p.  397). 

The  rectus  capitis  posticus  major  arises  from  the  spine  of  the  axis,  and  is 
inserted  into  the  occipital  Ijone  Ijeneath  the  obliquus  superior  and  complexus,  and 
below  th(j  inferior  curved  line  (Fig.  312,  p.  397). 

The  rectus  capitis  posticus  minor  arises  beneath  the  previous  muscle  i'rom  the 
spine  of  tlx;  athis,  and  is  inserted  into  the  occipital  bone  below  the  inferior  curved 
line  interii.'tl  to  and  bcjieatii  the  rectus  capitis  posticus  major  (Fig.  312,  p.  397). 

The  rotatores  dorsi  are  eleven  pairs  of  small  muscles  occupying  the  vertebral 
groove  in  tbe  tlioracic  region,  beneath  tin;  transvcrso-spinalcis,  of  wliich  they  form 
the  deepest  fibrcis.  Each  consists  of  a  small  slip  arising  I'rom  the  transverse  process, 
and  inserted  into  the  lamina  of  the  vertebra  directly  above. 


398  THE  MUSCULAE  SYSTEM. 

The  inter-spinales  are  bands  of  muscular  fibres  connecting  together  the  spinous 
processes  of  the  vertebrae. 

The  inter-transversales  are  slender  slips  extending  between  the  transverse 
processes.  They  are  double  in  the  neck,  the  anterior  divisions  of  the  spinal  nerves 
passing  between  them. 

The  rectus  capitis  lateralis,  extending  from  the  transverse  process  of  the  atlas 
to  the  jugular  process  of  the  occipital  bone  (Eig.  312,  p.  397),  is  homologous  with 
the  posterior  of  the  two  inter-transverse  muscles.  In  the  loin  the  inter-transversales 
muscles  are  usually  double,  but  they  are  often  absent,  or  are  replaced  by  membrane. 

Nerve-Supply. 

Witli  the  exception  of  the  vertebro- scapular  and  vertebro  -  humeral  muscles  (trapezius, 
latissimus  dorsi,  levator  anguli  scapulse,  rhomboidei,  p.  318),  the  mviscles  of  the  back  are  all 
suj^iDlied  Ijy  the  posterior  frimary  divisions  of  tlie  spinal  nerves.  In  the  upper  part  of  the  trunk 
the  muscles  are  supplied  mainly  by  the  external  branches ;  in  the  lower  part  chiefly  by  the 
internal  brandies  of  the  nerves.  In  the  cervical  and  sacral  regions  a  limited  plexiforni  arrange- 
ment of  the  nerves  occurs  (j>osterior  cervical  and  posterior  sacral  plexuses). 

Actions. 

The  action  of  these  muscles  is  extremely  complex.  Not  only  do  they  act  on  the  spinal 
column,  ribs,  head,  and  jjelvis,  in  conjunction  with  other  muscles,  but  some  of  them  act  also  in 
relation  to  the  movements  of  the  limbs  as  well.  In  this  section  will  be  given  an  analysis  of  their 
movements  in  relation  to  the  spinal  column,  head,  and  pelvis.  The  movements  of  the  limbs  and 
of  the  ribs  (resjiiration)  are  dealt  with  in  other  sections.  The  chief  muscles  are  engaged  in  pre- 
serving the  erect  position,  and  in  tlie  movements  of  the  trunk  they  are  assisted  in  large  measure 
by  muscles  whose  chief  movements  are  referred  to  elsewhere. 

1.  Movements  of  the  Spinal  Column. — The  movements  of  the  vertebral  column  are  flexion, 
extension,  and  lateral  movement  or  rotation.  These  movements  occur  in  all  regions — neck, 
thorax,  and  loin ;  flexion  and  extension  and  lateral  movement  are  most  limited  in  the  region  of 
the  thorax ;  wliile  rotation  is  most  limited  in  the  region  of  the  loin. 


a.  Flexion      and      Extension. 

Longus  colli 

Serrati  postici 

Rectus  capitis  anticus  major 

Splenius  capitis 

Scaleni  antici  (together) 

Splenius  colli 

Psoas  magnus  and  parvus 

Erector  spinas 

Levator  ani 

Semisjjinalis  dorsi 

Ischio-coccygeus 

Semisjjinalis  colli 

Complexus 

Sj)hincter  ani  externus 

Multifidus  sjDinse 

Eectus  abdominis 

Interspinales 

Pj^ramidalis  abdominis 

Obliquus  externus  abdominis 

Intercostal  muscles 

Obliquus  internus         „ 

Diaphragm 

Trans  versalis                 „ 

Triangularis  sterni 

h.  Lateral  Movement  (Rotation). 

Levator  anguli  scapulte 

Rectus  capitis  anticus  major 

Serrati  postici 

Scaleni,  anticus,  medius,  posticus 

Splenius  colli 

Psoas  (magnus  and  parvus) 

Erector  spinas 

Quadratus  lumborum 

Complexus 

Obliquus  externus  abdominis 

Semispinalis 

Obliquus  internus           „ 

Multifidus  spinse 

Transversalis                   „ 

Rotatores  dorsi 

Rectus                              „ 

Inter-transversales 

Pyramidalis                    „ 

Longus  colli 

2.  Movements  of  the  Head. — The  movements  of  the  head  are  flexion  and  extension,  at  the 
occij)ito-atlantoid  articulation  ;  lateral  movement  and  rotation  at  the  atlanto-axial  joint. 


FASCIA  AND  MUSCLES  OF  THE  HEAD  AND  NECK. 


399 


a.  Flexion       and       Extension. 


Digastric 

Stylo -hyoid 

S  ty  lo  -pharyngeus 

Mylo-liyoid 

Hyo-glossus 

Sterno-liyoid 

Sterno-thyroid 

Omo-hyoid  | 

Recti  capitis  antici  (major  and   minor)     | 

(J,he  muscles  of  both  sides  acting  together) 


Sterno-mastoid 

Splenius  capitis 

Trachelo-mastoid 

Complexus 

Obliquus  inferior 

Recti  capitis  postici  (major  and  minor) 


b.  Lateral  Movement. 

c.  notation. 

Sterno-mastoid 
Splenius  capitis 
Trachelo-mastoid 
Complexus 
Obliquus  superior 
Rectus  capitis  lateralis 

Sterno-mastoid 
Splenius  capitis 
Trachelo  -mastoid 
Complexus 
Obliquus  inferior 
„         superior 
Recti  capitis  postici  (major  and  minor) 

Movements  of  the  Pelvis. — The  movements  of  the  pelvis  (as  in  locomotion)  are  partly 
caused  by  certain  of  the  muscles  of  the  back.  Those  muscles,  which  are  attached  to  the  spinal 
column  or  the  ribs  on  the  one  hand,  and  to  the  innominate  bone  on  the  other,  produce  the 
movements  (flexion,  extension,  and  lateral  movement)  of  the  whole  pelvis.  In  addition,  the 
muscles  passing  between  the  innominate  bone  and  femur,  in  certain  positions  of  the  lower  limb, 
assist  in  these  movements. 


a.  Extension      and      Flexion. 


Latissimus  dorsi 

Erector  spin« 

Multifidus  S2:)in8e  (acting  on  both  sides) 


Psoas  magnus  and  joarvus 

Rectus  abdominis 

Pyramidalis  abdominis 

Obliquus  externus  abdominis 

Obliquus  internus         „ 

Transversal:  s  abdominis  (acting  on  both 

sides) 
Pyriformis 
Glutei 

Obturator  (externus  and  internus) 
Sartorius 

Tensor  fascise  femoris 
Iliacus 

Rectus  femoris 
Adductors  (in  the  erect  position) 


b.  Lateral  Movement. 


Flexors  and  extensors  of  side  only 


Quadratus  lumborum 


THE  EASCI^  AND  MUSCLES  OF  THE  HEAD  AND  NECK. 


FASCI.^. 

The  superficial  fascia  of  the  head  and  neck  possesses  certain  features  of  special 
interest.  Over  the  scalp  it  is  closely  adherent  to  the  skin  and  subjacent  epicranial 
aponeurosis,  and  contains  the  superficial  vessels  and  nerves.  Beneath  the  skin  of 
the  eyelids  it  is  loose  and  thin  and  contains  no  fat.  Over  the  face  and  at  the 
side  of  the  neck  it  is  separated  from  the  deep  fascia  by  the  facial  muscles  and 
the  platysma  myoides.  In  tbe  hollow  between  the  ])uccinator  and  the  masseter 
it  is  continuous  with  a  pad  of  fat  {suctorial  i)ad)  occupying  the  interval  between 
these  muscles. 


400 


THE  MUSCULAE  SYSTEM. 


The  deep  fascia  of  the  head  and  neck  presents  many  remarkable  characters. 
Over  the  scalp  it  is  represented  by  the  epicranial  aponeurosis,  the  tendon  of  the 
occipito-frontalis  muscle.  This  is  a  tough  membrane,  tiglitly  stretched  over  the 
calvarium,  from  which  it  is  separated  by  loose  areolar  tissue.  It  is  attached 
posteriorly,  partly  through    the  agency  of  the   occipitalis  muscle,  to  the  superior 

curved  line  of  the  oc- 
r  13  /  15  /  17/10  cipital  bone  ;  anteriorly 
'  '  ''  ''  it  joins  the  frontalis 
muscle  and  the  orbicu- 
laris palpebrarum,  and 
has  no  bony  attachment ; 
laterally  it  is  attached 
to  the  temporal  ridge 
and  the  mastoid  process. 
Below  the  temporal  ridge 
it  is  continuous  with  the 
temporal  fascia,  a  stout 
layer  of  fascia  attached 
to  the  temporal  ridge 
and  zygomatic  arch, 
which  covers  and  gives 
origin  to  the  temporal 
muscle.  This  fascia 
separates  into  two  layers 
above  the  zygoma,  to 
enclose  a  quantity  of  fat 
along  with  branches  of 
the  temporal  and  orbital 
arteries.  On  the  face 
the  fascia  is  practically 
non-existent  anteriorly 
in  relation  to  the  facial 
muscles.  Posteriorly  it 
forms  the  thin  masseteric 
fascia,  and  is  much 
thicker  in  relation  to 
the  parotid  gland,  for 
which  it  forms  a  capsule. 
In  the  neck  the  deep 
fascia  invests  the  muscles, 
and  forms  aponeurotic 
coverings  for  the  pharynx, 
trachea,  oesophagus, 
glands,  and  large  vessels. 
It  encloses  the  sterno- 
mastoid  muscle,  and  can 
be  traced  backwards  over 
the  posterior  triangle 
to  the  trapezius  and  deeper  muscles,  which  it  surrounds ;  it  can  be  traced  forwards 
over  the  anterior  triangle  to  the  middle  line  of  the  neck,  where  it  ibrms  a 
continuous  membrane.  Above  the  sternum  the  fascia,  after  enclosing  the  sterno- 
mastoid  muscles,  is  attached  in  the  form  of  two  layers  to  the  front  and  back  of  the 
episternal  notch.  The  layer  enclosing  the  infrahyoid  muscles  passes  across  the 
middle  line  of  the  neck  in  front  of  the  trachea,  and  is  attached  above  to  the  hyoid 
bone,  below  to  the  sternum,  clavicle,  and  first  rib.  A  third  layer  of  fascia  passes 
inwards  in  front  of  the  trachea,  enclosing  the  thyroid  body.  Beneath  the  steruo- 
mastoid  the  fascia  helps  to  form  the  carotid  sheath,  which  is  completed  by  septal 
processes  stretching  inwards  across  the  neck  in  relation  to  the  infrahyoid  muscles, 
trachea,  oesophagus,  and   pharynx,  and   the  prevertebral  muscles.     The   trachea. 


Fig.  313. 


-Transverse  Section  in  the  Cervical  Kegion  (between  the 
foiirtli  and  fifth  cervical  vertebrse). 


1.  Crico-thyroid  muscle. 

2.  Inferior  constrictor  muscle. 

3.  Pharynx. 

4.  Cricoid  cartilage. 

5.  Vocal  cord. 

6.  Thyro-arytenoid  muscle. 

7.  Thyroid  cartilage. 
S.  Glottis. 

9.  Layers  of  deep  cervical  fascia. 

10.  Sterno-hyoid  muscle. 

11.  Omohyoid  muscle. 

12.  Sterno-thyroid  muscle. 

13.  Cervical  fascia. 

14.  Thyroid  body. 

15.  Comnion  carotid  artery. 

16.  Descendens  hypoglossi  nerve. 

17.  Sterno-mastoid  muscle. 
IS.  Internal  jugular  vein. 

19.  Pneumogastric  nerve. 

20.  Syniimthetic  nerve. 

21.  Carotid  sheath. 

22.  Phrenic  nerve. 

23.  T.ONGUS  COLLI  MU.SCLK. 

24.  Rectus  capitis  anticus  major. 

25.  Scalenus  anticus. 


26.  Vertebral  vein. 

27.  Scalenus  medius. 

28.  Posterior  triangle. 

29.  Scalenus  posticus. 

30.  Levator  anguli  scapula. 
;U.  Spinal  accessory  nerve. 

32.  Splenius  colli. 

33.  Transversalis  crevicis. 

34.  Trachelo-mastoid. 

35.  Spinal  nerve. 

36.  Vertebral  artery. 

37.  Profunda  cervicis  vein. 

38.  Profunda  cervicis  artery. 

39.  Multifidus  spin^. 

40.  Semispinalis  colli. 

41.  Complexus. 

42.  Splenius  capitis. 

43.  Trapezius. 

44.  Liganientum  nuclide 

45.  Spine  of  fourth  cervical  vertebra. 

46.  Lamina  of  fifth  cervical  vertebra. 

47.  Dura  mater. 
4S.  Spinal  cord. 

49.  Transverse  process. 

50.  Disc  between  fourth  and  fifth  cervical 

vertebra?. 


THE  MUSCLES  OF  THE  HEAD.  401 

oesophagus,  and  pharynx,  are  likewise  encapsuled  in  cervical  fascia,  a  septal  layer 
passing  across  the  middle  line  of  the  neck  between  the  trachea  and  oesophagus. 
Lastly,  a  strong  praevertebral  fascia  passes  across  the  neck  in  front  of  the  pricvertebral 
muscles,  and  behind  the  oesophagus  and  pharynx. 

The  cervical  fascia  is  attached  above  to  the  bones  of  the  skull :  superficially  to 
the  superior  curved  line  of  the  occipital  bone,  the  mastoid  process,  the  zygoma 
(over  the  parotid  gland),  and  the  lower  border  of  the  mandible  ;  more  deeply  to  the 
styloid  and  vaginal  processes  of  the  temporal  bone,  the  great  wing  of  the  sphenoid 
and  the  basilar  process.  This  deeper  attachment  (jjrcevertehral  fascia)  is  behind  the 
parotid  gland  and  pharynx,  and  is  associated  with  the  formation  of  three  ligaments  : 
stylo-mandibular  ligament,  internal  lateral  ligament  of  the  lower  jaw,  and  pterygo- 
spinous  ligament.  The  fascia  is  attached  below,  through  its  muscular  connexions,  to 
the  sternum,  first  rib,  clavicle,  and  scapula.  By  means  of  its  connexion  with  the 
trachea  and  the  common  carotid  artery  it  is  carried  down  behind  the  first  rib  into 
the  superior  mediastinum,  and  so  becomes  continuous  with  the  pericardium. 
By  means  of  its  connexion  with  the  subclavian  vessels  and  brachial  nerves  it  is 
carried  down  to  the  axilla,  as  the  subclavian  sheath,  which  becomes  connected  with 
the  costo-coracoid  membrane. 

THE  MUSCLES  OF  THE  HEAD. 

The  muscles  of  the  head  are  divisible  into  three  separate  groups  with  very 
different  relations  and  uses — viz.,  superficial  muscles,  muscles  of  the  orbit,  and 
muscles  of  mastication. 

SuPEKFiciAL  Muscles. 

The  superficial  muscles  comprise  a  large  group,  including  the  muscles  of  the 
scalp  and  face,  and  the  platysma  myoides  in  the  neck. 

The  platysma  myoides  is  a  thin  quadrilateral  sheet  extending  from  chest  to 
face  over  the  side  of  the  neck,  between  the  superficial  and  deep  fasciae.  It  arises 
from  the  deep  fascia  of  the  pectoral  region  and  the  clavicle.  It  is  directed 
upwards  and  forwards,  and  is  partly  inserted  (by  its  intermediate  fibres)  into  the  lower 
border  of  the  mandible,  becoming  connected  with  the  depressor  labii  inferioris  and 
depressor  anguli  oris  muscles  (Fig.  319,  p.  407).  The  more  anterior  fibres  pass 
across  the  middle  line  of  the  neck  and  decussate  for  a  variable  distance  below  the 
chin  with  those  of  the  opposite  side.  The  posterior  fibres  sweep  over  the  angle  of 
the  jaw  and  become  continuous  with  the  risorius  muscle.  The  platysma  myoides 
is  the  rudiment  of  the  cervical  portion  of  the  panniculus  carnosus  of  lower  animals, 
in  which  it  has  a  much  more  intimate  connexion  with  the  muscles  of  the  face  than 
is  usually  the  case  in  man. 

The  Muscles  of  the  Scalp. 

The  muscles  of  the  scalp  comprise  the  muscles  of  the  external  ear  and  the 
occipito-frontalis  muscle. 

The  occipito-frontalis  is  a  muscle  with  two  bellies  and  an  intervening  tendon 
(the  epicranial  aponeurosis)  which  stretches  uninterruptedly  across  the  middle  line  of 
the  cranium.  The  posterior  belly  (occipitalis)  arises  as  a  broad  flat  band  from  the 
outer  two-thirds  of  the  superior  curved  line  of  the  occipital  bone.  The  anterior 
belly  (frontalis)  has  no  bony  attachments ;  arising  from  the  epicranial  aponeurosis 
about  the  level  of  the  coronal  suture,  it  passes  downwards  to  the  supra-orbital 
arch,  where  it  blends  with  the  orbicularis  palpebrarum  and  corrugator  supercilii 
muscles.  It  extends  across  the  full  width  of  the  forehead,  and  blends  in  the 
middle  line  with  the  muscle  of  the  opposite  side. 

The  epicranial  aponeurosis,  extending  between  the  two  fleshy  bellies,  is  a  con- 
tinuous membrane  which  glides  over  the  calvarium,  and  has  attachments  laterally 
to  the  temporal  ridge,  and  behind,  between  the  posterior  bellies,  to  the  superior 
curveil  line  of  the  occipital  bone.  It  has  no  osseous  attachment  anteriorly.  The 
occipito-frontalis  is  usually  rudimentary.  By  the  contraction  of  the  fibres  of  the 
frontalis  muscle  the  skin  of  the  forehead  is  tlirown  into  horizontal  parallel  folds. 
29      . 


402 


THE  MUSCULAK  SYSTEM. 


The  extrinsic  muscles  of  the  ear  are  three  in  number:  retrahens,.  attollens, 
and  attrahens  aurem. 

The  retrahens  aurem  (m.  auricularis  posterior)  is  a  narrow  fleshy  slip  which 
arises  from  the  surface  of  the  mastoid  process  and  is  inserted  into  the  deep  surface 
of  the  pinna.  It  bridges  across  the  groove  between  the  mastoid  process  and  the 
pinna,  and  conceals  the  posterior  auricular  vessels  and  nerve. 

The  attollens  aurem  (m.  auricularis  superior)  is  a  small  fan-shaped  muscle 
which  arises  from  the  temporal  fascia,  and  descends  to  be  inserted  into  the  top  of 
the  root  of  the  pinna. 

The  attrahens  aurem  (m.  auricularis  anterior)  is  a  similar  small  muscle,  placed 
in  front  of  the  attollens,  and  stretching  obliquely  between  the  temporal  fascia  and 
the  top  of  the  root  of  the  pinna. 

Epicranial  aponeurosis        Attrahens  aurem 


.-r^rt- 


Attollens      //     ' 

AUBEM      77~ 

^1    I 
Occipitalis 
Betrahbn 


Orbicularis  palpebrarum 
Pybamidalis  nasi 

Compressor  naris 

Levator  labii  superioris  al.eQue  nasi 

Levator  labii  superioris 

Zygomaticus  minor 

Depressor  al^  nasi 
Zygomaticus  major 
Stenson's  duct 
Orbicularis  oris 

RiSORIUS 

Buccinator 
Depressor  anguli  obis 
Depressor  labii  inferioris 

Masseter 


'Platysma  mtoides 


Fig.  314. — The  Mdscles  op  the  Face  and  Scalp  (muscles  of  expression). 

These  two  muscles  conceal  branches  of  the  temporal  vessels  as  they  lie  on  the 
temporal  fascia. 

The  ear  muscles  are  rudimentary  and  usually  functionless. 


The  Muscles  of  the  Face. 

The  facial  muscles  are  divided  into  three  groups,  associated  with  the  several 
apertures  of  the  eye,  nose,  and  mouth. 

1.  The  muscles  of  the  eyelids  include  four  muscles :  the  levator  palpebrse 
superioris  (described  with  the  orbital  muscles),  orbicularis  palpebrarum,  tensor  tarsi, 
and  corrugator  supercihi. 

The  orbicularis  palpebrarum  (m.  orbicularis  oculi)  is  a  transversely  oval 
sphincter  muscle  surrounding  and  occupying  the  eyelids.  It  is  divisible  into  an 
external  portion  (pars  orbitalis)  composed  of  coarse  fibres,  spreading  on  to  the  forehead, 
temple,  and  cheek,  and  an  internal  portion  (pars  palpebralis),  composed  of  finer 
fibres,  situated  beneath  the  skin  of  the  eyelids.  At  the  inner  canthus  of  the  eye 
the  muscle  (by  its  palpebral  fibres)  gains  an  attaclunent  to   the  tarsal  hgament 


THE  MUSCLES  OF  THE  HEAD.  403 

aud  the  borders  of  the  iiaso-lachrymal  groove.  Its  fibres  enclose  the  laclirymal 
sac  and  the  canaliculi.  The  posterior  fibres,  extending  between  tlie  posterior  edge 
of  tlie  naso-lachrymal  groove  and  the  tarsal  ligaments  behind  the  lachrymal  sac, 
constitute  the  tensor  tarsi  muscle.  The  fibres  of  the  muscle  which  extend  along  the 
margins  of  the  lids  constitute  a  separate  ciliary  bundle. 

Externally  the  orbicularis  palpebrarum  has  no  bony  attachment ;  so  that  when 
it  contracts  and  closes  the  eyelids,  both  lids  at  the  same  time  tend  to  be  drawn 
inwards  towards  the  inner  canthus  of  the  eye. 

The  corrugator  supercilii  arises  from  the  nasal  eminence,  and  passing  horizon- 
tally outwards,  blends  with  tlie  upper  fibres  of  the  orbicularis  palpebrarum  on  its 
under  surface.  The  contraction  of  this  muscle  throws  the  skin  of  the  forehead  into 
vertical  folds,  while  at  the  same  time  drawing  the  inner  half  of  the  eyebrow  upwards, 
it  produces  concentric  curved  folds  on  each  side  of  the  middle  line  of  the  forehead. 

2.  The  muscles  of  the  nose  comprise  five  small  muscles  proper  to  the  nose,  and 
one  common  to  the  nose  and  upper  lip :  the  pyramidalis  nasi,  compressor  naris. 
dilatores  naris  (anterior  and  posterior),  depressor  alee  nasi,  and  levator  labii 
superioris  alseque  nasi.     They  are  all  small  and  feeble. 

The  pyramidalis  nasi  arises  from  the  occipito-fron talis  muscle  and  the  skin 
over  the  glabella ;  it  is  inserted  into  a  membrane  stretching  over  the  nose,  which 
also  gives  attachment  to  the  compressor  naris. 

The  compressor  naris  (m.  nasalis)  arises  by  a  -narrow  origin  I'rom  the  superior 
maxilla,  under  cover  of  the  levator  labii  superioris  alseque  nasi.  It  passes  forwards 
over  the  bridge  of  the  nose,  and  ends  in  a  membranous  insertion  common  to  it  and 
the  previous  muscle. 

The  dilatores  naris  are  feeble  muscular  slips  placed  on  the  outer  side  of  the 
margin  of  the  nostril,  one  anteriorly,  the  other  posteriorly. 

The  depressor  alse  nasi  is  a  small  muscle  arising  from  the  upper  part  of  the 
incisor  fossa  of  the  maxilla ;  it  divides  into  two  parts  as  it  passes  upwards  and 
inwards,  and  is  inserted  into  the  ala  and  the  septum  of  the  nose  (depressor  septi). 

The  levator  labii  inferioris  alseque  nasi  is  a  narrow  band  arising  from  the  root 
of  the  nasal  process  of  the  maxilla.  It  descends  alongside  the  nose,  and  is  inserted 
partly  into  the  ala  of  the  nose  and  partly  into  the  orbicularis  oris  muscle. 

3.  The  muscles  of  the  mouth  comprise  eleven  muscles,  of  which  all  but  one, 
the  orbicularis  oris,  are  bilaterally  placed.  The  muscles  are  :  levator  labii  superioris 
alseque  nasi,  levator  labii  superioris,  levator  anguli  oris,  zygomatici  (major  and 
minor),  risorius,  orbicularis  oris,  depressor  anguli  oris,  depressor  labii  inferioris, 
levator  menti,  and  buccinator. 

The  orbicularis  oris  is  the  sphincter  muscle  surrounding  the  lips.  It  is  con- 
tinuous with  the  other  mu.scles  converging  to  the  mouth.  It  lies  between  the  skin 
and  mucous  membrane  of  the  mouth,  and  is  limited  above  by  the  nose,  below  by 
the  junction  of  lower  lip  and  chin.  Its  mesial  fibres  are  attached  above  to  the 
septum  of  the  nose  (naso-labial  band)  and  to  the  incisor  fossa  (superior  incisive 
bundle) ;  below  they  are  attached  to  the  lower  jaw  on  each  side  of  the  symphysis 
(inferior  incisive  bundle).  These  bundles  radiate  outwards  to  join  the  rest  of  the 
muscle,  which  is  joined  at  its  margin  by  the  levators  and  depressors  of  the  lower 
lip  and  angle  of  the  mouth,  and  by  the  buccinator  muscle.  The  loiver  fibres  of  the 
muscle  are  continued  laterallv  into  the  buccinator  and  levator  ano-uli  oris ;  its 
v/pper  firres  are  continued  into  the  buccinator  and  depressor  anguli  oris. 

The  levator  labii  superioris  aleeque  nasi  has  already  been  described. 

The  levator  labii  superioris  arises  from  the  superior  maxilla  just  above  the 
infra-orbital  foramen.  It  passes  almost  vertically  downwards  to  join  the  orbi- 
cularis oris  and  the  skin  of  the  upper  lip  between  the  attachments  of  the  levator 
labii  superioris  alyxjue  nasi  and  the  levator  anguli  oris.  It  conceals  the  infra- 
orbital vessels  and  nerve. 

The  levator  anguli  oris  arises  from  the  canine  fossa  of  the  upper  jaw  below  the 
infra -orbital  foramen  and  under  cover  of  the  foregoing  muscle.     It  is  directed 
outwards  and  downwards,  to  be  inserted  into  the  orbicularis  oris  and  the  skin  at 
the  angle  of  the  mouth. 
29  a 


404  THE  MUSCULAE  SYSTEM. 

The  zygomatici  (major  and  minor)  are  more  superficial  tlian  the  preceding 
muscle. 

The  zygomaticus  minor  is  the  anterior  muscle.  It  arises  from  the  malar  bone, 
and  is  often  continuous  with  the  most  peripheral  fibres  of  the  orbicularis  palpe- 
brarum. It  is  directed  obliquely  downwards  and  forwards  over  the  levator  anguli 
oris,  to  be  inserted,  along  with  the  levator  labii  superioris,  into  the  orbicularis  oris. 
The  zygomaticus  major  is  a  narrow  muscular  Ijaud  whicli  arises  from  the  malar 
portion  of  the  zygomatic  arch.  It  passes  to  the  angle  of  the  mouth,  to  be  inserted 
partly  into  the  skin,  partly  into  the  orbicularis  oris. 

The  risorius  is  a  thin  flat  muscle  which  forms  in  part  a  continuation  of  the 
platysma  myoides  on  the  face,  in  part  a  separate  muscle,  with  an  origin  from  the 
masseteric  fascia.  It  passes  transversely  forwards,  to  be  inserted  at  the  angle  of 
the  mouth  into  the  orbicularis  oris  and  skin. 

The  depressor  anguli  oris  arises  from  the  external  oblique  line  of  the  lower  jaw 
and  from  the  platysma  myoides  (Fig.  319,  p.  407).  It  is  triangular  in  form,  its 
fibres  converging  to  the  angle  of  the  mouth,  where  they  are  inserted  into  the 
orbicularis  oris  and  the  skin.  Some  of  the  fibres  reach  the  upper  lip  through  the 
orbicularis  muscle. 

The  depressor  labii  inferioris  arises  from  the  outer  surface  of  the  lower  jaw 
beneath  and  internal  to  the  depressor  anguli  oris  (Fig.  319,  p.  407).  It  is'' quadri- 
lateral in  form,  and  is  directed  upwards,  to  be  inserted  into  the  orbicularis  oris  and 
the  skin  of  the  lower  lip.  Its  external  fibres  conceal  the  mental  foramen,  and  are 
overlapped  by  the  depressor  angvili  oris.  Its  internal  fibres  join  with  those  of  the 
opposite  muscle. 

The  levator  menti  is  a  small  muscle  which  arises  from  the  incisor  fossa  of  the 
lower  jaw  (Fig.  319,  p.  407),  and  passing  forwards,  is  inserted  into  the  skin  of 
the  chin. 

The  buccinator  muscle  forms  the  lateral  wall  of  the  mouth,  and  is  in  series 
posteriorly  with  the  constrictor  muscles  of  the  pharynx.  It  arises  (1)  from  the 
alveolar  arches  of  the  upper  and  lower  jaws  (Fig.  319,  p.  407),  and  between  these 
attachments,  from  the  pterygo- mandibular  ligament.  Its  fibres  are  directed 
forwards  to  the  angle  of  the  mouth,  where  they  blend  with  the  corresponding 
(upper  and  lower)  portions  of  the  orbicularis  oris  muscle.  The  middle  fibres  of  the 
muscle  decussate  at  the  angle  of  the  mouth,  so  as  to  pass,'  the  lower  set  to  the 
upper  lip,  the  upper  set  to  the  lower  lip.  The  buccinator  is  covered  on  its  deep 
surface  by  the  mucous  membrane  of  the  mouth.  Superficially  it  is  concealed  by 
the  muscles  above  mentioned,  which  converge  to  the  angle  of  the  mouth ;  it  is 
separated  from  the  masseter  by  the  suctorial  pad  of  fat ;  it  is  pierced  by  the  duct 
of  the  parotid  gland,  and  by  branches  of  the  long  buccal  nerve. 

Neeve-Supply. 

The  facial  and  scalp  muscles  are  all  innervated  by  the  facial  nerve.  The  jwsferto?-  auricular 
branch  supplies  the  retrahens  aurem  and  occij^italis  ;  the  branches  forming  the  pes  anserinus 
supply  the  frontalis,  attollens,  and  attrahens  aurem,.  the  several  muscles  associated  with  the 
apertures  of  the  eye,  nose,  and  mouth  (incliiding  the  buccinator),  and  the  platysma  myoides. 

Actions. 

The  almost  iirfinite  variety  of  facial  expression  is  produced  j)artly  by  the  action  of  these 
muscles,  partly  by  their  inactivity,  or  by  the  action  of  antagonising  muscles  (antithesis).  On  the 
one  hand  joy  is,  for  example,  betrayed  by  the  action  of  one  set  of  muscles,  while  grief  is  accom- 
panied by  the  contraction  of  another  (opposing)  set.  Determination  or  eagerness  is  accompanied 
by  a  fixed  exjaression  due  to  a  combination  of  muscles  acting  together ;  despair,  on  the  other 
hand,  is  expressed  by  a  relaxation  of  muscular  action.  For  a  philosojjhical  account  of  the  action 
of  the  facial  muscles,  the  student  should  consult  Darwin's  Expression  of  the  Emotions  in  Man  and 
Animals,  and  Duchenne's  Mechanisme  de  Ice  Physiologie  humaine. 

The  platysma  myoides  retracts  and  depresses  the  angle  of  the  mouth,  and  de^^resses  the  lowe 
jaw.  The  occipito- frontalis,  by  its  anterior  belly,  raises  the  eyebrows  ;  both  bellies  acting 
together  tighten  the  skin  of  the  scalp ;  acting  along  with  the  oi'bicularis  palpebrarum,  it  shifts 
the  scalp  backwards  and  forwards.  The  corrugator  supercilii  draws  inwards  the  eyebrow 
and  vertically  wrinkles  the  skin  of  the  foreliead.  The  pyramidalis  nasi  draws  cloA^oiwards  the 
skin  between  the  eyebrows,  as  in  frowning.  The  ujDper  eyelid  is  raised  by  the  levator  palpebrse 
superioris.     The  closure  of  the  lids  is  effected  by  the  orbicularis  palpebrarum,  whose  fibres  also 


FASCIA  AND  MUSCLES  OF  THE  CEBIT. 


405 


Levator  p^LPEKRyE  .superioris 
Rectus  superior 

OBLiQDUb  Superior 

Rectus  inteknus 


Rectus  externus 
Obliquus  infeeiok 


Rectus  inferior 


assist  in  the  lowering  of  the  eyebrows,  in  the  protection  of  the  eyeball,  and,  by  pressure  on 
tlie  lachrymal  gland,  in  the  secretion  of  tears.  The  tensor  tarsi,  acting  along  with  the  orbicularis 
palpebrarum,  compresses  the  lachrymal  sac  and  aids  in  the  passage  of  its  contents  into  the  nasal 
duct.  The  muscles  of  the  ear  and  nose  have  quite  rudimentary  actions  expressed  by  their 
names.  Of  the  muscles  of  the  moutli,  the  orbicularis  oris  has  a  comjilex  action,  depending  on  the 
degree  of  contraction  of  its  component  j)arts.  It  causes  compression  and  closure  of  the  lips  in 
various  ways,  tightening  the  lips  over  the  teeth,  contracting  them  as  in  osculation,  or  causing 
pouting  or  jarotrusion  of  one  or  the  other.  The  accessory  muscles  of  the  lips  draw  them  upwards 
(zygomatici,  levator  anguli  oris,  levator  labii  superioris  alseque  nasi,  levator  labii  superioris), 
outwards  (zygomaticus  major,  risorius,  platysma,  depressor  anguli  oris,  buccinator),  and  down- 
wards (depressor  anguli  oris,  depressor  labii  inferioris,  platysma).  The  levator  menti  elevates  the 
skin  of  the  chin  and  protrudes  the  lower  lip.  The  buccinator  retracts  the  angles  of  the  mouth, 
flattens  the  cheeks,  and  brings  them  in  contact  with  the  teeth. 

The  Fascia  and  Muscles  of  the  Oebit. 

Tlie  eyeball  with  its  muscles,  vessels,  and  nerves,  is  lodged  in  a  mass  of  soft 
and  yielding  fat  which  entirely  fills  up  the  cavity  of  the  orbit.  Surrounding 
the  posterior  part  of  the  eye- 
ball is  the  capsule  of  Tenon, 
which  constitutes  a  large 
lymph  space  or  synovial 
bursa  in  relation  to  the  eye- 
ball. Anteriorly  the  capsule 
is  in  contact  with  the  con- 
junctiva, and  intervenes 
between  the  latter  and  the 
eyeball;  posteriorly  it  is 
pierced  by  and  prolonged 
along  the  optic  nerve.  It  is 
a  smooth  membrane  connected 
to  the  globe  of  the  eye  by 
loose  areolar  tissue.  It  is 
pierced  by  the  tendons  of  the 
ocular  muscles,  along  which  it  sends  prolongations  continuous  with  the  muscular 

sheaths. 

The  muscles  of  the  orbit  are  seven 
in  number :  one,  the  levator  palpebrse 
superioris,  belongs  to  the  upper  eyelid ; 
the  other  six  are  muscles  of  the  eyeball. 
The  levator  palpebrae  superioris 
lies  immediately  beneath  the  orbital 
periosteum  and  covers  the  superior 
rectus  muscle.  It  has  a  narrow  origin 
above  that  muscle  from  the  margin 
of  the  optic  foramen.  It  expands  as  it 
passes  forwards,  to  end,  in  relation  to 
the  upper  lid,  in  a  membranous  ex- 
pansion which  is  inserted  in  a  fourfold 
manner:  (1)  slightly  into  the  orbicularis 
palpebrarum  and  skin  of  the  upper 
lid,  (2)  mainly  into  the  upper  border  of 
the  tarsal  cartilage,  (3)  slightly  into  the 
conjunctiva,  and  (4)  by  its  edges  into 
the  upper  border  of  the  margin  of  the 
orbital  opening. 

The  recti  muscles  are  four  in 
number — superior,  inferior,  internal,  and 
external.  .  They  all  arise  from  a  mem- 
branous ring  surrounding  the  optic 
foramen,  which  is  separable  into  two 
giving  origin    to  the   superior   and  internal 


Fig.  315. — Transverse  Vertical   Section   through   the   Orbit 
BEHIND  the  Eyeball  to  show  the  Arrangement  of  Muscles. 


Orbicularis  palpebrarum 


Lbvatoh  i'Ai,pi;iiR/ij; 

SUPEBIf)IUM 


FKi.  :',](■>.- 


-The  Muscles  ok 
(from  aljovc). 


THE    OlIlilT 


parts - 


-a   superior 
2^h 


common    tendon, 


406 


THE  MUSCULAE  SYSTEM. 


recti  and  the  upper  head  of  the  external  rectus ;  and  an  inferior  common  tendon, 
giving  origin  to  the  internal  and  inferior  recti  and  the  lower  head  of  the  external 
rectus.  The  two  origins  of  the  external  rectus  muscle  are  separated  by  the  passage 
into  the  orbit  of  the  oculo-motor,  nasal,  and  abducent  nerves.  Fornung  flattened 
bands  which  traverse  the  fat  of  the  orbit  around  the  optic  nerve  and  eyeball,  the 

four     muscles    end 


ObLKJUUS  SUl  I  RIOR 

\ 


Lr:\  AfOR  PALPEBRiE  SUPERIORIS  (cUt) 
RlCTUS  SUPERIOR 

Reltus  extern  us 

Oculo-motor 
nerve 


Abducent  nerve 


Rectus  inj'erior 


in  tendons  which 
pierce  the  capsule 
of  Tenon,  and  are 
inserted  into  the 
sclerotic  about  eight 
millimetres  (three 
to  four  hnes)  behind 
the  margin  of  the 
cornea.  The  sup- 
erior and  inferior 
recti  are  inserted  in 
the  vertical  plane 
slightly  internal  to 
the  axis  of  the  eye- 
ball ;  the  external 
and  internal  recti  in 
the  transverse  plane 


Obliquus  inferior 
Fig.  317. — The  Muscles  of  the  Orbit  (from  without) 

of  the  eyeball ;  and  all  are  attached  in  front  of  the  equator  of  the  eyeball. 

The  obliquus  superior  arises  from  the  margin  of  the  optic  foramen  between 
the  recti  superior  and  internus.  It  passes  forwards  as  a  narrow  muscular  band 
internal  to  the  rectus  superior,  and  at  the  anterior  margin  of  the  orbit  forms  a 
narrow  tendon  which  passes  through  a  special  fibrous  pulley  (trochlea)  attached 
to  the  roof  of  the  orbit.     Its  direction   is  then  altered,  and  passing  outwards 


Lachrymal  giand 


Frontal  nerve 


Supra-orbital  nerve 


Lachrymal  nerve. 


Nerves  to  rectus  superior  and 

levator  palpebral  superioris, 

from  oculo-motor  nerve 

Trochlear  nerve 


Rectus  externus' 


Abducent  nerve 

Oculo-motor  nerve  (Inferioi 
division) 

Lenticular  ganglioi 

Nerve  to  rectus  inferior,  from 

oculo-motor  nervu 

Nerve  to  obliquus  inferior, 

from  oculo-motor  nerve 


Supra-troclilear  nerve 

Levator  palpebr-e 

superioris 
.Rectus  superior 

— Obliquus  superior 

Nasal  nerve 

Infra-trochlear  nerve 

Rectus  internus 

Nerve  to  rectus  internus  from 

oculo-motor 

.Ophthalmic  artery 

Optic  nerve 
^         -  -Long  ciliary  nerves 

Rectus  inferior 


Fig.  318. 


Obliquus  inferior 
-Schematic  Representation  of  the  Nerves  which  traverse  the  Cavity  of  the  Orbit. 


between  the  tendon  of.  the  superior  rectus  and  the  eyeball,  it  is  inserted  into  the 
sclerotic  between  the  superior  and  external  recti,  midway  between  the  margin  of 
the  cornea  and  the  entrance  of  the  optic  nerve. 

The  obliquus  inferior  arises  from  the  inner  side  of  the  floor  of  the  orbit  just 
behind  its  anterior  margin,  and  external  to  the  naso-lachrymal  groove.  It  forms 
a  slender  rounded  slip,  which  curls  round  the  inferior  rectus  tendon,  and  passes 
between  the  external  rectus  and  the  eyeball,  to  be  inserted  into  the  sclerotic 
between  the  superior  and  external  recti,  and  farther  back  than  the  superior 
oblique  muscle. 

Miiller's  muscle  is  a  rudimentary  bundle  of  non-striated  muscular  fibres  bridging  across  the 


MUSCLES  OF  MASTICATION. 


407 


splieno-maxillary  fissure  and  infra-orbital  groove.     It  is  supplied  by  fibres  from  the  sympathetic, 
and  may  have  a  slight  influence  in  the  protrusion  of  the  eyeball. 

Nerve-Supply. 

The  muscles  of  the  orbital  cavity  are  supplied  by  the  third,  fourth,  and  sixth  cranial  nerves. 
The  fourth  nerve  (trochlearis)  supplies  the  obliquus  superior ;  the  sixth  (abducens)  supplies  the 
rectus  externus  ;  the  third  nerve  (motor  oculi)  suj)plies  the  others — levator  palpebras  superioris, 
recti,  superior,  inferior  and  internus,  and  obliquus  inferior. 

Actions. 

The  levator  palpebrae  superioris  elevates  the  uj^per  eyelid  and  antagonises  the  orbicularis 
palpebrarum  muscle.  The  six  muscles  inserted  into  the  eyeball  serve  to  move  the  longitudinal 
axis  of  the  eyeball  upwards,  downwards,  inwards,  and  outwards,  besides  causing  a  rotation  of  the 
eyeball  on  its  own  axis.  The  following  table  expresses  the  action  of  individual  muscles.  It  must 
be  remembered  that,  while  similar  movements  occur  simultaneously  in  the  two  eyeballs,  the 
horizontal  movements  may,  by  adduction  of  the  muscles  of  both  sides,  cause  convergence  of  the 
axes  of  the  two  eyeballs  for  the  purposes  of  near  vision. 


a.  Adduction       and      Abduction. 

Rectus  internus 
Rectus  superior) 
Rectus  inferior  / 

Rectus  externus 

Obliquus  superior  \  {correcting 

Obliquus  inferior  J  adductors) 

h.  Elevation       and      Depression. 

Rectus  superior 
Obliquus  inferior 

Rectus  inferior 
Obliquus  superior 

c.  Rotation  outwards.                                 Rotation  inwards. 

0blic|uus  inferior 

Obliquus  superior 

Rectus  superior \,.       ,,     ,.    , 

Rectus  inferior  1^'^^^'^^^^^*^'^) 

Muscles  of  Mastication. 


comprise   the   masseter,   temporal,  external  and 


Temporal  (part 
of  insertion)" 


External  Ptery- 
goid (insertion)"" 


The  muscles  of  mastication 
internal  pterygoids, 
and  buccinator  (de- 
scribed above). 

The  masseter 
has  an  origin  which 
is  partly  tendinous 
and  partly  fleshy.  It 
arises  in  two  parts  : 
(1)  superficially  from 
the  lower  border  of 
the  zygoma  in  its 
anterior   two-thirds.  ^^^^^^^^^^ 

and  (2)  more  deeply  anguii  oris(oryni) 
from  the  deep  or 
inner  surface  of  the 
zygoma  in  its  whole 
length.  The  super- 
ficial fibres  are 
directed  downwards 
and  backwards  to- 
wards  the  angle  of 

tFu;  jaw ;  the  deeper  fibres  are  directed  vertically  downwards.  The  muscle  is 
inserted  by  fieshy  and  tendinous  fibres  into  the  outer  surface  of  the  ramus  and 
angle  of  the  lower  jaw  and  the  coronoid  process  (Fig.  319,  p.  407).  The  deepest 
fibres  blend  with  the  fibres  of  the  subjacent  temporal  muscle. 


Depressor  labu 

inf'eriori.s  (origin) 

Levator  menti 

(origin) 

Platysma 

(in.sertion) 


Fig.  319. — Muscle-Attachments  to  the  Outer  Aspect  of  the  Lower  Jaw. 


408 


THE  MUSCULAE  SYSTEM. 


The  masseter  muscle  occupies  the  posterior  part  of  the  cheek.     It  is  covered  by 
the  parotid  gland,    and  is  crossed   by   Stenson's  duct   and    the    branches    of   the 


Epicranial  aponeurosis  ^ 


Temporal  fascia 


Temporal  fascia 


occipito-frontalis 
Temporal  muscle 


Superficial  temporal 
artery 


Masseter  (deep  fibres). 


Parotid  gland 

(drawn  backwards- 

and  downwards) 


Auriolo-temporal        Wv\\\wv  . 


Orbicularis 
palpebrarum 


— Zygomaticus  major 


Masseter  (superficial 

fibres) 

Stenson's  duct 


Buccinator 
Depressor  anguli  oris 


Facial  artery 


Fig.  320. — Muscles  of  Mastication  (superficial  view). 

facial  nerve.     It  conceals  the  lower  jaw  and  a  part  of  the  temporal  muscle,  and  is 
separated  from  the  buccinator  muscle  anteriorly  by  a  pad  of  fat. 

The  temporal  mus- 
cle is  a  fan  -  shaped 
muscle  arising  from  the 
whole  area  of  the 
temporal  fossa,  as  well 
as  from  the  temporal 
fascia  which  covers  it. 
Its  converging  fibres 
pass  beneath  the  zygo- 
matic arch.  In  the 
pterygoid  region  the 
muscle  is  inserted,  into 
the  deep  surface  and 
apex  of  the  coronoid 
process,  and  into  the 
anterior  border  of  the 
ramus  of  the  lower  jaw 
(Figs.  319,  p.  407,  and 
321,  p.  408). 

The  muscle  is  con- 
cealed by  the  temporal 
fascia,  zygoma,  the  mas- 
It  crosses  over  the  external  pterygoid 


Fig.  321. 


-Muscle-Attachments  on  the  Inner  Side  of  the 
Lower  Jaw. 


seter  muscle,  and  the  coronoid   process, 
muscle  and  the  internal  maxillary  artery. 

The  external  pterygoid  muscle  arises  by  t^vo  heads,  upper  and  lower.  The 
upper  head  is  attached  to  the  under  surface  of  the  great  wing  of  the  sphenoid ;  the 
lower  head  takes  origin  from  the  outer  surface  of  the  external  pterygoid  plate.     The 


MUSCLES  OF  MASTICATION. 


409 


muscle  is  directed  outwards  and  backwards,  to  be  inserted  into  (1)  the  depression  in 
front  of  the  neck  of  the  lower  jaw  (Figs.  319,  p.  407,  and  321,  p.  408),  and  (2;  the 
inter-articular  fibro-cartilage  and  capsule  of  the  temporo-maxillary  articulation. 


Temporal  muscle 


Auriculo-temporal 
nerve 


Superficial  temporal 
artery 


External  pterygoid 

Nerve  to  masseter 

Parotid  gland 

Massetee  (cut) 


Posterior  dental 
nerve 


Long  buccal  nerve 
Stenson's  duct. 


Buccinator 

MUSCLE 


Fig.  322. — Muscles  of  Mastication,  Deeper  View  (zygoma  aud  masseter  muscle  removed). 

The  muscle  is  placed  deeply  in  the  pterygoid  region.     Covered  by  the  temporal 
muscle  and  coronoid  process,  it  partially  conceals  the  internal  pterygoid  muscle 


Epicranial  aponeurosis.' 


Temporal  muscle- 


Temporal  branch  ol 
buccal  nerve 
\  Temporal  brandies  of 
/  inferior  maxillary  nerve 


Auriculo-temporal  nerve 

Superficial  temporal 

artery 

External  carotid  artery 

Internal  lateral  ligament 

Posterior  auricular  artery 

Lingual  nerve 

Mylo-byoid  iiervo' 

Parotid  gland 

Inf<;rior  detital  nerve 
MAssF/rEii  (cut/ 


External  pterygoid 

Posterior  dental  artery 

Posterior  dental  nerve 

Long  buccal  nerve 
Pterygo-nmndibular 


Mental  branch  of  inferior 
dental  nerve 


Fl(i.   323.  — PTEHYflOlU   Keoion. 


and  the  trunk  and  branches  of  the  inferior  maxillary  nerve.  The  internal  maxillary' 
artery  passes  over  or  under  th(;  muscle,  and  disapjicars  between  its  two  heads  of 
origin  on  its  way  to  the  s])b(;no-maxillary  fossa. 


410  THE  MUSCULAE  SYSTEM. 

The  internal  pterygoid  muscle  has  likewise  a  double  origin — (1)  from  the  deep 
surface  of  the  external  pterygoid  plate  and  the  tuberosity  of  the  palate,  and  (2) 
by  a  stout  tendon  from  the  tuberosity  of  the  upper  jaw.  Its  two  heads  of  origin 
embrace  the  lower  hbres  of  the  external  pterygoid  muscle.  It  is  quadrilateral  in 
form,  and  is  directed  downwards,  outwards,  and  backwards,  to  be  inserted  into  a 
triangular  impression  on  the  inner  surface  of  the  lower  jaw,  between  the  mylo- 
hyoid groove  and  the  angle  of  the  bone  (Fig.  321,  p.  408). 

The  muscle  is  covered  over  by  the  external  pterygoid  muscle,  by  branches  of 
the  inferior  maxillary  nerve,  and  by  the  internal  lateral  ligament  and  ramus  of 
the  lower  jaw.  Beneath  it  are  the  Eustachian  tube,  muscles  of  the  soft  palate,  and 
the  pharynx  (superior  constrictor). 

Nerve-Supply. 

The  inferior  maxillary  division  of  tlie  fifth  nerve  su^jplies  all  the  muscles  of  mastication 
except  the  buccinator,  which  is  sui^plied  by  the  facial  nerve.  The  internal  jDterygoid  muscle  is 
supplied  by  the  nerve  before  its  division  into  anterior  and  posterior  parts ;  the  other  muscles  are 
innervated  by  the  anterior  trunk. 

Actions. 

The  above  muscles,  assisted  by  others  in  the  neck,  produce  the  various  movements  of  the 
lower  jaw,  as  follows  : — 


a.  Opening        and        Closure  of  the  Jaw. 


Weight  of  the  jaw 

Digastric 

Mylo-hyoid 

Genio-hyoid 

Genio-hyo-glossus 

Infra -hyoid  muscles 


Masseter 
Temporal 
Internal  pterygoid 


h.  Protrusion        and        Retraction. 


External  pterygoid 
Internal  pterygoid 
Temporal  {anterior  fibres) 


Temporal  {posterior  fibres) 


c.  Lateral  Movement  of  the  Jaw. 


External  pterygoidj^^^^^^^.^^^ 


Internal 


THE  MUSCLES   OF   THE  NECK. 

The  muscles  in  the  neck  include,  in  addition  to  those  included  in  the  description 
of  the  muscles  of  the  back  (p.  395),  the  following  series :  (1)  sterno-cleido- 
mastoid ;  (2)  the  muscles  of  the  hyoid  bone  (supra-hyoid  and  infra-hyoid) ;  (3)  the 
muscles  of  the  tongue  (extrinsic  and  intrinsic) ;  (4)  the  muscles  of  the  pharynx  and 
soft  palate  ;  and  (5)  the  prasvertebral  muscles. 

The  sterno-cleido-mastoid  muscle  is  the  prominent  muscle  projecting  on  the 
side  of  the  neck.  It  arises  by  two  heads — (1)  a  narrow  tendinous  sternal  head, 
from  the  anterior  surface  of  the  manubrium  sterni  (Fig.  246,  p.  322),  and  (2)  a 
broader  clavicular  origin,  partly  tendinous,  partly  fleshy,  from  the  upper  surface  of 
the  clavicle  in  its  inner  third  (Fig.  243,  p.  319).  The  muscle  is  inserted  into  the 
outer  surface  of  the  mastoid  process  and  into  the  superior  curved  line  of  the  occipital 
bone  (Fig.  324,  p.  411). 

The  sterno-cleido-mastoid  muscle  stretches  obliquely  across  the  neck,  and 
separates  the  anterior  and  posterior  triangles  from  one  another.  Superficially  it 
is  covered  by  the  platysma  myoides  muscle,  the  external  jugular  vein,  and  some 
of  the  superficial  branches  of  the  cervical  plexus.  It  conceals  the  splenius  capitis, 
digastric,  levator  anguli  scapulse,  scaleni   and   infra-hyoid   muscles,  the   carotid 


THE  MUSCLES  OF  THE  HYOID  BONE. 


411 


sheath,  the  cervical  plexus,  and  the  spinal  accessory  nerve.     The  last-named  nerve 
pierces  the  muscle. 

The  sterno-cleido-mastoid  muscle  is  properly  divisible  into  tliree  parts  :  (1)  sterno -mastoid, 
placed  superficially,  and  passing  obliquely  from  the  sternum  to  the  mastoid  process  ;  (2)  cleido- 
mastoid,  placed  more  deeply,  and  directed  vertically  upwards  from  the  clavicle  to  the  mastoid 


Complexus  (insertion) 


Rectus  capitis  posticus  minor 
(insertion) 


Rectus  capitis  posticus  major 
(insertion' 


Trapezius  (origin) 


Sterno-cleido-mastoid 
(insertion) 


Splenius  capitis 
insertion) 


Obliquus  superior  (insertion)' 


Rectus  capitis  lateralis  (inseition) 

Rectus  capitis  anticus  mmor  (mseition) 


Superior  constrictor  of  pharynx  (insertion) 


Rectus  capitis  anticus  major  (mseition)- 

FiG.  324. — Muscle-Attachments  to  Occipital  Bone  (Inferior  Surface). 

process  ;  and  (3)  cleido-occipitalis,  passing  obliquely  upwards  and  backwards  behind  the  cleido- 
mastoid  to  the  suj^erior  curved  line  of  the  occipital  bone. 

The  sterno-mastoid  muscle  is  innervated  by  the  spinal  accessory  nerve,  joined  by  a  branch 
from  the  cervical  plexus  (C.  2). 

The  action  of  the  muscle  is  referred  to  below. 


The  Muscles  of  the  Hyoid  Bone. 

The  muscles  attached  to  the  hyoid  bone  are  in  three  series :  (1)  infra-hyoid 
muscles,  connecting  the  hyoid  bone  to  the  scapula,  thorax,  and  thyroid  cartilage ; 

(2)  supra-hyoid  muscles,  connecting  it  to  the  lower  jaw,  cranium,  and  tongue ;  and 

(3)  the  middle  constrictor  muscle  of  the  pharynx. 

The  infra-hyoid  muscles  comprise  the  omo-hyoid,  sterno-hyoid,  sterno-thyroid, 
and  thyro-hyoid  muscles. 

The  omo-hyoid  is  a  muscle  with  two  bellies,  anterior  and  posterior.  The 
posterior  belly  arises  from  the  superior  border  of  the  scapula  and  the  suprascapular 
ligament  (Fig.  250,  p.  325).  It  forms  a  narrow  muscular  band,  which  is  directed 
obliquely  forwards  and  upwards,  to  end  in  an  intermediate  tendon  beneath  the 
sterno-mastoid  muscle.  From  this  tendon  the  anterior  belly  proceeds  upwards  to 
be  inserted  into  the  outer  part  of  the  lower  border  of  the  body  of  the  hyoid  bone. 

The  posterior  belly  of  the  muscle  separates  the  posterior  triangle  into  occipital 
and  subclavian  parts ;  the  anterior  belly  crosses  the  common  carotid  artery  at  the 
level  of  the  cricoid  cartilage,  and  in  the  anterior  triangle  forms  the  boundary 
between  the  muscular  and  carotid  triangles.  A  process  f)f  the  deep  cervical  fascia 
binds  down  tlie  tendon  and  tlio  ]K)sterior  belly  to  the  scapula  and  the  first  rib. 

The  sterno-hyoid  muscle  arises  from  the  ])OSterior  surface  of  the  presternum, 
from  the  back  of  the  first  costal  cartilage,  and  from  the  clavicle  (Fig.  243,  p.  319). 
It  passes  vertically  upwards  in  tlie  neck,  internal  to  the  omo-hyoid  and  in  front  of 
the  sterno-thyroid  nmscle,  to  be  inserted  into  the  inner  part  of  the  body  of  the 


412 


THE  MUSCULAK  SYSTEM. 


hjoid  bone.  Except  near  its  origin  the  muscle  lies  superficially  in  the  anterior 
triangle,  alongside  the  omo-liyoid  and  in  front  of  the  steruo-thyroid  and  thyro- 
hyoid muscles,  the  trachea  and  the  thyroid  body. 

The  sterno-thyroid  muscle  arises  beneath  the  sterno-hyoid  from  the  back  of 
the  presternum  and  first  costal  cartilage.  Broader  than  the  preceding  muscle,  it 
passes  upwards  and  slightly  outwards  in  the  neck  in  front  of  the  trachea  and 
thyroid  body,  and  beneath  the  omo-hyoid  and  sterno-hyoid  muscles,  to  be  inserted 

Hyiioglossal  nerve    Vagus  nerve 
Recurrent  branch     |      |        Superior  cervical  ganglinn  of  the  sympathetic 

First  cervical  nerve 


Second  cervical  nerve 


Glosso-pharyngeal 
nerve 


Third  cervical  nerve 

Stylo-pharyngeus  ^ ^^  _        ^ 

Hyg-glossus 

g  enio-hyo-glossus 


Pharyngeal  branch  of  vagus 

Digastric- 

Descendens  liypo-glossi- 

Middle  constrictor. 
Descendens  cervicis. 

Internal  laryngeal  nerve^^ 
Ansa  hypoglossi 
Inferior  constrictor' 


Omo-hyoid 


Gf.nio-hyoid 
Mylo-hyoid  (cut) 
Digastric 

Thyro-hyoid 


Fig.  .325. — The  Mcscles  of  the  Hyoid  Bone  and  Styloid  Process,  and  the  Extrinsic  Muscles 

OF  THE  Tongue,  with  their  Nerves. 


into  the  oblique  line  of  the  thyroid  cartilage.     The  muscle  is  marked  by  an  oblique 
tendinous  intersection  in  the  middle  of  its  length. 

The  thyro-hyoid  muscle  continues  the  line  of  the  preceding  muscle  to  the 
hyoid  bone.  Short  and  quadrilateral,  it  arises  from  the  oblique  line  of  the  thyroid 
cartilage,  and  passing  over  the  thyro-hyoid  membrane  beneath  the  omo-hyoid  and 
sterno-hyoid,  it  is  inserted  into  the  body  and  great  cornu  of  the  hyoid  bone. 

The  levator  glandulse  thyroidese  is  an  occasional  slip  stretching  between  the  hyoid  l^one 
and  the  isthmus  or  pyramid  of  the  thyroid  body. 

The  supra-hyoid  muscles  comprise  the  digastric,  stylo-hyoid,  mylo-hyoid, 
genio-hyoid  muscles,  and  also  two  muscles,  the  genio-hyo-glossus  and  hyo-glossus, 
which  will  be  described  along  with  the  extrinsic  muscles  of  the  tongue. 


THE  MUSCLES  OF  THE  HYOID  BONE. 


413 


The  digastric  muscle,  as  its  name  implies,  possesses  two  bellies — anterior  and 
posterior.  The  posterior  belly  arises  from  the  digastric  groove  beneath  the  mastoid 
process.  It  is  directed  forwards  and  downwards  to  end  in  an  intermediate  tetidon, 
which  is  connected  by  a  pulley-like  band  of  cervical  fascia  to  the  body  of  the  hyoid 
bone.  The  anterior  belly  of  the  muscle  is  directed  forwards  and  upwards  to  the 
chin,  and  is  inserted  into  an  oval  impression  on  the  lower  border  of  the  mandible 
close  to  the  symphysis  (Eig.  327,  p.  414).  The  muscle  forms  the  boundary  of  the 
submaxillary  space.     The  posterior  belly  is  concealed  at  its  origin  by  the  mastoid 


Sterno-cleido 

MASTOID 


Mylo-hyoid 

Digastric 

Hyoglossus 

Stylo-hyoid 

Middle  oonstrictok 

Thyro-hyoid 

Interior 

constrictor 

Omo-hyoid 

Inferior 
constrictor 

Stebno-hyoid 
I  Sterno-thyroid 


Fig,  326. — The  Triangles  of  the  Neck  (Muscles). 

process  and  the  muscles  attached  to  it.  In  company  with  the  stylo-hyoid  muscle 
it  crossas  the  carotid  vessels  and  the  hypoglossal  nerve  in  the  anterior  triangle. 
The  anterior  belly  of  the  digastric  covers  the  mylo-hyoid  muscle. 

The  stylo-hyoid  muscle  arises  from  the  styloid  process  of  the  temporal  bone 
near  its  Ijase,  and  is  inserted  into  the  body  of  the  hyoid  bone  by  two  slips  which 
enclose  the  tendon  of  the  digastric  muscle.  It  is  directed  downwards  and  forwards 
alongside  the  posterior  Ijclly  of  the  digastric,  and  crosses  the  anterior  triangle  in 
front  of  the  carotid  vessels. 

The  mylo-hyoid  muscle  arises  from  the  lower  three-fourths  of  the  mylo-hyoid 
ridge  of  tin-.  low(!r  jaw  (lug.  327,  p.  414),  It  is  directed  downwards  and  inwards, 
to  be  inserted  into  (1)  the  upper  border  of  the  body  of  the  hyoid  bone,  and  more 


414 


THE  MUSCULAE  SYSTEM. 


anteriorly  (along  with  the  opposite  muscle)  into  (2)  a  median  raphe  extending  from 
the  hyoid  bone  nearly  to  the  chin. 


External  Ptei-y- 
goifl  (insertion) 


Fig.  327.- 


-Muscle-Attach.ments  on  the  Inner  Side  of 
Lower  Jaw. 


The  muscle  forms  a  diaphragm  in  the  floor  of 
the  mouth,  and  has  in 
contact  with  its  super- 
ficial or  external  surface 
the  digastric  muscle  and 
the  submaxillary  gland. 
Its  deep  or  internal 
surface  is  partially 
covered  by  the  mucous 
membrane  of  the  floor 
of  the  mouth,  and  is 
separated  from  the  hyo- 
giossus  and  genio-hyo- 
giossus  muscles  by  the 
deep  part  of  the  sub- 
maxillary gland,  the 
sublingual  gland,  Whar- 
ton's duct  and  the  lingual 
and  hypoglossal  nerves. 
The  genio  -  hyoid 
muscle  arises  from  the 
lower  of  the  two  genial 
tubercles  on  the  back 
of  the  symphysis  of  the  lower  jaw  (Fig.  327,  p.  414).  It  is  directed  downwards 
and  backwards,  to  be  inserted  into  the  front  of  the  body  of  the  hyoid  bone.  The 
muscle  lies  along  the  lower  border  of  the  genio-hyoglossus,  and  is  concealed  by 
the  digastric  and  mylo-hyoid  muscles.  The  muscles  of  opposite  sides  are  often 
fused  together. 

The  Muscles  of  the  Tongue. 

The  muscular  substance  of  the  tongue  consists  of  two  symmetrical  series  of 
muscles  placed  on  either  side  of  a  membranous  raphe  in  the  middle  line.  It  is 
composed  of  (1)  extrinsic  muscles  arising  from  the  soft  palate,  styloid  process,  hyoid 
bone  and  lower  jaw,  and  (2)  intrinsic  muscles  proper  to  the  tongue  itself.  Each 
set  consists  of  foiir  series  of  muscles. 

The  extrinsic  muscles  are  four  in  number:  (1)  genio-hyo-glossus,  (2)  hyo- 
glossus,  (o)  stylo-glossus,  and  (4)  palato-glossus. 

The  genio-hyo-glossus  muscle  (Fig.  325)  is  an  extrinsic  muscle  of  the  tongue 
as  well  as  a  supra-hyoid  muscle.  It  is  a  fan-shaped  muscle  arising  by  its  apex 
from  the  upper  of  the  two  genial  tubercles  behind  the  symphysis  of  the  lower  jaw 
(Fig.  327,  p.  414).  From  this  origin  the  muscular  fibres  diverge ;  the  lowest  fibres 
are  directed  downwards  and  backwards,  to  be  inserted  into  the  body  of  the  hyoid 
bone;  the  highest  fibres  curve  forwards,  to  be  attached  to  the  tip  of  the  tongue; 
the  intermediate  fibres  are  attached  to  the  substance  of  the  tongue  in  its  whole 
length  between  the  base  and  tip.  The  muscles  of  opposite  sides  are  separated  by 
the  median  raphe  of  the  tongue.  On  the  outer  side  of  each  are  the  hyo-glossus  and 
mylo-hyoid  muscles.  Between  the  hyo-glossus  and  genio-hyo-glossus  are  placed  the 
stylo-hyoid  ligament,  the  lingual  artery,  and  the  glosso-pharyngeal  nerve. 

The  hyo-glossus  muscle  is  also  an  extrinsic  muscle  of  the  tongue  as  well  as  a 
supra-hyoid  muscle.  It  arises  from  the  hyoid  bone  (body  and  great  cornu),  and  is 
directed  upwards  and  forwards, to  be  inserted  into  the  side  ot  the  tongue,its  fibres  inter- 
lacing at  its  insertion  with  the  fibres  of  the  stylo-glossus.  The  muscle  is  quadrilateral, 
and  lies  between  the  genio-hyo-glossus  and  mylo-hyoid  muscles,  separated  from  the 
latter  by  the  mucous  membrane  of  the  floor  of  the  mouth,  the  sublingual  and  part 
of  the  submaxillary  glands,  the  lingual  and  hypoglossal  nerves,  and  Wharton's  duct. 

The  chondro-glossus  is  a  small  separated  slip  of  the  hyo-glossus,  not  always  jaresent. 

The  stylo-glossus  muscle  arises  beneath  the  parotid  gland  from  the  lower  end 


THE  MUSCLES  OF  THE  TONGUE. 


415 


of  the  styloid  process  and  from  the  stylo-mandibular  ligament.  It  sweeps  forwards 
and  inwards,  and  is  inserted  into  the  side  and  under  surface  of  the  tongue,  its 
fibres  spreading  out  to  decussate  with  those  of  the  palato-glossus  and  hyo-glossus 
muscles.  It  is  covered  by  the  internal  pterygoid  muscle  and  by  the  mucous 
membrane  of  the  tongue. 

The  palato-glossus  is  a  thin  sheet  of  muscular  fibres  arising  from  the  under 
surface  of  the  soft  palate,  where  it  is  continuous  with  fibres  of  the  opposite  muscle. 
It  passes  downwards  in  the  anterior  pillar  of  the  fauces,  and  spreads  out,  to  be  in- 
serted into  the  sides  of  the  tongue,  blending  with  the  stylo-glossus  and  the  deep 
transverse  fibres  of  the  tongue.  The  muscle  is  placed  directly  beneath  the  mucous 
membrane  of  the  soft  palate  and  tongue. 

Intrinsic  Muscles  of  the  Tongue. — Besides  receiving  the  fibres  of  insertion 
of  the  extrinsic  muscles,  the  substance  of  the  tongue  is  composed  of  four  intrinsic 
muscles  on  either  side,  two  in  the  sagittal  plane,  the  superior  and  inferior  linguales  ; 
two  in  the  coronal  plane,  the  transverse  and  vertical  fibres. 

The  superior  lingualis  muscle  extends  from  base  to  tip  of  the  tongue,  placed  on 
its  dorsum  immediately  under  the  mucous  membrane,  into  which  many  of  its  fibres 
are  inserted. 

The  inferior  lingualis  is  a  cylindrical  band  of  muscular  fibres  occupying  the  under 
part  of  the  organ  on  each  side,  in  the  interval  between  the  genio-hyo-glossus  and 
the  hyo-glossus  muscles.     Posteriorly  some  of  its  fibres  extend  to  the  hyoid  bone. 

The  transverse  fibres  arise  from  the  median  raphe,  and  radiate  outwards  to  the 
dorsum  and  sides  of  the  tongue,  decussating  with  the  extrinsic  muscles  and  the 
fibres  of  the  vertical  muscle.  They  occupy  the  substance  of  the  tongue  between 
the  superior  and  inferior  linguales. 

The  so-called  vertical  fibres  arise  from  the  dorsal  surface  of  the  tongue,  and 
sweep  downwards  and  outwards  to  its  sides,  intermingled  with  the  fibres  of  the 
previous  muscle  and  the  insertions  of  the  extrinsic  muscles.  These  two  muscles 
form  a  very  considerable  part  of  the  total  muscular  substance  of  the  organ. 

Nerve-Supply. 


The  muscles  of  the  hyoid  bone  and  of  the  tongue  are  for  the  most  part  supplied  by  the  ansa 
cervicalis  (C.  1.  2.  3.)  and  by  the  hypoglossal  nerve.  A  few  of  the  muscles  are  supplied  by  the 
trigeminal,  facial,  and  spinal  accessory  nerves. 


Muscles. 

Nerves. 

Origin. 

Omo-hyoid 

Sterno-hyoid        .... 
Stemo-thyroid     .... 
Thyro-hyoid         .... 
Genio-hyoid         .... 
Genio-hyo-glossus 
Hyo-glossus          .... 
Stylo-glossus        .... 
Intrinsic  muscles  of  tongue 
Palato-glossus      .... 
Mylo-hyoid          .... 
Digastric 

Anterior  belly 

Posterior  belly 
Stylo-hyoid         .... 

[-Ansa  cervicalis  , 

[Hypoglossal 

Pharyngeal  plexus    . 

1  Mylo-hyoid  branch  of  in- 
r     ferior  dental  nerve 

1  Facial        .... 

C.  1.  2.  3. 
[c.  1.  2. 

[^  Hypoglossal 

Spinal  accessory. 
[Trigeminal. 

Facial. 

Actions. 


These  muscles  have  a  complexity  of  action,  owing  to  their  numerous  attachments  to  more 
or  leas  movable  points.  The  movements  for  which  tliey  are  responsible  in  whole  or  part  are  (1) 
movements  of  the  hyoid  bone  in  mastication  and  deglutition,  (2)  movements  of  the  thyroid 
wirtilage,  (3j  moveirieuts  of  tlie  tongue,  (4)  movements  oi  the  head,  (5)  movements  of  the  shoulder, 
and  (())  rcHj))' ration. 

(1;  Movements  of  the  Hyoid  Bone. — The  byoid  bone  is  elevated  or  depressed,  and  moved 


416 


THE  MUSCULAE  SYSTEM. 


forwards  or  backwards   along   with    the   lower  jaw   and    tongue,   in   speech,  mastication,  and 
swallowincr. 


a.  Elevation    and    Depression. 

b.  Protraction    and     Retraction. 

Digastric 

Stylo-hyoid 
Mylo-hyoid 
Genio-hyoid 
Genio-hyo-glossus 
Hyo-glossus 
Muscles    closing    the 
mouth 

Thyro-hyoid 

Sterno-hyoid 

Omo-liyoid 

Sterno-thyroid 

Genio-hyoid 
Genio-hyo-glossus 

Stylo-hyoid 
Middle  constrictor 

(2)  Movements  of  the  Thyroid  Cartilage. — The  thyroid  cartilage  is  raised  and  lowered 
dtiring  speech  and  deglutition. 


Elevation. 

Depression. 

Thyro-hyoid 

S  tylo  -pharyngeus 

Palato-pharyngeus 

Elevators  of  hyoid  bone 

Muscles  closing  mouth 

Sterno-thyroid 
Crico-thyroid 
Depressors  of  hyoid  bone 

(3)  Movements  of  the  Tongue. — The  chief  movements  of  the  tongue  in  speech  and  de- 
glutition are  elevation  and  depression,  protrusion  and  retraction,  and  lateral  movements. 


a.  Elevation      and      Depression. 


Stylo-glossus  (base) 

Palato-glossus 

Muscles  elevating  hyoid  bone 

Muscles  closing  mouth 


Genio-hyo-glossus 

Hyo-glossus 

Chondro-glossus 

Muscles  dejjressing  the  hyoid  bone 


h.  Protrusion 

and      Retraction. 

Genio'hyo-glossus  {posterior  fibres) 

Genio-hyo-glossus  {anterior  fibres) 
Stylo-glossus 

c.  Lateral  Movements. - 

—The  muscles  of  one  side  only. 

(4)  Movements  of  the  Head. — The  sterno -mastoid  muscles,  acting  together,  flex  the  head  on 
the  spinal  column,  assisted  by  the  supra-hyoid  and  infra-hyoid  muscles.  The  sterno-mastoid 
muscle  of  one  side,  acting  alone,  bends  the  head  to  the  same  side,  and  simultaneously  rotates  it 
to  the  opposite  side,  as  seen  in  torticollis  (wryneck). 

(5)  Movements  of  the  Shoulder  Girdle. — The  omo-hyoid  and  sterno-mastoid  muscles  have 
already  been  included  among  the  elevators  of  the  shoulder  girdle. 

(6)  Respiration. — The  muscles  in  the  front  of  the  neck  are  auxiliary  muscles  in  extraordinary 
or  difficult  inspiration.  The  masseter  and  temjaoral  muscles  fix  the  lower  jaw  ;  the  hj-oid  bone 
is  raised  and  fixed  by  the  supra-hyoid  muscles  ;  and  the  sternum  is  raised  by  the  sterno-mastoid 
and  infra-hyoid  muscles. 

The  Muscles  of  the  Pharynx. 

The  muscular  envelope  of  the  pharynx  is  composed  of  two  strata.  The  external 
or  circular  layer  consists  of  the  three  constrictor  muscles ;  the  internal  or  longi- 
tudinal layer  consists  of  the  fibres  of  the  stylo-pharyngeus  and  palato-pharyngeus 
muscles. 

The  superior  constrictor  muscle  is  triangular  or  fan -shaped.  It  arises 
successively  from  the  lower  half  of  the  posterior  border  of  the  internal  pterygoid 
plate,  from  the  pterygo-mandibular  ligament,  from  the  mylo-hyoid  ridge  of  the 


THE  MUSCLES  OF  THE  PHAEYNX. 


417 


lower  jaw  (Fig.  327,  p.  414),  and  from  the  mucous  membrane  of  the  floor  of  the 
mouth  iglosso-pharyngeus).  The  muscular  fibres  radiate  backwards,  and  are  inserted 
for  (he  most  part  into  a  median  raphe  extending  down  the  back  wall  of  the  pharynx 
in  the  middle  line.     The  highest  fibres  are  attached  to  the  pharyngeal  spine  of  the 


3^ 


421),  and  the    lowest    fibres  are   overlapped  by 

Fibrous  apnnpuiosis  of  the  pliaryiix 


the 


Eustachian  tubi 

Levator  palati 
MUSCLE  (cut) 

Tensor  palati 

Superior 

constrictor 

Buccinator 

Pterygo-mandi- 
bular  ligament 

Stylo 
pharyngeus 

Middle 
constrictor 


Inferior  constrictor 


occipital  bone  (Fig 
middle  constrictor.  A  crescentic  in- 
terval occurs  above  the  muscle,  below 
the  base  of  the  skull,  in  which  the 
Eustachian  tube  and  the  levator  and 
tensor  palati  muscles  appear.  Its 
lower  border  is  separated  from  the 
middle  constrictor  by  the  stylo- 
pharyngeus  muscle  and  the  glosso- 
pharyngeal nerve.  The  superior 
constrictor  muscle  separates  the  in- 
ternal carotid  artery  from  the  cavity 
of  the  pharynx  and  tonsil. 

The  middle  constrictor  muscle 
arises  from  the  stylo-hyoid  ligament 
and  from  both  cornua  of  the  hyoid 
bone.  From  its  origin  the  muscular 
fibres  radiate  backwards,  to  be  in- 
serted into  the  median' raphe  on  the 
posterior  aspect  of  the  pharynx.  The 
upper  fibres  overlap  the  lower  part  of 
the  superior  constrictor;  the  lower 
fibres  are  concealed  from  view  by  the 
inferior  constrictor  muscle.  In  the 
interval  between  the  middle  and 
inferior  constrictors  are  found  the 
internal  laryngeal  artery  and  nerve. 

The  inferior  constrictor  muscle 
arises  from  the  oblique  line  of  the 
thyroid  cartilage,  and  from  the  side 
of  the  cricoid  cartilage.  Its  fibres 
radiate  backwards,  to  be  inserted  into 
the  median  raphe  on  the  back  of  the 
pharynx,  the  upper  fibres  overlapping  the  lower  part  of  the  middle  constrictor, 
the  lower  fibres  blending  with  the  muscular  fibres  of  the  oesophagus.  Below  the 
lower  border  of  the  muscle  the  inferior  laryngeal  artery  and  nerve  enter  into  relation 
with  the  larynx. 

The  deeper  longitudinal  stratum  of  muscles  in  the  pharyngeal  wall  is  com- 
posed of  the  insertions  of  the  stylo-pharyngeus  and  palato-pharyngeus  muscles. 

The  stylo-pharyngeus  arises  from  the  root  of  the  styloid  process  on  its  inner 
side,  and  passes  downwards  between  the  external  and  internal  carotid  arteries.  It 
enters  the  wall  of  the  pharynx  in  the  interval  between  the  superior  and  middle 
constrictor  muscles.  Spreading  out  beneath  the  middle  constrictor  muscle,  it  is 
inserted  into  the  superior  and  posterior  borders  of  the  thyroid  cartilage  and  into 
the  wall  of  the  pharynx  itself,  becoming  continuous  posteriorly  with  the  palato- 
]jharyngeu8.  In  the  neck  the  glosso-pharyngeal  nerve  winds  round  it  on  its  way 
to  the  tongue 

'J'he  palato-pharyngeus  occupies  the  soft  palate  and  the  pharyngeal  wall.  In 
the  substance  of  tlie  soft  palate  it  consists  of  two  layers,  a  postero-superior  layer, 
thin,  and  continuous  across  the  middle  line  with  the  corresponding  layer  on  the 
opposite  side,  and  an  antero-inlerior  layer,  which  is  thicker,  and  is  attached  to  the 
y)Osterior  border  of  the  liard  palate.  The  levator  palati  and  azygos  uvuke  muscles 
are  (jnclosed  between  the  two  layers,  which  unite  at  the  posterior  edge  of  the  palate, 
receiving  at  the  HaniM  time  additional  fibres  arising  from  the  Eustachian  tube 
(HnJ'pviujo-'iili.aryngeuH).  'Yho,  muscle  descends  to  the  pharynx  in  tlie  posterior  pillar 
'30 


Fig. 


.328. — Posterior  View  of  the  PHARVfix  and 
Constrictor  Mdscles. 


418 


THE  MUSCULAE  SYSTEM. 


of  the  fauces.  Its  fibres  spread  out  in  the  form  of  a  thin  sheet  in  the  wall  of 
the  pharynx,  in  continuity  anteriorly  with  the  stylo-pharyngeus,  and  are  inserted 
into  the  posterior  border  of  the  thyroid  cartilage,  and  behind  that  into  the 
aponeurosis  of  the  pharynx,  reaching  down  as  far  as  the  lower  border  of  the  inferior 
constrictor.  The  muscle  is  placed  beneath  the  middle  and  inferior  constrictors  in 
the  pharyngeal  wall,  and  the  fibres  of  the  muscles  of  opposite  sides  decussate  in  the 
middle  line  beneath  the  median  raphe. 


The  Muscles  of  the  Soft  Palate. 

The  soft  palate  and  uvula  form  a  muscular  fold,  covered  on  each  surface  by 
mucous  membrane,  projecting  backwards  into  the  pharynx,  and  forming  tlie  posterior 

part  of  the  roof  of 
the  mouth. 

The  muscular 
fold  is  composed  of 
five  pairs  of  mus- 
cles— the  palato- 
pharyngeus  (and 
salpingo  -  pharyn  - 
geus),  azygos 
uvulse,  levator 
palati,  tensor 
palati,  and  palato- 
glossus. 

The  palato- 
pharyngeus  mus- 
cle has  been  already 
described  (p.  417) 
among  the  muscles 
of  the  pharynx. 

The  azygos 
uvulse  consists  of 
two  narrow  bundles 
enclosed,  along 
with  the  insertion 
of  the  levator 
palati,  between  the 
layers  of  the  palato- 
pharyngeus.  The 
slips  arise  from  the 
posterior  nasal 
spine  and  the  apo- 
neurosis of  the  soft 
palate,  and  unite 
as  they  proceed 
backwards  to  end 
in  the  uvula. 

The  levator 
palati  has  a  double 
origin :  (1)  from 
the  under  surface 

of  the  apex  of  the  petrous  portion  of  the  temporal  bone,  and  (2)  from  the 
lower  part  of  the  cartilaginous  Eustachian  tube.  It  passes  obliquely  down- 
wards and  inwards,  across  the  upper  border  of  the  superior  constrictor  muscle, 
and  enters  the  soft  palate  between  the  two  layers  of  the  palato-pharyngeus  muscle. 
It  is  inserted  into  the  aponeurosis  of  the  soft  palate,  and  some  of  its  fil^res  become 
continuous    with  those  of  the  opposite  muscle.     It  is  separated  from  the  tensor 


Buccinator 


Mylo-hyoid 

Hyo-glossus 

Digastric 

Stvlo-hyoid 


Omo-hyoid 
Sterno-hyoid 


Thyro-hyoid 


Crico-thyroii 


Tensor  palati  muscle 

Eustachian  tube 

Levator  palati 

Pterygo-iiiandibular 

ligament 

Superior  constrictor 

Stylo-pharyngeus 

Stylo-glossus 

Glosso-pharyngeal 

nerve 

Stylo-hyoid  ligament 

Hypoglossal  nerve 

Middle  constrictor 

Digastric 
Superior  laryngeal 
nerve 

Inferior  constrictor 


External  laryngeal 
nerve 


ffisophagus 
Inferior  laryngeal 
nerve 


Lateral  View  op  the  Wall  of  the  Pharynx. 


LATEEAL  AND  PEJ5VEETEBEAL  MUSCLES  OF  THE  NECK.     419 

palati  muscle  by  the  Eustachian  tube  and  the  deeper  layer  of  the  palato-pharyngeus 
muscle. 

The  tensor  (circumflexus)  palati  arises  (1)  from  the  scaphoid  fossa  and  the  alar 
spine  of  the  sphenoid  bone,  and  (2 ,  from  tlie  outer  side  of  the  cartilaginous  Eustachian 
tube.  It  descends  between  the  internal  pterygoid  muscle  and  the  internal  ptery- 
goid plate,  and  ends  in  a  tendon  which  hooks  round  the  hamular  process,  and  is 
inserted  beneath  the  levator  palati  into  the  posterior  border  of  the  hard  palate,  and 
into  the  aponeurosis  of  the  soft  palate. 

The  palato-glossus  muscle,  occupying  the  under  surface  of  the  soft  palate  and 
the  anterior  pillar  of  the  fauces,  has  already  been  described  with  the  muscles  of  the 
tongue  (p.  415). 

Nervb-Supply. 

The  chief  nerve  supplying  the  muscles  of  the  pharynx  and  soft  palate  is  the  spinal  accessory 
nerve,  aided  by  the  fifth  (otic  ganglion)  and  the  ninth  (glosso-pharyngeal)  nerves  and  the  laryngeal 
branches  of  the  vagus  nerve. 


Muscles. 

Nerves,                         Origin. 

Constrictors  of  pharynx  ~ 

Palato-glossus 

Palato-pharyngeus 

Levator  palati 

Azygos  uvulse                  J 

Tensor  jDalati  .         .         .         .         . 

Stylo-pharyngeus   .... 

Inferior  constrictor 

Pharyngeal  plexus    .         .   '      XI. 

Otic  ganglion    .         .         .V. 

Glosso-jDharyngeal     .         .         IX. 
r External  laryngeal!                     -^ 
\  Inferior  laryngeal  / 

1 

Actions. 

The  muscles  of  the  pharynx  and  soft  palate  are  chiefly  brought  into  action  in  the  act  of 
swallowing.  This  act  is  divided  into  a  volimtary  stage,  in  which  the  bolus  lies  in  front  of  the 
pillars  of  the  fauces,  and  an  involuntary  stage,  during  which  the  food  passes  from  the  mouth 
through  the  pharynx.  The  movements  occurring  during  the  passage  of  food  through  the  mouth 
are  as  follows  :  the  cheeks  are  compressed  by  the  action  of  the  buccinator  muscles ;  the  tongue, 
hyoid  bone,  and  thyroid  cartilage  are  successively  raised  upwards  by  the  action  of  the  muscles 
which  close  the  mouth  and  elevate  the  hyoid  bone.  By  these  means  the  food  is  pushed  back- 
wards between  the  pillars  of  the  fauces. 

At  the  same  time,  by  the  contraction  of  the  palato-glossus  and  palato-jDharyngeus,  the  pillars  of 
the  fauces  are  narrowed,  while  the  muscles  of  the  soft  palate,  contracting,  tighten  the  soft  palate, 
and  by  bringing  it  in  contact  with  the  posterior  wall  of  the  pharynx,  shut  off  the  upper  (nasal) 
portion  of  the  cavity.  The  elevation  of  the  tongue,  hyoid  bone,  and  larynx  simultaneously  causes 
the  elevation  of  the  epiglottis  and  the  aperture  of  the  glottis,  which  is  closed  by  the  approximation 
of  the  arytenoid  cartilages  and  the  combined  action  of  laryngeal  muscles  (arytenoideus,  thyro- 
arytenoideus,  and  thyro-aryteno-epiglottideus).  The  food  thus  slips  over  the  posterior  surface  of 
the  epiglottis  and  the  closed  aperture  of  the  glottis,  and  between  the  pillars  of  the  fauces  on 
either  side,  into  the  pharynx.  It  is  now  clasped  by  the  constrictor  muscles,  which,  by  their 
contractions,  force  it  down  into  the  oesophagus.  The  contraction  of  the  constrictor  muscles  results 
in  a  flattening  of  the  pharynx  and  elevation  of  its  anterior  attachments. 

During  the  act  of  swallowing,  it  is  generally  thought  that  the  Eustachian  tube  is  opened  by 
the  contraction  of  the  tensor  palati  muscle  which  arises  from  it.  It  has  been  held,  on  the  other 
hand,  that  the  Eustachian  tube  is  closed  during  swallowing  by  the  compression  of  its  wall  by  the 
contraction  of  the  levator  palati. 

Deep  Lateral  and  Ph^veetebeal  Muscles  of  the  Neck. 

Three  series  of  muscles  are  comprised  in  this  group  :  (1)  vertebro-costal  (scaleni, 
auticus,  niedius,  and  posticus),  (j!)  vertubro-cranial  (recti  capitis  antici,  major  and 
minor,  and  lateralis;,  and  ('6)  vertel)ral  (loiigus  colli). 

The  scalenus  anticus  arises  from  the  anterior  tubercles  of  the  transverse 
processes  of  the  third,  iburth,  fifth,  and  sixtii  cervical  vertebrai,  and  descends 
behind  the  carotid  sheath,  to  be  inserted  into  the  scalene  tubercle  and  ridge  on  the 
first  rib  TFig.  3.':50,  p.  420).  In  front  of  the  muscle  are  the  subclavian  and 
internal  jugular  veins,  and  the  nerves  descending  through  the  neck.     T3ehind,  it  is 

yo  a 


420 


THE  MUSCULAK  SYSTEM. 


Serratus  posticus 
superior  (insertion) 


Scalenus  posticus 
(insertion) 


Scalenus  medius(insertion) 


Spiiatus  magnus  (origin) 


Serratus 


nus  anticus  (in  sertion) 


Pectoralis  minor  (occasional  origin) 


Rectus  capitis 
anxious  minok 


YiG    330  —Muscle -Attachments  to  the  Upper  Surface  of  the 

First  Rib,  and  the  Outer  Surface  of  the  Second  JIib. 

A,  First  rib  ;  B,  Second  rib. 

and  sixth  cervical  trans- 
verse processes,  and  is 
inserted  into  a  linear 
impression  on  the  outer 
side  of  the  second  rib. 
It  is  concealed  behind 
by  the  levator  anguli 
scapulse,  and  is  in  con- 
tact anteriorly  with  the 
scalenus  medius. 

The  rectus  capitis 
anticus  major  arises 
from     the      anterior 

tubercles  of   the  trans- 
verse   processes    of    the 

third,  fourth,  fifth,  and 

sixth  cervical  vertebrae. 

It  forms  a  flat  triangular 

muscle,  which  is  directed 

upwards,  to  be  inserted 

into    an    impression    on 

the  under  surface  of  the 

basilar   process    of    the 

occipital  bone  in  front 

and  to  the  outer  side  of 

the     pharyngeal     spine 

(Fig.  333,  p.  421).      It 

lies    on   the   cervical 

vertebrffi      behind     the 

carotid  vessels  and  the 


separated  from  the  scalenus 
medius  by  the  cords  of  the 
brachial  plexus,  the  subclavian 
artery,  and  the  pleura. 

The  scalenus  medius 
arises     from     the     posterior 
tubercles    of    the    transverse 
processes     of     the     cervical 
vertebrae,  from  the  second  to 
the  sixth  inclusive.      It  de- 
scends in  the  floor  of  the  pos- 
terior triangle,  to  be  inserted 
into  the  rough  impression  on 
the  first  rib  behmd  the  sub- 
clavian artery  (Fig.   330,  p. 
420).     The  muscle  is  covered 
anteriorly  by  the  cords  of  the 
brachial    plexus,    the     sub- 
subciavius  clavian  artery,  and  the  omo- 
(origm)       y^jq]^^  muscle,  and  is  in  con- 
tact behind  with  the  levator 
anguh     scapulae      and     the 
scalenus     posticus.        It     is 
pierced     by     the     posterior 
scapular     and     posterior 
thoracic  nerves. 

The  scalenus  posticus 
arises  from  the  posterior 
tubercles  of  the  fourth,  fifth. 


Rectus  capitis 
lateralis 

Rectus  capitis 
anticus  minor 

Rectus  capitis 
anticus  major 


LONOUS  COLLI 


Scalenus  postici 


Fig.  331.— The  Pr.eyertebral  Muscles  of  the  Neck. 


THE  MUSCLES  OF  THE  THOKAX. 


421 


pharynx,  external   to  the  longus  colli,  and  internal  at  its  origin  to  the  scalenus 
anticus. 

The  rectus  capitis  anticus  minor  arises  from  the  anterior  arch  of  the  atlas,  and 


Scalenus  medius 

Levator  anguli  scapula 

Spleniuc)  colli 

Posterior 

tubercles  of 

transverse" 

processes  Scalenus  posticus 

Cervicalis  ascendens 

Transversalis  ceevicis 


r  Trachelo-mastoid 

I  Complexus 

Articular  processes-! 


Semispinalis  colli 
moltifidus  spin^ 


Rectus  capitis 
anticus  major 


-LONGUS  COLLI 


Anterior 
tubercles  of 
'transverse 
processes 


Fig.  332. — Scheme  op  Muscular-Attachments  to  Cervical  Vertebra. 


is  inserted  into  the  basilar  process  between  the  previous  muscle  and  the  occipital 
condyle  (Fig.  333,  p.  421).     It  is  concealed  by  the  rectus  capitis  anticus  major. 
The  longus  colli  is  a  flattened  muscular  band  extending  from  the  third  thoracic 


Complexus  (insertion) 


Rectus  capitis  postieu',  minor 
(insertion) 


Rectus  capitis  ]iosticus  major 
(insertion) 


Trapezius  (origin) 


Stemo-cleido-mastoid 
(insertion) 


Splenius  capitis 
(insertion) 


Obliquns  superior  (insertion) 


Rectus  capitis  lateralis  (iiiserlioji) 

Rectus  capitis  anticus  minor  (inseitJon) 


lis  major  (inseition) — pT"   \ 


.^Superior  constrictor  of  pliai-ynx  (insertion) 


Ri.'ctus  capitis  anticus 

Fio.  333. — Mu.sclk-Attachmknth  to  Owjuntai,   Honk  (Inferior  Surface). 


vertebra  to   the  atlas.     It  is  divisible   into  three  portions — a  vertical,  a  lower 
oblique,  and  an  iijjpcr  oblique  portion. 

'J'he  vertical  portion  of  the  muscle  arises   I'rom  tlio  bodies  of  the    Hrst   three 


422  THE  MUSCULAE  SYSTEM. 

thoracic  and  the  last  three  cervical  vertebrae ;  aud  passing  vertically  upwards,  it  is 
inserted  into  the  bodies  of  the  second,  third,  and  fourtli  cervical  vertebrse. 

The  lower  oblique  portion  arises  from  the  bodies  of  the  first  three  thoracic 
vertebrae,  and  is  inserted  into  the  anterior  tubercles  of  the  fifth  and  sixth  cervical 
vertebrse. 

The  upper  oblique  portion  arises  from  the  anterior  tubercles  of  the  transverse 
processes  of  tlie  tliird,  fourth,  and  fifth  cervical  vertebrae,  and  is  directed  upwards, 
to  be  inserted  into  the  anterior  tubercle  of  the  atlas. 

The  louo-us  colli  muscle  clothes  the  front  of  the  vertebral  column  in  the  neck, 
and  is  separated  by  the  deep  cervical  fascia  from  the  carotid  vessels,  pharynx,  and 
oesopliagus. 

The  rectus  capitis  lateralis,  in  series  with  the  posterior  inter -transverse 
muscles  in  the  necl^,  arises  from  tlie  transverse  process  of  the  atlas,  and  is  inserted 
into  the  under  surface  of  the  ex-occipital  bone.  It  is  placed  alongside  tJie  recti 
capitis  antiei,  separated  from  tliem  by  the  anterior  primary  division  of  the  first 
cervical  nerve. 

Nerve-Supply. 

Tlie  prsevertebral  muscles  are  all  supplied  by  anteiior  primary  divisions  of  the  cervical  spinal 
nerves  :  the  rectus  caj^itis  anticus  minor,  and  rectus  cajiitis  lateralis,  by  the  loop  between  tlie  first 
two  nerves  ;  tbe  rectus  cajjitis  anticus  major  by  the  first  four  ;  the  longus  colli  by  the  second, 
third,  and  fourth  ;  the  scaleni  by  the  lower  four  or  five  cervical  nerves. 

Actions. 

The  movements  produced  by  these  muscles  are  considered  along  with  those  of  other  muscles 
acting  on  the  head,  sj)inal  column,  and  thorax  (pp.  398,  426). 

THE  MUSCLES  OF  THE  THORAX. 

Muscles  of  Eespieation. 

The  muscles  which  complete  the  boundaries  of  the  thorax  are  the  diaphragm 
and  intercostal  muscles  (external  and  internal),  along  with  three  series  of  smaller 
muscles — the  triangularis  sterni,  the  levatores  costarum,  and  the  infra-costales. 

The  intercostal  muscles  are  arranged  in  eleven  pairs,  forming  thin  layers 
filling  up  the  intercostal  sj)aces. 

Each  external  muscle  arises  from  the  sharp  lower  border  of  a  rib,  and 
is  directed  downward  and  forward,  to  be  inserted  into  the  outer  edge  of  the 
upper  border  of  the  rib  below.  It  extends  from  the  tubercle  of  the  rib  behind 
nearly  to  the  costal  cartilage  in  front.  The  anterior  intercostal  aponeurosis  is 
continuous  with  it  anteriorly,  and  extends  forwards  to  the  side  of  the  sternum. 

Eacli  internal  muscle  arises  from  the  costal  cartilage  and  the  inner  edge  of  the 
subcostal  groove,  and  is  directed  downwards  and  backwards,  to  be  inserted  into  the 
inner  edge  of  the  upper  border  of  the  rib  and  costal  cartilage  below.  It  extends 
from  the  side  of  the  sternum  in  front  to  the  angle  of  the  rib  behind,  where  it 
becomes  continuous  with  tlie  posterior  intercostal  aponeurosis  extending  to  the 
tubercle  of  the  rib. 

The  external  intercostal  muscles  are  covered  by  the  pectoral  muscles,  serratus 
magnus,  and  the  muscles  of  the  back ;  the  internal  muscles  are  in  contact  with 
the  pleura.  The  intercostal  vessels  and  nerve  lie  between  the  two  muscles  in  the 
posterior  part  of  the  thorax. 

The  levatores  costarum  are  in  series  with  the  external  intercostal  muscles. 
They  are  twelve  small  slips  arising  from  the  transverse  processes  of  the  seventh 
cervical  and  upper  eleven  thoracic  vertebrae.  They  spread  oi.t  in  a  fan-like  manner 
as  they  descend,  to  be  inserted  into  the  outer  surface  of  the  ribs  posterior  to  the 
angles.     They  lie  under  cover  of  the  longissimus  dorsi  muscle. 

The  infra-costales  (subcostales)  are  slips  of  muscles  found  on'  the  inner  surface 
of  the  lower  ribs  near  their  angles.  They  are  in  series  with  the  internal  inter- 
costal muscles,  but  pass  over  the  deep  surface  of  several  ribs. 

The  triangularis  sterni  (m.  transversus  thoracis)  occupies  the  posterior  aspect 


THE  MUSCLES  OF  THE  THOEAX. 


423 


of  the  anterior  thoracic  wall.  It  arises  from  the  back  of  the  ensiform  cartilage 
and  mesosternum  as  high  as  the  level  of  the  third  costal  cartilage.  From  this 
origin  its  fibres  radiate  outwards,  the  lower  ones  horizontally,  the  upper  ones 
obliquely  upwards,  to  be  inserted  into  the  costal  cartilages  of  all  the  true  ribs 
except  the  first  and  seventh.  The  muscle  lies  against  the  pericardium  and  pleura. 
It  is  separated  from  the  chest  wall  by  the  internal  mammary  vessels  and  the 
anterior  branches  of  the  intercostal  nerves.  The  muscle  is  continuous  below  with 
the  transversalis  abdominis. 

The  diaphragm  is  the  great  membranous  and  muscular  partition  sajjarating 
the  cavities  of  the  thorax  and  abdomen.     It  forms  a  thin  lamella  archincr  over 


External  intercostal 

MUSCLE 


OBLIQUUS  EXTI  I'M 

ABDOMINIS  (refle'-L,'- 


Anterior  intercostal 
membrane 


Internal  inter- 
costal MUSCLE 


Rectus  abdominis 
(insertion) 


feheath  of  the  rectus 
abdominis 


Fig.  334. — The  Muscles  of  the  Thoracic  Wall. 


the  liver,  stomach,  and  spleen,  with  its  convex  upper  surface  in  contact  with  the 
pericardium,  pleurte,  and  cliest  wall.  It  possesses  a  peripheral  origin  from  the 
sternum,  ribs,  and  vertebral  column,  and  an  insertion  into  a  central  tendon.  It 
arises  (1)  anteriorly  from  the  posterior  surface  of  the  ensiform  cartilage  by  two 
slender  fleshy  slips,  directed  backwards ;  (2)  laterally,  from  the  deep  surface  of  the 
lower  six  rib-cartilages  on  each  side  by  fleshy  bands  which  interdigitate  with  those 
of  the  transversalis  abdominis;  (3)  'posteriorly,  from  the  lumbar  vertebra3,  by  the 
crura,  find  from  tin;  arcuate  ligaments.  The  crura  are  two  elongated  fibro-muscular 
bundles  which  arise  from  the  front  of  the  bodies  of  the  lumbar  vertebraj,  on  the 
right  side  from  tFie  first  three,  on  the  left  side  from  the  first  two  vertebry3.  They 
are  directed  upwards  and,  passing  in  front  of  the  aorta,  decussate  across  the  middle 
line  in  front  of  that  vessel,  the  fibres  of  the  right  cms  passing  in  front  of  those  of 
the  left  cms.  The  fibres  then  encircle  the  ccsopliagus,  forming  an  ellipticyl  opening 
30  & 


424 


THE  MUSCULAR  SYSTEM. 


for  its  passage,  and  finally  join  the  central  tendon,  after  a  second  decussation  in 
front  of  the  gullet. 

The  arcuate  ligaments  are  tive  in  number. 

The  middle  arcuate  ligament  is  a  fibrous  arch  connecting  together  tiie  crura  of 
the  diaphragm  in  front  of  the  aorta,  and  giving  origin  to  fibres  which  join  the  crura 
as  they  decussate  to  encircle  the  gullet. 

The  internal  arcuate  ligament  is  a  thickening  formed  by  the  attachment  of  the 
psoas  fascia  to  the  body  of  the  first  lumbar  vertebra  internally  and  its  transverse 
process  externally.  Stretching  across  the  upper  end  of  the  psoas  muscle,  the 
ligament  gives  origin  to  muscular  fibres  directed  upwards  on  each  side  of  the 
crura. 

The  external  arcuate  ligament  is  the  thickened  upper  end  of  the  fascia  over  the 
quadratus  lumborum  (anterior  layer  of  the  lumbar  fascia.),  and  is  attached  inter- 
nally to  the  transverse  process  of  the  first  lumbar  vertebra,  and  externally  to  the 


0^s(i]ili,igns  and  its 


Foramen  quadiatuin 
(for  inferior  cava)  -^ 


Middle  aicuate  ligd 

ment  (in  liont  of 

aortic  opening) 


ternal  arcuate 
ligament 
^ —   External  arcuate 
ligament 

Quadratus  lumborum 

MUSCLE 


P'sOAS  MUSCLE 

Left  crus  of  diaphragm 
Right  crus  of  diaphragm 

Fig.  335. — The  Diaphragm  (from  below). 

last  rib.  It  gives  origin  to  another  broad  band  of  muscular  fibres,  separated  from 
those  arising  from  the  internal  arcuate  ligament  by  an  interval,  and  passing 
upwards  to  the  central  tendon  of  the  diaphragm. 

From  this  extensive  origin  the  muscular  fibres  of  the  diaphragm  converge  to 
an  insertion  into  a  large  trilobed  central  tendon.  Of  its  lobes  the  right  one  is  the 
largest,  the  middle  or  anterior  is  intermediate  in  size,  and  the  left  is  the  smallest. 
It  does  not  occupy  the  centre  of  the  muscle,  being  placed  nearer  the  front  than 
the  back.  The  fibres  of  the  crura  are  consequently  the  longest ;  those  from  the 
sternum  are  the  shortest. 

The  diaphragm  is  pierced  by  numerous  structures.  The  superior  epigastric 
artery  enters  the  sheath  of  the  rectus  abdominis  between  its  sternal  and  costal 
origins ;  the  musculo-phrenic  artery  passes  between  its  attachments  to  the  seventh 
and  eighth  ribs.  The  sympathetic  cord  and  the  splanchnic  nerves  pierce  or  pass 
behind  the  diaphragm  ;  the  last  thoracic  nerve  passes  beneath  the  external  arcuate 
ligament ;  and  the  aorta,  the  vena  azygos  major,  and  thoracic  duct  pass  between 
the  crura,  underneath  the  middle  arcuate  ligament  (aortic  opening).  The  special 
foramina  are  two  in  number.  The  foramen  quadratum  in  the  right  lobe  of  the 
central  tendon  transmits  the  inferior  vena  cava,  and  small  branches  of  the  right 


THE  MUSCLES  OF  THE  THOIIAX. 


425 


phrenic  nerve.  The  oisophageal  opening  is  in  the  muscular  substance  of  the 
diaphragm,  behind  the  central  tendon,  and  is  surrounded  by  a  sphincter-like 
arrangement  of  the  crural  fibres.  Besides  the  oesophagus,  this  opening  transmits 
the  two  pneumogastric  nerves.  The  upper  convex  surface  of  the  diaphragm  forms 
the  sloping  floor  of  the  thorax,  and  is  in  contact  with  the  pleura  and  the  peri- 
cardium (which  is  firmly  bound  down  to  the  central  tendon,  and  less  firmly  to  the 


Vena  caval  opening    (Esophageal  opening    Central  tendon  (middle  part) 


Central  tendon  (right  jiart) 
Diaphragm,  costal  fibres  Q  ° 

\\ 
Internal  arcuate  ligament  - 

External  arouate  ligament 

End  of  last  rib  — 
Last  thoracic  nerve  „  ^^ 

Ant.  layer  of  lumbar  fascia LU 

Lumbar  fascia 

Ilio-hypogastric  _  l*^ 

Lumbar  vessels  and  synipa-       jT 

thetic  communicating  nerves  — W 

Ilio-inguinal       '  ^ 

QUADEATUS  LDMBOEUM 


External  cutaneous  nerve 


Psoas  magnus 

Iliactjs  '^- 
Luinbo- sacral  cord 


Genito-crnral  neive 

Anterior  crural  ner\e 

Obturator  nerve 

Great  sciatic  neive 


Diaphragm,  right  cbus 

Middle  arcuate  ligament 
Aortic  opening 


Central  tendon 
(left  part) 
Diaphragm,  left 

CRUS 


i_Last  thoracic  nerve 
End  of  last  rib 
Lumbar  nerve  I. 

Ilio-hypogastric 
Lumbar  nerve  IL 

.Uio-inguinal 

QUADRATUS 
LUMBORUM 

Lumbar  nerve  II L 

Genito-crnral 
Lumbar  nerve  IV. 


Lumbo-sacral  cord 


\^\X External  cutaneous  nerve 

Anterior  crural  nerve 

—  Obturator  nerve 
Great  sciatic  nerve 


Vu:.  .3.36.— Vjkw  ok  thk  Posteiuok 


Obtuiatoi  nen  e 
Addqctor  lon&ds  (Ollglll) 
,  '    Adductor  brevis  (origin) 

I     1    Gracilis  (origin) 
Adductor  magnus  (origin) 
1^     Pectineus  (cut) 
I     Superticial  branch  of  obturator  nerve 
Deep  brancli  of  obturator  nerve 
Obturator  externus 

Abdominal  Wall,  to  show  the  Muscles  and  the  Nerves  of 
THE  Lumbo-Sacral  Plexus. 


imLscu  ar  fibres  on  the  left  side).  By  its  lateral  margins  the  diaphragm  is  in 
contact  on  each  side  with  the  thoracic  wall  beyond  the  reflection  of  the  iileura 
ami  behind  with  the  cesophagus  and  descending  thoracic  aorta.  The  under  surface 
ot  the  diaphragm  is  concave,  a,nd  is  for  the  most  ].art  invested  hj  peritoncuim  It 
18  in  relation  with  tbc  liver,  stomach,  spleen,  kidneys,  supntrenal' bodies,  duodenum 
and  pancreas,  the  inferior  v(!na  cava,  and  the  branches  of  the  coeliac  axis.  Its 
vault  IS  higher  on  the  riglit  side  tiian  on  the  left,  owing  to  the  upward  projection 
ol  the  liver  on  that  side.  i  i     j 


426  THE  MUSCULAE  SYSTEM. 

The  diaphragm  is  found  as  a  complete  septum  between  the  thorax  and  abdomen  only  in 
mammals.  It  is  occasionally  deficient  in  the  human  subject,  producing  hernia  of  the  diaxihragw,, 
either  into  the  pericardial  cavity  through  the  central  tendon,  or  into  the  thoracic  cavity  through 
the  lateral  portions  of  the  muscle.  A  rare  condition  is  congenital  deficiency  of  a  part  of  the 
lateral  lialf  of  the  muscle,  generally  placed  posteriorly,  and  on  the  left  side.  This  produces,  Ijy 
continuity  of  the  peritoneum  and  pleura  behind  the  diaphragm,  a  congenital  diaj}hragmatic 
hernia. 

NERVE-SuprLY. 

The  intercostal  muscles,  levatores  costarum,  infra-costal  muscles,  and  triangularis  sterni,  are 
all  supplied  by  the  anterior  primary  divisions  of  the  intercostal  nerves.  The  diaphragm  receives 
its  chief,  if  not  its  entire,  motor  supply  from  the  phrenic  nerves  (C.  3.  4.  5.)  It  is  innervated 
also  by  the  diaphragmatic  plexus  of  the  sympathetic,  and  is  said  to  receive  fibres  from  the  lower 
intercostal  nerves. 

Actions. 

The  act  of  respiration  consists  of  two  ojjposite  movements,  inspiration  and  expiration. 

1.  The  movement  of  expiration  is  performed  by  (1)  the  elasticity  of  the  lungs,  (2)  the  weight 
of  the  chest  walls,  (3)  the  elevation  of  the  diaphragm,  (4)  the  action  of  muscles— triangularis 
sterni  and  muscles  of  the  abdominal  w^all.  It  is  sometimes  stated  that  the  interosseous  fibres  of 
the  internal  intercostal  muscles  are  depressors  of  the  ribs. 

2.  The  movement  of  inspiration  results  in  the  enlargement  of  the  thoracic  cavity  in  all 
its  diameters.  Its  antero-posterior  and  transverse  diameters  are  increased  l3y  the  elevation  and 
forward  movement  of  the  sternum,  and  by  the  elevation  and  eversion  of  the  ribs,  while  its 
vertical  diameter  is  increased  by  the  descent  of  the  diaphragm. 

The  muscles  of  inspiration  are  divided  into  two  series — ordinary  and  accessory. 


a.  Ordinary  Muscles. 

b.  Extraordinary  and  Accessory  Muscles 

Diaphragm 
Intercostals 
Scaleni 
Serrati  postici 
Levatores  costaruni 

Quadratus  lumborum 
Pectorales 
Serratus  magnus 
Sterno-niastoid 
Latissimus  dorsi 
Infra-hyoid  muscles 
Extensors  of  the  spine 

Of  the  ordinary  muscles  the  diaphragm  is  the  most  important.  Its  action  is  twofold — 
centrifugal,  elevating  the  ribs  and  increasing  the  transverse  and  antero-posterior  diameters  of 
the  thorax,  and  centripetal,  drawing  dowaiwards  the  central  tendon  and  increasing  the  vertical 
diameter  of  the  thorax.  Of  the  two  movements  the  former  is  the  more  important.  There  has 
been  considerable  diversity  of  opinion  regarding  the  action  of  the  intercostal  muscles.  It  is 
generally  agreed  that  the  external  muscles  elevate  the  ribs ;  it  is  probable  that  the  whole  of  each 
internal  muscle  acts  in  the  same  w^ay,  although  it  has  been  stated  by  dift'erent  observers  that  the 
whole  internal  muscle  is  a  depressor;  or  that  the  interosseous  part  is  a  depressor,  the  inter- 
chondral  portion  of  the  muscle  an  elevator  of  the  ribs. 

FASCIA  AND  MUSCLES  OF  THE  ABDOMINAL  WALL. 

The  space  between  the  margins  of  the  bony  thorax  and  the  pelvis  is  j&lled  np  by 
a  series  of  muscular  sheets,  covered  externally  and  internally  by  fascise. 

FASCIA. 

The  fasciae  of  the  abdominal  v^all  are — externally,  the  superficial  and  deep  fasciae ; 
internally,  the  fascia  transversahs,  which  is  continuous  with  the  diaphragmatic, 
lumbar,  psoas,  iliac,  and  pelvic  fasciae,  and  is  lined  within  by  the  extra-peritoneal 
tissue. 

The  superficial  fascia  of  the  abdomen  is  liable  to  contain  a  large  quantity 
of  fat.  It  is  separated  in  the  groin  into  two  layers :  a  superficial  fatty  layer  con- 
tinuous over  Poupart's  ligament  with  the  fascia  of  tlie  front  of  the  thigh  (p.  356), 
and  a  deeper  membranous  layer  attached  to  the  inner  half  of  Poupart's  hgament, 
•  and  more  externally  to  the  fascia  lata  of  the  thigh  below  Poupart's  ligament.  The 
two  layers  are  separated  by  the  lymphatic  glands  and  the  superficial  vessels  of  the 
o-roin.     Higher  up  in  the  abdominal  wall  the  two  layers  blend  together,  and  passing 


THE  MUSCLES  OF  THE  ABDOMINAL  WALL. 


427 


Suijerficial  layer  of 
superficial  fascia 


Superflcial  circumflex  iliac  vessels 

Inguinal  lymphatic  gland? 

Deep  layer  of  superficial  fascia 
Femoral  lymphatic  glands 


Crural  branch  of 
genito-erural  nerve 
Superficial  layer  of 

superficial  fascia 

Internal  saphenous  veil 


Deeij  layer  <A' 
superficial  fascia 
Superficial 
epigastric  vessels 
t-^^^^^T"*)      Superficial  layer  of 
Y  —;p-r'^  superficial  fascia 
I         /       Superioi  external 
^^^^X'-^pudic  vessels 


Ilio-ingninal  nerve 
Spermatic  cord 


downwards  over  the  spermatic  cord,  they  unite  to  form  the  fascia  and  dartos 
muscle  of  the  scrotum.  The  attachment  of  the  fascia  to  the  groin  prevents  the 
jjassage  into  the  thigh  of  fluid  extravasated  in  the  abdominal  wall. 

The  deep  fascia  of  the  abdominal  wall  resembles  similar  fasci£e  in  other  situa- 
tions. It  forms  an  investment  for  the  obliquus  externus  muscle,  and  becomes  thin 
and  almost  im- 
perceptible in  re- 
lation to  the 
aponeurosis  of 
that  muscle. 

The  fascial 
lining  of  the  ab- 
dominal cavity 
(fascia  transver- 
salis)  consists  of  a 
continuous  layer 
of  membrane 
which  receives 
different  names  in 
different  parts  of 
its  extent.  It 
covers  the  deep 
surface  of  the 
transversalis  mus- 
cle, and  is  con- 
tinuous internally 
(through  the  lum- 
bar fascia)  with 
the  fascise  of  the 
quadratus      lum- 

borum  and  the  psoas  muscles.  It  is  continuous  above  with  the  diaphragmatic 
fascia,  and  below  (the  iliac  crest  and  Poupart's  ligament  intervening)  with  the 
fascia  iliaca.  Along  with  the  last-named  fascia  it  forms  the  femoral  sheatli.  It  is 
pierced  by  the  spermatic  cord  or  round  ligament  of  the  uterus  at  the  internal 
abdominal  ring,  and  its  prolongation  into  the  inguinal  canal  around  the  cord  forms 
the  infundibuliform  fascia.  It  is  lined  internally  by  the  peritoneum,  from  which  it 
is  separated  by  a  layer  of  extra-peritoneal  tissue. 

The  extra-peritoneal  tissue  is  usually  loaded  with  fat ;  it  envelops  the  kidneys, 
ureters,  suprarenal  capsules,  abdominal  aorta  and  inferior  vena  cava  and  their 
branches,  and  forms  sheaths  for  the  vessels  and  ducts  (ureter,  vas  deferens, 
etc.)  It  is  continued  upwards  into  the  posterior  mediastinum  of  the  thorax 
through  the  aortic  opening  in  the  diaphragm,  and  below  is  in  continuity  with  the 
extra-jjeritoneal  tissue  in  the  pelvis.  It  not  only  comYjletely  invests  the  kidneys 
and  suprarenal  capsules,  but  it  also  becomes  interpolated  between  the  layers  of 
peritoneum  upholding  and  enveloping  the  intestines.  This  tissue  is  absent  in 
relation  to  the  diaphragm,  on  the  under  surface  of  which  there  is  also  no  fat. 


Fig.  337.— The  Groin. 


Structures  between  the  Layers  of  the 
Superficial  Fascia. 


THE  MUSCLES  OF  THE  ABDOMINAL  WALL. 

The  muscles  of  the  abdominal  wall  are  in  three  series — lateral,  anterior,  and 
posterior. 

The  lateral  muscles  of  the  abdominal  wall  comprise  the  obliquus  externus, 
obliquus  intornus,  and  transversalis  abdominis. 

The  obliquus  externus  abdominis  is  a  broad  thin  sheet  of  muscle,  with  an 
origin  from  the  outer  surfaces  of  the  lower  eiglit  ribs,  by  slips  which  inter- 
digitato  with  the  serratus  magnus  and  latissimus  dorsi  muscles.  Tlie  muscular 
fibres  radiate  downwards  and  Ibrwards,  the  lowest  fibres  passing  vertically  down- 
wards. Tlie  lower  and  posterior  part  of  the  muscle  is  inserted  directly  by  fleshly 
fibres  into  the  outer  lip  of  the  iliac  crest  in  its  anterior  half  or  two-thirds  (Fig. 


428 


THE  MUSCULAE  SYSTEM. 


Rectus  abdominis 


Obliquus  externus 

Obliquus  internus 
Transversmis 

ABDOMIM'3 

Fascia  transverb.il  i 
Peritoneum 


290,  p.  373).  The  rest  of  the  muscle  is  inserted  into  an  extensive  triangular  apo- 
neurosis cover- 
ing the  anterior 
abdominal  wall. 
This  aponeurosis 
is  broader  below 
than  above  ;  it  is 
united  with  part 
of  the  aponeurosis 
of  the  obliquus 
internus  in  the 
upper  three- 
fourths  of  its  ex- 
tent, to  form  the 
anterior  layer  of 
the  sheath  of  the 
rectus  muscle.  It 
thus  gains  an  at- 
tachment, above 
to  the  ensiform 
cartilage,  below 
to  the  symphysis 
pubis,  and  by  its 
in  ter mediate 
fibres  to  the  linea 
alba,  a  broad  in- 
terlacing band  of 
fibres  about  half 
an  inch  in  width 
which      occupies 

the  middle  line  of  the  anterior  abdominal  wall  in  its  whole  extent,  and  forms  the 
greater  part  of  the  ultimate  insertion  of  all  the  lateral  abdominal  muscles. 


Extraperitoneal 
tissue 

Kidnej 


Lumbar  fascia-^ 

LaTISSIMUS  DOR'il" 
QUADRATUIb  LUJIBORUM 


Psoas  fascia 

Second  lumbar 
vertebi'a 

Psoas 

Anterior  layer  of 
lumViar  fascia 

MULTIFIDUS 

SPIN/E 

Semispinalis 

DORSI 


Middle  layer  of  lum 


ar  lascia 
Ilio-costalis 


Vertebral  aponeurosis 


LONGISSIMUS  DORSI 


Fig. 


3-38. — Transverse  Section  through  the  Abdomen,  opposite  the 
Second  Lumbar  Vertebra. 


Obliquus  externus  musclE' 

Aponeurosis  of  obliquus  externus 

Intercolunmar  fibres- 

Poupart's  ligament 

Iliac  portion  of  fascia  lata 
External  cutaneous  nerve — 


Falciform  ligament- 
Crural  sheatli 
Femoral  vein— 
Femoral  arter)  - 
Geuito-crural  nervi  — ' 

Inferior  cornu  of  saphenous 

opening 
Femoral  lymjjhatic  gland 


Internal  saphenous  vein 


Eleventh  thoracic  nerve 
rwelfth  thoracic  nerve 


[lio-hypogastric  nerve 

lnten"al  f  P^^^^''^  of  external  abdominal  ring 

External  abdominal  ring  and  spermatic  cord 


■suspensory  ligament  of  penis 
I — llio-inguinal  nerve 


IBody  of  penis 

Dartos  muscle  of  scrotum 


Middle  cutaneous  nerves 


Pubic  portion  of  fascia  lata 


Pig.  339. — The  Groin.     The  Structures  seen  on  removal  of  the  Superficial  Fascia. 
The  upper  part  of  the  aponeurosis  covers  the  insertion  of  the  rectus  abdominis 


THE  MUSCLES  OF  THE  ABDOMINAL  WALL. 


429 


muscle  on  the  chest  wall,  and  gives  origin  to  fibres  of  the  pectoralis  major.  Below, 
in  the  groin,  it  gives  rise  to  Poupart's  ligament,  Gimbernat's  ligament,  the  external 
abdominal  ring  with  its  two  pillars,  the  intercolumnar  fascia  and  fibres,  and  the 
triangular  fascia. 

Poupart's  ligament  is  a  fascial  band  which  extends  from  the  anterior  superior 


STrRNO  MASTOID 

Trapfziuv 


Platisma  m\oidls. 


Coracoid 
process 

Pectoralis 
MAJOR  (divided) 

Pectoralis 

MINOR 

Pectoralis 
MAJOR  (divided) 


Pyramidalis  abdominis 

Poupart's  ligament 
External  abdominal  ring, 

Triangular  fascia 


Fio.  340. — Anterior  Muscles  ok  thr  Trunk. 

iliac  spine  to  the  spine  of  tlie  pubis,  arcliing  over  the  iliacus,  ])Koas,  and  pectineus 
miisclcH.  It  represents  the  lower  limit  oi'  the  aponeurosis  of  the  obliquus  externus 
abdominis,  and  gives  attachment  below  to  the  fascia  lata  of  the  thigh.  Its  outer 
jjart  affords  partial  origin  to  the  deeper  lateral  muscles  of  the  abdominal  wall, 
and  receives  the  attachment  of  the  fascia  transversalis  and  fascia  iliaca  ;  the  inner 
part  forms  the  gutter-like  floor  of  the  inguinal  canal.  At  its  inner  end  a  triangular 
band  of  fibres  is  reflected  horizontally  backwards  to  the  ilio-pectincal  line;,  forming 


430 


THE  MUSCULAK  SYSTEM. 


Gimbemat's  ligament,  the  outer  edge  of  which  limits  iuternally  the  crural  ring.  The 
femoral  vessels  enclosed  in  the  femoral  sheath  enter  the  thigh  beneath  Poupart's 
ligament,  in  front  of  the  psoas  muscle,  and  the  term  saperjicial  crural  arch  is  given 
to  the  part  of  the  ligament  which  covers  the  vessels. 

The  external  abdominal  ring,  the  place  of  exit  of  an  inguinal  hernia,  is  a  split  in 
the  aponeurosis  of  the  obliquus  externus,  just  above  the  spine  of  the  pubis.  It 
transmits  the  spermatic  cord,  or  round  ligament  of  the  uterus,  covered  by  the 
cremaster  muscle  or  cremasteric  fascia.  The  opening  is  of  consideraljle  extent,  and 
its  edges  are  drawn  together  by  a  thin  fascia,  strengthened  superficially  by  a  number 
of  arched  and  horizontal  fibres,  called  the  intercolumnar  fibres,  which  arise  from 
Poupart's  ligament  and  sweep  inwards  across  the  cleft  in  the  aponeurosis. 

The  margins  of  the  ring  constitute  its  pillars.  The  external  pillar  is  narrow, 
and  is  formed  from  that  part  of  the  aponeurosis  which  joins  the  pul»ic  spine,  and  is 
continuous  with  the  inner  end   of  Poupart's  ligament.     The  internal  pillar  is  the 

part  of  the  apo- 
neurosis internal 
to  the  ring  which 
^^^^  is  attached  to  the 

physis  of  the 
pubis.  It  is  flat 
and  broad. 

The  inter- 
columnar fibres 
and  the  pillars  of 
the  external  ab- 
dominal ring  are 
continuous  with 
a  thin  tubular 
sheath,  the  inter- 
columnar or  ex- 
ternal spermatic 
fascia,  which  is 
attached  to  the 
margins  of  the 
"ring," and  forms 
an   envelope   for 

the  spermatic  cord  or  round  ligament  in  their  further  passage  beyond  the  abdominal 
wall. 

The  triangular  fascia,  lastly,  is  a  triangular  band  of  fibres  placed  behind  the 
internal  pillar  of  the  external  abdominal  ring.  It  consists  of  fibres  from  the 
opposite  external  oblique  aponeurosis,  which,  having  traversed  the  linea  alba,  gain 
an  insertion  into  the  crest  and  spine  of  the  pubis. 

The  obliquus  externus  muscle  is  superficial  in  almost  its  whole  extent.  It  is 
overlapped  posteriorly  by  the  latissimus  dorsi  muscle,  but  may  be  separated  from 
it  just  above  the  iliac  crest  by  an  angular  interval  (triangle  of  Petit). 

The  obliquus  internus  abdominis,  a  broad  thin  sheet  lying  between  the 
obliquus  externus  and  the  transversalis,  arises  from  (1)  the  lumbar  fascia,  (2)  the 
anterior  half  of  the  iliac  crest,  and  (3)  the  outer  half  of  Poupart's  ligament. 
Directed  for  the  most  part  upwards  and  forwards,  its  highest  fibres  are  inserted 
directly  into  the  last  three  ribs.  The  rest  of  the  fibres  form  an  extensive  aponeu- 
rosis, broader  above  than  below,  which  splits  along  the  linea  semilunaris,  to  form,  along 
with  the  aponeuroses  of  the  obliquus  externus  and  transversalis  muscles,  the  sheath 
of  the  rectus  abdominis,  and  is  thereafter  inserted  into  the  seventh,  eighth,  and  ninth 
costal  cartilages,  and  into  the  linea  alba  from  the  ensiform  cartilage  to  the  symphysis 
pubis.  The  fibres  arising  from  Poupart's  ligament  join  with  those  of  the  trans- 
versalis muscle  having  a  similar  origin  to  form  the  conjoint  tendon,  which  passes 
altogether  in  front  of  the  rectus  muscle,  to  be  attached  to  the  pubic  crest  and  spine 
and  to  the  ilio-pectineal  line. 


Obliquus  internus- 

Uio-hj'pogastric  nerve- 

Ilio-inguinal  nerve —    f- 

Cremaster 

Aponeurosis  of  _ 
obliquus  externus  (cut) 

Saphenous  opening  — 

Genito-crural  nerve — ■ 
Internal  saphenous  vein— 


Aponeurosis  of 
obliquus 
externus  (cut) 
Twelfth  thoracic 
nerve 


Triangular  fascia 

Spermatic  cord 
Suspensory  liga- 
ment of  penis 

Intercolumnar 
fascia 
Dartos  muscle 


Fig.   341.- 


-The  Gkoin.     The  Structures  seen  on  removal  of  part  of  the 
Obliquus  Externus. 


THE  MUSCLES  OF  THE  AJ5D0MINAL  WALL. 


431 


The  obliquus  internus  is  limited  above  by  the  costal  arch.  Its  lower  fibres, 
arching  over  the  spermatic  cord,  assist  in  forming,  externally,  the  anterior  wall  of 
the  inguinal  canal;  internally,  by  means  of  the  conjoint  tendon,  it  helps  to  form 
the  posterior  wall  of  the  canal. 

Its  lowest  fibres  are  continued  into  the  cremaster  muscle,  which  is  prolonged 
along  the  spermatic  cord  through  the  inguinal  canal. 

The  cremaster  muscle  may  be  said  to  have  an  origin  from  the  lower  border  of  the 
obliquus  internus,  and  from  the  centre  of  Poupart's  ligament.  It  forms  a  thin  sheet, 
enveloping  the  testicle  and  spermatic  cord  ;  its  fibres  are  arranged  in  loops  which  arch 
over  the  cord,  and  are  inserted  into  the  fascia,  and  to  a  less  extent  (uppermost  fibres)  into 
the  pubic  spine.  The  muscle  is  more  largely  represented  by  fascia  in  the  female,  and 
constitutes  the  cremasteric  fascia. 

The  transversalis  muscle  arises  (1)  from  the  under  surface  of  the  costal 
cartilages  of  the  lower  six  ribs,  inter-digitating  with  the  origins  of  the  diaphragm  ; 
(2)  from  the  lumbar  fascia ;  (3)  from  the  anterior  half  of  the  inner  lip  of  the  iliac 
crest ;  and  (4)  from  the  outer  third  of  Poupart's  ligament.     The  muscular  fibres 


Obliquus  externus 

Obliquus  internus 

Obliquus  internus  (cut) 
Deep  circumflex  iliac  artery 

Internal  abdominal  ring  and 
infundibulifonn  fascia 

Cremaster  muscle 
Obliquus  externus 

Spermacic  cord  passing 
through  cremaster  muscle 


Obliquus  externus 
Obliquds  internus  (cut) 

Transversalis  muscle 

Over  deep  epigastric  artery 

Fascia  transversalis 

Deep  epigastric  artery 

Conjoint  tendon 

Over  outer  border  of  rectus  abdominis 

Spermatic  cord 

Triangular  fascia 


Fig.  342. — The  Groin.     The  Structures  seen  on  reflexion  of  part  of  the  Obliquus  Internus. 

are  directed  for  the  most  part  horizontally  forwards,  and  end  in  an  aponeurosis 
which  has  a  twofold  insertion.  (1)  After  forming  (along  with  the  aponeurosis  of 
the  obliquus  internus)  the  posterior  layer  of  the  sheath  of  the  rectus,  the 
aponeurosis  is  attached  to  the  ensiform  cartilage  and  linea  alba.  (2)  The  lower 
fibres  of  the  muscle  arising  from  Poupart's  ligament  are  joined  by  the  lower  part 
of  the  obliquus  internus  to  form  the  larger  part  of  the  conjoint  tendon,  which  passes 
in  front  of  the  lower  part  of  the  rectus  muscle,  to  be  inserted  into  the  crest  and  spine 
of  the  pubis  and  the  ilio-pectineal  line. 

The  transversalis  muscle  is  separated  by  the  lower  intercostal  nerves  from  the 
obliquus  internus  muscle,  and  is  lined  on  its  deep  surface  by  the  transversalis  fascia. 
Its  lower  border  I'ornis  a  concave  edge,  septarated  from  Poupart's  ligament  by  a 
lunuhir  interval  in  which  the  transversalis  fascia  appears,  and  through  which  the 
spermatic  cord  emerges  at  the  internal  abdominal  ring,  under  cover  of  the  obli([uu8 
internus  muscle  and  the  aponeurosis  of  the  obliquus  externus. 

The  anterior  muscles  of  the  abdominal  wall  include  the  pyramidalis  and 
rectus  abflomiiiis,  enveloped  by  the  sheath  of  tlie  rectus  on  either  side  of  the  linea 
alba. 

'I'he  pyramidalis  abdominis  is  a  small  triangular  muscle  arising  from  the  pubic 
crest  in   frrjiit  ol    the  rectus  musculo  (l^'ig.  282,  p.   360).      It  is  directed  oldicpiely 


432 


THE  MUSCULAE  SYSTEM. 


vipwards,  to  be  inserted  for  a  variable  distance  into  the  linea  alba.       The  muscle 
is  often  abssnt. 

The  rectus  abdominis  muscle  is  broad  and  strap-like,  and  arises,  by  an  inner 
and  an  outer  head,  from  the  symphysis  and  crest  of  the  pubis  (Fig.  282,  p.  366). 
Expanding  as  it  passes  upwards,  the  muscle  is  inserted  from  within  outwards  into 
the  front  of  the  ensiform  cartilage  (Eig.  246,  p.  322),  and  into  the  front  of  the 
seventh,  sixth,  and  fifth  costal  cartilages.  On  its  anterior  surface,  but  not 
extending  through  the  entire  substance  of  the  muscle,  are  three  or  more  transverse 
tendinous  intersections  (linese  transversse),  adlierent  to  the  sheath  of  the  muscle  ; 
the  lowest  opposite  tlie  umlilicus,  and  the  highest  about  the  level  of  the  ensiform 
cartilage.     Enclosed  in  its  sheath,  and  covered  anteriorly  by  the  pyramidalis  muscle, 

the  rectus  conceals  the  superior  and  deep 
epigastric  vessels,  the  terminal  branches 
of  the  lower  thoracic  nerves  (which 
pierce  the  muscle  to  reach  tlie  anterior 
abdominal  wall),  the  fold  of  Douglas, 
and  the  fascia  transversalis.  The  inner 
border  of  the  muscle  lies  alongside  the 
linea  alba;  its  outer  border  is  convex, and 
corresponds  to  the  linea  semilunaris. 

The  sheath  of  the  rectus  muscle  is 
derived  from  the  aponeuroses  of  the 
lateral  muscles  of  the  abdominal  wall, 
which,  after  enclosing  the  muscle,  give 
rise  in  the  middle  line  to  the  linea  alba. 
At  the  linea  semilunaris,  at  the  outer 
border  of  the  rectus  muscle,  the  apo- 
neurosis of  the  obliquus  internus  splits 
into  anterior  and  posterior  layers.  The 
anterior  layer,  joined  by  the  aponeurosis 
of  the  obliquus  externus,  passes  in  front 
of  the  rectus,  and  constitutes  theanterior 
lamina  of  the  sheath.  The  posterior 
layer,  joined  by  the  aponeurosis  of  the 
transversalis  muscle,  passes  behind  the 
rectus,  and  constitutes  the  posterior 
lamina  of  its  sheath.  This  arrangement 
obtams  in  the  upper  three-fourths  of 
the  abdominal  wall.  Below  the  level 
of  the  iliac  crest  the  sheath  of  the 
muscle  is  deficient  posteriorly,  and  a 
crescentic  border,  the  fold  of  Douglas, 
marks  the  lower  limit  of  the  posterior 
lamina.  In  consequence,  the  rectus  in 
the  lower  fourth  of  the  abdominal  wall 
rests  upon  the  fascia  transversalis 
directly.  Close  exammation,  however, 
usually  reveals  a  thin  layer  behind  the  muscle  in  continuity  with  the  fold  of 
Douglas,  and  merging  below  with  the  fascia  transversalis.  In  this  region  the  rectus 
is  covered  anteriorly  by  the  conjoint  tendon  of  the  obliquus  internus  and  trans- 
versalis, and  by  the  aponeurosis  of  the  obliquus  externus,  which  is  gradually 
becoming  separate  from  the  subjacent  aponeurosis.  The  upper  part  of  the  rectus, 
lying  on  the  chest  wall,  is  only  covered  anteriorly  by  a  single  layer  of  aponeurosis 
derived  from  the  obliquus  externus,  which  in  this  situation  is  giving  origin  to  the 
pectoralis  major  muscle. 

Inguinal  Canal. — The  spermatic  cord  in  the  male,  and  the  round  ligament  in 
the  female,  in  their  passage  through  the  lower  part  of  the  abdominal  wall,  pass 
through  the  inguinal  canal,  which  is  bounded  by  these  abdominal  muscles.  The 
canal  begins  at  the  internal  abdominal  ring,  placed  half  an  inch  above  Poupart's 


Fig.  343. — The  Sheath  of  the  Rectus  Abdominis 
Muscle. 

(I.)  In  the  thoracic  wall  ;  (II.)  In  the  npper  three- 
quarters  of  the  abdominal  wall  ;  (III.)  In  the  lower 
fourth  of  the  abdominal  wall. 

A,  Rectus  muscle  ;!  B,  Obliquus  externus;  C,  Dia- 
phragm ;  D,  Obliquus  internus  ;  E,  Transver- 
salis abdominis,  a,  Anterior  layer  of  rectus  sheath  ; 
6,  Fifth  costal  cartilage  ;  c,  Sixth  costal  cartilage  ; 
d,  Xiphoid  cartilage  ;  e,  Posterior  layer  of  rectus 
sheath  ;  /,  Transversalis  fascia  ;  g,  Peritoneum  ;  h, 
Linea  alba.      1,  Deep  epigastric  artery. 


THE  MUSCLES  OF  THE  ABDOMINAL  WALL. 


433 


ligament,  and  midway  between  the  anterior  superior  iliac  spine  and  the  symphysis 
pubis.  It  ends  at  the  external  abdominal  ring,  placed  above  the  spine  and  crest 
of  the  pubis.  The  front  ivall  of  the  canal  is  formed  by  the  aponeurosis  of  the 
obliquus  externus,  and  in  its  outer  part  by  the  muscular  fibres  of  tbe  obliquus 
internus  ;  the  back  toall  of  the  canal  is  formed  by  the  fascia  transversalis,  and  in 
its  inner  part  by  the  conjoint  tendon ;  while  the  Jioor  of  the  canal  is  formed  by 


Vena  caval  opening    OOsophageal  opening     Central  tendon  (middle  jiart) 


Central  tendon  (ris^ht  part) 

Diaphragm,  costal  fibres 

Internal  arcuate  ligament 

External  arcuate  ligament 

End  of  last  rib 

Last  thoracic  nerve 

Ant.  layer  of  lumbar  fascia 

Lumbar  fascia     -fr- 
Ilio-hypogastric      ,  n 
Lumbar  vessels  and  sympa-      |j 
thetic  communicating  nerves 
Ilio-inguinal 

QUADRATUS  LUMBORUM 


External  cutaneous  nerve 

Psoas  magnus 

Iliacus 

Lumbo-sacral  cord 

Genito-crural  naive 

Anterior  crural  nerve 

Obturator  nerve 

Great  sciatic  nerve 


Diaphragm,  right  crus 

Middle  arcuate  lit<ament 
/   Aortic  opening 

Central  tendon 
(left  part) 
Diaphragm,  left 

CRUS 


Last  thoracic  nerve 

jtf-  End  of  last  rib 

==— — ITTT   Lumbar  nerve  I. 
■     ^-fi-T-  Ilio-hypngastric 
H-    Lumbar  nerve  IL 

n-    Ilio-inguinal 
Qltadratus 
\\\\     lumborum 

Lumbar  nerve  IIL 


Genito-crural 
Lumbar  nerve  IV. 


Lumbo-sacral  cord 


External  cutaneous  nerve 
Anteiior  crural  nerve 

Obtuiator  nerve 
Gieat  sciatic  nerve 


Fig.  344. 


Obtuiator  nerve 
Adductor  longus  (origin) 
Adductor  brevis  (origin)  '•  ': 

Gracilis  (origin) 
Adductor  magnus  (origin) 
I     Pectin Eus  (cut) 
Superficial  branch  of  obturator  nerve 
Deep  branch  of  obturator  nerve 
Obturator  externus 

-View  of  thk  Posteuior  Abdominal  Wall,  to  show  the  Muscles  and  the  Nerves  of 
THE  Lumbo-Sac'ral  Pi.e.xus. 


Poupart's  ligament,  and  in  its  inner  ])art  by  (;limbornat's  ligament.  Tlic  spermatic 
cord,  piercing  the  transversalis  fascia,  enters  the  inguinal  canal  at  the  internal 
abdominal  ring,  and  is  there  invested  by  its /m's/5  envelope,  i\\Q  infundibuliform  or 
internal  spermatic  fascia,  a  sheath  of  fuscia  derived  from  the  margin  ol'  tiic  ring  and 
continuous  with  the  fascia  transversalis.  It  then  ])asses  obliquely  inwards,  down- 
wards, and  forwfirds,  and  escajies  below  the  lower  border  of  th(i  oblir(uus  internus 
muscle,  from  which  it  carries  off  a  second  invedment,  partly  fascial,  partly  muscular 
31 


434  THE  MUSCULAE  SYSTEM. 

— the  cremaster  muscle  or  cremasteric  fascia.  Continuing  its  course  in  front  of  the 
conjoint  tendon,  it  emerges  tlirough  the  external  abdominal  ring,  from  the  edges  of 
which  the  intercolumnar  fascia  is  derived,  the  third  or  external  investment  for  the  cord. 

Hesselbach's  triangle,  bounded  below  by  the  line  of  Poupart's  ligament,  internally 
by  the  rectus  abdominis  muscle,  and  externally  by  the  deep  epigastric  artery  on 
the  mesial  side  of  the  internal  abdominal  ring,  is  the  site  of  one  form  of  inguinal 
hernia.  The  spermatic  cord  passes  over  the  base  of  the  triangle,  covered  over 
by  the  aponeurosis  of  the  obliquus  externus.  Behind  the  cord,  and  forming  the 
floor  of  the  triangle,  are  the  fascia  transversalis  and  the  conjoint  tendon  of  the 
obliquus  internus  and  transversalis  muscles. 

Inguinal  Hernia. — For  an  account  of  the  anatomical  relations  of  the  inguinal 
canal  to  the  various  forms  of  inguinal  hernia,  see  the  section  on  "  Applied  Anatomy." 

The  posterior  muscles  of  the  abdominal  Avail  and  false  pelvis  include  the 
psoas  (maguus  and  parvus)  and  iliacus,  described  already  (p.  363),  and  the  quadratus 
lumborum. 

The  quadratus  lumborum  lies  on  the  posterior  wall  of  the  abdomen  external 
to  the  psoas,  and  extends  between  the  iliac  crest  and  the  last  rib.  It  arises  from 
the  posterior  part  of  the  iliac  crest,  from  the  ilio-lumbar  ligament,  and  from  the 
transverse  processes  of  the  lower  lumbar  vertebrae.  It  is  inserted  above  into  the 
inner  part  of  the  lower  border  of  the  last  rib  and  the  transverse  processes  of 
the  upper  lumbar  vertebrse.  It  is  enclosed  between  the  anterior  and  middle 
layers  of  the  lumbar  aponeurosis  (p.  391),  and  is  placed  behind  the  colon,  kidney, 
and  psoas  muscle,  in  front  of  the  multifidus  spinse  and  the  lumbar  transverse 
processes.     Its  outer  border  is  directed  obliquely  upwards  and  inwards. 

Nerve-Supply. 

The  nerve  -  supply  of  all  the  foregoing  muscles  except  the  jasoas,  cremaster,  quadratus 
luiuborum,  and  iliacus,  is  derived  from  the  anterior  primary  divisions  of  the  lower  six  thoracic 
nerves.  Tlie  pyramidalis  muscle  is  innervated  by  the  last  thoracic  nerve.  The  cremaster  muscle 
receives  its  supply  troni  the  genito-crural  nerve,  whilst  the  quadratus  lumborum  is  innervated 
by  the  first  three  or  four  lumbar  nerves.  The  jjsoas  and  iliacus  muscles  are  sujjplied,  directly  or 
through  the  anterior  crural  nerve,  from  the  second,  third,  and  fourth  lumljar  nerves. 

Actions. 

Many  of  the  actions  of  the  above  muscles  have  already  been  given  in  previous  sections.  (1) 
Their  chief  action  is  to  retract  the  abdominal  walls,  and,  by  comj^ressing  the  contents  of  the 
abdomen,  they  are  powerful  agents  In  vomiting,  defyecation,  micturition,  parturition,  and 
laboured  expiration.  (2)  They  are  also  flexors  of  the  spine  and  j)elvis — the  muscles  of  both  sides 
acting  together  ;  the  spine  and  pelvis  are  laterally  flexed,  when  one  set  of  muscles  acts  alone.  (3) 
Tlie  quadratus  lumborum  is  a  muscle  of  inspiration,  an  extensor  of  the  spine,  and  a  lateral  flexor 
of  the  spine  and  pelvis. 

FASCIJE   AND   MUSCLES    OF    THE    PERINEUM   AND    PELVIS. 
FASCIJE  OF   THE   PERINEUM. 

The  superficial  fascia  of  the  perineum  possesses  certain  special  features.  It 
is  continuous  with  the  superficial  fascia  of  the  abdominal  wall,  thigh,  and  buttock, 
and  is  prolonged  on  to  the  penis  and  scrotum.  In  relation  to  the  penis,  it  is 
devoid  of  fat  and  consists  only  of  areolar  tissue.  In  relation  to  the  scrotum,  it  is 
intermingled  with  involuntary  muscular  fibres,  and  constitutes  the  dartos  muscle, 
which  assists  in  suspending  the  testicles  and  corrugating  the  skin  of  the  scrotum. 
This  fascia  also  forms  the  septum  of  the  scrotum,  which,  extending  upwards,  in- 
completely separates  the  two  testicles  and  their  coverings.  In  the  female  the 
superficial  fascia  takes  a  large  share  in  the  formation  of  the  mons  veneris  and 
labia  majora,  in  which  a  considerable  quantity  of  fat  occurs. 

The  fascia  over  the  jwsterior  po.rt  of  the  perineum  fills  up  the  ischio-rectal  fossae, 
in  the  form  of  two  pads  of  adipose  tissue,  on  either  side  of  the  rectum  and  anus. 
Over  the  tuberosities  of  the  ischium  the  fat  is  largely  replaced  by  bands  of  fibrous 
tissue  closely  adherent  to  the  subjacent  deep  fascia. 


THE  MUSCLES  OF  THE  PERINEUM. 


435 


The  fascia  in  the  anterior  part  of  the  perineum  closely  resemVjles  the  same 
fascia  in  the  groin.  It  is  divisible  into  a  superficial  fatty  and  a  deeper  membranous 
layer ;  tlie  former  continuous  with  the  same  layer  in  the  thigh,  and  with  the  fat 
of  the  ischio-rectal  fossa  posteriorly.  The  deeper  membranous  layer  is  attached 
laterally  to  the  pubic  arch,  posteriorly  to  the  base  of  the  triangular  ligament,  and 
in  the  middle  line  to  the  root  of  the  penis  (bulb  and  corpus  spongiosum)  by  a 
median  raphe  continuous  farther  forwards  with  the  septum  of  the  scrotum 
mentioned  above.  Anteriorly  the  fascia  is  continued  over  the  spermatic  cords  to 
the  anterior  abdominal  wall.  The  importance  of  this  fascia  lies  in  relation  to  the 
extravasation  of  urine  from  a  rupture  of  the  urethra.  By  the  fascial  attachments 
the  fluid  is  prevented  from  passing  backwards  into  the  ischio-rectal  fossa,  or 
laterally  into  the  thigh.  It  is  directed  forwards  into  relation  with  the  scrotum 
and  penis,  and  along  the  spermatic  cord  to  the  anterior  abdominal  wall.  The 
septum  of  the  scrotum  being  incomplete,  fluid  extravasated  on  one  side  can  pass 
across  the  middle  line  to  the  opposite  half  of  the  perineum  and  scrotum. 

The  deep  fascia  of  the  perineum  only  exists  in  the  form  of  the  delicate 
aponeuroses  of  the  muscles. 

THE   MUSCLES    OF   THE    PERINEUM. 

The  perineal  muscles  are  naturally  separated  into  a  superficial  and  a  deep  set  by 
the  triangular  ligament.     Superficially  are  the  sphincter  ani  externus,  transversus 


-CAyERNOSDS 


Erector  penis 


Transversus 

PERINEI 


Ischial  tuberosity 


Levator  ani 


Gluteal 
branches  of  j 
small  sciatic 
nerve 


Parietal  jjelvic 
fascia 


Inferior  hemorrhoidal  uei  \ 


Perforating  cutaneous  nerve 
Perineal  branch  of  fourth  sacral  nerve 


Levator  ani 
External  sphincter  ani 


Anterior  sacro-coccygeal  nerve 
Fig.  345. — The  Muscles  and  Nerves  ok  the  Male  Peuineum. 


perinei  superficialis,  bulbo-cavernosus,  and  ischio-cavernosus  ;  beneath  the  triangular 
ligament  is  the  compressor  urethrte. 

Sphincter  ani  Externus. — This  muscle  is  fusiform  in  outline,  flattened,  and 
ob]iqiu;ly  ]>l;u;(;d  jiroiind  the  anus  and  anal  canal.  It  can  be  separated  into 
three  layers, — subcutaneous,  superficial,  and  deep.  (1)  The  most  superficial  lamina 
consists  of  subcutaneous  fibres  decussating  behind  and  in  front  of  the  anus,  but 
without  bony  attachments.  (2)  llie  sphincter  ani  superficialis  constitutes  the 
main  portion  of  the  muscle.  It  is  attached  posteriorly  to  the  coccyx,  and  in 
front  of  th(;  anus  reaches  the  central  point  of  the  perineum,     (.'i)  The  deep  fibres 


436 


THE  MUSCULAE  SYSTEM. 


of  the  muscle  form  for  the  most  part  a  complete  sphincter  for  the  anal  canal.  They 
are  continuous  with  the  filires  of  the  levator  ani ;  they  encircle  the  anal  canal,  and 
blend  anteriorly  with  the  central  point  of  the  perineum  and  the  transversus 
perinei. 

The  muscle  surrounds  the  anus,  covered  only  by  the  skin,  superficial  fascia,  and 
the  corrugator  cutis  ani  (a  series  of  non-striated  muscular  fibres  radiating  from  the 
anal  opening).  It  rests  on  the  edge  of  the  levator  ani,  and  forms  the  median 
boundary  of  tlie  ischio-rectal  fossa. 

The  transversus  perinei  superficialis  is  not  always  present.  It  consists  of  a 
more  or  less  feeble  bundle  of  fibres,  arising  from  the  asceudmg  ramus  of  the  ischium 
and  the  fascia  over  it,  and  from  the  base  of  the  triangular  ligament.  It  is  directed 
inwards  and  forwards  to  be  inserted  into  the  central  point  of  the  perineum.  It 
conceals  the  base  of  the  triangular  ligament,  and  has  a  variable  relation  to  the 
superficial  perineal  vessels  and  nerves. 

The  bulbo-cavernosus  (ejaculator  urinse),  in  the  male,  surrounds  the  bulb,  corpus 
spongiosum,  and  root  of  the  penis.  It  is  sometimes  separated  into  two^  parts— 
posterior  (compressor  bulbi),  and  anterior  (compressor  radicis  penis).  It  arises  from 
the  central  point  of  the  perineum,  and  from  a  median  raphe  on  the  under  surface  of 

the  bulb  and  corpus 
spongiosum.  The  mus- 
cular fibres  are  directed 
outwards  and  forwards, 
and  have  a  triple  inser- 
tion :  from  behind  for- 
wards, (1)  into  the 
under  surface  of  the 
triangular  ligament ; 
(2)  into  the  membrane 
covering  the  corpus 
spongiosum ;  and  (3), 
after  encircling  the 
corpora  cavernosa,  into 
the  fascia  covering  the 
dorsum  of  the  penis. 


Bulbo- 
cavernosus 


_Tkansversus 

PERINEI 


Levator  ani 


Gluteus 

MAXIMUS 


The    ischio-bul- 

bosus,  not  ahvays 
present,  arises  from  the 
ischium,  and  passes  ob- 
hquely  inwards  and  for- 
wards over  tlie  bulbo- 
cavernosus,  to  be  in- 
serted into  the  raphe 
superficial  to tliat muscle. 
It  belongs  to  the  same 
stratum  as  the  trans- 
versus perinei  and  erector 
penis. 

The  compressor 
hemispherium  bulbi 
is  frequently  absent.     It 

consists  of    a  thin  cap-hke  layer  of    muscular  fibres  surrounding  the  extremity  of    the 

bulb  under  cover  of  the  bulbo-cavernosus. 

The  bulbo-cavernosus  (sphincter  vaginae),  in  the  female,  is  separated  into  lateral 
halves  by  the  vaginal  and  urethral  openings.  It  forms  two  thin  lateral  layers 
covering  the  vaginal  bulbs,  and  arises  behind  the  vaginal  orifice  from  the  central 
point  of  the  perineum.  Anteriorly  it  is  inserted  into  the  root  of  the  clitoris, 
some  of  its  fibres  embracing  the  corpora  cavernosa  so  as  to  reach  the  dorsum  of 
the  clitoris. 

The  ischio-cavernosus  (erector  penis),  in  the  male,  covers  the  crus  penis.     It 


Sphincter  ani  externus 

Fia.  346. — The  Muscles  of  the  Female  Perineum  (after  Peter 
Thomp.sou). 


THE  MUSCLES  OF  THE  PEETNEUM. 


437 


arises  from  the  ischial  tuberosity  and  the  great  sacro-sciatic  ligament,  and  passing 
forwards,  is  inserted  by  a  fascial  attachment  into  the  under  surface  of  the  crus 
penis,  and  into  the  outer  side  and  dorsal  aspect  of  the  corpus  cavernosum. 

The  isohio-cavernosus  (erector  clitoridis),  in  the  female,  has  a  similar  disposition, 
but  is  of  ]uuch  smaller  size  than  in  the  male. 

The  pubo-cavernosus  is  an  occasional  slip  arising  from  the  pubic  ramiLS,  and  inserted  into 
the  dorsum  of  the  penis.     It  corresponds  to  the  levator  j)enis  of  lower  animals. 

The  compressor  urethrae  (constrictor  urethrse)  constitutes  the  deeper  muscular 
stratum  of  the  perineum.  It  is  placed  on  the  pelvic  aspect  of  the  triangular 
ligament.  It  arises  from  the  lower  part  of  the  pubic  ramus,  and  is  directed  inwards, 
its  fibres  radiating  so  as  to  enclose  the  membranous  urethra.  It  is  inserted  into  a 
median  raphe,  partly  in  front  of  the  urethra,  but  for  the  most  part  behind  it.  The 
fibres  most  intimately  related  to  the  urethra  form  a  tubular  sheath  for  the  canal, 
and  have  no  bony  attachments. 

The  most  anterior  and  most  posterior  fibres  of  the  compressor  urethrse  exist  sometimes 
as  separate  muscles. 

The  transversus  perinei  profundus  consists  of  a  bundle  of  fibres  on  either  side, 
arising  from  the  ascending  ramus  of  the  ischium  just  below  the  compressor  urethrse.  It 
is  inserted  into  a  median  raphe  continuous  with  that  of  the  compressor  urethrse.  The 
muscle,  in  fact,  constitutes  a  separate  bundle  below  and  behind  the  compressor  urethras. 

The  ischio-pubicus   is  a    term    applied    to    a  feeble    bundle  of    fibres  which,    when 


Corpus  cavernosum 

(cut) 

Nerve  to  corpus 

cavernosum 

Nerve  to  dorsum 

of  penis 

Compressor  ukethr/e 

Nerve  to  bulb 

Triangular  ligament 

(posterior  layer) 

Internal  pudic  nerve 


Bulb  of  penis 

Triangular  ligament 
(anterior  layer) 

Crus  peuis 


Levator  ani 


Fig.  347. — The  Triangular  Ligament  of  the  Perineum,  and  the  Termination  of  the  Pudic  Nerve. 

present,  lies  above  and  in  front  of  the  compressor  urethrse.  It  arises  from  the  pubic 
ramus,  and  is  inserted  into  a  median  raphe  in  front  of  the  membranous  urethra.  This 
muscle  is  homologous  with  the  compressor  venae  dorsalis  penis  of  lower  animals. 

The  compressor  urethrse  in  the  female  is  smaller  than  in  the  male.  Its 
insertion  is  modified  by  the  relations  of  the  urethra  to  the  vagina.  The  anterior 
fijjres  are  continuous  with  those  of  the  opposite  side  in  front  of  the  urethra  ;  the 
intermediate  fibres  pass  between  the  urethra  and  vagina,  and  the  posterior  fibres 
are  attached,  along  witli  the  transversus  perinei  profundus  (transversus  vaginae),  into 
the  side  of  the  vagina. 

Nkrvk-Si'I'ply. 

Tli<;  pudic  nerve  fS.  2.  ?>.  4.)  Hiip])]i(!,s  all  tin;  muscles  in  this  j^noiij)  ;  tlic  c.xti'nial  sphincter 
throiif,'li  tin-,  inferior  hemorrhoidal,  and  the  others  through  the  ])erinca,]  hraiich  (»!'  (lie  ncive. 
The  external  Hphincter  is  also  supplied  hy  the  perineal  branch  of  the  fourth  sacral  nerve. 


438 


THE  MUSCULAR  SYSTEM. 


Actions. 
The  external  sphincter  closes  the  anal  canal.  The  transversus  perinei  superficialis  draws 
V)ack  and  fixes  the  central  jjoint  of  the  perinenm,  assisted  by  the  external  sj^hincter.  The  bulbo- 
cavernosus  of  the  male  constricts  the  bnlb  and  cor^jns  spongiosnm,  and  so  expresses  the  last  drops 
of  urine  or  semen.  In  the  female  it  acts  as  a  feeble  sphincter  of  the  vagina.  The  ischio- 
cavernosus  and  bulbo-cavernosus  help  in  erection  of  the  penis  or  clitoris.  Tlie  compressor 
urethrae  constricts  the  membranous  urethra,  and  in  the  female  helps  to  flatten  and  tix  tlie  wall  of 
tlie  vagina.  It  also  assists  in  causing  erection  of  the  penis  or  clitoris  by  compression  of  the  veins 
in  relation  to  it. 

FASCIA  OF  THE  PELVIS. 

The  pelvic  basin,  placed  obliquely,  deeper  and  more  hollowed  behind  than  in 
front,  and  imperfect  in  its  bony  boundaries,  is  to  a  large  extent  completed  by  liga- 
ments. The  sacro-sciatic  ligaments  behind,  the  obturator  membrane  laterally,  and 
the  triangular  ligament  in  front  assist  in  filling  up  its  osseous  deficiencies.  It  is 
almost  entirely  clothed  internally  by  muscles:  by  the  pyriformis  on  each  side 
behind,  the  obturator  internus  at  the  side,  and  the  compressor  urethrce  in  C(jntact 


Pubo-prostatic  ligaments 
Capsule  of  prostate  gland 
Prostate  gland 


Corpus  spongiosum  penis 
Corpus  cavernosum 
I        I  Superficial  fascia  of  perineum 

Compressor  Urethr/e  muscle 
Triangular  ligament 
J><^  I  I         Posterior  layer  of  triangular  ligament 
~'  Pubic  arch 


Obturator  membrane 

OBTnRATOR  INTERNUS 

Parietal  (obturator)  layer  of 
pelvic  fascia 
Ischio-rectal  fossa 

Anal  fascia 

Obturator  externus 

Levator  ani 

Visceral  layer  of  pelvic  fascia 

Innominate  bone  (ischium) 

Recto-vesical  layer  of  pelvic 
fascia  (enclosing  vasa  deferentia 
and  vesiculse  seminales) 

Rectal  layer  of  pelvic  fascia 
Rectum 

Pyriformis 


Sacrum 


Fig.  348. — Dissection  of  the  Pelvic  Fascia  from  Above  (diagrammatic). 

with  the  triangular  ligament  in  front.  Indeed,  the  bones  of  the  pelvis  only 
project  into  the  cavity  in  three  places ;  the  spines  of  the  ischium  project  into  the 
cavity  on  each  side,  and  the  pubis  appears  in  its  anterior  wall. 

The  pelvic  fascia  forms  a  cylindrical  membrane  lining  the  wall  of  the  pelvis,  as 
an  aponeurosis  for  its  muscles.  It  is  attached  above  and  below  to  the  inlet  and 
outlet  of  the  pelvis  ;  above  to  the  promontory  of  the  sacrum,  ilio-pectineal  line,  and 
back  of  the  pubis  ;  below  to  the  coccyx,  great  sacro-sciatic  ligament,  tuber  ischii, 
and  the  base  of  the  triangular  ligament.  This  cylindrical  membrane  is  the 
parietal  pelvic  fascia ;  it  forms  the  pyriformis  fascia  behind,  the  obturator  fascia 
at  the  side  of  the  pelvis,  and  the  so-called  posterior  layer  of  the  triangular  ligament 
in  front.  As  this  fascia  lines  the  pelvic  wall  it  obtains  attachments  to  the  pro- 
jecting bones,  to  the  back  of  the  pubis  anteriorly,  and  to  the  spine  of  the  ischium 
on  each  side.  It  is  deficient  in  relation  to  the  obturator  groove,  through  which 
the  obturator  artery  and  nerve  pass  to  reach  the  thigh. 

The  white  line,  a  thickened  band  of  the  fascia,  extends  between  the  back  of 
the  pubis  and  the  spine  of  the  ischium,  and  roughly  indicates  the  line  of  separation 
of  the  pelvic  cavity  from  the  ischio-rectal  fossa.  The  white  line  serves  two 
purposes  :  it  gives  origin  to  fibres  of  the  levator  ani  muscle,  and  also  to  a  secondary 


FASCIA  OF  THE  PELVIS. 


439 


Iliacus  muscle 
Fascia  iliaca 

Pelvic  peritoneum 

Pelvic  fascia 

Extra-peritoneal 
tissue 

Obturator  internus 

Parietal  (obturator) 
layer  of  pelvic  fascia 


Visceral  (recto-vesical) 

layer  of  pelvic  fascia 

Fascial  canal  containing 

pudic  artery  and  nerve 

Anal  fascia 

Fat  of  ischio-rectal  fossa 
Levator  ani 

Gluteus  maximus 


Sphincter  ani  externus 


Fig.  349. — Oblique  Section  across  the  Pelvis,  to  show  the  Disposition  of 
THE  Pelvic  Fascia  and  the  Boundaries  of  the  Ischio-Rectal  Fossa. 


sheet  of  fascia,  known  as  the  visceral  pelvic  fascia,  which  arches  downwards  and 
inwards  across  the  floor  of  the  pelvis  to  be  connected  with  the  XJelvic  viscera.  This 
membrane  is  thin  and  unimportant  behind,  as  it  passes  forwards  from  the  lower 
sacral  vertebrae  to  the  rectum.  It  is  thicker  at  the  sides  and  front  of  the  pelvis, 
where  it  forms 
a  stout  membrane 
concave  upwards, 
continuous  mesi- 
ally  with  the 
fibrous  coats  of 
the  rectum  and 
bladder,  and  en- 
veloping the  pros- 
tate gland  and 
vesiculse  semin- 
ales.  At  the  front 
of  the  pelvis  this 
layer  extends 
from  the  back  of 
the  pubis,  to 
which  it  is  di- 
rectly attached, 
to  the  neck  of  the 
bladder  and  pros- 
tate   gland,   and 

gives  rise  to  two  lateral  folds — the  pubo- prostatic  ligaments,  which  enclose 
between  them  a  hollow  on  the  pelvic  aspect  of  the  fascia,  known  as  the  cavum 
Retzii.  The  lateral  portion  of  the  visceral  pelvic  fascia  constitutes  the  recto-vesical 
layer,  divisible  into  three  parts — vesical,  rectal,  and  between  these  the  recto-vesical 

layer,  a  partition  insinuated 
Internal  iliac  artery^  .  ,  1.1         -•  between    the    rectum    and 

bladder,  and  enclosing  the 
vesiculse  seminales  and  vasa 
deferentia.  This  visceral 
pelvic  fascia  thus  forms  a 
support  for  the  pelvic  vis- 
cera, and  at  the  same  time 
acts  as  a  partition  between 
the  pelvic  cavity  and  the 
perineum.     It  is  separated 

fy^fascia^^  ^'^'''''  froi^  the  pelvic  cavity  by 
/^^ — Attacinnentto  the    pcritoueum    and    the 

jj^j        ischial  spine  ,       '-         ..  ,    ,.  . 

■^^  extra-pentoneal  tissue,  and 

is  in  contact  with  the  levator 
ani  muscle  on  its  perineal 
surface.  The  internal  iliac 
vessels  and  their  branches 
lie  on  the  pelvic  aspect  of 
the  fascia,  and  the  parietal 
vessels  pierce  it,  and  are  en- 
sheathed  by  it  as  they  leave  the  pelvis.  On  the  other  hand  the  spinal  nerves 
forming  the  sacral  plexus  lie  outside  the  fascia  with  one  exception.  The  obturator 
nerve,  after  piercing  tlie  inner  })order  of  the  psoas  muscle  and  the  psoas  fascia,  leaves 
the  pelvis  through  a  sp(!cial  hole  in  the  pelvic  wall,  after  traversing  the  extra- 
peritoneal tissue. 

The  'pdvic  fascia  in  the  female  only  diffeis  in  slight  detail  from  that  of  the 
male.  It  encloses  the  neck  of  the  bladder  and  vagina  instead  of  the  prostate 
gland,  and  invests  the  lower  part  of  the  neck  of  the  uterus  inst(!ad  of  the  vesicuhe 
seminales. 


Obturator  nerve 


Anterior  layer 
triangular  ligament 

Posterior  layer 
triangular  ligament 


Visceral  pelvic  fascia 


White  line 

Origin  of  levator  ani 
White  line 
Obturator  fascia 


Fic.  350.— The  Outer  Wall  of  the  Pelvis  (Pelvic  Fascia). 


440 


THE  MUSCULAR  SYSTEM. 


MUSCLES  OF  THE  l^ELVIS. 

The  pelvic  diaphragm  consists  of  several  more  or  less  rudimeutary  muscular 
slips,  constituting  the  levator  ani  and  ischio-coccygeus  muscles,  which  serve  to 
uphold  tlie  pelvic  tioor,  and  are  related  to  the  rectum  and  the  prostate  gland  or 
vagina. 

Tlie  levator  ani  arises  from  (1)  the  back  of  the  body  of  the  pubis,  (2)  the 
parietal  pelvic  fascia  above  or  along  the  %ohite  line,  and  (3)  the  spine  of  the  ischium. 


Sphincter  asi 
f.xternus 


Fig.  351. 


-The  Fascial  and  Muscdlar  Wall  of  the  Pelvis  after  Removal  of  Part  of  the  Left 

Innominate  Bone. 


Its  fibres  are  directed  downwards  and  backwards,  to  be  inserted  into  (1)  the  central 
point  of  the  perineum,  (2)  the  external  sphincter  around  the  anus  and  the  ano- 
coccygeal raphe  behind  the  anus,  and  (3)  into  the  sides  of  the  lower  sacral  and  the 
coccygeal  vertebrse. 

The  concave  upper  surface  of  the  muscle  is  covered  in  part  by  the  visceral 
pelvic  fascia;  in  part  it  is  in  contact  with  the  rectum  behind  and  the  prostate 
gland  or  vagina  in  front.  The  inferior  convex  surface  of  the  muscle  forms  the 
inner  wall  of  the  ischio-rectal  fossa.  Its  posterior  edge  is  overlapped  by  the 
ischio-coccygeas ;  its  anterior  edge  is  in  contact  with  the  posterior  layer  of  the 
triangular  ligament. 


MOEPHOLOGY  OF  THE  SKELETAL  MUSCLES.  441 

The  levator  ani  is  divisible  into  four  parts — pubo-rectalis,  pubo-coccygeus,  ilio- 
coccygeus,  and  ilio-sacralis.  The  pubo-rectalis  (levator  prostatte)  is  the  part  inserted  into 
the  central  point  of  the  perineum.  The  pubo-coccygeus  is  the  part  inserted  into  the  anus 
and  the  ano-coccygeal  raphe,  and  the  ilio-coccygeus  and  ilio-sacralis  are  represented  by 
the  fibres  attached  to  the  sacrum  and  coccyx.  The  first  two  are  best  developed ;  the  last 
two  series  of  fibres  are  the  most  rudimentary.  These  several  parts  of  the  muscle  represent 
the  remains  of  the  flexor  caudse  of  tailed  animals. 

The  ischio-coccygeus  is  a  rudimentary  muscle  overlapping  the  posterior  border 
of  the  levator  ani.  It  arises  from  the  ischial  spine  and  the  small  sacro-sciatic 
ligament,  and  is  inserted  into  the  sides  of  the  lower  two  sacral  and  upper  two 
coccygeal  vertebrae.  The  muscle  is  separated  from  the  rectum  by  the  visceral 
pelvic  fascia,  and  is  in  contact  externally  with  the  sacro-sciatic  ligaments. 

Nerve-Supply. 

The  levator  ani  is  supplied  from  two  sources  :  by  the  perineal  (muscular)  branch  of  the  pudic 
nerve,  and,  on  its  pelvic  surface,  by  special  branches  from  the  third  and  fourth  sacral  nerves. 
The  ischio-coccygeus  is  supplied  on  its  pelvic  surface  by  the  third  and  fourth  sacral  nerves. 

Actions. 

(1)  The  levator  ani  and  ischio-coccygeus  serve  to  uphold  and  slightly  raise  the  pelvic  floor. 
(2)  They  are  likewise  capable  of  producing  slight  flexion  of  the  coccyx.  (3)  The  anterior  fibres 
of  the  levator  ani,  in  the  female,  sweeping  round  the  vagina,  compress  its  walls  laterally,  and 
along  with  the  sphincter  vaginse,  help  to  voluntarily  diminish  the  lumen  of  the  tube.  (4)  The 
same  part  of  the  muscle  in  the  male  elevates  the  prostate  gland  (levator  prostatee).  (5)  The  chief 
action  of  the  levator  ani  is  in  defcecation.  Along  with  the  external  sphincter  it  acts  as  a  sphincter 
of  the  rectum,  closing  the  anal  canal.  During  defsecation  the  muscle  draws  upwards  the  anus 
over  the  fsecal  mass,  and  so  assists  in  its  expulsion.  (6)  In  parhmtion,  in  the  same  way,  the 
muscle,  contracting  below  the  descending  foetal  head,  retards  delivery.  Contracting  on  the  foetal 
head,  it  draws  upwards  the  pelvic  floor  over  the  foetus,  and  so  assists  delivery. 

THE  DEVELOPMENT  AND  MORPHOLOGY  OF  THE  SKELETAL  MUSCLES. 

Our  knowledge  of  the  development  and  morphology  of  the  muscular  system  is  very 
incomplete.  It  has  already  been  shown,  in  the  chapter  on  general  embryology,  that  the 
mesoblast  on  either  side  of  the  embryonic  medullary  tube  separates  into  three  main  parts — 
the  myotome,  nephrotome,  and  sclerotome  or  lateral  plates  (somatopleure  and  splanchno- 
pleure). 

The  myotomes  are  probably  directly  or  indirectly  the  source  of  the  striated  muscles 
of  the  whole  body.  Each  consists  at  first  of  a  quadrilateral  bilaminar  mass,  resting 
against  the  medullary  tube  and  notochord  on  either  side.  The  cleft  between  its  two  layers 
represents  the  remains  of  the  coelomic  cavity.  In  the  early  stages  of  embryonic  life  the 
growth  of  the  myotome  is  rapid.  On  its  inner  side  masses  of  cells  arise,  which  grow  in- 
wards and  surround  the  medullary  tube  and  notochord  to  form  the  foundation  of  the 
vertebral  column.  On  its  outer  side  cells  appear  to  be  given  off  which  participate  in  the 
formation  of  the  cutis  vera.  At  the  same  time  the  dorsal  and  ventral  borders  of  the 
myotome  continue  to  extend,  and  present  extremities  (growing  points)  with  an  epithelial 
structure  for  a  considerable  period.  On  the  dorsal  side  it  overlies  the  medullary  tube,  and 
gives  rise  to  the  muscles  of  the  back ;  while  by  its  ventral  extension,  which  traverses  the 
somatopleuric  mesoblast  in  the  body  wall,  it  produces  the  lateral  and  ventral  muscles  of 
the  trunk.  By  an  inward  extension  it  probably  gives  rise  also  to  the  hypaxial  muscles  of 
the  neck  and  loin.  The  cells  of  the  inner  layer  of  the  myotome  are  responsible  for  the 
formation  of  the  muscle  fibres.  The  cells  elongate  in  a  direction  parallel  to  the 
long  axis  of  the  embryo,  and  give  rise,  by  fusion  with  the  cells  of  neighbouring  myotomes, 
to  the  colunms  and  sheets  of  muscles  of  the  back  and  trunk.  For  the  most  part  {e.g.  back 
and  abdomen)  the  originally  segmental  character  of  the  muscular  elements  is  lost  by  the 
more  or  less  complete  fusion  of  adjacent  myotomes.  The  intercostal  muscles,  however, 
are  tlie  direct  derivatives  of  individual  myotomes. 

Muscles  of  the  Limbs. — In  fishes  and  (doubtfully)  reptiles  there  is  evidence  that 
the  myotomes  are  concerned  in  the  formation  of  the  limb-muscles  by  their  extension  into 
the  limV)-bud  in  a  manner  similar  to  that  described  for  the  trunk.  Li  birds  and  mammals, 
however,  in  which  the  limb-Vjud  arises  as  an  undifferentiated,  unsegmcntcd  mass  of 
mosoblastic  tissue,  partly  from  the  mesoblast  surrounding  the  notochord,  and  partly  from 
the  somatopleuric  mewjblast,  the  myotomes  stoj)  short  at  the  root  of  each  limb,  and 
do  not  penetrate  into  its  substance.  Instead,  the  muscular  elements  of  the  limb  take 
?,2 


442 


THE  MUSCTLAE  SYSTEM. 


origiu  independently  as  double  dorsal  and  ventral  strata  of  fusiform  cells  on  the  dorsal  and 
ventral  surfaces  of  the  limb-bud.  These  strata  are  unsefjmented  ;  they  are  grouped  around 
the  skeletal  elements  of  the  limb,  and  they  gradually  become  differentiated  into  the  muscle 
masses  and  individual  muscles  of  the  limb. 

Muscles  of  the  Head. — Xotwithstanding  the  obscurity  and   complexity  of  this 


Fig.  3.52. 

Scheme  to  Illustrate 
THE  Disposition  of  the 
Myotomes  in  the  Em- 
bryo IN  Relation  to 
the  Head,  Trunk,  and 
Limbs. 

A,  B,  C,  First  three  cephalic 
myotomes  ;  X,  1,  2,  3,  4, 
Last  persisting  cephalic 
myotomes  ;  C. ,  T.,  L.,  S., 
Co.,  The  myotomes  of  the 
cervical,  thoracic,  lumbar, 
sacral,  and  caudal  regions  ; 
I.,  IL.  IIL,  IV.,  v.,  VI., 
VIL,'jVin.,IX.,X.,  XL, 
XII., ''refer  to  the  cranial 
nerves  and  the  structures 
■with  which  they  may  be 
embryologically  associ  - 
ated. 


subject,  it  appears  certain  that  at  least  two  series  of  elementary  structures  are  concerned 
in  the  formation  of  the  muscles  of  the  head  and  face — the  cephalic  myotomes  and  the 
muscular  structure  of  the  branchial  arches. 

The  number  of  myotomes  originally  existing  in  the  region  of  the  head  is  not  known, 
although  it  is  stated  ^vith  some  authority  that  nine  is  the  perfect  number.  The  first  three 
are  described  as  persisting  in  the  form  of  the  ocular  muscles,  the  last  three  in  relation  to 
the  muscles  of  the  tongue,  while  the  three  intervening  myotomes  disappear. 

The  following  table  shows  the  possible  fate  of  the  cephalic  myotomes : — 

First,  Superior,  internal  and  inferior  recti,  ohliquus  inferior,  levator  palpebrae  superioris. 

Second,  Obliquus  superior. 

Third,  Rectus  extemus. 

Fourth,  Fifth  and  Si:cth,  Absent. 

Seventh,  A 

Eighth,  I  Muscles  of  the  tongue. 

Ninth,  I  Muscles  connecting  the  cranium  and  shoulder  girdle. 

Tenth  (first  cervical)    J 

The  mesohlastic  tissue  of  the  branchial  arches  is  probably  concerned  in  the  production  of 
the  following  muscles  of  the  face  and  neck  : — 

First  {rnandibidar)  arch  .  Muscles  of  mastication. 

( Platysma  myoides  and  facial  muscles. 
Second  {hyoid)  arch         .         .         .         l  Muscles  of  the  soft  palate. 

I  Stapedius,  stylo-hyoid,  and  digastric. 

Third  (thyro-hymd)  arch  .         .         {|J^\°;£r'SfStor. 

7-.      .7        7  7-.-j^i  /I        7.  •  r        7  f  Middle  and  inferior  constrictors. 

Fourth  and  Fifth  {branchiar)  arches         -^^Muscles  of  the  larvnx. 


THE    XERYOUS    SYSTEM. 

THE  BRAIN  AND  SPINAL  COED,  WITH  THEIR  MENINGES. 

Bj  D.   J.    CUNNINGHAJVL 

The  nerTOUs  syatem  connects  the  various  parts  of  the  bodj  with  each  other  and 
co-ordinates  them  into  one  harmonious  whole.  Its  relatively  great  bulk  and  its 
extreme  complexitv  constitute  two  of  the  most  distinctive  structural  features 
of  man.  It  consists  of  two  parts,  viz.  the  cerebrospinal  nervous  system  and  the 
sympathetic  nervous  system. 

The  sympathetic  nervous  system  is  composed  of  a  chain  of  serially  disposed 
ganglia,  bound  to  each  other  by  intervening  nervous  cords,  and  placed  one  on  either 
aide  of  the  vertebral  column.  In  addition  to  these  gangliated  cords,  the  sympathetic 
system  includes  certain  dense  plexuses  of  nerves  and  numerous  scattered  ganglia. 
The  whole  is  most  intimately  connected  with  the  cerebrospinal  nervous  system,  and 
both  have  apparently  a  common  developmental  origin.  The  separation  of  the 
nervous  system  into  the  two  leading  subdivisions  of  sympathetic  and  cerebro- 
spinal is  therefore  of  a  somewhat  arbitrary  kind. 

The  cerebrospinal  nervous  system  consists  of  the  braiu,  which  very  nearly 
completely  fills  the  cranial  cavity,  and  the  spinal  cord  or  spinal  marrow,  which  only 
partially  fills  the  vertebral  canal.  These  are  continuous  with  each  other,  and  together 
constitute  the  cerebrospinal  axis.  Attached  to  the  brain  and  spinal  cord  are  the 
numerous  nerves  which  bring  the  various  parts  of  the  body  into  connexion  with  the 
central  nervous  axis.  There  are  thirty-one  pairs  of  symmetrically  disposed  spinal 
nerves  attached  to  the  sides  of  the  spinal  cord.  Each  of  these  nerves  is  connected 
to  the  side  of  the  cord  by  a  ventral  or  anterior  and  a  dorsal  or  posterior  root,  and 
the  dorsal  root  is  distinguished  by  presenting  a  distinct  oval  swelling,  termed  a 
spinal  ganglion,  on  that  part  of  its  course  immediately  internal  to  the  place  where 
the  two  roots  unite  to  form  the  spinal  nerve-trunk  (Fig.  365,  p.  453). 

The  cranial  nerves  are  twelve  in  number  on  each  side,  but  one  only  (viz.  the 
fifth  or  trigeminal;  presents  a  double-rooted  attachment  similar  to  a  spinal  nerve 
Several,  however,  possess  ganglia  in  every  respect  comparable  with  the  ganglia  on 
the  dorsal  roots  of  the  spiaal  nerves.  These  are  the  fifth  or  trigeminal,  the  seventh 
or  facial,  the  eighth  or  auditory,  the  ninth  or  glosso-pharyngeal,  and  the  tenth  or 
vagus  cranial  nerves. 

CEREBROSPINAL  NERVOUS  SYSTEM. 

The  brain  and  spinal  cord  are  composed  of  two  substances  which  present  a 
dift^^-rent  appearance  to  the  eye,  and  which  are  distinguished  by  the  terms  white 
matter  aa<l  gray  matter.  The  difference  in  colour  between  these  two  substances 
depiends  not  only  upon  the  ditterent  elements  which  enter  into  their  formation,  but 
also  upon  the  fact  that  the  gray  matter  is  the  more  vascular  of  the  two.  The 
white  matter  Is  chiefly  composed  of  nerve-fibres,  whilst  the  essential  constituents 
of  the  jrray  matter  are  nerve-cells  which  give  origin  to  nerve-fibres.  An  all  per- 
vading matrix  termed  the  neuroglia  forms  the  bed  in  which  the  nerve-fibres  and 

443 


444 


THE  NEEVOUS  SYSTEM. 


nerve-cells  lie,  and  is  present  both  in  the  gray  and  the  white  matter.  The  elements, 
therefore,  which  constitute  nervous  tissue  are  nerve-cells,  nerve-fibres,  and  neuroglia. 
Nerve-fibres. — Nerve-fibres  arranged  in  bundles  of  greater  or  less  bulk  form 
the  nerves  which  pervade  every  part  of  the  body.  They  also  constitute  the  greater 
part  of  the  brain  and  spinal  cord.  Nerve-fibres  are  the  conducting  elements  of  the 
nervous  system ;  they  serve  to  bring  the  nerve-cells  into  relation  both  with  each 
other  and  with  the  various  tissues  of  the  body. 

There  are  different  varieties  of  nerve-fibres,  but  in  all  the  leading  and  essential 
constituent  is  a  delicate  thread-like  band,  termed  the  axis-cylinder.  The  difference 
between  individual  fibres  depends  upon  the  fact  that  in  some  cases  the  axis-cylinder 
becomes  invested  by  one  or  two  coats,  whilst  in  other  cases  it  remains  naked.  When 
the  axis-cylinder  is  coated  on  the  outside  by  a  more  or  less  thick  sheath  of  a  fatty 
substance  termed  myelin,  it  is  said  to  be  a  myelinated  or  meduUated  fibre.  When  the 
coating  of  myelin  is  absent,  the  fibre  is  termed  a  non-myelinated  or 
a  non-medullated  fibre.  A  second  sheath — thin,  delicate,  and 
membranous,  and  placed  externally — may  also  be  present  in  both 
cases.  It  is  termed  the  primitive  sheath  or  the  neurolemma.  From 
a  structural  point  of  view,  therefore,  four  different  forms  of  nerve- 
fibre  may  be  recognised  : — 


Axis 
'cylinder 


Myelin 


Primitive 
sheath 


M  r\   ]]  i-  r\  J  ^'  ^^^^^  axis-cylinders. 

\  2.  Axis-cylinders  with  primitive  sheaths. 
j  3.  Primitive  sheath  absent. 


MeduUated 


\  4.  Primitive  sheath  present. 


Every  nerve-fibre  near  its  origin  and  as  it  approaches  its  termination 
is  unprovided  with  sheaths  of  any  kind,  and  is  simply  represented 
by  a  non-medullated  naked  axis  -  cylinder.  The  fibres  of  the 
olfactory  nerves  afford  us  an  example  of  non-medullated  fibres 
furnished  with  a  primitive  sheath. 

MeduUated  fibres  are  present  in  greater  quantity  in  the  cerebro- 
spinal system  than  non-medullated  fibres.  Thus  all  the  nerves 
attached  to  the  brain  and  cord,  with  the  exception  of  the  olfactory 
and  optic,  are  formed  of  meduUated  fibres  provided  with  a  primitive 
sheath ;  whilst  the  entire  mass  of  the  white  substance  of  the  brain 
and  cord,  and  also  the  optic  nerves,  are  formed  of  meduUated  fibres 
devoid  of  a  primitive  sheath. 

It  is  important  to  note  that  the  distinction  between  the  medul- 
lated  and  non-medullated  fibres  is  not  one  which  exists  throughout 
all  stages  of  development.  As  will  be  presently  pointed  out,  every 
fibre  is  a  direct  outgrowth  from  a  cell,  and  in  the  first  instance  it  is 
not  provided  with  a  meduUary  sheath.  Indeed,  it  is  not  until 
about  the  fifth  month  of  foetal  life  that  those  fibres  which  are  to 
form  the  white  substance  of  the  cerebrospinal  axis  begin  to  acquire 
their  coating  of  myeUn.  Further,  this  coating  appears  in  the  fibres 
of  different  strands  or  tracts  at  different  periods,  and  a  knowledge 
^TKsniSrr^'^  of  this  fact  has  enabled  the  anatomist  to  follow  out  the  connexions 
of  the  tracts  of  fibres  which  compose  the  white  matter  of  the 
brain  and  cord. 

But  it  may  be  asked :  How  does  a  nerve-fibre  arise  and  how  does  it  end  ? 
Every  fibre  is  directly  continuous  by  one  extremity  with  a  nerve-cell,  whilst  its 
opposite  extremity  breaks  up  into  a  number  of  ramifications,  all  of  which  end 
freely  in  relation  to  another  nerve-cell,  or  in  relation  to  certain  tissues  of  the  body, 
as,  for  example,  to  muscle-fibres  or  to  the  epithelial  cells  of  the  epidermis.  The 
length  of  nerve-fibres,  therefore,  varies  very  greatly.  Some  fibres  are  short  and 
merely  bring  two  neighbouring  nerve-cells  into  relation  with  each  other :  others 
travel  long  distances.  Thus  a  fibre  arising  from  one  of  the  motor  cells  of  the  lower 
end  of  the  spinal  cord  may,  after  leaving  the  •  cord,  extend  to  the  most  outlying 
muscle  in  the  sole  of  the  foot  before  it  reaches  its  destination.  But  even  when  a 
fibre  does  not  leave  the  central  axis  a  great  length  may  be  attained,  and  cells 


Pig.  353. 
Nebve-fibre 


CEEEBROSPINAL  NERVOUS  SYSTEM. 


445 


X. 


Axon 


situated  in  the  motor  area  of  the  cortex  of  the  cerebrum  give  origin  to  fibres  whicii 
pass  down  to  the  lower  end  of  the  cord. 

Physiologists  classify  the  fibres  which  form  the  nerves  into  two  sets,  afferent 
and  efferent.  Afferent  nerve-fibres  conduct  the  impulse  of  imjjressions  from  the 
peripheral  organs  into  the  central  nervous  system  ;  and  as  a  change  of  consciousness, 
or,  in  other  words,  a  sensation  is  a  frequent  result,  these  fibres  are  often  called 
sensory.  '  Efferent  nerve-fibres  carry  impulses  out  from  the  brain  and  cord  to  peri- 
pheral organs.  The  majority  of  these  fibres  go  to  muscles  and  are  termed  motor ; 
others,  however,  go  to  glands  and  are  called  secretory ;  whilst  some  are  inhibitory 
and  serve  to  carry  impulses  which  restrain  or  check  movement  or  secretion.  As 
previously  stated, 
the  spinal  nerves  are 
each  attached  to  the 
cord  by  a  ventral  or 
anterior  root,  and  a 
dorsal  or  posterior 
root;  the  fibres  com- 
posing the  former 
areefierent;  whilst 
the  fibres  of  the 
posterior  root  are 
almost  entirely 
afferent.  ] 

Nerve  -  cells.  — 
The  nerve-cells  con- 
stitute the  active 
and  all-essential 
elements  of  nerve- 
tissue.  At  the  very 
start  it  is  necessary 
to  draw  a  broad 
distinction  between 
the  ganglionic  cells, 
which  are  found  in 
the  spinal  ganglia, 
and  the  cells  which 
are  so  plentifully 
scattered  through 
the  gray  matter  of 
the  brain  and  cord. 
They  differ  not  only 
in  their  mode  of 
origin  and  in  their 
subsequent  develop- 
ment, but  also  in  the  connexions  of  the  nerve-fibres  to  which  they  give  origin. 

Nerve-cells  of  the  Brain  and  Cord. — The  cells  in  the  gray  matter  of  the 
cerebrospinal  axis  are  variable  both  in  size  and  form.  Some  are  relatively  large, 
as,  for  examyjle,  certain  of  the  pyramidal  cells  of  the  cerebral  cortex  and  the  motor 
cells  in  the  gray  matter  of  the  cord,  which  almost  come  within  the  range  of  unaided 
vision ;  others  are  exceedingly  minute,  and  require  a  high  power  of  the  microscope 
to  bring  them  into  view.  The  cell  consists  of  a  protoplasmic  nucleated  body,  from 
which  certain  processes  proceed.  One  process  is  termed  the  axis-cylinder  process  or 
axon ;  and  as  a  rule  it  is  (vasily  distinguislied  from  the  others,  which  are  collectively 
called  tlie  protoplasmic  processes  of  Deiters,  or  the  dendrites. 

Tlje  axon  presents  a  uniform  diameter  and  a  smootli  and  even  outline.  It  gives 
off  in  its  course  fine  collateral  branches,  but  does  not  suffer  thereby  any  marked 
diminution  in  its  girth.  The  most  important  point  to  note  in  connexion  with  the 
axon,  liowever,  is  the  fact  that  it  becom(!s  continuous  with  the  axis-cylinder  of  a 
nerve- fibre.     1'he  significance  of  this  is  obvious,  and  will  become  more  striking 


Fig.  354. — Three  Neeve-Cells  feom  the  Anterior  Horn  op  Gray 
Matter  op  the  Human  Spinal  Cord. 


446 


THE  NEKVOUS  SYSTEM. 


when  the  development  of  the  nerve-cells 
is  studied.  The  axon  then  is  simply  a 
nerve-fibre,  and  in  certain  circumstances  it 
assumes,  as  already  stated,  one  or  two 
investing  sheaths.  The  axon  may  run  its 
entire  course  within  the  substance  of  the 
brain  or  cord  either  for  a  short  or  a  long 
distance,  or  it  may  emerge  from  the  brain 
or  cord  in  one  of  the  cranial  or  spinal 
nerves  as  the  essential  part  of  an  efferent 
nerve -fibre,  and  run  a  variable  distance 
before  it  finally  reaches  the  peripheral 
structure  in  relation  to  which  it  ends.  The 
axon  and  the  collaterals  which  spring  from 
it  terminate  either  in  small  button-like 
swellings  or  knobs,  or  more  frequently  in 
terminal  arborisations,  the  extremities  of 
which  are  free  and  are  furnished  with  ex- 
ceedingly small  terminal  varicosities.  In 
those  cases  where  the  axon  or  its  collaterals 
end  within  the  brain  or  cord,  some  of  the 
terminal  arborisations  interlace  with  the 
dendrites  of  nerve-cells,  whilst  others  are 
twined  around  the  bodies  of  other  cells. 
In  the  latter  case  the  interlacement  may 
be  so  close  and  complete  that  it  almost 
presents  the  appearance  of    an   enclosing 


Fig.  355. — Two  Multipolar  Nerve- 
Cells,  from  a  specimen  prepared 
by  the  Golgi  method. 


basket  -  work.  In  cases 
where  the  axon  emerges 
from  the  cerebrospinal  axis 
its  terminal  arborisation 
ends  in  relation  to  a  muscle- 
fibre  or  some  other  tissue 
in  the  manner  already  re- 
ferred to.  In  all  cases, 
however,  it  would  appear 
that  the  terminal  branches 
of  the  axon,  no  matter  how 
complicated  the  connexion 
may  seem,  are  free,  and 
that  the  connexion  is 
simply  one  of  contact  or 
contiguity,  and  not  one  of 
continuity. 

Held  maintains  that, 
although  at  first  the  terminal 
arborisations  of  an  axon  are 
quite  free,  in  the  process  of 
growth  and  development  they 
exhibit  a  tendency  to  become 
fused  with  the  dendrites  and 
even  the  bodies  of  other 
nerve-cells. 


Fig.   356.  —  Nerve-Cell   from   Cerebellum    (Cell   of   Poekinje) 

SHOWING    THE    BRANCHING    OF     THE     DeNDRITIC     PROCESSES    (from 

a  lantern  slide  by  Professor  Symington). 


CEREBEOSPINAL  NERVOUS  SYSTEM. 


447 


The  dendrites,  or  protoplasmic  processes  of  the  nerve-cell,  are  thicker  than  the 
axon,  and  present  a  rough -edged  irregular  contour.  They  divide  into  numerous 
branches,  and  these  gradually,  as  they  pass  from  the  cell-body,  become  more  and 
more  attenuated  until  they  finally  end  in  free  extremities.  The  branching  of  the 
dendritic  processes  sometimes  attains  a  marvellous  degree  of  complexity  (Fig.  356), 
but  except  in  exceptional  circumstances,  there  is  no  anastomosis  between  the 
dendrites  of  neighbouring  cells,  or  between  the  dendrites  of  the  same  cell.  It 
would  appear,  therefore,  that  nothing  in  the  shape  of  a  network  is  formed  by  these 
processes. 

In  the  chapter  upon  Embryology  it  has  been  shown  that  in  the  early  condition 
of  the  cerebrospinal  axis  the  brain  and  cord  consist  simply  of  a  tube  (p.  21).  The 
wall  of  this  tube  is  formed  of  a  single  layer  of  tall  columnar  neuro-epithelial  cells, 


MID-DORSAL  LAMINA 


MYELO- 

SPONGIUM 


MID-VENTRAL  LAMINA 


Fig.  357. — Transverse  Section  through  the  early  Neural 
Tube,  diagrammatically  represented  (Alfred  H.  Young). 

The  left  side  of  the  section  exhibits  an  earlier  stage  of 
development  than  the  right  side. 


Fig.  358.  — The  Developmental 
Stages  exhibited  by  a  pyra- 
MiDAi;  Cell  of  the  Brain  (after 
Ramon  y  Cajal). 

a,  Neuroblast  with  rudimentary 
axon,  but  no  dendrites  ;  b  and  c, 
The  dendrites  beginning  to  sprout 
out  ;  d  and  e,  Further  develop- 
ment of  the  dendrites  and  ap- 
pearance of  collateral  branches 
on  the  axon. 


and  in  its  deepest  or  most  internal  part  large  round  cells  make  their  appearance 
in  the  intervals  between  the  epithelial  columns.  These  new  cells  are  termed  the 
germinal  cells,  and  from  them  the  nerve-cells  are  derived.  They  are  present  in 
consideraljle  numbers,  and  towards  the  fourth  week  of  embryonic  Life  they  form  an 
almost  continuous  layer.  Although  these  cells  ultimately  become  nerve-cells  they 
are  absolutely  without  processes  in  their  early  state,  and  therefore  at  this  period, 
although  there  is  a  neirvous  system,  there  are,  as  His  remarks,  no  nerves.  In 
course  of  time,  and  as  the  wall  of  the  neural  tube  thickens,  the  germinal  cells 
begin  to  migrate  in  an  outward  direction.  They  leave  the  deep  part  of  the  wall 
of  the  neural  tube  and  proceed  to  take  up  the  positions  they  occupy  in  the  gray 
matter  of  the  cord  and  brain  of  the  adult.  These  nngratiug  cells  assume  a  pyriform 
Kha])e,  and  are  termed  neuroblasts.  The  drawn-out  portion  or  stalk  of  the  pear- 
shaped  neuroblast  represents  the  early  axon,  and  tliis  continues  to  grow  and  increase 
in  length  until  it  ultimately  attains  the  terminal  relations  characteristic  of  the 
adult.  The  study  of  embryology  presents  few  more  remarkable  phenomena  than  the 
manner  in  which  this  axon  grows  out,  and,  in  the  efferent  nerve-fibres,  emerges 


448  THE  NEEYOUS  SYSTEM. 

from  the  central  axis,  and  yet  pursues  its  allotted  path  with  the  most  unerring 
exactitude  and  precision  until  it  ultimately  reaches  the  nerve-cell  or  the  peripheral 
tissue  element  with  which  it  becomes  associated.  The  growing  point  of  both  it 
and  its  collaterals  is  slightly  bulbous,  and  it  is  out  of  this  that  the  terminal 
arborisation  is  formed. 

This  conception  in  regard  to  the  outgrowth  of  the  axon  in  the  case  of  the  peripheral 
nerve-fibres  has  not  been  allowed  to  pass  unchallenged,  and  it  must  be  admitted  that 
certain  facts  recently  observed  militate  against  it. 

Whatever  opinion  may  be  held  in  regard  to  the  developmental  origin  of  the  axis- 
cylinder  and  medullary  sheath  of  a  peripheral  nerve-fibre,  there  is  every  reason  for  the 
belief  that  the  neurolemma  is  mesodermic  in  its  origin,  and  is  therefore  formed  from  cells 
outside  the  ectodermic  neural  tube.  There  are  some  who  think  that  the  axis-cylinder  is 
secreted  in  situ  by  a  chain  of  these  cells,  whilst  others  consider  that  the  mesoblastic  cells 
of  a  nerve-fibre  merely  constitute  a  cellular  tube  through  which  the  growing  axon  worms 
its  way  to  its  destination,  and  perhaps  also  supply  the  pabulum  necessary  for  its  growth. 

The  -dendritic  processes  of  the  nerve-cell  appear  at  a  later  period  than  the  axon. 
The  surface  of  the  neuroblast  becomes  rough  and  then  somewhat  spiny.  By  the 
growth  and  subdivision  of  these  spiny  projections  the  dendrites  are  formed.  As 
His  remarks,  the  nerve-cell  is  therefore  the  genetic  centre  from  which  all  the  parts 
of  a  nervous  element  proceed. 

It  must  now  be  clear  that  each  nerve-cell  is  a  unit  which  is  separate  and  distinct 
from  the  nerve-cells  which  lie  around  it.  Further,  it  is  obvious  that  it  is  wrong  to 
consider  the  nerve-cell  as  something  apart  from  the  nerve-fibre.  The  nerve-cell 
with  its  dendrites  and  axon,  however  wide-spreading  these  processes  may  be, 
constitutes  an  independent  system  to  which  the  term  neuron  is  applied,  and 
the  only  relation  which  it  has  with  other  neurons  or  with  peripheral  tissues  is  one 
of  contact. 

Ganglionic  Nerve-Cells. — The  ganglionic  neurons  found  in  the  ganglia  of  the 
cranial  nerves  and  in  the  ganglia  on  the  dorsal  roots  of  the  spinal  nerves  have  a 
different  origin,  and  present  many  points  of  contrast  with  neurons  in  the  gray  matter 
of  the  brain  and  cord.  As  already  indicated  in  the  chapter  on  Embryology  (p.  21) 
the  ganglia  in  question  are  derived  from  the  neural  crest.  The  cells  forming  these 
ganglionic  masses  are  somewhat  oval  in  form,  and  from  either  extremity  or  pole  a 
process  grows  out,  and  the  neurons  in  this  manner  become  bipolar.  These  processes 
are  distinguished  as  central  and  peripheral,  according  to  the  direction  which  they 
take.  The  central  processes  grow  inwards,  and  penetrate  the  wall  of  the  neural 
tube.  In  the  region  of  the  spinal  cord  they  form  almost  the  whole  of  the  fibres 
which  enter  into  the  composition  of  the  dorsal  roots  of  the  spinal  nerves.  In  the 
substance  of  the  cerebrospinal  axis  they  give  off  numerous  collaterals,  and  after  a 
course  of  varying  extent  they  end,  after  the  manner  of  an  axon,  in  terminal 
arborisations,  which  enter  into  relationships  of  contact  with  certain  nerve-cells  in 
the  cerebrospinal  axis.  The  peripheral  processes  grow  outwards  along  the  path  of 
the  particular  nerve  with  which  they  are  associated,  and  they  finally  establish 
peripheral  contact  relations.  Thus,  to  take  one  example  :  the  majority  of  the  fibres 
which  go  to  the  skin  break  up  into  fine  terminal  filaments,  which  end  freely 
between  the  epithelial  cells  of  the  epidermis.  The  two  processes  of  a  ganglion  cell, 
therefore,  form  the  afferent  fibres  of  the  cerebrospinal  nerves,  and  constitute  the 
path  along  which  the  influence  of  peripheral  impressions  is  conducted  towards  the 
brain  and  cord.  The  body  of  the  cell  is  as  it  were  interposed  in  the  path  of  such 
impulses. 

But  the  original  bipolar  character  of  these  cells,  with  very  few  exceptions 
(ganglia  in  connexion  with  the  auditory  nerve  and  the  bipolar  nerve-cells  in  the 
olfactory  mucous  membrane),  gradually  undergoes  a  change  which  ultimately  leads 
to  their  transformation  into  unipolar  cells.  This  is  brought  about  by  the  tendency 
which  the  cell-body  has  to  grow  to  one  side,  viz.  the  side  towards  the  surface  of  the 
ganglion  (v.  Lenhossek).  This  unilateral  growth  leads  to  a  gradual  approxima- 
tion of  the  attached  ends  of  the  processes,  and  finally  to  a  condition  in  which  they 
appear  to  arise  from  the  extremity  of  a  short  common  stalk  in  a  T-shaped  manner 


CEREBEOSPINAL  NERVOUS  SYSTEM. 


449 


certain  fish   the 


,p^L 


(Fig.  360).       It  is  interesting  to  note  that    in 
condition  of  these  cells  is  retained  throughout 
life  without  change. 

Both  the  central  and  peripheral  processes 
of  these  ganglionic  cells  become  the  axis- 
cylinders  of  nerve-fibres,  which,  acquiring  a 
medullarj  sheath,  belong  therefore  to  the 
medulla  ted  variety.  From  this  it  might  very 
naturally  be  thought  that  the  ganglionic 
neuron,  with  its  two  axons  and  no  typical 
dendrites,  is  a  nervous  unit  very  different 
from  a  neuron  in  the  gray  matter  of  the 
cerebrospinal  axis.  It  is  believed,  by  some, 
however  (van  Gehuchten  and  Cajal),  that  the 
peripheral  process,  in  spite  of  its  enclosure 
within  a  medullary  sheath,  and  though  pre- 
senting all  the  characters  of  a  true  axon,  is  in 
reality  a  dendrite.  If  this  be  the  case,  the 
morphological  difference  between  a  dendrite 
and  an  axon  disappears,  and  van  Gehuchten's 
functional  distinction  alone  remains  character- 
istic, viz.  that  the  axon  is  cellulifugal  and 
conducts  impulses  away  from  the  cell,  whilst 
the  dendrites  are  cellulipetcd  and  conduct  im- 
pulses towards  the  cell. 

In  the  foregoing  brief  account  of  the  elements  which 
build  up  the  nervous  system,  the  neuron  doctrine,  as  it 
has  been  enunciated  by  Waldeyer,  has  been  followed. 
The  observations  of  Ramon  y  Cajal  and  His  form 
the  foundation  upon  which  this  doctrine  mainly  rests, 
although  it  should  not  be  forgotten  that  many  other 
anatomists,  amongst  whom  may  be  mentioned  v. 
Kolliker,  van  Gehuchten,  and  v.  Lenhossek,  have  by 
their  investigations  greatly  strengthened  the  concep- 
tion.    Two  primary  considerations  may  be  considered 

to  constitute  its  leading  support 


original 


bipolar 


Fig.  359. — Diagram  of  the  Connexion  estab- 
lished BT  A  Ganglionic  and  a  Motor 
Neuron  (Ramon  y  Cajal). 

A.  Fibre  coming  down  from  a  pyramidal  cell  in  the 
motor  area  of  the  cerebral  cortex. 

B.  Motor  cell  in  gray  matter  of  spinal  cord. 

C.  Muscle-fibres. 

D.  Collateral  branch  from  the  pyramidal  fibre. 

E.  Cell  in  the  medulla  oblongata  sending  its  axon 
upwards  to  the  cerebral  cortex. 

F.  Cells  in  the  spinal  ganglion. 

G.  Periplieral  process  of  ganglionic  cell  ending  in  skin. 
I.    Collateral   branches   of    central   process   of   gan- 
glionic cell. 

S.N.  Spinal  nerve. 


yOO.  — 'I'huek  Stacks  i.s  thk  Dkvki.oi'Mknt 
oi'  A  Cell  from  a  Spinal  GANaLiON. 


(1)  the  absolute 
independence  of  the  early  nerve-cell  or  neuroblast 
and  its  processes,  as  was  first  clearly  shown  by  His ; 
(2)  the  fact  that  when  nerve  tissue  is  treated  by  the 
Golgi  method  or  by  the  vital  methylene  blue  method 
no  continuity  of  any  kind  can  be  observed  between 
neighbouring  cells,  although  the  jjrocesses  of  the  cells 
can  apparently  be  traced  to  their  ultimate  divisions. 
Further,  it  should  be  noted  that  the  neuron  doctrine 
receives  strong  supjDort  from  pathological  observa- 
tions, and  that  before  it  assumed  concrete  form  ideas 
of  a  somewhat  similar  kind  were  present  in  the 
minds  of  pathologists. 

Still  the  neuron  theory  is  not  accepted  by  several 
leading  Histologists.  Apathy,  Nissl,  and  Bethe  at 
the  j^resent  moment  form  a  powerful  combination 
against  it.  It  is  therefore  necessary  to  indicate  the 
views  entertained  by  these  observers. 

More  than  thirty  years  ago  Max  Schultze  called 
attention  to  the  fact  that  the  axis  -  cylinder  of  a 
nerve-fibre  is  composed  of  exceedingly  fine  fibrils^ 
which,  when  traced  to  the  cell  from  which  the 
fibre  takes  origin,  are  there  seen  to  enter  the  cell- 
Ijody  and  spread  out  within  it.  By  more  delicate 
methods  of  research,  Apathy  and  Bethe  have  been 
a))le  to  place  this  early  observation  of  Schultze 
b(iyond  the  realm  of  douljt.  Apathy,  who  worked 
chiefly  at  the  invertebrate  nervous  system,  not  only 
traced  the  neuro-fibrilbjo  through  tlie  cell-body  Imt 


'  it  may  be  ri)<;ntione<I  tliat  Rernak,  tlu;  (Hscov(Tcr 
.striated  in  the  longitudinal  direction. 


of  tlie  a.\is-cyliiiil(M'   in   IKJJS,  .stated  tliat  it  was  finely 


450 


THE  NERVOUS  SYSTEM. 


into  all  its  processes,  and  he  believes  that  he  has  been  able  to  follow  them  beyond  these  into  a 
delicate  fibi'illar  interlacement  which  constitutes  a  bond  of  union  between  all  the  nerve-cells  of  the 
nervous  system.  Bethe's  oljservations  have  been  carried  out  in  vertebrates.  Two  illustrations  from 
his  1>ook  are  reproduced  in  Fig.  361.  The  cell  represented  in  A  is  from  the  gray  matter  of  the 
anterior  horn  of  the  human  spinal  cord,  and  the  relation  presented  by  the  neuro-fibrils  within  the 
cell  and  to  its  various  processes  are  very  clearly  depicted.  The  axon  appears  to  receive  a  con- 
tribution of  neuro-fibrillai  from  all  the  dendritic  processes  ;  tliis,  according  to  Bethe,  is  character- 
istic of  the  great  majority  of  nerve-cells.  In  the  cells  indicated  Ijy  the  letter  B,  which  are  from 
the  cerebral  cortex  of  man,  it  will  be  noticed  that  the  axons  as  they  leave  the  cell  Ijecome  ex- 
ceedingly fine  and  delicate,  and  the  neuro-fibrillse  wliich  comi^ose  them  are  so  closely  j^acked 
together  that  all  trace  of  their  individual  existence  disappears.  When  the  medullary  sheath 
is  assumed  liy  the  fibre  the  neuro-fibrilla3  of  the  axis-cylinder  again  become  apjiarent. 


Axon 


Fig.  361. — Nerve  Cells  as  depicted  by  Bethe. 

A,  A  cell  from  the  anterior  horn  of  gray  matter  of  the  spinal  cord  of  man. 

B,  Two  cells  from  the  human  cerebral  cortex. 

In  vertebrates  Bethe  lias  not  been  able  to  trace  the  neuro-fibrils  into  an  all-pervading 
fibrillar  network  such  as  Apathy  has  described  as  binding  the  various  nerve  elements  together  in 
the  invertebrates,  but  he  has  followed  them  into  the  finest  of  the  dendritic  brandlings,  and  he 
assumes  that  the  connecting  network  exists  in  the  higher  as  well  as  in  the  lower  members  of  the 
animal  kingdom. 

This  conception  of  the  structure  of  the  axon  renders  the  giving  off  by  the  nerve-fibre  of 
collateral  branches  and  also  its  terminal  splitting  or  arborisation,  matters  which  can  be  the  more 
easily  understood. 

On  the  strength  of  the  observations  detailed  above,  A^iathy,  Bethe,  and  Nissl,  all  of  whom  are 
authorities  who  deserve  the  highest  degree  of  attention,  have  assailed  the  neuron  theory. 
AiJathy  has  advanced  the  hyjjothesis  that  the  all-i^ervading  fibrillar  interlacement,  which  streams 
continuously  throughout  the  whole  nervous  system  and  is  found  not  only  in  the  cell  and  its 
processes  but  also  in  the  form  of  a  connecting  network  outside  the  cells,  is  the  essential  part 
of  the  nervous  system  and  not  the  so-called  indei^endent  neurons  of  the  neuron  theory.  It  is 
also  contended  that  axons  or  axis-cylinders  may  arise  in  two  ways  :  (1)  directly  from  the  nerve- 
cells  ;  (2)  indirectly  from  the  neuro-fibrillar  network  between  the  nerve-cells. 

In  a  striking  address  recently  delivered  by  Professor  Waldeyer  to  the  Eoyal  Society  of  Edin- 


CEREBEOSPINAL  NERVOUS  SYSTEM. 


451 


burgh  the  essential  points  of  the  neuron  doctrine  were  vigorously  maintained  and  several  new 
preparations  by  Ram6n  y  Cajal  and  Beilschowsky  were  demonstrated.  In  the  latter  the  neuro- 
ftbrillcB  were  seen  to  enter  the  cell- body,  spread  out  and  break  up  into  a  plexus  within  it,  but 
none  could  be  detected  pursuing  an  uninterrupted  course  right  through  the  cell  and  then  passing 
out  from  it. 

As  Edinger  remarks,  investigation  in  the  immediate  future  will  be  largely  concerned  in  the 
attempt  to  further  elucidate  the  following  questions  :  (1)  Are  the  connexions  between  neurons 
merely  those  of  contact  ?  (2)  Do  the  fibres  which  proceed  from  one  cell  fuse  with  the  constituent 
parts  of  another  neuron  ?  (3)  Do  the  neuro-fibrillfe  form  an  inter-connecting  network  between 
the  nerve-cells,  and  do  axons  or  axis-cylinders  arise  from  such  a  network  ?  It  is  questionable 
even  if  the  last  two  of  these  queries  are  answered  more  or  less  in  the  affirmative  whether  it  will 
be  necessary  to  abandon  the  essential  points  in  the  neuron  theory. 

Since  the  foregoing  has  been  printed  an  instructive  monograph  on  the  subject  has  been 
published  by  Professor  Gustaf  Retzius  ("  Punktsubstanz  '  Nervoses  Grau '  und  Neuronenlehre," 
Biologische  Uritersuchungen,  Neue  Folge,  xii.). 

Neuroglia. — The  neuroglia  is  the  supporting  tissue  of  the  cerebrospinal  axis. 
It  may  be  considered  to  include  two  different  forms  of  tissue,  viz.  the  lining 
ependymal  cells  and  the  neuroglia  proper.  We  place  these  under  the  one  heading, 
seeing  that  in  all  probability  they  both  have  a  common  developmental  origin. 

The  ependymal  cells  are  the  columnar  epithelial  cells  which  line  the  central 
canal  of  the  spinal  cord  and  the  ventricles  of  the  brain.  In  the  embryonic  condi- 
tion a  process  from  the  deep  extremity  of  each  cell  traverses  the  entire  thickness 
of  the  neural  wall  and  reaches  the  surface.  It  is  not  known  whether  this  process 
exists  in  the  adult. 

The  neuroglia  proper  is  present  in  both  the  white  and  the  gray  matter  of  the 
cerebrospinal  axis.  It  constitutes  an  all- 
pervading  basis  substance,  in  which  the 
various  nerve  elements  are  embedded  in 
such  a  way  that  they  are  all  bound  together 
into  a  consistent  mass  and  are  yet  all  sever- 
ally isolated  from  each  other.  Neuroglia 
consists  of  cells  and  fine  filaments.  The 
fibrils  are  present  in  enormous  numbers, 
and  by  their  interlacements  they  constitute 
what  appears  to  be  a  fine  feltwork.  At  the 
points  where  the  fibrils  intercross  may  be 
seen  the  flattened  glial  cells.  Whilst  the 
neuroglia  is  for  the  most  part  intimately 
intermixed  with  the  nerve  elements,  there 
are  in  both  brain  and  cord  certain  localities 
where  it  is  spread  out  in  more  or  less  pure 
layers.  Thus  upon  the  surface  of  the  brain 
and  of  the  spinal  cord  there  is  such  a  layer ; 
likewise  beneath  the  epithelial  lining  of  the 
central  canal  and  of  the  cavities  of  the  brain 
there  is  a  thin  stratum  of  neuroglia. 

The  ependymal  cells  are   derived  from 
the   original   neuro- epithelial   cells   of   the 
early  neural   tube,  and   in    all   probability 
the  neuroglia  proper  has  a  similar  origin.     They  both,  therefore,  are  products  of  the 
ectoderm. 

Summary. — 1.  The  cerebrospinal  nervous  system  is  composed  of  two  parts,  viz. 
(a)  a  medullary  part,  consisting  of  the  brain  and  spinal  cord,  with  the  efferent  nerve- 
fibres  which  ]>ass  out  from  them;  (b)  the  ganglionic  part,  with  the  afferent  nerve-fibres. 

2.  Eacli  of  tiiese  parts  has  a  different  origin  and  is  composed  of  neurons  which 
possess  cliaracteristic  features. 

3.  The  ganglionic  neurons  are  derived  from  the  primitive  cells  of  the  neural 
crest,  and  hav(^  each  one  process  which  divides  into  two.  Of  these  the  central 
division  enters  the  cerebrospinal  axis  and  proba})ly  r(;])resents  the  axon,  whilst  the 
peripheral  division,  wliich  becomes  connected  with  a  peripheral  part,  may  pro- 
visionally be  regarded  as  a  dendrite.     The  central  fibres  from  the  ganglionic  cells 


Fig.  362.  —  Section    through     the     Central 
Canal  of  the  Spinal  Cord  of  a  Human 
Embryo,  showing  Ependymal  and  Neur- 
oglial Cells  (after  v.  -Lenhossek). 
A,  Ependymal  cell.  B,  Neuroglial  cell. 


452 


THE  NEEVOUS  SYSTEM. 


in  the  region  of  the  cord  form  the  dorsal  or  posterior  roots  of  the  spinal  nerves. 
These  roots  have  thus  an  origin  outside  the  cord,  and  grow  into  its  substance  in 
the  process  of  development  in  the  same  manner  that  the  roots  of  a  plant  strike 
into  the  soil. 

4.  The  cerebrospinal  neurons  are  derived  from  the  germinal  cells  in  the  wall 
of  the  early  neural  tube.  Certain  of  these  furnish  efferent  nerve-fibres,  which 
issue  from  the  cord  in  separate  bundles  termed  the  anterior  or  ventral  roots  of  the 
spinal  nerves.  In  the  case  of  the  cranial  nerves,  however,  with  the  exception  of 
the  trigeminal  and  facial  nerves,  the  efferent  fibres  are  not  thus  separated  from  the 
afferent  fibres  at  their  attachment  to  the  brain. 

5.  The  brain  and  cord  when  studied  by  the  naked  eye  are  seen  to  be  composed 
of  white  matter  and  gray  matter.  The  white  matter  forms  very  nearly  two-thirds 
of  the  entire  cerebrospinal  axis.  It  is  composed  of  meduUated  nerve -fibres 
embedded  in  neuroglial  tissue.  The  gray  matter  is  composed  of  nerve-cells  with 
their  dendrites  and  axons.  Some  of  the  axons  are  in  the  form  of  naked  axis 
cylinders,  whilst  others  have  a  coating  of  medulla.  Intimately  intermixed  with 
these  parts  is  the  neuroglia,  which  isolates  them  more  or  less  completely  from 
each  other. 

SPINAL  COED. 


Cerebellum 
Fourth  ventricle 


Cervical  swelling 
of  the  cord 


The  spinal  cord  is  that  part  of  the  cerebrospinal  axis  which  occupies  the  upper 
two-thirds  of  the  spinal  canal  of  the  vertebral  column.  It  is  an  elongated  cylin- 
drical structure,  slightly  flattened  in  front  and  behind,  which  extends  from  the 
margin  of  the  foramen  magnum  to  the  level  of  the  lower  border  of  the  body  of  the 

first  lumbar  vertebra  or  to  the  upper  border  of 
the  body  of  the  second  lumbar  vertebra.  Its 
average  length  in  the  male  is  45  cm.  and  in  the 
female  43  cm. 

Mesencephalon 

A  considerable  amount  of  variation  within  certain 
limits  (viz.  the  mid-point  of  the  body  of  the  last  dorsal 
vertebra  and  the  upper  border  of  the  body  of  the 
third  lumbar  vertebra)  is  observed  in  different  in- 
dividuals as  to  the  precise  level  at  which  the  spinal 
cord  ends  inferiorly,  and  in  the  female  there  would 
appear  to  be  a  tendency  for  the  cord  to  reach  a 
slightly  lower  point  in  the  canal  than  in  the  male. 
Further,  the  relation  presented  by  the  spinal  cord  to 
the  vertebral  column  differs  in  a  marked  degree  in  the 
foetus  and  infant  at  different  periods  of  development. 
Up  to  the  third  month  of  intrauterine  life  the  cord 
occupies  the  entire  length  of  the  spinal  canal  ;  it  ex- 
tends downwards  to  the  lowest  limit  of  the  canal.  But 
from  this  time  on,  as  growth  proceeds,  the  vertebral 
column  lengthens  at  a  more  rapid  rate  than  the  cord. 
The  spinal  cord,  therefore,  has  the  appearance  of 
shrinking  in  an  upward  direction  within  its  canal,  and 
at  birth  its  lower  end  is  usually  found  to  be  opposite 
the  body  of  the  third  lumbar  vertebra. 

The  attitude  assumed  by  the  individual  affects  to 

a  small  degree  the  position  of  the  lower  dffd  of  the 

cord.     Thus,  when  the  trunk  is  bent  well  forwards, 

it  is  noticed  that  the  terminal  part  of  the  cord  rises 

EXPOSED   slightly  within  its  bony  canal. 

At  the  margin  of  the  foramen  magnum  the 
spinal  cord  becomes  continuous  with  the  medulla  oblongata  of  the  brain,  whilst 
below,  it  tapers  rapidly  to  a  point  and  forms  a  conical  extremity  termed  the  conus 
medullaris.  From  the  end  of  the  conus  medullaris  a  slender  glistening  thread  is 
prolonged  downwards  within  the  spinal  canal,  and  finally  anchors  the  spinal  cord 
to  the  back  of  the  coccyx.      This  prolongation  receives  the  name  of  the  filum 


Lumbar  swelling 
of  the  cord 


Fig.  363. — Human  Fcetus  in  the  Third 
Month   of   Development,   with   the 
Brain    and    Spinal    Cord 
FROM  behind. 


SPINAL  COED. 


453 


1^ 

i!'  ■■'-" '    OonuK  iii«dullai-is 


Filinn  tcriiiiiiale 
intc'i'Mum 


Roots  of  third  lumbar 
nerve 


Termination  of 
tlieca  of  dura 
mater 


terminale.     The  diameter  of  the  cord  is  very  luuch  shorter  than  that  of  the  spinal 

canal  within  which  it    lies.      A  wide  interval 

is  left  between  its   surface   and  the  walls  of 

its  canal,  and  this  excess  of  space  is  clearly  a 

provision    for  allowing    free  movement  of   the 

vertebral  column  without  producing  any  jar- 
ring contact  between  the  delicate  spinal  cord 

and  the  surrounding  bones. 

Three   protective  membranes   are  wrapped 

around  the  cord.     From  within  outwards  these 

are  termed  (1)  the  pia  mater,  (2)  the  arachnoid 

mater,  and  (3)  the  dura  mater.     The  pia  mater 

is  a    fibrous    membrane  which   forms   the  im- 

jnediate  investment.     It   is  closely  applied  to 

the  cord,  and  from  its  deep  surface  numerous 

fine  septa  penetrate  into  the  substance  of  the 

cord.     The  arachnoid  mater  is  an  exceedingly 

deKcate  transparent  membrane  which  is  loosely 

wrapped   around    the   cord    so   as    to   leave   a    g- 

considerable  interval,  termed  the  subarachnoid 

space,  between  itself  and  the  pia  mater,  in  which    | 

there  is  always  a  varying  amount  of  cerebro-   '* 

spinal  fluid.     Outside  the  arachnoid  mater,  the 

dura  mater  forms  a  wide,  dense,  fibrous,  tubular 

sheath,  which  extends  downwards  within  the 

spinal  canal  for  a  considerable  distance  beyond 

the  conical  extremity  of  the  cord.     The  spinal 

cord  is  suspended  within  its  sheath  or  t/ieca  of 

dura  mater  by  two  lateral  wing-like  ligaments,  Fk;.  364.— The  conds  Medullaris  and  the 

termed  the  ligamenta  denticulata.     These  extend      Filum  Terminale  exposed  within  the 

outwards  from  the  sides  of  the  cord  and  are      '  ^^^^^ 

attaclied  by  a   series  of  pointed    or  tooth-like    processes   to   the   inner  surface  of 

the  theca  of  dura  mater.  Between  the  wall 
of  the  spinal  canal  and  the  dura  mater 
there  is]a  narrow  interval,  which  is  filled  up 
by  soft 'areolo- fatty  tissue  and  numerous 
thin-walled  veins  arranged  in  a  plexiform 
13  .     ,  ,    ,  manner. 

Postero-lateral  mi   •    <  •  f  •       i 

groove  ihirty-one  pairs  oi  spmal  nerves  arise 


Anterior  nerve-root 
J'osteriur  nerve-i'oot 


<liiiial  ganglion 


Anterior  priniaiy 
division  of  nci'X'e 
•■—  I'osterior  ])rii]iary 
li\  isioM  of  n(!i'vc 


i-'io,  .'56.5. — The  Rootij  ok  Okigin  ok  tiik 
Seventh  Dorsal  Neiivk  (senii-diagram- 
malic). 


Hoots  of  lirst 
lumbar  nerve 

Cauda  equina 


I'Ki.  366.— Section  thuouoh  the  Conus  Mkdui.lakis  and 
■iHK  Oatida  Equina  as  thev  lie  in  the  Spinal  Canal. 


Ir.nii  tlie  sides  of  the  H|)i)iiil  coid.     'i'licso  ar(!  classilied  into  eight  cervical,  twelve 


454  THE  NEEVOUS  SYSTEM. 

dorsal,  five  lumbar,  five  sacral,  and  one  coccygeal;  and  according  to  the  attach- 
ments of  these  groups  of  nerves  the  spinal  cord  is  arbitrarily  subdivided  into 
cervical,  dorsal,  lumbar,  and  sacral  regions.  In  employing  these  terms,  therefore, 
for  different  districts  of  the  cord,  it  must  be  understood  that  the  regions  are  deter- 
mined by  the  nerve  attachments,  and  not  by  any  direct  relationship  between  these 
parts  of  the  cord  and  the  sections  of  the  vertebral  column  which  l^ear  the  same 
names. 

Each  spinal  nerve  is  attached  to  the  cord  by  a  ventral  and  a  dorsal  root,  and  as 
these  are  traced  to  their  central  attachments  they  are  seen  to  break  up  into  a 
number  of  separate  nerve  fascicles  or  bundles,  which  spread  out,  in  some  cases  very 
widely  from  each  other,  as  they  approach  the  side  of  the  cord  (Fig.  365).  Each 
pair  of  nerves  is  therefore  attached  to  a  portion  of  spinal  cord  of  some  length,  and 
such  a  portion,  with  its  pair  of  nerves,  receives  the  name  of  a  "  segment  of  the 
spinal  cord."  It  must  be  clearly  understood,  however,  that,  in  so  far  as  the  surface 
of  the  cord  is  concerned,  there  is  absolutely  no  means  of  marking  off  one  segment 
from  another,  except  by  the  nerve  attachments. 

In  the  cervical  and  lumbar  regions  of  the  cord  the  nerve-roots  are  somewhat  crowded 
together,  so  that  little  or  no  interval  is  left  between  the  adjoining  root  fascicles  of  neighbouring 
nerves.  In  the  dorsal  region,  however,  distinct  intervals  may  be  observed,  and  the  root  fascicles 
are  more  loosely  arranged.  From  this,  it  will  be  evident  that  the  cord  segments  in  different  parts 
of  the  cord  are  not  of  equal  length.  In  the  cervical  region  the  segments  measure  about  12  mm. 
in  length,  in  the  dorsal  region  from  20  to  24  mm.,  and  in  the  lumbar  region  about  10  mm.  The 
number  of  fascicles  whicli  attach  the  different  nerve -roots  to  the  cord  is  very  different  in 
different  nerves,  and  is  not  necessarily  the  same  in  the  same  nerve-root  in  different  individuals. 

Owing  to  the  great  difference  which  exists  between  the  length  of  the  spinal 
cord  and  the  length  of  the  vertebral  column,  the  farther  we  pass  down  the  greater 
the  distance  becomes  between  the  attachment  of  the  various  nerve-roots  to  the 
cord  and  the  invertebral  foramina  through  which  the  corresponding  nerves  leave 
the  spinal  canal.  The  lower  nerve-roots,  therefore,  have  to  traverse  the  spinal  canal 
for  a  considerable  distance  before  they  reach  their  apertures  of  emergence.  It  thus 
happens  that  the  nerve-roots  which  spring  from  the  lumbar  and  sacral  regions  of 
the  cord  attain  a  very  great  length  and  descend  vertically  in  the  lower  part  of 
the  spinal  canal  in  a  bunch  or  leash,  in  the  midst  of  which  lie  the  conus  medullaris 
and  the  filum  terminale.  This  great  bundle  of  nerve-roots  receives  Ihe  appropriate 
name  of  the  cauda  equina. 

Enlargements  of  the  Cord. — Throughout  the  greater  part  of  the  dorsal  region, 
the  spinal  cord  presents  a  uniform  girth  and  a  very  nearly  circular  outline  when 
seen  in  transverse  section.  In  the  cervical  and  lumbar  regions,  however,  it  shows 
marked  swellings.  The  cervical  enlargement  (intumescentia  cervicalis)  is  the  more 
evident  of  the  two.  It  begins  very  gradually  at  the  upper  end  of  the  cord,  attains 
its  greatest  breadth  (12  to  14  mm.)  opposite  the  fifth  or  sixth  cervical  vertebra, 
and  finally  sul^sides  opposite  the  second  dorsal  vertebra.  To  this  portion  of  the 
cord  are  attached  the  great  nerves  which  supply  the  upper  limbs.  The  lumbar 
enlargement  (intumescentia  lumbalis)  begins  at  the  level  of  the  tenth  dorsal 
vertebra,  and  acquires  its  maximum  transverse  diameter  (11  to  13  mm.)  opposite 
the  last  dorsal  vertebra.  Below,  it  rapidly  tapers  away  into  the  conus  medullaris. 
To  the  lumbar  enlargement  are  attached  the  great  nerves  of  the  lower  limbs. 

These  enlargements  of  the  cord  are  associated  with  the  outgrowth  of  the  limbs.  In 
the  earlier  developmental  stages  of  the  spinal  cord  they  are  not  present,  and  they  only 
take  form  as  the  limbs  become  developed.  In  the  lower  mammalia  their  size  corresponds 
with  the  degree  of  development  of  the  limbs.  Thus,  in  the  long-armed  orang  and  gibbon, 
the  cervical  swelling  stands  out  with  a  remarkable  degree  of  prominence.  It  is,  however, 
interesting  to  note  that  although  in  the  cetacea  there  are  no  visible  hind-limbs,  there  is 
nevertheless  a  well-marked  lumbar  enlargement  of  the  cord. 

Fissures  and  Furrows  of  the  Cord. — When  cross-sections  of  the  spinal  cord 

are  made,  it  is  seen  to  be  a  bilateral  structure  which  is  partially  subdivided  into  a 
right  and  left  half  by  two  median  clefts — one  upon  the  anterior  and  the  other  upon 
the  posterior  aspect.  These  clefts  are  termed  the  antero-median  and  the  postero- 
median fissures,  and  they  extend  along  the  entire  length  of  the  cord.     At  the  same 


SPINAL  CORD. 


4.55 


time  it  must  he  noted  that  these  two  median  clefts  present 
ence.  The  antero-median  fissure  (fissura  mediana  anterior)  is 
its  length  much  shallower  than  the  postero-median  fissure. 
In  the  cervical  and  dorsal  regions  it  only  penetrates  for  a 
distance  corresponding  to  somewhat  less  than  a  third  of  the 
antero-posterior  diameter  of  the  cord.  Further,  the  antero- 
median cleft  is  much  the  wider  and  more  apparent  of  the 
two,  and  the  pia  mater  dips  down  into  it  and  forms  a  fold 
or  reduplication  within  it.  The  postero-median  fissure 
(fissura  mediana  posterior)  in  the  cervical  and  dorsal  regions 
penetrates  into  the  cord  until  it  reaches  a  point  somewhat 
beyond  its  centre.  It  is  extremely  narrow,  and  contains 
a  single  septum  which  is  derived  from  ependymal  and 
neuroglial  elements,  and  is  intimately  connected  with  the 
adjacent  sides  of  the  two  halves  of  the  cord,  between  which 
it  intervenes.  The  pia  mater,  which  invests  the  surface  of 
the  cord,  passes  continuously  over  the  postero-median  fissure 
and  sends  no  prolongation  of  any  kind  into  it.  In  the 
lumbar  region  of  the  cord  the  postero-median  fissure  becomes 
shallower,  whilst  the  antero-median  fissure  deepens,  and 
ultimately  in  the  lower  part  of  the  cord  the  two  fissures 
pi^esent  a  very  nearly  equal  depth. 

The  two  halves  of  the  cord,  which  are  marked  off  from 
each  other  by  the  median  fissures,  may  show  trifling  differ- 
ences in  the  arrangement  of  the  parts  which  compose  them ; 
but  to  all  intents  and  purposes  they  are  symmetrical.  They 
are  joined  together  by  a  more  or  less  broad  band  or  com- 
missure, which  intervenes  between  the  two  median  fissures. 

An  inspection  of  the  surface  of  each  lateral  half  of  the 
cord  brings  into  view  a  longitudinal  groove  or  furrow,  at 
some  little  distance  from  the  postero-median  cleft,  which 
extends  along  the  whole  length  of  the  cord.  Along  the 
bottom  of  this  groove  the  fascicles  of  the  posterior  nerve- 
roots  enter  the  cord  in  accurate  linear  order.  It  is  called 
the  postero-lateral  sulcus  (sulcus  lateralis  posterior).  There 
is  no  corresponding  furrow  on  the  forepart  of  each  lateral 
half  of  the  cord  in  connexion  with  the  emergence  of  the 
fascicles  of  the  anterior  nerve-roots.  These  fascicles  emerge 
irregularly  over  a  broad  strip  of  the  surface  of  the  cord, 
which  corresponds  in  its  width  to  the  thickness  of  the 
subjacent  extremity  of  the  anterior  horn  of  gray  matter. 

The  postero-lateral  groove  subdivides  each  lateral  half  of 
the  cord  into  a  small  posterior  column  (funiculus  posterior) 
and  a  much  larger  antero-lateral  column,  and  it  is  customary 
to  arbitrarily  map  off  the  latter  into  a  lateral  column 
(funiculus  lateralis)  and  an  anterior  column  (funiculus 
anterior)  by  a  line  corresponding  to  the  emergence  of  the 
outermost  fascicles  of  the  anterior  nerve-roots. 

In  the  cervical  region  a  distinct  longitudinal  groove 
may  be  observed  on  the  surface  of  the  posterior  column.  It 
is  placed  rather  nearer  to  the  postero-median  than  to  the 
postero-lateral  furrow,  and  as  it  is  traced  down  into  the 
dorsal  region  it  gradually  becomes  indistinct  and  finally 
disappears.  This  is  called  the  posterior  paramedian  groove, 
and  it  marks  on  the  surface  the  position  of  a  se^jtum  of 
pia  niator  which  dips  into  the  cord  and  subdivides  the 
posterior  cohimn  into  an  outer  part,  termed  the  funiculus 
cuneatus  or  tlio  column  of  Burdach,  and  an  inner  portion,  wh 
of  the  funiculus  gracilis  or  tfie  column  of  Goll. 


many  points  of  differ- 
for  the  greater  part  of 


— CVi 


Postero-median 
fissure 


Cervical  swelling— | 
Posterior  ijara 
median  fissure 

Postero-lateral \ 

fissure 


Lumbar  swelling- 


-CVv 


-DVxn 


-LViii 


Fig.  367. — Diagram  of  the 
Spinal  Cord  as  seen 
from  behind. 

C'Vi  shows  the  level  of  the  1st 
cervical  vertebra  ;  CVv  of  the 
Sth  cervical  vertebra ;  DVii 
of  the  2nd  dorsal  vertelira ; 
DVx  of  tlie  lOtli  dorsal  verte- 
bra  :  UVxii  of  the  12th  dorsal 
vertebra;  LVii  of  tlic  2nd 
lumbar  vertebra. 

ich  receives  the  name 


456 


THE  NEEVOUS  SYSTEM. 


Internal  Structure  of  the  Spinal  Cord. 

The  spinal  cord  is  composed  of  a  central  core  of  gray  matter  thickly  coated  on 
the  outside  by  white  matter.  At  only  one  spot  does  the  gray  matter  come  close  to 
the  surface,  viz.  at  the  bottom  of  the  postero-lateral  groove. 

Gray  Matter  of  the  Cord. — The  gray  matter  in  the  interior  of  the  cord  has 
the  form  of  a  fluted  column,  but  it  is  customary  to  describe  it  as  it  appears  in 
transverse  sections  through  the  cord.  It  then  presents  the  appearance  of  the 
capital  letter  H.  In  each  lateral  half  of  the  cord  there  is  a  semilunar  or  crescentic 
mass,  shaped  somewhat  like  a  comma,  the  concavity  of  which  is  directed  outwards 
and  the  convexity  inwards.  The  two  crescents  of  opposite  sides  are  connected 
across  the  middle  line  by  a  transverse  band,  which  receives  the  name  of  the  gray 
commissure  (commissura  grisea).  The  postero- median  fissure  cuts  through  the 
cord  until  it  reaches   the  gray  commissure.     The   bottom   of  the  an tero- median 

fissure,however,is  separated 
from  it  by  an  intervening 
strip  of  white  matter,  which 
is  termed  the  anterior  white 
commissure  (commissura an- 
terior alba).  In  tlie  gray 
commissure  may  be  seen 
the  central  canal  of  the 
cord  (canalis  centralis), 
which  tunnels  the  entire 
length  of  the  cord  and  is 
just  visible  to  the  naked 
eye  as  a  minute  speck.  The 
portion  of  the  gray  com- 
missure which  lies  behind 


Column  of  GoU 


Posterior  coliini 


Coluiim  of  Burdacli 


Pormatio  reticularis 

Lateral  column 

Central  canal 

Spinal  accessory  root- 
Origin  of  spinal 
accessory  nerve 


Anterior  column 
Fig.  368. — Transverse  Section  through  the  Upper   Part  of  the 

Cervical  Region  of  the  Cord  of  an  Orang.     (Prom  a  specimen    the  central   canal   is   called 
prepared  by  the  Weigert-Pal  method;  by  which  the  white  matter 
is  rendered  dark  whilst  the  gray  matter  is  bleached. ) 


the  'posterior  gray  commis- 
sure (commissura  grisea 
posterior) ;  whilst  the  portion  in  front  receives  the  name  of  the  anterior  gray 
commissure  (commissura  grisea  anterior). 

Each  crescentic  mass  of  gray  matter  presents  certain  well-defined  parts.  The 
projecting  portions  which  extend  behind  and  in  front  of  the  connecting  transverse 
gray  commissure  are  termed  respectively  the  posterior  and  the  anterior  cornua  of 
gray  matter  (columnse  grisese).  These  stand  out  in  marked  contrast  to  each  other. 
The  anterior  cornu  (columna  grisea  anterior)  is  short,  thick,  and  very  blunt  at  its 
extremity.  Further,  its  extremity  falls  considerably  short  of  the  surface  of  the 
cord  and  is  separated  from  it  by  a  tolerably  thick  coating  of  white  matter. 
Through  this  the  fascicles  of  the  anterior  nerve-roots,  as  they  emerge  from  the 
gray  matter  of  the  anterior  horn,  pass  on  their  way  to  the  surface.  The  thickened 
end  of  the  anterior  cornu  is  called  the  caput  cornu,  whilst  the  part  close  to  the 
gray  commissure  is  termed  the  cervix  or  basis  cornu.  Throughout  the  greater  part 
of  the  cord  the  posterior  cornu  (columna  grisea  posterior)  is  elongated  and  narrow, 
and  is  drawn  out  to  a  fine  point,  which  almost  reaches  the  bottom  of  the  postero- 
lateral sulcus.  This  pointed  extremity  receives  the  name  of  the  apex  cornu ;  the 
slightly  swollen  part  which  succeeds  it  is  the  caput  cornu;  whilst  the  slightly 
constricted  part  adjoining  the  gray  commissure  goes  under  the  name  of  the  cervix 
or  basis  cornu. 

The  apex  or  tip  of  the  posterior  cornu  differs  considerably  in  appearance  from 
the  general  mass  of  the  gray  matter.  It  is  composed  of  a  material  which  presents 
a  lighter  hue  and  has  a  somewhat  translucent  look.  It  is  called  the  substantia 
gelatinosa  Rolandi,  and,  when  seen  in  transverse  section,  it  exhibits  a  V-shaped  out- 
line and  fits  on  the  caput  cornu  like  a  cap. 

A  pointed  and  prominent  triangular  projection  juts  out  from  the  external 
aspect  of  gray  matter  nearly  opposite  the  gray  commissure.  This  is  the  lateral 
horn  (columna  grisea  lateralis),  and  it  is  best  marked  in  the  upper  dorsal  region  (Fig. 


INTEliNAL  STEUCTURE  OF  THE  SPINAL  CORD.  457 

369,  B).  Traced  upwards  it  becomes  aljsorbed  in  the  greatly  expanded  anterior  horn 
of  the  cervical  swelling,  but  it  reappears  again  in  the  upper  part  of  the  cord  and 
is  particularly  noticeable  in  the  second  and  third  cervical  segments ;  followed  in  a 
downward  direction  it  blends  with  the  anterior  horn  in  the  lumbar  swelling  and 
contributes  to  the  thickening  of  that  coruu. 

The  gray  matter  is  for  the  most  part  mapped  off  from  the  surrounding  white  matter 
with  a  considerable  degree  of  sharpness ;  but  in  the  cervical  region,  on  the  outer 
aspect  of  the  crescentic  mass  and  in  the  angle  between  the  anterior  and  posterior 
horns,  fine  bands  of  gray  matter  penetrate  the  white  matter,  and,  joining  with  each 
other,  form  a  network  the  meshes  of  which  enclose  small  islands  of  white  matter. 
This  constitutes  what  is  called  the  formatio  or  processus  reticularis.  Although 
best  marked  in  the  cervical  region,  traces  of  the  same  reticular  formation  may  be 
detected  in  lower  segments  of  the  cord. 

Characters  presented  by  the  Gray  Matter  in  Different  Regions  of  the  Cord. 
— The  gray  matter  is  not  present  in  equal  quantity  nor  does  it  exhibit  the  same 
form  in  all  regions  of  the  cord.  Indeed,  each  cord  segment  presents  its  own 
special  characters  in  both  of  these  respects.  It  is  not  necessary,  however,  in  the 
present  instance  to  enter  into  this  matter  with  any  degree  of  minute  detail.  It 
will  be  sufficient  if  we  point  out  the  broad  distinctions  which  are  evident  in  the 
different  regions. 

It  may  be  regarded  as  a  general  law  that,  w^herever  there  is  an  increase  in  the 
size  of  the  nerves  attached  to  a  particular  part  of  the  cord,  a  corresponding 
increase  in  the  amount  of  gray  matter  will  be  observed.  It  follows  from  this 
that  the  regions  where  the  gray  matter  bulks  most  largely  are  the  lumbar  and 
the  cervical  swellings.  The  great  nerve-roots  which  go  to  form  the  nerves  of  the 
large  limb-plexuses  enter  and  pass  out  from  those  portions  of  the  cord.  In  the 
dorsal  region  there  is  a  reduction  in  the  quantity  of  gray  matter  in  correspondence 
with  the  smaller  size  of  the  dorsal  nerves. 

In  the  dorsal  region  (Fig.  369,  B)  both  horns  of  gray  matter  are  narrow,  although 
the  distinction  between  the  anterior  horn  and  the  still  more  attenuated  posterior 
horn  is  sufficiently  manifest.  In  this  region  the  lateral  horn  of  gray  matter  is 
likewise  characteristic,  and  the  substantia  gelatinosa  Rolandi  in  transverse  section 
is  pointed  and  spear-shaped. 

In  the  upper  three  segments  of  the  cervical  region  the  anterior  horns  of  gray 
are  not  large  and  resemble  the  corresponding  horns  in  the  dorsal  region.  A  lateral 
horn  is  also  present.  But  in  these  segments  (and  more  especially  in  the  first  and 
second)  there  is  a  marked  attenuation  of  the  neck  of  the  posterior  horn,  and  the 
posterior  gray  commissure  is  very  broad. 

In  the  cervical  sioelling  of  the  cord  the  contrast  between  the  two  cornua  is 
most  striking ;  the  anterior  horn  is  of  great  size  and  presents  a  very  broad  surface 
towards  the  anterior  aspect  of  the  cord,  whilst  the  posterior  horn  remains  narrow. 
This  great  increase  in  the  bulk  of  the  anterior  horn  is  due  to  a  marked  addition 
of  gray  matter  on  the  outer  side  of  the  horn,  and  seeing  that  this  additional  matter 
is  traversed  by  a  greater  numljer  of  fibres,  it  stands  out,  in  well-prepared  specimens, 
more  or  less  distinctly  from  the  part  of  the  horn  which  lies  to  the  inner  side,  and 
which  may  be  considered  to  represent  the  entire  anterior  horn  in  the  dorsal  and 
upper  cervical  segments.  Within  this  lateral  addition  to  the  anterior  horn  are 
placed  those  collections  of  cells  which  constitute  the  nuclei  of  origin  of  the  motor 
nerves  of  the  muscles  of  the  ujjper  limb.  The  characteristic  thickening  of  the 
anterior  horn  of  gray  matter  is  evident,  therefore,  in  those  segments  of  the  cord 
to  which  the  nerves  which  enter  the  brachial  plexus  are  attached,  viz.  the  lower 
five  cervical  segments  and  the  first  dorsal  segment. 

In  the  lumbar  svjelling  the  anterior  horns  ;igain  broaden  out,  and  for  the  same 
reason  as  in  the  case  of  the  corresponding  horns  in  the  cervical  swelling.  The 
nuclear  masses  which  contain  the  cells  from  which  the  motor  fibres  which  supply 
the  muscles  of  the  lower  limbs  take  origin  are  added  to  the  outer  aspect  of  the 
horns  and  give  th(!ni  a  very  cliaracteristic  appearance.  In  this  region  of  the  cord, 
however,  tlie  posterior  horns  arc  also  })roa(l  and  capped  by  substantia  gelatinosa 
Rolandi,  which    in    transverse   section  itresents  a  semilunar   outline.      There   is 


458 


THE  NEKVOUS  SYSTEM. 


consequently  no  difficulty  in  distinguishing  from  an  inspection  of  the  gray  matter 
alone  between  transverse  sections  of  the  cord  taken  from  the  cervical  and  lumbar 
swellings  of  the  cord. 


A.- 


-Cervioal  region — at  the  level  of  the  fifth  cervical  nerve. 
(From  a  specimen  prepared  by  Dr.  A.  Bruce. ) 

1.  Postero-iiiediau  fissure. 

2.  Paramedian  septum. 

3.  Postero-lateral  groove. 

4.  Posterior  nerve-root. 

5.  Substantia  gelatinosa  Rolandi. 


S.  Central  canal. 
9.  Nuclei     from    which    motor- 
fibres  for  muscles  of  upper 
liinb  arise. 
10.  Anterior  commissure. 

6.  Root-fibres  entering  gray  matter.  11.  Anterior  nerve-root. 

7.  Formatio  reticularis.  12.  Antero-median  fissure. 


'■^ 


■'V 


B. — Through  the  mid-dorsal  region. 

1.  Postero-median  fissure. 

2.  Postero-lateral  groove. 

3.  Posterior  cornu. 

4.  Posterior  vesicular  column  of  cells. 

5.  Lateral  cornu. 

6.  Central  canal. 

7.  Anterior  cornu. 

8.  Antero-median  fissiu'e. 


^Hh 


-Through  the  lumbar  region  at  the  level  of  the 
fourth  lumbar  nerve. 


Nuclei  of  origin  from 
whicli  the  motor- 
fibres  for  nmscles  of 
the  lower  limb  arise. 

Anterior  nerve-root. 

Antero-median  fissure. 


-Through  the  sacral  region  at  the  level  of  the 
third  sacral  nerve.  (From  a  specimen  pre- 
pared by  Dr.  A.  Bruce. ) 

1.  Postero-median  lis.sure. 

2.  Posterior  nerve-root. 

3.  Substantia  gelatinosa  Rolandi. 

4.  Posterior  gray  commissure. 
.5.  Aiterior  commissure. 
6.  Antero-median  fissure. 


1.  Posterior  nerve-root. 

2.  Postero-median  fissure. 

3.  Substantia  gelatinosa  Rolandi. 

4.  Root  -  fibres      entering      gray 
matter. 

5.  Central  canal. 

6.  Anterior  commissure. 

Fig.  369. — Section  through  each  of  the  Four  Regions  of  the  Cord.  (From  specimens  prepared  by 
the  Weigert-Fal  method,  therefore  the  white  matter  is  rendered  dark  in  colour  whilst  the  gray 
matter  is  bleached. ) 

In  the  lower  part  of  the  conus  meduUaris  the  gray  matter  in  each  lateral  half 
of  the  cord  assumes  the  form  of  an  oval  mass  joined  to  its  fellow  of  the  opposite 
side  by  a  thick  gray  commissure.     Here  almost  the  entire  bulk  of  the  cord  consists 


IN  TEEN  AL  STEUCTUEE  OF  THE  SPINAL  COED.  459 

of  gray  matter,  seeing  that  the  white  matter  is  reduced  to  such  an  extent  that  it 
forms  only  a  thin  coating  on  the  outside. 

White  Matter  of  the  Spinal  Cord. — In  transverse  sections  of  the  cord  the 
three  columns  into  which  the  white  matter  is  subdivided  become  very  apparent. 
The  posterior  column  is  wedge-shaped,  and  lies  between  the  postero-median  fissure 
and  the  posterior  horn  of  gray  matter.  The  lateral  column  occupies  the  concavity 
of  the  gray  crescent.  Behind,  it  is  bounded  by  the  posterior  horn  of  gray  matter 
and  the  postero-lateral  sulcus,  whilst  in  front  it  extends  as  far  as  the  outermost 
fasciculi  of  the  anterior  nerve-roots  as  they  pass  out  from  the  anterior  gray  horn. 
The  anterior  column  includes  the  white  matter  between  the  antero-median  fissure 
and  the  anterior  horn  of  gray  matter,  and  also  the  white  matter  which  separates  the 
broad  extremity  of  the  anterior  gray  cornu  from  the  surface  of  the  cord.  This 
latter  portion  of  the  anterior  column  is  traversed  by  the  emerging  fascicles  of  the 
anterior  nerve-roots. 

In  cross-sections  of  the  cord  the  partition  of  pia  mater,  which  dips  in  at  the 
posterior  paramedian  groove  and  divides  the  posterior  column  into  the  column  of 
Goll  and  the  column  of  Burdach,  jS  very  strongly  marked  in  the  cervical  regions, 
but  as  it  is  traced  downwards  into  the  dorsal  region  it  becomes  shorter  and  fainter, 
and  finally  disappears  altogether  at  the  level  of  the  eighth  dorsal  nerve.  Below 
this  point  there  is  no  visible  demarcation  of  the  posterior  column  into  two  parts. 

The  white  matter  is  not  present  in  equal  quantity  throughout  the  entire  length 
of  the  cord.  It  increases  steadily  from  below  upwards,  and  this  increase  is  most 
noticeable  in  the  lateral  and  posterior  columns.  In  the  lower  part  of  the  conus 
medullaris  the  amount  of  gray  matter  is  actually  greater  than  that  of  the  white 
matter  :  but  very  soon  this  state  of  affairs  is  changed,  and  in  the  lumbar  region  the 
proportion  of  gray  to  white  matter  is  approximately  as  1:2-1;  in  the  dorsal  region 
as  1:5:  and  in  the  cervical  region  as  1 :  5'1.  When  it  is  remembered  how  the  gray 
matter  expands  in  the  lumbar  and  cervical  regions,  and  how  greatly  it  becomes  reduced 
in  the  dorsal  region,  the  significance  of  these  figures  will  become  more  apparent. 

Central  Canal  (canalis  centralis). — As  previously  stated,  the  central  canal  is 
found  in  the  gray  commissure.  It  is  a  very  minute  tunnel,  barely  visible  to  the 
naked  eye  when  seen  in  transverse  section,  and  it  traverses  the  entire  length  of  the 
cord.  Above,  it  passes  into  the  medulla  oblongata,  and  finally  opens  into  the  fourth 
ventricle  of  the  brain ;  below,  it  is  continued  for  a  variable  distance  into  the  filum 
terminale,  and  in  this  it  ends  blindly.  Only  in  the  lumbar  region  does  the  central 
canal  occupy  the  centre  of  the  cord.  Above  this  level,  in  the  dorsal  and  cervical 
regions,  it  lies  very  much  nearer  the  anterior  than  the  posterior  aspect  of  the  cord ; 
whilst  below  the  lumbar  region,  as  it  is  traced  down  into  the  conus  medullaris,  it 
inclines  backwards  and  approaches  the  posterior  aspect  of  the  cord.  The  calibre  of 
the  canal  likewise  varies  somewhat  in  different  parts  of  the  cord.  It  is  narrowest 
in  the  dorsal  region ;  and  in  the  lower  part  of  the  conus  medullaris  it  expands  into 
a  distinct  fusiform  dilatation  (very  nearly  1  mm.  in  transverse  diameter),  which  is 
termed  the  ventriculus  terminalis  (Krause). 

The  central  canal  is  lined  by  a  layer  of  ciliated  columnar  cells,  the  deep  taper- 
ing ends  of  which  are  prolonged  into  slender  processes,  which  penetrate  into  the 
substance  of  the  cord.  These  cells  constitute  the  lining  ependymal  cells  of  the 
canal.  The  cilia  of  the  epithelial  cells  are  very  early  lost,  and  it  is  not  uncommon 
to  find  the  canal  blocked  up  by  ej)ithelial  debris. 

The  central  canal  is  of  interest  because  it  represents  in  the  adult  the  relatively 
wide  lumen  of  the  early  ectodermal  neural  tube  from  which  the  spinal  cord  is 
developed. 

Filum  Terminale. — Tiie  delicate  thread  to  which  this  name  is  applied  is  con- 
tinuous with  the  lower  tapered  end  of  the  conus  medullaris.  It  is  easily  distin- 
guished by  its  silvery  and  glistening  appearance  from  the  numerous  long  nerve-roots 
(cauda  equina)  amidst  which  it  lies.  It  is  about  six  inches  long,  and  down  to  the 
level  of  the  second  sacral  vertebra  it  is  inclosed  with  the  surrounding  nerve-roots 
within  the  theca  of  dura  mater.  Piercing  tlie  tapered  and  chjsed  end  of  the  theca 
at  this  point,  and  receiving  an  iiivestiiKmt  I'roiu  it,  tlui  filum  termiua](!  proceeds 
downwards  in  the  sacral  canal,  and  finally  receives  attachment  to  the  periosteum  on 


460 


THE  NEEVOUS  SYSTEM. 


tlie  dorsal  aspect  of  the  coccyx  (Fig.  364,  p.  453).  It  is  customary  to  speak  of  the 
fikiin  as  consisting  of  two  parts,  viz.  the  fikim  terminale  internum  and  the  filum 
terminale  externum,  or  the  part  inside  and  the  part  outside  the  theca  of  dura  mater. 
The  filum  terminale  externum  is  simply  a  Rljrous  thread,  strengthened  by  the 
prolongation  it  receives  as  it  pierces  the  dura  mater.  The  filum  terminale  internum 
is  largely  composed  of  pia  mater  ;  but  in  its  upper  half  it  incloses  tlie  terminal  part 
of  the  central  canal,  and  around  this  a  variable  amount  of  the  gray  substance  of  the 
cord  is  prolonged  downwards  into  the  filum.  When  transverse  sections  are  made 
through  the  upper  part  of  the  filum  terminale  internum  some  bundles  of  medul- 
lated  nerve-fibres  are  observed  chnging  to  its  sides,  and  with  these  are  associated 
some  nerve-cells  identical  with  those  in  the  spinal  ganglia.  These  represent  rudi- 
mentary or  aborted  caudal  nerves  (Eauber). 


SUMMAEY    OF   THE    GhIEF    CHARACTERS    PRESENTED    BY   THE    CORD    IN    ITS 

Different  Eegions. 


Cervical  Region. 

Dorsal  Region. 

Lumbar  Region. 

Sacral  Region. 

Ill     transverse     section, 

lu     transverse    section, 

In     transverse     section. 

In     transverse     section, 

outline  of  cord  trans- 

outline of  cord  more 

outline  of  cord  more 

outline    of    cord, 

versely    oval  ;   in    the 

nearly    circular  ;    but 

nearly  circular  than  in 

nearly    circular,     but 

middle  of  the  cervical 

still  the  transverse  di- 

dorsal region. 

still    somewhat    com- 

swelling the  transverse 

ameter  is  greater  than 

pressed    from    before 

diameter  being  nearly 

the    antero  -  posterior 

backwards. 

one -third  longer  than 

diameter. 

the    antero  -  posterior 

diameter. 
Postero  -  median  cleft 

Postero  -  median    cleft 

Postero  -  median  cleft 

Postero  -  median     and 

very    deep,    extending 

vevy  deep,    extending 

not  nearly  so  deep  as 

antero-median  clefts 

beyond  the  centre  of 

beyond  centre  of  cord  : 

in  regions  above  :  an- 

of equal  depth. 

cord;  antero-median 

antero-median   cleft 

tero-median  cleft,  on 

cleft  shallow. 

shallow. 

the  other  hand,  much 

deeper. 

Gray  matter  greatly  in- 

Gray   matter    greatly 

Gray  matter  greatly  in- 

Both    horns     of    gray 

creased  in  quantity  in 

i-educed   in    quantity. 

creased  in  the  lumbar 

matter  very  thick  and 

the  cervical  swelling  : 

Both    horns    .slender. 

swelling.     Both  horns 

massive.    Lateral  horn 

anterior    horn     thick 

Lateral      horn      well 

very  thick  and  m  assive. 

apparent.     No    form- 

andmassive; posterior 

marked.       Formatio 

Lateral  horn  absorbed 

atio  reticularis. 

horn  slender  in  com- 

reticularis scarcely  ap- 

in anterior  horn.   For- 

parison.   Lateral  horn 

parent. 

matio    reticularis    ab- 

only evident  above  the 

sent. 

level  of  the  fourth  cer- 

vical nerve.    Formatio 

reticularis  strongly 

marked. 

White  matter  in  great 

White    matter   less 

White  matter  small  in 

White      matter     very 

quantity,  and   especi- 

in   quantity    than    in 

quantity  in  relation  to 

small   in   quantity   in 

ally    massed    in    the 

cervical     region,     Ijut 

higher     regions,     and 

comparison    with    the 

lateral    and    posterior 

bulking      largely      in 

very  small  in  amount 

gray  matter. 

columns. 

comparison    with    the 

•    in     relation      to     in- 

quantity   of     gray 

creased     quantity     of 

matter. 

gray  matter. 

No   posterior   para- 

Posterior paramedian 

Posterior  paramedian 

No   posterior   para- 

groove   and    septum 

groove    absent  ;    but 

median    groove    or 

median  groove  and  no 

well  marked. 

the  corresponding  sep- 
tum can  be  traced  as 
low  down  as  the  eighth 
dorsal  nerve. 

sejitum. 

corresponding  septum. 

Central  canal  consider- 

Central canal  consider- 

Central  canal    in    the 

Central    canal  in    the 

ably  nearer  the  anterior 

ably  nearer  the  anterior 

centre  of  the  cord. 

centre  of  the  cord. 

surface  than  the  pos- 

surface than  the  pos- 

terior   surface   of   the 

terior   surface   of   the 

cord. 

cord. 

COMPONENT  PARTS  OF  GRAY  MATTER  OF  SPINAL  CORD.     461 

Component  Parts  of  the  Gray  Matter  of  the  Spinal  Cord. 

Neuroglia  enters  largely  into  the  constitution  of  the  gray  matter  of  the  cord. 
It  forms  a  bed  within  which  the  nervous  elements  are  distributed.  These  nervous 
elements  consist  of  (1)  nerve-cells  and  (2)  nerve-fibres — both  medullated  and  non- 
medullated.  The  nerve-cells  lie  in  small  s^jaces  within  the  neuroglia,  whilst  the 
nerve-fibres  traverse  fine  passages  the  walls  of  which  are  formed  of  the  same  sub- 
stance. The  neuroglia  is  thus  an  all-pervading  basis  substance,  which  isolates  more 
or  less  completely  the  nervous  elements  from  each  other,  and  at  the  same  time 
binds  them  together  into  a  consistent  solid  mass.  In  two  situations  the  gray 
matter  presents  special  characteristics  w^hich  have  earned  for  it  the  name  of 
substantia  gelatinosa,  viz.  the  gray  matter  which  constitutes  the  immediate  sur- 
rounding of  the  central  canal,  and  which  is  called  the  substantia  gelatinosa 
centralis ;  and  that  which  forms  the  apical  part  of  the  posterior  horn  of  gray 
matter,  and  which  receives  the  name  of  substantia  gelatinosa  Rolandi.  In  both 
situations  the  substantia  gelatinosa  stains  more  deeply  with  carmine  and  presents 
a  more  translucent  appearance ;  in  other  respects  the  substantia  centralis  and  the 
substantia  Rolandi  are  very  different. 

The  substantia  gelatinosa  centralis  forms  a  thick  ring  around  the  central  canal, 
which  is  traversed  by  the  fine  processes  which  proceed  from  the  deep  ends  of  the 
ependymal  cells  which  line  the  canal.     It  is  almost  entirely  composed  of  neuroglia. 

In  transverse  sections  of  the  cord  the  substantia  Rolandi,  in  the  cervical  and 
dorsal  regions,  presents  the  appearance  of  a  V-shaped  mass,  embracing  the  extremity 
of  the  caput  of  the  posterior  horn  of  gray  matter ;  in  the  lumbar  region  this  cap 
assumes  a  semilunar  outline. 

In  the  substantia  gelatinosa  Rolandi  the  neuroglia  is  present  in  small  quantity, 
and  small  nerve-cells  are  developed  within  it  in  considerable  numbers. 

Nerve-Cells. — The  nerve-cells  are  scattered  plentifully  throughout  the  gray 
matter,  but  perhaps  not  in  such  great  numbers  as  might  be  expected  when  we  note 
the  enormous  number  of  nerve-fibres  with  which  they  stand  in  relation.  They  are 
all,  without  exception,  multipolar,  and  send  off  from  their  various  aspects  several 
branching  protoplasmic  processes  or  dendrites,  and  one  axon,  which  becomes  the 
axis-cylinder  of  a  nerve- fibre.  In  size  they  vary  considerably,  and  it  is  generally 
admitted  that  the  bulk  of  a  nerve-cell  has  a  more  or  less  definite  relation  to  the 
length  of  the  axis-cylinder  which  proceeds  from  it. 

When  the  nerve-cells  are  studied  in  a  series  of  transverse  sections  of  the  cord, 
it  will  be  noticed  that  a  large  proportion  of  them  are  grouped  in  clusters  in  certain 
districts  of  the  gray  matter ;  and  as  these  groups  are  seen  in  very  much  the  same 
position  in  successive  sections,  it  is  clear  that  these  cells  are  arranged  in  longitudinal 
columns  of  greater  or  less  length.  Thus  we  recognise  (1)  a  ventral  group  or  column 
of  cells  in  the  anterior  horn  of  gray  matter;  (2)  an  intermedio-lateral  group  or 
column  in  the  lateral  horn  of  gray  matter,  where  this  exists ;  and  (3)  a  posterior 
vesicular  column  of  cells  (Clarke's  column),  forming  a  most  conspicuous  group  in 
the  mesial  part  of  the  cervix  of  the  posterior  horn  in  the  dorsal  region  of  the 
cord. 

Other  cells  besides  those  forming  these  columns  are  scattered  somewhat  irregu- 
larly throughout  the  gray  matter  of  the  posterior  horn  and  the  part  of  the  gray 
crescent  which  lies  between  the  two  horns ;  and  although  these  also  in  some  measure 
may  be  classified  into  groups,  the  arrangement  thus  effected  is  not  of  so  definite  a 
character  as  to  justify  us  in  dwelling  upon  it  in  the  present  instance. 

Ventral  Cell-Column  and  the  Origin  of  the  Fibres  of  the  Anterior  Nerve- 
Roots. — The  ventral  cell-group  occupies  the  anterior  horn  of  gray  matter,  and  in 
it  are  found  the  largest  and  most  conspicuous  cells  in  the  spinal  cord.  It  extends 
from  one  end  of  the  cord  to  the  other.  These  ventral  nerve-cells  have  numerous 
wide-spreading  dendritic  processes,  and  it  is  to  be  noticed  that  certain  of  these 
dendrites  do  not  confine  their  ramifications  to  the  gray  matter.  Thus,  some  of  the 
cells  along  the  mesial  border  of  the  anterior  horn  of  gray  matter  send  dendrites 
across  the  mesial  plane  in  the  anterior  commissure  to  end  in  the  anterior  gray 
horn  of  the  opposite  side ;  whilst  others,  lying  along  the  lateral  or  outer  margin  of 


462 


THE  NEEVOUS  SYSTEM. 


the  anterior  horn  of  gray  matter,  send  dendrites  in  amongst  the  nerve-fibres  of  the 
adjoining  white  matter. 

The  axons  or  axis-cylinder  processes  of  a  large  proportion  of  the  ventral  cells 
converge  together ;  and,  becoming  medullated,  form  bundles  which  pass  out  from 
the  gray  matter,  and  through  the  white  matter  which  separates  the  thick  end  of 
the  anterior  horn  from  the  surface  of  the  cord,  to  finally  emerge  as  the  fascicles  of 
the  anterior  nerve-roots.     These  cells,  then,  are  the  sources  from  which  the  nerve- 

Postero-latei'al  fuiTow 

Posterior  horn  of 
"i-;iv  matter 


Postero-median  fissure 


Gray  commissure- 


Postero-lateral  group  of 
motor  cells 


Antero-mediaii 
furi'ow 


Antero-mesial  group 
of  motor  cells 


Antero-lateral 
grouj)  of  motor  cells 


Fig.  370. — Section   through  the   Fifth   Cervical  Segment  of  the  Cord.     (To  a  large  extent  founded 

on  Plates  in  Dr.  Bruce's  Atlas.) 

fibres  of  the  anterior  nerve-roots  proceed,  and  in  consequence  they  are  frequently 
spoken  of  as  the  "  motor  cells  "  of  the  cord.  Whilst  this  is  the  arrangement  of  the 
axons  of  the  great  majority  of  the  motor  cells,  it  should  be  noted  that  a  few  cross 
the  mesial  plane  in  the  anterior  white  commissure  and  emerge  in  the  fascicles  of 
origin  of  the  opposite  anterior  nerve-root. 

The  ventral  cells  are  not  scattered  uniformly  throughout  the  anterior  horn  of  gray 
matter.  They  are  aggregated  more  closely  together  in  certain  parts  of  the  anterior  horn, 
and  thus  form  sub-groups  or  columns  more  or  less  perfectly  marked  off  from  each  other. 

Thus  one  sub-group  or  column  of  ventral  cells  occupies  the  inner  or  mesial  part  of  the 
anterior  horn  of  gray  matter  throughout  almost  its  whole  length.  In  only  two  segments 
of  the  cord  is  it  absent,  viz.  the  fifth  lumbar  and  the  first  sacral ;  at  this  level  in  the  cord 
alone  is  its  continuity  broken  (Bruce).  It  is  termed  the  ventro-mesial  column  or  group  of 
ventral  cells.  Behind  this  cell-column  there  is  another  which  is  classed  with  it  to  which 
the  name  of  dorso-'inesial  column  or  group  is  given,  but  this  column  of  cells  is  not  con- 
tinuous throughout  the  entire  length  of  the  cord.  It  is  present  in  the  dorsal  region  of 
the  cord  where  the  motor  nuclei  for  the  muscles  of  the  limbs  are  absent,  and  it  is  also  seen 
in  two  or  three  of  the  segments  of  the  cervical  region  and  in  the  first  lumbar  segment 
(Bruce)  ;  elsewhere  it  is  not  represented. 

In  the  cervical  and  lumbar  swellings  of  the  cord,  where  the  marked  lateral  outgrowth 
is  added  to  the  outer  side  of  the  anterior  horn  of  gray  matter,  certain  groups  of  large 
multipolar  cells  are  visible.  These  are  the  nuclei  of  origin  of  the  motor-fibres  which 
supply  the  muscles  of  the  limbs,  and  consequently  they  are  not  represented  in  the  upper 
three  cervical  segments  of  the  cord ;  nor  in  any  of  the  dorsal  segments,  with  the  exception 
of  the  first  dorsal  segment ;  nor  in  the  two  lowest  sacral  segments. 

These  lateral  cells  are  arranged  in  several  columns,  which  extend  for  varying  distances 
in  the  superadded  lateral  parts  of  the  anterior  horn  of  gray  matter.  The  two  main 
columns  are  a  ventro-lateral  and  a  dorso-lateral  column ;  in  certain  segments  thei^e  is 
likewise  a  post<lorso-lateral  column,  and  in  a  number  of  segments  in  the  lumbar  and  sacral 
regions  a  central  column  of  cells  (Bruce). 


COMPONENT  PAETS  OF  GKAY  MATTER  OF  SPINAL  CORD.     463 


Postero-median 
Hssure 


Posterior  vesicular 
columji  (Clarke's 
column  of  cells) 


Gray  commissure 


Antero-mediau 
furrow 


Posterior  horn 
of  gray  matter 


Antero-mesial  sroup 
of  motor  cells 


Intermedio-lateial 
tract  of  cells 


Postero-mesial  group 
of  motor  cells 


Fig.  371. — Section  through  the  Eighth  Dorsal  Segment  of  the 
Spinal  Cord.  (To  a  large  extent  founded  on  Plates  in  Dr. 
Bruce's  Atlas.) 


There  cannot  be  a  d(jabt  tliat  the  grouping  of  the  motor  cells  in  the  anterior  horn  of 
gray  matter  of  the  cord  stands  in  relation  to  the  muscle  groups  to  which  their  axis-cylinder 
processes    are   distributed ;  but 

from  what  has  been  said    it  will  I,     /  /  i  /   /   |   ^^^^  Postero-lateral  furrow 

be  apparent  that  sharply  defined 

cell-clusters  associated  with  par- 
ticular  muscles    do    not    exist. 

Still,  much  can  be  learned  re- 
garding the  localisation  of  the 

motor   nuclei    in    the    anterior 

horn  of  gray  matter  of  the  cord 

from  the  study  of  the  changes 

which  occur  in  the  cell-columns 

afteratrophiesof  isolated  muscles 

or  groups  of  muscles,  and  after 

complete  or  partial  amputations 

of  limbs.     It  has  been  pointed 

out  that    the    long  muscles    of 

the  trunk  (as,  for  example,  the 

different   parts    of    the    erector 

spinae    muscle)    receive    nerve - 

fibres    from    all    the    segments 

of    the    cord.     Now,    we    have 

noted   that    there    is  only    one 

cell-column,  the   ventro-mesial 

column,  which  pursues  an  almost 

uninterrupted  course  throu.ghout  the  entire  length  of  the  cord.      It  may  be   assumed, 

therefore,  that  the  nerve-fibres  which  go  to  these  long  trunk-muscles  take  origin  in  these 

mesial  cells. 

Edinger  states  that  in  the  anterior  horn  of  gray  matter  the  nuclei  of  origin  of  the 

nerves  which  supply  the 
proximal  muscles  are  medially 
placed ;  that  those  for  the 
distal  muscles  are  in  general 
situated  laterally.  If  this 
be  the  case,  the  cells  con- 
nected with  the  shoulder 
muscles  would  lie  nearer  the 
middle  of  the  anterior  horn 
of  gray  matter  than  those 
which  are  connected  with 
the  hand-muscles.  In  cases 
w^here  the  forearm  and  hand, 
or  the  leg  and  the  foot,  are 
amputated,  it  would  appear 
that  it  is  the  postero-lateral 
column  of  cells  that  shows 
changes  in  consequence  of  its 
separation  from  the  muscles 
to  which  its  fibres  ai'e  dis- 
tributed.^ 


Postero  median 
fissure 


Postero-lateral  farrow 


Posterior  horn  of 
matter 


Antero-mediau 
furrow 


iteral  Ki'oup 

Intermedio- lateral  Cell- 
column. —  The  intermedio- 
lateral  cells  form  a  long- 
slender  column  which  ex- 
tends throughout  the  entire 
dorsal  region  of  the  cord  in  the  lateral  horn  of  gray  matter.  It  is  also  prolonged 
downwards  into  the  first  and  second  lumbar  segments,  where  it  disappears.     In 


Antero-mesial        Cfiitral  ;j;rou|i         Antero-lateral 
group  of  cells  of  cells  group  of  cells 

Fig.  372,— Section  through  the  Third  Lumbar  Secjment  ok 
Si'iNAL  Cord  to  .show  the  grouping  ok  the  Motor  Cells. 
a  large  extent  founded  on  Plates  in  Dr.  Biuce'.s  Alias.) 


thic 
(To 


'  Those  who  .seek  further  information  regarding  the  grouping  of  the.  ventral  cells  of  the  cord,  may  with 
advantage  study  Dr.  Alexander  Hruce's  AI.Ik.h  of  the,  Spinal  (Junt. 


464 


THE  NERVOUS  SYSTEM. 


Postero-mediaii 
fissure 


Antero-median 

fuiTOW 


Central  gi-oup  of  cells 


Postero-lateral  group 
of  cells 


Antero-lateral  group  of  cells 


Fig.  373. — Section  through  the  First  Sacral  Segment  of  the 
Spinal  Cord  to  show  the  grouping  of  the  Motor  Nerve- cells. 
(To  a  large  extent  founded  on  Plates  in  Dr.  Bruce's  A  tlas. ) 


transverse  sections  through  the  cord  this  cell-group  presents  a  very  characteristic 
appearance,  because  the  cells  which  compose  it  are  small  and  are  closely  packed 

together.  Although  these 
cells,  as  a  continuous 
column,  are  restricted  to 
the  region  indicated,  it 
should  be  noted  that  the 
same  group  of  cells  re- 
appears above  in  certain  of 
the  cervical  segments  and 
also  in  the  third  and  fourth 
sacral  segmen  ts.  The  func- 
tion   and    connexions    of 

Gray  commis- ^  "^— ^— :_^/'  \  thcsc  cclls   are   unknown. 

sme  s  .,//  \  It  has  been  suggested  that 

they  give  origin  to  vaso- 
motor, pilo  -  motor,  and 
sweat  -  gland  nerves,  and 
have  a  very  close  connexion 
with  the  sympathetic  ner- 
vous system. 

In  a  recent  researcli  by 
Bruce  the  following  important 
points  in  regard  to  the  inter- 
medio-lateral  cell-column  liave 
been  determined. 

It  is  not  quite  continuous. 
In  the  eighth  cervical,  first 
dorsal,  and  also  in  a  part  of  the 
second  dorsal  segment,  as  well 
as  in  the  first  and  second  lumbar  segments,  the  cells  are  in  separate  clusters.  Throughout  the 
rest  of  the  dorsal  region  it  forms  a  moniliform  chain  of  cells,  situated  partly  in  the  lateral  horn 
and  partly  in  the  gray  matter  behind  it.  Some  outlying  cells  are  situated  in  the  white  matter 
in  the  neighbourhood  of  tlie  lateral  horn. 

The  limits  of  the  tract  are  from  lower  two-thirds  of  eighth  cervical  to  the  lower  end  of  the 
second  lumbar  or  perhaps  the  upper  end  of  the  third  lumbar  segment.  It  is  found  also  in  the 
first,  second,  and  third  cervical,  and  in  the  third  and  fourth  sacral  segments.  It  reaches  its 
maximum  size  in  the  tliird  and  fourth  dorsal  segments. 

Posterior  Vesicular  Column — Clarke's  Column. — This  occupies  the  posterior 
horn  of  gray  matter  and  is  the  most  conspicuous  of  all  the  cell-groups  in  the 
cord.  It  does  not,  however,  extend  along  the  whole  length  of  the  cord;  indeed 
it  is  almost  entirely  confined  to  the  dorsal  region,  and  in  consequence  it  is  some- 
times referred  to  as  the  "  dorsal  nucleus."  Above,  it  begins  opposite  the  seventh  or 
eighth  cervical  nerve,  whilst  l)elow,  it  may  be  traced  to  the  level  of  the  second 
lumbar  nerve,  where  it  disappears.  In  transverse  section  of  the  cord  it  presents  an 
oval  outline,  and  is  seen  in  the  inner  part  of  the  cervix  of  the  posterior  horn  of 
gray  matter  immediately  behind  the  gray  commissure  (Fig.  369  B,  p.  458).  On  the 
outer  side  it  is  circumscribed  by  numerous  curved  fibres  from  the  entering  posterior 
nerve-root,  and  in  the  lower  dorsal  region  of  the  cord  (opposite  the  eleventh  and 
twelfth  dorsal  nerves)  it  becomes  so  marked  that  it  forms  a  bulging  on  the  inner 
aspect  of  the  posterior  gray  horn. 

The  cells  of  Clarke's  column  are  large,  and  possess  several  dendritic  processes. 
The  axons  enter  the  lateral  column  of  white  matter  and  there  form  a  strand  of 
fibres,  which  will  later  on  be  described  under  the  name  of  the  direct  cerebellar  tract. 

In  addition  to  the  topograjahical  subdivision  of  the  nerve-cells  of  the  cord  indicated  above,  it 
is  now  usual  to  classify  them  according  to  the  nature  of  the  axons  which  proceed  from  them. 
Thus  we  have  (1)  the  cells  of  Golgi  or  cells  with  short  axons,  and  (2)  cells  with  long  axons. 

The  cells  of  G-olgi  jjossess  axons  which  do  not  emerge  from  the  gray  matter,  but  bring  neigh- 
bouring cells  into  touch  with  each  other.  Tlie  cells  with  long  axons  are  of  two  kinds,  viz. 
radicular  cells  and  strand-cells. 

The  radicular  cells  are  those  from  which  the  axon  emerges  from  the  cord  in  the  shaj)e  of  an 
efferent  nerve-fibre.     Thus  the  "  motor  cells "  which  supply  the  axis-cylinder  processes  of  the 


COMPONENT  TAETS  OF  WHITE  MATTER  OF  SPINAL  CORD.     465 

anterior  nerve-roots  belong  to  tliis  class.  Tlie  strand-cells  are  those  which  contribute  their  axons 
to  the  formation  of  those  filjres  which  form  certain  of  the  strands  or  tracts  which  are  found  in 
the  white  matter  of  the  cord. 

Nerve-fibres  in  the  Gray  Matter  of  the  Cord. — Nerve-fibres  botli  of  the 
meduUated  and  non-meduUated  variety  pervade  every  part  of  the  gray  matter. 
They  are  of  three  kinds,  viz.  (1)  collaterals,  (2)  terminations  of  nerve-fibres,  (3) 
axons  given  off  by  the  cells.  Many  of  the  nerve-fibres  which  compose  the  columns 
of  white  matter  of  the  cord  give  off  numerous  fine  collateral  branches,  which  pass 
into  the  gray  matter  from  all  sides  and  finally  end  in  relation  with  the  nerve- 
cells.  The  majority  of  the  nerve-fibres  themselves,  which  thus  give  off  collaterals, 
finally  enter  the  gray  matter,  and  end  similarly.  As  already  noted,  the  axons  of 
the  cells  of  Golgi  remain  within  the  gray  matter,  but  the  others  emerge  either  for 
the  purpose  of  entering  a  peripheral  nerve  or  for  the  purpose  of  entering  a  strand 
of  fibres  in  the  white  matter  of  the  cord. 

The  nerve-fibres  thus  derived  are  interwoven  together  in  the  gray  matter  of  the 
cord  in  a  dense  inextricable  interlacement. 


Component  Parts  of  the  White  Mattee  of  the  Cord. 

The  white  matter  of  the  cord  is  composed  of  medullated  nerve-fibres  embedded 
in  neuroglia.  The  fibres,  for  the  most  part,  pursue  a  longitudinal  course ;  and 
from  the  deep  surface  of  the  pia  mater  which 
surrounds  the  cord  fibrous  septa  or  partitions  are 
carried  in  along  vertical  planes  between  the  fibres,  so 
as  to  form  an  irregular  and  very  imperfect  fibrous 
framework  of  support.  The  neuroglia  is  disposed  in 
a  layer  of  varying  thickness  around  the  cord,  sub- 
jacent to  the  pia  mater,  and  is  carried  into  the  cord 
so  as  to  give  a  coating  to  both  sides  of  the  various  pial 
septa.  The  neuroglia  also  is  disposed  around  the 
various  nerve- fibres,  so  that  each  of  these  may  be  said 
to  lie  in  a  canal  or  tunnel  of  this  substance.  The 
nerve -fibres  are  all  medullated,  but  they  are  not 
provided  with  primitive  sheaths.  It  is  the  medullary 
substance  of  the  nerve -fibres  which  gives  to  the 
white  matter  its  opaque,  milky -white  appearance. 
When  a  thin  transverse  section  of  the  cord  is  stained 
in  carmine  and  examined  under  the  microscope  the 
white  matter  presents  the  appearance  of  a  series  of 
closely- applied  circles,  each  with  a  dot  in  the  centre. 
The  dot  is  the  transversely  divided  axis -cylinder  of 
a  nerve-fibre,  and  the  dark  ring  which  forms  the 
circumference  of  the  circle  represents  the  wall  of  the 
neuroglial  canal  which  is  occupied  by  the  fibre. 
The  medullary  substance  is  very  faintly  seen.  It 
presents  a  filmy  or  cloudy  appearance  between  the 
axis-cylinder  and  the  neuroglial  ring. 

Arrangement  of  the  Nerve-fibres  of  the  White 
Matter  in  Strands  or  Tracts. — When  the  white 
matter  of  a  healtliy  adult  cord  is  examined  the  fibres  which  compose  it  are 
seen  to  vary  considerably  in  point  of  size ;  and  although  there  are  special  places 
where  large  fibres — or  it  may  be  small  fibres — are  present  in  greater  numbers 
than  elsewhere,  yet  as  a  rule  both  great  and  small  fibres  are  mixed  u\) 
together.  Absolutely  no  evidence  can  be  ol)tained  in  such  a  cord,  by  any  means 
at  our  disposal,  of  the  fact  that  the  longitudinally  arranged  fibres  are  grouped 
together  in  more  or  less  definite  tracts  or  strands,  tlie  fibres  of  which  run  a  definite 
course  and  present  definite  connexions.  Yet  we  know  this  to  be  the  case,  and  the 
existence  (jf  tliese  H(;[)arate  tracts  has  been  proved  both  by  physiological  and  by 
embryological  investigation. 
34 


Fig.    374. — Transverse     Section 

THROUGH  THE  WhITE   MaTTEH  OF 

the    Cord,    as  seen  through   the 
microscope. 


466  THE  NERVOUS  SYSTEM. 

The  physiological  evidence  depends  on  the  fact  that  when  a  nerve-fibre  is  severed  the  2"»art 
which  is  detached  from  the  nerve-cell  from  which  it  is  an  offshoot  degenerates,  whilst  the  part 
which  remains  connected  witli  the  nerve-cell  undergoes  little  or  no  change.  This  is  called  the 
law  of  "  Wallerian  "  degeneration.  Thns,  if  in  a  living  animal  one-half  of  the  cord  be  cut  across, 
and  after  a  few  weeks  the  animal  be  killed  and  the  cord  examined,  it  will  be  seen  tliat  there 
are  degenerated  tracts  of  fibres  in  the  white  matter,  both  above  and  l)elow  the  plane  of  division ; 
but,  still  further,  it  will  also  be  manifest  that  the  tracts  which  are  degenerated  aboA'e  the  plane 
of  division  are  not  the  same  as  those  which  are  degenerated  in  the  j^art  of  the  cord  which  lies 
below  this  level.  The  interpretation  of  this  is  obvious.  The  nerve-tracts  which  have  degenerated 
above  the  plane  of  section  are  the  offshoots  of  nerve-cells  which  lie  in  lower  segments  of  the  cord 
or  in  spinal  ganglia  below  the  plane  of  section.  Severed  from  these  nerve-cells,  they  undergo 
what  is  called  ascending  degeneration.  The  nerve-tracts,  on  the  other  hand,  which  have 
degenerated  in  the  portion  of  the  cord  below  the  plane  of  division  are  the  axons  of  cells  which 
lie  at  a  higher  level  than  the  plane  of  section,  either  in  higher  segments  of  the  cord  or  in  the 
brain  itself.  Cut  off  from  the  nerve-cells  from  which  they  proceed,  they  present  an  example  of 
descending  degeneration. 

The  embryological  evidence  we  owe  to  Flechsig,  and  it  is  no  less  satisfactory.  It  depends 
ujjon  the  fact  that  nerve-fibres  in  the  earliest  stages  of  their  develoj^ment  consist  of  naked  axis- 
cylinders,  and  are  not  provided  with  medullary  sheaths.  Further,  the  nerve-fibres  of  different 
strands  assume  the  medullary  sheaths  at  different  periods.  By  examining  the  foetal  cord  at 
different  stages  of  its  develoj^ment,  it  is  a  comparatively  easy  matter  to  locate  the  different  tracts 
of  fibres  by  evidence  of  this  kind.  Speaking  broadly,  the  tracts  which  myelinate  first  are  those 
which  bring  the  cord  into  relation  with  the  peripheral  parts  (skin,  muscles,  etc.) ;  then  those 
fibres  which  bind  the  various  segments  of  the  cord  together ;  next,  those  which  connect  the  cord 
with  the  cerebellum ;  and,  lastly,  the  tracts  which  connect  the  cord  with  the  cerebrum.  The 
nervous  aj^paratus  for  the  jaerformance  of  automatic  movements  is  fully  provided,  therefore,  before 
this  is  jjut  under  the  control  and  direction  of  the  higher  centres.  It  by  no  means  follows  that  in 
all  the  higher  animals  corresponding  strands  myelinate  at  relatively  corresjjonding  periods.  Take 
the  case  of  a  young  animal  which  from  the  time  of  its  birth  is  able  to  move  about  and  perform 
voluntary  movements  of  various  kinds  in  a  more  or  less  perfect  manner,  and  compare  it  with  the 
heljaless  new-born  human  infant  which  is  only  capable  of  exhibiting  automatic  movements.  In 
the  former  the  i^yramidal  tracts,  or  motor  tracts,  which  descend  from  the  cerebrum  into  the  cord, 
and  which  are  the  paths  along  which  the  mandates  of  the  will  travel,  myelinate  at  an  early  jieriod  ; 
whilst  in  the  human  infant  the  corresponding  fibres  do  not  obtain  their  medullary  sheaths  until 
after  birth.  The  study  of  the  dates,  therefore,  at  which  the  various  strands  of  nerve-fibres 
myelinate  not  only  gives  the  anatomist  a  means  of  locating  their  position  in  the  white  matter  of 
the  cord,  but  it  also  affords  the  physiologist  most  imiDortant  information  regarding  their  functions, 
and  also  the  periods  at  which  these  functions  are  called  into  Y>la,j. 

It  is  a  raatter  of  interest  to  note  that  influences  which  either  accelerate  or  retard  the  periods 
at  which  nerve  fibres  are  brought  into  functional  activity  have  also  an  effect  in  determining  the 
dates  at  which  these  fibres  assume  their  sheaths  of  myelin.  Thus,  when  a  child  is  j^rematurely 
born  the  whole  process  of  myelinisation  is,  as  it  were,  hurried  up  ;  and  further,  when  in  new 
born  animals  light  is  freely  admitted  to  one  eye  whilst  it  is  carefully  excluded  from  the  other, 
the  fibres  of  the  optic  nerve  of  the  former  myelinate  more  rapidly  than  those  of  the  opposite  nerve. 

Posterior   Column   of  the   Cord   and  the   Posterior   Roots  of  the   Spinal 

Nerves. — In  the  cervical  and  upper  dorsal  regions  of  the  cord  the  posterior  column 
is  divided  by  the  posterior  paramedian  septum  into  the  tract  of  Burdach,  which 
lies  externally  and  next  the  posterior  horn  of  gray  matter,  and  the  tract  of  GoU, 
which  lies  internally  and  next  the  postero-median  septum.  The  tract  of  Burdach 
is  composed  of  nerve-fibres,  which  are  for  the  most  part  larger  than  those  entering 
into  the  formation  of  Goll's  tract,  and  both  tracts  have  a  most  intimate  relation 
to  the  posterior  nerve-roots ;  indeed,  they  are  both  almost  entirely  composed  of 
fibres  which  enter  the  cord  by  these  roots  and  then  pursue  a  longitudinal  course. 

The  nerve-fibres  which  form  the  posterior  nerve-roots,  on  entering  the  cord  along  the 
postero-lateral  groove,  divide  within  the  tract  of  Burdach  into  ascending  and  descending- 
branches.  These  branches  diverge  abruptly  from  each  other ;  and  the  former  take  an 
upward  course,  wliilst  the  latter  proceed  downwards.  The  descending  fibres  are  as  a  rule 
short,  and  soon  end  in  the  gray  matter  of  the  cord.  These  descending  fibres  occupy  an 
area  in  the  posterior  column  near  to  the  place  of  entrance  of  the  nerve-root.  This  area, 
when  the  spinal  cord  is  divided,  undergoes  descending  degeneration  and  then  presents  a 
comma-shaped  outline.  The  fibres  in  question  are  included  under  the  name  of  the  comma 
tract  of  Schultze. 

The  ascending  fibres  vary  greatly  in  length,  and  at  varying  disttmces  from  the  point 
where  the  parent  fibres  enter  the  cord  they  end  in  the  gray  matter.  A  small  contribution 
of  ascending  fibres,  however,  from  each  postei'ior  nerve-root,  extends  upwards  to  the  upper 
end  of  the  cord,  to  end  in  the  medulla  oblongata. 

As  each  posterior  nerve-root  enters,  its  fibres  range  themselves  in  the  outer  part  of 


COMPONENT  PARTS  OF  WHITE  MATTER  OF  SPINAL  CORD.     467 


the  tract  of  Burdach  close  up  against  the  posterior  horn  of  gray  matter.     The  nerve- 

The  oval  field  of  Flechsig  CoTiiina  tract  of  Scbultze 


Fig.  375. — Diagram  to  show  the  Arrangement  of  the  Fibres  of  the  Posterior  Nerve-Roots  in 
THE  Posterior  Columns  of  the  Cord.  The  oval  field  of  Flechsig  is  present  in  the  lumbar  region 
and  is  composed  of  fibres  which  degenerate  in  a  downward  direction,  and  which  are  not  derived  from 
the  posterior  nerve-roots.     In  all  probability  they  are  commissural  fibres  (from  Edinger,  modified). 

fibres  of  the  nerve-root  next  above  take  the  same  position,  and  consequently  those  which 
entered  from  the  nerve  immediately  below  are  displaced 
inwards,  and  come  to  lie  in  the  tract  of  Burdach  nearer 
to  the  mesial  plane.  This  process  goes  on  as  each 
nerve-root  enters,  and  the  result  is  that  the  fibres  of 
the  lower  nerves  are  gradually  pushed  nearer  and  nearer 
to  the  postero-median  septum  in  a  successive  series  of 
lamellar  tracts.  Of  course  the  greater  proportion  of 
the  fibres,  which  are  thus  carried  upwards  from  the 
posterior  nerve-roots,  sooner  or  later  leave  the  posterior 
column  and  enter  the  gray  matter,  to  end  there  in  relation 
to  some  of  its  cells ;  but,  as  we  have  said,  every  posterior 
nerve-root  sends  a  few  fibres  up  the  whole  length  of  that 
portion  of  the  cord  which  lies  above,  and  thus  the  posterior 
column  gradually  increases  in  bulk  as  it  is  traced  upwards, 
and  in  the  upper  reaches  of  the  cord  a  tract  of  Goll 
becomes  evident.  This  tract  of  Goll  is  composed  of  the 
long  ascending  fibres  of  the  posterior  nerve-roots,  which 
have  entered  the  lower  segments  of  the  cord.  To  put 
the  matter  diff'erently,  the  fibres  of  the  sacral  roots 
are  displaced  inwards  by  the  entering  lumbar  fibres, 
while  the  fibres  of  the  lumbar  roots  are  in  their  turn 
pushed  inwards  by  the  entering  dorsal  fibres,  and,  lastly, 
the  fibres  of  the  cervical  roots  displace  the  dorsal  fibres. 
The  difference  between  the  tract  of  Goll  and  the  tract  of 
Burdach  simply  consists  in  this,  that  the  former  is  com- 
posed of  the  fibres  of  posterior  nerve-roots  which  have 
entered  the  cord  at  a  lower  level  than  those  which  enter 
into  the  formation  of  the  column  of  Burdach.  The 
fibres  of  Goll's  tract,  taking  them  as  a  whole,  must  there- 
fore necessarily  run  a  very  much  longer  course. 

Our  knowledge  of  tiio  constitution  of  the  posterior 
columns  of  the  cord  is  largely  derived  from  studying 
the  course  of  degeneration  in  monkeys,  in  which  the  cord 
has  beeti  cut  across— either  partially  or  completely.  It 
would  appear,  from  the  examination  of  the  human  cord    '*'"'•    37t5.— DrAOHAiw    to    show   the 

which  has  boon  injured  or  compressed,  that  the  lamination  ^'^^^"''^  '^  ""!,'/'"  '''":;  """'"'"  "^^ 

-    ,      ,. ,  .     •       /.  1  •        r.        .     •  ,  thh  PoHTKitioii  Nkiive- Hoots  ENTER 

of  the  nitres  ontoruig  trom  the  soriosot  posterior  nerve-roots  ^^j^jj    ascend    in    the    Postkrior 

is  not  nearly  so  complete  as  in  the  case  of  the  monkey.  Column  of  the  Cord  (from  Edinger). 


468  THE  NEEYOUS  SYSTEM. 

Numerous  collateral  fibrils  stream  into  the  gray  matter  of  the  posterior  horn  both 
from  the  ascending  and  descending  branches  of  the  entering  fibres  of  the  posterior  nerve- 
roots.  These  are  classified  into  long  and  short  collaterals.  The  long  collaterals  extend 
forward  into  the  anterior  horn  of  gray  matter  and  end  in  relation  to  the  ventral  nerve- 
cells.  The  short  collaterals  end  in  relation  to  the  nerve-cells  in  the  substantia  Rolaudi, 
and  other  nerve-cells  of  the  posterior  horn  of  gray  matter. 

The  majority  of  the  fibres  of  the  posterior  nerve-root  enter  the  cord  on  the  inner  side 
of  the  apex  of  the  posterior  horn  of  gray  matter.  The  manner  in  which  these  are  related 
to  the  columns  of  Burdach  and  Goll  has  been  noticed  ;  but  a  certain  number  of  those  fibi-es 
Avhich  lie  most  externally  take  a  curved  course  forwards  on  the  inner  side  of  the  posterior 
horn  of  gray  matter  and  then  pass  into  it.  In  the  dorsal  region  these  curved  fibres  end  in 
connexion  with  the  cells  of  Clarke's  column  (Fig.  .369,  p.  458). 

Tract  of  Lissauer. — This  is  a  small  tract  of  nerve-fibres  of  minute  calibre  which 
assume  their  medullary  sheaths  at  a  comparatively  late  period.  It  is  placed  at  the 
surface  of  the  cord  close  to  the  postero-lateral  furrow.  It  is  formed  by  some  of  the 
outer  fibres  of  the  posterior  nerve-roots,  which  do  not  enter  the  tract  of  Burdach,  and 
which  pass  upwards  in  the  cord  close  to  the  substantia  gelatinosa  Rolandi,  in  which  they 
ultimately  end. 

It  must  now  be  evident  that  the  fibres  which  enter  the  cord  through  each  posterior  nerve-root 
have  three  main  modes  of  distribution  :  (1)  the  majority  take  part  in  the  formation  of  the  coliunns 
of  Burdach  and  Goll  ;  (2)  a  few  lie  close  to  the  posterior  horn  of  gray  matter  and  describe  a  series 
of  graceful  curves  as  they  pass  forwards  prior  to  turning  outwards  into  the  gray  matter,  to  end,  in 
the  dorsal  region,  in  Clarke's  vesicular  column  ;  (3)  a  third  series  form  Lissauer's  tract  and  end  in 
connexion  with  the  cells  of  the  substantia  gelatinosa  Rolandi  and  other  cells  in  the  posterior  and 
anterior  horns  of  gray  matter. 

The  fibres  derived  from  the  j)Osterior  nerve-roots  which  ascend  in  the  posterior  columns  of  the 
cord  to  the  medulla  oblongata  of  the  brain  constitute  a  direct  sensory  tract ;  other  fibres  are 
described  which  give  rise  to  a  crossed  sensory  tract  termed  the  spino-thalamic  tract.  These 
latter  fibres  arise  as  the  axons  of  certain  of  the  cells  in  the  posterior  horn  in  connexion  with 
which  fibres  from  the  posterior  nerve-roots  have  ended,  and  crossing  to  the  opposite  side  of 
the  cord  tliroiigh  the  anterior  coinmissure  they  ascend  in  the  anterolateral  column  to  the  brain, 
where  they  ultimately  reach  the  optic  thalamus.  As  the  spino-thalamic  tract  ascends  in  the 
cord  its  fibres  are  not  gathered  into  a  comj^act  strand,  but  are  more  or  less  loosely  scattered 
in  the  lateral  column. 

Association  Fibres  in  the  Posterior  Column. — But  the  whole  of  the  fibres  of  the 
posterior  column  are  not  derived  from  the  posterior  nerve-roots.  A  few  fibres  exist  in 
this  column  which  have  a  different  origin.  They  are  derived  from  certain  of  the  cells  of 
the  gray  matter  of  the  cord,  and  entering  the  posterior  column  divide^  into  ascending  and 
descending  branches  which  pass  upwards  and  doAvnwards  in  the  column  for  a  varying 
distance  before  they  finally  turn  in  to  end  in  the  gray  matter  at  a  higher  and  a  lower  level. 
These  fibres,  therefore,  constitute  links  of  connexion  between  different  cord  segments,  and 
thus  they  are  termed  association  or  longitudinal  commissural  fibres.  Our  information 
regarding  these  fibres  at  present  is  somewhat  defective  ;  but  it  is  believed  that  the  deepest 
part  of  the  column,  i.e.  the  part  next  the  posterior  gray  commissure  and  termed  the 
ventral  field,  and  also  the  descending  septo-marginal  tract  of  Bruce,  placed  in  apposition 
with  the  postero-median  septum  and  in  the  adjoining  part  of  the  surface,  belong  mainly  to 
this  category. 

Lateral  Column  of  the  Cord. — In  the  lateral  column  of  the  cord  the  well- 
established  tracts  are : — 

1.  The  direct  cerebellar  tract. 

2.  The  tract  of  Gowers. 

3.  The  crossed  pyramidal  tract. 

The  remainder  of  the  column  goes  under  the  name  of  the  lateral  basis-bundle. 

The  direct  cerebellar  tract  (fasciculus  cerebello-spinalis)  is  a  band-like  strand 
which  lies  in  relation  to  the  surface  of  the  cord  immediately  in  front  of  the  postero- 
lateral groove.  It  is  an  ascending  tract,  and  is  composed  for  the  most  part  of 
coarse,  large  nerve-fibres,  which  are  derived  from  the  nerve-cells  of  the  posterior 
vesicular  column  (Clarke's  column)  in  the  posterior  horn  of  gray  matter.  It  is, 
therefore,  not  found  throughout  the  whole  length  of  the  cord.  It  first  appears  in 
the  lower  part  of  the  dorsal  region ;  and  as  it  ascends  it  gradually  increases  in  size 
as  it  is  joined  by  the  axons  of  the  cells  of  Clarke's  column,  which  lie  at  higher 
levels.  It  finally  enters  the  medulla  oblongata,  and  through  this  proceeds  to  the 
cerebellum,  in  which  it  ends. 


COMPONENT  PAETS  OF  WHITE  MATTER  OF  SPINAL  CORD.     4G9 


Entering  posterior 

root 

/ 

Lis'^auprb  tiact 


It  must  not  be  forgotten  that  each  posterior  nerve-root  in  the  dorsal  region  of  the  cord  gives 
a  contribution  of  filjres  to  the  posterior  vesicular  column  of  cells  from  which  the  fibres  of  the  direct 
cerebellar  tract  arise  (see  p.  468).  In  this  way  a  connexion  is  established  between  the  posterior 
roots  of  the  dorsal  nerves  and  the  cortex  of  the  cerebellum.  It  is  believed  that  tlie  direct  cerebellar 
tract  is  an  important  factor  in  bringing  about  a  proper  co-ordination  of  muscular  movements. 

Gowers's  tract  (fasciculus  antero-lateralis  superficialis)  lies  in  front  of  the  direct 
cerebellar  tract,  and,  like  it,  next  the  surface  of  the  lateral  column.  It  is  also  an 
ascending  tract,  and  it  likewise  (in  part  at  least)  ultimately  reaches  the  cerebellum, 
although  after  leaving  the  cord  it  takes  a  different  route  to  gain  its  destination. 
In  transverse  sections  of  the  cord  it  presents  a  comma-shaped  appearance,  the 
thick  part  abutting 
against  the  direct  cere- 
bellar tract,  and  the 
narrower  portion  taper- 
ing forwards  into  the 
region  of  the  emerging 
anterior  nerve-roots. 
The  tract  of  Gowers 
begins  at  a  lower  level 
in  the  cord  than  the 
direct  cerebellar  tract 
and  it  increases  in  vol- 
ume as  it  is  traced  up- 
wards. The  fibres  of 
this  tract  have  probably 
their  origin  in  the  cells 
of  the  posterior  horn  of 
gray  matter,  but  on  this 
point  there  is  at  present 
no  precise  information. 

The  crossed  pyramidal 
tract  (fasciculus  cerebro- 
spinalis  lateralis)  is  a 
large  well-defined  de- 
scending tract,  which  lies  immediately  in  front  of  the  posterior  horn  of  gray 
matter  and  subjacent  to  the  direct  cerebellar  tract,  which  shuts  it  out  from 
the  surface  of  the  ccrd.  Below  the  point  where  the  direct  cerebellar  tract  begins 
the  crossed  pyramidal  tract  becomes  superficial,  and  in  this  position  it  can  be 
traced  as  low  as  the  fourth  sacral  nerve,  at  which  level  it  ceases  to  exist  as  a 
distinct  strand.  The  crossed  pyramidal  tract  is  composed  of  an  admixture  of  both 
large  and  small  fibres.  These  arise  in  the  brain  from  the  large  pyramidal  cells 
of  the  motor  or  Eolandic  area  of  the  cerebral  cortex,  and  pass  downwards  through 
various  subdivisions  of  the  brain  to  gain  the  spinal  cord.  As  they  enter  the  cord 
they  cross  the  mesial  plane  from  one  side  to  the  other,  and  it  thus  happens  that 
the  crossed  pyramidal  tract  in  the  right  lateral  column  of  the  cord  has  its  origin 
in  the  cortex  of  the  left  cerebral  hemisphere,  and  vice  versa.  As  the  tract  descends 
in  the  cord  it  gradually  diminishes  in  size ;  and  this  is  due  to  the  fact  that,  as  it 
traverses  each  spinal  segment,  numerous  fibres  leave  it  to  enter  the  anterior  horn 
of  gray  matter,  and  end  in  connexion  with  the  ventral  motor  cells  from  which  the 
fibres  of  the  anterior  nerve-roots  arise.  The  entire  strand  is  ultimately  exhausted 
in  this  way.  Numerous  collateral  fibrils  spring  from  the  pyramidal  fibres,  and, 
entering  the  gray  matter,  end  in  a  similar  manner,  and  in  this  way  a  single  pyra- 
midal fibre  may  be  connected  with  several  spinal  segments  before  it  finally  ends. 
The  crossed  pyramidal  tract  must  be  regarded  as  a  great  motor  strand  which 
brings  the  spinal  motor  apparatus  under  the  control  of  the  will. 

Schafcr  believes  that  iiuiuy  of  tho  pyrainidal  fibres  end  in  connexion  witli  the  cells 
of  Clarke's  column. 

In  the  rat,  mouse,  f^uinea-pig,  squirrel,  sheep,  kangaroo,  etc.,  the  pyramidal  truet  lies 
in  the  posterior  ecjlumn  of  the  cord. 


Fig.  377. 


Emerging  anterior  root 
Diagrammatic  Representation  of  a  Transverse  Section 

THROUGH    THE    SpINAL    CORD. 

The  nerve  tracts  in  the  white  matter  and  the  clusters  of  nerve-cells 
in  the  gray  matter  are  shown. 


470  THE  NEEVOUS  SYSTEM. 

The  lateral  basis-bundle  (fasciculus  lateralis  proprius)  represents  the  remainder 
of  the  lateral  column.  Our  information  regarding  it  is  still  imperfect ;  but  it 
would  appear  that  its  fibres  are  largely  derived  from  the  cells  situated  in  all  parts 
of  the  gray  matter,  and  also  from  the  nerve-cells  of  the  opposite  side  of  the  cord. 
After  a  course  of  very  varying  length  in  the  basis-lnindle,  these  fibres  turn  inwards 
and  re-enter  the  gray  matter.  Such  fibres  may  thus  be  regarded  as  inter- segmental 
association  fibres  binding  two  or  more  segments  of  the  cord  together.  It  may  be 
mentioned  that  the  association  fibres  which  link  together  segments  of  the  cord 
which  are  near  to  each  other  lie  close  to  the  gray  matter,  whilst  tliose  which 
connect  the  more  distant  segments  are  situated  further  out  in  the  lateral 
basis-bundle. 

Anterior  Column  of  the  Cord. — One  well-defined  tract  is  situated  in  the 
anterior  column.  This  is  termed  the  direct  pyramidal  tract.  The  remainder  of 
the  column  receives  the  name  of  the  anterior  basis-bundle. 

The  direct  pyramidal  tract  (fasciculus  cerebro-spinalis  anterior)  is  usually  a 
nerve-strand  of  small  size  which  lies  next  the  antero-median  fissure.  As  a  rule, 
it  cannot  be  traced  lower  than  the  middle  of  the  dorsal  region  of  the  cord.  It  is 
a  descending  tract  and  must  be  associated  with  the  crossed  pyramidal  tract  of  the 
opposite  side,  seeing  that  both  of  these  strands  arise  from  the  motor  area  of  the 
cortex  of  the  same  cerebral  hemisphere.  Erom  this,  it  must  be  clear  that  the 
direct  pyramidal  tract  does  not  cross  the  mesial  plane  as  it  enters  the  cord,  but 
descends  on  the  side  of  the  cord  corresponding  to  the  cerebral  hemisphere  in 
which  it  arises.  All  the  same  its  fibres  do  not  end  in  the  same  side  of  the 
cord,  but  at  every  step  along  the  path  of  the  strand  they  make  use  of  the  anterior 
commissure  and  cross  to  the  opposite  side  of  the  cord,  to  terminate  in  relation 
to  the  opposite  ventral  motor  cells  in  the  same  manner  as  the  crossed  pyramidal 
fibres. 

From  tills  crossing  of  the  pyramidal  tracts,  it  results  tbat  tbe  destruction  of  tlie  fibres  whieb 
compose  tliem  as  they  descend  in  one  side  of  the  brain  must  result  in  paralysis  of  the  muscles 
supplied  by  the  eff'erent  nerves  of  the  opposite  side  of  the  cord. 

In  cases  of  old  brain  lesion  it  is  sometimes  possible  to  detect  some  degenerated  fibres  in  tlie 
crossed  pyramidal  tract  of  the  sound  side  of  tlie  spinal  cord,  and  from  this  it  is  supposed  that  this 
tract  contains  a  few  uncrossed  fibres.  If  this  be  the  case,  each  side  of  the  cord  stands  in 
connexion  with  the  motor  area  of  both  cerebral  hemispheres. 

It  is  well  to  note  that  the  fibres  of  both  pyramidal  tracts  are  not  meduUated  until  the  time  of 
birth.     They  are  the  latest  of  all  the  cord-tracts  to  myelinate. 

The  anterior  basis-bundle  (fasciculus  anterior  proprius),  like  the  lateral  basis- 
bundle,  is  composed  largely  of  fibres  which  arise  from  the  cells  of  the  gray  matter 
of  the  cord,  and  act  the  part  of  intersegmental  association  fibres. 

Summary  of  the  Constitution  of  the  White  Matter  of  the  Cord. — The 
white  columns  of  the  cord  are  formed  of  two  kinds  of  nerve-fibres  : — 

1.  Those  which  enter  the  cord  from  without. 

2.  Those  which  take  their  origin  from  the  cells  within  the  gray  matter  of  the 
cord  itself. 

Under  the  first  category  we  include  (a)  the  greater  part  of  the  fibres  of  the 
posterior  column  (columns  of  Burdach  and  GoU),  which  arise  from  the  cells  of  the 
spinal  ganglia,  and  which  enter  the  cord  as  the  posterior  nerve-roots ;  and  (&)  the 
crossed  and  direct  pyramidal  tracts  which  come  from  the  motor  cells  of  the  cerebral 
cortex. 

The  fibres  which  arise  within  the  gray  matter  of  the  cord  may  be  classified 
thus :  (a)  Fibres  which  pass  out  from  the  cord  as  efferent  nerves  (anterior  nerve- 
roots)  ;  (h)  fibres  which  form  long  tracts  and  pass  up  the  cord  to  enter  the  brain 
(direct  cerebellar  tract  and  the  tract  of  Gowers) ;  (c)  fibres  which  form  short  tracts, 
linking  together  different  segments  of  the  cord  (intersegmental  association  fibres  in 
each  of  the  three  columns  of  the  cord). 

Anterior  White  Commissure. — The  anterior  commissure  is  composed  of 
meduUated  nerve-fibres  passing  from  one  side  of  the  cord  to  the  other  and  entering 
the  anterior  horn  of  gray  matter,  and  also  the  anterior  column  of  white  matter.  It 
is  to  be  regarded  more  as  a  decussation  than  as  a  commissure,  and  its  width,  which 


DEVELOPMENT  OF  THE  SPINAL  COED. 


471 


varies  somewhat  in  diflerent  regions,  fluctuates  in  correspondence  with  the  diameter 
of  the  cord. 

Amongst  the  fibres  which  cross  in  the  anterior  commissure  may  be  mentioned  :  (1)  The  fibres 
of  the  direct  pyramidal  tract ;  (2)  collaterals  from  both  the  ventral  and  lateral  columns  ;  (3)  axons 
of  many  of  the  cells  of  the  gray  matter  ;  (4)  the  dendritic  processes  of  some  of  the  mesial  ventral 
cells. 

Posterior  Gray  Commissure. — Although  this  is  composed  of  gray  matter  with 
a  large  admixture  of  neuroglia,  numerous  transverse  nerve-fibres  pass  through  it,  so 
as  to  bind  the  cells  of  one  side  of  the  cord  to  those  of  the  other. 


MYELO- 

SPONGIUM 


Development  of  the  Spinal  Cord. 

In  the  chapter  upon  General  Embryology  it  has  been  pointed  out  (p.  21)  that  the 
brain  and  cord  first  take  shape  in  the  form  of  a  tube  of  ectoderm,  which  receives  the  name 
of  the  neural  tube.  Three  expansions,  placed  one  behind  the  other  at  the  cephalic  end  of 
the  tube,  represent  the  early  brain ;  whilst  behind  these  primitive  cerebral  vesicles  comes 
the  elongated  narrower  part  of  the  tube,  which  at  this  stage  represents  the  spinal  cord. 
By  a  developmental  process,  which  we  now  have  to  study,  the  walls  of  this  portion  of  the 
neural  canal  give  rise  to  the  various  elements  which  build  up  the  substance  of  the  cord, 
whilst  a  portion,  if  not  the  whole,  of  the  primitive  cavity  is  preserved  as  the  central  canal 
of  the  cord.  The  account  which  is  here  given  of  the  development  of  the  cord  is  taken 
almost  entirely  from  the  writings  of  Professor  His. 

When  first  formed,  the  neural  tube  is  compressed  from  side  to  side  and  presents  an  oval 
outline  in  transverse  section  (Fig.  16,  p.  21).  The  two  lateral  walls  are  very  thick,  whilst 
the  narrow  dorsal  and  ventral  portions  of  the  wall  are  thin,  and  are  termed  the  mid-dorsal 
and  mid-ventral  laminae  (Fig.  378).  The  cavity  of  the  tube  in  transverse  section  appears  as 
a  narrow  slit.  At  this  stage  the  wall  of  the  neural  tube  is  formed  of  a  series  of  elongated 
neuro-epithelial  columnar  cells,  closely  applied  to  each  other  and  extending  throughout  the 
whole  thickness  of    the  wall.      The  mid-dorsal  lamina 

inner  ends  of  these  long  columnar 
cells  unite  to  form  a  delicate  mem- 
brane tei'med  the  internal  limiting 
membrane,  which  lines  the  lumen  of 
the  tube,  whilst  their  outer  ends 
present  a  similar  relation  to  an  ex- 
ternal limiting  membrane,  which 
invests  the  outer  surface  of  the  tube. 
The  name  of  spongioblasts  is  given 
to  these  cells,  and  they  soon  develop 
in  such  a  manner  as  to  form  the 
sustentacular  framework  of  the 
growing  cord.  Between  their  inner 
parts,  immediately  subjacent  to  the 
internal  limiting  membrane,  a  series 
of  clefts  or  open  spaces  are  formed, 
in  which  appear  large  numbers  of 
round  cells  called  germinal  cells. 
The  precise  origin  of  these  germinal 
cells  is  not  at  present  satisfactorily 
established ;  but  they  rapidly  in- 
crease in  number,  and  in  the  human 
embryo  of  four  weeks  they  are  seen 
to  form  an  almost  continuous  layer 
beneath  the  internal  limiting  mem- 
brane, ft  is  well  to  note,  however, 
that  in  the  thin  mid-dorsal  and  mid- 
ventral  laminu;  no  germinal  colls  are 
formed.  Here  the  wall  remains 
purely  spongioblastic.  The  peri- 
pheral portions  of  the  spongioblasts  likewise  undergo  a  marked  transformation.  They 
give  off  branches  or  processes,  and  by  the  interlacement  of  these  a  sponge-like  network 
with  irregular  meshes  is  formed  in  the  outer  portion  of  tiic  wall  of  tlie  neural  tube.     'J'hc 


MID  VENTRAL  LAMINA 

Fkj.  378. — Schema  ov  a  TitANSVKnsE  Skction  THitoudu  thk 
Eaiily  Neural  TuBji  (Young). 

Tlu!  left  side  of  the  .section  shows  an  earlier  stage  tlian 
the  right  side. 


472 


THE  NERVOUS  SYSTEM. 


entire  sustentacular  framework  into  which  the  spongioblasts  are  developed  is  termed 
the  myelosponge. 

The  numerous  germinal  cells  which  are  placed  in  the  clefts  between  the  inner 
columnar  portion  of  the  myelosponge  are  the  progenitors  of  the  nerve-cells.  Alany  of 
them  show  karyokinetic  stages,  and  by  their  division  they  give  rise  to  the  neuroblasts  or 
young  nerve-cells.  A  neui'oblast  presents  a  very  characteristic  pear-shaped  appearance. 
From  the  body  of  the  cell  a  tapering  process  grows  out,  and  this  represents  the  early  axis- 
cylinder  process  or  axon  of  the  cell.  But  the  crowds  of  neuroblasts  which  are  thus  formed 
do  not  remain  in  their  early  primitive  position  beneath  the  internal  limiting  membrane. 
They  migrate  outwards,  and  in  the  course  of  time  they  come  to  lie  in  the  part  of  the 
myelosponge  immediately  adjoining  the  reticular  meshwork,  which  is  formed  by  the  outer 
parts  of  the  spongioblasts.  Here  their  further  outward  migration  is  arrested.  The 
reticular  meshwork  would  almost  appear  to  act  as  a  sieve  or  a  filter,  which  prevents  their 
progress  towards  the  periphery  of  the  wall  of  the  tube.  It  offers  no  impediment  to  the 
actively  growing  axons  of  the  neuroblasts,  however,  which  freely  enter  it  and  thread  their 
way  through  it.  At  this  stage  the  thick  lateral  wall  of  the  neural  tube  presents  thi'ee 
layers,  viz.  : — 

1.  An  inner  layer,  formed  by  the  columnar  part  of  the  myelosponge  forsaken  by  the 
neuroblasts.  This  is  termed  the  ependymal  layer,  and  it  ultimately  resolves  itself  into 
the  layer  of  columnar  ciliated  epithelial  cells  which  lines  the  central  canal  of  the  cord. 

2.  An  intermediate  layer,  in  which  the  neuroblasts  are  pi'esent,  and  which  is  afterwards 
converted  into  the  gray  matter  of  the  cord.     This  is  called  the  mantle  layer. 

3.  An  outer  layer,  formed  of  the  sponge-like  meshwork  of  the  outer  parts  of  the 
original  spongioblasts.  Into  this  the  axons  of  many  of  the  neuroblasts  are  seen  threading 
their  way.  This  layer  is  ultimately  transformed  into  the  white  matter  of  the  cord,  and 
at  this  stage  it  may  be  termed  the  peripheral  reticular  layer. 

Alar  and  Basal  Laminae  of  the  Lateral  Wall  of  the  Neural  Tube.— From 

what  has  been  said,  it  must  be  evident  that  the  changes  detailed  above  are  confined  to 
the  thick  lateral  walls  of  the  neural  tube.  In  these  alone  do  neuroblastic  cells  arise, 
whilst  the  thin  mid-dorsal  and  mid-ventral  laminae  remain  spongioblastic  throughout. 
But  whilst  these  changes  are  going  on,  the  thick  lateral  wall  begins  to  bulge  outwards  in 
an  angular  fashion,  so  as  to  widen  the  central  cavity  of  the  tube  and  become  itself,  along 
the  line  where  the  cavity  is  widest,  demarcated  into  two  portions — a  narrow  dorsal  strip 
termed  the  alar  lamina,  and  a  broader  ventral  strip  called  the  basal  lamina.     The  cavity 


MDL 


AH 


Fig.  379. 


AiMF  AC  AMF  AC 

-Three  Stages  in  the  Development  op  the  Spinal  Cohd  (His). 


AC. 
AH. 


Anterior  column.  BC. 

Anterior  lioni   of  gray  BL. 

matter.  E. 

AL.       Alar  lamina.  GO. 

AMF.  Antero-median  fissure.  LC. 

AR.       Anterior  nerve-root.  MDL. 


Column  of  Burdach. 
Basal  lamina. 
Ependyma. 
Column  of  Goll. 
Lateral  column. 
Mid-dorsal  lamina. 


MVL.   Mid- ventral  lamina. 
PC.       Early  posterior  column. 
PH.       Posterior  horn   of  gray 

matter. 
PMF.    Postero-niedian  fissure. 
PR.       Posterior  nerve-root. 


of  the  tube  now  appears  on  transverse  section  more  or  less  lozenge-shaped,  and  it  is  at  the 
lateral  angles  of  the  lozenge  that  this  subdivision  of  the  lateral  wall  becomes  evident. 

This  subdivision  is  a  fundamental  one,  being  present  in  the  brain-part  as  well  as  the 


DEVELOPMENT  OF  THE  SPINAL  COIiD.  473 

cord-part  of  the  neural  tube.  By  it  the  thick  lateral  wall  is  resolved  into  two  longitudinal 
strips  (the  alar  and  basal  laminee),  which  extend  along  the  whole  length  of  the  tube,  and 
which  present  definite  and  precise  relations  with  the  entering  and  emerging  roots  of  the 
various  cranial  and  spinal  nerves.  Confining  our  attention  to  the  spinal  cord,  the  posterior 
nerve-root  is  seen  to  enter  the  alar  lamina,  whilst  the  anterior  nerve-root  takes  origin 
within  and  emerges  from  the  basal  lamina. 

Further  Development  of  the  Gray  and  White  Matter  of  the  Cord. — In  the 
ventral  part  of  the  basal  lamina  the  mantle  layer  thickens  into  a  mass,  which  is  readily 
recognised  as  the  rudiment  of  the  anterior  horn  of  gray  matter,  and  in  this  neuroV)lastic 
cells  congregate  in  much  larger  numbers  than  elsewhere.  Further,  these  neuroblastic 
cells  begin  to  ai'range  themselves  into  groups,  and  the  axis-cylinder  processes  of  a  large 
proportion  of  them  converge  and  form  bundles  of  fibres,  which  penetrate  into  the  peri- 
pheral layer,  and  finally  pierce  the  external  limiting  membrane,  to  emerge  as  the  fascicles 
of  the  anterior  nerve-roots.  Behind  the  anterior  horn  the  mantle  layer  still  remains  very 
thin,  and  the  neuroblasts  are  few  in  number.  There  is,  therefore,  at  this  stage  no  appear- 
ance of  the  posterior  horn  of  gray  matter.  Many  of  the  axons  of  the  neuroblasts  which 
occupy  this  region  are  seen  curving  forwards,  and,  after  traversing  the  anterior  horn,  they 
find  their  way  across  the  middle  line  in  the  mid-ventral  lamina.  In  this  manner  is  laid 
down,  at  a  very  early  stage,  the  rudiment  of  the  anterior  white  commissure  of  the  cord. 

The  white  matter  of  the  anterior  and  lateral  columns  is  gradually  established  by  axons 
from  various  neuroblasts  in  diff'erent  parts  of  the  mantle  layer,  entering  the  peripheral 
reticular  layer  and  taking  a  longitudinal  course  within  it.  The  anterior  horn  is  well 
coated  with  white  matter,  however,  before  the  lateral  column  takes  definite  shape. 

The  posterior  columns  of  white  matter  are  formed  in  a  totally  different  manner,  viz. 
by  the  introduction  into  the  cord  of  nerve-fibres  from  without.  The  fibres  of  the  posterior 
nerve-roots  coming  from  the  spinal  ganglia  strike  the  outer  surface  of  the  alar  lamina  of 
the  lateral  wall  of  the  neural  tube,  and,  piercing  the  external  limiting  membrane,  take  a 
longitudinal  course  in  the  peripheral  reticular  layer.  On  cross  section  these  fibres  first 
appear  as  an  oval  bundle,  which  lies  in  the  outer  part  of  the  alar  lamina  (Fig.  379  Pc). 
This  bundle  is  the  rudiment  of  Burdach's  column,  and  at  first  it  has  a  somewhat  loose 
connexion  with  the  cord ;  but  as  the  posterior  horn  of  gray  matter  gradually  takes 
shape,  the  bundle  in  question  increases  in  volume,  and,  changing  its  position,  comes  to  lie 
on  the  inner  aspect  of  the  posterior  horn.  The  column  of  Goll  gradually  assumes  form 
between  the  tract  of  Burdach  and  the  postero-median  septum.  Later  on  the  lateral  and 
anterior  columns  are  increased  in  bulk  by  the  descent  into  them  of  the  pyramidal  tracts 
from  the  brain. 

The  gray  matter,  in  the  fii'st  instance,  is  chiefly  massed  in  the  basal  lamina ;  but  as 
the  posterior  columns  of  white  matter  begin  to  take  shape  it  extends  backward,  and  in 
the  course  of  time  the  posterior  horns  are  developed. 

The  manner  in  which  the  dendritic  processes  of  the  neuroblasts  are  developed  has 
been  sufficiently  described  (p.  447).  The  ensheathment,  also,  of  the  axons  by  medulla 
has  been  referred  to,  and  the  fact  that  the  different  tracts  of  fibres  receive  their  mediillary 
sheaths  at  different  periods  mentioned.  It  is  now  only  necessary  to  state  that  the  order 
of  myelinisation  of  the  several  tracts  is  as  follows  : — (1)  Fibres  of  the  anterior  nerve-roots  ; 
(2)  tract  of  Burdach ;  (3)  fibres  in  the  basis-bundles ;  (4)  tract  of  Goll ;  (5)  direct  cere- 
bellar tract ;  (6)  tract  of  Gowers ;  (7)  pyramidal  tracts  (Kahler). 

Development  of  the  Median  Fissures  and  of  the  Central  Canal. — As  the 
anterior  horns  of  gi'ay  matter  covered  by  the  anterior  columns  of  white  matter  increase  in 
size,  the  anterior  surface  of  the  cord  on  either  side  of  the  mesial  plane  bulges  forwards, 
and  the  antero-mcdian  fissure  is  produced  as  the  natural  result. 

The  inanner  in  which  the  postero-median  fissure  comes  into  existence  is  not  fully 
understood,  but  the  majority  of  embryologists  believe  that  it  is  produced  by  the  approxi- 
mation and  fusion  of  the  walls  of  the  posterior  part  of  the  primitive  cavity  of  the  neural 
tube.     The  postero-median  septum  would  thus  appear  to  be  formed  of  spongioblastic  tissue. 

If  the  above  view  of  the  formation  of  the  postero-median  fissure  be  correct,  it  must 
be  evident  that  the  central  canal  of  the  cord  does  not  represent  the  whole  of  the  primitive 
cavity  of  the  early  neural  tube,  but  only  the  anterior  portion  of  it. 

Among  those  oh8f;rver.s  who  do  not  Ixjld  tli;it  the  ceiiti'al  canal  and  ptwtc.rioT  fissure  liave  this 
nicle  of  origin  the  most  jjroniiiicnt  in  Pj^jfcKHor  A.  W.  llolniisoii,  of  liiriuiiigliam  ;  and  he  has 
brought  forward  evidence  wliich  Keeni.s  to  indicate  tliat  it  is  doubtful  if  tlic  fusion  of  the  walls 
i)\  the  ])OHt,erior  part  of  the  canal,  I'eferi'wl  to  aliove,  tak(;H  place.  Gurtaiidy  the  arivuigeiMcnt  of 
the  epf^ndynial  eleinents  of  the  jjostero-niedian  septuin,  as  seen  in  the  })reparations  of  (Jajal 
and  v.  Leuho.Hsek,  are  extremely  difficult  to  understand  on  the  fusion   theory.     'JMiey  run  in  llie 


474 


THE  NEEVOUS  SYSTEM. 


antero-posterior  direction,  whereas,  if  fusion,  has  taken  place,  most  of  them  would  present  a 
transverse  arrangement,  and  thus  lie  at  right  angles  to  the  postero-median  septum. 


THE  BRAIN  OR  ENCEPHALON. 

The  brain  is  the  enlarged  and  greatly  modified  upper  part  of  the  cerebrospinal 
nervous  axis.  It  is  surrounded  by  the  same  menibranes  that  envelop  the  spinal 
cord  (viz.  the  dura  mater,  the  arachnoid  mater,  and  the  pia  mater),  and  it  almost 
completely  fills  up  the  cavity  of  the  cranium.  So  closely,  indeed,  is  the  skull 
capsule  moulded  upon  the  brain  that  the  impress  of  the  latter  is  almost  everywhere 
evident  upon  the  deep  surface  of  the  cranial  wall.  The  relations,  therefore,  of 
cranium  to  brain  are  totally  different  from  those  presented  by  the  vertebral  canal 


Optic  tract 


Iiifiindibulum 


Corpora  mainmillana 


Locus  perforatus  posticu 


Crus  cerebri 


Olfactory  bulb 


,  Olfactory  tract 


Optic  nerve 


Sixth  ner\ e 


Hypoglossal  nerve 


Locus  jjerforatus 
anticus 

Optic  tract 


Tuber  cinereum 
riiird  nerve 

Fourth  nerve 
Fifth  nerve 

Facial  nerve 
Auditory  nerve 
Pars  intermedia 
Glosso-pharyngeal  nerve 


Pyramid 
Spinal  cord  (cut) 


accessory  nerve 
Hypoglossal  nerve 


Fig.  380. — The  Base  op  the  Brain  with  the  Cranial  Nerves  attached. 

to  the  spinal  cord.  As  we  have  noted,  the  cord  occupies  only  a  part  of  its  bony 
case ;  and  there  is  not  only  a  wide  and  roomy  space  between  the  arachnoid  mater 
and  pia  mater,  but  also  an  interval  of  some  width  between  the  dura  mater  and  the 
walls  of  the  vertebral  canal. 

General  Appearance  of  the  Brain. — When  viewed  from  above  the  brain 
presents  an  ovoid  figure,  the  broad  end  of  which  is  directed  backwards.  Its 
greatest  transverse  diameter  is  usually  found  in  the  neighbourhood  of  that  part 
which  Ues  between  the  two  parietal  eminences  of  the  cranium.  The  only  parts 
which  are  visible  when  the  brain  is  inspected  from  this  point  of  view  are  the  two 
convoluted  cerebral  hemisplieres.  These  present  an  extensive  convex  surface,  which 
is  closely  applied  to  the  deep  aspect  of  the  cranial  vault,  and  are  separated  from 
each  other  by  a  deep  median  cleft,  termed  the  great  longitudinal  fissure,  which 
extends  from  the  front  to  the  back  of  the  brain. 


THE  BEAIN  OR  ENCEPHALON.  475 

The  inferior  aspect  of  the  brain  is  usually  termed  the  "  base."  It  presents  an 
uneven  and  irregular  surface,  which  is  more  or  less  accurately  adapted  to  the 
inequalities  on  the  floor  of  the  cranium.  Upon  this  aspect  of  the  brain  some  of 
its  main  subdivisions  may  be  recognised.  Thus  behind  is  seen  the  short  cylindrical 
portion,  called  the  bulb  or  medulla  oblongata,  through  which,  at  the  foramen  magnum, 
the  brain  becomes  continuous  with  the  spinal  cord.  The  bulb  lies  on  the  ventral 
aspect  of  the  cerebellum,  and  occupies  the  vallecula  or  hollow  which  intervenes 
between  the  two  cerebellar  hemispheres.  The  cerebellum  is  a  mass  of  considerable 
size  which  is  placed  below  the  hinder  portions  of  the  two  cerebral  hemispheres.  It 
is  easily  recognised  on  account  of  the  closely-set,  curved,  and  parallel  fissures  which 
traverse  its  surface  and  give  it  a  foliated  appearance.  Above  the  medulla,  and  in 
close  connexion  with  it,  is  a  prominent  white  elevation  called  the  pons  Varolii.  Im- 
mediately in  front  of  the  pons  there  is  a  deep  hollow  or  recess.  This  is  bounded 
behind  by  the  pons  Varolii,  on  either  side  by  the  projecting  temporal  lobe  of  the 
cerebral  hemisphere,  and  in  front  by  the  orbital  portions  of  the  frontal  lobes  of  the 
cerebral  hemispheres.  Passing  out  from  either  side  of  the  fore-part  of  this  recess  is 
the  deep  Sylvian  fissure  which  intervenes  between  the  pointed  and  projecting 
extremity  of  the  temporal  lobe  and  the  frontal  lobe  of  the  cerebrum,  whilst  in  the 
middle  line  in  front  the  great  longitudinal  fissure,  which  separates  the  frontal 
portions  of  the  cerebral  hemispheres,  opens  into  it. 

Within  the  limits  of  this  deep  hollow,  in  the  base  of  the  brain,  two  large  rope- 
like strands,  the  crura  cerebri,  may  be  seen  issuing  from  the  upper  aspect  of  the 
pons  Varohi.  Placed  close  together  as  they  emerge  from  the  pons,  these  crura 
diverge  as  they  proceed  upwards  and  forwards,  and  finally  each  disappears  by 
plunging  into  the  corresponding  side  of  the  cerebrum.  Turning  round  the  outer 
side  of  each  crus,  where  it  enters  the  cerebrum,  a  flattened  band  termed  the  optic 
tract  may  be  observed.  These  bands  converge  in  the  fore-part  of  the  hollow,  and 
are  finally  joined  together  by  a  short  commissural  portion,  termed  the  optic  chiasma. 
The  optic  nerve  is  continued  forwards  and  outwards,  on  either  side,  from  the  chiasma 
and  tract. 

The  crura  cerebri,  the  optic  tracts,  and  the  optic  chiasma  enclose  a  deep 
rhomboidal  or  lozenge-shaped  interval  on  the  base  of  the  brain,  which  is  termed 
the  interpeduncular  space.  Within  the  limits  of  this  area  the  following  parts  may 
be  seen  as  we  pass  from  behind  forwards :  (1)  the  locus  perforatus  posticus  ;  (2)  the 
corpora  mammillaria :  (3)  the  tuber  cinereum  and  the  stalk  of  the  pituitary  body. 

At  its  posterior  angle,  immediately  in  front  of  the  pons  Varolii,  the  inter- 
peduncular space  is  very  deep  and  is  floored  by  a  layer  of  gray  matter,  which  is 
perforated  by  numerous  small  apertures.  This  is  the  locus  perforatus  posticus. 
Through  the  apertures  which  are  dotted  over  its  surface  the  small  postero-mesial 
basal  branches  of  the  posterior  cerebral  artery  enter  the  brain. 

The  corpora  mammillaria  are  two  small  white  pea-like  eminences  placed  side  by 
side  in  front  of  the  locus  perforatus  posticus. 

The  tuber  cinereum  is  a  slightly  raised  field  of  gray  matter,  which  occupies  the 
interval  between  the  anterior  portions  of  the  optic  tracts  in  front  of  the  corpora 
mammillaria.  Springing  from  the  fore-part  of  the  tuber  cinereum,  immediately 
behind  the  optic  chiasma,  is  the  infundibulum,  or  the  stalk  which  connects  the 
pituitary  body  with  the  base  of  the  brain. 

Outside  the  limits  of  the  fore-part  of  the  interpeduncular  space  there  is  on 
either  side  a  small  depressed  triangular  field  of  gray  matter,  which  leads  outwards 
into  the  Sylvian  fissure.  It  is  perforated  by  tbe  antero-mesial  and  the  antero- 
lateral groups  of  basal  arteries,  and  receives  the  name  of  the  locus  perforatus 
anticus. 

General  Connexions  of  the  Several  Parts  of  the  Brain. — The  medulla 
oblongata,  the  pons  Varolii,  and  the  cerebellum  occupy  the  posterior  cranial  fossa, 
and  tliey  are  separated  from  the  cerebral  hemis])heres  which  lie  above  them  by  a 
partition  of  dura  mater,  termed  the  tentorium  cerebelli.  Further,  tliey  surround 
a  cavity,  a  ])ortion  of  the  primitive  cavity  of  the  early  neural  tube,  which  is  termed 
the  fourth  ventricle  of  the  brain,  and  they  all  stand  in  intimate  connexion  with 
each  other.     The  medulla  is  Ibr  the  most  part  carried   upwards  into  the  pons 


476 


THE  NERVOUS  SYSTEM. 


Varolii ;  but  at  the  same  time  two  large  strands  from  its  dorsal  aspect,  termed  the 
restifurm  bodies,   are   prolonged  into   the  cerebellum,  and  constitute  its  inferior 

peduncles,  or  the  chief  bonds  of  union 
between  the  medulla  and  the  cere- 
bellum. The  pons  Varolii  has  large 
numbers  of  transverse  fibres  enter- 
ing into  its  composition,  and  the 
great  majority  of  these  are  gathered 
together  on  either  side  in  the  form 
of  a  large  rope-like  strand.  This 
plunges  into  the  corresponding  hemi- 
sphere of  the  cerel^ellum,  and  con- 
stitutes its  middle  peduncle. 

The  cerebrum,  which  forms  the 
great  mass  of  the  brain,  occupies  the 
anterior  and  middle  cranial  fossse, 
and  extends  backwards  into  the  oc- 
cipital region  above  the  tentorium 
and  the  cerebellum.  The  greater  part 
of  the  cerebrum  is  formed  by  the 
cerebral  hemispheres,  which  are 
separated  from  each  other  in  the 
mesial  plane  by  the  great  longi- 
tudinal fissure.  At  the  bottom  of  this  fissure  is  the  corpus  callosum,  a  broad 
commissural  band  which  connects  the  two  hemispheres  with  each  other.  Each 
hemisphere  is  hollow,  the  cavity  in  its  interior  being  termed  the  lateral  ventricle 
of  the  brain.  Between  and  below  the  cerebral  hemispheres,  and  almost  com- 
pletely concealed  by  them,  is  the  inter-brain  or  diencephalon.  The  principal  parts 
forming  this  portion  of  the  brain  are  two  large  masses  of  gray  matter,  termed 
the  optic  thalami.  Between  these  is  the  third  ventricle  of  the  brain — a  deep  narrow 
cavity  occupying  the  mesial  plane.  The  third  ventricle  communicates  with  the 
lateral  ventricles  by  two  small  apertures,  called  the  foramina  of  Monro. 

The  cerebrum  is  connected  with  the  parts  in  the  posterior  cranial  fossa  (pons 
Varolii,  cerebellum,  and  bulb)  by  a  narrow  stalk  called  the  mid -brain,  or 
mesencephalon.  The  mid-brain  is  built  up  of  the  crura  cerebri,  passing  from  the 
pons  A'^arolii  to  the  cerebrum ;  the  corpora  quadrigemina,  forming  its  dorsal  part ;  and 
the  superior  cerebellar  peduncles,  proceeding  from  the  cerebellum  to  the  cerebrum. 
It  is  tunnelled  by  a  narrow  passage,  the  aqueduct  of  Sylvius,  which  extends  between 
the  fourth  and  third  ventricles. 


Mesencephalon 

Superior  cerebellar  peduncle 

Middle  cerebellar  peduncle 
Inferior  cerebellar  peduncle 


Fig.  381. — Schema,  showing  the  conue.xions  of  the  several 
parts  of  the  brain. 


General  Outline  of  the  Development  of  the  Brain. 

The  brain  is  developed  from  the  expanded  anterior  portion  of  the  primitive 
neural  tube.  In  the  section  dealing  with  the  general  principles  of  Embryology  it 
has  been  pointed  out  that  this  part  of  the  neural  tube  is  marked  off  by  two  con- 
strictions into  three  primitive  cerebral  vesicles,  which  are  termed  respectively  the 
hind-brain  or  rhombencephalon,  the  mid -brain  or  mesencephalon,  and  the  fore- 
brain  or  prosencephalon. 

Hind-brain  or  Rhombencephalon. — The  hind-brain  is  the  largest  of  the  three 
primary  expansions  of  the  neural  tube :  indeed,  it  may  be  said  that  in  the  earlier 
stages  of  brain  development  it  is  larger  than  both  of  the  other  primary  subdivisions 
taken  together.  The  portion  immediately  adjoining  the  mid-brain  is  constricted, 
and  is  termed  the  isthmus  rhombencephali.  This  is  a  very  small  part,  forming  the 
extreme  upper  end  of  the  vesicle,  and  from  its  walls  are  developed  the  superior 
cerebellar  peduncles  and  a  thin  lamina,  which  is  stretched  across  the  middle  line 
between  them,  called  the  valve  of  Vieussens  or  the  superior  medullary  velum. 
Immediately  behind  the  isthmus  the  hind-brain  expands  suddenly,  and  then  slowly 
and  gradually  tapers  as  it  passes  downwards  towards  the  spinal  cord  part  of  the 
neural  tube.     Its  junction  with  the  latter  is  very  early  indicated  by  a  sharp  bend 


GENEKAL  OUTLINE  OF  DEVELOPMENT  OF  THE  BRAIN.      477 


in  the  tube,  which  is  termed  the  cervical  flexure.  The  large  portion  of  hind-brain 
which  extends  from  the  isthmus  to  the  cervical  flexure  is  usually  considered  as 
being  composed  of  two  parts,  viz.  an  upper  portion,  termed  the  metencephalon,  and 
an  inferior  portion,  called  the  myelencephalon. 

From  the  metencephalon  are  derived  the  cerebellum  and  pons  Varolii.  The 
cerebellum  arises  by  a  thickening  of  the  dorsal  wall  of  this  portion  of  the  vesicle, 
whilst  the  pons  is  formed  by  a  thickening  of  the  lateral  and  ventral  walls.     The 


^\0-S/f, 


<=^PHALIC    FH 


OPTIC  VESICLE 


Fig.  382. — Two  Stages  in  the  Development  of  the  Human  Brain  (after  His). 
A.  Brain  of  an  embryo  of  the  third  week.     B.   Brain  of  an  embryo  of  five  weeks. 

myelencephalon  gives  origin  to  the  bulb  or  medulla  oblongata.  This  is  chiefly 
formed  by  a  thickening  of  the  lateral  walls  of  this  part  of  the  vesicle.  These  fall 
away  from  each  other  in  an  outward  direction,  and  thus  the  ventral  angle  between 
them  becomes  greatly  opened  up.  The  growth  which  leads  to  the  formation  of  the 
bulb  appears,  therefore,  to  take  place  chiefly  on  the  ventral  aspect  of  the  vesicle. 
The  dorsal  wall  remains  thin  and  epithelial,  and  undergoes  little  or  no  development 
into  nervous  elements. 

The  cavity  of  the  original  hind-brain  is  retained  in  the  adult  brain  as  the  fourth 
ventricle ;  and  from  what  has  been  said  regarding  the  development  of  the  different 
portions  of  the  wall  of  the 
primitive  hind-brain,  it  will 
be  seen  that  in  its  lower  or 
medullary  part  its  dorsal 
wall  or  roof,  to  a  large 
extent,  remains  epithelial. 

The  parts  of  the  adult 
brain  which  are  derived 
from  the  rhombencephalon 
or  hind -brain  are  those 
which  lie  below  the  ten- 
torium cerebelli  in  the 
posterior  cranial  Ibssa  of 
the  skull. 

Mesencephalon  or 
Mid -brain. — The  mid -brain  takes  a  much  more  prominent  part  in  the  forma- 
tion of  the  early  primitive  brain  than  it  does  in  the  construction  of  the  adult 
brain.  It  forms  a  very  small  part  of  the  adult  brain,  and  constitutes  a  stalk  of 
connexion  betw(!en  tlie  ])arts  whi{;h  are  developed  i'rom  the  walls  of  the  rhoml)en- 
cephalon  and  tliose  which  are  developed  from  the  walls  of  the  prosencephalon 
or  fore- brain.  Ti)e  entire  wall  of  the  mid-lmiin  is  transformed  into  nervous 
tiH.siie.  TliuH,  by  the  special  developnuait  of  the  dorsal  section  of  the  wall,  the 
corjiora  quadrigeiiiina  are  formed.  The  lat(!ral  and  ventral  sections  of  the  wall 
undergo  a  still  more  marked  degree  of  growth-thickening,  and  the  result  is  the 


OPTIC  VESICLE 


OPTIC  VE5. 
OPTiC  STALK 


A  B 

Fig.  383. — Two  Cross  Sections  through  the  Fore-Brain. 
A.  Throngh  the  fore-brain  of  the  early  human  embryo.     B.  Through, 
tlie  fore-brain  and  optic  vesicles  of  a  Lepidosteus  embryo  of  eight 
days  (after  Balfour  and  Parker,  modified). 


478 


THE  NERVOUS  SYSTEM. 


formation  of  the  two  crura  cerebri.  The  cavity  of  the  mid-brain  is  retained  as  the 
narrow  passage  termed  the  aqueduct  of  Sylvius,  which  connects  the  third  ventricle 
of  the  brain  with  the  fourth  ventricle. 

Prosencephalon  or  Fore-brain. — In  its  early  condition  one  of  the  leading 
peculiarities  of  the  fore-brain  is  its  great  width.  It  extends  outwards  on  either 
side  for  a  considerable  distance  beyond  the  lateral  walls  of  the  mid- brain.  These 
lateral  expansions  of  the  fore-brain  are  the  optic  vesicles,  and  at  this  stage  they  are  in 
no  way  constricted  off  from  the  central  part  of  the  cavity  (Fig.  383).  Soon,  however, 
the  central  portion  of  the  fore-brain  begins  to  expand  upwards  and  forwards,  whilst 
the  terminal  portions  of  the  optic  vesicles  likewise  undergo  enlargement ;  and  the 
result  is,  that  the  originally  single  chamber  shows  subdivision  into  three  parts, 
viz.  a  central  portion  or  fore-brain  proper,  and  two  expanded  optic  vesicles,  which 

r  ORE  ^^®    joined    to    the    lower 

parts  of  the  lateral  aspects 
of  the  fore-brain  proper  by 
two  short  constricted 
tubular  passages  termed 
the  optic  stalks. 

The  optic  vesicle  and 
the  optic  stalk  become  ulti- 
mately transformed  into  the 
retina  of  the  eye-ball  and 
the  optic  nerve.  The 
changes  which  lead  to  this 
result  are  detailed  in  the 
section  dealing  with  the 
anatomy  of  the  organ  of 
vision. 

The  fore-brain  under- 
goes a  series  of  remarkable 
developmental  changes,  the 
most  striking  of  which  is 
the  formation  of  the  cere- 
bral hemispheres.  The 
terminal  or  fore-portion  of 
the  fore-brain,  in  the  first 
instance,  expands  in  a  for- 
ward and  downward  direc- 
tion, and  from  the  upper 
and  lateral  aspects  of  the 
new  portion  of  the  vesicle 
thus  formed  the  cerebral 
hemispheres  bulge  outwards 
in  the  form  of  two  hollow 
The  hinder 
part  of  the  fore- 
brain  is  termed  the  thal- 
mamencephalon  or  dien- 
cephalon,  whilst  the  an- 
terior part  with  the  cerebral  hemispheres,  which  protrude  out  from  it,  receives  the 
name  of  telencephalon. 

The  side  walls  of  the  diencephalon  become  thickened  into  the  two  large  masses 
of  gray  matter  termed  the  optic  thalami ;  the  floor  or  ventral  wall  develops  into 
those  structures  which  occupy  the  interpeduncular  space  in  the  base  of  the  brain 
(viz.  the  posterior  perforated  spot,  the  corpora  mammillaria,  and  the. tuber  cinereum) ; 
whilst  the  roof  or  dorsal  wall  remains  thin  and  epithelial,  and  undergoes  no 
nervous  development. 

The  hollow  cerebral  hemispheres  soon  outstrip  all  the  other  parts  of  the  brain 
in  their  development.     They  expand  not  only  in  an  upward  and  forward  direction, 


Fig.  384. — The  Brain  of  a  Human  Embryo  in  the  Fifth  Week 
(from  His). 

A,  Brain  as  seen  in  profile.     B,   Mesial  section  through  the  same  brain. 

M,  Mammillary  eminence;  Tc.  Tuber  cinereum;  Hp,  Hypophysis  r)oucheS 
(pituitary  diverticulum  from  buccal  cavity)  ;  Opt,  Optic  stallc  ;  ^  .  .  ,  ' 
TH,  Optic  thalamus  ;  Tg,  Tegmental  part  of  mesencephalon  ;  Ps,  Original 
Pars  subthalamica  ;  Cs,  Corpus  striatum  ;  FM,  Foramen  of  Monro  ; 
L,  Lamina  terrniualis  ;  RO,  Recessus  opticus  ;  Ri,  Recessus  iufun- 
dibuli. 


GENERAL  OUTLINE  OF  DEVELOPMENT  OF  THE  BRAIN.      479 


but  chiefly  in  a  backward  direction ;  and  by  their  excessive  growth  backwards 
they  gradually  come  to  overlie  the  diencephalon,  the  mesencephalon,  and  at 
last  the  parts  derived  from  the  rhombencephalon.  It  thus  comes  about  that, 
when  the  adult  brain  is  viewed  from  above  nothing  but  the  cerebral  hemispheres 
are  visible — all  the  other  parts  of  the  brain  lie  under  cover  of  them. 

At  first  the  cavity  of  each  cerebral  hemisphere  is  connected  with  the  cavity 
of  the  front  portion  of  the  fore-brain  by  an  exceedingly  short  but  relatively  wide 
passage.  This  is  the  early  condition  of  the  foramen  of  Monro.  The  fore-part  of 
the  fore-brain  is  now  seen  to  be  bounded  in  front  between  the  two  hollow  cerebral 
hemisphere-pouches  by  a  narrow  thin  strip,  which  represents  the  extreme  anterior 
wall  of  the  neural  tube,  and  consequently  it  receives  the  name  of  lamina  terminalis. 
The  cavity  of  the  fore-brain  not  only  in  its  hinder  diencephalic  part,  but  also  in 
its  anterior  telencephalic  part  {i.e.  the  part  from  which  the  cerebral  hemispheres 
bud  out),  persists  as  the  third  ventricle  of  the  brain,  whilst  the  cavities  of  the 
primitive  cerebral  hemispheres  are 
represented  in  the  adult  by  the 
lateral  ventricles  of  the  brain.  The 
foramina  of  Monro,  relatively  much 
reduced  in  size,  are  preserved  as 
narrow  throats  of  communication 
between  the  lateral  ventricles  and 
the  third  ventricle.  The  olfactory 
lobes  are  formed  as  hollow  out- 
growths from  the  cerebral  hemi- 
spheres. 

Flexures  of  the  Brain-tube. — 
At  a  very  early  period,  and  while  the 
changes  detailed  above  are  being 
carried  on,  the  cerebral  portion  of  the 
neural  tube  becomes  sharply  bent 
upon  itself  at  certain  points.  The 
first  flexure  which  occurs  is  the 
primary  cephalic  flexure.  It  occurs 
in  the  region  of  the  mesencephalon, 
and  involves  the  entire  head.  The 
fore-brain  becomes  bent  in  a  ventral 
direction  round  the  fore-end  of  the 
notochord  and  the  fore-gut,  until  the 
long  axis  of  the  fore-bra,in  forms  an 
acute  angle  with  the  long  axis  of 
the  hind-brain  and  the  ventral  wall 
of  the  one  comes  to  lie  nearly  parallel  with  the  corresponding  wall  of  the  other. 
Through  this  curvature  the  mid-brain  is  considerably  modifled  in  form,  and  for  a 
time  it  comes  to  occupy  the  most  prominent  and  foremost  part  of  the  embryonic  head. 
The  primary  cephalic  flexure  is  soon  followed  by  the  cervical  flexure.  This 
occurs  at  the  junction  of  the  hind-brain  with  the  spinal  cord.  Here  the  entire 
head  is  bent  in  a  ventral  direction,  and  at  the  end  of  the  flfth  week  the  flexure  is 
so  pronounced  that  the  cerebral  and  spinal  cord  portions  of  the  neural  tube  meet 
each  other  ut  a  right  angle  (Fig.  385).  In  the  later  stages  of  development  the 
cervical  flexure  becomes  obliterated  by  the  elevation  of  the  head  and  the  straighten- 
ing of  the  neck  of  the  embryo. 

The  third  bend  takes  place  in  the  region  of  the  future  pons  Varolii  (meten- 
cephalon),  and  is  consequently  termed  the  pontine  flexure.  It  differs  from  the 
other  flexures  in  being  confined  to  the  brain  tube  and  in  not  in  any  way  involving 
the  entire  head.  Further,  the  bend  is  much  more  marked  in  the  thick  ventral 
wall  than  in  the  thin  dorsal  wall  of  the  tube.  The  neural  tube  is  doubled  forwards 
on  itself  and  the  pons  Varolii  becomes  developed  in  connexion  with  the  summit  of 
the  curvature.  In  the  further  growth  of  the  brain  the  pontine  flexure  becomes 
almost  completely  obliterated. 


Fig.  385. — Profile  View  op  the  Brain  op  a  Human 
Embryo  op  Ten  Weeks  (His). 

The  various  cranial  nerves  are  indicated  by  numerals. 

A,  Cerebral  diverticulum  of  pituitary  body.     B,  Buccal 
diverticulum  of  pituitary  body. 


480 


THE  NEEVOUS  SYSTEM. 


By  reason  of  these  curvatures  the  early  brain  assumes  a  sinuous,  zigzag  or 
S-shaped  outline  when  viewed  from  the  side,  and  the  relationship  of  its  various 
parts  becomes  materially  altered.  The  essential  factor  at  work  in  the  production 
of  the  brain  flexures  is  clearly  the  very  unequal  growth  which  takes  place  in 
different  parts  of  the  cerebral  wall. 

Basal  and  Alar  Laminse  of  His. — It  has  been  pointed  out  that,  in  the 
development  of  the  spinal  cord,  each  of  the  thick  lateral  walls  of  the  neural  tube 
is  marked  off  into  a  dorsal  or  alar  and  a  ventral  or  basal  lamina.  This  subdivision 
is  also  noticeable  in  the  cerebral  part  of  the  neural  tube,  and  the  furrow  on  the 
inner  aspect  of  the  lateral  wall,  which  indicates  this  subdivision,  can  be  traced 
even  in  the  adult  brain  throughout  a  considerable  part  of  its  length. 

In  the  spinal  cord  the  motor  cells  are  gathered  in  the  basal  lamina  in  more  or 

less  continuous 
"^'o  >-  columns.     In  the 

brain  the  corre- 
sponding cells 
from  which  the 
efferent  fibres  of 
the  cranial  nerves 
are  given  off  are 
also  placed  within 
the  basal  lamina, 
but  they  are  ar- 
ranged differently. 
They  are  collected 
together  in  dis- 
connected clusters 
termed  the  motor 
nuclei,  and  they 
do  not  extend 
higher  up  than 
the  mid-brain. 
No  motor  nuclei 


111  both 


)rain.     Indeed, 
the  importance  of 


Fig.  386. — Diagrams  to  illustrate  the  Alar  and  Basal  Lamina. 
cases  the  embryonic  brain  is  represented  in  mesial  section  (His). 

A.  The  diflferent  subdivisions  of  the  brain  are  marked  off  from  each  other  b}^  dotted    ocCUr  in  the   fore- 
lines,  and  the  dotted  line  running  in  the  long  axis  of  the  neural  tube  indicates  the 
separation  of  the  alar  from  the  basal  lamima  of  the  lateral  wall. 

B.  Mesial  section  through  the  brain  of  a  human  embryo  at  the  end  of  the  first  ■■  -, 
month.  Dotted  lines  mark  off  the  different  regions  and  also  the  alar  and  basal  the  iDasai  lamina 
laminse  from  each  other.  diminishes  aS  we 
H,  Buccal  part  of  pituitary  body;  RL,    Olfactory  lobe;    C.Str,    Corpus   striatum;  paSS     from      the 

A,  Entrance  to  optic  stalk;  0,  Optic  recess;  I,  Infundibular  recess;  T,  Tuber   Inwprfo  thehio-her 
ciiiereuni  ;  M.  Mammillary  eminence.  ^  . 

parts  of  the  bram. 

In  the  rhombic  or  hind-brain  the  greater  part  of  the  medulla  oblongata  and  of 
the  pons  Varolii  is  formed  from  the  basal  laminae,  whilst  the  cerebellum,  with  its 
superior  and  inferior  cerebellar  peduncles,  is  derived  from  the  alar  laminse.  In 
the  mid-brain  the  crura  cerebri  are  the  derivatives  of  the  basal  laminse,  whilst  the 
corpora  quadrigemina  are  developed  from  the  alar  laminse.  In  the  fore-brain  the 
subthalamic  region  and  the  optic  vesicles  are  products  of  the  growth  of  the  basal 
laminse,  whilst  the  optic  thalami  and  cerebral  hemispheres  spring  from  the  alar 
laminse. 

The  fact  that  the  cerebellum  and  the  cerebral  hemispheres  owe  their  origin 
to  the  alar  laminse  is  sufficient  to  show  the  predominant  part  which  these  laminse 
play  in  brain  development,  and  the  higher  we  ascend  in  the  animal  scale  the  more 
pronounced  does  this  predominance  become. 

The  following  table  gives  a  summary  of  the  various  developmental  processes 
which  have  been  described  in  the  foregoing  pages : — 


MEDULLA  OBLONGATA  OR  BULB. 


481 


Encephalon 

or 

Brain 


Rhombencephalon 

or 

Hind-brain 

(posterior  cerebral 

vesicle) 


Mesencejihalon 

or  Mid-brain 

(middle  cerebral 

vesicle) 


I 


Prosenceiahalon 
or  Fore-brain 
(anterior  cerebral  ' 
vesicle) 


L 


Myelencephalon 


Metencephalon 

Isthmus  rhombencephali 

(narrow  constricted  part 

immediately  adjoining 

the  mesencephalon) 

Mesencephalon 

or 

Mid-brain 


Thalamencephalon 

or 

Diencephalon 


Telencephalon 


[Bulb 

1  Lower  2>art  of 


or  medulla  oblojigata 

the  fourth  ven- 
tricle 
rCerebellum 
J  Pons  Varolii 

I  \J])])ev  part  of  the   fourth  veii- 
*-     tricle 

'.Superior  cerebellar  peduncles 
I  Valve  of  Vieussens 

j  Corpora  quadrigemina 
-  Crura  cerebri 
I^Aquedu^ct  of  Sylvius 

'Optic  thalami 

Subthalamic  tegmental  regions 

Pituitary  and  pineal  bodies 

Structures  in  interpeduncular 
space 

Optic  nerve  and  retina 

Hinder  part  of  the  third  ven- 
tricle 

Cerebral  hemispheres 

Olfactory  lobes 

Lateral  ventricles 

Foramina  of  Monro 

Anterior  portion  of  the  third 
ventricle 


THE  PAETS  OE  THE  ENCEPHALON  DEEIVED  FEOM  THE 

HIND-BEAIN. 


MEDULLA  OBLONGATA  OR  BULB. 

The  medulla  oblongata  or  bulb  is  the  continuation  upwards  of  the  spinal  cord. 
It  is  not  more  than  one  inch  in  length,  and  it  may  be  regarded  as  beginning  at  the 
decussation    of     the 

pyramidal    tracts,  r^„^.-„  „.,.•„„,„„  \    ^_y^2 -optic nerve 

which  takes  place 
about  the  level  of 
the  foramen  magnitm. 

Erom  this  it  proceeds      corpus  gemculatum 

upwards  in  a  very, 
nearly  vertical  direc- 
tion, and  ends  at  the 
lower  border  of  the 
pons  Varolii.  At  first 
its  girth  is  similar  to 
that  of  the  cord,  but 
it  rapidly  expands  as 
it  apj)roaches  the 
pons,  and  conse- 
quently it  presents  a 
more  or  less  conical 
form.  Its  ventral 
surface  lies  behind 
the  grooved  surface 
of  the  basilar  pfjrtion 
of  the  occiijital  bone, 
whilst  its  dorsal  sur- 
face is  sunk  into  the  vallecula  of  the  cere})ellum.  The  medulla  ol)longata  is  a 
bilateral  structure,  and  this  is  indicated  on  the  surface  by  a  continuation  upwards 
of  tbo  ant(;ro-median  and  ])Ostero-median  fissures  of  the  cord  on  the  ventral  and 
dorsal  aspects  of  the  medulla. 
35 


Optic  chiasma 

Optic  tract 

Corpus  geniculatum 
externum' 


internum 
Locus  perforatus 
posticus 


Middle  peduncle 
of  the  cerebellum 


Restiform  body 
Olive 
Pyramid- 
Anterior  superficial 
arcuate  fibres 

Decussation  of 
pyramids 


Infundibulum 

Tuber  cinereum 

Corpora  mammillaria 

Oculo-motor  nerve  (III.) 

Trochlear  nerve  (IV.) 
winding  round  the  crus 
cerebri 

Trigeminal  nerve  (V.) 

Abducent  nerve  (VI.) 
—  Facial  nerve  (VII.) 
Auditory  nerve  (VIII.) 

Vago-glossopharyngeal 
nerve  (IX.  and  X.) 

Hypoglossal 
nerve  (XII.) 

Spinal  accessory 
nerve  (Xt.) 

First  cervical  nerve 


Fiii.  387. — FiioNT  View  oi'  thk  Medulla,  Pons,  and  Mesencephalon  of 
h'ULL-TiME  Human  F(ktus. 


482 


THE  NEEVOUS  SYSTEM. 


The  antero-median  groove  (fissura  mediana  anterior),  as  it  passes  from  the  oord 
on  to  the  medulla,  is  interrupted  at  the  level  of  the  foramen  magnum  by  several 
strands  of  fibres,  which  cross  the  mesial  plane  from  one  side  to  the  other.  This 
intercrossing  is  termed  tlie  decussation  of  the  pyramids.  Above  this  level  the 
furrow  is  carried  upwards  to  the  lower  border  of  the  pons,  but  is  often  rendered 
very  shallow  by  numerous  superficial  arcuate  fibres  which  emerge  upon  the  surface 
between  its  lips  and  then  curve  outwards  to  reach  the  hinder  part  of  the  medulla. 
At  the  lower  margin  of  the  pons  Varolii  it  expands  slightly  and  ends  in  a  blind  pit, 
which  receives  the  name  of  the  foramen  csecum  of  Vicq  d'Azyr.  The  postero-median 
fissure  (fissura  mediana  posterior)  is  only  carried  up  on  the  lower  lialf  (if  the 
medulla.  As  it  ascends  it  rapidly  becomes  shallower,  and,  halfway  up,  the  central 
canal  of  the  cord  opens  on  the  dorsal  surface  of  the  medulla.  At  this  point  the 
lips  of  the  postero-median  fissure  are  thrust  apart  from  each  other  and  constitute 
the  boundaries  of  a  triangular  field,  which  is  thus  opened  up  on  the  dorsal  aspect 
of  the  medulla.  This  triangular  field  is  the  lower  part  of  the  fossa  rhomboidalis, 
or  the  fioor  of  the  fourth  ventricle  of  the  brain.  The  lower  half  of  the  medulla, 
containing  as  it  does  the  continuation  of  the  central  canal  of  the  cord,  is  frequently 
termed  the  closed  part  of  the  medulla  ;  the  upper  half,  above  the  opening  of  the 
canal,  which  by  its  dorsal  surface  forms  the  lower  part  of  the  floor  of  the  fourth 
ventricle,  is  then  called  the  open  part  of  the  medulla. 

Deferring  for  the  present  the  examination  of  the  medullary  part  of  the  floor 
of  the  fourth  ventricle,  the  appearance  presented  by  the  surface  of  each  side  of 
the  medulla,  from  the  antero-median  fissure  in  front  to  the  postero-median  fissure 
and  the  lateral  limit  of  the  floor  of  the  fourth  ventricle  behind,  may  now  engage 
our  attention.  In  the  spinal  cord  the  corresponding  surface  area  is  divided  into 
three  districts  or  columns  by  the  emerging  motor  roots  and  the  entering  sensory 
roots  of  the  spinal  nerves.  Of  these  the  latter  enter  along  the  bottom  of  the 
postero-lateral  groove,  whilst  the  motor  fascicles  are  spread  over  a  relatively  broad 

surface  area  and  have 
no  groove  in  connexion 
with  their  emero;ence 
from  the  cord.  In  the 
case  of  the  medulla 
corresponding  rows  of 
nerve  -  fascicles  enter 
and  emerge  from  the 
surface  of  each  side. 
The  efferent  fascicles 
are  the  root -bundles  of 
the  hypoglossal  nerve, 
and  they  carry  up  the 
line  of  the  anterior 
nerve-roots  of  the  cord. 
In  one  respect,  however, 
they  differ:  they  emerge 
in  linear  order  and  along 
the  bottom  of  a  dis- 
tinct furrow,  termed  the 
antero  -  lateral  furrow, 
which  proceeds  upwards 
on  the  surface  of  the 
medulla.  The  fascicles 
which  carry  up  the  line 
of  the  posterior  nerve- 
roots  on  the  surface  of 
the  medulla  are  the  root-bundles  of  the  spinal  accessory,  the  vagus,  and  the  glosso- 
pharyngeal nerves.  These  are  attached  along  the  bottom  of  a  furrow  which  is  the 
direct  continuation  upwards  of  the  postero-lateral  furrow  of  the  cord,  and  therefore 
receives  the  name  of  the  postero-lateral  furrow  of  the  medulla.      The  root-bundles 


Frenulum 


Valve  of  Vieusseus, 


Superior  peduncle  of 
the  cerebellum 

Middle  peduncle  of 
the  cerebellum 


Strise  acusticpe 
Area  acusticse 


TriRonuni  vasri 


Cuneate  tubercle 
Funiculus  srracilis 


Ta;'nia  thalami 

Pineal  body 

Superior  quadri- 
geminal  body 

Inferior  quadri- 
geminal  body 


Crus  cerebri 

Pontine  part  of  floor 
of  ventricle  IV. 

Emiuentia  teres 

Fovea  superior 

Restiforin  body 
Trigonuni  hypoglossi 
Clava 

Rolandic  tubercle 
Funiculus  euneatus 


Fia.  388. 


-Back  View  of  the  Meddlla,  Pons,  and  Mesencephalon 
a  full-time  human  fcetus. 


MEDULLA  OBLONGATA  OE  BULB. 


4S.- 


of  these  nerves  differ,  however,  in  so  far  that  they  are  not  all  composed  of  afferent 
fibres  springing  from  ganglionic  cells  placed  without  and  entering  the  medulla. 
Certain  of  them  are  purely  efferent  (spinal  accessory  roots),  whilst  others  likewise 
contain  a  considerable  number  of  efferent  fibres,  and  are  therefore  to  be  regarded 
as  mixed  roots. 

By  the  postero-lateral  and  the  antero-lateral  grooves,  and  also  by  the  two  rows 
of  nerve  fascicles  attached  along  the  bottom  of  these  furrows,  the  surface  of  the 
medulla  on  each  side  is  divided  into  three  districts,  viz.  an  anterior,  a  lateral,  and  a 
posterior,  similar  to  the  surface  areas  of  the  three  columns  on  the  side  of  the  cord. 
Indeed,  at  first  sight,  they  appear  to  be  a  direct  continuation  upwards  of  these  three 
portions  of  the  cord ;  this  is  not  the  case,  however,  because  the  fibres  of  the  three 
columns  of  the  cord  undergo  a  rearrangement  as  they  proceed  upwards  into  the 
medulla. 

Anterior  Area  of  the  Medulla — Pyramid  (pyramis). — The  district  between 
the  antero-median  fissure  and  the  antero-lateral  furrow,  along  the  bottom  of 
which  the  root-fascicles  of  the  hypoglossal  nerve  issue  from  the  medulla,  receives 
the  name  of  the  pyramid.  An  inspection  of  the  surface  is  sufficient  to  show 
that  the  pyramid  is  composed  of  a  compact  strand  of  longitudinally  directed 
nerve-fibres.  Tapering  below,  it  expands  and  assumes  a  prominent  appearance 
as  it  is  traced  upwards,  and,  finally  reaching  the  lower  border  of  the  pons  Varolii, 
it  becomes  slightly  constricted  and  disappears  from  view  by  plunging  into  that 
portion  of  the  brain.  The  two  pyramids,  separated  from  each  other  by  the  antero- 
median furrow,  are  the  great  motor  strands  of  the  medulla. 

Although  the  pyramid  at  first  sight  appears  to  be  continuous  with  the  anterior 
column  of  the  cord,  only  a  very  small  pro- 
portion of  the  fibres  contained  in  the  latter 
are  derived  from  the  pyramid.  This  at  once 
becomes  manifest  when  the  lips  of  the 
antero-median  fissure  are  thrust  apart  at  the 
place  of  junction  between  the  cord  and  the 
medulla.  The  pyramid  is  then  seen  to  divide 
at  this  level  into  two  parts,  viz.  a  small 
portion  composed  of  a  variable  number  of 
the  outermost  fibres  of  the  pyramid,  termed 
the  direct  pyramidal  tract,  and  a  much  larger 
portion  situated  next  the  antero-median 
fissure,  called  the  crossed  pyramidal  tract. 
The  direct  pyramidal  tract  is  continued  down 
into  the  anterior  column  of  the  cord,  and 
in  this  it  takes  up  a  mesial  position  next 
the  antero-median  fissure.  The  crossed  pyra- 
midal tract  is  broken  up  into  three  or  more 
coarse  bundles,  which  sink  backwards  and  at 
the  same  time  cross  the  mesial  plane,  to  take 
up  a  position  in  the  posterior  part  of  the 
opposite  lateral  column  of  the  cord.  The 
term  decussation  of  the  pjrramids  (decussatio 
pyramidum;  is  applied  to  the  intercrossing 
of  the  corresponding  bundles  of  the  crossed 
pyramidal  tracts  of  opposite  sides.  Fig.   389.— Diacram  of  the   Decussation  of 

The   direct   pyramidal   tract    is,   therefore,     ™^  Pyramids  (modified  from  van  Gehuchten). 

the  only  part  of  the  pyramid  which  has  a  NH,  Nucleus  hypogiossi ;    nv,   Vago-giosso- 

place     in    the    anterior    column    of    the    cord.  I'l'-'ry'.g^al   nudeu.s  ;    FS,    Fasciculus  soli- 

^.  ,     ,  r.     1  •  1  •,  tarms  ;  NA,  Nucleus  anibiguiis. 

Itie  much  larger  part  ot  this  column,  termed 

the  anterior  basis-bundle,  as  it  is  traced  up  into  the  medulla  is  seen  to  be 
thrust  aside  by  the  decussating  bundles  of  the  crossed  pyramidal  tract.  It  thus 
comes  to  occupy  a  deep  position  in  the  su})stance  of  the  medulla  behind  and  to  the 
outer  side  of  the  pyramid. 

Lateral  Area  of  the  Medulla. — This  is  Uw,  district  on  tlie  surface  of  the  medulla 


CROSSED  PYR.TR, 


484 


THE  NEEVOUS  SYSTEM. 


which  is  included  between  the  two  rows  of  nerve-roots,  viz.  the  hypoglossal  roots  in 
front,  and  the  root-bundles  of  the  spinal  accessory,  the  vagus,  and  the  glosso- 
pharyngeal nerves  behind.  It  presents  a  very  different  appearance  in  its  upper  and 
lower  parts.  In  its  lower  portion  it  simply  appears  to  be  a  continuation  upwards 
of  the  lateral  area  of  the  cord  ;  in  its  upper  part  a  striking  oval  prominence  bulges 
out  on  the  surface  of  the  medulla,  and  receives  the  name  of  the  olivary  eminence. 

The  lower  part  of  this  district,  however,  is  very  far  from  being  an  exact  counter- 
part of  the  lateral  column  of  the  cord.  The  large  crossed  pyramidal  tract  is  no 
longer  present,  seeing  that  it  forms  in  the  medulla  the  greater  part  of  the  pyramid 
of  the  opposite  side.  Another  strand  of  fibres,  viz.  the  direct  cerebellar  tract, 
prolonged  upwards  in  the  lateral  column  of  the  cord,  gradually  leaves  this 
portion  of  the  medulla.  This  tract  lies  on  the  surface,  and  is  frequently  visible 
to  the  naked  eye  as  a  white  band,  which  inclines  obliquely  backwards  into 
the  posterior  district  of  the  medulla  to  join  its  upper  part,  or  in  other  words  the 
restiform  body.  The  remainder  of  the  fibres  of  the  lateral  column  of  the  cord, 
comprising  the  lateral  basis-bundle  and  the  tract  of  Gowers,  are  continued  upwards 
in  the  lateral  area  of  the  medulla,  and  at  the  lower  border  of  the  olive  the  majority 
of  these  fibres  disappear  from  the  surface  by  dipping  into  the  substance  of  the 
medulla  under  cover  of  that  projection.  A  small  proportion  of  the  fibres,  how- 
ever, are  retained  on  the  surface  and  travel  upwards  towards  the  pons  in  the  interval, 
which  exists  between  the  hinder  border  of  the  olive  and  the  roots  of  the  vagus  and 
glosso-pharyngeal  nerves. 

The  olivary  eminence  (oliva)  is  a  smooth  oval  projection  which  bulges  out  from 
the  upper  part  of  the  lateral  area  of  the  medulla.  Its  long  axis  is  vertical  and  is 
about  half  an  inch  long.  It  marks  the  position  of  the  subjacent  inferior  olivary 
nucleus,  a  flexuous  lamina  of  gray  matter  (nucleus  olivaris  inferior),  which  is  only 
separated  from  the  surface  by  a  very  thin  layer  of  superficial  white  matter. 

Posterior  Area  of  the  Medulla. — In  its  lower  half,  this  district  is  bounded 
behind  by  the  postero-median  fissure,  and  in  its  upper  half  by  the  lateral  margin 
of  the  medullary  part  of  the  floor  of  the  fourth  ventricle  of  the  brain.  In  front 
it  is  separated  from  the  lateral  area  by  the  row  of  root-fascicles  belonging  to 

the  spinal  accessory,  vagus,  and  glosso- 
pharyngeal nerves.  As  in  the  lateral 
area,  we  recognise  a  lower  portion  and  an 
upper  portion,  which  appear  continuous 
but  in  reality  are  almost  quite  distinct 
from  each  other. 

The  lower  part  of  the  posterior  area 
corresponds  more  or  less  closely  with  the 
posterior  column  of  the  cord.  In  the 
cervical  part  of  the  cord  the  posterior 
column  is  divided  by  the  paramedian 
septum  of  pia  mater  into  an  inner  column 
of  GoU  and  an  outer  column  of  Burdach. 
These  are  prolonged  upwards  into  the 
medulla,  and  in  the  lower  part  of  the 
posterior  area  they  stand  out  distinctly, 
and  are  separated  from  each  other  by  a 
continuation  upwards  from  the  cord  of  the 
paramedian  groove.  In  the  medulla  the 
inner  of  these  strands  is  called  the  funiculus 
gracilis,  whilst  the  outer  one  is  designated 
the  funiculus  cuneatus.  Each  of  these 
strands,  when  it  reaches  the  level  of 
the  lower  part  of  the  floor  of  the  fourth 
ventricle,  ends  in  a  slightly  expanded 
bulbous  prominence.  The  swollen  extremity  of  the  funiculus  gracilis  is  called  the 
clava.  This  is  thrust  aside  from  its  neighbour  of  the  opposite  side  by  the  opening 
up  of  the  medulla  to  form  the  floor  of  the  fourth  ventricle,  and  the  central  canal  of 


Optic  tract 

Crus  cerebri 
Corpus  geniculatum 
externum 

Pulviuar 

Corpus  geniculatum 
internum 

Superior  bracliium 
Inferior  bracliium 
^Inferior  quadrigeminal  body 
Lateral  fillet 

Superior  cerebellar  peduncle 
Taenia  pontis 

Middle  peduncle  of 
cerebellum 


Restiform  body 
Ligula  bounding  lateral 
recess  of  ventricle  IV. 
Olivary  eminence 

Arcuate  fibres  (anterior  superficial) 

Clava 

Cuneate  tubercle 

Rolandic  tubercle 

Lateral  district  of  medulla 

Anterior  column  of  cord 


Fig.    390.  —  Lateral  View   of  the 
Pons,  and  Mesencephalon  of  a 

Human  Fcetus. 


Medulla, 
full-time 


MEDULLA  OBLONGATA  OE  BULB.  485 

the  cord  opens  on  the  surface  in  the  angle  between  the  two  clavw.  The  bulbous 
end  of  the  fasciculus  cuneatus  receives  the  name  of  the  cuneate  tubercle  (tuberculum 
cinereum),  but  it  is  only  in  the  foetal  or  very  young  brain  that  it  is  well  marked. 

The  elongated  prominences  formed  on  the  surface  of  the  medulla  by  these  two 
strands  and  their  enlarged  extremities  are,  in  a  great  measure,  due  to  the  presence 
of  two  elongated  nuclei  or  collections  (if  gray  matter  which  make  their  appearance 
subjacent  to  the  strands,  and  which  gradually  increase  in  bulk  as  they  are  traced 
upwards.  These  are  termed  respectively  the  gracile  (nucleus  funiculi  gracilis)  and 
cuneate  (nucleus  funiculi  cuneati)  nuclei,  and  it  can  be  easily  shown  that  as  the 
gray  matter  increases  in  quantity  the  fibres  of  the  two  corresponding  strands 
diminish  in  number  by  coming  to  an  end  in  connexion  with  the  cells  of  the 
subjacent  nuclei.  Indeed,  it  is  doubtful  if  any  of  the  fibres  of  the  gracile  and 
cuneate  strands  extend  upwards  beyond  these  nuclei. 

But  a  third  longitudinal  elevation  is  also  apparent  on  the  surface  of  the  lower 
part  of  the  posterior  area  of  the  medulla.  This  is  placed  on  the  outer  side  of  the 
funiculus  cuneatus — between  it  and  the  posterior  row  of  nerve-roots — and  it  has 
no  counterpart  in  the  posterior  column  of  the  cord.  It  is  called  the  funiculus  of 
Rolando,  because  it  is  produced  by  the  substantia  gelatinosa  Eolandi,  which  caps  the 
posterior  horn,  coming  close  to  the  surface  and  forming  a  bulging  in  this  situation. 
The  funiculus  of  Eolando  is  wedge-shaped  in  outline.  Extremely  narrow  below,  it 
widens  as  it  is  traced  upwards,  and  finally  ends  in  an  expanded  extremity  called 
the  tubercle  of  Rolando  (tuberculum  Eolandi).  A  thin  layer  of  white  matter,  com- 
posed of  longitudinally  arranged  fibres,  is  spread  over  this  district,  and  separates  the 
substantia  Eolandi  from  the  surface.  These  fibres  constitute  the  spinal  root  of  the 
fifth  or  trigeminal  nerve,  which  here  assumes  a  superficial  position  as  it  descends 
in  the  medulla. 

The  restiform  body  (corpus  restiforme)  forms  the  upper  part  of  the  posterior 
area  of  the  medulla.  It  lies  between  the  floor  of  the  fourth  ventricle  and  the 
roots  of  the  vagus  and  glosso-pharyngeal  nerves.  It  is  a  large  and  prominent 
rope -like  strand,  which  inclines  upwards  and  outwards,  and  then  finally  takes 
a  turn  backwards  and  enters  the  cerebellum.  It  forms  the  great  link  of  connexion 
between  the  cerebellum  on  the  one  hand  and  the  medulla  apd  spinal  cord 
on  the  other,  and  consequently  it  also  receives  the  name  of  the  inferior  cerebellar 
peduncle.  At  the  same  time  it  must  be  understood  that  it  is  not  formed  by  fibres 
which  are  prolonged  into  it  from  the  funiculus  cuneatus  and  funiculus  gracihs 
of  the  medulla.  It  is  true  that  a  surface  inspection  of  the  medulla  might  very 
naturally  lead  the  observer  to  this  supposition,  because  there  is  no  sharp  line  of 
demarcation  marking  it  off  from  the  tubercles  of  these  strands.  Such  a  conclusion, 
however,  would  be  altogether  erroneous,  because  it  would  appear  that  none  of  the 
filjres  of  the  posterior  columns  of  the  cord  are  carried  beyond  the  gracile  and  cuneate 
nuclei  of  the  medulla.  A  study  of  the  surface  of  the  medulla  yields  some  important 
information  regarding  the  constitution  of  the  restiform  body.  Thus  the  direct 
cerebellar  tract  from  the  lateral  column  of  the  cord  can  be  traced  into  it,  and  large 
numbers  of  fibres  which  take  a  curved  course  on  the  surface  of  the  medulla  may 
likewise  be  followed  into  it.  These  are  the  superficial  arcuate  fibres.  Numerous 
other  fibres  enter  the  restiform  body  on  its  deep  aspect,  but  these  will  be  studied 
at  a  later  stage. 

Superficial  Arcuate  Fibres  (fibrse  arcuatas  externae). — These  fibres  enter 
into  tlie  constitution  of  the  restiform  body,  and  they  may  be  regarded  as  con- 
sisting of  two  sets,  viz.  the  anterior  superficial  arcuate  fibres  and  the  posterior 
superficial  arcuate  fibres,  both  of  which  present  this  feature  in  common  that  they 
run  on  the  surface  of  the  medulla. 

The  anterior  superficial  arcuate  fibres  are  more  particularly  seen  in  the  neighbour- 
hood of  the  olivary  (jniincince,  round  the  lower  border  of  which,  and  also  over  the 
surface  of  which,  they  may  be  observed  coursing  in  the  form  of  a  number  of  coarse 
curvfid  bundles.  Tl)ey  vary  greatly  in  number  and  in  distinctness,  and  they  are 
RometimeH  so  numerous  as  to  cover  over  almost  entirely  the  eminence.  An  attentive 
examination  will  show  that  they  come  to  the  surface  in  the  antero-median  fissure 
between   the   pyramids,   and   also  not   un frequently  in    the   groove  between   the 


486  THE  NEEVOUS  SYSTEM. 

pyramid  and  olive,  or  through  the  substance  of  the  pyramid  itself.  The  antero- 
median fissure  in  its  upper  part  is  often  almost  completely  blocked  up  by  these 
emerging  fibres.  The  anterior  superficial  arcuate  fibres  reaching  the  surface  of  the 
medulla  in  this  manner  turn  backwards,  and  the  great  majority  enter  the  restiform 
body  and  form  a  considerable  part  of  its  outer  portion. 

The  posterior  superficial  arcuate  fibres  arise  in  the  cuneate  and  gracile  nuclei,  and 
enter  the  restiform  body  of  the  same  side. 

THE  PONS  VAROLII. 

The  pons  Varolii  is  a  marked  white  prominence  on  the  basal  aspect  of  the  brain 
which  is  interposed  between  the  medulla  and  the  crura  cerebri,  and  which  lies  in 
front  of  the  cerebellum.  It  is  convex  from  side  to  side,  as  well  as  from  above 
downwards,  and  transverse  streaks  on  its  surface  show  that,  superficially  at  least,  it 
is  composed  of  bundles  of  nerve-fibres  which  course  transversely  over  it.  On  either 
side  these  transverse  fibres  are  collected  together  in  the  form  of  a  large  compact 
strand,  which  sinks  in  a  backward  and  outward  direction  into  the  white  matter  of 
the  corresponding  hemisphere  of  the  cerebellum.  This  strand  is  termed  the  middle 
peduncle  of  the  cerebellum,  and  the  term  "pons,"  applied  to  the  entire  structure, 
expresses  in  an  admirable  way  the  arch-like  manner  in  which  this  portion  of  the 
brain  bridges  across  between  the  two  cerebellar  hemispheres. 

The  ventral  surface  of  the  pons  is  in  relation  to  the  basilar  process  of  the 
occipital  bone  and  the  dorsum  sellee  of  the  sphenoid  bone.  It  presents  a  mesial 
groove  (sulcus  basilaris),  which  gradually  widens  as  it  is  traced  upwards,  and  in 
which  the  basilar  artery  lies.  This  mesial  depression  is  produced  by  the  prominence 
which  is  caused  on  either  side  by  the  passage  of  the  pyramidal  tract  of  fibres 
downwards  through  the  pons.  The  trigeminal  or  fifth  cranial  nerve,  with  its  large 
entering  sensory  root  and  its  small  emerging  motor  root,  is  attached  to  the  side  of 
the  ventral  aspect  of  the  pons,  nearer  its  upper  than  its  lower  border.  It  is  usual 
to  restrict  the  term  "  pons  "  to  that  portion  of  the  structure  which  lies  between  the 
two  trigeminal  nerves,  and  to  apply  the  designation  of  middle  cerebellar  peduncle 
to  the  part  which  extends  beyond  the  nerve  into  the  hemisphere  of  the  cerebellum. 
The  sixth  or  abducent  nerve,  the  seventh  or  facial  nerve,  and  the  eighth  or  auditory- 
nerve  are  attached  to  the  brain  at  the  lower  border  of  the  pons.  The  sixth  emerges 
at  the  outer  border  of  the  pyramid,  the  seventh  immediately  in  front  of  the  resti- 
form body,  whilst  the  auditory  nerve  reaches  the  brain  close  to  the  facial  nerve,  on 
the  ventral  aspect  of  the  restiform  body. 

The  whole  of  the  medulla  enters  the  loicer  aspect  of  the  pons,  and,  with  the 
exception  of  the  restiform  bodies,  its  constituent  parts  are,  to  a  large  extent,  carried 
up  within  it.     The  crura  cerebri  emerge  from  its  upper  aspect. 

The  dorsal  surface  of  the  pons  looks  backwards  towards  the  cerebellum,  and 
presents  a  triangular  area  covered  with  gray  matter,  which  forms  the  upper  part  of 
the  anterior  wall  or  floor  of  the  fourth  ventricle.  This  area  is  directly  continuous 
below  with  the  medullary  part  of  the  floor  of  the  fourth  ventricle,  and  is  bounded 
on  either  side  by  a  band  of  white  matter  termed  the  superior  peduncle  of  the 
cerebellum. 

Superior  Cerebellar  Peduncles  (Ijrachia  conjunctiva). — Tliese  are  hidden  from 
view  by  the  upper  part  of  the  cerebellum,  under  cover  of  which  they  lie.  They 
emerge  from  the  lateral  hemispheres  of  the  cerebellum,  and,  as  they  proceed, 
upwards  on  the  dorsal  aspect  of  the  pons,  they  converge  towards  each  other  until, 
at  the  level  of  the  inferior  corpora  quadrigemina,  the  inner  margins  of  the  two 
peduncles  almost  become  contiguous  (Fig.  388,  p,  482).  At  first  they  form  the 
lateral  boundaries  of  the  upper  part  of  the  fourth  ventricle ;  but,  as  they  ascend 
and  approach  closer  to  each  other,  they  gradually  come  to  overhang  that  cavity 
and  thus  enter  into  the  formation  of  its  roof.  They  disappear  from  the  surface 
by  dipping  under  cover  of  the  quadrigeminal  bodies  and  entering  the  substance  of 
the  mesencephalon. 

Valve  of  Vieussens  or  the  Superior  Medullary  Velum  (velum  medullare 
anterius). — Filling   up   the   triangular   interval   between    the  two  superior  cere- 


THE  PONS  VAEOLII. 


487 


bellar  peduncles,  and  stretching  across  from  the  inner  and  free  margin  of  the  one 
to  the  corresponding  margin  of  the  other,  is  a  thin  layer  of  white  matter  which 
completes  the  roof  or  dorsal  wall  of  the  upper  part  of  the  fourth  ventricle,  and 
receives  the  name  of  the  superior  medullary  velum.  When  traced  downwards,  it 
is  seen  to  be  carried  with  the  superior  peduncles  into  the  white  matter  of  the  cere- 
bellum. fSpread  out  on  its  dorsal  surface  is  a  small,  thin,  tongue-shaped  prolongation 
of  gray  matter  from  the  cortex  of  the  cerebellum,  which  is  termed  the  lingula, 
whilst  issuing  from  its  substance  close  to  the  inferior  quadrigeminal  bodies  are  the 
two  fourth  or  trochlear  cranial  nerves. 

Fourth  Ventricle  of  the  Brain  (ventriculus  quartus). — The  fourth  ventricle  is 
somewhat  rhomboidal  in  form.  Below,  it  tapers  to  a  point  and  becomes  continuous 
with  the  central  canal  of  the  cord ;  above,  it  narrows  in  a  similar  manner  and  is 
continued  into  the  aqueduct  of  Sylvius,  which  tunnels  the  mesencephalon.  The 
posterior  wall  is  termed  the  roof  and  is  concealed  by  the  cerebellum.  The  anterior 
wall  is  called  the  floor  and  is  formed  by  the  dorsal  surfaces  of  the  medulla  and 
pons.  On  either  side  a  long,  curved  and  narrow  prolongation  of  the  ventricular 
cavity  is  carried  outwards  from  its  widest  part  and  curves  round  the  upper  part 
of  the  corresponding  restiform  body.  This  is  termed  the  lateral  recess.  The  roof 
of  the  cavity  is  very  thin  and  intimately  connected  with  the  cerebellum.  It 
is  better,  therefore,  to  defer  its  description  until  that  part  of  the  brain  has  been 
studied. 

Floor  of  the  Fourth  Ventricle  (fossa  rhomboidea). — In  its  lower  part  the 
floor  of  the  fourth  ventricle  is  formed  by  the  dorsal  surface  of  the  open  part  of  the 


Valve  of  Vieussens^ 
with  lingula 


Eminentia  teres  - 


Area  acustica 
crossed  by  strise- 
acustiCiE 

Fovea  inferior - 

Triffonuin  _ 
liypoglossi 


-  Inferior  quadrigeminal  body 

-  Fourth  nerve 


Superior  cerebellar 
peduncle 


-•Fovea  superior 

Middle  cerebellar 
'peduncle 
Superior  cere- 
bellar peduncle 

Inferior  cere- 
bellar peduncle 

-Striae  acusticaa 

-Area  acusticae 

•  Trigonum  vagi 
-Funiculus  separans 

""■f  'Area  postrema 

-  ~  Obex 

— Clava 


Funiculus  cuneatus 


Fio.  .391.— Fj.ooii  OF  THE  l''ouRTH  VENTRICLE.  Oil  the  riglit  side  the  right  liair  of  the  cerebellum  h;is  beeu 
removed  ],y  cutting  througli  its  three  peduncles  and  dividing  it  in  the  mesial  plane.  On  tlie  left  side 
the  left  half  of  the  cerebellum  is  drawn  over  to  the  left  so  as  to  expose  fully  tlie  floor  of  the  ventricle. 

medulla,  whilst  in  its  upper  part  it  is  formed  by  the  dorsal  surface  of  the  pons 
Varolii  (Fig.  388,  p.  482).  The  area  thus  constituted  is  lozenge-shaped,  its  widest 
part  being  opposite  the  upper  ends  of  the  restiform  bodies  or  inferior  peduncles 
of  the  cerebellum.  A  thick  layer  of  gray  matter,  continuous  with  that  which 
surrounds  the  central  canal  of  the  cord,  is  spread  out  like  a  carpet  over  the 
ventricular  floor,  and  covering  this  is  the  usual  ependymal  layer,  which  lines  all 
the  ventricles  of  the  brain.     The  area  is  circumscribed  by  definite  lateral  boundaries. 


488  THE  NEEVOUS  SYSTEM. 

Thus,  helow  it  is  bounded  on  either  side  by  the  clava,  the  cuneate  tubercle,  and 
the  restiform  body ;  whilst  above  the  lateral  limits  are  formed  by  the  superior 
cerebellar  peduncles. 

The  floor  of  the  fourth  ventricle  is  divided  into  two  lateral  and  symmetrical 
portions  by  a  median  groove.  Its  lower  narrow  pointed  portion  between  the  two 
clavae  receives  the  name  of  the  calamus  scriptorius,  from  its  fancied  resemblance  to 
the  point  of  a  pen.  Crossing  each  half  of  the  floor,  at  its  widest  part,  are  several 
more  or  less  conspicuous  bundles  of  flbres  termed  the  striae  acusticse.  They  appear 
to  emerge  from  the  mesial  groove  and  they  are  carried  outwards  over  the  floor  of 
the  ventricle  in  the  region  between  its  upper  pontine  and  lower  medullary  portions. 
The  strias  acusticce  exhibit  a  large  amount  of  variation  in  different  individuals  both 
in  their  degree  of  prominence  and  also  in  the  direction  which  they  pursue.  As  a 
general  rule  they  proceed  towards  the  upper  part  of  the  restiform  body,  where  they 
are  connected  with  the  cochlear  nuclei.  Except  for  this  break  on  the  surface,  the 
medullary  and  pontine  portions  of  the  floor  of  the  fourth  ventricle  are  quite 
continuous  with  each  other. 

On  the  lower  medullary  district  of  the  ventricular  floor  a  small  triangular 
depression,  placed  immediately  below  the  striae  acusticse,  catches  the  eye.  This  is 
termed  the  fovea  inferior.  It  is  shaped  somewhat  like  an  arrow-head.  The  apex 
or  point  looks  towards  the  strise,  whilst  the  lateral  angles  of  the  base  are  prolonged 
downwards  in  the  form  of  diverging  grooves  (Fig.  391,  p.  487).  Of  these,  the  inner 
groove  runs  towards  the  opening  of  the  central  canal  at  the  calamus  scriptorius, 
whilst  the  outer  groove  runs  towards  the  lateral  boundary  of  the  floor.  In  this 
manner  the  portion  of  the  floor  which  lies  below  the  strise  acusticse  is  mapped  out 
into  three  triangular  areas.  The  mesial  subdivision  is  slightly  elevated  and  is 
termed  the  trigonum  hypoglossi,  because  subjacent  to  the  inner  part  of  this  area  is 
the  nucleus  of  origin  of  the  hypoglossal  or  twelfth  cranial  nerve.  The  intermediate 
area  between  the  two  diverging  grooves  which  proceed  from  the  base  of  the  fovea 
inferior  is  the  trigonum  vagi  (ala  cinerea),  so  called  because  the  nucleus  of  the 
vagus  or  tenth  and  the  glosso-pharyngeal  or  ninth  cranial  nerves  lies  subjacent  to 
it.  The  external  area  is  the  trigonum  acustici.  The  base  of  this  area  is  directed 
upwards  and  runs  continuously  into  an  eminence — the  acustic  area  (area  acustica) 
— over  which  the  striae  acusticse  pass.  Subjacent  to  this  district  of  the  floor  of  the 
ventricle  lies  the  large  terminal  chief  nucleus  of  the  vestibular  division  of  the 
auditory  or  eighth  cranial  nerve. 

A  close  inspection  of  the  medullary  part  of  the  floor  of  the  fourth  ventricle  in  tlie  region  of 
the  calamus  scriptorius  will  show  that  the  base  of  the  trigonum  vagi  is  separated  from  the  inner 
margin  of  the  clava  by  a  narrow  lanceolate  strip  of  the  ventricular  floor,  to  which  Eetzius  has 
given  the  name  of  area  postrema.  Beneath  this  area  is  some  vascular  tissue  (Streeter),  and  mark- 
ing it  off  on  its  upper  and  inner  aspect  from  the  base  of  the  trigonum  vagi  there  is  a  translucent 
cord-like  ridge  called  the  funiculus  separans. 

When  the  floor  of  the  ventricle  is  examined  under  water  with  a  magnifying  glass,  the 
trigonum  hypoglossi  is  seen  to  consist  of  a  narrow  inner  strip  which  corresponds  to  the  hypo- 
glossal nucleus,  and  a  wider  lateral  part  which  has  been  shown  to  be  the  surface  representation 
of  another  nucleus  termed  the  nucleus  intercalatus  (Streeter). 

On  the  part  of  the  floor  of  the  ventricle  which  lies  above  the  striae  acusticae,  and 
which  corresponds  to  the  dorsal  surface  of  the  pons,  there  is  also  a  slight  depression 
termed  the  fovea  superior.  Between  it  and  the  median  groove  is  a  marked  pro- 
minence called  the  eminentia  teres.  Interiorly  this  elevation  passes  downwards 
and  becomes  continuous  with  the  trigonum  hypoglossi,  whilst  above  it  is  carried 
upwards  towards  the  opening  of  the  aqueduct  of  Sylvius.  In  both  directions  it 
becomes  gradually  less  prominent,  but  still  it  forms  a  distinct  elongated  elevation, 
which  stretches  along  the  whole  length  of  the  median  groove.  As  already  stated, 
the  area  acustica  extends  upwards  into  the  pontine  part  of  the  ventricular  floor  and 
forms  an  elevated  region  in  the  outermost  part  of  its  widest  portion,  below  and  to 
the  outer  side  of  the  fovea  superior.  Proceeding  upwards  from  the  fovea  superior 
to  the  opening  of  the  Sylvian  aqueduct  there  is  a  shallow  depression  termed  the 
locus  caeruleus,  seeing  that  it  usually  presents  a  faint  slate-gray  colour.  When  the 
ependyma  is  scraped  away  from  the  surface  of  this  part  of  the  floor,  the  colour  is 
seen  to  be  due  to  the  substantia  ferruginea, — a  name  applied  to  a  linear  group  of 


INTERNAL  STRUCTURE  OF  THE  MEDULLA. 


489 


strongly  pigmented  cells,  which  lies  in  the  lateral  part  of  the  gray  matter  covering 
this  portion  of  the  ventricular  floor.  When  transverse  sections  are  made  through 
the  upper  part  of  the  pons,  the  substantia  ferruginea  appears  on  the  cut  surface 
as  a  small  black  spot  or  dot. 


INTERNAL  STRUCTURE  OF  THE  MEDULLA. 

The  internal  structure  of  the  medulla  differs  in  a  marked  degree  from  that  of 
the  spinal  cord ;  indeed,  in  its  upper  part  it  presents  very  little  in  common  with  the 
latter.  The  various  strands  of  the  cord  either  come  to  an  end  within  the  medulla 
or  undergo  changes  in  their  relative  position,  whilst  the  gray  matter  is  much  modi- 
fied and  new  masses  are  added.  Like  the  cord,  however,  the  medulla  consists  of 
two  nearly  symmetrical  right  and  left  halves.  When  transverse  sections  are  made 
through  it  at  different  levels  each  lateral  half  is  seen  to  be  partly  marked  off  from 
the  other  in  the  lower  closed  part  of  the  medulla  by  the  anterior  and  posterior 
median  fissures,  whilst  in  the  upper  open  part  of  the  medulla  the  subdivision  is 
rendered  evident    in   transverse   sections    by   the  presence   of   a  distinct  median 


Funiculus  gracilis  Gracile  nucleus 


Funiculus  cuneatus 


Cuneate  nucleus 


.^r 


Spinal  root  of  trigeminal 
/  nerve 

__&ubstantia  gelatinosa 
^-•s'^'Rolandl 


Central  gray  mattei_ 


Central  canal 
Anterior  basis-bundle 


Pyramid 


NCrnssed  pyramidal  tract 


■^     Detached  head  of  anterior  horn  of 
gi  ay  matter 

I  Decussation  of  pyramids 

Pyramid 


Fig.  392. — Section  through  the  Lower  End  of  the  Meddlla  Oblongata  of  a  Chimpanzee 
TO  show  the  Decussation  of  the  Pyramids. 


line,  called  the  raphe,  which  occupies  the  mesial  plane.  The  raphe  is  formed  by  the 
close  intersection  of  fibres  running  in  different  directions  and  crossing  from  one  side 
to  the  other. 

Each  half  of  the  medulla  is  composed  of :  (a)  strands  of  white  matter ;  (5)  gray 
matter ;  and  (c)  the  formatio  reticularis. 

The  white  matter,  as  in  the  cord,  is  to  a  large  extent  disposed  on  the  surface,  and 
the  gray  matter  in  the  interior ;  but  in  the  upper  open  part  of  the  medulla  the  gray 
matter  comes  to  the  surface  on  the  dorsal  aspect,  and  is  spread  out  over  that  area 
which  forms  the  medullary  part  of  the  floor  of  the  fourth  ventricle.  In  the  cord 
the  white  matter,  in  the  shape  of  massive  longitudinal  strands  of  fibres,  forms  a 
thick  coating  round  the  central  gray  matter.  In  the  medulla  the  only  massive 
longitudinal  strands  which  are  seen  on  the  surface  are  the  gracile  and  cuneate 
strands  (until  tliey  become  absorbed  by  the  subjacent  nuclei),  the  inferior  cerebellar 
peduncles  or  restiforrn  bodies  and  the  pyramidal  tracts.  Elsewhere  the  coating  of 
white  matter  is  thin,  and  in  certain  yjlaces  is  composed  chiefly  of  the  superficial 
arcuate  fibres.  New  longitudinal  strands,  however,  take  shape  within  the  medulla, 
and  two  of  the  most  important  are  placed  on  either  side  of  the  median  raphe. 

The  gray  matter  ol'  the   cord,  as  it  is  continued   upwards  into   the  medulla, 


490  THE  NEEVOUS  SYSTEM. 

becomes  greatly  modified.  A  considerable  part  of  it  is  broken  up  in  the  formatio 
reticularis,  whilst  the  only  portions  which  remain  as  compact  masses  in  direct 
continuity  with  the  gray  matter  of  the  cord  are :  (1)  the  thick  layer  which 
surrounds  the  central  canal,  and  which,  in  the  open  part  of  the  medulla,  becomes 
spread  out  on  the  floor  of  the  fourth  ventricle ;  and  (2)  the  substantia  gelatinosa 
liolandi.  New  masses  of  gray  matter,  whicli  are  not  represented  in  the  cord,  and 
which  in  some  cases  appear  in  isolated  clumps,  are  also  added.  The  chief  of  these 
are  the  gracile  and  cuueate  nuclei,  the  inferior  olivary  nuclei,  and  the  arcuate  or 
pyramidal  nuclei. 

The  formatio  reticularis  is  only  feebly  represented  in  the  cord,  Ijut  in  the 
medulla  it  forms  a  very  considerable  part  of  its  bulk.  It  is  composed  of  gray 
matter  coarsely  broken  up  Ijy  fibres,  which  traverse  it  in  different  directions. 

In  the  following  detailed  account  of  the  internal  structure  of  the  medulla,  it 
must  be  understood  that  the  appearances  described  are  such  as  are  seen  when 
successive  transverse  sections  through  the  bulb  are  examined. 

Decussation  of  the  Pyramids  and  the  Changes  produced  thereby. — As  we 
pass  under  the  microscope  a  series  of  successive  transverse  sections  through  the 
upper  end  of  the  cord  and  the  lower  end  of  the  medulla,  the  most  striking  change 
which  meets  the  eye  is  the  decussation  of  the  pyramids.  The  crossed  pyramidal 
tract  in  the  lateral  column  of  the  cord  is  seen  to  become  looser  in  its  formation ; 
then  coarse  strands  leave  it,  pass  right  through  the  anterior  horn  of  gray  matter, 
and,  crossing  the  mesial  plane,  take  up  their  position  in  the  other  side  of  the 
medulla,  close  to  the  antero-median  fissure.  Strands  from  the  right  crossed 
pyramidal  tract  alternate  with  corresponding  strands  from  the  left  side,  and  the 
interval  between  the  bottom  of  the  antero-median  furrow  and  the  gray  matter 
surrounding  the  central  canal  becomes  filled  up  with  a  great  mass  of  intercrossing 
bundles  of  fibres.  When  the  decussation  is  completed  the  pyramid  is  seen  to  be 
composed  of  a  solid  and  compact  bundle  of  fibres,  well  marked  off  from  the 
surrounding  structures,  which  lies  at  the  side  of  the  antero-median  fissure  of  the 
medulla. 

As  a  rule  the  inner  three-fourths  of  the  pyramid  is  composed  of  fibres  which,  lower 
down  in  the  opposite  lateral  column  of  the  cord,  form  the  crossed  pyramidal  tract,  whilst 
che  outer  fourth  of  the  pyramid  proceeds  downwards  in  the  anterior  column  of  the  cord  of 
the  same  side  as  the  direct  pyramidal  tract.  A  considerable  amount  of  variation,  however, 
occurs  in  the  proportion  of  fibres  which  is  allotted  to  the  formation  of  these  two  tracts  of 
the  cord.  Sometimes  the  crossed  pyramidal  tract  is  much  larger  than  usual,  and  then 
the  direct  pyramidal  tract  suffers  a  corresponding  diminution  in  size.  Cases  indeed  occur 
in  which  the  entire  pyramid  enters  into  the  decussation,  and  in  these  there  is  no  direct 
pyramidal  tract  in  the  cord.  Further,  it  is  not  uncommon  to  meet  Avith  variations  of  an 
opposite  kind  which  lead  to  an  increase  of  the  direct  pyramidal  tract  at  the  expense  of  the 
crossed  tract.  In  the  majority  of  cases  the  decussation  appears  to  be  symmetrical — the 
division  of  the  pyramid  at  the  lower  end  of  the  medulla  being  into  parts  of  corresponding 
size  on  the  two  sides ;  in  certain  instances,  however,  the  decussation  is  asymmetrical,  and 
the  corresponding  pyramidal  tracts  on  ojjj^osite  sides  of  the  cord  are  then  unequal  in  size. 
Seeing  that  the  direct  pyramidal  tracts  undergo  a  gradual  decussation  in  the  anterior 
commissure,  as  they  descend  in  the  cord,  the  final  result  is  the  same,  no  matter  what 
variations  occur  in  the  decussation  at  the  lower  part  of  the  medulla. 

The  variations  indicated  above  receive  an  additional  interest  Avhen  viewed  in  the  light 
of  comparative  anatomy.  It  would  appear  that  only  in  man  and  the  anthropoid  apes  is 
the  decussation  of  the  pyramids  in  the  lower  part  of  the  medulla  incomplete.  According 
to  Sherrington,  a  direct  pyramidal  tract  in  the  cord  of  the  anthropoid  apes  stands  in  con- 
nexion with  the  arm-centre  in  the  cerebral  cortex.  If  this  be  the  case  in  man  it  must  like- 
wise have  other  connexions  as  well,  seeing  that  it  is  carried  doM'u  the  cord  for  a  considerable 
distance  beyond  the  level  of  the  cord-segments  which  give  motor  fibres  to  the  arm.  In 
the  lower  apes  a  direct  pyramidal  tract  does  not  seem  to  exist :  the  whole  pyramid  crosses 
over  to  the  opposite  side  of  the  cord  in  the  shape  of  the  crossed  pyramidal  tract. 

As  we  have  noted,  the  decussating  pyramidal  bundles  pass  through  the  anterior 
horn  of  gray  matter  of  the  cord,  and  cut  it  into  two  portions  (Figs.  392  and  395). 
The  basal  part  remains  in  position  on  the  anterior  and  lateral  aspect  of  the  central 
canal,  and  forms  part  of  the  thick  layer  of  gray  matter  which  surrounds  it.     The 


INTERNAL  STEUCTURE  OF  THE  MEDULLA. 


491 


Gracile  nucleus 


Funiculus 

cuneatus 

Spinal  root 
of  fifth  nerve 


detached  head  of  the  anterior  horn  is  set  free ;  and  from  the  large  multipolar  cells 
which  lie  in  its  midst  some  of  the  fihres  of  the  anterior  root  of  the  first  cervical 
nerve,  and  also  some  of  the  root  fibres  of  the  spinal  accessory  nerve,  take  origin. 

On  proceeding  up  into  the  medulla  another  effect  of  the  decussation  of  the 
pyramids  is  seen  in  the  submergence  from  the  surface  of  the  strand  of  fibres  which, 
in  the  anterior  column  of  the  cord,  lies  to  the  outer  side  of  the  direct  pyramidal 
tract,  and  which  receives  the  name  of  the  anterior  basis-bundle.  While  tlie  decus- 
sation is  going  on  the  anterior  basis-bundle  is  thrust  aside,  and,  sinking  from  the 
surface,  it  takes  up  its 

"^^^z  ii      "^  "^ — 5^ — Funiculus  ^lacilis 


position  as  a  flattened 
band -like  strand  on 
the  outer  side  of  the 
gradually  increasing 
pyramid  (Fig.  393). 
When  the  decussation 
is  completed,  this 
strand  is  seen  to  lie 
close  to  the  median 
plane  on  the  dorsal 
aspect  of  the  pyramid, 
where  it  is  separated 
from  its  fellow  of  the 
opposite  side  by  the 
median  raphe  alone 
(Fig.  394).  In  the 
upper  part  of  the 
medulla  it  approaches 
still  nearer  to  the 
dorsal   surface   and    appears 


Decussation  o^ 
pyramids 


Detached  head 
of  anterior 
cornu 


Anterior  basis- 
bundle 


Fig.  393. 


THE  Medulla 


Antero-median  furrow 

Transverse  Section  through  Lower  End 
of  a  full-time  fcetus, 

Treated  by  the  Weigert-Pal  method.     The  gray  matter  is  bleached  white,  and 
the  medullated  tracts  of  fibres  are  blaclc. 


to  form  the  greater  part  of  a  strand,  which  is 
termed  the  posterior  longitudinal  bundle  (Figs.  397  and  398).  The  detached  head 
of  the  anterior  horn  of  gray  matter  of  the  cord,  as  it  is  traced  upwards,  is  observed 
to  cling  closely  to  its  original  relationship  with  the  anterior  basis-bundle.  It  is 
applied  to  the  outer  side  of  this  strand,  and,  gradually  becoming  smaller,  finally 
disappears  at  the  level  of  the  lower  part  of  the  inferior  olivary  nucleus. 

Cuneate  and  Gracile  Strands,  with  their  Nuclei. — As  the  funiculus  gracilis 
and  the  funiculus  cuneatus  of  the  posterior  column  of  the  cord  are  traced  up 
into  the  medulla  they  seem  to  increase  in  bulk,  and  in  transverse  sections  they 
assume  the  form  of  massive  wedge-shaped  strands,  quite  distinct  from  each  other. 
When  the  decussation  of  the  pyramids  is  fully  established  they  change  their  shape. 
They  increase  in  width  and  lose  considerably  in  depth,  and  consequently  the 
transverse  diameter  of  the  area  which  they  occupy  becomes  greater.  As  a  result 
of  this,  and  also  owing  to  the  removal  of  the  crossed  pyramidal  tract  from  the 
lateral  region  of  the  cord  immediately  in  front,  the  posterior  horn  of  gray  matter 
is  gradually  rotated  forwards  and  comes  to  lie  transversely  and  in  the  same  straight 
line  with  its  fellow  of  the  opposite  side  (Figs.  393  and  395).  The  substantia 
gelatinosa  Eolandi,  at  the  same  time,  becomes  increased  in  quantity  and  presents 
a  horseshoe-shaped  outline  in  transverse  section.  It  clasps  within  its  concavity  the 
somewhat  reduced  head  of  the  posterior  horn,  and  forms  with  it  a  conspicuous 
circular  mass  of  gray  matter  which  lies  close  to  the  surface,  and  produces  upon  it 
the  bulging  termed  the  funiculus  and  tubercle  of  Rolando.  Tlie  basal  portion  of 
the  posterior  horn  of  gray  matter  remains  upon  the  dorsal  and  lateral  aspect  of  the 
central  canal,  and  forms  a  portion  of  the  central  gray  mass  of  the  closed  part  of 
the  medulla;  but  very  soon  the  neck  of  the  horn,  which  at  this  level  is  greatly 
reduced  owing  to  the  aljsence  of  entering  posterior  nerve-roots,  is  invaded  by 
bundles  of  fibres  which  traverse  it  in  different  directions  and  convert  it  into  a 
formatio  reticularis,  iiy  tliis  means  the  rounded  head  of  the  posterior  horn  l)ecomes 
cut  off  from  the  central  gray  matter,  and  from  this  point  upwards  it  remains  as 
an  isolated  gray  column  iiitima,tely'aHsociated  with  the  spinal  root  of  the  trigeminal 
nerve. 


492 


THE  NEEVOUS  SYSTEM. 


The  gracile  and  cuneate  nuclei  take  shape  before  the  decussation  of  the  pyramids 
is  fully  completed  (Fig.  395).  The  gracile  nucleus  appears  in  the  form  of  a  small 
irregular  mass  of  gray  matter  in  the  interior  of  the  funiculus  gracihs,  which 


Funiculus  gracilis 

Gracilp  nuclpus 

r  miculns  cuneatns 

Cuneate  nucleus 


Central  canal 


Internal  arcuate      ^  ''^* 
fibres 


Anterior  basis- 
bundle 

Decussation  of      \ 
fillet 


Inferior 
olivary  nucleus 


Mesial  olivary 
nucleus 


Pyramid 


Arcuate  nucleus  covered 
superficially  by  anterior 
superficial  arcuate  fibres 


Fig.  .394. 


-Section  through  the  Closed  Part  of  Human  Medulla  immediately  above  the 
Decussation  of  the  Pyramids  (Weigert-Pal  Sijecimen). 


Cuneate  nucleus 


Gracile  nucleus 


gradually  infiltrates  the  entire  strand.  At  first  it  is  not  directly  connected  with 
the  gray  matter  which  surrounds  the  central  canal ;  but  as  it  is  traced  upwards 
it  increases  in  bulk,  absorbs  more  of  the  strand  in  which  it  lies,  and  such  a  con- 
nexion becomes  established  (Figs.  393  and  394). 

The  cuneate  nucleus,  from  the  first,  is  a  direct  offshoot  from  that  part  of  the  base 

of  the  posterior  horn  of  gray 
matter  which  is  preserved  as  a 
portion  of  the  central  gray  mass. 
In  transverse  section  it  is  seen  to 
invade  the  funiculus  cuneatus 
Roiandi*"^  ^^^^*'°°*^  upon  its  dccp  aspect,  and  it 
Direct  cerebellar  tract  gradually  grows  backwards  into 
its  substance.  It  presents  a  very 
different  appearance  from  the 
gracile  nucleus,  because  through- 
out its  whole  length  the  gray 
nucleus  and  the  fibres  of  the 
strand  are  separated  from  each 
other  by  a  sharp  line  of  demarca- 
tion. A  second  and  much  smaller 
mass  of  gray  matter  appears  in 
the  funiculus  cuneatus,  super- 
ficial to  the  main  nucleus,  soon  after  the  region  of  the  decussation  of  the  pyramids 
is  left.     This  is  termed  the  accessory  or  the  external  cuneate  nucleus  (Fig.  394). 

Gradually  the  fibres  of  the  gracile  and  cuneate  strands  become  absorbed  in  these 
nuclei.  As  the  gray  masses  gain  in  size  a  corresponding  diminution  in  the  number 
of  fibres  composing  the  corresponding  tracts  is  observed,  until,  at  the  level  of  the 
clava  and  cuneate  tubercles,  it  is  seen  that  these  eminences  are  composed  almost 


Cuneate  nucleus 
Spinal  I'oot  of  fifth 
nerve 


Crossed  pyramidal 
tract 


Detached  anterior 
horn  of  gray  matter 

Decussation  of 
pyramids 


Anterior  basis-bundle 
Fig.  395. — Section  through  the  lower  part  of  the 
Medulla  of  the  Orang. 


INTEKNAL  STRUCTUEE  OF  THE  MEDULLA. 


493 


entirely  of  the  gray  nuclei,  covered  by  a  thin  skin  of  the  few  remaining  fibres  of 
the  two  strands  involved.  It  would  appear  that  no  fibres  belonging  to  the  funiculus 
gracilis  and  funiculus  cuneatus  get  beyond  these  nuclei.  They  all  end  in  fine 
terminal  ramifications  around  the  cells  of  the  nuclei.  In  the  case  of  the  funiculus 
cuneatus  the  bundles 


of    fibres, 
pass   from 


Funiculus 

Funiculus 
ounpatus 

Spinal 
root  of  fifth— ^ 
ner^  e   /, 

Forniatio  |- 
reticulari  ^ 
\i 
Direct  cere 
bellar  tract 


(  rdcile  nucleus 


Lower  end 
of  olivary 
eminence 


Cuneate 
nucleus 


Substantia 
gelatinosa 
Rolandi 

Decussation  of 
fillet 


Mesial 

accessory 

olivaiy  nucleus 
Fascicles  of 
hypoglossal 
nerve 


Pyramid 


Fig.  396. — Transverse  Section  through  the  Closed  Part  of  a  Fcetal 
Medulla,  immediately  above  the  Decussation  of  the  Pyramids. 

Treated  by  Weigert-Pal  method. 


Graoile  nucleus 


as  they 
the  sur- 
face into  the  sub- 
jacent gray  nucteus, 
are  very  distinctly 
seen  in  transverse 
sections  through  the 
medulla. 

When  the  med- 
ulla oblongata  opens 
up  into  the  fourth 
ventricle  the  gracile 
and  cuneate  nuclei 
are  pushed  outwards 
by  the  expanding 
ventricular  floor,  and 
the  gracile  nucleus 
soon  comes  to  an 
end;  but  the  cuneate 

nucleus  extends  upwards  for  a  short  distance  farther,  and  only  terminates  when 
the  restiform  body  begins  to  take  definite  shape  on  its  outer  aspect. 

Decussation  of  the  Fillet  (decussatio  lemniscorum). — Immediately  above  the 
level  of  the  decussation  of  the  pyramids  another  decussation  of  fibres  in  the  median 
plane,  and  upon  the  dorsal  aspect  of  the  pyramids,  takes  place  in  the  substance  of 

the  medulla.  This 
is  termed  the  decus- 
sation of  the  fillet, 
or  the  sensory  de- 
cussation, in  contra- 
distinction to  the 
term  "  motor  decus- 
sation," which  is 
sometimes  applied 
to  the  decussation 
of  the  pyramids. 
The  fibres  which 
take  part  in  this 
decussation  are 
called  deep  arcuate 
fibres  (fibrse  arcuatse 
internse),  and  they 
are  derived  from 
the  cells  of  the 
gracile  and  cuneate 
nuclei.  From  the 
deep  aspects  of  these 
nuclei  these  fibres 
stream  forwards  and 
inwards  towards  the 
median  raphe,  form- 
ing a  series  of  con- 
centric curves  in  the  substance  of  the  medulla.  They  cross  the  mesial  plane 
and  decussate  with  the  corresponding  fibres  of  the  opposite  side,  upon  the  dorsal 
aspect  of  the  pyramids.     Having  thus  gained  the  opposite  side  of  the  medulla  they 


Cuneate  strand- 


Cuneate  nucleus 


Fasciculus  solitarius 

Spinal  root  of. 

trigeminal  nerve 

Substantia 

gelatinosa  Rolandi 

Deep  arcuate  fibres 
Hypoglossal  nerve 


Anterior  superficial 
arcuate  fibres 


Inferior  olivary 
nucleus 


Mesial  accessory, 
olivary  nucleus 

i'yramid 


Central  canal 


Hypoglossal 

/<^5>V1  nucleus 

^  .  Posterior 
.^l  longitudinal 
fasciculus 

Hypoglossal 
nerve 


Raphe 


Fillet 


Superficial 
anterior 
arcuate  fibres 


Fir;.  397. — Tuansvekse  Section  through  the  Human  Medulla  in  the 
Lower  Olivary  Region. 


494  THE  NEEVOUS  SYSTEM. 

immediately  turn  upwards  and  form  a  conspicuous  strand  of  longitudinal  fibres, 
which  ascends  close  to  the  mesial  plane  and  is  separated  from  its  fellow  of  the 
opposite  side  by  the  median  raphe  alone.  This  strand  is  termed  the  fillet  or 
lemniscus. 

As  we  proceed  ;ip  the  medulla  the  deep  arcuate  fibres  which  first  come  into  sight 
ajDpear  as  coarse  buudles  which  curve  forwards  in  a  narrow  group  around  the  central  gray 
matter  (Figs.  39-i  and  396).  Soon  other  finer  bundles  appear,  which  describe  wider  curves 
on  the  outer  side  of  the  coarser  group  until  a  very  large  part  of  each  lateral  half  of  the 
medulla  is  seen  to  be  traversed  by  these  arcuate  fasciculi  (Fig.  397).  As  they  approach 
the  mesial  plane  they  come  in  contact  with  the  remains  of  the  anterior  basis-bundle, 
which  at  this  level,  as  already  mentioned,  lies  upon  the  dorsal  aspect  of  the  yjyramid, 
flattened  up  against  the  raphe.  The  deep  arcuate  fibres  pierce  the  anterior  basis-bundle 
obliquely,  and  in  the  interval  between  it  and  the  corresponding  strand  of  the  opposite  side 
they  decussate  in  the  middle  line  with  the  deep  arcuate  fibres  of  the  opposite  side.  They 
then  change  their  direction  and  tiirn  upwards,  and  the  fillet,  as  already  stated,  takes 
form  and  gradually  increases  in  volume  as  it  ascends.  This  great  and  important  ti'act  is 
thus  laid  down  between  the  pyramid  and  the  anterior  basis-bundle ;  and  the  consequence 
of  this  is  that  the  latter  tract  is  pushed  still  farther  backwards,  and,  when  the  fillet  is 
fully  established,  it  comes  to  lie  immediately  beneath  the  gray  matter  of  the  floor  of  the 
fourth  ventricle  (Fig.  398). 

It  is  important  that  we  should  realise  at  this  stage  the  full  significance  of  the  decussation 
of  the  fillet  and  have  a  clear  conception  of  the  connexions  of  the  fibres  which  take  part  in  it. 
The  columns  of  Burdacli  and  GoU,  which  end  in  the  cuneate  and  gracile  nuclei,  are  derived  from 
the  jjosterior  roots  of  the  spinal  nerves.  The  fillet  fibres  therefore  carry  on  the  continuity  of  the 
posterior  columns  of  the  cord,  the  gracile  and  cnneate  nuclei,  which  are  thrown  across  their  j^ath 
in  the  lower  part  of  the  medulla,  merely  constituting  an  internodal  interruption.  At  this  j)oint 
the  fillet  strand  is  transferred  to  the  ojDjDosite  side  of  the  medulla.  But  it  will  be  remembered 
that  a  large  proportion  of  the  fibres  of  the  entering  posterior  nerve-toots  of  the  spinal  nerves  end 
in  connexion  with  the  cells  of  the  jjosterior  hom  of  gray  matter  of  the  cord.  It  must  not  be 
supposed  that  the  path  represented  by  these  latter  fibres  comes  to  a  termination  thereby ;  from 
these  23osterior  horn  cells  other  fibres  arise  which  cross  to  the  opposite  side  of  the  cord  in  the 
anterior  white  commissure  and  proceed  up  the  cord  to  the  lateial  part  of  the  medulla.  These 
fibres  constitute  the  spino-thalamic  tract  already  referred  to.  The  practical  bearing  of  this  is 
that  owing  to  the  crossing  of  the  fillet  and  lower  down  of  the  spino-thalamic  tract  unilateral 
lesions  of  the  medulla  are  apt  to  produce  complete  henii-anpesthesia  ;  whilst  unilateral  lesions  of 
the  cord  produce  only  r>artial  hemi-anaesthesia. 

When  the  fillet  is  fully  formed  three  longitudinal  strands  are  observed  travers- 
ing the  medulla,  close  to  the  mesial  plane.  From  before  backwards  these  are  :  (1) 
the  pyramid,  (2)  the  fillet,  and  (3)  the  posterior  longitudinal  bundle. 

The  pyramid  forms  a  massive  tract  in  front  of  and  quite  distinct  from  the 
fillet.  The  fillet  and  the  posterior  longitudinal  bundle  are,  in  the  first  instance, 
not  marked  off  from  each  other.  They  appear  as  a  broad  flattened  band  applied 
to  the  raphe.  One  edge  of  this  band  is  directed  backwards  and  reaches  the  gray 
matter  on  the  floor  of  the  fourth  ventricle,  while  the  other  edge  looks  forwards, 
and  is  in  contact  with  the  pyramid.  In  the  upper  part  of  the  medulla  the  fillet 
and  the  posterior  longitudinal  fasciculus  begin  to  draw  asunder  from  each  other. 
The  intermediate  longitudinal  fibres  become  reduced  in  number  and  the  two 
strands  grow  denser — the  one  on  the  dorsal  aspect  of  pyramid,  and  the  other 
immediately  beneath  the  gray  matter  of  the  floor  of  the  fourth  ventricle  (Fig.  398). 

The  posterior  longitudinal  bundle  (fasciculus  longitudinalis  medialis)  is  thus 
largely  formed  out  of  fibres,  which  in  the  cord  constitute  the  anterior  basis-bundle. 
These  fibres  are  thrust  back  by  the  two  decussations :  the  first  decussation  pushing 
them  behind  the  pyramids,  and  the  second  decussation  displacing  them  still  farther 
backwards  to  a  position  behind  the  fillet. 

Olivary  Nuclei. — The  most  conspicuous  of  the  isolated  clumps  of  gray  matter 
in  the  medulla  are  the  inferior  olivary  nucleus  and  the  two  accessory  olivary 
nuclei.  The  inferior  olivary  nucleus  (nucleus  olivaris  inferior)  lies  subjacent  to  the 
olivary  eminence,  and  constitutes  a  very  striking  object  in  transverse  sections 
through  this  region.  It  presents  the  appearance  of  a  thick  wavy  or  undulating  line 
of  gray  matter,  folded  on  itself,  so  as  to  enclose  a  space  filled  with  white  matter. 
It  is  in  reality  a  crumpled  lamina  arranged  in  a  purse-like  manner,  with  an  open 


INTERNAL  STRUCTURE  OF  THE  MEDULLA. 


495 


mouth  or  slit,  which  is  called  the  hilum  (hiluin  nuclei  olivaris).  directed  towards  tlie 
mesial  plane.     The  hilum  does  not  reach  either  extremity,  so  that  in  transverse 


Eestiform  body 


Vago- 
glossopharyngeal 
roots 


Nucleus  of  tlie 
fasciculus  solitarius 


Vagus  nucleus 

Fasciculus  solitarius 

/        Dpscending  root  of  vestibular 
neive  (VIII.) 

Vago-glossopharyngeal  roots 


Posterior  longitudinal 

fasciculus 

Substantia  gelatinosa 

Roland  i 

Spinal  root  of  fifth  nerve 

Xucleus  ambiguus 


^Ceiebello-olivary  fibres 
—  Doisal  accessory  olivary  nucleus 

\uteiioi  superficial  arcuate  fibres 

I  illet 

Mesial  accessory  olivary  nucleus 

Interior  olivary  nucleus 


-  Pyramid 
Arcuate  nucleus 


— Anterior  supeificial  arcuate  fibres 


Fig.  398. — Transverse  Section  through  the  Middle  of  the  Olivary  Region  op  the  Human  Medulla 

OR  Bulb. 

The  floor  of  the  fourth  ventricle  is  seen,  and  it  will  be  noticed  that  the  restiform  body  on  each  side  has 

now  taken  definite  shape. 

sections  through  each  end  of  the  nucleus  the  gray  lamina  is  seen  in  the  form  of  a 
completely  closed  capsule.  Into  and  out  of  the  open  mouth  of  the  olivary  capsule 
streams  a  dense  crowd  of  fibres.     These  constitute  what  is  called    the   olivary 

peduncle. 

The  accessory  olivary 
nuclei  are  two  band-like 
laminfe  of  gray  matter,  which 
are  respectively  placed  on  the 
dorsal  and  mesial  aspects  of 
the  main  nucleus.  In  trans- 
verse section  each  of  these 
nuclei  presents  a  rod  -  like 
appearance  (Fig.  398). 

The  mesial  accessory  oli- 
vary nucleus  (nucleus  olivaris 
accessorius  mesialis)  extends 
lower  down  in  the  medulla  than 
the  main  nucleus,  and  it  is  much 
larger  in  its  lower  than  its  upper 
part.  It  begins  immediately 
above  the  decussation  of  the 
pyramids,  where  it  is  seen  lying 
on  the  outer  side  of  the  pyramidal  tract  and  the  anterior  basis-bundle  (Figs.  394  and  396). 
Higlicr  up  it  lies  across  the  month  of  the  main  nucleus  and  on  the  outer  side  of  the  fillet 
The  dorsal  accessory  olivary  nucleus  (nucleus  olivaris  accessorius  dorsalis)  is  placed 
close  to  the  (hji'Siii  jispect  of  tlie  main  micleus.  The  two  accessory  nuclei  fuse  together 
before  they  finally  disappear. 

The  gray  matter  forming  tiie  throe  iwl'crior  olivjury  nuclei  consists  of  a  close  feltwork 
"of  iieun)glia  in  which  are  interspersed  numerous  small  round  cells,  each  of  which  is 
provided  with  one  axon  and  numerous  dendritris.     Ti  is  ti'aversed  by  fibres,  some  of  which 


i99. — The  Inferior  (jr.iVAuy  Nucleus,  as  reconstructed  and 
figureil  by  Miss  Florence  R.  Sabin. 

View  of  tlie  dorso-lateral  and  lateral  surfaces. 


496 


THE  NEEVOUS  SYSTEM. 


.GRACILENUCL. 

CUNEATENUCL. 


Fig.  400. — Diagram, 

Wliicli  shows  in  part  the  fibres  which  enter  into 
the  constitution  of  the  restiform  body. 


jxiss  straight  through  the  gray  lamina,  whilst  others  end  in  connexion  with  the  cells.  It 
is  only  in  man  and  the  higher  apes  that  the  inferior  olivary  nuclei  are  found  strongly 
developed.  In  other  mammals  they  are  much  smaller.  The  size  of  the  olive  appears  to 
be  correlated  with  that  of  the  lateral  hemisphere  of  tlie  cerebellum  and  not  in  any  way  to 
be  dependent  on  the  development  of  the  cerebral  hemisphere.  Thus  in  cetacea  with  a 
very  extensive  cerebral  cortex  the  inferior  olivary  nuclei  are  small  (Edinger). 

As  the  fibres  of  the  fillet  decussate  and  assume  a  longitudinal  direction  they 

come  to  lie  between  the  olivary  nuclei  of 
opposite  sides,  and  hence  the  term  inter- 
olivary  stratum  (stratum  interolivare  lem- 
nisci)  is  frequently  applied  to  them. 

Restiform  Body  (corpus  restiforme). — 
The  gracile  and  cuneate  nuclei  gradually  give 
place  to  the  restiform  body  in  the  upper  part 
of  the  posterior  district  of  the  medulla.  Fibres 
from  various  quarters  converge  to  form  this 
great  strand.  It  first  takes  shape  as  a  thin 
superficial  layer  of  longitudinal  fibres,  which 
are  gathered  together  on  the  outside  of  the 
cuneate  nucleus ;  but  after  that  nucleus  has 
come  to  an  end,  and  as  the  upper  part  of  the 
medulla  is  reached,  the  restiform  body  is 
seen  to  have  grown  into  a  massive  strand, 
which  presents  a  kidney-shaped  or  oval  out- 
line on  transverse  section  (Eig.  398),  and 
which  ultimately  enters  the  white  central 
core  of  the  cerebellum  as  its  inferior  peduncle.  The  fibres  which  build  up  the 
restiform  body  are  the  following :  (1)  the  direct  cerebellar  tract ;  (2)  the  posterior 
superficial  arcuate  fibres ;  (3)  the  anterior  superficial  arcuate  fibres ;  and  (4) 
cerebello-olivary  fibres. 

The  direct  cerebellar  tract  extends  upwards  from  the  lateral  column  of  the  cord. 
In  the  lateral  district  of  the 
medulla  it  occupies  a  similar 
position  ;  but  before  the  olivary 
eminence  is  reached  it  inclines 
backwards,  crosses  the  postero- 
lateral furrow  and  passes  ob- 
liquely upwards  into  the  resti- 
form body.  As  its  fibres  diverge, 
backwards  they  pass  over  the 
tubercule  of  Eolando  and  cover 
up  the  spinal  root  of  the  tri- 
geminal nerve  and  the  substantia 
Eolandi,  thus  shutting  them  out 
from  the  surface.  The  fibres 
of  the  direct  cerebellar  tract 
in  the  first  instance  enter  into 
the  outer  or  superficial  part  of 
the  restiform  body. 

Bruce  has  shown  that  the  fibres  of  the  direct  cerebellar  tract  ultimately  lie  in  the  centre  of  the 
restiform  body,  forming  as  it  were  its  central  core,  and  that  in  the  cerebellum  they  can  be  traced 
to  the  superior  vermis. 

The  posterior  superficial  arcuate  fibres  take  origin  from  the  gracile  and  cuneate 
nuclei,  and  enter  the  superficial  part  of  the  restiform  body  of  the  same  side. 

The  anterior  superficial  arcuate  fibres  proceed  from  the  lower  portions  of  the 
gracile  and  cuneate  nuclei  of  the  opposite  side.  After  decussating  in  the  middle 
line,  it  can  easily  be  determined  that  all  the  deep  arcuate  fibres  which  arise  from 
these  nuclei  do  not  enter  the  fillet.  A  large  proportion  of  them  gain  the  surface  by' 
sweeping  round  the  inner  aspect  of  the  pyramid  in  the  antero-mesial  fissure.     Many 


Funicnlus  gracilis 

Gracile  nucleus 


Funiculus  cuneatus 


Substantia  gelatinosa 
Rolandi' 

Spinal  root  of 
trigeminal  nerve' 

Direct  cerebellar 
tract 

Crossed  pyramidal 
tract 


Decut.1 


till  c  mil 
ilien  ul  1  \iainids 


Detached  anterior  liorn  of  graj'  matter 

Fig.  401. — Section   through   the   Junction   between 
THE  Cord  and  Medulla  of  the  Orang. 

The  direct  cerebellar  tract  is  well  seen,  especially  on  the  right  side. 


INTERNAL  STRUCTURE  OF  THE  MEDULLA. 


497 


of  them  likewise  gain  the  surface  by  piercing  the  pyramid  or  by  passing  out 
between  it  and  the  olive.  These  fibres  constitute  the  anterior  superficial  arcuate 
group,  and  on  the  surface  of  the  medulla  they  sweep  backwards  around  it,  forming 
a  tliin  layer  over  the  olivary  eminence  and  ultimately  reaching  the  restiform  body. 
The  anterior  superficial  arcuate  fibres,  as  well  as  the  direct  cerebellar  tract-fibres, 
cover  over  the  trigeminal  spinal  root,  which  thus  comes  to  take  up  a  deeper  posi- 
tion in  the  substance  of  the  medulla  (Figs.  397  and  398). 

Amongst  the  fibres  which  reach  the  surface  of  the  medulla  in  this  way  KoUiker  includes 
fibres  from  the  striae  acusticte.  If  this  be  the  case,  these  fibres  connect  the  cochlear  nucleus 
with  the  cerebellum,  the  path  being  striae  acusticae,  superficial  arcuate  fibres,  and  restiform 
body  {vide  p.  522). 

The  fibres  of  the  direct  cerebellar  tract,  which  come  from  the  cells  of  the  posterior  vesicular 
column  of  the  cord,  and  the  superficial  posterior  arcuate  fibres,  which  are  derived  from  the  cells 
of  the  gracile  and  cuneate  nuclei,  do  not  cross  the  mesial  jjlane,  but  enter  the  restiform  body  of 
the  same  side.  The  anterior  superficial  arcuate  fibres  arise  from  the  cells  of  the  cuneate  and 
gracile  nuclei,  and  cross  the  mesial  plane  so  as  to  gain  the  restiform  body  of  the  opposite  side. 

The  cerebello-olivary  fibres  are  only  seen  in  the  upper  part  of  the  medulla.     They 
form  the  deep  part  of  the  restiform  body  and  constitute  its  chief  bulk.     Streaming 


XII. 
\       ^%S5\  >/[hypoglossal] 

'ARCUATE       ^**Si__^-^'^ 
NUCLEUS 

Fig.  402. — Diagram  of  the  Cerebello-Olivary  Fibres. 
(This  diagram  has  been  constructed  from  the  specimen  figured  on  p.  495.) 
N.X.,  Vago-glossopharyngeal  nucleus.  N.XII.,  Hypoglossal  nucleus, 

out  from  the  hilum  of  the  inferior  olivary  nucleus,  they  cross  the  mesial  plane,  and 
in  the  opposite  side  of  the  medulla  they  either  pass  through  the  inferior  olivary 
nucleus  of  that  side  or  sweep  around  it.  Ultimately,  on  the  dorsal  aspect  of  the 
olivary  nucleus,  they  are  gathered  together  in  the  form  of  a  conspicuous  group  of 
arcuate  fibres,  which  curve  backwards  to  take  up  a  position  in  the  deep  j)art  of  the 
restiform  body.  In  passing  back,  they  traverse  the  spinal  root  of  the  trigeminal 
nerve  and  break  it  up  into  several  separate  bundles.  The  cerebello-olivary  fibres 
thus  connect  the  inferior  olivary  nucleus  of  one  side  with  the  opposite  side  of  the 
cerebellum. 

Although  we  have  traced  the  cerebello-olivary  tract  in  an  upward  direction  from  the  olive  to 
the  c'Tebelliim,  and  liave  thus  iiifeiTcd  that  it  is  composed  of  fibres  which  pi'oceed  from  the  cells 
of  the  inferior  olivaiy  nucleus  of  the  opposite  side,  it  is  right  to  state  that  this  view  is  not  uni- 
vei-sally  acci;j)ted.  Thei'e  are  some  who  regard  these  fibres  as  constituting  an  efferent  tract  from 
the  c<;r<'beniiin,  or,  in  other  worfls,  as  arising  in  the  cerebellar  cortex  (probably  as  the  axons  of 
the  cells  of  I'urkinjej,  and  descending  in  the  inferior  cerebellar  peduncle  to  establish  connexions 
with  tlie  cfdls  of  the  inferior  olivary  nucleus  of  the  opposite  side.     If  this  view  be  correct,  the 

36 


4:98  THE  MIBVOrS  SYSTEM. 

destmafiicm.  of  tb&  sasme  of  tiie  edis  oi  tb&  J^ferStw  alivarir  BodenB  ht  ii  iipiiiii     a  difiodtjr,  !:■£ 

KoIIikex  eonsHeirs  tliat  tiiejr  eaifia'  tbs  lafesral  eotismn  ef  Idke  easd. 

Arcuate  Nndeiis  (nmdeois  aieoatiis}. — Tinme<Katalj-  aboTe  the  deeiieasasim  of 
the  pyramids,  a.  small  flattaM^  mai^  of  gisjr  matter,  ccnneied  h;f  sapexSmmL  azeoale 
Ebres,  makes  its  appearanee  on  the  T^ntzal  or  soperficaal  aspect  <tf  tiie  pnrEaniid 
(Fig.  S9->).  At  a  h^faer  leTel^  wfaen  the  ofen  pazt  ol^  the  medulla  is  reaped,  this 
gray  mass  sMfts  ifis  poeiti«Mi  aad  eotues  to  lie  wposi  the  mesia]  aspect  of  the 
pjrramid,  and  thos  constitutes  the  immediate  boondazj  of  the  antezo-median 
iassBze  (Fig:  $93).  Pzom  its  intimate  eonnexian  with  the  aateiiar  sopeifiaal 
aresiiSte  ^bires,  ss  tliey  sweep  out  frmsk  the  anteto-mei^an  S^^oie.  it  zee^vcs  tiie 
name  of  theaieaate 


Tbs-  H!eTT&-eeiI!te  wMefei  He  im  its-  mi'lst;  are  sanaHsr  tflaa  ukoee-  <iii  t?ft»?-  Emjfera'ir  'Mim^aBy 
asd  aire  fiifetfeMiam  im  sbap&.  It  htq^iM  appear  tltatr  laige  miiBBBli€ES  of  tihe  aBfezMrsiispedieialaiieaafee 
filares  exsi  £el  tMs  TxncBeiii^  m^Ufisfe  «)6ke9!S  tiake  miiij|»iiii  wi^biBL  i)L  Maagr  of  lAm  aafttaimr  axaaie 
filH%£y  1k)  wereTr  swis^p  eonfenuMMBslir  tgvsx  i^  ssn&ee  and  lisad  it  down  to  t&S'  pnmuud.  At  Itke 
appef  esd.  ^i  thi  niediolla  t&e  ai^iate  imefieiss  imeseas^  im  ^a^  and  nltinate^  it  lunniwiii  n  eon- 
txniKKBS  vitEi  th&  g^sir  usaattsr  €£  t&e  Tiaitial  paurt  ^  tiie  pons. 

Fanoatio  Seticnlsois. — Behind  Idie  oiire  and  the  pjxamid  is  the  HormatiD 
retiem]aii&  In  the  medulla  it  oeeoggies  a  potationL  idiidi,  to  a  faa^  extent,  eone- 
^omds  with  that  of  tiie  lateral  eolumn  in  the  ^^inal  eord.  In  txan^r^tse  seetim.  it 
appeals  as  an  extamre  azea,  which  is  diTided  into  a  lateral  and  a  me^al  field  bjr 
the  root  &@oicles  of  the  hypoglossal  nerfe  as  ther^  ficavfase  tiie  smhstanee  of  tbe 
mednDa  to  zeaeh  tiie  snE&ee.  In  the  lateral  poetion.  which  lies  behind  the  oiiiB 
thexe  is  a  eoei^derahle  qfoantitj  of  gia j  matter,  eontinDODs  with  that  in  the  eosd, 
present  in  the  r^iealar  formation;  it  is,  th@t^or^  eaDed  the  fiiiiMiiliin  xetiadaiiB 
gdsea.  In  the  me^bl  pazt;  whi^  li^  hehind  tiie  pjramid  tiie  gmj  matter  is 
ex^emelj  semty;  and  the  ledenlar  matter  here  is  tenmed  the  Bwjitiin  irtirwlaiiB 

bomdlesaf fi.' ::  -  -      -.nifnwuBaJfcL  "Ik^piiseBests^iKfrasi^nWkie^serreiDlna 

.raaaniaas  adirily  ea^Sbifeed  h^  Ibe  macfca  e£  £he  vagai^  fkesal  and  jArmatc 

r  ^f  xe^iiatM^  ^  attained  tfciani^k  i^.  smSemr  eoanexBoas  esKaU^aed  lirr 

C^^ctain  eontpastr  nuas^s  sf  S^3(y  B^abhifS'  ase  aks^  ssst  in.  ^he  &nnatti9 

.;-  lie  sn^ttisBed  (a}i  '^e  d«sal  aee^ESB^  dSxw^  mm^ieaE^  whoA  has  been 

-i  (^  tbe  nnd^as  laiaaife.    The  asKlenB  fateinliHi  fe  sesn  in  dbe  i^hb 

:  tL  t  ?!:L^'?f:3aSia  ge-tatinflsa  Itnihnwdi.    In  Itke  '"pp^  pwEt  «f  Ike  lednlUa  i& 

..imtjef  tiie  sapb^&efiHxalin  a&anat^lse  said  lls»  Ik  deiadoff' 

.  oj^-cesi^iac^  clgrey  Inswiiiewa;.  femas  an  iaJaiBed  waB^aeft  bmsb  off  ggJy  Tiftliwr  wjdildn 

TheneEve  fibres  whidi  tiainatse  tiie  fonnatiDietiealans ran  botii  ina  tnaisi«se 
and  a  Itmgitadiiial  diiedioa.  IDie  fnasvaae  flkreB  axe  tiie  deep  areoate  fibres. 
Tlie  Iwifliliiiia  il  flhras  are  demied  feoma  di^rent  awnees  in  the  fcro  fidds.  Inthe 
fosmatio  giisea  the)r  lepresent  to  a  lai^  extent  the  fibres  of  tiie  latexal  colnmn  of 
the  cord,  afto- the  zemoval  of  the  diieet  cer^idlar  and  the  erosaed  pyramidal  tsaetB. 
The^  e«m^tj.  therefore,  of  the  Sixes  of  the  tzaet  of  Gowers  and  of  fibres  eon^pond- 
ing  to  the  lateral  basab-bondle  of  the  eosd.  In.lhe  formatio  alba  the  ha^itiidinal 
fibzes  aze  the  trac^  of  the  Sll^  and  tibe  po^enar  kngitiidinal  bundle,  both  of  whieh 
haye  already  be^i  snffi^esktijr  described. 

Genlna  Gual  aad  the  &ay  MaUerwIoA  sanraods  it— The  central  canal, 
as  it  proceeds  npwafds  thnragli  the  dosed  part  of  the  medulla,  is  gradoaJDtr  fiseed 
to  assome  a  more  dsKsal  position,  owio^  to  the  aeeamniatian  of  fibres  on  ifts  Tentzal 
a^peel.  Hist  the  deeiesation  of  tiie  p^paraids,  and  then  the  deo^sation  of  the 
fiU^  both  &i  whidi  taJke  place  in  finmt  of  the  canal,  t€»d  to  posh  it  bai^wards: 
and  tifie  foranation  of  the  loi^iitifidinal  ^^tar^jwis  in  whidbi  these  intacrussingis  result 
(yix.  tiie  pjiamid  and  the  fiD^),  together  witii  the  continuation  i^fwards  of  tiie 
antexior  basis-bondle,  lead  to  a  gieat  increase  in  the  amount  of  tissue  wbidk 
sepaiates  it  fsaok  the  anl^oor  suzfiKe  of  the  meduUa.  In  the  dosed  part  of  the 
meimlla  it  i?  sEmrewmfei  by  a  thick  fey^r  of  sisr  usaSter.  wM-?!*  bs  eots'iiniao'as:  "with 


INTEE>^AL  STEUCTUEE  OF  THE  MEDULLA.  499 

the  basal  portions  of  the  anterior  and  posterior  horns  of  gray  matter  in  the  cord. 
This  central  gray  matter  is  sharply  defined  on  each  side  by  the  deep  arcuate  fibres 
which  curve  forwards  and  inwards  around  it.  Finally,  the  central  canal  opens  on 
the  dorsal  aspect  of  the  medulla  into  the  cavity  of  the  fourth  ventricle.  Tlie 
central  mass  of  gray  matter  which  surrounds  the  canal  in  the  closed  part  of  the 
medulla  is  now  spread  out  in  a  thick  layer  on  the  floor  of  the  fourth  ventricle,  and 
in  such  a  manner  that  the  portion  which  corresponds  to  the  basal  part  of  the 
anterior  horn  of  the  cord  is  situated  close  to  the  mesial  plane,  whilst  the  part  which 
represents  the  base  of  the  posterior  horn  occupies  a  more  lateral  position.  This  ia 
important,  because  the  nucleus  of  origin  of  the  motor  hypoglossal  nerve  is  placed 
in  the  mesial  part  of  the  floor,  whilst  the  nuclei  of  termination  of  the  afferent  fibres 
of  the  vagus,  glosso-pharyngeal,  and  auditory  nerves  lie  in  the  lateral  part  of  the 
floor.     The  gray  matter  of  the  ventricular  floor  is  covered  by  ependyma. 

Tliree  Areas  of  Flechsig. — In  transvei-se  sections,  tlirougli  tte  upper  open  part  of  tte 
medulla,  the  root  fibres  of  the  hypoglossal  and  vagus  nerves  are  seen  traversing  the  substance  of 
the  medulla.  The  nucleus  of  origin  of  the  hypoglossal  is  placed  in  the  gray  matter  of  the  floor 
of  the  foiuth  ventricle  close  to  the  mesial  plane ;  the  nucleus  of  the  vagus  is  situated  in  the 
gray  matter  of  the  ventricular  floor  immediately  to  the  outer  side  of  the  hypoglossal  nucleus. 
From  these  nuclei  the  root-bundles  of  the  two  nerves  diverge  from  each  other  as  they  are  traced 
to  the  sui'face  and  subdivide  the  substance  of  the  medulla,  as  seen  in  transverse  section,  into  the 
three  areas  of  Flechsig,  viz.  an  anterior,  a  lateral,  and  a  posterior. 

The  anterior  area,  which  is  bounded  internally  by  the  median  raphe  and  externally  by  the 
hypoglossal  roots,  presents  within  its  limits  :  (a)  the  formatio  alba ;  (V)  the  pyramid ;  (c)  the 
fillet ;  (d)  the  posterior  longitudinal  fasciculus ;  (e)  the  mesial  accessory  olivary  nucleus  ;  (f)  the 
arcuate  nucleus. 

The  lateral  area  lies  between  the  root  fibres  of  the  hypoglossal  and  those  of  the  vagus.  It 
contains  :  (a)  the  inferior  olivary  nucleus  ;  (6)  the  dorsal  accessory  olivary  nucleus  ;  (c)  the  nucleus 
lateralis ;  (d)  the  nucleus  ambiguus,  or  the  motor  nucleus  of  the  vagus  and  glosso-pharyngeal 
nerves  ;  (e)  the  formatio  reticularis  grisea. 

The  posterior  area  is  situated  beliind  the  vagus  roots,  and  within  its  limits  are  seen :  (1)  the 
restiform  body ;  (2)  the  upper  part  of  the  cuneate  nucleus  ;  (3)  to  the  inner  side  of  this  a  crowd 
of  transversely-cut  bundles  of  fibres,  loosely  arranged  and  forming  the  descending  root  of  the 
vestibular  part  of  the  auditory  nerve ;  (4)  close  to  these,  but  placed  more  deeply,  a  round,  com- 
pact, and  very  conspicuous  bundle  of  transversely- cut  fibres,  viz.  the  fasciculus  solitarius,  or 
descending  root  of  the  vagus  and  glosso-pharyngeal  nerves  ;  (5)  the  substantia  gelatinosa  Rolandi, 
much  reduced,  with  the  large  spinal  root  of  the  trigeminal  nerve  close  to  its  outer  side. 

INTERNAL  STEUCTUEE  OF  THE  PONS  VAEOLII. 

When  transverse  sections  are  made  through  the  pons,  it  is  seen  to  be  composed 
of  a  ventral  part  and  a  dorsal  or  tegmental  part.  The  ventral  part  is  much  the 
larger  of  the  two,  and,  broadly  speaking,  it  corresponds  to  the  pyramidal  portions 
of  the  medulla  and  the  pedal  portions  of  the  two  crura  cerebri,  which  lie  above  it  and 
appear  to  issue  from  it.  The  dorsal  tegmental  part  may  be  regarded  as  the  con- 
tinuation upwards  of  the  formatio  reticularis  grisea  and  the  formatio  reticularis 
alba.  As  these  parts  are  traced  upwards  into  the  pons  they  become  much  modified, 
and  new  constituents  are  added. 

Ventral  Part  of  the  Pons  (pars  basilaris  pontis). — This  constitutes  the  chief 
bulk  of  the  pons.  It  is  composed  of:  (1)  transverse  fibres  arranged  in  coarse 
bundles ;  (2)  longitudinal  fibres,  gathered  together  in  massive  bundles ;  and  (3)  a 
large  amount  of  gray  matter,  termed  the  nucleus  pontis,  which  fills  up  the  inter- 
stices between  the  intersecting  bundles  of  fibres. 

The  longitudinal  fibres,  to  a  large  extent,  consist  of  the  same  fibres  which,  lower 
down,  are  gathered  together  in  the  two  solid  pyramidal  tracts  of  the  medulla. 
When  the  pyramids  are  traced  upwards  they  are  seen  to  enter  the  pons  in  the 
form  of  two  compact  bundles.  Soon,  however,  they  become  broken  up  into 
smaller  bundles  by  the  transverse  fibres  of  the  pons,  and  are  spread  out  over  a 
wider  area.  At  the  upper  border  of  the  pons  they  acjain  come  together  and  form 
two  soHd  strands,  each  of  which  is  carried  into  the  central  part  of  the  coiTCspond- 
ing  pedai  jjortiou  of  the  crus  cerebri. 

The  transverse  fibres  at  tlie  lower  border  of  the  pons  are  placed  on  the  super- 
ficial or  ventral  aspect  of  the  pyramidal  bundles.  As  we  proceed  upwards  they 
increa.se  in  number,  and  many  are  seen  breaking  through  the  pyramids  and  even 


500 


THE  NEEVOUS  SYSTEM. 


passing  across  upon  the  dorsal  aspect  of  the  latter.  Laterally  these  transverse 
fibres  are  collected  together  into  one  compact  mass,  which  enters  the  white  central 
core  of  the  cerebellum  and  constitutes  the  middle  cerebellar  peduncle.  At  the 
mesial  plane  the  transverse  filjres  of  the  two  sides  of  the  ventral  portion  of  the 
pons  intercross  and  form  a  coarse  decussation. 

The  gray  matter  (the  nucleus  pontis)  forms  a  considerable  part  of  the  bulk  of 
the  ventral  portion  of  the  pons.  It  is  packed  into  the  intervals  between  the  inter- 
secting transverse  and  longitudinal  bundles. 

There  is  a  close  analogy  between  the  pyramidal  portions  of  the  medulla  and  the  ventral 
part  of  the  pons.  In  the  medulla  fine  arcuate  fibres  on  their  way  to  the  surface  pass  through 
the  pyramids.  Other  superficial  arcuate  fibres  sweep  over  the  surface  of  the  pyramids.  These 
present  a  strong  resemblance  to  the  transverse  fibres  of  the  pons.  They  Ukewise  reach 
the  cerebelhim,  although  by  a  difi^erent  route,  viz.  the  inferior  cerebellar  peduncle.  The 
nucleus  pontis  is  also  represented  in   the  pyi-amidal  part  of  the  medulla  by  the  arcuate 


Spinal  root  of 
fifth  nerve- 

Substantia  gela- 
tinosa  Rolandi' 

Facial  nerve 
Facial  nucleus 
Superior  olive- 


Middle  peduncle  ot 
cerebellum 


\  Transverse  fibres  of 
pons 


F}  lamidal  bundles 
Transverse  fibres  of  pons 

Fig.  403. — Section  through  the  Lower  Part  of  the  Human  Pons  Varolii  immediately  above 

THE  Medulla. 


nuclei,  which  are  covered  over  by  the  superficial  arcuate  fibres,  and  even  tend  to  penetrate, 
to  a  slight  extent,  into  the  pyramidal  tracts.  These  arcuate  nuclei,  as  already  pointed  out, 
are  continuous  with  the  nucleus  pontis. 

Connexions  of  the  Longitudinal  and  Transverse  Fibres. — Our  knowledge  of 
the  connexions  of  the  longitudinal  and  transverse  fibres  of  the  ventral  part  of  the  pons  is 
very  far  from  being  complete.  When  a  transverse  section  through  the  upper  part  of  the 
pons  is  compared  with  one  close  to  its  lower  border,  it  becomes  at  once  apparent  that  the 
numerous  scattered  bundles  of  longitudinal  fibres  which  enter  the  ventral  part  of  the  pons 
from  above,  if  brought  together  into  one  tract,  would  form  a  strand  very  much  larger  than 
the  two  pyramids  which  leave  its  lower  aspect  and  enter  the  medulla.  It  is  clear,  there- 
fore, that  many  of  the  longitudinal  fibres  which  pass  into  the  pons  from  above  do  not  pass 


INTERNAL  STRUCTURE  OF  THE  PONS  VAROLII. 


)01 


out  from  it  below  into  the  medulla.  What  becomes  of  these  fibres  that  are  thus  absorbed  in 
the  j)ons  ?  It  is  known  that  the  pyramidal  bundles  suffer  a  small  loss  by  the  filjres  which 
they  send  to  the  nuclei  of  origin  of  the  efferent  nerves  which  arise  within  the  pons  (viz.  the 
motor  root  of  the  fifth,  the  sixth,  and  seventh  nerve  nuclei) ;  but  this  loss  is,  comparatively 
speaking,  trifling.  It  is  clear,  therefore,  that  other  longitudinal  bundles  enter  the  pons 
from  above  than  those  which  form  the  pyramidal  tracts.  These  bundles  occupy  a  lateral 
and  dorsal  position  in  the  ventral  part  of  the  pons,  and  may  be  termed  the  cortico-pontine 
fibres,  seeing  that  they  come  from  the  cerebral  cortex  and  end  in  fine  ramifications  around 
the  cells  of  the  nucleus  pontis. 

The  transverse  fibres  are  of  two  kinds,  viz.  :  (1)  those  which  arise  in  the  cortex  of  the 
cerebellum ;  and  (2)  those  which 
take  origin  in  the  nucleus  pontis. 
The  former  are  the  axons  of  certain 
of  the  cells  of  the  cortex  of  the  cere- 
bellum (cells  of  Purkinje).  They 
come  chiefly  from  the  lateral  hemi- 
sphere, but  also  to  some  extent  from 
the  median  lobe  of  the  cerebellum, 
and  enter  the  pons  by  the  middle 
peduncle.  They  end  in  fine  rami- 
fications around  the  cells  of  the 
nucleus  pontis,  some  on  the  same 
side  as  the  peduncle  through  which 
they  reach  the  pons,  but  the  majority 
in  the  gray  matter  of  the  opposite 
side. 

The  transverse  fibres  which  arise 
in  the  pons  take  origin  as  axons  of 
the  cells  of  the  nucleus  pontis. 
Crossing  the  mesial  plane,  they  enter 
the  middle  peduncle  of  the  opposite 
side,  and  thus  reach  the  cerebellar 
cortex,  where  they  end  in  ramifica- 
tions round  certain  of  the  cortical 
cells.  The  middle  peduncle  thus 
contains  both  efferent  and  affei'ent 
cerebellar  fibres,  and  no  fibres  pass 
continiiously  through  the  pons  from 
one  middle  peduncle  into  the  other. 
In  opposition  to  this  view,  Klimoff 
and  others  hold  that  the  middle 
peduncle  is  composed  solely  of  centri- 
petal or  afferent  fibres,  which  pass 
from  the  nucleus  pontis  to  the  cere- 
bellum. Some  of  these  fibres  are 
crossed  and  others  direct. 

Certain  of  the  transverse  fibres  Fig.   404 
of    the    pons    turn    backwards    and 
enter  the  dorsal  or  tegmental  part 


Inferior  olivary 
nucleus 


Posterior  nerve, 
root 


Posterior  vesicular 
column  of  cells 


■Diagram   to   show  connexions   of   the   Direct 
Cerebellar  and  the  Olivo-Cerebellar  Tracts.      The 
connexions  of  the  fibres  of  the  middle  peduncle  of  the  cere- 
-     .  1  1     J     V 1  ■  bellum  are  likewise  diacframmatically  shown  (from  Edinger, 

of   the  pons,  but   the  precise    con-         modified) 

nexions  of  these  are  doubtful. 

Corpus  Trapezoides. — This  name  is  applied  to  a  group  of  transverse  fibres 
which  traverse  the  lower  part  of  the  pons  (Fig.  405).  They  are  quite  distinct  from 
those  which  have  been  just  described  as  entering  the  middle  peduncle  of  the 
cerebellum,  and  they  lie  in  the  boundary  between  the  dorsal  and  ventral  parts  of 
the  jjons,  but  encroacliing  consid(;ra])]y  into  the  ground  of  the  former.  They  arise 
from  the  colls  of  the  terminal  nucleus  of  the  cochlear  division  of  the  auditory  nerve, 
and  constitute  a  tract  which  establishes  certain  central  connexions  for  that  nerve. 
They  will  Ijo  more  fully  described  when  we  tniat  of  tlie  cerebral  connexions  of  the 
auditory  nerve. 

Dorsal  or  Tegmental  Part  of  the  Pons  (])ars  dorsalis  pontis). — On  the  dorsal 
surlacc  of  tlie   tf-ginrjiital   part   ol'  i]ui  j>ons  there  is  spread  a   thick   layer  of  gray 


502  THE  NERVOUS  SYSTEM. 

matter,   covered   by   ependyma,  which   forms  the  floor  of  the   upper  or  pontine 
.part  of  the  fourth  ventricle.     Beneath  this  the  mesial  raphe  of  the  medulla  is 
continued  up  into  the  pons,  so  as  to  divide  its  tegmental  part  into  two  symmetrical 
halves. 

In  the  lower  part  of  the  pons,  immediately  beyond  the  medulla,  the  restiform 
body  is  placed  on  the  outer  side  of  the  tegmental  part  (Fig.  403).  In  transverse 
sections  through  the  pons  it  appears  as  a  large,  massive  oval  strand  of  fibres  which 
gradually  inclines  backwards  into  the  cerebellum,  and  thus  leaves  the  pons. 
Between  the  restiform  body  and  the  median  raphe  the  tegmental  part  of  the  pons 
is  composed  of  formatio  reticularis,  continuous  with  the  same  material  in  the 
medulla.  Thus  arcuate  or  transverse  fibres,  curving  in  towards  the  raphe,  and  also 
longitudinal  fibres,  are  seen  breaking  through  a  mass  of  gray  matter  which  occupies 
the  interstices  of  the  intersecting  fibres.  To  the  naked  eye  the  formatio  reticularis 
presents  a  uniform  gray  appearance,  but  its  constituent  parts  are  revealed  by  low 
powers  of  the  microscope  in  properly-stained  and  prepared  specimens.  Embedded 
in  this  formatio  reticularis  are  various  clumps  of  compact  gray  matter  and  certain 
definite  strands  of  fibres.  These  we  shall  describe  as  we  pass  from  the  restiform 
body  inwards  towards  the  median  raphe. 

(1)  Spinal  root  of  the  trigeminal  nerve  and  the  substantia  gelatinosa  Rolandi. — 
Close  to  the  inner  side  of  the  restiform  body,  but  separated  from  it  by  the  vesti- 
bular root  of  the  auditory  nerve  as  it  proceeds  backwards  through  the  pons,  is  seen 
a  large  crescentic  group  of  coarse  transversely- divided  bundles  of  fibres.  This  is  the 
spinal  root  of  the  fifth  nerve,  and  applied  to  its  inner  concave  side  is  a  small  mass 
of  gray  matter,  which  is  the  direct  continuation  upwards  of  the  substantia  gelatinosa 
Rolandi. 

(2)  The  nucleus  of  the  facial  or  seventh  nerve  comes  next.  It  is  sunk  deeply 
in  the  tegmental  part  of  the  pons  and  lies  close  to  the  transverse  fibres  of  the 
corpus  trapezoides.  It  is  a  conspicuous,  obliquely  placed,  ovoid  clump  of  gray 
matter.  From  its  outer  and  dorsal  aspect  the  root-fibres  of  the  facial  nerve 
stream  backwards  and  inwards  towards  the  gray  matter  on  the  floor  of  the  fourth 
ventricle.  Passing  forwards  between  this  nucleus  and  the  substantia  Rolandi  a 
solid  nerve-bundle  may  be  observed.  This  is  the  facial  nerve,  traversing  the  pons 
towards  its  place  of  emergence  from  the  brain. 

(3)  Immediately  internal  to  the  facial  nucleus,  but  placed  more  deeply  in  the 
tegmental  part  of  the  pons,  is  the  superior  olivary  nucleus  (nucleus  olivaris  superior). 
It  lies  in  a  bay  formed  for  it  by  the  transverse  fibres  of  the  corpus  trapezoides. 
These  fibres  curve  round  its  ventral  aspect,  and  many  of  them  may  be  observed  pene- 
trating into  its  substance.  In  man  it  is  a  very  small  mass  of  gray  matter,  and 
presents  little  resemblance  to  the  inferior  olivary  nucleus,  except  in  the  size  and 
shape  of  its  constituent  cells.  In  sections  through  the  part  of  the  pons  where  it 
attains  its  greatest  size,  it  appears  in  the  form  of  two,  or  it  may  be  three,  small 
isolated  masses  of  gray  matter.  It  is  intimately  connected  with  the  trapezial 
fibres,  many  of  which  end  in  it,  whilst  others  take  origin  within  it. 

Upon  the  inner  and  dorsal  aspect  of  the  superior  olive  there  is  a  dense  group  of  longitudinal 
fibres.  These  constitute  the  central  tegmental  tract ;  but  as  precise  information  in  regard  to 
its  connexions  is  still  to  a  large  extent  wanting,  it  is  not  necessary  to  do  more  than  indicate  its 
position. 

(4)  The  posterior  longitudinal  bundle  and  the  fillet  come  next.  As  they  proceed 
upwards  through  the  tegmental  part  of  the  pons,  these  longitudinal  tracts  occupy 
the  same  relative  position  as  in  the  medulla.  They  are  placed  close  to  the  median 
raphe ;  but  they  have  drawn  further  apart  from  each  other,  and  their  fibres  are 
more  distinctly  concentrated  into  separate  strands,  with  an  interval  of  some  little 
width  between  them.  The  posterior  longitudinal  bundle  lies  immediately  under 
cover  of  the  gray  matter  of  the  floor  of  the  fourth  ventricle.  The  fillet  is  placed 
close  to  the  trapezial  fibres,  many  of  which  traverse  it  as  they  pass  towards  the 
mesial  plane. 

(5)  The  nucleus  of  the  sixth  nerve  also  forms  a  conspicuous  object  in  sections 
through  the  lower  part  of  the  pons.  It  is  a  round  mass  of  gray  matter,  which  is 
situated  close  to  the  outer  side  of  the  posterior  longitudinal  bundle,  and  immediately 


INTERNAL  STRUCTURE  OF  THE  PONS  VAROLII. 


503 


under  cover  of  the  gray  matter  of  the  floor  of  the  fourth  ventricle.  From  its  inner 
side  numerous  root- bundles  of  the  sixth  nerve  pass  out  and  proceed  forwards 
bevi^een  the  fillet  and  the  superior  olivary  nucleus.  They  occupy  in  the  pons, 
therefore,  a  position  similar  to  that  occupied  by  the  hypoglossal  root-fibres  in  the 
medulla. 

Up  to  the  present  only  the  lower  part  of  the  tegmental  portion  of  the  pons 
has  been  described,  i.e.  the  portion  immediately  adjoining  the  medulla.  As  we 
proceed  upwards  and  gain  a  point  above  the  level  of  the  trapezicd  fibres,  many  of 
the  structures  which  have  attracted  attention  lower  down  gradually  disappear 
from  the  formatio  reticularis.  The  posterior  longitudinal  bundle,  the  fillet,  and 
the  spinal  root  of  the  fifth  nerve,  however,  are  still  carried  upwards.     Further,  the 


Superior  cerebellar  peduncle 

Mesencephalic  root  of  tlie  fifth  nerve 

Motor  nucleub  of  the  fifth  ner\  e       '^ 
Motor  loot  of  the  fifth  nei\e. 


Superior  medullary  velum 
or  valve  of  Vieussens 


Sensory  nucleus  of  the  fifth  neive 
Superior  olive  ^^^^ 


Sensory  root  of 
tifth  nerve 


Middle  peduncle 
of  cerebellun 


i^^^Pyramidal 
'     bundles 


Fig.   405. 


-Transverse  Section  through  the  Pons  Varolii  at  the  Level  of  the  Nuclei  of 
THE  Trigeminal  Nerve  (Orang). 


floor  of  the  fourth  ventricle  becomes  narrower,  and  other  objects  appear  in  the 
tegemental  substance. 

The  superior  cerebellar  peduncle  (brachium  conjunctivum)  is  a  very  con- 
spicuous object,  in  sections,  through  the  middle  and  upper  parts  of  the  pons.  In 
transverse  section  it  presents  a  semilunar  outline,  and  as  it  emerges  from  the 
cerebellum  it  lies  immediately  on  the  outer  side  of  the  fourth  ventricle,  towards 
which  its  concave  aspect  is  turned  (Fig.  405).  Its  dorsal  border  is  joined  with  the 
corresponding  peduncle  of  the  opposite  by  the  thin  lamina  of  white  matter, 
termed  the  superior  medullary  velum,  whilst  its  ventral  border  is  sunk  to  a  small 
extent  in  the  dorsal  part  of  the  pons.  As  it  is  traced  upwards  it  sinks  deeper  and 
deeper  into  the  x^ons  until  it  becomes  completely  submerged,  with  the  exception 
of  the  posterior  border  to  whicli  the  superior  velum  is  attached.  It  now  lies  on 
the  outer  side  of  the  tegmental  or  reticular  substance  of  the  pons,  and  this  position 
it  maintains  until  the  iiics(;ncephalon  is  reached  (Fig.  406). 

About  half-ivay  uj)  Ui,e  pons  the  nuclei  of  the  trigeminal  or  fifth  cranial  nerve 
mark  a  very  important  stage  in   its  tegmental  portion.     These  nuclei  are  two  in 


604 


THE  NEEVOUS  SYSTEM. 


number  on  each  side,  viz.  a  large  oval  terminal  nucleus  for  certain  of  the  sensory 
fibres  of  the  nerve  and  a  nucleus  of  origin  equally  conspicuous  for  certain  of  the 
motor  fibres  (Eig.  405).  The  sensory  nucleus  lies  close  to  the  outer  surface  of  the 
pons,  deeply  sunk  in  its  tegmental  part,  and  in  the  interval  between  the  submerged 
anterior  border  of  the  superior  cerebellar  peduncle  and  the  ventral  part  of  the  pons. 
The  motor  nucleus  is  placed  on  the  inner  side  of  the  sensory  nucleus,  but  somewhat 
nearer  the  dorsal  surface  of  the  pons.  At  this  level  the  spinal  root  of  the  fifth 
nerve  disappears  by  joining  the  fibres  of  the  sensory  portion.  The  sensory  and 
motor  roots  of  the  fifth  nerve  traverse  the  ventral  part  of  the  pons  on  their  way 
to  and  from  the  region  of  the  nuclei. 

Above  the  level  of  the  nuclei  of  the  trigeminal  nerve  a  new  tract  of  fibres 
comes  into  view.  This  is  the  mesencephalic  root  of  the  fifth  nerve,  as  it  descends 
to  join  the  emerging  fibres  of  the  motor  part  of  the  fifth  nerve.  It  is  a  small 
bundle  of  nerve  fibres,  semilunar  in  cross  section,  which  lies  close  to  the  inner  side 


Uppei  end  of  Ventricle  IV 


Valve  of  Vieussens 

Gray  matter  on  floor  of  Ventricle  IV. 
"~S^^ — -Superior  cerebellar  peduncle 

is 

Lateral  fillet 


Commencing  decussa- 
tion of  superior 
cerebellar  peduncles 

Mesial  fillet 


ly  _!  Transverse  fibres 

of  pons 


Pyramidal  bundle 


Fig. 


406. — Section  through  the  Upper  Part  of  the  Pons  Varolii  of  the  Orang,  above  the 
Level  of  the  Trigeminal  Nuclei. 


of  the  superior  cerebellar  peduncle  and  on  the  outer  and  deep  aspect  of  the  gray 
matter  on  the  floor  of  the  fourth  ventricle  (Figs.  406  and  407). 

On  a  slightly  deeper  plane  than  the  mesencephalic  root  of  the  fifth  nerve, 
between  it  and  the  posterior  longitudinal  bundle,  and  in  close  relation  to  the  gray 
matter  of  the  floor  of  the  ventricle,  is  the  collection  of  pigmented  cells  which  con- 
stitutes the  substantia  ferruginea. 

The  posterior  longitudinal  bundle,  as  it  is  traced  upwards  through  the  tegmental 
part  of  the  pons,  maintains  the  same  position  throughout,  and  as  it  ascends  it 
becomes  more  clearly  mapped  out  as  a  definite  and  distinct  tract.  It  lies  close 
to  the  mesial  raphe,  and  immediately  subjacent  to  the  gray  matter  of  the  floor  of 
the  fourth  ventricle. 

The  fillet  as  it  ascends  through  the  tegmental  part  of  the  pons  undergoes 
striking  changes  in  shape.  In  the  lower  portion  of  the  pons  its  fibres,  which  in 
the  medulla  are  spread  out  along  the  side  of  the  median  raphe,  are  collected 
together  in  the  form  of  a  loose  bundle,  which  occupies  a  wide  field,  somewhat 
triangular  in  shape,  on  either  side  of  the  median  raphe  and  immediately  behind 
the  ventral  portion  of  the  pons.  As  it  proceeds  up,  the  fibres  spread  out  laterally 
until  a  compact  ribbon-like  layer  is  formed  in  the  interval  between-  the  tegmental 
and  ventral  portions  of  the  pons.  This  constitutes  what  is  termed  the  mesial 
fillet  (Figs.  406  and  407). 

Above  the  level  of  the  trigeminal  nuclei  another  flattened  layer  of  fibres  comes 


THE  CEREBELLUM. 


505 


into  view  to  the  outer  side  of  the  mesial  fillet.  To  this  the  name  of  lateral  fillet  is 
given.  These  fibres  spread  outwards  and  backwards,  and  finally  take  up  a  position 
on  the  outer  surface  of  the  su]oerior  cerebellar  peduncle.  In  the  angle  between 
the  mesial  and  lateral  fillets  a  little  knot  of  compact  gray  matter,  termed  the  lateral 


Upper  end  of  ventricle  IV, 
Trochlear  nerve 
Mesencephalic  root  of  fifth  nerve 

Gowers  tract 
Posterior  longi . 
tudinal  bundle 

Superior  cere- 
bellar peduncle 

Lateral  fillet 


Inferior  quadri- 
gemmal  body 
-.  Decussation 
[-  of  trochlear 
-*  nerves 
Upper  end  of 
ventricle  IV. 

Superior  cere- 
bt  liar  ijeduncle 
Posterior  longi- 
tudinal bundle 
Lateral  fillet 


Formatio — 
reticularis     \i  i? 


Mesial  fillet 


^^,^ — L  Mesial  fillet 


Fig.  407. — Two  Sections  through  the  Tegmentum  of  the  Pons  at  its  Upper  Part,  close  to 

THE  Mesencephalon. 

A  is  at  a  slightly  lower  level  than  B. 

fillet  nucleus,  comes  into  view  (Fig.  406).  This  appears  to  be  in  more  or  less 
direct  continriity  with  the  superior  olivary  nucleus.  Many  of  the  fibres  of  the 
lateral  fillet  take  origin  in  this  nucleus.  Bruce  has  called  attention  to  the  continuity 
between  the  superior  olive  and  the  lateral  fillet  nucleus  in  man,  and  the  writer 
can  confirm  his  statement  in  so  far  as  the  orang  brain  is  concerned. 


THE    CEREBELLUM. 


The  cerebellum  lies  behind  the  pons  Varolii  and  the  medulla  oblongata,  and 
below  the  hinder  portions  of  the  cerebral  hemispheres.     From  the   latter  it  is 


Central  lobule 


Mesencephalon 


Anterior  crescentic  lobule 


Posterior  cres- 
centic lobule 


Postero- 
uperior  lobule 


Folium  cacuiiunis 


I'ostero-mterior  lobule 


Tuber  va)\ 
KfG.  408. 


Posterior  nnlrh 
-Ul'I'Ell    Suitl^'ACE    (JI'"    THK    CeI!EI!BLI.UM. 


separated  by  an  iiiterv(;ning  jjartition  of  dura  mater,  termed  the  tentorium  cerebelli. 
It  is  distinguished  by  the  numerous  parallel  and  more  or  less  curved  sulci,  which 
traverse  its  surface  and  give  it  a  foliated  or  laminated  appearance.  It  is  composed 
of  a  cortex  of  gray  matter  (substantia  corticalis)  spread  over  its  surface,  with  white 
matter  in  the  interior,  forming  a  central  core  (corpus  medullare). 


506  THE  NEEVOUS  SYSTEM. 

The  cerebellum  is  subdivided  somewhat  arbitrarily  into  a  median  portion 
termed  the  vermis,  and  two  much  larger  lateral  portions,  called  the  lateral  hemi- 
spheres (hemisphseria  cerebelli).  The  demarcation  between  these  main  subdivisions 
of  the  organ  is  not  very  evident  from  every  point  of  view.  In  front,  and  also 
behind,  there  is  a  marked  deficiency  or  notch.  The  posterior  notch  (incisura  cere- 
belli posterior)  is  smaller  and  narrower  than  the  anterior  notch.  It  is  bounded 
laterally  by  the  lateral  hemispheres,  whilst  its  bottom  is  formed  by  the  median  lobe 
or  vermis.  It  is  occupied  by  a  fold  of  dura  mater,  called  the  falx  cerebelli.  The 
anterior  notch  (incisura  cerebelli  anterior)  is  wide,  and,  when  viewed  from  above,  it 
is  seen  to  be  occupied  by  the  inferior  quadrigeminal  bodies  and  by  the  superior 
peduncles  of  the  cerebellum.  As  in  the  case  of  the  hinder  notch,  its  sides  are 
formed  by  the  lateral  hemispheres  and  the  bottom  by  the  vermis. 

On  the  superior  surface  of  the  cerebellum  there  is  little  distinction  to  be  noted 
between  the  median  lobe  and  the  upper  surface  of  each  lateral  hemisphere.  On 
this  aspect  the  median  lobe  receives  the  name  of  superior  vermis,  and  it  forms  a 
high  median  elevation,  from  which  the  surface  slopes  gradually  downwards  on  each 
side  to  the  margin  of  the  hemisphere.  The  superior  vermis  is  highest  in  front, 
immediately  behind  the  anterior  notch,  and  from  this  it  shows  a  somewhat  sharp 
descent  towards  the  posterior  notch.  This  elevation  of  the  superior  worm  is 
frequently  called  the  monticulus  cerebelli.  The  folia  on  the  surface  of  the  superior 
vermis  are  thicker  and  fewer  in  number  than  those  on  the  upper  surface  of  the 
lateral  hemisphere.  It  is  this  which  gives  it  the  worm-like  appearance  from  which 
it  derives  its  name. 

On  the  inferior  surface  of  the  cerebellum  the  distinction  between  the  three  main 
constituent  parts  of  the  organ  is  much  better  marked  (Fig.  409).  On  this  aspect 
the  lateral  hemispheres  are  full,  prominent,  and  convex,  and  occupy  the  cerebellar 
fossffi  in  the  floor  of  the  cranium.  They  are  separated  by  a  deep  mesial  hollow, 
which  is  continued  forwards  from  the  posterior  notch.  This  hollow  is  termed  the 
vallecula  cerebelli,  and  in  its  fore-part  is  lodged  the  medulla  oblongata.  When  the 
medulla  is  raised  and  the  lateral  hemispheres  are  pulled  apart,  so  as  to  expose  the 
bottom  of  the  vallecula,  it  will  be  seen  that  this  is  formed  by  the  vermis  inferior, 
or  inferior  aspect  of  the  median  lobe,  and,  further,  that  the  latter  is  separated  on 
each  side  from  the  corresponding  lateral  hemisphere  by  a  distinct  furrow,  termed 
the  sulcus  valleculse. 

Sulci  Cerebelli. — Certain  of  the  fissures  which  traverse  the  surface  of  the 
cerebellum  are  deeper  and  longer  than  the  others,  and  they  map  out  districts  which 
are  termed  lobes.  One  of  the  most  conspicuous  of  these  clefts  is  the  great  horizontal 
fissure. 

The  great  horizontal  fissure  (sulcus  horizontalis  cerebelli)  of  the  cerebellum 
begins  in  front  and  passes  continuously  round  the  circumference  of  the  organ, 
cutting  deeply  into  its  outer  and  posterior  margins.  In  front,  its  lips  diverge  to 
enclose  the  three  cerebellar  peduncles  as  they  pass  into  the  interior  of  the 
cerebellum.  The  great  horizontal  fissure  divides  the  organ  into  an  upper  and  a 
lower  part,  which  may  be  studied  separately. 

The  prominence  which  is  accorded  to  the  great  horizontal  fissure  in  desci'li^tive  anatomy  is 
not  justified  by  its  develoismental  history  and  morphological  status.  It  is  very  late  in  making 
its  appearance  in  the  foetal  cerebellum,  and  not  infrequently  the  part  of  the  fissure  on  the  one 
side  fails  to  establish  a  continuity  across  the  vermis  with  the  part  of  the  fissure  on  the  other 
side  of  the  organ. 

Lobes  on  the  Upper  Surface  of  the  Cerebellum. — When  examined  from 
before  backwards,  the  superior  vermis  presents  the  following  subdivisions:  (1)  the 
lingula;  (2)  the  central  lobule  (lobulus  centralis);  (3)  the  culmen  monticuli;  (4)  the 
clivus  monticuli ;  (5)  the  folium  cacuminis  (folium  vermis).  With  the  exception  of 
the  lingula,  each  of  these  is  continuous  on  either  side,  with  a  corresponding  district 
on  the  upper  surface  of  the  hemisphere,  thereby  forming  a  cerebellar  lobe.  Thus 
the  central  lobule  is  prolonged  outwards  on  either  side  in  the  form  of  a  small, 
flattened,  wing-like  expansion  called  the  ala ;  the  culmen  constitutes  the  median 
connecting  piece  between  the  two  anterior  crescentic  lobules  of  the  hemispheres ; 
the  clivus  stands  in  the  same  relation  to  the  two  posterior  crescentic  lobules ;  and 


THE  CEREBELLUM.  507 

the  folium  cacuminis  is  the  connecting  band  between  the  postero-superior  lobules  of 
the  hemispheres. 

It  should  be  noted  tliat  this  sulidivision  of  the  upper  surface  of  the  cerebellum  is  to  some 
extent  conventional,  and  in  certain  particulars  receives  little  support  from  morphological  data. 

The  lingula  can  only  be  seen  when  the  part  of  the  cerebellum  which  forms  the 
bottom  of  the  anterior  notch  is  pushed  backwards.  It  consists  of  four  or  five  small 
flat  folia  continuous  with  the  gray  matter  of  the  vermis  superior,  which  are  pro- 
longed forwards  on  the  upper  surface  of  the  superior  medullary  velum  in  the  interval 
between  the  two  superior  cerebellar  peduncles. 

Lobus  Centralis  with  its  Alee. — The  lobulus  centralis  lies  at  the  bottom  of 
the  anterior  cerebellar  notch,  and  is  only  seen  to  a  very  small  extent  on  the  upper 
surface  of  the  organ.  It  is  a  little  median  mass  which  laterally  is  prolonged  out- 
wards for  a  short  distance  round  the  anterior  notch  in  the  form  of  two  expansions, 
termed  the  alee. 

Lobus  Culminis. — The  culmen  monticuli  constitutes  the  highest  part  or  summit 
of  the  monticulus  of  the  vermis  superior.  It  is  bounded  behind  by  a  deep  and 
strongly  marked  fissure  called  the  fissura  prima  (Elliot  Smith),  and  is  prolonged 
outwards  on  either  side  into  the  lateral  hemisphere  as  the  anterior  crescentic  lobule. 
This  is  the  most  anterior  subdivision  on  the  upper  surface  of  the  hemisphere.  The 
two  anterior  crescentic  lobules,  with  the  culmen  monticuli,  form  the  lobus  culminis 
cerebelli. 

Lobus  Clivi. — The  clivus  monticuU  lies  behind  the  culmen,  from  which  it  is 
separated  by  the  fissura  prima,  and  it  forms  the  sloping  part  or  descent  of  the 
monticulus  of  the  vermis  superior.  On  each  side  it  is  continuous  with  the  posterior 
crescentic  lobule  of  the  lateral  hemisphere,  and  the  three  parts  are  included  under 
the  one  name  of  lobus  clivi. 

The  two  crescentic  lobules  on  the  upper  surface  of  the  hemisphere  are  sometimes  classed 
together  and  described  as  the  lobulus  quadrangularis.  They  are  separated  from  each  other  by  a 
lateral  extension  on  the  upper  surface  of  the  hemisphere  of  the  fissura  prima,  whilst  the 
posterior  crescentic  lobule  is  bounded  behind  by  a  curved  sulcus  termed  by  Elliot  Smith  the 
fissura  postlunata.  The  union  of  the  two  postlunate  furrows  across  the  vermis  sejaarates  the 
clivus  from  the  folium  cacuminis,  but  in  many  cases  this  junction  fails  to  take  place. 

Lobus  Cacuminis. — The  folium  cacuminis  forms  the  most  posterior  part  of  the 
vermis  superior,  and  when  the  right  and  left  portions  of  the  great  horizontal  fissure 
are  continuous  across  the  vermis  it  bounds  that  fissure  superiorly  at  the  posterior 
notch.  It  is  a  single  folium,  subject  to  considerable  variation  in  the  degree  of  its 
development,  and  its  surface  may  be  smooth  or  beset  with  rudimentary  secondary 
folia.  It  is  the  median  connecting  link  between  the  two  postero-superior  lobules 
of  the  hemispheres,  the  three  parts  forming  the  lobus  cacuminis.  As  the  folium 
cacuminis  is  traced  outwards  into  the  postero-superior  lobule,  it  is  found  to 
expand  greatly,  and  as  a  result  of  this  the  postero-superior  lobule  on  each  side 
forms  an  extensive  foliated  district  bounding  the  great  horizontal  fissure  above. 

Lobes  on  the  Under  Surface  of  the  Cerebellum. — The  connexion  between 
the  several  parts  of  the  inferior  vermis  and  the  corresponding  districts  on  the 
under  surface  of  the  two  hemispheres  is  not  so  distinct  as  in  the  case  of  the  vermis 
superior  and  the  lobules  on  the  upper  surface  of  the  hemispheres.  A  groove,  the 
sulcus  valleculas,  intervenes  between  the  vermis  inferior  and  the  hemisphere  on 
each  side. 

From  behind  forwards  the  following  subdivisions  of  the  vermis  inferior  may  be 
recognised :  (1)  the  tuber  valvulse  (tuber  vermis) ;  (2)  the  pyramid  (pyramis) ;  (3) 
the  uvula;  f4)  the  nodule  (nodulus). 

On  the  under  surface  of  the  hemisphere  there  are  four  main  lobules  mapped  out 
by  intervening  fissures.  From  behind  forwards  these  are  :  (1)  the  postero-inferior 
lobule,  a  large  subdivision  whicli  l)Ounds  the  great  horizontal  fissure  on  its  under 
asyject ;  (2)  the  biventral  lobule  (lobulus  Ijivcntor)  which  lies  in  front  of  the  postero- 
inferior  lobule,  and  is  partially  divided  into  two  parts  by  a  curved  fissure  which 
traverscH  its  surface;  (8)  the  tonsil  or  amygdala  (tonsilla),  a  small  rounded  lobule 
sviiich  bounds  the  fore-part  of  the  vallecula,  and  is  lodged  in  a  deep  concavity  on 


508 


THE  NEKVOUS  SYSTEM. 


the  inner  aspect  of  the  biveutral  lobule ;  (4)  the  flocculus,  a  minute  lobule  situated 
on  the  middle  peduncle  of  the  cerebellum  in  front  of,  and  partially  overlapped  by, 
the  anterior  border  of  the  biventral  loljule. 

These  lobules,  with  the  corresponding  portions  of  the  vermis  inferior,  constitute 
the  lobes  on  the  under  surface  of  the  cerebellum.  Still,  it  should  be  noted  that, 
just  as  in  the  case  of  the  upper  surface  of  the  organ,  this  subdivision  is  to  some 
extent  artificial,  and  is  not  in  every  particular  provided  with  a  sound  morphological 
basis. 

Lobus  Tuberis. — The  tuber  valvulse,  which  forms  the  most  posterior  part  of 
the  vermis  inferior,  is  composed  of  several  transversely  arranged  folia  which,  on 
either  side,  run  directly  into  the  postero-inferior  lobule.  The  three  parts  of  the 
lobus  tuberis  are  thus  linked  together. 

The  postero-inferior  lobule,  which  is  wider  towards  the  vallecula  than  it  is 
further  out,  is  traversed  by  two  or  it  may  be  three  curved  fissures.  The  most 
anterior  of  these  cuts  off  a  narrow,  curved  strip  of  cerebellar  surface,  which  presents 
a  more  or  less  uniform  width  throughout  its  whole  length.  This  is  the  so-called 
lobulus  gracilis. 

Lobus  Pyramidis. — The  pyramid  is  connected  with  the  biventral  lobule  on 
each  side  by  an  elevated  ridge  which  crosses  the  sulcus  vallecula.  The  term  lobus 
pyramidis  is  applied  to  the  three  lobules,  which  are  thus  associated  with  each 
other. 

Tlie  pyramid  is  separated  from  the  tuber  valvulae  by  a  deep  furrow  which  has  been  termed 
by  Elliot  Smith  the  suprapyramidal  fissure.  It  is  in  a  measure  continuous  with  the  curved 
fissure,  which  on  the  under  surface  of  the  hemisphere  intervenes  between  the  biventral  lobule 
and  the  lobulus  gracilis  or  fore  part  of  the  postero-inferior  lobule.  The  name  applied  to  the 
latter  fissure  by  Elliot  Smith  is  flssura  parapyramidalis. 

Lobus  Uvulse. — The  uvula  is  a  triangular  elevation  of  the  vermis  inferior.  It 
lies  between  the  two  tonsils,  and  is  connected  with  each  of  these  by  a  low-lying 


Superior  pediinr  li^  of  ri^i  (  hi  llnni 
Middle  peduncle  of  cerebellm  ^ 


Ventiicle  IV. 


Central  lobule    Superior  medullary  velum 


Nodule 


Postero-iuferior  lobule 


Great  horizontal 
fisbure 


Postero-inferior  lobule' 

Lobulus  gracilis/^ 

Bnential  lubuli 

Pyiamid  Tuber  valvule 

Fig.  409. — Lower  Surface  of  the  Cerebellum. 

The  tonsil  on  the  right  side  has  been  removed  so  as  to  display  more  fully  the  inferior  medullary  velum  and 

the  furrowed  band. 


band-Hke  ridge  of  gray  matter  scored  by  a  few  shallow  furrows,  and  in  consequence 
termed  the  furrowed  band.     The  two  tonsils  and  the  uvula  form  the  lobus  uvulse. 

Between  the  pyramid  and  the  uvula  there  is  a  deep  cleft  which  may  be  termed  the  infra- 
pyramidal  fissure  (the  fissura  secunda  of  Elliot  Smith).  This  is  more  or  less  directly  connected 
with  the  retrotonsillar  fissure  which  curves  round  ■  the  tonsil.  The  large  size  of  the  tonsil  is 
characteristic  of  the  brain  of  man  and  the  anthropoid  ajaes. 

Lobus  Noduli. — The  lobus  noduli  comprises  the  nodule  and  the  flocculus  of 
each  side,  with  a  delicate  connecting  lamina  of  w^hite  matter  termed  the  inferior 
medullary  velum. 


THE  CEREBELLUM. 


509 


Culmen  rnonticuli 


The  cleft  between  the  nodule  and  the  uvula  is  termed  the  postnodular  fissure  (Elliot  Smith) ; 
that  between  the  flocculus  and  the  bi  ventral  lobule  is  called  tlie  floccular  fissure. 

The  flocculus  will  usually  be  observed  to  be  jjartially  divided  into  two  pieces.  The  smaller 
hinder  portion,  which,  as  a  rule,  is  completely  overlapped  by  the  overhanging  edge  of  the 
biventral  lobule,  is  the  paraflocculus.  This  assumes  very  large  proportions  in  certain  of  the 
lower  mammals. 

Arrangement  of  the  Gray  and  White  Matter  of  the  Cerebellum.— The  white 
matter  of  the  cerebellum  forms  a  solid  compact  mass  in  the  interior,  and  over  this 
is  spread  a  con- 
tinuous and  uni- 
form layer  of  gray 
matter.  In  each 
lateral  hemi- 
sphere the  white 
central  core  is 
more  bulky  than 
in  the  median 
lobe  or  worm,  in 
which  the  central 
white  matter  is 
reduced  to  a  re- 
latively thin 
bridge  thrown 
across  between 
the  two  lateral 
hemispheres.  The 
white  matter  in 
the  interior  of  the 


/_  Corpus 

dentatum 


Inferior  olivary  nucleus 


Fig.  410. — Sagittal  Section  through  the  Left  Lateral  Hemisphere 
OF  THE  Cerebellum, 

Showing  the  "  arbor  vitse"  and  the  corpus  dentatum. 


median  lobe  or  worm  is  termed  the  corpus  trapezoides.  When  sagittal  sections 
are  made  through  the  cerebellum,  the  gray  matter  on  the  surface  stands  out  clearly 
from  the  white  matter  in  the  interior.     Further,  from  all  parts  of  the  surface  of 


Pulvinar"  " 
Inferior  quadrigeminal  body — 

Middle  cerebellar  jjeduncle 

Inferior  cerebellar  peduncle 


,_  A Third  ventricle 

■Teenia  thalami 

^i^k > Trigonum  liabenul» 

.  Pineal  body 

-Superior  quadrigeminal  body 

-Inferior  bracbium 
-  Fourth  nerve 


-  Valve  of  Vieussens 
-Superior  cerebellar  peduncle 


g Corpus  dentatum 


Vu..  411.— From  u  dissection  by  Dr.  Edward  B.  .Jamieson  in  the  Anatomical  Department  of  the  University  of 
Edinburglj.  1'he  corpus  dentatum  is  displayed  from  above  and  the  superior  cerebellar  peduncle 
has  \)S'A:n  traced  from  it  to  the  rtiesencc^phaloii. 

the  central  core  Htout  HtcniH  of  white  matter  are  seen  projecting  into  the  lobes  of 
the  cerebellum.     From  the  sides  of  these  white  stems  secondary  branches  proceed 


510  THE  NEKVOUS  SYSTEM. 

at  various  angles,  and  from  these  again  tertiary  branches  are  given  oif.  Over  the 
various  lamellae  of  white  matter  thus  formed  the  gray  cortex  is  spread,  and  the 
fissures  on  the  surface  show  a  corresponding  arrangement,  dividing  up  the  organ 
into  lobes,  lobules,  and  folia.  When  the  cerebellum  is  divided  at  right  angles  to 
the  general  direction  of  its  fissures  and  folia,  a  highly  arljorescent  appearance  is 
thus  presented  by  the  cut  surface.  To  this  the  term  arbor  vitse  cerebelli  is  applied. 
Corpus  Dentatum  and  other  Gray  Nuclei  in  the  White  Matter  of  the 
Cerebellum. — Embedded  in  the  midst  of  the  mass  of  white  matter  whicli  forms  the 
central  core  of  each  lateral  hemisphere  there  is  an  isolated  nucleus  of  gray  matter, 
which  presents  a  strong  resemblance  to  the  inferior  olivary  nucleus  of  the  medulla. 
It  is  called  the  corpus  dentatum  (nucleus  dentatus),  and  it  consists  of  a  corrugated 
or  plicated  lamina  of  gray  matter,  which  is  folded  on  itself  so  as  to  enclose,  in  a 
flask-like  manner,  a  portion  of  the  central  white  matter  (Figs.  410  and  411). 
This  gray  capsule  is  not  completely  closed.  It  presents  an  open  mouth,  termed 
the  hilum,  which  is  directed  inwards  and  upwards,  and  out  of  this  stream  the 
great  majority  of  the  fibres  of  the  superior  cerebellar  peduncle. 

Thi'ee  small  additional  masses  of  gray  matter  are  also  present  on  either  side  of  the  mesial 
plane  in  the  central  white  matter  of  the  cerebellum.  These  are  termed  the  nucleus  emboli- 
formis,  the  nucleus  globosus,  and  the  nucleus  fastigii.  The  nucleus  emboliformis  or  embolus  is  a 
small  lamina  of  gray  matter  which  lies  immediately  internal  to  the  hilum  of  the  corpus  dentatum, 
being  thus  related  to  it  somewhat  in  the  same  manner  that  the  mesial  accessory  olivary  nucleus 
is  related  to  the  main  inferior  olivary  nucleus.  The  nucleus  globosus  lies  internal  to  the  embolus 
and  on  a  somewhat  deeper  horizontal  plane.  The  nucleus  fastigii  or  roof  nucleus  is  placed  in 
the  white  substance  of  the  worm  (cor^^us  trapezoides)  close  to  the  mesial  plane  and  its  fellow  of 
the  opposite  side.     It  is,  therefore,  situated  on  the  mesial  aspect  of  the  nucleus  globosus. 

Although  isolated  from  the  gray  matter  of  the  surface,  these  small  nuclei  and  the  corpus 
dentatum  are  connected  at  certain  points  with  each  other.  The  corpus  dentatum  and  the 
embolus  present  a  structure  very  similar  to  that  of  the  inferior  olivary  nucleus.  In  the  nucleus 
globosus  and  the  nucleus  fastigii  the  cells  are  somewhat  larger  in  size. 

Cerebellar  Peduncles. — These  are  three  in  number  on  each  side,  viz.  the  middle, 
the  inferior,  and  the  superior  (Fig.  391,  p.  487).  The  fibres  of  which  they  are 
composed  all  enter  or  emerge  from  the  white  medullary  centre  of  the  cerebellum. 

The  middle  peduncle  is  much  the  largest  of  the  three,  and  has  already  been 
described  on  pp.  486  and  501.  It  is  formed  by  the  transverse  fibres  of  the  pons, 
and  it  enters  the  cerebellar  hemisphere  on  the  outer  aspect  of  the  other  two 
peduncles.  The  lips  of  the  anterior  part  of  the  great  horizontal  fissure  are 
separated  widely  from  each  other  to  give  it  admission  (Fig.  409).  Within  the 
cerebellar  hemisphere  its  fibres  are  distributed  in  two  great  bundles.  Of  these, 
one,  composed  of  the  upper  transverse  fibres  of  the  pons,  radiates  out  in  the  lower 
part  of  the  hemisphere ;  whilst  the  other,  consisting  of  the  lower  transverse  fibres 
of  the  pons,  spreads  out  in  the  upper  part  of  the  hemisphere. 

The  inferior  peduncle  is  simply  the  restiform  body  of  the  medulla.  After 
leaving  the  medulla  it  ascends  for  a  short  distance  on  the  dorsal  surface  of  the 
pons  and  then  turns  sharply  backwards,  to  enter  the  cerebellum  between  the  other 
two  peduncles. 

The  superior  peduncle,  as  it  issues  from  the  cerebellum,  lies  close  to  the  inner 
side  of  the  middle  peduncle  (Fig.  409).  Its  further  course  upwards  on  the  dorsum 
of  the  pons  to  the  inferior  quadrigeminal  body  has  been  previously  described  (pp. 
486  and  503). 

Connexions  established  by  the  Peduncular  Fibres. — The  fibres  of  the  middle 
peduncle  are  both  afferent  and  efferent.  The  connexions  which  they  establish  in  the 
pons  are  described  on  p.  501.  Tlie  efferent  fibres  arise  from  cells  in  the  gray  cortex  of  the 
lateral  hemisphere  (also  probably  to  some  small  extent  in  the  cortex  of  the  vermis),  and 
end  in  connexion  with  tlie  cells  of  the  nucleus  pontis,  and  likewise  in  the  tegmental  part 
of  the  pons.  The  afferent  fibres,  arising  in  the  pons,  end  in  the  gray  cortex  of  the  lateral 
hemisphere  of  the  cerebellum,  and  perhaps  also  in  the  cortex  of  the  worm. 

The  inferior  peduncle  is  also  composed  of  afferent  and  efferent  fibres  (see  p.  496)  ;  only 
the  more  important  connexions  which  these  establish  in  tlie  cerebellum  can  be  touched  on 
here.  The  principal  afferent  strand  is  the  direct  cerebellar  tract.  The  fibres  of  this 
strand  end  in  the  cortex  of  the  superior  worm  on  both  sides  of  the  mesial  plane,  but 
chiefly  on  the  opposite  side.     The  cerehello-olivary  fibres  are  also  probably  affei-ent.     It 


THE  CEEEBELLAR  PEDUNCLES.  511 

appears  that  they  end  in  connexion  with  cells  in  the  cortex  of  both  the  worm  and  lierni- 
sphere,  and  also  cells  in  the  nucleus  dentatus.  The  numerous  arcv/xte  fihren  which  enter 
the  inferior  peduncle  establish  connexions  with  cells  in  the  cortex  of  the  lateral  henaisphere 
and  of  the  worm. 

The  superior  peduncle  is  an  efferent  tract.  The  majority  of  its  fibres  come  from 
the  cells  of  the  nucleus  dentatus,  whilst  a  small  proportion  appear  to  come  from  the  cere- 
bellar cortex.  According  to  Risien  Russell,  the  fibres  which  form  the  dorsal  edge  of  the 
band  come  from  the  opposite  side  of  the  cerebellum  and  cross  the  mesial  plane  to  join  the 
peduncle. 

Our  knowledge  of  the  connexions  of  the  peduncles  of  the  cerebellum  has  been  greatly 
extended  by  Ferrier  and  Aldren  Turner ;  and  the  account  which  is  given  above,  and  also  at 
p.  501,  is  largely  derived  from  their  memoir  on  this  subject. 

Commissural  and  Association  Fibres. — In  addition  to  those  fibres  of  the  white 
medullary  centre  which  belong  to  the  system  of  peduncles,  there  are  others  which  have 
exclusively  cerebellar  connexions.  Thus  the  various  folia  ax-e  bound  together  by  numerous 
association  fibres,  which  pass  from  one  folium  into  another  around  the  bottom  of  the  inter- 
vening fissure.  Tracts  of  transversely-directed  commissural  fibres  cross  the  mesial  plane 
in  the  white  centre  of  the  vermis,  connecting  corresponding  parts  of.  opposite  sides.  These, 
in  some  measure,  are  analogous  to  the  corpus  callosum  of  the  cerebrum.  The  roof  nuclei 
are  also  closely  bound  by  connecting  fibres  with  the  cortex. 

Medullary  Vela. — The  medullary  vela  are  closely  associated  with  the  cerebellar 
peduncles.  They  consist  of  two  thin  laminae  of  white  matter,  which  are  projected 
out  from  the  white  central  core  of  the  cerebellum. 

The  superior  medullary  velum  is  described  on  p.  486.  Laterally,  it  is  continuous 
with  the  dorsal  edges  of  the  superior  cerebellar  peduncles ;  whilst,  inferiorly,  it 
is  prolonged  downwards  and  backwards  under  the  Hngula  and  the  central  lobule  of 
the  superior  worm,  to  become  continuous  with  the  central  white  matter  or  corpus 
trapezoides  of  the  worm. 

The  inferior  medullary  velum  is  more  complicated  in  its  connexions.  It  presents 
much  the  same  relations  to  the  nodule  of  the  inferior  vermiform  process  that  the 
superior  velum  presents  to  the  lingula  of  the  superior  vermiform  process.  It  is  a 
wide  thin  lamina  of  white  matter — so  thin  that  it  is  translucent — which  is  pro- 
longed out  from  the  white  centre  of  the  cerebellum  above  the  nodule.  From  the 
nodule  it  stretches  outwards  to  the  flocculus  on  each  side,  thereby  bringing  these 
three  small  portions  of  the  cerebellum  into  association  with  each  other  (Fig.  409). 
Where  it  issues  from  the  white  matter  of  the  cerebellum  it  is  in  contact  with  the 
superior  medullary  velum,  but,  as  the  two  laminae  are  traced  forwards,  they 
diverge  from  each  other.  The  superior  velum  is  carried  upwards  between  the 
two  superior  cerebellar  peduncles,  whilst  the  inferior  medullary  velum  is  curved 
forwards  and  then  downwards  round  the  nodule,  and  ends  at  a  variable  point  in 
a  free,  slightly  thickened,  crescentic  edge.  The  cavity  of  the  fourth  ventricle 
is  carried  backwards  into  the  cerebellum  between  the  two  vela,  which  thus  form 
a  peaked  and  tent-like  root  for  it. 

Relation  of  the  Tract  of  Gowers  to  the  Superior  Medullary  Velum. — The 

ascending  tract  of  Gowers  has  been  noticed  in  connexion  with  the  lateral  column  of  the 
cord  (p.  469).  The  fibres  which  compose  it  are  carried  upwards  through  the  formatio 
reticularis  grisea  of  the  medulla  and  the  corresponding  part  of  the  tegmental  portion  of 
the  pons.  In  this  part  of  its  course  the  fibres  are  scattered  and  do  not  form  a  compact 
strand.  Reaching  the  upper  end  of  the  pons  the  tract  turns  backwards,  enters  the 
superior  medullary  velum,  and  proceeds  downwards  in  it  into  the  cerebellum. 

Roof  of  the  Fourth  Ventricle. — In  its  upper  part  the  roof  of  the  fourth 
ventricle  is  formed  by  the  superior  medullary  velum  as  it  stretches  across  between 
the  two  superior  cerebellar  peduncles,  and  also,  to  some  extent,  by  the  approximation 
of  these  yjedunoles  thems(dves  as  they  approach  the  mesencephalon. 

In  its  lower  part  tlie  roof  of  tlie  ventricle  is  exceedingly  thin  and  is  not  all 
formed  of  nervous  matter.  The;  inferior  medullary  velum  enters  into  its  formation, 
and,  wliere  this  fails,  the  epithelial  lining  of  the  cavity,  supported  by  pia  mater,  is 
carried  downwards  towards  the  lower  boundaries  of  the  floor  of  the  ventricle.  At 
the  lowest  part  of  the  calamus  scriptorius,  and  also  along  each  lateral  boundary  of 


512 


THE  NEEVOUS  SYSTEM. 


the  floor,  a  thin  lamina  of  white  matter  is  carried  for  a  short  distance  over  the 
epithelial  roof.  The  small  semilunar  lamina  which  stretches  across  between  the 
lower  parts  of  the  two  clav«  at  the  calamus  scriptorius  and  overhangs  the  opening 


Fornix        \      V-- \.  -    * '  '      * 

Foramen  of  Monro       ^ 


\ 


Septum  lucidum 

Genu  of  corpus     / 
callosum 


Anterior  commissure 

Corpus  mammillare ' 
Lamina  cinerea  ' 


Optic  nerve' 


Tuber 
valvulse 


Pyramid 


Pituitary  body 

Tuber  cinereum 

Third  nerve 


Pons 
Valve  of  Vieussens 

Ventricle  IV. 
Medulla 


■^-     Uvula 


I       I  Central  lobule 

I     Nodule 
Choroid  plexus  in  ventricle  IV. 

Fig.  412. — Mesial  Section  through  the  Corpus  Callosum,  the  Mesencephalon,  the  Pons,  Medulla, 

AND  Cerebellum. 

Showing  the  third  and  fourth  ventricles  joined  by  the  aqueduct  of  Sylvius. 

of  the  central  canal  is  termed  the  obex  (Fig.  391,  p.  487).  The  lamina  in  connexion 
with  the  lateral  boundary  of  the  ventricular  floor  is  more  extensive,  and  is  called 
the  ligula  (Figs.  388  and  390).  It  begins  on  the  clava  and  passes  upwards  over  the 
cuneate  tubercle  to  the  restiform  body.  On  the  outer  surface  of  the  restiform  body 
it  turns  outwards  so  as  to  bound  the  lateral  recess  of  the  ventricle  below,  and  in  some 
cases  it  may  be  seen  to  become  continuous  around  the  extremity  of  the  lateral 
recess  with  the  inferior  medullary  velum. 

A  short  distance  above  the  calamus  scriptorius  there  is,  in  the  mesial  plane,  an 
opening  in  the  epithelial  and  pial  roof  of  the  ventricle,  by  which  the  cavity  of  the 
ventricle  communicates  with  the  subarachnoid  space.  This  opening  is  termed  the 
foramen  of  Majendie.  There  is  also  an  aperture  of  a  similar  nature  in  the  epithelial 
and  pial  roof  at  the  extremity  of  each  lateral  recess. 

Two  choroid  plexuses,  or  highly  vascular  infoldings  of  the  pia  mater,  invaginate 
the  lower  part  of  the  roof  of  the  fourth  ventricle.  These  are  placed  one  on  either 
side  of  the  mesial  plane,  and,  although  they  appear  to  lie  within  the  cavity,  they 
are  in  reality  excluded  from  it  by  the  epithelial  lining  of  the  ventricle,  which  covers 
over  and  is  adapted  to  every  sinuosity  on  their  surface. 

Two  lateral  offshoots  from  these  longitudinal  choroid  plexuses  proceed  outwards, 
and  protrude  in  a  similar  manner  into  the  lateral  recesses. 


Minute  Steucture  of  a  Cerebellar  Folium. 

A  cerebellar  folium  is  composed  of  a  central  core  of  white  matter,  covered  by  a  layer 
of  gray  matter.  The  gray  cortex  is  arranged  in  two  very  evident  layers,  viz.  a  superficial 
molecular  layer  and  a  subjacent  rust-coloured  granular  layer.  Between  these  strata  a 
single  layer  of  large  cells,  termed  the  cells  of  Purkinje,  are  disposed  in  the  form  of  a 
very  nearly  continuous  sheet.  The  cells  of  Purkinje  constitute  the  most  characteristic, 
and  probably  the  most  essential,  constituents  of  the  cerebellar  cortex. 

The  cells  of  Purkinje  are  most  numerous  on  the  summit  of  the  folium.  At  the 
bottom  of  the  sulci  which  intervene  between  the  folia  they  become  fewer  in  number,  and, 
therefore,  looser  in  their  arrangement.     Each  consists  of  a  large  flask-shaped  or  pyriform 


MINUTE  STEUCTUEE  OF  A  CEEEBELLAE  FOLIUM. 


513 


cell  body,  the  narrow  end  of  which  projects  into  the  molecular  layer,  whilst  the  thicker, 
deeper  end  rests  on  the  granular  layer.  From  the  latter  arises  a  single  axon,  which  passes 
into  the  granular  layer  and  presents  the  peculiarity  of  almost  immediately  assuming  its 
medullary  sheath.  From  this  axon  a  few  collateral  branches  soon  arise,  which,  taking  a 
recurrent  course,  enter  the  molecular  layer,  to  end  in  connexion  with  certain  of  the 
adjoining  cells  of  Purkinje.  They  would  seem  to  have  the  function  of  binding  together 
adjacent  cells,  and  thus 
enabling  them  to  carry  on 
their  operations  in  harmony 
with  each  other. 

The  dendritic  processes 
sj)ring  from  the  narrow  end 
of  the  cell  either  in  the  form 
of  one  or  perhaps  two  stout 
stalks.  These  ascend  into 
the  molecular  layer,  branch- 
ing and  rebranching  until 
an  aborescent  arrangement 
of  extraordinary  richness  and 
extent  results.  The  den- 
dritic branches  extend 
throughout  the  entire 
thickness  of  the  molecular 
layer,  and  the  branching 
takes  place  in  one  plane  only, 
viz.  in  a  plane  which  is  trans- 
verse to  the  long  axis  of  the 
folium.  Consequently,  it  is 
only  when  transverse  sections 
are  made  through  a  folium 
that  the  full  dendritic  effect 
is  obtained  ;  in  sections 
made  parallel  to  the  long 
axis  of  the  folium  the  cells 
are  seen  in  profile,  and  are 
observed  to  occupy  quite  a 
narrow  area  (Fig.  414).    The 


Fig.  413. — Transverse  Section  through  a  Cerebellar  Folium 
(after  Kolliker). 

Treated  by  the  Golgi  method. 

Axon  of  cell  of  Purkiuje. 

branching  of  the  dendrites  ^-      ^^^^^  fibres. 

K  and  K^.   Fibres  from  white  core  of  folium  ending  in  molecular  layer  iu 

connexion  with  the  dendrites  of  the  cells  of  Purkinje. 
M.      Small  cell  of  the  molecular  layer. 
that  which   takes    place    in  GR.   Granule  cell. 
the     case      of     a     fruit-tree  G-R^.  Axons  of  granule  cells  in  molecular  layer  cut  transversely. 

M^    Basket-cells. 

Basket-work  around  the  cells  of  Purkinje. 

Neuroglial  cell. 

Axon  of  an  associatiou  cell. 


of  a  cell  of  Purkinje  may, 
therefore,  be    compared    to 


which  is    trained  against  a  2^; 
wall.  GL.' 

In  the  molecular  layer  n. 
the  cells  are  not  particularly 

numerous,  and  of  these  the  most  characteristic  are  the  basket -cells  which  lie  in  the 
deeper  part  of  the  layer.  In  addition  to  numerous  dendrites  the  basket-cell  gives  off  an 
axon  which  runs  transversely,  as  regards  the  long  axis  of  the  folium,  between  the  planes 
of  adjacent  dendritic  arborisations  of  the  cells  of  Purkinje.  At  first  very  fine  these  axons 
gradually  become  coarse  and  thick,  and  at  intervals  they  give  oif  collaterals  which  run 
towards  the  bodies  of  the  cells  of  Purkinje.  Reaching  these,  they  break  up  into  an 
enormous  number  of  fine  terminal  branches,  which  enclose  the  cells  of  Purkinje,  as  well 
as  the  short  non-medullated  portions  of  their  axons,  in  a  close  basket-work  of  fine 
filaments. 

The  granular  layer  is,  for  the  most  part,  composed  of  large  numbers  of  small 
granule-like  bodies  closely  packed  together.  Each  of  these  possesses  a  somewhat  large 
nucleus,  with  a  very  small  amount  of  surrounding  protoplasm.  From  the  cell  body  three 
or  four,  or  perhaps  five,  dendrites  and  one  axon  proceed.  The  dendrites  are  short  and 
radiate  out  from  different  aspects  of  the  cell  body.  They  end  in  tufts  of  claw-like  twigs, 
which  either  embrace  or  are  otherwise  in  contact  with  neighbouring  graimlc  cells.  The 
whole  nniltitude  of  granule  cells,  therefore,  are  brought  into  intimate  connexion  with 
each  other.  Tlie  axon  passes  into  the  molecular  layer,  in  which  it  ends  at  a  varying 
37 


514 


THE  NEEVOUS  SYSTEM. 


distance  from  the  surface  b}^  dividing  into  two  branches.  These  diverge  so  sharply  from 
each  other  that  they  almost  form  a  right  angle  with  the  parent  stem,  and  they  run 
parallel  to  the  long  axis  of  the  folium,  threading  their  way  between  the  branches  of  the 
various  dendritic  planes  of  the  cells  of  Purkinje  and  entering  into  contact  association  with 
them.  When  the  great  number  of  granule  cells  is  borne  in  mind,  and  the  fact  that  each 
sends  an  axon  into  the  molecular  layer,  the  important  part  which  these  fibres,  with  their 
longitudinal  branches,  take  in  building  up  the  molecular  layer  will  be  understood.  They 
are  found  pervading  its  entire  thickness — from  the  surface  down  to  the  bodies  of  the  cells 
of  Purkinje. 

Near  the  cells  of  Purkinje  a  few  scattered  cells  are  seen  in  the  granular  layer  of  a 

different  kind.  These  are  much  larger  than  the 
ordinary  granule  cells,  and  are  probably  of  the 
nature  of  association  cells.  They  ai-e  stellate  in 
form,  and  have  numerous  long  branching  dendrites 
and  an  axon  which  divides  up  in  the  granular 
layer  to  a  singular  extent. 

The  white  centre  of  the  folium  becomes 
thinner  as  it  approaches  the  summit.  This  is  due 
to  the  fibres  which  compose  it  gradually  entering 
the  gray  matter  on  the  surface.  These  fibres 
are  of  three  kinds,  viz.  :  (1)  axons  of  the  cells 
of  Purkinje ;  (2)  fibres  which  apparently  end 
in  the  granular  layer;  and  (3)  fibres  which 
end  in  the  molecular  layer. 

The  axons  of  the  cells  of  Purkinje  are 
medullated  fibres  which,  entering  the  white 
centre  of  the  folium,  form  a  not  inconsiderable 
part  of  it. 

The   fibres  which  end   in  the  granular  layer 
are  called  moss-fibres.     This  name  is  applied  to 
Fig.  414.— Section  through  the  Molecular   them    because,     in    the    granular     layer,     they 
AND  Granular  Layers  in  the  Long  Axis   present   at  certain  points  moss-like  thickenings, 

from  which  short  rough  twigs  proceed. 

The  fibres  which  proceed  into  the  molecular 
layer  give  ofi^  few  or  perhaps  no  branches  as  they 
traverse  the  granular  layer.  In  the  deeper  part 
of  the  molecular  layer  they-  break  up  into 
varicose  branches,  which  twine  around  the 
primary  and  secondary  stems  of  the  Purkinje  dendrites. 

Entering  into  the  constitution  of  the  molecular  layer  are  the  following  elements :  (1) 
dendrites  of  the  cells  of  Purkinje ;  (2)  basket-cells  and  somewhat  smaller  cells  nearer  the 
surface ;  (3)  axons  of  the  granule  cells,  with  their  longitudinally  arranged  branches ;  (4) 
the  terminations  of  certain  fibres  from  the  Avhite  core  of  the  folium,  which  end  in  contact 
with  the  Purkinje  dendrites. 

In  the  granular  layer  are  found:  (1)  granule  cells;  (2)  larger  stellate  association 
cells;  (3)  axons  of  the  cells  of  Purkinje;  (4)  moss-fibres  ;  (5)  fibres  traversing  this  laj-er, 
to  end  in  the  molecular  layer. 


OF  A  Cerebellar  Folium  (after  Kolliker) 

Treated  by  the  Golgi  method. 

P.      Cell  of  Purkinje. 

GR.  Granule  cells. 

N.     Axon  of  a  granule  cell. 

N-"^.    Axons  of  granule  cells  in  molecular  layer. 


THE  DEEP  CONNEXIONS  OF  THE  CRANIAL  NERVES  ATTACHED  TO  THE 

MEDULLA  AND  PONS. 

There  are  tv^elve  pairs  of  cranial  nerves,  of  which  the  lov^er  eight  are  attached 
to  the  medulla  and  pons  Varolii.  From  above  downwards  these  are  named  the 
fifth  or  trigeminal,  the  sixth  or  abducent,  the  seventh  or  facial,  the  eighth  or 
auditory,  the  ninth  or  glossopharyngeal,  the  tenth  or  vagus,  the  eleventh  or  spinal 
accessory,  and  the  twell'th  or  hypoglossal.  The  hypoglossal,  the  spinal  accessory, 
the  greater  part  of  the  facial,  the  abducent,  and  the  motor  root  of  the  trigeminal 
are  efferent  nerves ;  the  auditory,  the  pars  intermedia  of  the  facial,  and  the  sensory 
root  of  the  trigeminal  are  purely  afferent  nerves ;  whilst  the  vagus  'and  the  glosso- 
pharyngeal are  composed  of  both  efferent  and  afferent  fibres.  In  all  cases  afferent 
fibres  arise  from  ganglionic  cells  placed  outside  the  brain  and  penetrate  the  brain- 
stem, to  end  in  connexion  with  the  cells  of  certain  nuclei  of  termination.     Efferent 


THE  DEEP  CONNEXIONS  OF  THE  CKANIAL  NERVES.         515 

fibres,  on  the  other  hand,  take  origin  within  the  brain  as  the  axons  of  cells  which 
are  grouped  together  in  certain  places  in  the  form  of  nuclei  of  origin. 

Nuclei  of  Origin,  or  Motor  Nuclei. — In  the  spinal  cord  the  nuclei  of  origin  are 
represented  by  elongated  columns  of  cells  which  run  more  or  less  continuously  in 
the  anterior  horn  of  gray  matter  of  successive  cord-segments,  and  from  these  the  series 
of  efferent  anterior  nerve-roots  take  origin.  In  the  medulla  and  pons  the  nuclei  of 
origin,  or,  in  other  words,  the  motor  nuclei  of  the  individual  nerves  become,  for  the 
most  part,  discontinuous,  and  are  represented  by  certain  isolated  clumps  of  compact 
gray  matter,  in  which  are  placed  the  clusters  of  cells  from  which  the  fibres  of  the 
efferent  nerves  arise.  The  nucleus  ambiguus,  however,  which  consists  of  a  column  of 
cells  from  which  root  fibres  of  the  medullary  part  of  the  spinal  accessory,  of  the  vagus, 
and  possibly  also  of  the  glossopharyngeal  are  derived,  is  an  exception  to  this  rule. 
At  the  decussation  of  the  pyramids,  the  anterior  horn  of  gray  matter  of  the  cord  is 
broken  up  by  the  intercrossing  bundles  into  a  detached  head  and  a  basal  part  which 
remains  in  relation  with  the  ventro-lateral  aspect  of  the  central  canal.  Certain 
of  the  efferent  or  motor  nuclei  of  the  medulla  and  pons  lie  in  the  line  of  the  basal 
portion  of  the  ventral  horn  of  gray  matter  of  the  spinal  cord,  and  thus  close  to 
the  mesial  plane.  These  are  termed  mesial  nuclei  of  origin,  and  are  met  with  at 
different  levels  in  the  brain-stem.  This  group  comprises  the  hypoglossal  nucleus, 
the  dorsal  motor  nucleus  of  the  vago-glossopharyngeal  nerve,  the  abducent  nucleus 
(and,  in  the  mesencephalon,  the  trochlear  nucleus  and  the  oculo-motor  nucleus). 
Other  motor  nuclei  of  origin  are  present  in  the  form  of  isolated  clumps  or  columns 
of  gray  matter,  which  lie  at  different  levels  in  the  medulla  and  pons  in  the  line  of 
the  detached  head  of  the  anterior  horn  of  gray  matter.  They  are  the  nucleus 
ambiguus  of  the  spinal  accessory,  the  vagus  and  glossopharyngeal,  the  facial 
nucleus,  and  the  nucleus  of  the  motor  root  of  the  trigeminal  nerve.  Erom  their 
position  in  the  tegmental  substance  of  the  medulla  and  pons  they  constitute  a  group 
to  which  the  name  of  lateral  motor  nuclei  is  applied. 

The  different  nuclei  of  origin  of  the  efferent  fibres  which  belong  to  the  various 
cranial  nerves,  both  mesial  and  lateral,  are  connected  with  the  motor  area  of  the 
cerebral  cortex  by  fibres  from  the  pyramidal  tract,  which  enter  the  nuclei  and  end 
in  connexion  with  their  cells. 

Nuclei  of  Termination. — In  the  brain  the  nuclei  of  termination  are  likewise 
discontinuous,  and  are  represented  by  more  or  less  isolated  clusters  or  columns  of 
cells.  Unlike  the  motor  nuclei,  however,  these  nuclei  show  no  regular  or  definite 
position  within  the  medulla  and  pons.  Some  are  found  in  the  gray  matter  which 
surrounds  the  central  canal,  and  in  its  continuation  upwards  as  the  gray  matter  in 
the  floor  of  the  fourth  ventricle ;  others  are  placed  in  the  tegmental  substance  ;  whilst 
two  actually  lie  on  the  surface  of  the  brain-stem,  viz.  the  lateral  and  ventral  nuclei 
of  the  cochlear  or  outer  division  of  the  auditory  nerve. 

The  axons  of  the  cells  of  the  nuclei  of  termination  enter  the  reticular  formation 
of  the  tegmental  substance  as  arcuate  fibres,  and,  crossing  the  mesial  plane,  are 
carried  upwards  in  the  tegmental  substance  of  the  opposite  side  to  establish  direct 
connexions  with  the  optic  thalamus  and  indirect  connexions  with  the  cerebral 
cortex. 

Hypoglossal  Nerve  (nervus  hypoglossus). — The  nucleus  of  origin  of  the  hypo- 
glossal nerve,  the  motor  nerve  of  the  tongue,  lies  in  the  substance  of  the  medulla 
oblongata.  It  is  composed  of  several  groups  of  large  multipolar  cells,  which  closely 
resemble  the  cells  in  the  ventral  horn  of  gray  matter  in  the  spinal  cord,  and  is 
pervaded  by  an  intricate  network  of  fine  fibrils.  In  form  it  is  elongated  and 
rod-like,  and  in  length  it  is  somewhere  about  18  mm.  It  extends  from  a  point 
immediately  above  the  decussation  of  the  pyramids  up  to  the  level  of  the  striee 
acustic^.  Tlie  lower  yjortion  of  tlie  nucleus  is  thus  placed  in  the  closed  part  of  the 
medulla  CFig.  397,  p.  493),  whilst  its  upper  part  is  situated  in  the  open  part  of  the 
medulla  (Fig  402,  p.  497).  The  former  lies  in  that  part  of  the  central  gray  matter 
which  is  continuous  with  the  basal  part  of  the  ventral  horn  of  gray  matter  of  the 
cord.  It  is  thus  placed  on  the  ventral  and  lateral  aspect  of  the  central  canal, 
close  to  the  mesial  plane  and  the  corresyxmdirig  nucleus  of  the  opposite  side.  The 
uplK;r  part  of  the  nucleus  occupies  a  position  in  the  gray  matter  on  the  floor  of 


516 


THE  NEEVOUS  SYSTEM. 


the  fourth  ventricle,  subjacent  to  the  inner  part  of  the  surface  area,  which  has  been 
described  under  the  name  of  the  trigonum  hypoglossi.  Witliin  the  nucleus  the 
axons  of  the  cells  arrange  themselves  in  converging  bundles  of  fine  fibres,  which 
come  together  and  leave  the  ventral  aspect  of  the  nucleus  as  the  fasciculi' of  the 
nerve.  The  nerve  bundles  thus  formed  traverse  the  entire  antero-posterior  thickness 
of  the  medulla  between  the  formatio  reticularis  grisea  and  the  formatio  reticularis 
alba,  and  emerge  on  the  surface  in  linear  order  at  the  bottom  of  the  furrow  between 
the  olivary  eminence  and  the  pyramid.  In  the  sul)stance  of  the  medulla  the  root- 
bundles  of  the  hypoglossal  pass  between  the  main  inferior  olivary  nucleus  and  the 
mesial  accessory  ohvary  nucleus,  and  many  of  them  on  their  way  to  the  surface 
pierce  the  ventral  lamina  of  the  main  olivary  nucleus. 

No  decussation  between  the  nerves  of  opposite  sides  takes  place  in  the  medulla,  but 
commissural  fibres  pass  between  the  two  nuclei  (Kolliker).  Further,  numerous  fibres  from 
the  opposite  pyramidal  tract  enter  the  nucleus  and  end  in  connexion  with  its  cells.  The 
nucleus  is  thus  brought  into  connexion  with  the  motor  area  of  the  opposite  side  of  the 
cerebral  cortex. 

Spinal  Accessory  Nerve  (nervus  accessorius). — The  spinal  accessory  is  likewise 
a  motor  nerve,  and  it  is  generally  described  as  consisting  of  a  spinal  and  a  medullary 
or  accessory  part. 


Column  of  Goll 


Column  of  Burdach 


POST.R007 


ANTHOC 


Fig.  415. — Diagram  of  the  Spinal 
Origin  of  the  Spinal  Accessory 
Nerve  (after  Bruce). 


Entering 
posterior  nerve 
root 


Substantia 
gelatinosa 
Rolandi 


Emerging 
fascicle  of  spinal 
accessory  nerve 
Fibres  of  origin 
■of  spinal 
accessory 
Emerging 
■anterior  nerve 
root 


Fig.  416. — Section  through  the  Upper  Part  of  the 

Cervical  Region  of  the  Cord  (Orang), 

Showing  the  origin  of  the  spiual  part  of  the  spinal  accessory 

nerve. 


The  spinal  part  of  the  nerve  emerges  by  a  series  of  roots  which  issue  from  the 
surface  of  the  lateral  column  of  the  upper  part  of  the  cord  as  low  down  as  the  fifth 
cervical  nerve.  These  take  origin  in  a  column  of  cells  situated  in  the  anterior  horn 
of  gray  matter  of  the  cord  close  to  its  lateral  margiu,  and  immediately  behind  the 
nerve-cells  which  give  rise  to  the  fibres  of  the  anterior  roots  of  the  upper  five 
cervical  nerves.  The  cells  of  the  accessory  nucleus  are  large,  multipolar,  and  in 
every  respect  similar  to  the  motor  cells  of  the  spinal  nerves.  The  axons  from  these 
cells  leave  the  dorsal  aspect  of  the  nucleus  in  converging  groups  to  form  the  root- 
bundles  of  the  nerve.  These,  in  the  first  place,  proceed  straight  backwards  in  the 
anterior  horn  of  gray  matter.  Eeaching  the  bay  between  the  two  horns  of  gray 
matter,  they  turn  sharply  outwards  into  the  white  matter  and  traverse  the  lateral 
column  to  gain  their  points  of  exit  from  the  cord.  At  the  decussation  of  the 
pyramids,  root-bundles,  which  join  the  spinal  accessory  nerve,  are  seen  to  proceed 
from  the  detached  head  of  the  anterior  horn  of  gray  matter. 

The  medullary  part  of  the  spinal  accessory  nerve  has  its  nucleus  of  origin  in  the 
medulla ;  and  its  root-bundles,  as  they  proceed  outwards  from  this,  can  be  distin- 


THE  DEEP  CONNEXIONS  OF  THE  CEANIAL  NERVES.  517 

guished  by  the  fact  that  they  pursue  a  course  on  the  ventral  side  of  the  spinal  root 
of  the  trigeminal  nerve,  whereas  the  vagus  roots,  with  which  they  are  apt  to  he 
confused,  pass  through  or  lie  on  the  dorsal  aspect  of  the  trigeminal  root  (Kolliker). 
The  nucleus  of  origin  of  the  medullary  part  of  the  accessory  nerve  is  formed  Ly  the 
same  column  of  cells  which  constitutes  the  nucleus  ambiguus,  and  which,  at  a  higher 
level,  gives  motor  fibres  to  the  vagus  and  glossopharyngeal  nerves. 

The  i^art  of  the  spinal  accessory  nerve  which  takes  origin  in  the  spinal  cord  supplies  the 
sterno-mastoid  and  trapezius  muscles.  The  medullary  or  accessory  portion  joins  the  vagus,  and 
through  the  external  and  recurrent  laryngeal  nerves  it  supplies  the  muscles  of  the  larynx.  The 
portion  of  the  nucleus  ambiguus  from  which  it  arises  has  thus  been  termed  the  laryngeal  nucleus 
(Edinger). 

Collaterals  and  fibres  of  the  opposite  pyramidal  tract  end  in  connexion  with  the  cells  of 
origin  of  the  accessory  nerve,  and  thus  bring  its  nucleus  into  connexion  with  the  motor  area  of 
the  cerebral  cortex.  Fibres  also  from  the  posterior  roots  of  the  spinal  nerves  (afferent  or  sensory 
fibres)  end  in  the  nucleus. 

Vagus  and  Glossopharyngeal  Nerves  (nervus  vagus,  nervus  glossopharyn- 
geus). — These  nerves  present  similar  connexions  with  the  brain,  and  they  may 
therefore  be  studied  together.  The  greater  part  of  both  nerves  is  composed  of 
afferent  fibres,  which  arise  outside  the  brain-stem  from  ganglionic  cells  placed  in 
relation  to  the  nerve-trunks.  Both  nerves  likewise  possess  motor  or  efferent  fibres, 
which  spring  from  two  special  nuclei  of  origin  situated  within  the  medulla  and 
termed  respectively  the  dorsal  motor  nucleus  and  the  nucleus  ambiguus.  The  alferent 
ganglionic  fibres  of  the  vagus  and  glossopharyngeal  enter  the  brain  by  a  series  of 
roots  which  penetrate  the  medulla  along  the  outer  or  ventral  side  of  the  restiform 
body.  Within  the  medulla  they  separate  into  two  sets,  viz.  a  series  of  bundles 
(chiefly  composed  of  vagus  fibres),  which  end  in  the  dorsal  nucleus  of  termination 
of  the  vagus  and  glossopharyngeal  nerves,  and  another  series  of  bundles  (chiefly 
composed  of  glossopharyngeal  fibres),  which  join  a  conspicuous  longitudinal  tract 
of  fibres  called  the  fasciculus  solitarius. 

The  dorsal  nucleus  (Eigs.  398,  p.  495,  and  402,  p.  497)  of  the  vagus  and  glosso- 
pharyngeal nerves  is  mixed,  and  contains  both  motor  cells  which  give  origin  to 
efferent  fibres  and  cells  around  which  afferent  fibres  of  the  vagus,  and  possibly  also 
of  the  glossopharyngeal  nerve,  break  up  into  terminal  arborisations.  It  very  nearly 
equals  in  length  the  nucleus  of  the  hypoglossal  nerve,  with  which  it  is  closely 
related.  Above,  it  reaches  as  high  as  the  striae  acusticse,  whilst  below  its  lower  end 
falls  slightly  short  of  that  of  the  hypoglossal  nucleus.  In  specimens  stained  by 
the  Weigert-Pal  method  the  two  nuclei  offer  a  marked  contrast.  The  hypoglossal 
nucleus  presents  a  dark  hue,  owing  to  the  enormous  numbers  of  fine  fibres  which 
twine  in  and  out  amidst  its  cells ;  the  vago-glossopharyngeal  dorsal  nucleus  is  pale 
from  the  scarcity  of  such  fibres  within  it.  In  the  closed  part  of  the  medulla  the 
dorsal  vago-glossopharyngeal  nucleus  lies  in  the  central  gray  matter  immediately 
behind  the  hypoglossal  nucleus,  and  upon  the  lateral  aspect  of  the  central  canal ; 
in  the  open  part  of  the  medulla  it  lies  in  the  gray  matter  of  the  floor  of  the  fourth 
ventricle,  immediately  to  the  outer  side  of  the  hypoglossal  nucleus  and  subjacent 
to  the  surface  area  termed  the  trigonum  vagi. 

The  cells  in  the  portion  of  the  dorsal  nucleus  which  acts  as  a  nucleus  of 
termination  are  spindle-shaped  in  form  and  similar  to  those  found  in  the  posterior 
horn  of  gray  matter  in  the  cord.  In  connexion  with  these  cells,  the  greater 
number  of  the  afferent  fibres  of  the  vagus  nerve,  and  a  small  proportion  of  the 
afferent  fibres  of  the  glossopharyngeal  nerve  end  in  fine  terminal  arborisations. 
A  small  part  of  the  upper  portion  of  the  nucleus  may  be  said  to  l^elong  to  the 
glosso-pharyngeal  nerve  and  the  remainder  of  the  nucleus  to  the  vagus  nerve. 

Th(i  cells  which  constitute  the  dorsal  motor  or  efferent  nucleus  as  seen  in  trans- 
verse section  appear  in  a  more  or  less  compact  cluster,  which  lies  immediately  to 
the  outer  side  of  the  hypoglossal  nucleus.  These  cells,  although  very  conspicuous, 
are  not  so  large  as  those  in  the  liypoglossal  nucleus,  nor  as  those  in  the  anterior 
horn  of  gray  niatt(;r  (d'  tlu;  cord ;  nor  do  they  stain  so  deeply. 

Tlic  fasciculus  solitarius  TFigs.  397,  p.  493;  398,  p.  495;  and  402,  p.  497)  is  a 
round  bundle  of  longitudinal  fibn^s  which  forms  a  very  conspicuous  object  in  trans- 
verse sections  through  the  medulla.     It  begins  at  the  u])per  limit  of  the  medulla, 
37  « 


518 


THE  NEEVOUS  SYSTEM 


and  can  be  traced  downwards  through  its  whole  length.  Its  precise  point  of 
termination  is  not  known,  but  it  is  believed  that  it  is  carried  for  some  distance 
downwards  into  the  upper  part  of  the  cord,  viz.  to  the  level  of  the  fourth  cervical 
nerve,  according  to  Kolliker.  The  relations  of  the  fasciculus  solitarius  are  not 
the  same  in  all  parts  of  its  course.  It  lies  immediately  to  the  outer  side  of  the 
dorsal  vago-glossopharyngeal  nucleus;  but  whereas  in  the  upper  part  of  the  medulla 
it  is  situated  somewhat  on  the  ventral  side  of  that  nucleus,  in  the  lower  closed  part 
of  the  medulla  it  is  placed  on  its  dorsal  aspect.     Throughout  its  entire  length  it  is 

intimately  associ- 
ated with  a  column 
of  gelatinous  gray 
substance  which 
constitutes  the 
nucleus  of  ter- 
mination in  which 
its  fibres  end. 
When  traced  from 
above  downwards, 
the  solitary  tract 
is  observed  to  be- 
come gradually 
smaller  from  the 
loss  of  fibres  which 
it  thus  sustains. 
The  great  bulk  of 
the  solitary  tract 
is  formed  of  fibres 
derived  from  the 
gl  0  s  s  op  hary  n  geal 
nerve  ;  only  a  few 
of  the  afferent 
fibres  of  the  vagus 
enter  it.  As  the 
fibres  of  the  two 
nerves  join  the 
tract  they  im- 
mediately turn 
downwards,  and  at 
different  levels 
come  to  an  end  in 
the  associated 
gelatinous  gray 
nucleus. 

As    the    root- 

FiG.  417.— DiAtiRAM,  showing  tlie  braia  connexions   of  the   vagus,  glosso-  bundles  of  the  vagus 

pharyngeal,  auditory,  facial,  abducent,  and  trigeminal  nerves.  and     the     glosso- 

pharyngeal nerves 
traverse  the  substance  of  the  medulla  in  a  backward  and  inward  direction  to  reach  the 
fasciculus  solitarius  and  the  dorsal  nucleus  of  termination,  they  pass  through  the  spinal 
root  of  the  trigeminal  nerve  and  the  substantia  gelatinosa  Rolandi  associated  with  it. 
The  term  ascending  root  is  sometimes  applied  to  the  fasciculus  solitarius ;  but  as  this 
conveys  an  altogether  false  conception  of  its  character  it  should  be  discarded.  The 
axons  of  the  nucleus  of  termination  and  of  the  nucleus  of  the  fasciculus  solitarius 
form  central  connexions  with  other  parts  of  the  brain,  but  these  have  not  as  yet  been 
completely  elucidated. 

The  dorsal  efferent  nucleus  gives  off  fibres  which  join  the  afferent  fibres  of  the 
vago-glossopharyngeal  rootlets  as  they  traverse  the  medulla,  and  mixing  with 
them  they  pass  along  the  same  path  to  emerge  from  the  medulla. 

The  nucleus  ambiguus  (Figs.  398,  p.  495,  and  402,  p.  497)  also  gives  origin  to 


THE  DEEP  CONNEXIONS  OF  THE  CRANIAL  NERVES.         519 

motor  or  efferent  fibres  which  join  the  vagus  and  glossopharyngeal  nerves.  'J'he 
cells  which  compose  it  are  large,  multipolar,  and  similar  in  every  respect  to  the 
large  cells  in  the  ventral  horn  of  gray  matter  of  the  sjjinal  cord.  These  cells  are 
arranged  in  a  slender  column  which  is  best  developed  in  the  upper  open  part  of  the 
medulla.  Here  the  nucleus  can  easily  be  detected  in  transverse  sections  as  a  small 
area  of  compact  gray  matter  which  lies  in  the  formatio  reticularis  grisea,  midway 
between  the  dorsal  accessory  olive  and  the  substantia  gelatinosa  Rolandi.  It  there- 
fore lies  more  deeply  in  the  substance  of  the  medulla  than  the  mixed  dorsal  vago- 
glossopharyngeal nucleus.  Kolliker  states  that  it  can  be  traced  downwards  as  low 
as  the  level  of  the  decussation  of  the  fillet,  and  upwards  as  high  as  the  place  of 
entrance  of  the  cochlear  root  of  the  auditory  nerve.  From  its  dorsal  aspect  the 
axons  of  the  cells  proceed,  and  in  the  first  instance  they  pass  backwards  towards 
the  floor  of  the  fourth  ventricle ;  then,  bending  suddenly  outwards  and  forwards, 
they  join  the  afferent  roots  of  the  vagus  and  possibly  also  of  the  glossopharyngeal 
nerves,  and  emerge  from  the  brain  in  company  with  these. 

Upon  anatomical  grounds  it  might  be  questioned  whetlier  the  glossopharyngeal  nerve  contains 
any  efferent  fibres.  It  gives  off,  it  is  true,  one  motor  branch,  viz.  to  the  stylo-pharyngeus 
muscle,  but  there  are  paths  by  means  of  which  these  fibres  might  enter  the  nerve  other  than  by 
coming  directly  from  the  motor  nuclei,  which  have  been  described  in  connexion  with  the  vago- 
glossopharyngeal nerve-roots. 

There  is,  further,  some  ground  for  the  belief  that  all  the  fibres  of  the  glossopharyngeal  pass 
into  the  fasciculus  solitarius.  In  a  very  instructive  case  described  by  Alexander  Bruce  in  which 
the  glossopharyngeal  was  destroyed  in  the  jugular  foramen  by  the  pressure  of  a  tumour,  no 
degenerated  fibres  could  be  traced  beyond  the  fasciculus  solitarius. 

Auditory  Nerve  (nervus  acusticus). — This  is  a  large  nerve  which  joins  the  brain 
at  the  lower  border  of  the  pons  Varolii  and  on  the  ventral  aspect  of  the  restiform 
body.  It  is  an  afferent  nerve,  and  its  fibres  spring  from  bipolar  ganglionic  cells 
either  within  or  in  the  immediate  neighbourhood  of  the  labyrinth  or  internal  ear 
(see  section  dealing  with  the  organs  of  sense).  Reaching  the  brain  the  auditory 
nerve  divides  into  two  parts,  viz.  the  nervus  cochlearis  and  the  nervus  vestibularis, 
which  present  totally  different  connexions  and  apparently  exercise  absolutely 
distinct  functions.  In  their  further  course  these  two  divisions  deviate  from  each 
other  so  as  to  embrace  the  restiform  body — the  vestibular  part  entering  the  pons 
on  the  inner  or  mesial  aspect  of  the  restiform  body,  whilst  the  cochlear  part 
sweeps  round  its  outer  surface.  Special  nuclei  of  termination  require  to  be 
studied  in  connexion  with  each  part  of  the  nerve. 

The  cochlear  nerve  is  composed  of  finer  fibres  than  the  vestibular  nerve, 
and  these  acquire  their  medullary  sheaths  at  a  later  period.  It  is  the  true  nerve 
of  hearing,  and  its  fibres  end  in  a  ganglion  which  lies  in  intimate  relation  to  the 
restiform  body,  and  which  may  be  described  as  consisting  of  two  parts.  Of  these 
one,  called  the  tuberculum  acusticum  or  the  lateral  cochlear  nucleus,  is  a  pyriform 
mass  which  is  placed  on  the  outer  aspect  of  the  restiform  body — -between  it  and 
the  flocculus  of  the  cerebellum.  The  second  part,  termed  the  ventral  cochlear 
nucleus,  does  not  extend  so  low  down  as  the  tuberculum  acusticum.  It  is  a  wedge- 
shajjed  nuclear  mass  which  is  placed  on  the  ventral  aspect  of  the  restiform  body  in 
the  interval  between  the  cochlear  and  vestibular  divisions  of  the  auditory  nerve, 
after  they  have  separated  from  each  other.  The  fibres  of  the  cochlear  nerve  enter 
these  two  ganglia  and  end  around  the  cells  in  terminal  arborisations,  which  are 
finer,  closer,  and  more  intricate  than  those  met  with  in  any  other  nerve  nucleus  in 
the  brain. 

The  vestibular  nerve  enters  the  brain  at  a  slightly  higher  level  than  the  cochlear 
nerve  and  on  the  mesial  aspect  of  the  ventral  cochlear  nucleus.  It  forces  its  way 
backwards  tlirough  the  pons  between  the  restiform  body,  which  lies  on  its  outer 
side,  and  the  spinal  root  of  the  fifth  nerve,  which  is  placed  on  its  inner  side.  Its 
fibres  come  to  an  end  in  three  nuclei  of  termination,  which  are  situated  in  the 
dorsal  part  of  tlie  pons  and  medulla,  viz.  (1)  the  principal  nucleus  or  dorsal  nucleus; 
(2;  the  nucleus  of  the  descending  root;  and  (3)  the  nucleus  of  Deiters. 

The  principal  nucleus  (Figs.  403,  p.  500,  and  418,  p.  520)  is  a  large  diffuse 
nuclear  mass,  which  lies  in  the  floor  of  the  fourth  ventricle  subjacent  to  the  surface 
37  h 


520 


THE  NERVOUS  SYSTEM. 


CORPORA  QUADRIGEMINA 


district  known  as  the  area  acustica  (Fig.  391,  p.  487).  It  is  situated,  therefore,  in 
both  the  pons  and  the  medulla  to  the  outer  side  of  the  fovea  superior  and  the  fovea 
inferior.     In  transverse  section  it  is  prismatic  iu  outline,  and  crossing  the  surface 

of  its  upper  or  pontine  part 
immediately  under  the 
ependyma  of  the  ventricle 
are  the  strite  acusticffi. 

When  the  nervus  vesti- 
bularis, as  it  tra\'erses  the 
brain,  reaches  the  inner 
aspect  of  the  dorsal  portion 
of  the  restiform  body,  a 
very  large  proportion  of 
its  fibres  turn  vertically 
downwards  in  separate 
bundles  and  form  the  de- 
scending root  of  the  vesti- 
bular nerve  (Figs.  398,  p. 
495;  402,  p.  497:  403, 
p.  500:  418,  p.  520). 
This  proceeds  through  the 
lower  part  of  the  pons  into 
the  medulla,  in  which  it 
may  be  traced  as  far  as 
the  level  of  the  decussa- 
tion of  the  lillet.  As- 
sociated with  the  descend- 
ing root  there  is  a  column 
of  gray  matter,  with  nerve- 
cells  strewn  sparsely 
throughout  it.  This  is 
the  nucleus  of  the  de- 
scending root,  and  the 
fibres  end  in  fine  arborisa- 
tions around  these  nerve- 
cells. 


Fig. 


418. — Central  Connexions   of   the   Cochlear  and  Vestibular 
Divisions  op  the  Auditory  Nerve. 

(Diagram  founded  on  drawings  by  Edinger  and  Perrier  and  Turner.) 


The  fibres  of  the  vestibular  nerve  likewise  end  in  the  nucleus  of  Deiters.  This 
nucleus  is  composed  of  a  number  of  large  and  conspicuous  multipolar  nerve-cells, 
which  are  scattered  amidst  the  bundles  of  the  upper  part  of  the  descending  root 
of  the  vestibular  nerve.  As  it  is  traced  upwards  into  the  pons  the  nucleus 
gradually  inclines  backwards,  and  finally  it  occupies  a  place  in  the  lateral  wall  of 
the  fourth  ventricle.  It  attains  its  greatest  development  at  the  level  of  the 
emerging  part  of  the  facial  nerve,  and  this  upper  part  is  sometimes  termed  the 
nucleus  of  Bechterew. 


Central  Connexions  of  the  Cochlear  Nerve.— The  cochlear  nerve  is  brought 
into  connexion  with  the  inferior  quadrigeminal  body,  and  the  corpus  geiiiculatum 
internum  of  the  opposite  side  by  the  fibres  of  the  corpus  trapezoides  and  the  lateral 
fillet.  But  this  connexion  is  not  direct ;  the  chain  is  composed  of  several  separate  links 
or  neurons  superimposed  one  over  the  other. 

The  fibres  of  the  cochlear  nerve  end  in  the  ventral  cochlear  nucleus  and  iu  the  tuber- 
culum  acusticum.  From  the  cells  of  these  nuclei  two  tracts  arise,  viz.  a  ventral  tract, 
composed  of  the  fibres  of  the  corpus  trapezoides,  and  a  dorsal  tract,  which  is  represented 
by  the  strite  acustica^. 

The  corpus  trapezoides  (Figs.  418  and  419)  is  formed  of  the  axons  of  the  cells  of  the 
ventral  cochlear  nucleus,  as  well  as  certain  of  the  axons  of  the  cells  of  tuberculum 
acusticum.  In  the  midst  of  the  corpus  trapezoides  are  lodged  large  cells' which  are  known 
as  the  nucleus  trapezoideus,  and  these  give  off"  axons  which  join  the  strand  with  which 
they  are  associated.  Further,  the  suj^erior  olive  forms  an  important  internode  in  the 
path  of  the  corpus  trapezoides.     Many  of  the  fibres  of  the  corpus  trapezoides  end  in  this 


THE  DEEP  CONNEXIONS  OF  THE  CEANIAL  NERVES.  521 

inteniode,  whilst  others  are  added  tu  the  tract  from  the  cells  of  that  nuclear  mass.  So 
constituted,  the  trapezial  fibres  cross  the  mesial  plane  and  decussate  with  the  correspond- 
ing fibres  of  the  opposite  side.  Reaching  the  opposite  superior  olivary  nucleus  a  further 
interchange  of  fibres  takes  place,  and  almost  immediately  after  this  the  strand  turns 
upwards  and  becomes  the  lateral  fillet  (Figs.  405,  p.  503  ;  406,  p.  504).  But  still 
another  nucleus  is  interposed  in  its  path,  viz.  the  nucleus  of  the  lateral  fillet.  Here 
some  fibres  are  dropped,  whilst  from  the  nuclear  cells  others  are  acquired,  and  the  lateral 
fillet  then  proceeds  onwards  without  further  interruption  until  it  reaches  the  inferior 
quadrigeminal  body  and  the  corpus  geniculatum  internum,  in  which  its  fibres  end.  It  is 
probable,  however,  that  some  likewise  extend  into  the  superior  quadrigeminal  body. 

But  the  lateral  fillet  also  includes  the  fibres  of  the  striae  acusticse  of  the  opposite 
side.  These  fibres  arise  from  the  cells  of  the  tul^erculum  acusticum,  and  arrange  them- 
selves in  the  conspicuous  bundles  which  sweep  round  the  dorsal  aspect  of  the  resti- 
form  body  a.nd  proceed  inwards  across  the  floor  of  the  fourth  ventricle,  immediately 
beneath  the  ependyma  (Fig.  391,  p.  487).  Reaching  the  middle  line  they  dip  forwards 
into  the  substance  of  the  medulla,  and,  crossing  the  mesial  plane,  they  join  the  lateral 
fillet. 

It  is  well  to  remember  that  the  connexion  between  the  terminal  cochlear  nuclei  and 
the  inferior  quadrigeminal  body  is  not  altogether  with  that  of  the  opposite  side,  as  the 
foregoing  description  and  the  diagram  (Fig.  418)  might  lead  one  to  infer.  A  few  fibres 
pass  directly  to  the  inferior  quadrigeminal  body  of  the  same  side,  but  none  to  the  corre- 
sponding corpus  geniculatum  internum  :  the  connexion  with  the  latter  is  entirely  crossed 
(Ferrier  and  Turner). 

From  the  corpus  geniculatum  internum  there  proceeds  a  tract  to  the  gray  cortex  of 
the  superior  convolution  of  the  temporal  lobe.  The  whole  nervous  apparatus  is  thus 
linked  on  to  the  cerebral  cortex,  and  the  succession  of  neurons  which  build  up  the  entire 
chain  are  therefore  :  (1)  the  bipolar  cells  of  the  ganglion  spirale ;  (2)  the  neurons  of  the 
terminal  cochlear  nuclei ;  (3)  the  neurons  of  the  superior  olive  and  the  nucleus  of  the 
lateral  fillet ;  (4)  the  neurons  of  the  corpus  geniculatum  internum. 

It  must  be  borne  in  mind  that  all  the  axons  of  the  cells  of  the  superior  olive  do  not 
join  the  trapezoid  strand.  Many  leave  its  dorsal  aspect  and  pass  backwards  in  a  group 
called  the  pedicle  of  the  superior  olive,  to  end  in  the  nucleus  of  the  sixth  nerve,  and, 
through  the  posterior  longitudinal  bundle,  in  the  nuclei  of  the  fourth  and  third  nerves. 
In  this  way  the  organ  of  hearing  is  brought  into  connexion  with  the  nuclei,  which  preside 
over  the  movements  of  the  eyeballs  (Figs.  403,  p.  500,  and  420,  p.  523). 

Central  Connexions  of  the  Vestibular  Nerve. — Although  the  central  con- 
nexions of  the  vestibular  nerve  have  been  closely  studied  by  many  observers,  they  are 
still  very  far  from  being  fully  understood.  The  principal  nucleus  and  the  nucleus  of 
Deiters  both  stand  in  intimate  relation  with  the  superior  vermis  of  the  cerebellum ;  and 
in  consideration  of  the  fact  that  the  vestibular  nerve  is  the  nerve  of  equilibration,  this 
is  an  important  and  significant  circumstance.  The  strand  which  establishes  this  con- 
nexion has  been  termed  by  Edinger  "  the  direct  sensory  cerebellar  tract,"  and  in  all 
probability  it  is  an  eft'erent  ti'act  from  the  cerebellum.  Its  fibres  arise  to  a  large  extent 
in  the  cerebellar  roof  nuclei  of  the  opposite  side,  and,  crossing  the  mesial  plane,  they 
sweep  forwards  around  the  outer  side  of  the  superior  cerebellar  peduncle  as  it  emerges 
from  the  cerebellum  to  end  in  the  nucleus  of  Deiters,  the  chief  vestibular  nucleus,  and 
very  possibly  also  in  the  terminal  sensory  nuclei  of  certain  other  cranial  nerves,  such  as 
the  trigeminal,  vagus,  and  glossopharyngeal. 

Until  the  precise  nature  of  the  nucleus  of  Deiters  is  discovei'ed,  the  exact  character 
of  the  central  connexions  of  the  vestibular  nerve  will  remain  more  or  less  obscure.  It 
cannot  be  regarded  as  a  nucleus  specially  given  over  to  the  vestibular  nerve.  Composed 
of  large  cells  scattered  amidst  the  bundles  of  the  upper  part  of  the  descending  root  of  the 
vestibular  nerve,  it  only  becomes  a  compact  nucleus  above  the  level  of  that  nerve,  viz. 
at  the  point  where  the  restiform  body  turns  backwards  into  the  cerebellum,  or,  in 
other  words,  at  the  level  of  the  emerging  facial  nerve  and  the  lower  end  of  the  abducent 
nucleus.  Here,  in  the  outer  part  of  the  floor  of  the  fourth  ventricle,  its  cells  are  gathered 
together  in  a  crowded  mass.  Deiters  himself  considered  that  this  nucleus  should  be 
regarded  as  an  internode  between  the  cerebellum  and  the  spinal  cord,  and  Ferrier  and 
Turner  have  brought  forward  strong  evidence  in  support  of  this  view.  Klimofi"  attaches 
a  very  high  importance  to  the  direct  "sensory"  tract  of  Edinger.  From  his  description 
it  would  appear  that  he  regards  it  as  the  only  cerebellar  efferent  tract  which  takes  a 
downward  direction.  He  believes,  further,  that  the  axons  of  the  cells  of  Deiters  form  the 
anterior  marginal   tract  of    Lowenthal    (tractus   vestibulo-spinalis  of   Monakow),   which 


522 


THE  NERVOUS  SYSTEM. 


descends  in  the  antero-lateral  column  of  the  cord  as  far  as  the  lumbar  region.  It  is 
supposed  that  the  fibres  of  this  tract  end  in  the  cord  in  arborescent  terminations  around 
the  motor  cells  in  the  ventral  horn  of  gray  matter. 

From  what  has  been  said  it  must  be  apparent  that  the  nucleus  of  Deiters  plays  a  most 
important  part  in  connexion  with  the  maintenance  of  the  equilibrium  of  the  body  and 
the  co-ordination  of  its  muscular  movements.  Thus  it  constitutes  an  internode  in  the 
path  of  those  fibres  which  connect  the  cortex  and  roof  nuclei  of  the  cerebellum  with  the 
motor  apparatus  of  the  spinal  cord ;  it  receives  fibres  through  the  vestibular  nerve  from 
the  labyrinth  of  the  ear ;  and  it  sends  fibres  into  the  posterior  longitudinal  bundle, 
through  which  it  in  all  probability  exercises  some  influence  over  the  nuclei  of  the  ocular 
nerves. 

Opinion  is  also  divided  as  to  the  composition  and  nature  of  the  so-called  descending 
root  of  the  vestibular  nerve.  After  division  of  the  eighth  nerve,  Ferrier  and  Turner  were 
unable  to  detect  any  degeneration  in  this  root,  and  they  therefore  are  inclined  to  call  in 
question  its  direct  continuity  with  the  nerve.  They  consider  that  in  all  probability  it 
forms  an  internuncial  connexion  between  the  nucleus  of  Deiters  and  the  cuneate  nucleus, 
in  which  Bruce  has  seen  its  lower  end  to  terminate. 


Fig.  419. — Section  through  the  Pons  Varolii  of  the  Orang, 

Showing  the  nucleus  and  intrapontine  course  of  the  facial  nerve.     The  left  side  of  the  drawing  is  taken 
from  a  section  at  a  slightly  lower  level  than  the  section  from  which  the  right  side  is  taken. 


1. 


Ascending  part  of  facial  nerve. 

2.  Posterior  longitudinal  bundle. 

3.  Descending  root  of  eighth  nerA-e. 

4.  Radicular  fibres  of  facial  nerve. 

5.  Kestilorni  body. 
0.  Facial  nucleus. 

7.  Spinal  root  of  fifth  nerve. 

8.  Vestibular  nerve. 

9.  Superior  olive. 

10.  Fillet. 

11.  Pyramidal  tract. 

12.  Transverse  fibres  of  pons. 


B 

1.  Ascending  part  of  facial  nerve. 

2.  Emergent  portion  of  facial  nerve. 

3.  Restiform  body. 

4.  Nucleus  of  sixth  ner\'e. 

5.  Sixth  Nerve. 

6.  Emergent  part  of  facial  nerve. 

7.  Peduncle  of  superior  olive. 

8.  Superior  olive. 

9.  Corpus  trapezoides. 

10.  Facial  nerve. 

11.  Sixth  nerve. 

12.  Pyramidal  tract. 

13.  Transverse  fibres  of  pons. 


Facial  Nerve  (nervus  facialis)  (Figs.  419  and  420). — The  facial  nerve  is  com- 
posed of  two  distinct  parts,  viz.  a  large  efferent  or  motor  portion,  the  facial  nerve 
proper,  and  a  small  efferent  sensory  portion  termed  the  pars  intermedia  of  Wrisberg. 
The  facial  nerve  emerges  from  the  brain  at  the  lower  border  of  the  pons,  immediately 
in  front  and  to  the  inner  side  of  the  auditory  nerve,  whilst  the  pars  intermedia 
sinks  into  the  upper  part  of  the  medulla  between  the  facial  and  auditory  nerves. 
The  three  nerves,  therefore,  lie  in  intimate  relation  with  each  other,  where  they 
are  attached  to  the  surface  of  the  brain,  and  they  pass  in  company  into  the  internal 
auditory  meatus. 


THE  DEEP  CONNEXIONS  OF  THE  CKANIAL  NERVES. 


523 


The  nucleus  of  origin  of  the  facial  nerve  is  an  oval  ruass  of  gray  matter,  aljout 
five  mm.  in  length,  and  containing  numerous  groups  of  large  multipolar  cells.  It 
is  sunk  deeply  in  the  dorsal  or  tegmental  part  of  the  lower  portion  of  the  pons 
Varolii,  and  is  placed  close  to  the  inner  side  of  the  spinal  root  of  the  fifth  nerve. 
When  transverse  sections  are  made  through  the  brain-stem,  the  facial  nucleus  is 
encountered  the  moment  the  boundary  line  between  the  medulla  and  pons  is 
passed,  and  the  region  immediately  above  the  inferior  olivary  nucleus  is  reached. 
At  first  it  lies  so  deeply  in  the  tegmentum  of  the  pons  that  it  actually  rests  upon 
the  dorsal  aspect  of  the  corpus  trapezoides ;  but  a  little  farther  up  the  superior 
olive  comes  into  view,  and  insinuates  itself  between  the  facial  nucleus  and  the 
trapezial  fibres.  The  upper  part  of  the  nucleus  is  in  this  way  tilted  somewhat 
backwards,  and  thus  comes  to  lie  on  the  dorsal  and  outer  aspect  of  the  superior 
olive. 

The  facial  nucleus  is  situated  close  to  the  place  where  the  nerve  emerges  from 
the  brain,  but  the  nerve  does  not  at  once  pass  to  this  point  of  exit.  It  pursues 
a  long  and  devious  path  within  the  pons  before  it  finally  reaches  the  surface. 
This  intrapontine  part  of  the  nerve  may  be  divided  into  three  parts,  viz. :  (1)  a 
radicular  part,  (2)  an  ascending  portion,  and  (3)  an  emergent  part. 

The  radicular  part  of  the  facial  nerve  (Fig.  420)  is  composed  of  a  large  number 
of  fine  loosely-arranged  bundles  of  fibres,  which  issue  from  the  outer  and  dorsal 
aspect  of  the  nucleus  and  proceed  backwards  and  slightly  inwards  through  the 
pons.  Reaching  the  floor  of  the  fourth  ventricle  they  curve  inwards,  and  the 
bundles  which  lie  highest  up  sweep  over  the  outer  and  dorsal  aspect  of  the  lower 
part  of  the  nucleus  of  the  sixth  nerve.  Close  to  the  mesial  plane  they  turn 
sharply  upwards  and  are  collected  into  a  single  solid  nerve-bundle,  which  consti- 
tutes the  ascending  part  of  the  facial  nerve  (Figs.  419  and  420).  This  proceeds 
vertically  upwards  immediately 
beneath  the  ependyma  of  the 
ventricular  floor,  on  the  dorsal 
aspect  of  the  posterior  longitudinal 
bundle,  and  along  the  inner  side 
of  the  sixth  or  abducent  nucleus 
for  a  distance  of  about  five  milli- 
metres. Suddenly  the  nerve  bends 
outwards  at  a  right  angle,  and 
curves  a  second  time  over  the 
dorsal  as^Dect  of  the  sixth  or 
abducent  nucleus.  The  nerve  now 
passes  straight  to  the  place  of  exit 
from  the  brain,  and  this  part  of 
the  intrapontine  trunk  may  be 
termed  the  emergent  portion  (Figs. 
419  and  420).  The  facial  nerve 
thus  forms  a  curved  loop  over  the 
dorsal  aspect  of  the  abducent 
nucleus.  The  emergent  part  of 
the  nerve  takes  an  oblique  course 
through  the  pons  to  reach  the 
surface.  It  inclines  outwards  and 
downwards  as  it  proceeds  towards 
the  ventral  aspect  of  the  pons, 
and  on  its  way  it  passes  between 
its  own  nucleus  and  the  spinal  root 
of  the  fifth  nerve. 


Fio.  420.- 


-Dtauram  of  the  Intkai'ontine  Course  pursued 
BY  THE  Facial  Nerve. 


Entci'iiig  th(i  facial  uuclcji.s,  and  c.iKlirig  in  fine  terminal  arborisations  around  its  cells,  are 
many  fihi'cs  from  tlie  ojijtosite  ]>yramidal  tract;  fibres  from  the  s])inal  root  of  tlie  fifth  nerve  ; 
fibres  from  the  corjdis  trapezoides,  etc.  The  nucleus  is  thus  brought  into  connexion  with  the 
motor  area  of  the  cerebral  cortex,  with  the  trigeminal  nerve  or  sensoiy  nerve  of  the  face,  and 
with  the  auditory  nerve,  etc. 


524  THE  NEEVOUS  SYSTEM. 

The  fibres  of  tlie  pars  intermedia  of  Wrisberg  arise  from  the  cells  of  the  geni- 
culate ganglion  of  the  facial  nerve.  These,  like  the  cells  of  a  spinal  ganglion,  are 
unipolar,  the  single  process  in  each  case  dividing  into  a  peripheral  and  a  central 
branch.  The  group  of  peripheral  fibres  represent  the  chorda  tympani  branch  of 
the  facial  nerve,  whilst  the  central  fibres  form  the  pars  intermedia.  The  latter 
penetrate  the  brain,  and,  passing  either  through  or  on  the  dorsal  side  of  the  spinal 
root  of  the  fifth  nerve,  they  finally  reach  the  upper  part  of  the  column  of  gray 
matter  in  connexion  with  the  fasciculus  solitarius,  and  in  this  they  end.  The  pars 
intermedia  presents,  therefore,  the  same  terminal  connexions  within  the  brain  as 
the  glossopharyngeal  nerve. 

Efferent  secretory  fibres  are  also  described  as  being  present  in  the  pars  intermedia.  These 
are  said  to  spring  from  cells  which  constitute  a  salivary  nucleus  placed  in  the  pons  on  the  dorsal 
aspect  of  the  facial  nucleus. 

Abducent  or  Sixth  Nerve  (nervus  abducens)  (Figs.  419  and  420). — This  is  a 
small  motor  nerve  which  emerges  from  the  brain  at  the  lower  border  of  the  pons 
on  the  outer  side  of  the  pyramid  of  the  medulla.  It  is  the  nerve  of  supply  to 
the  external  rectus  muscle  of  the  eyeball.  Its  nucleus  of  origin  is  a  small 
spherical  mass  of  gray  matter,  containing  large  multipolar  cells,  which  lies  in 
the  dorsal  part  of  the  tegmental  portion  of  the  pons,  close  to  the  mesial  plane  and 
immediately  subjacent  to  the  gray  matter  of  the  floor  of  the  fourth  ventricle.  Its 
position  can  be  easily  indicated  on  the  ventricular  floor,  seeing  that  it  is  placed 
subjacent  to  the  emenentia  teres  and  immediately  above  the  level  of  the  strise 
acusticse.  Its  peculiar  and  intimate  relation  to  the  intrapontine  portion  of  the 
facial  nerve  has  already  been  indicated.  It  lies  on  the  ventral  aspect  of,  and  within 
the  concavity  formed  by,  the  two  limbs  of  the  loop  of  that  nerve. 

The  axons  of  the  multipolar  cells  of  this  nucleus  emerge  from  the  inner  aspect 
of  the  nucleus  in  the  form  of  several  bundles,  which  proceed  through  the  whole 
antero-posterior  thickness  of  the  pons  towards  the  place  of  exit.  As  they  pass 
forwards  they  incline  downwards  and  slightly  outwards.  In  the  tegmental  part 
of  the  pons  they  proceed  forwards  on  the  inner  side  of  the  superior  olive,  whilst  in 
the  ventral  part  of  the  pons  they  keep  for  the  most  part  to  the  outer  side  of 
the  pyramidal  bundles,  although  several  of  the  nerve  fasciculi  pierce  these  on 
their  way  to  the  surface. 

It  would  appear  probable  that  certain  of  the  axons  of  the  cells  of  the  abducent  nucleus  enter 
the  posterior  longitudinal  fasciculus  and  proceed  upwards  in  it  to  join  the  third  or  oculo- 
motor nerve  of  the  opjjosite  side.  Further  mention  of  these  will  be  made  later  on.  Fibres 
and  collaterals  from  the  pj^ramidal  tract  of  the  opposite  side  enter  the  nucleus,  and,  ending 
around  the  cells,  bring  the  nucleus  into  connexion  with  the  motor  area  of  the  cerebral  cortex. 
The  pedicle  of  the  superior  olive  ends  partly  within  the  nucleus  of  the  abducent  nerve  (p.  521). 

Trigeminal  or  Fifth  Nerve  (nervus  trigeminus). — The  trigeminal  nerve  strikes 
its  roots  deeply  into  the  brain  and  establishes  a  connexion  with  it  which  extends 
from  the  upper  part  of  the  mesencephalon  above  to  the  level  of  the  second  cervical 
nerve  below.  No  other  cranial  nerve  presents  so  extensive  a  connexion  (Fig. 
417,  p.  518).  It  is  composed  of  two  roots — a  large  afferent  or  sensory  root  and 
a  small  efferent  or  motor  root.  Both  roots  appear  close  together  on  the  surface 
of  the  pons,  rather  nearer  its  upper  border  than  its  lower  border,  and  in  the  same 
line  as  the  facial  and  auditory  nerves. 

The  sensory  root  of  the  fifth  nerve  is  composed  of  fibres  which  arise  outside  the 
brain  from  the  cells  of  the  Gasserian  ganglion.  They  end  within  the  brain  in  two 
nuclei  of  termination.  One  of  these  is  situated  in  the  pons  and  is  termed  the 
sensory  nucleus  of  the  trigeminal  nerve,  and  the  other  is  a  long  column  of 
gray  matter  which  is  directly  continuous  below  with  the  substantia  gelatinosa 
Kolandi  of  the  spinal  cord. 

The  sensory  nucleus  (Fig.  421)  is  an  oval  mass  of  gray  matter  which  is  placed 
half-way  up  the  pons  in  the  outer  part  of  its  tegmental  portion.  .  It  lies  close  to 
the  outer  surface  of  the  pons  and  immediately  subjacent  to  the  ventral  submerged 
margin  of  the  superior  cerebellar  peduncle.  It  is  directly  continuous  with  the 
substantia  gelatinosa  Eolandi,  and  may  be  regarded  as  being  merely  the  enlarged 
upper  end  of  that  column  of  gray  matter. 


THE  DEEP  CONNEXIONS  OF  THE  CRANIAL  NERVES. 


525 


The  fibres  of  the  sensory  root  of  the  fifth  nerve,  on  reaching  the  sensory  nucltius, 
divide  in  a  manner  similar  to  the  fibres  of  the  entering  posterior  roots  of  the  spinal 
nerves  into  a  system  of  ascending  and  descending  branches  (Fig.  417,  p.  518). 
The  ascending  fibres  are  short,  and  almost  immediately  enter  the  sensory  nucleus 
and  end  within  it ;  the  descending  fibres  turn  sharply  downwards  and  form  the  spinal 
root  (tractus  spinalis :  the  ascending  root  of  many  text-books).  This  root  descends 
on  the  outer  side  of  the  column  of  gray  matter  formed  by  the  substantia  gelatinosa 
Rolandi,  which  constitutes  its  terminal  nucleus.  Fibres  constantly  leave  it  to 
enter  the  nucleus,  so  that  the  lower  it  gets  the  smaller  does  the  spinal  root  become 
until,  in  the  upper  part  of  the  spinal  cord,  about  the  level  of  the  first  or  second 
spinal  nerve,  it  disappears  altogether. 


Superior  cerebellar  perluncle- 

Mesencephalic  root  of  the  fifth  nerve 

Motor  nucleus  of  the  fifth  nen  e — 
Motor  root  of  the  fifth  nerve 

Sensory  nucleus  of  the  fifth  neive 

Superior  olive  ^__^ 

Sensory  root  of 

fifth  nerve  ^~ — -~  ___ 


Middle  peduncle_ 
of  cerebellum 


Superior  medullary  velum 
or  valve  of  Vieussens 


Floor  of 
ventricle  IV. 

Posterior 

longitudinal 

fasciculus 


Fig. 


421.— Section  through  the  Pons  Varolii  of  the  Orang,  at  the  Level  of  the  Nuclei 
OF  THE  Trigeminal  Neeve. 


The  large  spinal  root  of  the  fifth  nerve  is  a  conspicuous  object  in  sections  through  the 
pons  and  medulla.  In  the  former  it  traverses  the  tegmental  part,  first,  between  the 
emergent  part  of  the  facial  nerve  and  the  vestibular  nerve ;  and  then  lower  down,  between 
the  restiform  body  and  the  nucleus  of  the  facial  nerve  (Fig.  419,  A,  p.  522).  In  cross 
sections  it  presents  a  well-defined  semilunar  or  curved  pyriform  outline.  In  the  upper 
part  of  the  medulla  it  lies  on  the  ventral  aspect  of  the  restiform  body,  and  therefore 
neai-er  to  the  surface  (Fig.  398,  p.  495).  Here  it  is  traversed  and  broken  up  into 
separate  bundles  by  the  cerebello-olivary  fibres  and  the  roots  of  the  glossopharyngeal  and 
vagus  nerves.  Finally,  it  comes  to  the  surface  and  its  fibres  are  spread  over  the  area  on 
the  side  of  the  medulla  known  as  the  tubercle  and  funiculus  of  Rolando  (Fig.  394, 
p.  492). 

Tlie  small  motor  part  of  the  trigeminal  nerve  is  chielly  distributed  to  the  muscles 
of  mastication,  and  derives  its  fibres  from  two  sources,  viz.  from  the  motor  nucleus 
and  from  the  mesoncephalic  root  of  the  trigeiriinal  nerve. 

The  motor  nucleus  H^'ig.  421)  lies  in  the  lateral  part  of  the  tcgnjcntal  portion  of 
the  pons,  close  to  the  inner  side  of  the  sensory  terminal  nucleus,  but  somewhat 


526  THE  NEEVOUS  SYSTEM. 

nearer  to  the  floor  of  the  fourth  ventricle.  It  is  not  placed  in  the  exact  line  of  the 
facial  nucleus,  as  it  is  situated  somewhat  nearer  the  dorsal  aspect  of  the  pons ;  but, 
nevertheless,  it  may  be  considered  as  being  equivalent  in  this  region  to  the  detached 
head  of  the  anterior  horn  of  gray  matter  in  the  lower  part  of  the  medulla.  The 
cells  of  this  nucleus  are  large  and  multipolar,  and  their  axons  run  together  to  form 
the  greater  portion  of  the  motor  root  of  the  fifth  nerve. 

The  mesenceplialic  root  takes  origin  in  the  mesencephalon  from  a  column  of 
large  loosely-arranged  cells  which  are  placed  in  the  extreme  lateral  part  of  the 
gray  matter  which  surrounds  the  Sylvian  aqueduct.  As  the  lower  end  of  this  column 
of  cells  reaches  the  pontine  part  of  the  floor  of  the  fourth  ventricle  it  becomes 
continuous  with  the  dark  cells  of  the  locus  coeruleus.  The  mesencephalic  root 
as  it  is  traced  downwards  gradually  gains  strength  by  the  addition  of  new  fibres, 
and  it  assumes  a  crescentic  form  in  transverse  section  (Figs.  430,  p.  535  ;  432,  p. 
537 ;  407,  p.  505  ;  1406,  p.  504).  In  the  lower  part  of  the  mesencephalon  it  lies  on 
the  inner  side  of  the  superior  cerebellar  peduncle  ;  and  the  fourth  nerve,  on  its  way 
to  the  surface,  runs  downwards  in  its  concavity  and  on  its  mesial  aspect.  In  the 
upper  part  of  the  pons,  it  continues  its  course  downwards  on  the  outer  and  deep 
aspect  of  the  gray  matter  which  forms  the  floor  of  the  fourth  ventricle,  and  here  it 
stands  in  relation  to  the  cells  of  the  locus  coeruleus.  Finally,  reaching  the  level  of 
the  nuclei  of  the  trigeminal  nerve,  the  fibres  of  the  mesencephalic  root  turn 
forw^ards  and  join  the  motor  part  of  the  trigeminal  nerve  (Fig.  421). 

S.  Eanion  y  Cajal  lias  shown  that  an  intimate  relationship  is  established  between  the 
mesencephalic  nucleus  and  the  principal  motor  nucleus  of  the  trigeminal  nerve.  Large  numbers 
of  collaterals  from  the  fibres  of  the  mesencephalic  root  enter  the  latter  nucleus  and  break  up  into 
close  networks  around  its  cells.  It  has  been  suggested  that  through  this  connexion  a  weak 
impulse  proceeding  from  the  higher  nucleus  may  be  transformed  within  the  lower  or  principal 
nucleus  into  a  powerful  excitation. 

(1)  It  is  not  known  to  what  parts  the  fibres  of  the  mesencej^halic  root  go.  Kolliker  suggests 
that  they  supply  the  tensor  veli  palatini  and  the  tensor  tympani ;  j)erhaps,  also,  they  may  be  dis- 
tributed to  the  mylo-hyoid  and  the  anterior  belly  of  the  digastric.  (2)  Fibres  from  the  ojjposite 
pyramidal  tract  go  to  the  motor  nucleus  and  bring  it  into  connexion  with  the  motor  area  of  the 
cerebral  cortex.  (3)  By  degeneration  methods  the  root  of  the  fifth  nerve  has  been  traced  down  to 
the  level  of  the  second  cervical  nerve  (Ferrier  and  Turner).  (4)  The  axons  of  the  terminal  nuclei 
emerge  as  arcuate  fibres,  and,  proceeding  through  the  raphe,  assume  a  longitudinal  course  in  the 
tegmentum  of  the  oj^posite  side,  and  thus  establish  connexions  Avith  jaarts  higher  up  (tractus 
quinto-thalamicus).  (5)  Some  of  the  axons  of  the  cells  of  the  terminal  nucleus  enter  the  motor 
nucleus,  and  thus  establish  a  simple  reflex  apparatus. 

The  Development  of  the  Parts  derived  from  the  Ehombencephalon. 

A  general  sketch  of  the  development  of  the  medulla,  pons,  and  cerebellum  has  already 
been  given  (p.  476).  It  is  only  necessary,  therefore,  in  this  section  to  call  attention  to 
some  of  the  more  important  details  connected  with  the  process. 

Medulla. — In  the  embryo  the  cervical  flexure  indicates  in  a  sharp  and  definite  manner 
the  point  of  junction  between  the  cord  and  the  brain  (Fig.  382,  p.  477).  In  the  early 
condition  of  the  rhombencephalon  the  calamus  scriptorius  extends  downwards  to  tliis  level, 
so  that,  in  the  first  instance,  there  is  no  part  of  the  medulla  which  corresponds  to  the 
closed  portion  present  in  the  adult.  The  lower  closed  part  of  the  medulla  makes  its 
appearance  at  a  later  period,  and  is  termed  by  His  the  intercalated  portion  (Schaltstiick). 

In  our  stiidy  of  the  development  of  that  part  of  the  neural  tnhe  which  forms  the  spinal 
cord  we  have  recognised  two  thick  lateral  walls  comaected  in  front  and  behind  by  narrow 
mid-ventral  and  mid-dorsal  laminae.  The  same  parts  are  seen  in  the  developing  medulla. 
Owing,  however,  to  the  expansion  of  the  cavity  in  this  portion  of  the  tube  the  mid-dorsal 
lamina  is  stretched  out  into  an  extensive  and  thin  epithelial  membrane  which  forms  the 
dorsal  wall  or  roof  of  the  ventricle  in  this  section  of  the  early  brain.  The  thick  lateral 
walls  have  also  fallen  away  from  each  other,  and  are  joined  in  front  by  the  narrow 
niid-venti'al  lamina.  On  section,  therefore,  the  medullary  part  of  the  neural  tube  presents 
a  triangular  figure — the  base,  which  is  directed  backwards,  being  formed  by  the  thin 
epithelial  expansion  derived  from  the  mid-dorsal  lamina,  the  apex  by  the  narrow  mid- 
ventral  lamina,  and  the  sides  by  the  thick  lateral  walls  of  the  tube.  Further,  each  lateral 
wall  consists  of  an  alar  or  dorsal  and  a  basal  or  ventral  lamina.  This  subdivision  is  more 
clearly  indicated  than  in  the  cord,  and  on  the  inner  surface  of  the  lateral  wall  a  strongly- 
marked  longitudinal  furrow  marks  the  line  of  junction  of  the  two  laminse.     The  histo- 


DEVELOPMENT  OF  THE  MEDULLA. 


e^^s,„ 


logical  develojDment  of  these  several  parts  of  the  wall  of  the  medullary  portion  of  the 
neural  tube  proceeds  in  a  manner  very  similar  to  that  already  detailed  in  the  case  of  the 
cord.  No  neuroblasts  are  formed  in  the  mid-ventral  and  mid-dorsal  laminae ;  the  entire 
neuroblastic  formation  is  confined  to  the  basal  and  alar  laminae.  Within  the  basal  lamina, 
likewise,  are  collected  the  neuroblasts  which  form  the  nuclei  of  origin  of  the  efferent 
nerves ;  Avhilst  within  the  alar  lamina  are  developed  the  neuroblasts  which  constitute  the 
nuclei  of  termination  for  the  fibres  of  the 
afferent  nerves. 

As  development  proceeds,  the  two  laminse 
of  the  lateral  wall  fall  outwards  to  a  still 
greater  extent,  so  that  they  come  to  lie  very 
nearly  in  the  same  horizontal  plane.  In  this 
manner  their  originally  mesial  or  ventricular 
surfaces  come  to  form  the  floor  of  the  fourth 
ventricle.  Even  in  the  adult  the  groove, 
which  separates  the  basal  and  alar  lajninae 
so  clearly  from  each  other  in  the  early  con- 
dition, is  more  or  less  distinctly  perceptible  on 
the  ventricular  floor.  It  is  represented  by  the 
fovea  inferior  and  by  the  fovea  superior. 
Between  these  depressions  and  the  mesial 
groove  on  the  floor  of  the  fully -developed 
fourth  ventricle  there  is  an  elongated  eleva- 
tion, which,  in  its  lower  part,  forms  the  tri- 
gonum  hypogiossi,  above  this  the  emenentia 
teres,  whilst  higher  up  it  is  continued  towards 
the  commencement  of  the  Sylvian  aqueduct. 
This  clearly-marked  and  bulging  mesial  strip 
of  the  ventricular  floor  corresponds  to  the 
basal  lamina,  whilst  the  part  of  the  floor  which 
lies  to  the  outer  side  of  it  and  the  two  fovese 
is  derived  from  the  alar  lamina.  The  latter, 
therefore,  includes  the  trigonum  vagi,  the  area 
acustica,  and  the  locus  coeruleus. 

The  further  development  of  the  medulla 
takes  place  on  the  ventral  aspect  of  the  two 
laminae  by  the  deposition  of  new  parts  on 
those  which  are  already  formed.  An  oval 
bundle  of  longitudinal  fibres  makes  its  ap- 
pearance on  the  outer  surface  of  the  alar 
lamina,  at  the  point  where  this  joins  the 
basal  lamina.  This  is  the  early  fasciculus 
solitarius.  It  is  composed  of  afferent  fibres 
from  the  glossopharyngeal  and  vagus  nerves. 
These,  on  reaching  the  surface  of  the  medulla, 
turn  downwards  upon  it.  At  first  the  con- 
nexion of  the  fasciculus  solitarius  with 
the  medulla  is  very  loose,  and  it  may  be 
regarded  as  being  the  equivalent  in  this 
part  of  the  neural  tube  of  the  oval  bundle 
of  longitudinal  fibres  which,  in  the  early  cord, 
constitutes  the  first  stage  of  the  column 
of  Burdach.  Throughout  the  further  stages 
of  development  the  fasciculus  solitarius  in- 
dicates in  a  sufficiently  clear  manner  the  point  of  junction  between  the  alar  and 
basal  lamintc.  Very  soon  it  becomes  covered  over  by  parts  developed  on  its  ventral 
aspect,  and  it  ultimately  comes  to  lie  deeply  in  the  substance  of  the  medulla.  This 
change  in  the  position  of  the  fasciculus  solitarius  with  reference  to  the  surface  is  asso- 
ciated with  a  striking  developmental  process  which  leads  to  certain  remarkable  results, 
and  which  is  termed  the  formation  of  the  rhombic  lip  of  His  (Fig.  422,  B  and  C).  Before 
the  alar  lamina  falls  outwards,  while  it  still  stands  erect  and  its  inner  surface  faces  the 
corrcHponding  surface  of  the  opposite  lamina,  its  dorsal  edge  is  folded  outwards  and 
becomes  fused  with  the  outer  surface  of  the  remaining  portion  of  the  alar  lamina.     This 


RHOMBIC  LIP 


HYPOGLOSSAL 


Fifi.  422. — Three  Stages  in  the  Development  of 
THE  Medulla  Oblongata  (from  His — slightly 
modified). 


528  THE  NERVOUS  SYSTEM. 

is  the  rhombic  lip,  and,  when  the  fusion  is  complete,  a  multitude  of  neuroblasts  take  form 
■within  it  and  migrate  in  a  forward  and  inwards  direction  into  the  ventral  parts  of  the 
alar  and  basal  lamina;.  The  mid-ventral  lamina — which  consists  of  spongioblastic  cells 
alone,  and  which  forms  a  narrow  partition  between  the  two  basal  lamina) — is  reached  on 
either  side  by  the  axons  of  many  of  these  migrating  cells.  Whilst  acting  as  an  impassable 
barrier  to  the  neuroblasts,  this  spongioblastic  septum  gives  free  passage  from  one  side  to 
the  other  to  their  axons,  and  a  decussation  of  arcuate  fibres  in  the  mesial  plane  results. 
In  this  way  the  raphe  of  the  medulla  is  formed.  The  process  is  very  similar  to  that  which 
takes  place  in  tlie  coui'se  of  the  formation  of  the  anterior  connnissure  of  the  cord,  of 
which  the  raphe  may  be  regarded  as  the  equivalent  in  the  medulla. 

The  development  of  the  inferior  olivary  nucleus  and  of  its  two  accessory  parts  is  like- 
wise closely  connected  with  the  migration  of  the  neuroblasts  from  the  region  of  the 
rhombic  lip.  Many  of  these  cells  collect  together  so  as  to  form  a  nuclear  lamella,  which 
afterwards  assumes  its  characteristic  crumpled  form. 

As  the  neuroblasts  of  the  rhombic  lip  stream  inwards  they  pass  both  on  the  dorsal 
and  the  ventral  aspects  of  the  fasciculus  solitarius,  which  thus  comes  to  be  covered  over 
and  separated  from  the  surface.  The  spinal  root  of  the  trigeminal  nerve,  like  the 
fasciculus  solitarius,  is  also,  in  the  first  instance,  throughout  its  entire  course  on  the 
surface  of  the  medulla,  and  its  change  of  position  in  the  greater  part  of  its  course  within 
the  pons  and  medulla  is  due  to  the  subsequent  development  of  those  parts  which  cover  it 
over. 

The  importance  of  the  rhombic  lip  in  the  development  of  the  medulla  will  be  better 
appreciated  if  we  enumerate  the  parts  which  spring  from  it :  (1)  the  inferior  olivary  nuclei; 
(2)  the  cuneate  nucleus ;  (3)  the  substantia  gelatinosa  Rolandi ;  (4)  the  arcuate  nucleus ; 
(5)  the  internal  arcuate  fibres  ;  (6)  the  olivary  system  of  fibres ;  (7)  the  restiform  body. 
From  this  it  is  evident  that  the  formation  of  the  rhombic  lip  constitutes  an  extremely 
important  step  in  the  development  of  the  human  brain.  Recent  investigation,  however, 
makes  it  clear  that  in  most  of  the  lower  mammals  the  rhombic  lip  does  not  attain  any- 
thing like  the  degree  of  prominence  which  it  presents  in  the  early  brain  of  man. 

The  pyi'amidal  tracts  which  come  down  from  the  cerebral  cortex  are  late  in  making 
their  appearance  in  the  medulla.  The  formatio  reticularis  precedes  them  in  development. 
They  appear  in  the  fourth  month  of  foetal  life,  and  as  they  are  developed  the  antero- 
median furrow  between  them  takes  form  on  the  ventral  aspect  of  the  medulla. 

His  has  pointed  out  that  the  earliest  formed  part  of  the  medulla  is  the  floor  of  the 
fourth  ventricle,  and  that  the  other  parts,  speaking  generally,  are  added  in  succession  as 
we  pass  towards  the  surface.  "  The  oldest  layer  of  the  medulla  is  the  floor  of  the  fourth 
ventricle  with  its  nuclei.  It  is  followed,  in  the  first  instance,  by  the  reticular  formation, 
and  afterwards  by  the  layer  containing  the  olivary  and  other  nuclei.  Last  of  all  come 
the  pyramids  and  the  outer  (superficial)  arcuate  fibres  "  (His). 

Pons  Varolii. — The  information  which  we  possess  at  the  present  moment  regarding 
the  development  of  the  pons  Varolii  is  somewhat  deficient ;  but  there  is  little  doubt  that 
tlie  course  pursued  is,  in  general,  very  similar  to  that  which  has  been  described  for  the 
medulla.  It  has  been  seen  to  be  composed  of  parts  which  are  in  a  great  measure 
equivalent  to  those  met  with  in  the  medulla,  the  formatio  reticularis  of  the  latter 
passing  into  the  tegmental  substance  in  the  former,  while  the  pyramids  and  arcuate  nuclei 
and  anterior  superficial  arcuate  fibres  of  the  medulla  are  represented  by  the  large  ventral 
part  of  the  pons.  Further,  as  His  points  out,  similar  relations  between  the  chronological 
and  local  succession  of  layers  may  be  recognised.  Thus  the  primitive  position  of  the 
motor  nucleus  of  the  trigeminal  nerve,  and  also  of  its  spinal  root,  is  a  superficial  one,  and 
it  is  only  by  a  later  process  of  development  that  the  nucleus  pontis  and  the  thick  layer 
of  transverse  and  longitudinal  fibres  are  formed. 

From  the  phylogenetic  point  of  view  the  tegmentum  is  the  oldest  part  of  the  pons. 
The  study  of  the  comparative  anatomy  of  the  brain  makes  it  evident  that  the  large 
ventral  part  is  comparatively  a  recent  acquisition.  As  the  cerebral  cortex  extends  with 
the  increasing  evolution  of  the  cerebral  hemispheres  (pallium),  the  ventral  part  of  the 
pons  is  seen  to  keep  pace  with  it  in  its  development.  This  should  easily  be  understood 
from  what  has  been  said  in  regard  to  its  structure  and  connexions.  It  is  composed 
of  the  nucleus  pontis,  the  transverse  fibres,  and  the  pyramidal  and  cortico-pontine  fibres, 
all  of  which  stand  in  direct  relation  to  the  cerebral  cortex.  One  of  the  striking  features 
of  the  brain  of  a  microcephalic  idiot,  where  the  cerebral  cortex  is  greatly  reduced,  is  the 
corresponding  marked  diminution  in  the  size  of  the  ventral  part  of  the  pons. 

Cerebellum. — The  roof  of  the  fourth  ventricle  is  formed  for  the  most  part  by  the 
thin  epithelial  layer  already  described  as  being  formed  by  the  expanded  mid-dorsal  lamina. 


DEVELOPMENT  OF  THE  CEREBELLUM. 


529 


A 

Fig.  423 


B  C 

Drawings  to  illustrate  the  Development  of  the  Cerebellum 
(from  Kuithan). 

Transverse  section  througli  the  forepart  of  the  cerebellum  of  a  sheep  embryo. 
Transverse  section  through  the  hinder  part  of  the  cerebellum  of  a  sheep  embryo. 
Cerebellum  of  a  human  fcetus  17  cm.  long. 

1.  Sulcus  primarius.  3.  Sulcus  infrapyramidalis. 

2.  Sailcus  suprapyramidalis.  4.  Fissura  post-lunata. 
r.l.  Lateral  recess  ventricle  IV. 


This  does  not  stretch,  however,  over  its  entire  extent.  As  we  approach  the  upper  part  of 
the  ventricle,  it  is  seen  to  become  continuous  in  the  region  of  the  isthmus  with  a  thicker 
lamella.  This  lamella  is  bounded  above  by  the  intercrossing  of  the  two  trochlear  nerves, 
which  marks  on  the  dorsal  aspect  of  the  neural  tube  the  place  of  junction  between  the 
rhombencephalon  and  the  mesencephalon ;  below,  it  is  limited  by  a  forwardly-directed 
semilunar  fold  of 
the  thin  epithelial 
ventricular  roof, 
which  takes  place 
into  the  ventricular 
cavity  at  the  level 
of  the  pontine  flex- 
ure of  the  brain. 
The  fold  so  con- 
stituted is  termed 
the  plica  choroidea, 
seeing  that  meso- 
derm is  introduced 
between  its  two 
layers,  and  this  ul- 
timately gives  rise 
to     the    choroid 

plexus  of  the  fourth  ventricle  (Fig.  425,  A).  The  lamella  which  forms  the  roof  or  dorsal 
wall  of  the  ventricle  in  front  of  the  plica  choroidea  is  developed  into  the  cerebellum, 
and  the  superior  medullary  velum  (valve  of  Vieussens). 

The  cerebellar  part  of  this  lamella  consists  of  two  thick  lateral  plates  which  meet  in  the 
middle  line  and  are  joined  there  by  an  extremely  thin  dorsal  seam  or  lamina  (Fig.  423,  A). 
The  inner  extremities  of  the  two  cerebellar  plates  are  thus  separated  by  a  median  groove, 
which  opens  into  the  cavity  of  the  hind-brain  (fourth  ventricle).  The  statement,  there- 
fore, that  the  median  lobe  or  vermis  of  the  cerebellum  is  the  most  archaic  part  of  the 

organ  and  is  the  part  which 
is  developed  first  is  not 
supported  by  fact ;  indeed, 
the  reverse  of  this  is  the 
case,  because  at  this  early 
stage  the  lateral  portions 
are  alone  represented. 

In  the  course  of  time 
the  inner  ends  of  the  cere- 
bellar plates  become  fused 
in  the  middle  line,  and  the 
median  furrow  between 
them  disappears.  In  the 
process  of  this  fusion  the 
deep  part  of  the  intervening 
furrow  remains  enclosed 
within  the  substance  of 
the  median  part  of  the 
cerebellum  and  persists  for 
Fig,  424. — The  Brain  of  an  Embryo  of  eleven  weeks,  viewed  from  a  short  time  as  a  minute 
behind  to  show  the  development  of  the  cerebellum.  At  this  stage  the  cerebellar  ventricle  (Blake), 
cerebellum  is  in  the  form  of  a  simple  band  or  plate  which  arches  over  rpj^^  cerebellum  nownre- 

the  hinder  aspect  of  the  fore  part  of  the  cavity  of  the  hind  brain  (from  ,       ,i    •  „ 

His).  sents  the  appearance  of  a 

simple  uniform  arch  which 
bridges  across  the  doi'sal  aspect  of  the  upper  part  of  the  early  fourth  ventricle ;  and  very 
soon  the  sulci  begin  to  appear.  Of  late  years  the  development  and  morphological  import 
of  these  sulci  have  received  much  attention.  Stroud,  Kuithan,  Blake,  Elliot  Smith,  and 
Bradley  have  published  valuable  papers  on  this  subject,  and  what  is  written  here  is 
largely  gathered  from  the  writings  of  these  observers.  Further,  tlie  terminology 
suggested  by  Elliot  Smith  has  been  chiefly,  but  not  entirely,  followed. 

The  first  fissure  to  appear  is  tlie  floccular  fissure,  which  cuts  off"  the  postero-lateral 
comer  of  the  cerebellar  plate.     The  portion  thus  marked  off'  is  the  flocculus,  and  its  early 
appearance  and  relatively  large  size  at  this  stage  arc  significant  of  its  high  morphological 
38 


^ .  Mesencephalon 


Early  cerebellum 


Cavity  of 
'fourth  ventricle 


Medulla 


530 


THE  NERVOUS  SYSTEM. 


importance  as  a  lobule  of   the   cerebellmn. 


Sup 

MED 


B 


Fig.  425. 

A.    Mesial  section  tlirough  the  cerebellum  of  an  early  hiunan  fcetiis 

(semi-diagrammatic). 
Mesial  section  through  the  cerebellum  of  a  human  fcBtus  17  cm.  long 
(from  Kuithau). 

1.    Fissiiva  i")rima.  4.    Fissura  postuodularis. 

'2.    Fissura  suprapyramidalis.  T.  Transverse  groove  on  the  roof  of 

3.    Fissura  infrapyraniidalis.  the  fourth  ventricle. 


Nodule 


Uvula 


Post-nodular  fissure 
/ 


The  floccxilar  fissure  is  continued  inwards 
close  to  the  posterior  border 
of  the  cerebellar  plate,  join- 
ing its  fellow  of  the  opposite 
side  in  the  middle  line. 
Here  it  receives  the  name 
of  post-nodular  fissure.  A 
narrow  strip  of  cerebellar 
surface  is  thus  marked  out. 
The  median  part  of  this 
strip,  by  special  growth,  be- 
comes the  nodulus,  whilst  the 
part  which  extends  between 
this  and  the  flocculus  remains 
narrow  and  band-like,  and 
ultimately  forms  a  portion 
of  the  inferior  medullary 
velum. 

The  next  furrow  which 
appears  is  the  sulcus  prim- 
arius  (Kuithan)  or  fissura 
prima  (Elliot  Smith).  It 
cuts  deeply  into  the  vermis 
in  a  tx'ansverse  direction  be- 
tween the  culmen  monticuli 
and  the  clivus  monticuli,  and  is  then  carried  outwards  over  each  hemisphere  so  as  to 
separate  the  two  crescentic  lobules.  The  fissura  prima  is  the  deepest  of  all  the  fissures 
of  the  vermis,  and  it  is 
developed  towards  the  end 
of  the  third  month.  A 
little  later  two  other  fur- 
rows are  observed  in  the 
vermis.  These  are  the 
suprapyramidal  and  the 
infrapyramidal  (the  fissura 
secunda  of  Elliot  Smith). 
By  the  former  the  pyramid 
is  limited  above  ;  by  the 
latter  the  pyramid  is  separ- 
ated from  the  uvula. 

After  the  iiiain  fissures 
of    the  vermis   are    estab- 
lished, four  important  sulci 
on  the  surface  of  each  cerebellar  hemisphere  come   into   view,  viz.  the  postlunate,  the 
post-tonsillar,  the  parapyramidal,  and  the  great  horizontal  sulci. 

The  fissura  postlunata  ap- 
pears in  the  fourth  month,  and 
curves  inwards  on  the  upper 
surface  of  the  organ  behind  the. 
posterior  crescentic  lobule.  In 
many  cases  it  becomes  con- 
fluent with  its  fellow  of  the 
opposite  side  behind  the  clivus 
monticuli.  The  post-tonsillar 
fissure  is  seen  on  the  under 
surface  of  the  cerebellum  about 
the  beginning  of  the  fifth  month. 
It  circumscribes  the  pi'ominent 
and  conspicuous  tonsil  and 
becomes  confluent  with  the 
fissura  infrapyraniidalis.  The  parapyramidal  fissure  appears  on  the  under  surface  of  the 
cerebellar  hemisphere  behind  the  biventral  lobule,  and  usually  joins  the  suprapyramidal 
fissure  of  the  inferior  vermis. 


Floccular  fissure - 
Tonsil  - 
Biventral  lobule 


Flocculus 
Para  flocculus 

Peduncle  of 
flocculus 
Post-tonsillar 
sulcus 

Parapyramidal 
sulcus 

Postero-inferior 
obule 


Infrapyramidal  fissure  / 
Suprapyramidal  fissure 


Pyramid 
Tuber  valvula 


Great  horizontal  sulcus 
Fig.   426. — Under   Surface   op  the   Cerebellum   of  a  Human    Fcetus 

WHICH    has    reached    THE    EnD    OP    THE    FiFTH    MONTH    OF    DEVELOPMENT. 


f'ulinfiii  inniiticuli 


Clivus  montii 


Fissura  postlunata 


ssura  prima 


Postero-superior  lobule 


Fig 


reat  horizontal  fissure 
''  '  Postero-inferior  lobule 

Suprapyramidal  fissure         Intrapyramidalis  fissure 

427. — Cerebellum  of  a  Human  Fcetus  which  has  reached 
THE  End  of  the  Fifth  Month  of  Development.  Viewed  from 
above  and  behind. 


THE  MESENCEPIiALON.  531 

The  great  horizontal  fissure,  iu  spite  of  its  depth  in  the  adult  brain — a  depth  which 
is  due  to  tlie  excessive  growth  in  the  later  months  of  development  of  the  two  lobules  that 
bound  it — appears  very  late  in  the  development  of  the  cerebellum.  It  is  first  seen  as  a 
very  broad  shallow  groove  or  furrow  on  the  outer  margin  of  the  hemisphere.  From  this 
it  runs  forwards  to  the  middle  peduncle  and  backwards  towards  the  vermis,  where  it 
usually  joins  the  postlunate  fissure.  At  this  stage  there  is  no  folium  cacuminis,  so  that 
the  combined  portion  of  the  postlunate  and  great  horizontal  fissures  intervenes  between 
the  clivus  monticuli  and  the  tuber  valvulse.  Even  at  the  time  of  birth  the  folium 
cacuminis  is  not  seen  on  the  surface.  It  rises  up  from  the  bottom  of  the  combined  portions 
of  the  gi'eat  horizontal  and  postlunate  fissures  so  as  to  form  a  barrier  between  them. 

Very  early  a  transverse  groove  appears  on  the  smooth  anterior  or  ventricular  surface 
of  the  cerebellum  (Fig.  425,  B,  t).  This  is  placed  much  nearer  the  lower  than  the  upper 
border  of  the  organ,  and  it  represents  at  this  stage  the  angular  peak  of  the  tent-like  roof 
of  the  fourth  ventricle  in  the  adult  brain.  As  growth  goes  on,  the  portions  of  the  cere- 
bellum in  front  and  behind  this  groove  approach  each  other,  so  as  to  deepen  the  groove 
and  bring  about  the  backward  prolongation  of  the  ventricular  cavity  towards  the  cerebellum. 

The  leading  distinctive  characters  of  the  human  cerebellum  are:  (1)  the  small  size 
of  the  flocculus ;  (2)  the  large  size  of  the  tonsil ;  (3)  the  excessive  development  of  the 
lateral  hemisphere,  and  particularly  of  the  postero-superior  and  postero-inferior  lobules 
which  bound  the  great  horizontal  fissure. 

THE  MESENCEPHALON. 

The  mesencephalon  or  mid-brain  is  the  short,  narrow  part  of  the  brain-stem 
which  occupies  the  aperture  of  the  tentorium  cerebelli  (incisura  tentorii),  and 
connects  the  cerebrum  which  lies  above  with  the  parts  which  occupy  the  posterior 
cranial  fossa.  It  is  about  three-quarters  of  an  inch  in  length,  and  it  consists  of  a 
dorsal  part,  composed  of  the  corpora  ctuadrigemina,  and  a  much  larger  ventral  part, 
which  is  formed  by  the  two  crura  cerebri. 

In  the  undissecfced  brain  the  corpora  quadrigemina  are  completely  hidden  from 
view  by  the  splenium  of  the  corpus  callosum,  which  projects  backwards  over  them, 
and  also  by  the  superimposed  cerebral  hemispheres.  The  hinder  end  of  each  optic 
thalamus  likewise,  to  some  extent,  overhangs  the  upper  part  of  the  mesencephalon 
on  its  dorsal  and  lateral  aspect  (Fig.  388,  p.  482).  On  this  portion  of  the  optic 
thalamus  are  seen  two  projections,  which  are  specially  related  to  the  mesencephalon. 
These  are  the  cushion-like  pulvinar,  which  forms  the  inner  and  hinder  part  of  the 
thalamus,  and  the  corpus  geniculatum  externum,  an  ill-defined  oval  swelling  on  the 
outer  and  under  aspect  of  the  posterior  end  of  the  thalamus. 

The  crura  cerebri  can  to  some  extent  be  seen  on  the  base  of  the  brain,  where 
they  bound  the  posterior  part  of  the  interpeduncular  space.  Encircling  the  upper 
end  of  each  crus  cerebri,  where  it  plunges  into  the  cerebrum,  is  the  optic  tract 
(Fig.  380,  p.  474). 

The  mesencephalon  is  tunnelled  from  below  upwards  by  a  narrow  passage, 
called  the  aqueduct  of  Sylvius,  which  connects  the  fourth  ventricle  with  the  third 
ventricle  (Fig.  429,  p.  533).  This  channel  lies  much  nearer  the  dorsal  than  the 
ventral  aspect  of  the  mesencephalon. 

Corpora  Quadrigfemina. — This  name  is  applied  to  four  rounded  eminences  on 
the  posterior  aspect  of  the  mesencephalon  (Fig.  388,  p.  482).  The  superior  pair  are 
larger  and  broader  than  the  inferior  pair,  but  they  are  not  so  well  defined  nor  are 
they  80  prominent.  A  longitudinal  and  a  transverse  groove  separate  the  quad- 
rigemina! bodies  from  each  other.  The  longitudinal  groove  occupies  the  mesial  plane 
and  extends  upwards  to  the  posterior  commissure  of  the  brain.  The  upper  end  of 
this  groove  widens  out  into  a  shallow  depression,  in  which  the  pineal  body,  a  small 
conical  structure  which  belongs  to  the  diencephalon,  rests.  F'rom  the  lower  end  of 
the  same  groove  a  short  but  well-defined  and  ]jrqjecting  band,  the  frenulum  veli, 
passes  tf)  the  valve  of  Vieussens,  wliich  li(;s  immediately  below  the  inferior  pair 
of  quadrigeminal  Itodies.  The  transverse  groove  curves  round  below  each  of  the 
superior  pair  of  quadrigeminal  bodies  and  S(iparates  them  from  the  ini'erior  pair. 
It  is  also  continued  in  ;ui  upward  and  forward  direction  on  the  lateral  aspect 
of  the  meHencephalon. 


532  THE  NERVOUS  SYSTEM. 

The  quadrigeminal  bodies  are  not  marked  off"  laterally  from  the  sides  of  the 
mesencephalon,  but  each  has  in  connexion  with  it,  on  this  aspect,  a  prominent 
strand  of  white  matter,  which  is  prolonged  upwards  and  forwards  under  the 
projecting  pulvinar  and  corpus  geniculatum  externum.  These  strands  are  called 
the  brachia  of  the  corpora  quadrigemina,  and  they  are  separated  from  each  other  by 
a  continuation  on  the  side  of  the  mesencephalon  of  the  transverse  groove,  \vhich 
intervenes  between  the  two  pairs  of  bodies. 

The  corpus  geniculatum  internum  (corpus  geniculatum  mediale)  is  closely 
associated  with  the  jjrachia.  It  is  a  small,  sharply-defined  oval  eminence,  which 
lies  on  the  side  of  the  upper  part  of  the  mesencephalon  under  shelter  of  the  pulvinar 
of  the  optic  thalamus. 

The  inferior  brachium  (brachium  quadrigeminum  inferius),  proceeding  upwards 
from  the  lower  quadrigeminal  body,  advances  towards  the  corpus  geniculatum 
internum  and  disappears  from  view  under  cover  of  this  prominence.  Upon  the 
opposite  side  of  the  same  geniculate  body  the  mesial  root  of  origin  of  the  optic  tract 
takes  shape  on  the  surface,  and  the  appearance  is  such  that  the  conclusion  might 
very  naturally  be  arrived  at  that  the  inferior  brachium  and  this  root  of  the  optic 

tract  are  continuous  with  each  other  under  the  genicu- 
,corp:qen:ext:  latc   clcvation.      This   is   not   the  case,  however ;    the 

LATERAL  ROOT.  fibres  of  the   inferior    brachium,    to    a    large   extent, 

proceed  into  the  subjacent  tegmentum  under  cover  of 
the  internal  geniculate  body  and  help  to  constitute  an 
MESIAL  ROOT.  asccndlug  tract  from  the  inferior  quadrigeminal  body, 

^corp:genmnt:  which  proceeds  upwards  to  the  optic  thalamus.     Of  the 

fibres  of  the  mesial  root  of  the  optic  tract  some  end  in 
^suPR.QUAD:BODY=  tho  gray  matter  of  the  internal  geniculate  body,  whilst 

others  arise  within  it.     They  constitute  what  is  called 
Fig.  428.-DIAGRAM  of  the  roots  Qudden's  commissure. 

OF  THE  Optic  jSierve.  „i  •■,■••  /^        t  ■  i   •  • 

ihe    superior   bracnium    (brachium   quadrigeminum 

superius)  is  carried  upwards  and  forwards  between  the  overhanging  pulvinar 
and  the  corpus  geniculatum  internum.  A  surface  examination  of  the  mesen- 
cephalon is  sufficient  to  show  that,  while  a  large  part  of  this  strand  enters  the 
corpus  geniculatum  externum,  a  considerable  portion  runs  into  the  lateral  root  of 
the  optic  tract. 

The  optic  tract  is  thus  attached  to  the  brain-stem  by  two  roots,  viz.  a  mesial 
and  a  lateral,  which  are  separated  from  each  other  by  a  distinct  groove.  The 
mesial  root  disappears  under  the  internal  geniculate  body.  The  lateral  root  spreads 
out  and  some  of  its  fibres  enter  the  superior  quadrigeminal  body  through  its 
brachium,  whilst  others  find  their  way  into  the  corpus  geniculatum  externum  and 
the  pulvinar  of  the  optic  thalamus  (Fig.  428). 

Crura  Cerebri  (pedunculi  cerebri). — The  crura  cerebri  constitute  the  chief  bulk 
of  the  mesencephalon  (Fig.  429,  p.  533).  Upon  the  basal  aspect  of  the  brain  they 
appear  as  two  large  rope-like  strands,  which  emerge  close  together  from  the  upper 
aspect  of  the  pons  Varolii  and  diverge  as  they  proceed  upwards  to  enter  the 
cerebrum.  At  the  place  where  each  crus  disappears  into  the  corresponding  side 
of  the  cerebrum,  it  is  encircled  by  the  optic  tract. 

Each  crus  cerebri  is  composed  of  two  parts,  viz.  a  dorsal  tegmental  part  (teg- 
mentum), which  is  prolonged  upwards  into  the  region  below  the  optic  thalamus 
(subthalamic  tegmental  region),  and  a  ventral  pedal  portion  or  crusta  (basis  pedun- 
culi), which,  when  traced  upwards  into  the  cerebrum,  is  seen  to  take  up  a  position 
on  the  outer  side  of  the  optic  thalamus  and  to  be  continuous  with  the  internal 
capsule  of  the  brain.  When  the  base  of  the  brain  is  examined  it  is  the  crusta 
which  is  seen,  and  it  is  observed  to  be  wdiite  in  colour  and  streaked  in  the  longi- 
tudinal direction.  In  the  tegmentum  the  longitudinally-arranged  fibres  are,  for 
the  most  part,  corticipetal,  or,  in  other  words,  fibres  which  are  ascending  towards 
the  cortex  of  the  cerebrum ;  the  crusta,  on  the  other  hand,  is  entirely  composed  of 
longitudinal  strands  of  fibres  which  are  corticifugcd,  or  fibres  which  descend  from 
the  cortex  cerebri. 

On  the  surface  of  the  mesencephalon  the  separation  between  the  tegmental  and 


IJ^TEENAL  STRUCTURE  OF  THE  MESENCEPHALON. 


533 


pedal  portions  of  the  crus  cerebri  is  clearly  indicated  by  an  inner  and  an  outer  groove. 
The  inner  or  mesial  furrow  is  the  more  distinct  of  the  two.  It  looks  into  the 
interpeduncular  space,  and  from  it  emerge  the  fascicles  of  the  third  or  oculo-rnotor 
nerve.  It  is,  therefore,  termed  the  sulcus  oculo-motorii  (sulcus  nervi  oculo-motoriij. 
The  outer  groove,  which  is  placed  on  the  lateral  aspect  of  the  mesencephalon, 
receives  the  name  of  the  sulcus  lateralis  mesencepliali.  When  traced  downwards,  it 
is  observed  to  become  continuous  with  the  furrow  which  intervenes  between  the 
middle  and  superior  peduncles  of  the  cerebellum. 

^  A  close  inspection  of  the  outer  surface  of  the  tegmental  part  of  the  crus  cerebri, 
below  the  level  of  the  quadrigeminal  brachia,  will  reveal  some  faintly-marked 
bundles  of  fibres  curving  obliquely  upwards  and  backwards  to  reach  the  inferior 
quadrigeminal  body  (Fig.  390,  p.  484).  These  are  fibres  of  the  lateral  fillet,  coming 
to  the  surface  at  the  sulcus  lateralis  and  sweeping  over  the  subjacent  superior 
cerebellar  peduncle  to  gain  the  inferior  quadrigeminal  body. 


POSTERrOR 

LONGITUDINAL 

BUNDLE 


AQUEDUCT  OF  SYLVIUS. 


SULCUS  LATERALS 


INTERNAL  STRUCTURE  OF  THE  MESENCEPHALON. 

When  transverse  sections  are  made  through  the  mesencephalon  the  aqueduct  of 
Sylvius  is  seen  to  be  surrounded  by  a  thick  layer  of  gray  matter,  which  receives  the 
name  of  the  Sylvian  gray  matter  or  the  central  gray  matter  of  the  aqueduct  (stratum 
griseum  centrale).  On  the  dorsal  aspect  of  the  Sylvian  gray  matter  the  corpora 
quadrigemina  form  a  layer  which  separates  it  from  the  surface,  and  to  which  the 
term  lamina  quadrigemina  is  applied. 
On  the  ventral  and  lateral  aspects 
of  the  Sylvian  gray  matter  are  the 
tegmental  portions  of  the  crura 
cerebri;  whilst,  intervening  between 
each  of  the  latter  and  the  corre- 
sponding crusta,  there  is  a  con- 
spicuous mass  of  dark  pigmented 
matter  termed  the  substantia  nigra. 

Sylvian  Aqueduct  and  Sylvian 
Gray  Matter  (aqu^eductus  cerebri 
— stratum  griseum  centrale). — The 
aqueduct  of  Sylvius  is  the  canal 
which  leads  from  the  fourth  ventricle 
below,  upwards  through  the  mesen- 
cephalon, to  the  third  ventricle  above. 
It  is  not  quite  three-quarters  of  an  inch  in  length,  and  it  lies  much  nearer 
the  dorsal  than  the  ventral  surface  of  the  mesencephalon.  When  examined  in 
transverse  section,  it  presents  a  triangular  outline  as  it  passes  into  the  fourth 
ventricle  and  a  T-shaped  outline  close  to  the  third  ventricle.  In  the  intermediate 
part  of  its  course  it  assumes  different  outlines,  and  not  always  the  same  form  at 
the  same  level  in  different  individuals. 

The  aqueduct  of  Sylvius  is  lined  by  ciliated  epithelium,  and  outside  this  is  the 
thick  layer  of  Sylvian  gray  matter,  which  is  directly  continuous  below  with  the  gray 
matter  spread  out  on  the  floor  of  the  fourth  ventricle,  and  above  with  gray  matter 
on  the  floor  and  sides  of  the  third  ventricle.  Scattered  more  or  less  irregularly 
throughout  the  Sylvian  gray  matter  are  numerous  nerve-cells  of  varying  forms  and 
sizes,  whilst  in  addition  to  these  there  are  three  definite  collections  or  clusters  of 
cells,  which  constitute  the  nuclei  of  origin  of  the  trochlear  nerve,  the  oculo-motor 
nerve,  and  the  mesencephalic  root  of  the  trigeminal  nerve.  The  position  and 
relations  of  these  will  be  given  at  a  later  stage. 

Substantia  Nigra. — When  seen  in  transverse  section,  the  substantia  nigra 
{presents  a  semilunar  outline.  It  consists  of  a  mass  of  gray  matter,  in  the  midst  of 
which  are  large  numbers  of  deeply  pigmented  nerve-cells.  It  is  only  when  this 
substance  is  examined  in  bulk  that  it  appears  dark;  in  thin  sections  it  does  not 
differ  mucli  in  colour  from  ordinary  gray  matter,  although,  under  the  microscope, 
the  brown -coloured  cells  stand  out  very  conspicuously,  evezi   under  low  powers. 


SULCUS    OCULOMOTORIUS 


Fig.  429. — Diagrammatic  View  of  the  Cut  Surface  of 
A  Transverse  Section  through  the  Upper  Part 
of  the  Mesencephalon. 


534  THE  NEEVOUS  SYSTEM. 

The  substantia  nigra  is  disposed  in  the  form  of  a  thick  layer,  interposed  between 
the  tegmental  and  pedal  portions  of  the  crus  cerebri.  It  begins  below  at  the 
upper  border  of  the  pons  Varolii  and  extends  upwards  into  the  subthalamic 
reo-ion.  The  margins  of  this  layer  of  dark-coloured  substance  come  to  the  surface 
at  the  oculo-motor  and  the  lateral  sulci  of  the  mesencephalon,  and  its  inner  part  is 
traversed  by  the  emerging  fascicles  of  the  oculo-motor  nerve.  It  is  not  ecpially 
thick  throughout.  Towards  the  lateral  sulcus  it  becomes  thin,  whilst  it  thickens 
considerably  near  the  inner  aspect  of  the  crus  cerebri.  The  surface  of  the  sub- 
stantia nigra,  which  is  turned  towards  the  tegmentum,  is  concave  and  uniform ; 
the  opposite  surface  is  convex  and  rendered  irregular  by  the  presence  of  numerous 
slender  prolongations  of  the  substance  into  the  crusta. 

The  morphological  and  physiological  significance  of  the  substantia  nigra  is  not 
fully  understood,  and  the  connexions  established  by  its  cells  are  imperfectly 
known. 

Inferior  Quadrigeminal  Bodies  (colliculi  inferiores). — Each  of  the  inferior 
quadrigeminal  bodies  is  largely  composed  of  a  mass  of  gray  matter  which,  in 
transverse  section,  presents  an  oval  outline  (Fig.  432,  p.  537).  This  central 
nucleus  is,  to  a  large  extent,  encapsulated  by  white  matter.  Numerous  cells  of 
different  sizes  are  scattered  throughout  it,  and  the  whole  mass  is  pervaded  by  an 
intricate  interlacement  of  fine  fibres,  which,  to  a  large  extent,  are  derived  from  the 
lateral  fillet  and  the  inferior  brachium. 

In  transverse  sections,  through  this  region,  the  lateral  fillet  is  seen  to  abut 
against  the  outer  margin  of  the  central  nucleus.  Many  of  the  fibres  of  this  tract 
enter  it  at  once  and  become  dispersed  amongst  its  cells ;  others  sweep  over  its 
dorsal  surface,  so  as  to  give  it  a  superficial  covering ;  whilst  a  third  group  is  carried 
in  the  form  of  a  thin  layer  inwards  on  its  ventral  aspect,  so  as  to  mark  it  off  from 
the  subjacent  Sylvian  gray  matter  of  the  aqueduct  (Fig.  432,  p.  537).  In  this 
manner,  therefore,  the  inferior  quadrigeminal  nucleus  becomes  partially  circum- 
scribed by  the  fibres  of  the  lateral  fillet.  Several  of  the  lateral  fillet  fibres,  which 
proceed  over  the  superficial  or  dorsal  aspect  of  the  nucleus,  reach  the  mesial  plane  ' 
and  form  a  loose  decussation  with  the  corresponding  fibres  of  the  opposite  side. 

Tl;e  intimate  connexion  wMcL.  is  tlius  exhibited  between  the  fibres  of  the  lateral  fillet  and 
the  nucleus  of  the  inferior  quadrigeminal  body  is  very  significant.  It  has  already  been  shown 
that  the  lateral  fillet,  to  a  large  extent,  comes  from  the  nuclei  of  termination  of  the  cochlear* 
nerve  of  the  o^Dposite  side,  although  most  of  its  fibres  have  to  pass  through  several  nuclear  inter- 
nodes  before  they  reach  the  inferior  quadrigeminal  body.  We  must  associate,  therefore,  the 
inferior  quadrigeminal  body,  and  also  the  corpus  geniculatum  internum,  which  likewise  receives 
lateral  fillet  fibres,  with  the  organ  of  hearing. 

This  view  of  the  inferior  quadrigeminal  bodies  is  supported  both  by  exj)erimental  and  by 
morphological  evidence.  Speaking  broadlj^,  it  may  be  stated  that  the  inferior  quadrigeminal 
bodies  are  only  present  as  distinct  eminences  in  mammals,  and  then  they  are  invariably  correlated 
with  a  spirally-wound  and  well-developed  cochlea.  That  they  have  nothing  to  do  with  sight, 
is  shown  by  the  fact  that,  Avhen  the  eyeballs  are  extirpated  in  a  young  animal,  the  inferior 
quadrigeminal  bodies  remain  imaft'ected,  whilst  the  superior  quadrigeminal  bodies  after  a  time 
atrophy  (Gudden).  When,  on  the  other  laand,  the  cochlear  terminal  nuclei  are  destroyed,  fibres 
which  have  undergone  atrophy  may  be  followed  to  the  inferior  quadrigeminal  bodies  of  both 
sides,  but  particularly  to  that  of  the  opposite  side  (Baginski,  Bumm,  and  Ferrier  and  Turner).  A 
very  considerable  tract  of  ascending  fibres  takes  origin  within  the  inferior  quadrigeminal  body 
and  jaasses  upwards,  in  the  inferior  brachium,  into  the  tegmentum  subjacent  to  the  internal  geni- 
culate body.  Within  the  tegmentum  they  proceed  up  to  the  optic  thalamus  (Ferrier  and 
Turner). 

Superior  Quadrigeminal  Bodies  (colliculi  superiores). — The  superior  quadri- 
geminal body  presents  a  more  complicated  structure  (Fig.  431).  Superficially,  it  is 
coated  with  a  very  thin  layer  of  white  matter,  which  is  termed  the  stratum  zonale. 
Underneath  this  there  is  a  gray  nucleus,  called  the  stratum  cinereum,  which  in 
transverse  section  exhibits  a  crescentic  outline  and  rests  in  a  cap-like  manner  upon 
the  subjacent  part  of  the  eminence  The  succeeding  two  strata,  which  respectively 
receive  the  names  of  stratum  opticum  and  the  stratum  lemnisci,  present  this  feature 
in  common,  that  they  are  composed  of  gray  matter,  traversed  by  numerous  fibres. 
The  source  from  which  the  fibres  are  derived  differs,  however,  in  each  case. 

Nerve-fibres  reach  the  superior  quadrigeminal  body  through — (1)  the  lateral 
and  mesial  fillets,  and  (2)  through  the  superior  brachium.     The  fillet  fibres  enter 


INTERNAL  STRUCTUEE  OF  THE  ME8EXCEPHAL0X.  535 


Sylvian  gray_ 
matter 


Aqueduct  of_ 
Sylvius" 


the  stratum  lemnisci,  and,  in  all  probability,  end  there.  The  superior  brachium 
contains  fibres  of  two  difi'erent  kinds,  \dz.  fibres  from  the  optic  tract  and  fibres  Irom 
the  cortex  of  the  occipital  lobe  of  the  cerebrum.  By  the  former  it  is  connected 
with  the  retina,  and  by  the  latter  with  the  visual  centre  in  the  occix>ital  region  of 
the  cerebral  cortex.  The  retinal  fibres,  for  the  most  part,  spread  out  on  the  surface 
of  the  quadrigeminal  body  and  form  the  stratum  zonale.  Most  of  them  dip  down 
into  the  substance  of  the  body  and  end  in  connexion  with  the  cells  of  the  deeper 
layers ;  several,  however,  are  carried  across  the  mesial  plane,  to  end  in  the  superior 
quadrigeminal  body  of  the  opposite  side.  The  occipital  fibres,  and  xjrobably  also 
some  of  the  retinal  fibres,  enter  the  stratum  opticum.  The  fibres  from  the  occipital 
cortex  form  part  of  the  optic  radiation,  and  the  course  which  they  pursue  will  be 
dealt  with  later  on. 

Tegmental  Portions  of  the  Crura  Cerebri  (tegmenta).— The  tegmentum  of 
the  cms  cerebri  may  be  regarded  as  the  continuation  upwards  of  the  formatio 
reticularis  of  the  medulla 

^~~~-.,       ^.,--^  Inferior  quadrigeminal  body 


and  the  dorsal  or  tegmental 
portion  of  the  pons  into 
the  mesencephalon.  It 
therefore  consists  of  fine 
bundles  of  longitudinal 
fibres  intersected  by  arch- 
ing fibres,  which  take  a 
transverse  and  curved 
course.  The  interstices 
between  these  nerve- 
bundles  is  occupied  by 
gray  matter  containing  ir- 
regularly scattered  nerve- 
cells.  On  its  dorsal  aspect 
the  tegmentum  is  con- 
tinuous, at  the  side  of  the 
Sylvian'  gray  matter,  with 
the  bases  of  the  corpora 
quadrigemina,  whilst  ven- 
trally  it  is  separated  from 
the  crusta  by  the  sub- 
stantia nigra.  The  two 
tegmenta  of  opposite  sides 
are,  to  some  extent,  marked 
off  from  each  other  in  the 
mesial  plane  by  a  pro- 
longation upwards  of  the 
median  raphe  of  the  pons 
and  medulla,  although,  in 


IMesenfRplialir  root  of  fifi 
lJpr^  c 

Xucleub  of  lourth  ller^  e 

Brachium  mferius 


Posterior  longitudinal 
bundle 

^Jlpbial  fillet 


Raphe 


Substantia 
niari-a 


r^ 


~Crusta 


Fig.  4.30. — Teaxsverse  Sectiox  through  the  Hujiax  Mescencephalox 
AT  THE  Level  of  the  Txfekior  Quadrige.mixal  Bodt. 


the  lower  part  of  the  mesencephalon,  tliis  is  much 
obscured  by  the  decussation  of  the  superior  peduncles  of  the  cerebellum.  The  two 
longitudinal  strands,  termed  the  posterior  longitudinal  bundle  and  the  fillet,  are 
prolonged  upwards  throughout  the  entire  length  of  the  mesencephalon  :  and  they 
present  the  same  relations  to  the  tegmentum  as  in  the  lower  parts  of  the  brain. 
The  former  is  jjlaced  in  relation  to  its  dorsal  aspect,  whilst  the  fillet  is  carried  up 
in  its  ventral  part. 

The  tegmentum  of  the  crus  cerebri  may  be  considered  as  presenting  two  parts  : 
viz.  (1)  a  lower  part,  which  is  placed  subjacent  to  the  inferior  quadrigeminal  bodies 
and  which  is  largely  occupied  by  the  decussation  of  the  superior  cerebellar  peduncles 
(Fig.  430) ;  and  (2)  a  superior  part,  subjacent  to  the  superior  quadrigeminal 
bodies,  which  is  traversed  by  the  emerging  bundles  of  the  third  nerve  and  which 
contains  a  large  and  striking  nuclear  mass,  termed  the  nucleus  rtiljer  or  the  red  teg- 
mental nucleus  (Fig.  431).  In  the  lower  part  of  the  mesencephalon  is  the  nucleus 
oC  the  fourth  nerve ;  in  the  uyiyier  part,  the  nucleus  of  the  third  nerve. 

Superior  Cerebellar  Peduncles  (brachia  conjunctiva). — As  the  superior  cere- 


536 


THE  NEEVOUS  SYSTEM. 


bellar  peduncles  leave  the  pons  and  sink  into  the  tegmenta  of  the  mesencephalon, 
they  undergo  a  complete  decussation  subjacent  to  the  inferior  quadrigeminal  bodies 
and  the  Sylvian  gray  matter  (Figs.  407,  p.  505 ;  432,  p.  537  ;  and  430,  p.  535). 
In  this  manner  each  peduncle  is  transferred  from  one  side,  across  the  mesial 
plane,  to  the  opposite  side.  The  decussation  is  completed  at  the  level  of 
the  upper  borders  of  the  inferior  quadrigeminal  bodies,  and  then  each  peduncle 
proceeds  upwards  into  the  superior  part  of  the  tegmentum,  where  it  encounters 
the  red  nucleus.  Into  this  a  large  proportion  of  its  fibres  plunge  and  come  to  an 
end  in  connexion  with  the  nuclear  cells.  Many  of  the  peduncular  fibres,  how- 
ever, are  carried  around  the  nucleus  so  as  to  form  for  it  a  capsule  which  is  thicker 
on  the  inner  than  on  the  outer  side  (Fig.  431).  These  are  prolonged  into  the 
subthalamic  region,  and  ultimately  penetrate  the  ventral  aspect  of  the  optic  thala- 

Superior  quadrigeminal 
body 


External  geniculate 

body^ 


Inferior  brachium- 


Internal  geniculate 
body 


5^3-^'^y^'^'^''  Sray  matter 


Sylvian  aqueduct 

Tegmentum 
-f  Xucleus  of  third  nerve 

I  Posterior  longitudinal 
bundle 

-  Red  nucleus 


Crusta_ 


Optic  tract- 


■^ 


>if*l  i' 

-JhQ  I       Fibres  of  superior 

tyirm  ~  cerebellar  peduncle 


Third  nerve 
Substantia  nigra 


Fig.   431. 


Corpus  mammillare 


-Transverse  Section  through  the  Human  Mesencephalon  at  the  Level  of  the  Superior 
Quadrigeminal  Body. 


mus,  where  they  end  in  connexion  with  the  thalamic  cells.  The  superior  cerebellar 
peduncle  is,  therefore,  a  great  efferent  tract  which  issues  from  the  lateral 
hemisphere  of  the  cerebellum,  crosses  the  mesial  plane  in  the  lower  part  of  the 
mesencephalon,  and  ends  in  the  red  nucleus  and  the  ventral  part  of  the  optic 
thalamus. 

Red  Nucleus  (nucleus  ruber). — This  is  a  rounded  nuclear  mass,  of  a  reddish 
tint  in  the  fresh  brain,  which  lies  in  the  upper  part  of  the  tegmentum,  and  in  the 
path  of  the  superior  cerebellar  peduncle.  In  transverse  section  it  presents  a  circular 
outline.  It  begins  at  the  level  of  the  lower  border  of  the  superior  quadrigeminal 
body  and  it  extends  upwards  into  the  subthalamic  tegmental  region.  At  first  it  is 
small  and  is  placed  at  a  little  distance  from  the  mesial  plane ;  but  as  it  proceeds 
towards  the  subthalamic  region,  it  increases  in  bulk  and  approaches  more  nearly 
to  the  mesial  raphe,  and  its  neighbour  of  the  opposite  side.  The  curved  emerging 
bundles  of  the  third  nerve  pass  through  it  on  their  way  to  the'  surface.  The 
relation  which  the  fibres  of  the  opposite  superior  cerebellar  peduncle  present  to  it 
has  been  described.  These  fibres  traverse  its  low^er  part  in  such  numbers  that  in 
Weigert-Pal  specimens  it  presents  a  very  dark  colour ;  but  higher  up,  as  the  fibres 


INTEENAL  STKUCTUEE  OF  THE  MESENCEPHALON. 


537 


Decussating 
fibres 


Inferior 

qnarh-igeniinal 

nucleus 

Mesencephalic 

root  of  fifth 

nerve 

Fourth  nerve 

Posterior 

longitudinal 

bundle 


are  gradually  absorbed  by  the  nuclear  mass,  they  become  less    numerous  iu  its 
midst,  and  the  nucleus  assumes  a  paler  tint. 

Numerous  fibres  whicli  descend  from  the  cerebral  cortex  and  others  from  the  corpus  striatum 
enter  the  red  nucleus.  It  likewise  sends  out  filjres  which  proceed  in  two  directions  :  (1)  upwards 
into  the  thalamus ;  (2)  downwards  to  the  spinal  cord.  The  former  may  be  regarded  as  carrying 
on  the  continuity  of  the  superior  cerebellar  path  after  its  internodal  interruption  in  the  red 
nucleus.  The  fibres  to  the  spinal  cord,  called  the  rubrospinal  tract  and  first  described  by 
Monakow,  cross  to  the  opposite  side  and  then  descend  in  the  tegmentum  to  reach  the  lateral 
column  of  the  cord. 

Posterior  Longitudinal  Fasciculus. — This  is  a  very  consxjicuous  tract  of  longi- 
tudinal fibres  which  extends  throughout  the  whole  length  of  the  medulla,  pons,  and 
mesencephalon,  in  the  formatio  reticularis  or  tegmental  part  of  each.  Below,  at  the 
level  of  the  decussation  of  the  pyramids,  it  becomes  continuous  with  the  anterior 
basis-bundle  of  the  spinal  cord  (p.  491),  whilst,  by  its  opposite  or  upper  end,  it 
establishes  intricate  connexions  in 
the  region  immediately  above  the 
mesencephalon.  Throughout  its 
whole  length  it  lies  close  to  the 
mesial  plane  and  its  fellow  of  the 
opposite  side.  In  the  mesen- 
cephalon it  is  applied  to  the 
ventral  aspect  of  the  Sylvian  gray 
matter,  whilst  in  the  pons  and 
medulla  it  is  situated  immediately 
subjacent  to  the  gray  matter  of  the 
floor  of  the  fourth  ventricle.  One 
of  its  most  salient  features  is  the 
intimate  association  which  it  pre- 
sents with  the  three  motor  nuclei 
from  which  the  nerves  for  the 
supply  of  the  muscles  of  the  eye- 
ball take  origin,  viz.  the  oculo-motor 
or  third  nucleus,  the  trochlear  or 
fourth  nucleus,  and  the  abducent 
or  sixth  nucleus.  The  first  two  of 
these  are  closely  applied  to  its  inner 
and  dorsal  aspect,  whilst  the  ab- 
ducent nucleus  is  placed  on  its 
outer  side.  Into  each  of  these  nuclei  it  sends  many  collaterals,  and  probably  also 
some  of  its  constituent  fibres,  and  these  end  in  terminal  arborisations  around  the 
nuclear  cells.  It  would  appear,  therefore,  that  one  of  the  most  important  functions 
of  this  strand  is  to  bind  together  these  nuclei,  and  thus  enable  them  to  act  in 
harmony  with  each  other.  Fibres  also  enter  the  posterior  longitudinal  fasciculus 
from  the  auditory  system  and  perhaps,  also,  from  the  facial  and  other  motor 
nuclei.  The  results  obtained  by  degeneration  would  seem  to  indicate  that,  to  a 
large  extent,  it  is  formed  of  fibres  which  run  a  short  course  within  it. 

In  spite  of  the  large  amount  of  attention  which  has  been  given  to  the  study  of  the  jJosterior 
longitudinal  bundle,  it  must  be  admitted  that  there  is  little  imanimity  of  opinion  regarding  its 
annexions  and  functions.  That  it  is  a  brain  tract  of  high  importance,  is  evident  from  the  fact 
that  it  is  present  in  all  vertebrates,  and,  further,  that  its  fibres  assume  their  medullary  sheaths 
at  an  extremely  early  period.  In  fish,  amphibians,  and  reptiles,  it  is  one  of  the  most  powerful 
bundles  of  the  medulla.  In  man  its  fibres  medullate  between  the  sixth  and  seventh  months  of 
foetal  life,  and  at  the  same  time  as  the  fibres  of  the  anterior  basis-bundle  of  the  cord,  with  which 
it  stands  in  connexion. 

According  to  Van  Geliucliten  and  Ediiiger,  it  extends  upwards  beyond  the  level  of  the 
oculo-motor  nucleus,  and  in  the  subthalamic  region  its  fibres  take  origin  from  a  special  nucleus  of 
its  own  in  tlie  gray  matter  of  the  third  ventricle,  immediately  below  the  level  of  the  corpora 
manimiljaria.  Fibres  also  enter  the  posterior  longitudinal  bundle  from  a  luicleus  common  to  it 
?jTid  the  posterior  commissure  of  tin;  brain.  This  nucleus  is  ]}laced  in  the  foroj^U't  of  the  Sylvian 
gray  matter  of  the  mid-brain.  Held  asserts  that  numerous  filn-es,  arising  from  cells  in.  the  superior 
fpiadrigeminal  body,  curve  in  an  arcuate  manner  iu  the  tegmentum   outside  the  Sylvian  gray 


Fig.  432. — Section  through  the  inferior  Quadrigeminal 
Body  and  the  Tegmentom  of  the  Mesencephalon 
below  the  Level  of  the  Nucleus  of  the  Fourth 
Nerve  in  the  Orang.  (The  decussation  of  the  superior 
cerebellar  peduncles  and  the  course  of  the  fourth  nerve 
in  the  Sylvian  gray  matter  are  seen. ) 


538 


THE  NERVOUS  SYSTEM. 


Decussating 
fibi  es 

Nucleus  of  in- 
ferior qiuidii- 
geminal  body 
Mesencppluilic 
root  of  littli 
nerve 
Fourth  nerve 

Posterior 

longitudinal 

bundle 

-  Lateral  fillet 
Superior 

—  cerebellar 
peduncle 


Mesitil  llllet 


matter,  to  take  part  on  the  ventral  aspect  of  this  in  what  is  called  the  "  fountain  decussation." 

Reaching  the  oi^posite  side  these  fibres  turn  downwards  and  join  tlie  posterior  longitudinal 

fasciculus.      Tlie  same  authority  considers  that  fibres  from  the  ventral  jDart  of  the  jjosterior 

commissure  can  also  be  traced  down- 
wai'ds  into  the  posterior  longitudinal 
bundle.  Edinger,  on  the  other  hand, 
jjlaces  these  fibres  as  a  distinct  tract  on 
tlie  ventral  and  lateral  aspect  of  the 
posterior  longitudinal  bundle,  although 
in  apposition  with  it. 

Mendel  believes  that  fibres  from  the 
oculo-motor  nucleus  are  cari'ied  down  in 
the  posterior  longitudinal  bundle,  and, 
from  this,  into  the  facial  nerve  for  the 
supply  of  the  orbicularis  palpebrarum 
and  the  corrugator  supercilii,  bringing 
these  muscles  therefore  under  the  control 
of  the  same  nucleus  as  the  levator  j)alpe- 
brse  superioris  muscle.  This  view  has 
received  corroboration  at  the  hands  of 
Tooth  and  Turner.  It  has  been  further 
suggested  that  fibres  from  the  hypoglossal 
nucleus  may,  by  theposterior  longitudinal 
fasciculus,  reach  the  facial  nerve,  and 
through  it  the  orbicularis  oris.  In  this 
]nanner  the  same  nucleus  would  hold 
sway  over  the  tongue  and  the  sphincter 
muscle  of  the  lips.  The  close  relation 
which  exists  between  the  ascending  part 
of  the  intrapontine  portion  of  the  facial 

nerve  and  the  jjosterior  longitudinal  bundle  would  render  the  passage  of  fibres  from  one  to  the 

other  a  matter  which  could  easily  be  understood.     Aiiother  interchange  of  fibres  through  the 

posterior  longitudinal  bundle  has  been  described  by  Duval  and  Laborde.     According  to  these 

authorities,    tiljres   from  the  abducent  nucleus  ascend   in   the  ^„^^  ^^„ 

jjosterior    longitudinal    bundle   into   the   mesencejDhalon,   and 

establish  connexions  with  that  j)art  of  the  oculo-motor  nitcleus 

from  which  the  nerve  for  the  internal  rectus  of  the  oj^posite 

side   derives   its   fibres.     If  this   view  be  correct,  it  aft'ords  a 

ready  and  simple  anatomical  explanation  of  the   harmonious 

action  of  the  external  and  internal  recti  muscles  in  producing 

movements  of  the  two  eyeballs  simultaneously  to  the  right  and 

to  the  left.     From  the  investigations  of  E.  H.  Eraser  it  would 

a^jpear  that  no  fibres  from  the  abducent  nucleus  go  directly  into 

the  oculo-motor  nerve.      The  same   observer   has  shown  that 

many  fibres  from  Deiters'  nucleus,  through  the  path  afl'orded 

by  the  posterior  longitudinal  bundle,  enter  the  third  and  the 

fourth  nuclei. 


Fig.  433. — Section  through  the  inferior  Qcadrigemtnal 
Body   and   the  Tegmentum  of   the  Mesencephalon, 

AT    A    SLIGHTLY    LoWER    LeVEL    THAN    FiG.    432. 


Lateral  Fillet  (lemniscus  lateralis). — The  lateral 
fillet  is  a  definite  tract  of  longitudinal  fibres,  which 
extends  upwards  through  the  lateral  part  of  the  teg- 
mental substance  of  the  upper  portion  of  the  pons  and 
the  mesencephalon.  It  is  formed  by  the  fibres  of  the 
corpus  trapezoides  in  the  lower  part  of  the  pons, 
abruptly  turning  upwards  and  taking  a  course  towards 
the  quadrigeminal  region.  Entering  into  its  constitu- 
tion, therefore,  are  fibres  from  several  sources,  viz.  (1) 
from  the  terminal  cochlear  nuclei  of  the  opposite 
side ;  (2)  from  the  terminal  cochlear  nuclei  of  the 
same  side ;  (3)  from  the  superior  olivary  nuclei.  As 
the  tract  proceeds  upwards  a  continuation  of  the 
gray  matter  of  the  superior  olivary  nucleus  is  carried 
up  in  connexion  with  it  to  form  the  nucleus  of  the  lateral  fillet,  and  from  this 
fibres  are  also  added  to  the  strand.  «>In  the  mesencephalon  the  fibres  of  the 
lateral  fillet  end  in  the  nucleus  of  the  inferior  quadrigeminal  body  (p.  534)  and 
in  the  gray  substance  of  the  corpus  geniculatum  internum,  whilst  a  few  are 
carried  into  the  superior  quadrigeminal  body.  The  fibres  which  go  to  the  inferior 
quadrigeminal  liody  sweep  outwards  round  the  outer  side  of   the  superior  cere- 


FrG.  434. — Diagram  ok  the  Con- 
nexions OF  THE  Posterior 
Longitudinal  Bundle  (after 
Held — uiodilied). 


LATERAL  AND  MESIAL  FILLETS. 


539 


bellar  peduncle,  and  to  some  extent  appear  on  the  surface  of  the  mesencei^halon 
(p.  533). 

But  the  lateral  fillet  cannot  be  considered  as  a  tract  com2XJsed  entirely  of  ascending  fibres 
belonging  to  the  auditory  system.  It  also  contains  descending  fibres,  the  connexions  and 
functions  of  which  are  not  fully  understood.  These  have  been  traced  by  Ferrier  and  Turner 
through  the  pons  and  medulla  into  the  lateral  column  of  the  cord. 

Mesial  Fillet  (lemniscus  mesialis). — The  mesial  fillet  has  already  been  followed 
through  the  medulla  and  pons,  and  its  position  in  each  of  these  portions  of  the 
brain-stem  has  been  defined  (pp.  493  and  504).  In  the  tegmentum  of  the  lower 
part  of  the  mesencephalon  it  is  carried  up  in  the  form  of  a  more  or  less  flattened 
band  on  the  ventral  aspect  of  the  decussating  superior  cerebellar  peduncles.  To 
its  outer  side,  and  forming  an  angle  with  it  (as  seen  in  transverse  section),  is  the 
lateral  fillet  (Figs.  432  and  433),  and  at  this  level  there  is  no  clear  demarcation 
between  these  two  tracts.  In  the 
upper  part  of  the  mesencephalon  the 
appearance  of  the  red  nucleus  in  the 
tegmentum  causes  the  mesial  fillet  to 
take  up  a  more  lateral  and  dorsal 
position,  so  that  it  now  comes  to  lie 
subjacent  to  the  corpus  geniculatum 
internum  (Fig.  431,  p.  536).  At  this 
level  it  exhibits  a  crescentic  outline 
in  transverse  section,  and  the  lateral 
fillet  has  to  a  large  extent  disappeared 
from  its  outer  side. 

The  mesial  fillet  takes  origin  in 
the  lower  part  of  the  medulla  ob- 
longata from  the  gracile  and  cuneate 
nuclei  of  the  opposite  side  (p.  493). 
Seeing  that  the  posterior  column  of 
the  cord  ends  in  these  nuclei,  the  fillet 
may  be  considered  to  continue  that 
column  upwards  into  the  brain.  In 
the  mesencephalon  a  considerable  con- 
tribution of  fibres  is  given  by  the  mesial 
fillet  to  the  superior  quadrigeminal 
body,  and  then  the  remainder  of  the 
tract  proceeds  through  the  subthalamic 
tegmental  region  into  the  hinder  part 
of  the  lateral  nucleus  of  the  optic 
thalamus.  Here  its  fibres  end  in  ter- 
minal arborisations  around  the  thala-  p,^_  435. -Diagram  of  the  Connexions  ov  the 
mic  cells.  Mesial   Fillet    and   also    of   ceetain    op    the 

Thalamo-cortical  Fibres. 
Ganglion  Interpedunculare  and  Fasci- 
culus B/etroflexus. — On  the  ventral  aspect  of  the  tegmentum,  close  to  the  surface  and  to  the 
mesial  plane,  there  is  a  small  group  of  cells  in  the  lower  part  of  the  gray  matter  which  forms 
the  locus  perforatns  posticus.     This  is  termed  the  ganglion  interpedunculare. 

The  fasciculus  retrofleo-ALs  is  a  small  band  of  fibres  which  arises  above  in  the  ganglion 
habenuhf; — a  nuclear  mass  which  will  be  studied  in  connexion  with  the  diencephalon — and 
which  runs  downwards  and  forwards  in  the  tegmentum  of  the  upper  j)art  of  the  mesencephalon 
between  tlie  inner  aspect  of  the  nucleus  ruber  and  the  mesial  plane,  to  end  in  the  ganglion 
intftrp('diiiK;nl;i.T('. 

Fountain  Decussation. — If  the  region  in  front  of  tlie  posterior  longitudinal  bundles  be 
c.vaniined  in  tlie  u])per  part  of  tlie  mesencephalon  a  very  close  decussation  of  fibres  in  the  mesial 
plane  will  be  observed  in  the  interval  Ijetween  the  two  red  nuclei.  This  is  the  "fountain 
decussation."  According  to  Held,  the  fibres  which  talce  part  in  the  dorsal  portion  of  the 
fountain  decussation  (decussation  of  Meynei't)  come  from  the  superior  (luadrigc.niinal  Ixxlies,  and, 
after  th(-y  have  gained  the  ojiposite  side,  they  tui'U  downwards  in.  the  posterior  longitudinal 
fasciculus.  Tlie  ve.ntral  jtart  of  tlie  decussation  (decussation  of  Fore!)  would  appisar  to  l)e  formed 
by  arcuate  fibres  of  tlie  tegineTituin  wliich  arise,  in  the  gray  matter  of  this  Sylvian  a(pieduct. 

Crusta  or  Pes  of  the  Crus  Cerebri  (basis  pedunculi). — The  crusta  presents  a 


540 


THE  NEEVOUS  SYSTEM. 


somewhat  crescentic  outline  when  seen  in  section,  and  it  stands  quite  apart  from 
its  fellow  of  the  opposite  side.  It  is  composed  of  a  compact  mass  of  longitudinally 
directed  fibres,  all  of  which,  as  Dejerine  has  shown,  arise  in  the  cortex  of  the 
cerebrum  and  pursue  an  unbroken  corticifugal  course  into  and  through  the  crusta 
of  the  crus  cerebri.  These  fibres  may  be  classified  into  two  distinct  sets,  viz. 
cortico-pontine  and  pyramidal. 

The  cortico-pontine  fibres  possess  this  leading  peculiarity :  in  their  course  down- 
wards they  are  all  arrested  in  the  ventral  part  of  the  pons  Varolii  and  end  in 
fine  terminal  arborisations  around  the  cells  of  the  nucleus  pontis.  They  come  from 
certain  well-defined  areas  of  cerebral  cortex,  viz.  (1)  the  cortex  of  the  prefrontal 
part  of  the  frontal  lobe,  and  (2)  the  cortex  of  the  middle  portion  of  the  temporal 
lobe.  These  tracts  would  appear  to  hold  a  very  definite  position  within  the  crus. 
Thus  it  has  been  satisfactorily  established  that  the  tem2Joro-pontine  strand  forms  the 
outer  or  lateral  fifth  of  the  crusta,  whilst  the  researches  of  Terrier  and  Turner 
render  it  more  than  likely  that  the  fronto-pontine  strand  holds  a  similar  position 
in  the  inner  or  mesial  part  of  the  crusta. 

The  pyramidal  fibres  constitute  the  great  motor  tract  from  the  cerebral  cortex. 
They  occupy  a  position  corresponding  to  the  middle  three-fifths  of  the  crusta. 
The  pyramidal  tract  differs  from  the  cortico-pontine  strands  in  being  carried 
downwards  through  the  ventral  part  of  the  pons  and  on  the  ventral  aspect  of  the 
medulla  into  the  cord,  which  it  enters  in  the  form  of  the  crossed  and  direct 
pyramidal  tracts.  On  its  way  through  the  pons  and  medulla  it  sends  fibres  to  the 
various  motor  nuclei  in  those  sections  of  the  brain-stem. 


Deep  Origin  of  the  Cranial  Nerves  which  arise  within  the 

Mesencephalon. 

Two  of  the  motor  cranial  nerves,  viz.  the  oculo-motor  and  the  trochlear  nerves, 
as  well  as  the  mesencephalic  root  of  the  trigeminal  nerve,  obtain  origin  within  the 

mesencephalon.       The     nuclei 


Decussation-  ofdateral  fillet  fibres 


from  which  they  spring  are 
all  situated  within  the  gray 
matter  of  the  Sylvian  aque- 
duct. 

Mesencephalic  Root  of  the 
Trigeminal  Nerve  (radix  de- 
scendens).  —  The  fibres  of  this 
root  arise  from  a  column  of 
large,  sparsely -arranged  cells, 
which  extends  throughout  the 
entire  length  of  the  mesen- 
cephalon. These  cells  lie  in 
the  outer  part  of  the  Sylvian 
gray  matter,  close  to  the  teg- 
mentum. The  axons  which 
emerge  from  the  cells  run 
downwards  close  to  the  outer 
surface  of  the  Sylvian  gray 
matter  in  the  form  of  a  small, 
gradually-increasing  tract.  In 
the  lower  part  of  the  mesen- 
FiG.  436. — Section  through  the  Inferior  Quadrigeminal  Body  cephalon  this  tract  assumes  a 
AND  THE  Tegmentum  of  the  Mesencephalon  at  the  Level  crescentic  outline  and  ulti- 
mately comes  to  lie  on  the  inner 
aspect  of  the  superior  cerebellar 
peduncle  (Fig.  406,  p.  504).  The  further  course  of  the  mesencephalic  root  of  the 
fifth  nerve  through  the  upper  part  of  the  pons,  to  the  point  where  it  joins  the 
emerging  motor  root  of  the  trigeminal  nerve,  has  already  been  traced  (p.  526). 
Trochlear  or  Fourth  Nerve  (nervus  trochlearis).— The  trochlear  nerve  supplies 


Sylvian  aqueiluct 


Sylvian  gray  matter 

Nucleus  of  inferior, 
quadrigeminal  body 

Inferior  braoliium 

Mesencephalic  root 
of  fifth  nerve 

Nucleus  of  fourth 
nerve 

Posterior  longi- 
tudinal bundle 

Lateral  fillet 

Decussation  of  the 

superior  cerebellar 

peduncles 


Mesial  fillet 


OF  the  Middle  Part  of  the  Nucleus  of  the  Trochlear 
Nerve  (Oraiig). 


DEEP  OEIGIN  OF  THE  TROCHLEAR  NERVE. 


'Al 


the  superior  oblique  muscle  of  the  eyeball.  It  emerges  from  the  brain,  on  its 
dorsal  aspect,  at  the  upper  part  of  the  superior  medullary  velum,  immediately 
below  the  lower  border  of  the  inferior  quadrigeminal  body  (Fig.  438,  p  543).  The 
nucleus  from  which  it  arises  is  a  small  oval  mass  of  gray  matter,  placed  in  the 
ventral  part  of  the  Sylvian  gray  matter  at  the  level  of  the  upper  part  of  the 
inferior  quadrigeminal  body.  The  close  association  of  this  nucleus  with  the 
posterior  longitudinal  bundle  has  already  been  alluded  to.  It  is  sunk  deeply  in  a 
bay,  which  is  hollowed  out  on  the  dorsal  and  inner  aspect  of  that  tract.  The 
nerve  has  a  course  of  some  length  within  the  mesencephalon.  The  axons  of  the 
cells  leave  the  outer  aspect  of  the  nuclear  mass,  and  curve  backwards  and  outwards 
in  the  Sylvian  gray  matter  until  they  reach  the  concave  inner  surface  of  the 
mesencephalic  root  of  the  trigeminal  nerve.  Here  they  are  gathered  together  into 
one  or  two  round  bundles,  which,  bending  sharply,  turn  downwards  at  a  right 
angle  and  descend  on  the  inner  side  of  the  trigeminal  root.  When  the  region 
below  the  inferior  quadrigeminal  body  is  reached,  the  nerve  makes  another  sharp 
bend.  This  time  it  turns  inwards,  enters  the  upper  end  of  the  superior  medullary 
velum,  in  which  it  decussates  with  its  fellow  of  the  opposite  side.  Having  thus 
crossed  the  mesial  plane,  the  trochlear  nerve  emerges  at  the  inner  border  of  the 
superior  cerebellar  peduncle.  The  course  pursued  by  the  fourth  nerve  within  the 
Sylvian  gray  matter  may  be  traced  by  examining  in  succession  Fig.  437  ;  Fig.  432, 
p.  537 ;  Fig.  433,  p.  538 ;  and  Fig.  407,  p.  505. 

Oculo-motor  or  Third  Nerve  (nervus  oculo-motorius). — The  oculo-motor  nerve 
supplies  the  levator  palpebrse  superioris,  all  the  ocular  muscles,  with  the  exception 
of  the  superior  oblique  and 
the  external  rectus,  and  also 
two  muscles  within  the  eyeball, 
viz.  the  sphincter  iridis  and 
the  musculus  ciliaris.  The 
nucleus  of  origin  is  placed  in 
the  ventral  part  of  the  Sylvian 
gray  matter  subjacent  to  the 
superior  quadrigeminal  body 
(Fig.  431,  p.  536).  In  length 
it  measures  from  5  to  6  mm. 
Its  lower  end  is  partially  con- 
tinuous with  the  nucleus  of 
the  trochlear  nerve,  whilst  its 
upper  end  extends  upwards  for 
a  short  distance  beyond  the 
mesencephalon  into  the  gray 
matter  on  the  lateral  wall  of  / 
the  third  ventricle.  Its  relation  r 
to  the  posterior  longitudinal  I; 
bundle  is  even  more  intimate  L 
than  that  of  the  trochlear  Fig.  437.— Section  through  the  Inferior  Quadrigeminal  Body 
nucleus       It  is  closely  applied  ^nd    the    Tegmentum    of    the    Mesencephalon   at    the 

to  the  dorsal  and  inner  aspect  ^^rNERVE^o^rgT  ^^'''  ""'  ™'  ^"''''''  °'  ™'  ''''''''" 
of   this   strand ;    many  of  its 

cells  occupy  a  position  in  the  intervals  between  the  nerve  -  bundles  of  the 
tract,  and  some  even  are  seen  on  its  ventral  or  tegmental  aspect.  The  axons  of 
the  nuclear  cells  leave  the  nucleus  in  numerous  bundles,  which  describe  a  series 
of  curves  as  they  proceed  forwards  through  the  jjosterior  longitudinal  bundle,  the 
tegmentum,  red  nucleus,  and  inner  margin  of  the  substantia  nigra,  to  finally  emerge 
from  the  brain-stem  along  the  bottom  of  the  sulcus  oculo-motorius  on  the  inner 
aspect  of  the  crus  cerebri. 

Tlift  cells  of  th(;  ocuIo-iiiot,or  iiuclous  an;  not  iiiiit'ofiiily  (listi'ilmlc.d  thron^liout  it.  They  are 
grouped  into  Hcveral  more  or  Ichs  distinct  collections  or  clumps,  some  of  which 'possess  cells  which 
differ  in  size  and  ajtjiearance  from  the  others.  These  cell-clusters  ai'e  very  generally  believed  to 
jjOHsesH  a  definite  relation  to  the  several  branches  of  the  nerve  and  the  muscles  which  they 
supply.     Perlia  recogni.HCH  no  less  than  seven  such  cell-clusters  in  each  nucleus,  with  a  small 


Sylvian  gray 
matter 

Sylvian 
aqueduct 
Mesencephalic 
root  of  fifth 
nerve 

Fourth  nerve 
leaving 
nucleus 

Posterior 

longitudinal 

bundle 


Decussation  of 
the  superior 
cerebellar 
peduncles 


542  THE  NEEVOUS  SYSTEM. 

median  nucleus  2)laced  accurately  on  tlie  middle  line,  and  from  wliicli  tibres  for  botli  nerves 
spring.  Whilst  the  majority  of  the  fibres  in  the  oculo-raotor  nerve  arise  from  the  cell-groups 
which  lie  on  its  own  side  of  the  mesial  plane,  it  has  been  satisfactorily  established  that  a  certain 
proportion  of  its  fibres  are  derived  from  the  nucleus  of  the  opposite  side,  thus  forming  a  crossed 
connexion  and  giving  rise  to  a  median  decussation.  These  crossed  fibres  are  .supiiosed  by  some 
to  supply  the  internal  rectus  muscle  ;  and  we  have  seen  that  there  is  reason  to  believe  that  the 
part  of  the  nucleus  from  wliicli  these  fibres  are  derived  stands  in  connexion  through  the  posterior 
longitudinal  fasciculus  -with  the  abducent  or  sixth  nucleus  fi-om  which  proceeds  the  nerve  of 
supply  for  the  external  rectus  muscle.  The  hariuonious  action  of  the  internal  and  external  recti 
in  2^i'<J'^l^^cii'^g  the  conjugate  movements  of  the  eyel:)alls  is  thus  explained. 

The  oculo-motor  nucleus  is  connected — (1)  with  the  occipital  part  of  the  cerebral  cortex  by 
fibres  which  reach  it  through  the  optic  radiation  ;  (2)  with  the  trochlear  and  alxlucent  nuclei 
(and  probably  witli  other  nuclei)  by  fibres  which  come  to  it  through  the  posterior  longitudinal 
bundle  ;  (3)  possibly  with  the  facial  nerve  by  fibres  Avhich  pass  out  from  it  into  the  posterior 
longitudinal  bundle  (p.  538)  ;  (4)  with  the  visual  system  by  fibres  which  enter  it  from  the  cells  of 
the  superior  fpiadrigeminal  l)ody. 

Development  of  the  Mesencephalon. 

Even  in  the  early  embryo  the  mesencephalon  constitutes  the  smallest  section  of  the 
brain-tube,  although  the  disproportion  in  size  between  it  and  the  other  primitive  sub- 
divisions of  the  brain  is  not  nearly  so  marked  as  in  the  adult.  Owing  to  the  cephalic 
flexure,  the  mid-brain  for  a  time  occupies  the  highest  part  of  the  summit  of  the  head. 
Later  on  it  becomes  completely  covered  over  by  the  expanding  cerebral  hemispheres. 

The  corpora  quadrigemina  are  derived  from  the  alar  lamina3  of  the  lateral  walls  of  the 
brain-tube,  whilst  the  basal  laminae  thicken  and  ultimately  form  the  tegmenta  and  crustte 
of  the  two  crura  cerebri.  The  original  cavity  of  the  mid-brain  is  retained  as  the  aqueduct 
of  Sylvius. 

For  a  considerable  time  the  cavity  of  the  mesencephalon  remains  relatively  large,  and 
the  lower  part  of  its  dorsal  wall  is  carried  downwards  in  the  form  of  a  diverticulum  or 
recess,  which  overlaps  the  cerebellar  plate.  About  this  time,  also,  the  dorsal  wall  shows  a 
median  fold  or  ridge.  Both  of  these  conditions  are  transitory.  As  the  corpora  quadri- 
gemina take  shape,  the  median  ridge  disappears  and  is  replaced  by  the  median  longitudinal 
groove,  which  separates  the  quadrigeminal  bodies.  Only  its  lower  part  is  retained,  and  this 
is  represented  by  the  frenulum  veli  of  the  adult  bi-ain.  The  diverticulum  of  the  cavity 
gradually  becomes  reduced,  and  finally  disappears  as  the  aqueduct  assumes  form. 

FOEE-BEAIN. 

Parts  derived  from  the  Diencephalon. 

Under  this  heading  we  have  to  consider  :  (1)  the  thalamus  ;  (2)  the  epithalamus, 
which  comprises  the  pineal  body  and  the  hahenular  region  ;  (3)  the  metathalamus, 
or  the  corpora  geniculata  ;  and  (4)  the  hypothalamus. 

The  hypothalamus  consists  of  two  portions,  viz.  the  pars  mammillaris  hypothalami, 
which  comprises  the  corpus  mammillare  and  the  portion  of  the  central  gray  matter 
which  forms  the  floor  of  the  third  ventricle  in  its  immediate  vicinity ;  and  the  pars 
optica  hypothalami,  which  embraces  the  tuber  cinereum,  the  infundibulum,  the 
pituitary  body,  and  the  lamina  cinerea.  Strictly  speaking,  the  optic  part  of  the 
hypothalamus  does  not  belong  to  the  diencephalon,  but  it  is  convenient  to  study 
the  parts  which  it  represents  at  this  stage.  It  is  also  .convenient  to  examine,  at 
the  same  time,  the  subthalamic  tegmental  region,  although  a  very  considerable  part  of 
this  is  apparently  developed  in  connexion  with  the  mesencephalon. 

The  original  cavity  of  that  part  of  the  brain-tube  which  forms  the  diencephalon 
is  represented  by  the  greater  part  of  the  third  ventricle  of  the  brain. 

Optic  Thalamus  (thalamus). — The  optic  thalamus  is  the  principal  object  in 
this  section  of  the  brain  (Fig.  438).  It  is  a  large  ovoid  mass  of  gray  matter,  which 
lies  obliquely  across  the  path  of  the  cms  cerebri  as  it  ascends  into  the  cerebrum. 
The  smaller  anterior  end  of  the  thalamus  lies  close  to  the  mesial  plane,  and  is  only 
separated  from  the  corresponding  part  of  the  opposite  side  by.  a  very  narrow 
interval.  The  enlarged  posterior  ends  of  the  two  thalami  are  placed  more  widely 
apart,  and  in  the  interval  between  them  the  corpora  quadrigemina  are  situated, 
As  previously  stated,  the  crusta  of  the  crus  cerebri,  composed  of  corticifugal  fibres 


(Jl'TlCJ  THALAMUS. 


543 


gradually  inclines  outwards  as  it  is  traced  upwards,  and  thus  it  assumes  a  place  on 
the  outer  aspect  of  the  optic  thalamus  and  passes  into  the  internal  capsule  of  the 
brain.  The  tegmental  part  of  the  crus,  on  the  other  hand,  comes  into  relation 
with  the  under  surface  of  the  thalamus,  and  forms  in  this  situation  the  sub- 
thalamic tegmental  region.  To  a  large  extent  the  longitudinal  fibres  of  the 
tegmentum  are  corticipetal.  For  the  most  part  they  enter  the  thalamus,  and 
end  within  it  in  fine  arborisations  around  the  thalamic  cells. 

The  two  optic  thalami,  in  their  anterior  two-thirds,  lie  close  together  on  either 
side  of  a  deep  mesial  cleft,  which  receives  the  name  of  the  third  ventricle  of  the 
brain.  Each  thalamus  presents  an  anterior  and  a  posterior  extremity  and  four 
surfaces.  The 
inferior  and  ex- 
ternal surfaces 
are  in  apposition, 
and,  indeed,  di- 
rectly connected 
with  adjacent 
parts  of  the  brain, 
and  on  this  ac- 
count it  is  only 
possible  to  study 
them  by  means  of 
sections  through 
the  brain.  The 
superior  and  in- 
ternal surfaces 
are  free. 

The  external  p'^'^*  °^  thalamus 
or  lateral  surface 
of  the  thalamus 
is  applied  to  a 
thick  layer  of 
white  matter  in- 
terposed between 
it  and  the  lenti- 
cular nucleus, 
called  the  internal 
capsule,  and  com- 
posed of  fibres 
passing  both  up- 
wards towards 
and  downwards 
from  the  cerebral 

cortex.  A  large  proportion  of  these  fibres  descend  to  form  the  crusta  or  ventral 
part  of  the  crus  cerebri.  From  the  entire  extent  of  the  external  surface  of 
the  thalamus  large  numbers  of  fibres  stream  out  and  enter  the  internal  capsule, 
to  reach  the  cerebral  cortex  ;  over  the  same  area  other  fibres  which  arise  in  the  cortex 
of  the  cerebrum  enter  the  thalamus.  Both  of  these  sets  of  fibres  constitute  what  is 
termed  the  thalamic  radiation,  and  by  this  the  thalamus  establishes  a  double  con- 
nexion with  the  entire  extent  of  the  cerebral  cortex.  As  the  fibres  leave  and  enter 
the  thalamus  they  intersect  each  other  at  acute  angles,  and  over  the  whole  of  the 
external  surface  of  the  ganglionic  mass  they  form  a  very  distinct  reticulated  zone 
or  stratum,  which  is  termed  tlu;  external  medullary  lamina. 

Tlie  inferior  or  ventral  surface  of  the  tlialamus  rests  chiefly  on  the  subthalamic 
tegmental  region  and  the  corpus  mammillare.  In  front,  however,  as  the  tegmental 
substance  gradually  disappears,  the  thalamus  comes  to  lie  over  the  outer  part  of  the 
tuber  c'inereum.  From  the  subthalamic  region  many  fibres  enter  the  thalamus  on 
its  under  aspect,  whilst  other  fibres  leave  this  surface  of  the  thalamus  to  take  ■i)art 
in  the  thalamic  nuliation. 


Non-ventricular 


Groov 

corresponding. 

to  fornix 

Quadrigeminal 

bodies 

Trochlear  nerve. 
Middle  cere 
bellar  peduncle' 
Superior  cere- 
bellar peduncle 
Lingula 


Bulb- 


Genu  of  corpus 
callosum 
Corpus  callosum 
(cut) 


Ventricle  V. 
Septum  luciduni 


Caudate  nucleus 


Foramen  of  Monro 

Anterior  commissure 
Anterior  tubercle 
of  thalamus 

Gray  commissure 


Tliird  -^-entricle 

Tasnia  semicircularis 

Taenia  thalami 

Trigonum  habenulse 

Posterior 

commissure 

Stalk  of  ijineal  body 

Pulvinar 
Pineal  body 


Fig.  438. — The  Two  Optic  Thalami  (as  seen  from  above) 


544  THE  NEEVOUS  SYSTEM. 

The  superior  or  dorsal  surface  of  the  thalamus  is  free.  Externally  it  is  bounded 
by  a  groove,  which  traverses  the  floor  of  the  lateral  ventricle  of  the  brain  and 
intervenes  between  the  thalamus  and  the  caudate  nucleus.  In  this  groove  are 
placed  a  slender  band  of  longitudinal  fibres,  termed  the  teenia  semicularis,  and  in 
its  fore-part  the  vein  of  the  corpus  striatum.  Internally,  the  superior  surface  of 
the  thalamus  is  separated  from  the  internal  or  mesial  surface  in  its  anterior  half  by 
a  sharp  edge  or  prominent  ledge  of  the  ependyma  of  the  third  ventricle.  This  is 
termed  the  taenia  thalami,  and  the  ridge  which  it  forms  is  accentuated  by  the  fact 
that,  subjacent  to  it,  there  lies  a  longitudinal  strand  of  fibres  called  the  stria 
medullaris.  When  these  two  structures,  viz.  the  ependymal  ridge  and  the  subjacent 
tract,  are  traced  backwards,  they  are  seen  to  turn  inwards  and  become  continuous 
with  the  stalk  or  peduncle  of  the  pineal  body.  Behind  the  portion  of  the  taenia 
thalami  which  turns  inwards  towards  the  pineal  body  a  small  depressed  triangular 
area,  the  trigonum  habenulse,  situated  in  front  of  the  superior  quadrigeminal  body, 
forms  a  very  definite  inner  boundary  for  the  hinder  part  of  the  superior  surface  of 
the  thalamus. 

The  superior  surface  of  the  thalamus  is  slightly  bulging  or  convex,  and  is  of  a 
whitish  colour,  owing  to  the  presence  of  a  thin  superficial  covering  of  nerve-fibres, 
termed  the  stratum  zonale.  It  is  divided  into  two  areas  by  a  faint  oblique  groove, 
which  begins  in  front  at  the  inner  border,  a  short  distance  behind  the  anterior 
extremity  of  the  thalamus,  and  extends  outwards  and  backwards  to  the  outer  part 
of  the  hinder  end.  This  groove  corresponds  to  the  outer  edge  of  the  fornix.  The 
two  areas  which  are  thus  mapped  out  are  very  differently  related  to  the  ventricles 
of  the  brain,  and  also  to  the  parts  which  lie  above  the  thalamus.  The  outer  area, 
which  includes  the  anterior  extremity  of  the  thalamus,  forms  a  part  of  the  floor  of 
the  lateral  ventricle.  It  is  covered  with  ependyma,  overlapped  by  the  choroid 
plexus  of  this  ventricle,  and  lies  immediately  subjacent  to  the  corpus  callosum. 
Along  the  line  of  the  groove  the  epithelial  lining  of  the  lateral  ventricle  is  reflected 
over  the  choroid  plexus  of  this  cavity.  The  inner  area,  which  includes  the  hinder 
end  of  the  thalamus,  intervenes  between  the  lateral  and  third  ventricles  of  the 
brain,  and  takes  no  part  in  the  formation  of  the  walls  of  either.  It  is  covered  by  a 
fold  of  pia  mater,  termed  the  velum  interpositum,  above  which  is  the  fornix,  and 
these  two  structures  intervene  between  the  thalamus  and  the  corpus  callosum. 

The  anterior  extremity  of  the  thalamus,  called  the  anterior  tubercle  (tuberculum 
anterius  thalami),  forms  a  marked  bulging.  It  projects  into  the  lateral  ventricle, 
behind  and  to  the  outer  side  of  the  free  portion  of  the  anterior  pillar  of  the  fornix. 
The  foramen  of  Monro,  a  narrow  aperture  of  communication  between  the  lateral 
and  third  ventricles  of  the  brain,  is  bounded  in  front  by  the  anterior  pillar  of  the 
fornix  and  behind  by  the  anterior  tubercle  of  the  thalamus. 

The  posterior  extremity  of  the  thalamus  is  very  prominent  and  forms  a  cushion- 
like projection,  which  overhangs  the  brachia  of  the  corpora  quadrigemina.  This 
prominence  is  called  the  pulvinar.  Another  oval  bulging  on  the  hinder  part  of  the 
thalamus  receives  the  name  of  the  corpus  geniculatum  externum.  It  is  situated 
below,  and  to  the  outer  side  of,  the  pulvinar,  and  presents  a  very  intimate  connexion 
with  the  optic  tract. 

The  mesial  surfaces  of  the  two  thalami  are  placed  close  together,  and  are 
covered  not  only  by  the  lining  ependyma  of  the  third  ventricle,  but  also  by  a 
tolerably  thick  layer  of  gray  matter,  continuous  below  with  the  central  gray 
substance  which  surrounds  the  aqueduct  of  Sylvius  in  the  mesencephalon.  A  band 
of  gray  matter,  termed  the  gray  or  soft  commissure  (commissura  mollis),  crosses  the 
third  ventricle  and  joins  the  inner  surfaces  of  the  two  thalami  together. 

Intimate  Structure  and  Connexions  of  the  Optic  Thalamus. — The  upper 
surface  of  the  thalamus  is  covered  by  the  stratum  zonale,  a  thin  coating  of  white 
fibres  derived  to  some  extent  from  the  optic  tract,  and  probably  also  from  the  optic 
radiation.  The  inner  surface  has  a  thick  coating  of  central  gray  matter,  whilst 
intervening  between  the  internal  capsule  and  the  outer  surface  is  the  lamina 
medullaris  externa.     The  lower  surface  merges  iuto  the  subthalamic  region. 

The  gray  matter  of  the  optic  thalamus  is  marked  off  into  three  very  apparent 
parts — termed  the  anterior,  the  mesial,  and  the  lateral  thalamic  nuclei — by  a  thin 


OPTIC  THALAMUS.  545 

vertical  sheet  of  wliite  matter,  coutiriiioTis  with  the  stratum  zonale,  termed  the 
lamina  medullaris  interna.  The  lateral  nucleus  (nucleus  lateralis  thalami)  is  hy  far 
the  largest  of  the  three.  It  is  placed  between  the  internal  and  the  external 
medullary  laminae,  and  it  stretches  backwards  beyond  the  mesial  nucleus,  and  thus 
includes  the  whole  of  the  pulvinar  (Fig.  440).  The  mesial  nucleus  (nucleus  medialis 
thalami)  only  reaches  as  far  back  as  the  habenular  region.  It  is  placed  between 
the  central  gray  matter  of  the  third  ventricle  and  the  internal  medullary  lamina. 
The  lateral  nucleus  is  more  extensively  pervaded  by  fibres  than  the  mesial  nucleus. 
From  the  lateral  nucleus  by  far  the  greatest  number  of  the  fibres  which  form  the 
radiatio  thalami  pass,  and  these  are  seen  crossing  it  in  various  directions  towards 
the  lamina  medullaris  externa.  The  anterior  nucleus  (nucleus  anterior  thalami)  is 
the  smallest  of  the  three  thalamic  nuclei.  It  forms  the  prominent  anterior  tubercle, 
and  is  prolonged  in  a  wedge-shaped  manner,  for  a  short  distance,  downwards  and 
backwards  between  the  anterior  parts  of  the  mesial  and  lateral  nuclei.  The  internal 
medullary  lamina  splits  into  two  parts  and  partially  encloses  the  anterior  nucleus. 
In  connexion  with  its  large  cells  a  very  conspicuous  bundle  of  fibres,  the  bundle 
of  Vicq  d'Azyr  (fasciculus  thalamo-mammillaris).  which  arises  in  the  corpus 
mammillare,  comes  to  an  end 

A  diffuse  gray  mass  imperfectly  marked  off  from  the  under  surface  of  the  lateral  niicleus 
receives  the  name  of  the  ventral  nucleus.  Its  lower  part  is  composed  of  the  central  nucleus  of 
Luys  and  the  nucleus  arcuatus.  In  section  the  former  ajipears  as  a  circular  mass  of  gray  matter, 
which  comes  into  view  immediately  behind  the  point  where  the  internal  medullary  lamina 
disapi^ears.  It  would  seem  to  be  intimately  connected  with  fibres  which  reach  it  from  the  red 
nucleus  and  from  the  posterior  commissure.  These  fibres  pass  round  it  so  as  to  mark  it  off  from 
the  rest  of  tlie  thalamus,  and  in  front  of  the  nucleus  many  of  them  enter  the  internal  medullary 
lamina.  The  nucleus  arcuatus  is  a  small  semilunar  mass  of  gray  matter  placed  below  and  to  the 
outer  side  of  the  central  nucleus  of  Luys. 

The  connexions  of  the  thalamus  are  of  an  extremely  intricate  kind.  It  would 
appear  to  be  a  ganglionic  mass  interposed  between  the  tegmental  corticipetal  tracts 
and  the  cerebral  cortex.  In  its  hinder  part,  and  through  its  stratum  zonale,  it  also 
has  important  connexions  with  the  optic  tract.  The  corticipetal  tegmental  tracts, 
which  enter  it  from  below,  will  be  noticed  in  connexion  with  the  subthalamic 
region.  Suf&ce  it  to  say,  for  the  present,  that  these  fibres  end  in  the  midst  of  the 
thalamus  in  connexion  with  the  thalamic  cells.  In  addition  to  these,  enormous 
numbers  of  fibres,  arising  within  the  thalamus  as  the  axons  of  its  cells,  stream  out 
from  its  outer  and  under  surfaces  to  form  the  thalamic  radiation.  These  thalamo- 
cortical fibres  pass  to  every  part  of  the  cortex ;  and  although  there  is  no  separation 
of  them  into  distinct  groups  as  they  leave  the  thalamus,  it  is  customary  to  regard 
them  as  constituting  a  frontal  stalk,  a  parietal  stalk,  an  occipital  stalk,  and  a 
ventral  stalk.  But  fibres  from  the  cortex,  cortico-thalamic  fibres,  likewise  stream 
into  the  thalamus  in  large  numbers,  and  end  in  fine  arborisations  around  its  cells. 
A  double  connexion  with  the  cerebral  cortex  is  thus  established'  by  the  thalamus. 

The  frontal  stalk  of  the  thalamic  radiation  emerges  from  the  anterior  part  of  the  lateral 
surface  of  the  thalamus  and  passes  through  the  anterior  limb  of  the  internal  capsule,  to  reach  the 
cortex  of  the  frontal  loJje.  Many  of  these  fibres  end  in  the  caudate  and  lenticular  nuclei,  between 
wlaich  they  proceed.  The  parietal  stalk  issues  from  the  lateral  surface  of  the  thalamus,  and, 
passing  tlirough  the  internal  capsule  (and  to  some  extent,  also,  through  the  lenticular  nucleus 
and  the  external  cajwule),  gains  the  cortex  of  the  hinder  part  of  the  frontal  lobe  and  of  the 
parietal  lolje.  The  occipital  stalk  emerges  from  the  outer  aspect  of  the  pulvinar  and  constitutes 
the  so-called  optic  railiation.  Tliese  fibres  sweep  outwards  and  backwards  round  the  outer  side 
of  the  posterior  horn  of  tlie  lateral  ventricle  to  gain  the  cortex  of  the  occipital  lobe.  Tlie 
ventral  stalk  streams  out  from  tlie  under  aspect  of  the  anterior  part  of  the  thalamus,  in  front 
of  th(;  suljUialamic  tegmental  region  and  the  corpus  mammillare.  Its  fibres  arise  in  both  the 
me.sial  and  latei'al  nuclei,  and  sweep  downwards  and  outwairls  to  reach  the  region  below  the 
lenticular  nucleus.  One  very  distinct  band  which  lies  dorsal  to  the  other  fibres  (ansa  lenticu- 
kris)  enters  the  lenticular  nucleus,  whilst  the  remainder  (ansa  peduncvdaris)  continue  in  an 
out\yard  direction  below  the  lenticular  nucleus  and  gain  the  cortex  of  the  temporal  lolje  and  of 
the  insula  or  island  of  Reil. 

FJeclisig  divides  the;  thalamo-coitical  liln'cs  of  ordinaiy  sensation  into  three  sensory  systems. 
Thew;  lie  has  been  able  to  distinguish  by  studying  tlie  oi'd(!i'  in.  which  they  assume  tlie'ir  sluiaths 
of  myelin  in  the  fojtiis  and  infant. 

Ferrier  and  Turner,  by  the  degeiKU-ative  nuithod  of  investigation,  corro))orate  Flechsig's 
re.Hulls.     Tliey  confirm  the  observation  of  Flechsig  that,  while  thalamic  fibres  are  distributed  to 

39 


546 


THE  NEKVOUS  SYSTEM. 


the  several  regions  of  the  cerebral  cortex  to  an  almost  equal  extent,  there  is  one  district,  viz.  the 
frontal  pole,  to  which  the  sujij'!}'  i^^  scanty.     Another  very  important  result  has  been  obtained 

by  these  authors.     They  have  established 

,osS- -^  the  fact  that  many  of  the  thalamic  libres 

cross  the  mesial  ])lane  in  the  corj^us  cal- 
losum,  and  tlius  gain  tlie  cortex  of  the 
opposite  cerebral  hemis})here.  Hamilton's 
crossed  callosal  tract  thus  receives  con- 
formation. 


CALLOSUM 


?  LIMB 
NTVCAPSULF 


ME.SNEEPHALON 


TEMPORO-PONTINE 
TRACT 


Fig. 


LOBt 

439. — Schema.     Founded  on  the  observation 
Flechsig,  and  Ferrier  and  Turner. 


of 


Intimate  Structure  of  the  Corpus 
Geniculatum  Externum.  —  Sections 
through  the  external  geniculate  body 
reveal  the  fact  that  it  is  composed  of 
a  series  of  alternately  placed  gray  and 
white  curved  laminte.  This  gives  it 
a  very  characteristic  appearance.  The 
white  laminas  are  composed  of  fibres 
which  enter  the  body  from  the  optic 
tract  and  the  optic  radiation.  The 
SUP  (juADv BODY  connexions  of  the  geniculate  bodies 
will  be  studied  with  the  optic 
tract. 

Subthalamic  Tegmental  Region. 
— The  tegmental  part  of  the  crus  cere- 
bri is  prolonged  upwards  and  assumes 
a  position  below  the  hinder  part  of  the 
thalamus.  The  red  nucleus  is  a  con- 
spicuous objeetin  sections  through  the 
lower  part  of  this  region  (Eig.  440).  It 
presents  the  same  appearance  as  lower 
down  in  the  mesencephalon,  and, 
gradually  diminishing,  it  disappears 
before  the  level  of  the  corpus  mam- 
millare  is  reached.  Carried  up  around  it  are  the  same  longitudinal  tracts  of  fibres 
which  have  been  studied  in  relation  to  it  in  the  tegmental  part  of  the  mesencephalon. 
Certain  of  these  fibres,  placed  in  immediate  relation  to  the  red  nucleus,  form  a 
coating  or  capsule  for  it.  This  coating  is  partly  derived  from  those  fibres  of  the 
superior  cerebellar  peduncle  which  pass  directly  up  into  the  thalamus  and  also 
partly  from  fibres  which  issue  from  the  nucleus  itself.  The  mesial  fillet,  also, 
which  in  the  upper  part  of  the  mesencephalon  is  observed  to  take  up  a  position  on 
the  lateral  and  dorsal  aspect  of  the  red  nucleus,  maintains  a  similar  position  in  the 
subthalamic  region.  When  the  red  nucleus  comes  to  an  end  these  various  fibres 
are  continued  onwards  and  form,  in  the  position  previously  occupied  by  the  nucleus, 
a  very  evident  and  dense  mass  of  fibres.  The  fibres  of  the  mesial  fillet,  of  the 
superior  cerebellar  peduncle,  and  of  the  red  nucleus  are  prolonged  upwards  into  the 
ventral  part  of  the  thalamus,  where  they  end  in  connexion  with  the  thalamic  cells. 
The  substantia  nigra  is  likewise  carried  into  the  subthalamic  region,  where  it 
maintains  its  original  position  on  the  dorsal  aspect  of  the  crusta  of  the  crus  cerebri. 
As  it  is  traced  upwards,  it  is  seen  to  gradually  diminish  in  amount.  It  shrinks 
from  within  outwards,  and  finally  disappears  when  the  hinder  part  of  the  corpus 
mammillare  is  reached. 

In  coronal  sections  through  the  subthalamic  region,  the  most  conspicuous  object 
which  comes  into  view  is  the  corpus  subthalamicum  or  the  nucleus  of  Luys  (Fig.  440). 
It  is  a  small  mass  of  gray  matter,  shaped  like  a  biconvex  lens,  which  makes  its  appear- 
ance on  the  dorsal  aspect  of  the  crusta  of  the  crus  cerebri  immediately  to  the  outer 
side  of  the  substantia  nigra.  At  first  it  lies  in  an  angle,  which  is  formed  by  the 
meeting  of  the  crusta  and  the  internal  capsule  ;  but,  rapidly  enlarging  in  an  inward 
direction,  it  takes  the  place  of  the  diminishing  substantia  nigra  on  the  dorsal 
surface  of  the  crusta  at  the  level  of  the  lower  part  of  the  corpus  mammillare.  The 
corpus  subthalamicum  is  rendered  all  the  more  evident  by  the  fact  that  it  is 


SUBTHALAMIC  TEGMENTAL  KEGION. 


547 


Intersection  of 

the  coroii  i 

radiata  aii  1 

callosal  systf  uis 

offibi.s 

Caudate  nucleu^ 
Corpus  oallosum 


External  capsule 


sharply  defined  by  a  thin  capsule  of  white  fibres.  On  its  mesial  aspect  these  fibres 
proceed  inwards  and  form  a  very  evident  decussation  across  the  middle  line  in  the 
fioor  of  the  third 
ventricle,  immed- 
iately above  the 
hinder  ends  of  the 
corpora  mammil- 
laria. 

The  corpus 
subthalamicum,  in 
the  fresh  condi- 
tion, presents  a 
brownish  colour, 
partly  from  the 
fact  that  its  cells 


Fomiv 

are  pigmented,  and  Anterior  nucleus 
partly  also  on  s,,,,1,fXS: 
account    of  the 

.  1         Internal  capsul 
numerous  Capil-      j^temal  nucl.  us 

lary  blood-vessels         oftiiaianms 

which  pervade   its     External  nucleus 
,  ■■-  of  thalamus 

substance. 

Pineal    Body 

(corpus  pineale). 
— This  is  a  small, 
dark,  reddish  body, 
about  the  size  of  a 
cherry-stone  and 
shaped  after  the 
fashion  of  a  fir- 
cone. Placed  be- 
tween the  hinder 
ends    of   the    two 


Red  nucleus 
Nucleus  of  Luys 


Substantia  niara 


Crusta  of  cms 
cerehi  i 


Putamen 

Fronto-parietal 

opercalnm 


Globus  pallidus 

Caudate  nucleus 

Optic  tract 

Hippocampus 
major 


Fig.  440.- 


CoRONAL  Section  thkough  the  Cerebrum  of  an  Oeakg  passing 

THROUGH    the    SUBTHALAMIC    TEGMENTAL    EeGION. 


thalami,  it  occupies  the  depression  on  the  dorsal  aspect  of  the  mesencephalon, 
which  intervenes  between  the  two  superior  quadrigeminal  bodies.  Its  base,  which 
is  directed  upwards,  is  attached  by  a  hollow  stalk  or  peduncle.  This  stalk  is 
separated  into  a  dorsal  and  a  ventral  part  by  the  prolongation  backwards  into  it 
of  a  small  pointed  recess  of  the  cavity  of  the  third  ventricle.  The  dorsal  part  of 
the  stalk  curves  outwards  and  forwards,  and  on  each  optic  thalamus  becomes 
continuous  with  the  tasnia  thalami  and  the  subjacent  stria  meduUaris;  the 
ventral  part  is  folded  round  a  narrow  but  conspicuous  cord-like  band  of  white 
matter,  which  crosses  the  mesial  plane  immediately  above  the  base  of  the  pineal  body 
and  receives  the  name  of  the  posterior  commissure  of  the  cerebrum  (Fig.  438,  p.  543). 

The  pineal  body  is  not  composed  of  nervous  elements.  The  only  nerves  in  its  midst  are  the 
sympathetic  filaments  which  enter  it,  with  its  blood-vessels.  It  is  composed  of  spherical  and 
tubular  follicles,  filled  with  epithelial  cells,  and  containing  a  variable  amount  of  gritty,  calcareous 
matter. 

The  pineal  body  is  a  rudimentary  structure,  but  in  certain  vertebrates  it  attains  a  much 
higher  degree  of  development  than  in  man.  In  the  lizard,  blind-worm,  etc.,  it  is  present  in  the 
form  of  the  so-called  pineal  eye.  In  structure  it  resembles,  in  these  animals,  an  invertebrate  eye, 
and  it  possesses  a  long  stalk,  in  which  nerve-fibres  are  developed.  Further,  it  is  carried  through 
an  aperture  in  the  cranial  wall,  and  consequently  lies  close  to  the  surface  on  the  dorsum  of  the 
hi-xXd  ])(:U\t:i;T;i  the  ]iarietal  bones. 

Trigonum  Habenulae.— The  small,  triangular,  depressed  area  which  receives  this 
name  is  placed  immediately  in  front  of  the  superior  quadrigeminal  body  in  the 
interval  between  the  iicduncle  of  the  pineal  body  and  the  hinder  end  of  the  thalamus 
(Fig.  438,  p.  543).  it  marks  the  ])Osition  of  an  importiuit  collection  of  nerve-cells, 
which  constitute  the  ganglion  habenulae.  The  axons  of  tliesc  cells  are  collected  on 
tlie  ventral  aspect  of  th(i  ganglion  into  a  bundl(3,  called  the  fasciculus  retroflexus, 
which   ta,keH  a  curved  course  downwards  and   forwards  in  tlu;  teunientum  of  the 


548  THE  NERVOUS  SYSTEM. 

mesencephalon.  The  fasciculus  retroflexus  lies  close  to  the  inner  side  of  the 
red  nucleus,  and  finally  conies  to  an  end  in  a  group  of  cells  termed  the  ganglion 
interpedunculare,  situated  in  the  lower  part  of  the  locus  perforatus  posticus 
(see  p.  539). 

The  ganglion  habenulae  is  likewise  intimately  connected  with  the  stria  medul- 
laris  and  the  dorsal  part  of  the  stalk  of  the  pineal  body. 

As  previously  stated,  the  stria  meduUaris — a  very  evident  band  of  white 
matter — lies  on  the  optic  thalamus,  subjacent  to  the  ependymal  ridge  termed  the 
tsenia  thalanii.  When  traced  backwards,  many  of  the  fibres  of  the  stria  medullaris 
are  observed  to  end  amongst  the  cells  of  the  ganglion  habenulee,  whilst  others  are 
continued  past  the  ganglion  to  enter  the  peduncle  of  the  pineal  body,  and,  through 
it,  to  reach  the  ganglion  habenulse  of  the  opposite  side,  in  connexion  with  the  cells 
of  which  they  terminate.  The  stria  medullaris,  therefore,  ends  partly  in  the 
ganglion  habenulse  of  its  own  side  and  partly  in  the  corresponding  ganglion  of  the 
opposite  side.  The  decussation  of  fibres  across  the  middle  line  forms  the  dorsal 
part  of  the  pineal  stalk  or  peduncle,  and  is  frequently  termed  the  commissura 
habenularum. 

When  the  stria  medullaris  is  traced  in  the  opposite  direction,  it  is  noticed  to 
split  into  a  dorsal  and  ventral  part  near  the  anterior  pillar  of  the  fornix.  The 
dorsal  part  turns  abruptly  upwards,  and,  joining  the  fornix,  is  carried  in  it  to  the 
hippocampus  major  or  cornu  ammonis  from  cells  in  which  its  fibres  take  origin. 
The  ventral  'part  turns  downwards  and  appears  to  spring  from  a  collection  of  cells 
in  the  gray  matter  on  the  base  of  the  brain  close  to  the  optic  chiasma.  The  stria 
medullaris  is  believed  to  form  a  part  of  the  olfactory  apparatus. 

Commissura  Posterior. — The  posterior  commissure  is  a  slender  band  of  white 
matter,  which  crosses  the  middle  line  under  cover  of  the  stalk  of  the  pineal  body 
and  overlies  the  entrance  of  the  aqueduct  of  Sylvius  into  the  third  ventricle.  The 
fibres  wdiich  enter  into  the  formation  of  the  posterior  commissure  are  believed  to 
arise  in  a  special  nucleus,  which  is  placed  in  the  central  gray  matter  immediately 
above  the  oculo- motor  nucleus.  They  decussate  with  each  other  across  the  mesial 
plane  and  thus  the  commissure  is  formed.  The  other  connexions  of  this  little 
band  are  not  satisfactorily  established,  but  Held  believes  that  some  of  its  ventral 
fibres  pass  downwards  into  the  posterior  longitudinal  bundle. 

Locus  Perforatus  Posticus  (substantia  perforata  posterior). — This  has  already 
been  described  on  p.  475.  Some  delicate  bands  of  white  matter,  termed  the  taenia 
pontis,  may  frequently  be  seen  emerging  from  the  gray  matter  of  this  region ;  they 
then  curve  round  the  crura  cerebri  in  close  relation  to  the  upper  border  of  the 
pons,  into  which  they  ultimately  sink  (Fig.  390,  p.  484). 

Corpora  Mammillaria. — The  corpora  mammillaria  are  two  round  white  bodies, 
each  about  the  size  of  a  pea,  which  lie  side  by  side  in  the  interpeduncular  space  on 
the  base  of  the  brain,  immediately  in  front  of  the  locus  perforatus  posticus. 

Each  corpus  mammillare  is  coated  on  the  outside  by  white  matter  derived 
from  the  anterior  pillar  of  the  fornix,  and  contains,  in  its  interior,  a  composite  gray 
nucleus  with  numerous  nerve-cells.  Several  important  strands  of  fibres  are  con- 
nected with  the  corpus  mammillare :  (1)  The  anterior  pillar  of  the  fornix  curves 
downwards  in  the  lateral  wall  of  the  third  ventricle  to  reach  the  corpus  mammillare, 
and  its  fibres  end  amidst  the  cells  of  that  body.  (2)  A  bundle  of  fibres,  called 
the  bundle  of  ViccL  d'Azyr,  which  at  first  sight  appears  to  be  continuous  with  the 
anterior  pillar  of  the  fornix,  takes  origin  in  its  midst  and  extends  upwards  into 
the  optic  thalamus,  to  end  in  fine  arborisations  around  the  large  cells  in  the  anterior 
thalamic  nucleus.  (3)  Another  bundle  of  fibres,  the  pedunculus  corporis  mammillaris, 
takes  form  within  the  corpus  mammillare  and  extends  downwards  in  the  gray 
matter  of  the  floor  of  the  third  ventricle,  to  reach  the  tegmentum  of  the  mesen- 
cephalon.     The  ultimate  destination  of  these  fibres  is  doubtful. 

Tuber  Cinereum  and  Infundibulum. — ^The  tuber  cinereum  is  a  small,  slightly 
prominent  field  of  gray  matter,  which  occupies  the  anterior  part  of  the  inter- 
peduncular space  between  the  corpora  mammillaria  behind  and  the  optic  chiasma 
in  front.  From  its  fore-part  the  infundibulum,  or  stalk  of  the  pituitary  body, 
projects  downwards  and  connects  that  body  with  the  base  of  the  brain.     In  its 


riTUITAIlY  BODY. 


>49 


Foramen  of 

Monro 

Anterior 

commissure' 


upper  part  the  infundibulum  is  hollow,  a  small,  funnel-shaped  diverticulum  of  the 
cavity  of  the  third  ventricle  being  prolonged  downwards  into  it. 

Pituitary  Body  (hypophysis). 
— This  is  a  small  oval  structure, 
flattened  from  above  downwards, 
and  with  '  its  long  axis  directed 
transversely,  which  occupies  the 
pituitary  fossa  in  the  floor  of  the 
cranium.  It  is  composed  of  two 
lobes — a  large  anterior  lobe  and  a 
smaller  posterior  lobe,  which  are 
closely  applied  the  one  to  the  other. 
The  infundibulum,  which  extends 
downwards  from  the  tuber  cin- 
ereum,  is  attached  to  the  posterior 
lobe. 


The  infundibulum  and  posterior 
lobe  of  the  pituitary  body  are  de- 
veloped in  the  form  of  a  hollow  diver- 
ticulum, which  grows  downwards  from 
the  floor  of  that  part  of  the  embryonic 
brain  which  afterwards  forms  the 
third  ventricle.  The  original  cavity 
of  this  diverticulum  becomes  obliter- 
ated, except  in  the  upper  part  of  the 
infundibulum.  In  structure,  the  pos- 
terior lobe  of  the  pituitary  body  shows 


Fig.  441. — Mesial  Section  through  the  Pituitaet  Region 
IN  A  Child  of  Twelve  Months  old. 

In  this  section,  as  well  as  in  the  section  figured  in  Fig.  442,  the 
infundibulum  has  the  appearance  of  being  attached  to  the 
anterior  lobe.  This  is  due  to  the  way  in  which  the  larger 
anterior  lobe  grows  backwards  so  as  to  embrace  the  smaller 
posterior  lobe.  The  latter  is,  as  it  were,  accommodated  in  a 
hollow  in  the  hinder  aspect  of  the  anterior  lobe. 
.  .  From  a  photograph  by  Professor  Symington. 

little   trace    of   its    origin    from    the 

wall  of  the  brain-tube.     It  is  chiefly  composed  of  connective  tissue  and  blood-vessels,  with 

branched  cells  scattered  throughout  it. 

The  anterior  lobe  has  quite  a  different  origin,  and  may  be  regarded  as  the  functional 

part  of  the  pituitary  body.  It  is  de- 
rived fi-om  a  tubular  diverticulum, 
which  grows  upwards  from  the  primi- 
tive buccal  cavity  or  stomodseum.  Its 
connexion  with  the  latter  (canalis 
cranio-pharyngeus)  is  in  the  course  of 
time  cut  off,  and  the  diverticulum  be- 
comes encased  within  the  cranial  cavity 
in  intimate  association  with  the  cerebral 
portion  of  the  organ.  Structurally,  it 
consists  of  tubules  or  alveoli,  lined  by 
epithelial  cells  and  surrounded  by 
capillary  vessels.  Its  structure  is  in 
some  respects  not  unlike  that  of  the 
parathyroid  bodies.  In  giants,  and  in 
cases  of  acromegaly,  the  pituitary  body 
cisterna  pontis  IS  usually  greatly  enlarged. 

Lamina  Cinerea. — This  is  a 
thin,  delicate  lamina  which  may  be 
seen  on  the  basal  aspect  of  the 
brain,  stretching  from  the  upper 
aspect  of  the  optic  chiasma  in  an 
upward  direction  to  become  con- 
rostrum  of  the 
corpus  callosuni. 

Anterior  Commissure  of  the  Cerebrum. — In  the  anterior  part  of  the  cleft, 
bfitweon  the  two  optic  thalami  and  immediately  in  front  of  the  anterior  pillars  of 
the  fornix,  a  round  bunfllc  of  fibres  crosses  the  mesial  plane.  This  is  the  anterior 
commissure.     It  is  much  larger  tlian  tlio  posterior  commissure. 


Foramen  of  Monro 


Anterior  commissure 

Ventricle  III. 

■Corpus  mammillare 

Subarachnoid  tissue 
in  cisterna  basalis 


Infundibulum 


Pituitary  body 


Basi -occipital 


Fio.  442. 


Sphenoidal  sinus 


-Mesial  Section  thi{oij(!H  the  Pituitaky  Region  nected    with    the 
"  '""■''  ^"'^'■'''-  -—  MS  callosuii 


550 


THE  NERVOUS  SYSTEM. 


Third  Ventricle  (ventriculns  tertius).  —  This  is  the  narrow  cleft  which 
separates  the  two  optic  thalami.  Its  depth  rapidly  increases  from  behind  for- 
wards, and  it  may  be  said  to  extend  from  the  pineal  body  behind  to  the  lamina 
cinerea  in  front.  Its  floor  is  formed  by  the  structures  already  studied  within 
the  area  of  the  interpeduncular  space  on  the  base  of  the  brain,  viz.  the  tuber 
cinereum,  the  corpora  mammillaria,  the  gray  matter  of  the  locus  perforatus  posticus, 
and  also  to  some  extent  behind  this  by  the  tegmenta  of  the  crura  cerebri.  It  is 
interesting  to  note  that  the  central  gray  matter  which  surrounds  the  Sylvian 
aqueduct  is  directly  continuous  with  the  gray  matter  of  the  locus  perforatus  posti- 
cus and  tuber  cinereum,  and  in  this  way  it  comes  to  the  surface  in  the  base  of  the 
brain.  The  optic  chiasma  crosses  the  floor  in  front  and  marks  the  place  where  the 
latter  becomes  continuous  with  the  anterior  wall  of  the  cavity.  The  front  loall  of 
the  third  ventricle  is  formed  by  the  lamina  cinerea,  which  extends  upwards  from 
the  optic  chiasma.  The  anterior  commissure,  as  it  crosses  from  one  side  to  the  other, 
projects  into  the  ventricle,  but  of  course  it  is  excluded  from  the  cavity  by  the 
ventricular  epithelial  lining.  It  may  be  taken  as  indicating  the  place  where  the 
roof  joins  the  anterior  wall.  The  roof  of  the  third  ventricle  is  formed  by  a  thin 
epithelial  layer,  continuous  with  the  thin  epithehal  lining  of  the  cavity,  which 
stretches  across  the  mesial  plane  from  one  taenia  thalami  to  the  other.  Applied 
to  the  upper  surface  of  the  epithelial  roof  is  the  fold  of  pia  mater,  termed  the  velum 
interpositum,  and  the  roof  is  invaginated  into  the  cavity  along  its  whole  length  by 
two  delicate  choroid  plexuses,  which  hang  down  from  the  under  surface  of  this 
fold.  When  the  velum  interpositum  is  removed  the  thin  epithelial  roof  is  torn 
away  with  it,  leaving  only  the  lines  of  attachment  in  the  shape  of  the  taenia 
thalami. 

The  lateral  loall  of  the  third  ventricle  is  formed  for  the  greater  part  of  its 
extent  by  the  inner  surface  of  the  optic  thalamus,  covered  by  a  thick  layer  of 


O  P.  05^  O  S  «,o 
Fornix       \      *  — -^ 
Foramen  of  Monro      ^v 

Septum  lucidum 

Genu  of  corpus 
callosum 


Anterior  commissure 

Corpus  mammillare'' 
Lamina  cinerea  ' 


ri    .g  a>    fl  ;:  S5 


Aqueduct  of  Sylvius 
/ 

Culmen 


Declive 


Uvula 


Central  lobule 


Optic  nerve' 

Pituitary  body 

Tuber  cinereum 

Third  nerve 

Pons 
Valve  of  Vieusseiis    ]    '| 

Ventricle  IV.  |     |      -^^^^^-^^ 

Medulla  Qjio^oid  plexus  in  ventricle  IV. 

Fig.  443. — Mesial  Section  through  the  Corpus  Callosum,  Diencephalon,  etc. 
Shows  the  third  and  fourth  ventricles  conuected  by  the  aqueduct  of  Sjdvius. 

central  gray  matter  continuous  with  the  Sylvian  gray  matter  of  the  mesencephalon. 
A  little  in  front  of  the  middle  of  the  ventricle  the  cavity  is  crossed  by  the  middle 
or  soft  commissure,  which  connects  the  thalami  with  each  other,  and  in  front  of  this 
the  anterior  pillar  of  the  fornix  is  seen  curving  downwards  and  backwards  in  the 
lateral  wall.  At  first  the  bulging  which  it  forms  is  distinctly  prominent,  but  it 
gradually  subsides  as  the  strand,  on  its  way  to  end  in  the  corpus  mammillare, 
becomes  more  and  more  sunk  in  the  gray  matter  on  the  side  of  the  ventricle. 


THIRD  A^ENTRICLE. 


551 


The  third  ventricle  communicates  with  botli  of  the  lateral  ventricles,  and  also 
with  the  fourth  ventricle.  The  aqueduct  of  Sylvius,  the  narrow  channel  which 
tunnels  the  mesencephalon,  brings  it  into  communication  with  the  fourth  ventricle. 
The  opening  of  this  aqueduct  is  placed  at  the  posterior  part  of  the  floor  of  the  third 
ventricle,  immediately  below  the  posterior  commissure.      The  foramina  of  Monro 


ER  A  L       V  E/v- 


OPTIC  RECESS 


NFUNDIBULAR 
RECESS 


VENT.  IV. 


Fig.  444. — Profile  View  of  a  Cast  of  the  Ventricles  of  the  Brain  (from  Retziiis). 


R.SP.  Recessus  suprapinealis. 
R.P.    Recessus  pinealis. 


A.S.   Aqueduct  of  Sylvius. 
F.M.  Foramen  of  Monro. 


bring  it  into  communication  with  the  lateral  ventricles.  These  apertures  are 
placed  at  the  upper  and  fore  parts  of  the  lateral  walls,  and  lead  outwards  and 
slightly  upwards  between  the  most  prominent  parts  of  the  anterior  pillars  of  the 
fornix  and  the  anterior  tubercles  of  the  optic  thalami.  They  are  just  large  enough 
to  admit  a  crow-quill,  and  through  these  passages  the  epithelial  lining  of  the  three 
ventricles  becomes  continuous.  From  the  foramen  of  Monro  a  distinct  groove  on 
the  lateral  wall  of  the  ventricle  leads  backwards  towards  the  mouth  of  the  Sylvian 
aqueduct.  It  is  termed  the  sulcus  of  Monro,  and  is  of  interest,  inasmuch  as  it  is 
considered  by  His  to  represent  in  the  adult  brain  the  furrow  which  divides  the 
lateral  wall  of  the  embryonic  brain-tube  into  an  alar  and  a  basal  lamina. 

The  outline  of  the  third  ventricle,  when  viewed  from  the  side  in  a  mesial  section 
through  the  brain,  or  as  it  is  exhibited  in  a  plaster  cast  of  the  ventricular  system  of  the 
brain,  is  seen  to  be  very  irregular  (Fig  444).  It  presents  several  diverticula  or  recesses. 
Thus,  in  the  fore-part  of  the  floor  there  is  a  funnel-shaped  pit  or  recess,  leading  down 
through  the  tuber  cinereum  into  the  infundibulum  of  the  pituitary  body.  Another  recess, 
the  recessus  opticus,  leads  forwards  immediately  in  front  of  this,  above  the  optic  chiasma. 
Posteriorly  two  diverticula  are  present.  One,  the  recessus  pinealis,  passes  backwards 
above  the  posterior  commissure  and  the  mouth  of  the  Sylvian  aqueduct  for  a  short 
distance  into  the  stalk  of  the  pineal  body.  The  second  is  placed  above  this  and  is  carried 
backwards  for  a  greater  distance.  It  is  a  diverticulum  of  the  epithelial  roof,  and,  there- 
fore, is  difficult  to  demonstrate.     It  is  termed  the  recessus  suprapdnealis. 


Cerebral  Connexions  of  the  Optic  Tract. 

One  nerve,  the  optic  nerve  or  the  nerve  of  sight,  is  connected  with  this  section 
of  the  brain.  At  the  optic  chiasma  the  optic  nerves  of  the  two  sides  are  joined 
together  and  a  partial  decussation  of  fibres  takes  place.  The  fibres  which  arise  in 
the  mesial  lialf  of  each  retina  cross  tlio  mesial  plane  and  join  the  optic  tract  of  the 


552 


THE  NERVOUS  SYSTEM. 


opposite  side.  The  optic  tract  proceeds  backwards  round  the  crus  cerebri,  and  in 
the  neighbourhood  of  the  corpora  geniculata  divides  into  two  roots,  viz.  a  lateral 
and  a  mesial  (p.  532). 

Mesial  Root  of  the  Optic  Tract — Commissure  of  Gudden. — The  mesial  root 
of  the  optic  tract  disappears  under  cover  of  the  corpus  geniculatum  internum  and  a 
large  proportion  of  its  fibres  arise  or  end  in  this  nuclear  body.  As  to  the  connexions 
of  the  other  fibres,  we  possess  at  present  no  precise  information.  The  mesial 
root,  although  it  is  composed  of  fibres  which  run  in  the  optic  tract,  has  absolutely 
nothing  to  do  with  the  optic  nerve.  These  fibres,  when  traced  forwards,  cross  the 
mesial  plane  in  the  posterior  angle  of  the  optic  chiasma  and  are  carried  backwards 
in  the  opposite  optic  tract,  to  form  on  that  side  its  mesial  root.  The  fil^res,  there- 
fore, are  commissural,  and  constitute  a  bond  of  union,  called  the  commissure  of 
Grudden,  between  the  internal  geniculate  bodies. 

Lateral  Root  of  the  Optic  Tract. — The  lateral  or  true  visual  root  of  the 
optic  tract  is  composed  of  fibres  which  come — (1)  from  the  lateral  half  of  the  retina 
of  its  own  side ;  and  (2)  from  the  mesial  half  of  the  retina  of  the  opposite  side,  and 
which  have  crossed  the  mesial  plane  in  the  optic  chiasma.  But  in  addition  to  the 
afferent  retinal  fibres  there  are  a  certain  number  of  efferent  fibres  in  the  optic 
tract,  fibres  \yhich  take  their  origin  in  the  brain  and  end  in  the  retina.  These  are 
distinguished  from  the  afferent  retinal  fibres  by  their  exceeding  fineness. 

The  fibres  of  the  lateral  root  of  the  optic  tract  end  in  the  superior  quadrigeminal 
body,  in  the  external  geniculate  body,  and  in  the  pulvinar  of  the  optic  thalamus. 
The  fibres  to  the  superior  quadrigeminal  body  reach  it  through  the  superior  brachium 

(p.  435),  and  for  the  most  part  spread  out 
on  its  surface  in  the  stratum  zonale  before 
they  sink  into  its  substance,  to  end  in 
terminal  arborisations  around  its  cells.  The 
corpus  geniculatum  externum  receives  the 
largest  contribution  of  fibres  from  the 
lateral  root  of  tlie  optic  tract.  These  partly 
sink  into  its  interior  and  partly  spread  out 
over  its  surface.  The  former  enter  into 
the  construction  of  the  curved  lamellae 
of  white  matter  which  traverse  this  nuclear 
mass,  and  to  a  large  extent  end  in  the 
gray  matter  which  intervenes  between 
these  lamellae.  The  deep  fibres  which  are 
not  exhausted  in  this  way  proceed  onwards 
through  the  external  geniculate  body  and 
enter  the  pulvinar.  Of  the  superficial  fibres 
which  spread  over  the  surface  of  the  external 
geniculate  body  some  dip  into  its  substance 
and  end  there,  but  the  majority  are  carried 
over  it  and  enter  the  stratum  zonale  of 
the  pulvinar.  The  fibres  of  the  lateral 
root  of  the  optic  tract,  which  end  in  the 
pulvinar,  therefore  reach  their  destination 
by  passing  either  over  or  through  the 
external  geniculate  body. 

Cortical    Connexions    of    the   Optic 
Nerve. — The  superior  quadrigeminal  body, 
the  external  geniculate  body,  and  the  pul- 
vinar constitute  the  lower  visual  centres 
or    terminal   nuclei   of    the    visual    part 
of    the   optic   tract.     The    higher   visual 
centre    is   placed    in   the   cortex   of    the 
occipital  lobe  of  the  cerebral  hemisphere,  and  the  connexions  between  this  and 
the  lower  centres  are  established  by  a  large  strand  of  fibres  which  runs  in  the 
central  white  matter  of  the  hinder  part  of  the  cerebral  hemisphere,  and  which 


Fig.  445. — Diagram 


Connex- 


ions OF  THE  Optic  Nerve  and  Optic  Tract. 


CEREBKAL  HEMISPHERES.  553 

constitutes  the  optic  radiation.  The  optic  radiation  is  composed  botii  of  corticipetal 
and  corticifugal  fibres.  The  former  arise  as  the  axons  of  tiie  cells  in  the  external 
geniculate  body  and  the  pulvinar,  around  which  the  retinal  fibres  end,  and  they 
terminate  in  the  cortex  of  the  occipital  lobe.  The  corticifugal  fibres  take  origin 
in  the  cortex  of  the  occipital  lobe  and  end  in  the  pulvinar  and  superior  quadri- 
geminal  body  (Ferrier  and  Turner).  Thus  constituted,  the  optic  radiation  forms 
a  conspicuous  strand  (Figs.  462,  p.  576 ;  465,  p.  579  ;  473,  p.  592),  which,  reaching 
the  retrolenticular  part  of  the  internal  capsule,  sweeps  backwards  into  the  occipital 
lobe  of  the  cerebral  hemisphere  on  the  outer  side  of  the  posterior  horn  of  the 
lateral  ventricle.     Its  connexions  will  be  studied  more  fully  at  a  later  stage. 

Fleclisig  does  not  believe  that  the  pulvinar  is  an  internode  interposed  in  the  path  of  the  optic 
nerve  as  it  proceeds  towards  the  visual  area  of  the  cerebral  cortex.  He  states  that  he  has  not 
been  able  to  convince  himself  that  any  fibres  of  the  optic  tract  end  in  the  optic  thalamus. 

Other  Connexions  of  the  Lower  Group  of  Visual  Centres. — (1)  The  nuclei  of  the  nerves 
which  sujojjly  the  muscles  which  move  the  eyeball  would  appear  to  stand  in  intimate  connexion 
with  the  lower  grou^^  of  visual  centres.  Most  probably  this  connexion  is  established  through 
the  posterior  longitudinal  bundle.  As  previously  stated,  Held  believes  that  axons  of  certain  of 
the  cells  of  the  superior  quadrigeminal  body  enter  this  tract.  (2)  Through  the  mesial  fillet,  the 
superior  quadrigeminal  body  is  connected  with  the  medulla  and  cord. 

THE    PARTS    DERIVED    FROM    THE   TELENCEPHALON. 

Cekebral  Hemispheres. 

The  cerebral  hemispheres  form  the  largest  part  of  the  fully-developed  brain. 
When  viewed  from  above  they  form  an  ovoid  mass,  the  broadest  end  of  which  is 
directed  backwards,  and  the  longest  transverse  diameter  of  which  will  be  found  in 
the  vicinity  of  the  parts  which  lie  subjacent  to  the  parietal  eminences  of  the 
cranium.  The  massive  rounded  character  of  the  anterior  or  frontal  end  of  each 
cerebral  hemisphere  constitutes  a  leading  human  characteristic ;  but  the  hinder  or 
occipital  end  is  narrow  and  pointed,  and  is  directed  somewhat  downwards.  The 
two  cerebral  hemispheres  are  separated  from  each  other  by  a  deep  mesial  cleft, 
termed  the  great  longitudinal  fissure. 

Great  Longitudinal  Fissure  (fissura  longitudinalis  cerebri). — In  front  and 
behind  the  great  longitudinal  fissure  passes  from  the  dorsal  to  the  ventral  aspect  of 
the  cerebral  hemispheres,  so  as  to  separate  them  completely  from  each  other.  In 
its  middle  part,  however,  the  fissure  is  interrupted  and  floored  by  the  corpus 
callosum,  a  white  commissural  band,  which  passes  between  the  hemispheres  and 
connects  them  together.  The  upper  surface  of  the  corpus  callosum  can  be 
displayed  by  gently  drawing  asunder  the  contiguous  mesial  surfaces  of  the 
cerebral  hemispheres.  The  great  longitudinal  fissure  is  occupied  by  a  mesial 
fold  of  dura  mater,  termed  the  falx  cerebri,  which  partially  subdivides  the  part 
of  the  cranial  cavity  allotted  to  the  cerebrum  into  a  right  and  left  chamber. 

External  Configuration  of  each  Cerebral  Hemisphere. — Each  cerebral  hemi- 
sphere presents  an  external,  an  internal,  and  an  inferior  surface.  The  external 
surface  is  convex  and  is  adapted  accurately  to  the  deep  surface  of  the  cranial 
vault.  The  internal  or  mesial  surface  is  flat  and  perpendicular,  and  bounds  the 
great  longitudinal  fissure.  In  great  part  it  is  in  contact  with  the  falx  cerebri ;  and 
where  that  partition  is  deficient,  it  is  applied  to  the  corresponding  portion  of  the 
internal  surface  of  the  opposite  hemisphere.  The  inferior  surface  is  irregular  and 
is  adapted  to  the  anterior  and  middle  cranial  fossce  of  the  cranial  floor  and,  behind 
these,  to  the  upper  surface  of  the  tentorium  cerebelli.  Traversing  this  surface  in  a 
transverse  direction,  nearer  the  anterior  end  of  the  hemisphere  than  the  posterior 
end,  is  the  stem  of  the  Sylvian  fissure.  This  deep  cleft  divides  the  inferior  surface 
into  an  anterior  or  orhital  area,  which  rests  on  the  orbital  plate  of  the  frontal  bone, 
and  is  consequently  concave  from  side  to  side,  and  a  more  extensive  posterior  or 
tentorial  area,  which  lies  on  the  floor  of  the  lateral  part  of  the  middle  cranial  fossa 
and  upon  the  upper  surface  of  the  t(intoriiim  cerebelli.  This  surface  is  arched 
from  before  backwards,  and  lof)ks  inwards  as  well  as  downwards.  In  its  hinder 
two-thirds  it  lies  ;i,]k»vc  the  cerebellum,  from  which  it  is  separated  ])y  the  tentorium 
cerebelli. 


554  THE  NEEVOUS  SYSTEM. 

The  borders  which  intervene  between  these  surfaces  are  the  supero-mesial,  the 
superciliary,  the  infero-lateral,  and  the  internal  occipital.  The  supero-mesial 
harder,  convex  from  before  backwards,  intervenes  between  the  convex  external 
surface  and  the  flat  internal  surface  of  the  hemisphere.  The  suj^erciliary  border  is 
highly  arched  and  separates  the  orbital  surface  from  the  external  surface.  The 
ir^'ero-laieral  border  marks  off  the  tentorial  surface  from  the  external  surface.  The 
internal  occipital  border  can  only  be  seen  in  cases  where  the  brain  has  been  hardened 
in  situ  and  faithfully  retains  the  natural  form.  It  extends  from  the  posterior  end 
of  the  hemisphere  towards  the  hinder  extremity  of  the  corpus  callosum,  and  inter- 
venes between  the  mesial  and  tentorial  surfaces.  It  is  the  Ijorder  whicli  lies  along 
the  straight  blood  sinus,  and  it  therefore  occupies  the  angle  which  is  formed  by  the 
attachment  of  the  posterior  part  of  the  falx  cerebri  to  the  upper  surface  of  the 
tentorium  cerebelli. 

The  most  projecting  part  of  the  anterior  end  of  the  cerebral  hemisphere  is  called 
the  frontal  pole,  whilst  the  most  projecting  part  of  the  hinder  end  is  termed  the 
occipital  pole.  On  the  under  surface  of  the  hemisi^here  the  prominent  point  of 
cerebral  substance  which  extends  forwards  below  the  Sylvian  fissure  receives  the 
name  of  the  temporal  pole.  In  a  well-hardened  brain  a  broad  groove  is  usually 
present  on  the  inner  and  lower  aspect  of  the  occipital  pole  of  the  right  hemisphere. 
This  corresponds  to  the  commencement  of  the  right  lateral  venous  sinus.  A  less 
distinct  groove  on  the  occipital  pole  of  the  left  hemisphere  frequently  indicates  the 
commencement  of  the  left  lateral  sinus.  On  the  tentorial  surface,  a  short  distance 
behind  the  temporal  pole,  a  well-marked  depression  is  always  visible.  This  corre- 
sponds to  the  elevation  on  the  anterior  surface  of  the  petrous  portion  of  the 
temporal  bone  over  the  superior  semicircular  canal. 

Cerebral  Gyri  and  Sulci. — The  surface  of  the  cerebral  hemispheres  is  rendered 
highly  irregular  by  the  presence  of  convolutions  or  gyri,  separated  from  each  other 
by  intervening  furrows  of  very  varying  depth,  termed  sulci  or  fissures.  The  surface 
pattern  which  is  presented  by  these  gyri  and  sulci  is,  in  its  general  features,  the 
same  in  all  normal  human  brains ;  but  when  the  comparison  is  pushed  into  detail 
many  differences  become  manifest,  not  only  in  the  brains  of  different  individuals, 
but  also  in  the  two  cerebral  hemispheres  of  the  same  individual. 

There  are  two  varieties  of  furrows,  viz.  complete  and  incomplete.  The  complete 
fissures  are  few  in  number,  and  are  formed  by  inwardly -directed  infoldings 
involving  the  entire  thickness  of  the  cerebral  wall.  They  consequently  show 
in  the  interior  of  the  cerebral  cavity  or  lateral  ventricle  in  the  form  of  internal 
elevations  on  its  wall.  The  complete  fissures  are  the  following :  (1)  the  dentate  or 
hippocampal  fissure ;  (2)  the  anterior  part  of  the  calcarine  fissure ;  and  (3)  a 
portion  of  the  collateral  fissure.  The  incomplete  fissures  are  merely  surface  furrows 
of  varying  depth,  which  do  not  produce  any  effect  on  the  inner  surface  of  the 
ventricular  wall. 

General  Structure  of  the  Cerebral  Hemispheres.— Each  cerebral  hemisphere 
is  composed  of  an  outside  coating  of  gray  matter,  spread  in  a  continuous  and  un- 
interrupted layer  over  its  surface,  and  an  internal  mass  of  white  matter,  which  forms 
a  considerable  part  of  the  immediate  wall  of  the  ventricular  cavity.  The  gray 
coating  is  termed  the  cerebral  cortex,  and  the  internal  white  matter  is  called  the 
medullary  centre.  Each  convolution  shows  a  corresponding  structure.  On  trans- 
verse section  it  is  seen  to  present  an  external  covering  of  gray  cortex,  supported  by 
a  central  core  of  white  matter. 

But,  in  addition  to  the  gray  matter  on  the  outside,  there  are  certain  large 
deposits  of  gray  matter  embedded  in  the  basal  part  of  each  cerebral  hemisphere. 
These  cerebral  nuclei  constitute  the  corpus  striatum,  and,  although  to  some  extent 
isolated  from  the  gray  matter  on  the  surface,  it  can  be  easily  shown  that  at  certain 
points  they  are  directly  continuous  with  it. 

By  means  of  the  convolutions  and  sulci,  the  gray  matter  on  the  surface  of  the 
hemisphere  is  enormously  increased  in  quantity  without  unduly  adding  to  the  bulk 
of  the  organ ;  and,  further,  the  vascular  pia  mater,  which  dips  into  every  fissure,  is 
increased  in  extent  to  a  like  degree.  Opportunity  is,  therefore,  afforded  to  the 
cortical  vessels  of  breaking  up  into  twigs  of  exceeding  fineness  before  they  enter  the 


FISSUKE  OF  SYLVIUS. 


555 


substance  of  the  hemisphere.  The  distribution  of  blood  to  the  gray  cortex  is,  in 
this  way,  equahsed  and  rendered  uniform. 

Cerebral  Lobes  and  Interlobar  Fissures. — Certain  of  the  fissures  which 
traverse  the  surface  of  the  cerebrum  are  more  or  less  arbitrarily  chosen  for  sub- 
dividing the  surface  into  districts  or  areas,  which  are  termed  lobes.  These  fissures 
are  termed  interlobar,  and  are  the  following:  (1)  the  fissure  of  Sylvius;  (2)  the 
fissure  of  Eolando ;  (3)  the  parieto-occipital ;  (4)  the  calloso-marginal ;  (5)  the 
collateral ;  and  (6)  the  limiting  sulcus  of  Eeil. 

The  lobes  which  are  mapped  out  by  these  fissures  are :  (1)  the  frontal ;  (2)  the 
parietal ;  (3)  the  occipital ;  (4)  the  temporal ;  (5)  the  insula,  or  the  island  of  Eeil ; 
(6)  the  limbic.  To  these  may  be  added  a  seventh  lobe,  in  no  way  related  to  the 
interlobar  fissures,  viz.  the  olfactory  lobe.  With  the  exception  of  the  occipital  and 
olfactory  lobes  and  the  insula,  this  subdivision  of  the  hemisphere  possesses  little 
morphological  value,  and  is  chiefly  adopted  for  topographical  purposes. 

Fissure  of  Sylvius  (fissura  cerebri  lateralis).- — -This  is  the  most  conspicuous 


Fig.  446. — Gyri  and  Sulci,  on  the  outer  surface  of  the  cerebral  hemisphere. 


fi. 

i\ 

f.m. 

p.m. 

A. 

B. 

C. 

H. 


p.c.i. 
p.cs 


Sulcus  frontalis  superior. 
Sulcus  frontalis  inferior. 
Sulcus  frontalis  medius. 
Sulcus  paramedians. 
Pars  basilaris. 
Pars  triangularis. 
Pars  orbitalis. 
Sylvian  fissure. 

Anterior  horizontal  limb  (Sylvian  fissure). 
Ascending  limb  (Sylvian  fissure). 
Posterior  liorizoiital  limb  (Sylvian  fissure). 
Ascending  terminal  part  of  tlie  posterior  hori- 
zontal limb  of  the  Sylvian  fissure. 
Inferior  prsecentral  sulcus. 
Superior  prtecentral  sulcus. 


r.  Fissure  of  Rolando. 

g.s.  Superior  genu. 

g.i.  Inferior  genu. 

d.  Sulcus  diagonalis. 

t'.  Superior  temporal  sulcus  (parallel  sulcus). 

t'^.  Inferior  temporal  sulcus. 

pi.  Inferior  postcentral  sulcus. 

p-.  Superior  postcentral  sulcus. 

p''.  Ramus  horizontalis. 

p*.  Ramus  occipitalis. 

s.o.t.  Sulcus  occipitalis  transversus. 

occ.  lat.  Sulcus  occijiitalis  lateralis  (the  sulcus  lunatuf 

of  Elliot  Smith), 

cm.  Calloso-marginal  sulcus, 

c.t.r.  Inferior  transverse  furrow. 


fissure  on  the  surface  of  the  cerebral  hemisphere.  It  is  composed  of  a  short  main 
stem,  from  the  outer  extremity  of  which  three  branches  or  limbs  radiate.  The 
stem  of  the  Sylvian  fissure  is  placed  on  the  inferior  surface  of  the  hemisphere.  It 
begins  at  the  locus  perforatus  anticus  in  a  depression  termed  the  vallecula  Sylvii. 
From  tills-  it  passes  horizontally  outwards,  forming  a  deep  clel't  between  the 
temporal  pole  and  tlio  or})ital  surface  of  the  frontal  lobe.  Appearing  on  the 
outer  surface  of  the  homis])horc  at  a  point  called  tlie  Sylvian  point,  the  Sylvian 
fissure  immediately  ilividos   into   three   radiating   branches.     These   are:    (1)   the 


556  THE  NERVOUS  SYSTEM. 

ramus  horizontalis  posterior ;  (2)  the  ramus  horizontalis  auterior ;  (3)  the  ramus 
anterior  ascendens. 

The  posterior  horizontal  limb  i.s  the  longest  and  Ijest  marked  of  the  three  limbs. 
It  extends  backwards,  with  a  slight  inclination  upwards  on  the  outer  surface  of  the 
hemisphere  for  a  distance  which  may  vary  from  about  two  to  three  inches.  It 
intervenes  between  the  frontal  and  parietal  lobes  which  lie  above  it  and  the 
temporal  lobe  which  lies  below  it,  and  it  finally  ends  in  the  region  subjacent  to  the 
parietal  eminence  of  the  cranial  wall  by  turning  upwards  into  the  parietal  lobe  in 
the  form  of  an  ascending  terminal  apiece. 

The  anterior  horizontal  limb  extends  horizontally  forwards  in  the  frontal  lobe  for 
a  distance  of  about  three-quarters  of  an  inch  immediately  above  and  parallel  to  the 
posterior  part  of  the  superciliary  margin  of  the  hemisphere. 

The  ascending  limb  proceeds  upwards,  with  a  slight  inclination  forwards,  into  the 
lower  part  of  the  outer  surface  of  the  frontal  lobe  for  a  distance  of  abcnit  an  inch. 
In  many  cases  the  two  anterior  limbs  spring  from  a  common  stem  of  greater  or 
less  length,  and  not  infrequently  both  are  replaced  by  a  single  anterior  limb. 

Limiting  Sulcus  of  Reil  (sulcus  circularis  Eeilii). — If  the  lips  of  the  posterior 
horizontal  limb  of  the  Sylvian  fissure  be  widely  pulled  asunder  from  each  other,  the 
insula  or  island  of  Eeil  will  be  seen  at  the  bottom.  The  insular  district  of  the 
cortex  is  completely  hidden  from  view  when  the  Sylvian  fissure  is  closed  by  over- 
lapping portions  of  the  cerebral  hemisphere,  and,  when  brought  into  view  in  the 
manner  indicated,  it  is  observed  to  present  a  triangular  outline  and  to  be  surrounded 
by  a  limiting  sulcus,  of  which  three  parts  may  be  recognised,  viz. :  an  upper  part, 
bounding  it  above  and  separating  it  from  the  parietal  and  frontal  lobes ;  a  loiuer 
part,  marking  it  off  below  from  the  temporal  lobe;  and  an  anterior  part,  separating 
it  in  front  from  the  frontal  lobe. 

Opercula  Insulse. — The  overlapping  portions  of  the  cerebral  substance  which 
cover  over  the  insula  are  termed  the  insular  opercula,  and  they  form,  by  the  apposi- 
tion of  their  margins,  the  three  limbs  of  the  Sylvian  fissure.  The  opercula  are  four 
in  number  and  are  named  :  (1)  temporal ;  (2)  fronto-parietal ;  (3)  frontal ;  and  (4) 
orbital.  The  limbs  of  the  Sylvian  fissure  cut  right  through  between  the  different 
opercula  and  extend  from  the  exposed  surface  of  the  hemisphere  to  the  submerged 
surface  of  the  insula,  and,  in  this  manner,  separate  the  opercula  from  each  other. 

The  temporal  operculum  extends  upwards  over  the  insula  from  the  temporal  lobe, 
and  its  upper  margin  forms  the  lower  lip  of  the  posterior  horizontal  limb  of  the 
Sylvian  fissure. 

The  fronto-parietal  operculum  is  carried  downwards  from  the  parietal  and  frontal 
regions  over  the  insula,  and  its  lower  margin,  meeting  the  temporal  operculum, 
forms  the  upper  lip  of  the  posterior  limb  of  the  Sylvian  fissure. 

The  frontal  operculum  is  the  small  triangular  piece  of  cerebral  substance  which 
intervenes  between  the  ascending  and  anterior  horizontal  limbs  of  the  Sylvian 
fissure.  It  covers  over  a  small  part  of  the  anterior  portion  of  the  insula,  and  is 
sometimes  termed  the  pars  triangularis. 

The  orbital  operculum  is,  for  the  most  part,  on  the  under  surface  of  the  hemi- 
sphere. It  lies  below  and  to  the  inner  side  of  the  anterior  horizontal  limb  of  the 
Sylvian  fissure,  and  proceeds  backwards  from  the  orbital  aspect  of  the  frontal  lobe 
over  the  fore-part  of  the  insula. 

Development  of  the  Sylvian  Fissure  and  of  the  Insular  District  of  the  Cerebral  Hemi- 
sphere.— It  is  only  during  the  latter  half  of  the  intrauterine  period  of  development  that  the 
opercula  take  shape  and  grow  over  the  insula,  so  as  to  shut  it  out  from  the  surface.  In  its  early 
condition  the  insula  presents  the  form  of  a  depressed  area  on  the  side  of  tlie  cerehral  hemisphere, 
surrounded  by  a  distinct  boundary  wall  formed  by  the  surrounding  more  elevated  surface  of  the 
hemisphere  (Fig.  447,  A).  After  a  time  this  depressed  area,  which  is  called  the  Sylvian  fossa, 
assumes  a  triangular  outline,  and  then  the  bounding  wall  is  observed  to  be  composed  of  three 
distinct  parts,  viz.  :  an  upper  or  fi'onto-parietal,  a  lower  or  temporal,  and  an  anterior  or  orbital 
part  (Fig.  447,  B).  »  The  rounded  angle,  formed  \sj  the  meeting  of  the  upper  and  anterior  portions 
of  the  boundary,  now  becomes  flattened,  and  a  short  oblique  jjart  of  the  limiting  wall,  termed  the 
fi'ontal  portion,  assumes  shape  in  this  position.  Each  of  these  four  i^ortions  of  the  bounding 
wall  of  the  Syh'ian  fossa  becomes  a  line  of  growth,  from  which  an  ojDerculum  takes  origin,  and 
by  the  approximation  of  these  opercula,  as  they  grow  over  the  surface  of  the  Sylvian  fossa,  the 
insula  becomes  closed  in  and  the  limbs  of  the  Sylvian  fissure  are  formed  (Fig.  448). 


INSULAE  OPERCULA. 


557 


The  temporal  and  fronto- parietal  opercula  make  their  appearance  somewhere  alxjut  the  end 
of  tlie  fifth  month  of  fretal  development,  long  before  the  other  two  opercula  show  any  indication 
of  growth.  The  temporal  operculum  grows  more  rapidly  than  the  fronto-parietal  ;  so  that,  when 
the  margins  of  these  two  opercula  come  together  to  form  the  posterior  limb  of  the  Sylvian  fissure, 
there  is  a  greater  extent  of  the  Sylvian  fossa  covered  by  the  temporal  operculum  than  l>y  the  fronto- 
parietal operculum.  This  accounts  for  the  more  oblique  direction  of  the  Sylvian  fissure  in  the  foetal 
brain.  But  at  this  stage  a  growth -antagonism  between  the  two  opercula  takes  place,  and  in  this 
the  fronto-parietal 
operculum  j^i'oves  the 
victor.  The  contigu- 
ous lips  of  the  two 
opercula  become,  in  the 
first  instance,  tightly 
pressed  together,  and 
then,  as  the  upper  oper- 
culum  proves  the 
stronger  and  the  more 
vigorous  in  its  growth, 
the  posterior  limb  of 
the  Sylvian  fissure  be- 
comes gradually  de- 
pressed until  it  assumes 
the  inclination  char- 
acteristic of  the  adult. 
It  would  appear  that 
the  opercular  growth- 
antagonism  which  pro- 
duces this  effect  in  the 
human  brain  does  not 
occur  to  the  same  ex- 
tent, if  indeed  it  occurs 


Fig.  447. 


-Three  Stages  in  the  Development  of  the  Insula  and  the 
Insular  Opercula. 


In   C 


Right  cerebral  hemisphere  from  a  foetas  in  the  latter  part  of  the  fourth  month 
of  development  ;  B,  Right  cerebral  hemisphere  from  a  foetus  in  the  fifth 
month  of  development  ;  C,  Right  cerebral  hemisphere  from  a  foetus  in  the 
latter  part  of  the  eiglith  month  of  development. 

the  temiDoral  oi^erculum  has  been  removed,  and  thus  a  large  part  of  the 
insula  is  exposed.  The  outline  of  the  temporal  operculum  is  indicated  by  a 
dotted  line. 

F,  Frontal  operculum.      0,  Orbital  operculum. 


at  all,  in  the  ape.  This  F. P.  Fronto-parietal  operculum 
is  evident  from  the  ob- 
lique direction  of  the  posterior  limb  of  the  Sylvian  fissure  in  the  simian  brain.  The  greater 
growth-energy  of  the  fronto-parietal  operculum  in  the  human  brain  is  not  confined  to  the 
foetal  stage  of  development,  but  is  carried  into  the  earlier  stages  of  infantile  growth,  and  it  is 
probable  that  it  is  due  to  an  extension  of  that  district  of  the  cortex  in  which  the  centres 
for  the  skilled  movements  of  the  upper  limbs  reside,  and  also  to  an  extension  of  Flechsig's 
parieto-occipital  association  area. 

The  orbital  and  frontal  opercula  are  late  in  appearing  and  very  tardy  in  their  growth. 
Indeed,  it  is  only  during  the  course  of  the  first  year  of  infantile  life  that  they  come  into  apposition 


Fig.   448. — Diagram  to  Illustrate  the  Development  of  the  Opercula  which  cover  the  Insula. 

A,  Sylvian  fossa  before  opercula  begin  to  form  ;  B,  Fronto-parietal  and  temporal  opercula  well  advanced  ; 
C,  All  the  four  opercula  developed  but  not  in  apposition. 

F.P.  Fronto-parietal  operculum.      O.R.  Orbital  wall  of  fossa.        s^.   Anterior  horizontal  limb  of  Sylvian  fissure. 

T.      Temporal  operculum.  F.      Frontal  operculum.  s^.   Ascending  limb. 

F.R.  Frontal  wall  of  fossa.  0.      Orbital  operculum.  s^.    Posterior  horizontal  limb. 


with  each  other  and  with  the  other  two  opercula,  so  as  to  close  in  the  fore-part  of  the  Sylvian  fossa 
and  form  the  anterior  limbs  of  the  Sylvian  fissure.  They  do  not  begin  to  take  shape  until  more 
tlian  lialf  of  the  Sylvian  fossa  has  already  been  closed  by  tlie  fronto-jmrietal  and  the  tenq^oral 
opercula.  The  orbital  o])(;i'Ciilum  appears  first  and  is  much  more  constant  in  its  growth  than 
the  frontal  operculum,  which  iiidcecl  frequently  fails  altogether,  and,  even  when  present,  shows 
the  greatest  amount  of  variability  in  the  degree  to  which  it  is  develojjisd. 

Variations  in  the  degree  of  development  of  the  frontal  operculum  influencse  greatly  the  form 
presented  ]>y  the  two  anterior  limbs  of  the  Sylvian  fissure,  between  which  it  lies.  When  strongly 
developed,  it  sejjarates  the  two  Sylvian  limbs  from  each  other  to  such  an  extent  that  tli(!y  assume 
tlie,  ap]>earance  of  the  letter  U  ;  when  tlu;  frcmtal  o])ei'culum  is  less  strongly  marked,  the  anterior 
Sylvian  limbs  may  assume  a  V  form  or  a  Y  form.  In  the  latter  case,  the  orbital  and  the  fnjnto- 
parietal  opercula  meet  below  tlie  frontal  operculum  to  form  the  stem  of  the  Y.     In  those  cases 


558 


THE  NEEVOUS  SYSTEM. 


Interlocking 
gyi'i 


Ascending 

parietal 

convolution 


where  tlie  frontal  operculuiu  is  absent  altogether,  a  single  anterior  limb  of  the  Sylvian  fissnre  is 
the  resnlt. 

The  late  appearance,  the  slow  growth,  the  variability  of  tliese  two  opercula,  and  also  the 
tendency  to  abortive  growth  or  conij^lete  sujjjjression  of  the  frontal  ojjerculum,  all  bespeak  the 
fact  that,  from  a  jjliylogenetic  point  of  view,  the  frontal  and  orljital  opercula  are,  comj^aratively 
speaking,  recent  productions  in  the  evolution  of  th(i  human  brain.  In  tlie  anthropoid  ajje  they 
are  absent,  and,  consequently,  the  fore-ijart  of  the  island  of  Reil  is  exposed  on  the  surface  of  the 
simian  brain.  The  same  condition  is  not  at  all  an  uncommon  occurrence  in  the  brain  of  the 
microceplialic  idiot. 

Fissure  of  Rolando  (sulcus  centralis j. — The  fissure  of  Eolando  takes  an  oblique 
course  across  the  outer  convex  surface  of  the  cerebral  hemisphere,  and  intervening 
between  the  frontal  and  parietal  lobes  it  forms  the  immediate  posterior  boundary 
of  the  motor  area  of  the  cortex.  Its  upper  end  cuts  the  supero-mesial  border  of 
the  hemisphere  a  short  distance  behind  the  mid-point  between  tlie  frontal  and 
occipital  poles,  whilst  its  lower  end  terminates  above  the  middle  of  the  posterior 
horizontal  limb  of  tlie  fissure  of  Sylvius.     Its  superior  extremity,  as  a  rule,  turns 

round  the  supero-mesial  border  of  the 
hemisphere,  and  is  then  continued  back- 
wards for  a  short  distance  on  the  mesial 
surface.  Although,  in  its  general  direc- 
tion, the  fissure  is  oblique,  it  is  very  far 
from  being  straight.  It  takes  a  sinuous 
course  across  the  hemisphere.  This  is 
largely  due  to  the  area  of  cortex  which 
represents  the  motor  centre  for  the  arm, 
and  which  lies  in  front  of  the  sulcus, 
growing  backwards  in  the  course  of  its 
development  so  as  to  produce  a  bay  in 
the  fissure  within  which  this  portion  of 
the  cortex  is  accommodated.  The  bends 
in  the  fissure  which  indicate  the  upper 
and  lower  limits  of  the  arm  centre  (Grtin- 
bauni  and  Sherrington)  are  termed 
respectively  the  superior  and  iihferior 
genua.  The  angle  which  the  general 
direction  of  the  fissure  of  Eolando  makes 
with  the  mesial  plane  is  termed  the 
Rolandic  angle.  In  the  adult  brain  the 
average  Eolandic  angle  is  71°  7',  and  the  limits  of  variation  would  appear  to  be  69° 
and  74'. 

When  the  fissure  of  Rolando  is  widely  opened  up,  so  that  its  bottom  and  its  opposed  sides  may 
be  fully  inspected,  it  will  be  seen  that,  between  the  two  genua,  the  two  bounding  convolutions  are 
dovetailed  into  each  other  by  a  number  of  interlocking  gyri,  which  do  not  aj)pear  on  the  surface 
(Fig.  449).  Further,  two  of  these,  placed  on  opposite  sides  of  the  fissure,  are  frequently  joined 
across  the  bottom  of  the  sulcus  in  the  form  of  a  sunken  bridge  of  connexion,  which  constitutes 
what  is  termed  a  deep  annectant  gyrus.  The  continuity  of  the  fissure  is  thus,  to  some  extent, 
interrupted.  This  condition  is  rendered  interesting  when  considered  in  connexion  with  the 
development  of  the  sulcus.  The  deep  interlocking  gyri  indicate  a  great  exuberance  of  cortical 
growth  in  this  situation  in  the  early  stages  of  the  develojament  of  the  fissure  ;  and  the  j)resence  of 
the  deep  annectant  gyrus  is  exjilained  by  the  fact  that  the  fissure  of  Rolando  generally  develops  in 
two  pieces,  which  run  into  each  other  to  form  the  continuous  sulcus  of  the  adult,  viz.  a  part  cor- 
responding to  the  lower  two-thirds,  and  an  uj)per  part,  which  represents  the  upjDer  third  and 
which  appears  at  a  slightly  later  date.  In  certain  very  rare  cases  the  fissure  of  Rolando  is  found  to 
remain  double  throughout  life,  through  a  failure  of  its  two  pieces  to  unite.  In  such  cases  the  deep 
annectant  gyrus,  which  is  frequently  seen  at  the  bottom  of  the  furrow,  remains  on  the  surface. 
Heschl,  who  examined  2174  cerebral  hemisj)heres,  only  found  this  anomaly  six  times  ;  Eberstaller 
met  with  it  twice  in  200  brains. 

Parieto-occipital  Fissure. — A  small  part  of  this  fissure  appears  on  the  outer 
face  of  the  cerebral  hemisphere.  For  the  most  part  it  is  situated  on  the  internal 
surface.  It  is  customary,  therefore,  to  describe  an  external  parieto-occipital  and 
an  internal  parieto-occipital  fissure.  It  must  be  clearly  understood,  however,  that 
they  are  directly  continuous  with  each  other  round  the  supero-mesial  border  of  the 


Fig.  449. — Fissure  of  Rolaxdo  fully  opened  up, 
so  as  to  exhibit  the  interlocking  gyri  and  deep 
annectant  gyrus  within  it. 


PAEIETO-OCCIPITAL  AND  COLLATERAL  FISSUEES. 


559 


hemisphere.     The    parieto- occipital    fissure   intervenes    between   tlie  parietal  and 
occipital  lobes. 

The  external  parieto-occipital  fissure  cuts  the  supero-mesial  border  of  the  hemi- 
sphere in  a  transverse  direction  at  a 
distance  of  from  one  and  a  half  to  two 
inches  in  front  of  the  occipital  pole. 
It  is,  as  a  rule,  not  more  than  about  a 
half  an  inch  long,  and  it  is  brought 
to  an  abrupt  termination  by  an  arching 
convolution,  which   winds   round   its        Z'  ''p* 
extremity  and  receives    the  name  of       1 
arcus  parieto-occipitalis. 

The  internal  parieto-occipital  fissure 
is  carried  downwards  on  the  inner 
surface  of  the  hemisphere  in  a  nearly 
vertical  direction  as  a  conspicuous  and 
deep  cleft.  A  short  distance  behind 
the  hinder  end  of  the  corpus  callosum 
its  lower  extremity  runs  into  the 
calcarine  fissure. 


Fig.  450. — Left  Cebebral  Hemispheke,  from  a  foetus  in 
■    the  early  part  of  the  seventh  month  of  development. 

Sulcns  prsecentralis  superior. 
Sulcus  pi-asceutral is  inferior. 
Lower  part  of  Rolandic  fissure. 
Upper  part  of  Rolandic  fissure. 
Inferior  postcentral  sulcus  ^ 


p.c.s. 
l).c.i. 


Tlie  parieto-occipital  fissure  is  developed, 
as  a  rule,  after  tlie  manner  of  a  complete 
fissure.  In  the  foetal  brain  it  forms  a  very 
evident  infolding  of  tlie  cerebral  wall.  In 
the  adult  brain,  lioweA^er,  it  does  not  form 
any  eminence  on  the  inner  wall  of  the 
ventricle,  because  it  does  not  extend  down- 
wards as  far  as  the  cavity.  The  wall  of  the 
ventricle  during  the  growth  of  the  hemi- 
sphere has  thickened  to  such  an  extent  that  the  part  corresponding  to  the  fissure  has  become  solid. 

Collateral  Fissure  (fissura  collaterahs). — The  collateral  sulcus  is  a  strongly- 
marked  fissure  on  the  tentorial  face  of  the  cerebral  hemisphere.  It  begins  near 
the  occipital  pole  and  extends  forwards  towards  the  temporal  pole.  In  its  posterior 
part  it  is  placed  below,  and  parallel  to,  the  calcarine  fissure,  whilst  in  front  it  is 


p- 
P«. 

p^- 

e.p. 

t\ 

S. 

P.P. 

F. 

0. 


Ramus  horizontalis  V  Intraparietal  fissure. 

Ramus  occipitalis  j 

External  perpendicular  fissure  of  Bischoff. 

Parallel  sulcus. 

Sylvian  fossa. 

Fronto-parietal  wall. 

Frontal  wall. 

Orbital  wall. 


Fro.  4.')!.  -Thk  Gybi  and  Sulci  on  the  Mesial  Aspect  of  the  Cekebhal  Hemispheuh. 
r.  KisKiire  of  Rolando,     r.o.  Rostral  sulcus.     i.L  Incisura  temporalis. 

separated  from  the  hip])Ocam])al  or  dentate  fissure  by  the  ]ii]»p(icami>al  gyrus,  vvhicli 
is  the  innermost  convolution  on  the  tentorial  surface  of  the  hemisphere. 

In  front  of  the  anterior  extremity  of  the  collateral  fissure  a  shallow  sulcus  turns 
round  the  anterior  end  of  the  temporal  lobe,  so  as  to  inter v(me  between  the  temporal 


560 


THE  NEEVOUS  SYSTEM. 


pole  and  the  uncinate  or  hook-like  extremity  of  the  hippocampal  convolution. 
This  is  the  incisura  temporalis,  or  ecto-rhinal  fissure.  The  collateral  fissure  and  the 
incisura  temporalis  intervene  between  the  limbic  and  temporal  lobes. 

The  collateral  fissure  is  developed,  as  a  rule,  in  three  portions — a  hinder  or  occipital,  an 
intermediate,  and  an  anterior  or  temjjoral  part.  These  ultimately  run  into  each  other  and  form 
the  continuous  fissure.  The  middle  part  is  usually  a  complete  fissure  and  responsible  for  the 
production  of  the  eminentia  collateralis  posterior  in  the  floor  of  the  trigonum  of  the  lateral 
ventricle  ;  the  temporal  part  is  sometimes  a  complete  fissure,  forming  when  it  is  so  the  eminentia 
collateralis  anterior;  the  occipital  j^art  is  always  incomplete. 

Calloso-marginal  Fissure. — This  fissure  is  a  strongly-marked  sulcus  on  the 
fore-part  of  the  mesial  surface  of  the  hemisphere.  It  divides  the  front  portion  of 
the  mesial  surface  into  an  upper  marginal  and  a  lower  callosal  convolution,  and 
intervenes  between  the  frontal  and  limbic  lobes.  Beginning  below  the  fore-end  of 
the  corpus  callosum,  close  to  the  locus  perforatus  anticus,  the  calloso-marginal 
fissure  curves  round  in  front  of'  the  genu  of  the  corpus  callosum,  and  then  extends 
backwards  to  a  point  a  short  distance  behind  the  middle  of  the  mesial  surface.  It 
then  turns  upwards  and  cuts  the  supero-mesial  border  of  the  hemisphere,  immed- 
iately behind  the  upper  end  of  the  fissure  of  Eolando.  The  relation  presented  by 
the  two  extremities  of  these  fissures  is  such  that  they  can  both  be  readily  recognised 
either  when  examined  on  the  outer  or  mesial  aspect  of  the  cerebrum. 

The  calloso-marginal  sulcus  is  develoj)ed  in  two  or  three  separate  pieces,  which,  as  growth 
proceeds,  run  into  each  other  and  form  the  continuous  fissure.  The  irumerous  cases  of  irregular 
arrangement  met  with  in  connexion  with  this  fissure  can  generally  be  explained  by  this  inter- 
rupted mode  of  development. 

Frontal  Lobe. — The  Irontal  lobe  is  the  largest  of  the  cerebral  lobes.  On  the 
outer  surface  of  the  hemisphere,  it  is  bounded  behind  by  the  fissure  of  Eolando 
and  below  by  the  posterior  horizontal  limb  of  the  fissure  of  Sylvius.  On  the  mesial 
face  it  is  limited  by  the  calloso-marginal  fissure,  whilst  on  the  inferior  surface  of 
the  hemisphere  the  stem  of  the  Sylvian  fissure  forms  its  posterior  boundary.  It 
presents  an  outer  surface,  a  mesial  surface,  and  an  inferior  or  orbital  surface. 

On  the  outer  surface  of  the  frontal  lohe  the  following  sulci  and  gyri  may  be 
recocjnised : — 


Sulci  -, 


Sulcus  prsecentralis  inferior. 
Sulcus  praecentralis  superior. 
Sulcus  jjaramedialis. 
Sulcus  frontalis  superior. 
Sulcus  frontalis  medius. 
Sulcus  frontalis  inferior. 
Sulcus  diagonalis. 
V  Sulcus  fronto-mareinalis. 


Gyrus  frontalis  ascendens  or  gyrus 
centralis  anterior. 


Gyri  J. 


Gyrus  frontalis  superior 
Gyrus  frontalis  medius 

V  Gyrus  frontalis  inferior 


(j)SLTS  superior. 
\l3ars  inferior. 
fj)ars  superior. 
\_pars  inferior, 
/"pars  basilaris. 
I  pars  triangul- 
j  aris. 

I  pars  orbi talis. 


The  inferior  praecentral  sulcus  consists  of  a  vertical  and  a  horizontal  part,  and 
when  developed  in  a  typical  manner,  it  presents  a  figure  like  the  letter  T  or  F. 
The  vertical  portion  lies  in  front  of  the  lower  part  of  the  fissure  of  Eolando,  whilst 
the  horizontal  part  extends  obliquely  forwards  and  upwards  into  the  middle  frontal 
convolution. 

The  superior  prsecentral  sulcus  is  a  short  vertical  sulcus  which  lies  at  a  higher 
level  than  the  inferior  prsecentral  furrow,  in  front  of  the  upper  part  of  the  fissure 
of  Eolando.  It  is  almost  invariably  connected  with  the  hinder  end  of  the  superior 
frontal  sulcus. 

The  anterior  central  convolution  (ascending  frontal  gyrus)  is  a  long  continuous 
gyrus,  which  is  limited  in  front  by  the  two  prsecentral  furrows  and  behind  by 
the  fissure  of  Eolando.  It  extends  obliquely  across  the  hemisphere  from  the 
supero-mesial  margin  above  to  the  posterior  horizontal  limb  of  the  Sylvian  fissure 
below. 

The  superior  frontal  sulcus  extends  forwards  in  a  more  or  less  horizontal  direc- 
tion from  the  sulcus  prsecentralis  superior. 

The  gyrus  frontalis  superior  is  the  narrow  convolution  between  the  supero-mesial 


FEONTAL  LOBE.  561 

border  of  the  hemisphere  and  the  superior  frontal  sulcus.  It  takes  a  horizontal 
course  to  the  frontal  pole. 

The  inferior  frontal  sulcus  occupies  a  lower  level  than  the  superior  frontal  furrow. 
Its  hinder  end  is  placed  in  the  angle  between  the  vertical  and  horizontal  parts  of 
the  inferior  prsecentral  sulcus,  and  is  not  infrequently  confluent  with  one  or  other 
of  these.  It  proceeds  forwards  towards  the  superciliary  margin  of  the  hemisphere 
and  ends  a  short  distance  from  this  in  a  terminal  bifurcation. 

The  gyrus  frontalis  medius  is  the  name  given  to  the  broad  convolution  which 
lies  between  the  superior  and  inferior  frontal  sulci. 

The  gyrus  frontalis  inferior  is  that  portion  of  the  outer  surface  of  the  frontal 
lobe  which  is  placed  in  front  of  the  inferior  prsecentral  sulcus  and  below  the  inferior 
frontal  sulcus.  The  inferior  frontal  convolution  is  cut  into  three  pieces  by  two 
anterior  limbs  of  the  Sylvian  fissure.  These  are  termed  the  pars  basilaris,  the  pars 
triangularis,  and  the  pars  orbitalis. 

The  pars  basilaris  is  that  part  which  lies  between  the  vertical  limb  of  the  inferior 
prsecentral  sulcus  and  the  ascending  limb  of  the  Sylvian  fissure.  It  forms  the  anterior 
part  of  the  fron to-parietal  operculum,  and  it  is  traversed  in  an  oblique  direction  by 
a  shallow  but  constant  furrow,  termed  the  sulcus  diagonalis.  The  pars  triangularis  is 
simply  another  name  for  the  frontal  operculum.  It  is  triangular  in  form,  and  lies 
between  the  anterior  ascending  and  the  anterior  horizontal  limbs  of  the  Sylvian 
fissure.  The  pars  orbitalis  is  placed  below  the  anterior  horizontal  limb  of  the 
Sylvian  fissure. 

The  inferior  frontal  conyoliition  possesses  a  special  interest  on  account  of  the  localisation 
within  it,  on  the  left  side,  of  the  speech  centre.  From  it,  also,  the  front  ^^art  of  the  fronto-parietal 
and  the  whole  of  the  frontal  operculum  are  developed.  This  opercular  development  in  connexion 
with  the  inferior  frontal  gyrus  constitutes  a  leading  jDoint  of  difference  between  the  brain  of  man 
and  that  of  the  ape.  Even  in  the  highest  ape  the  inferior  frontal  convolution  is  not  opercular. 
The  frontal  oj)erculum  is  not  present  and  the  anterior  part  of  the  insula  is  exposed  on  the  surface. 
Probably  the  excess  of  growth  which  determines  the  formation  of  the  frontal  operculum  in  man 
has  some  connexion  with  the  development  of  the  speech  centre. 

The  sulcus  paramedians  is  the  term  applied  to  a  series  of  short  irregular  depres- 
sions or  furrows,  arranged  longitudinally,  close  to  the  supero-mesial  border  of  the 
hemisphere.  These  rudimentary  sulci  partially  subdivide  the  superior  frontal  con- 
volution into  an  upper  and  a  lower  part,  and  they  are  of  interest  in  so  far  that  they 
are  not  as  a  rule  developed  in  the  higher  apes,  and  are  deeper  and  better  marked  in 
the  higher  than  the  lower  types  of  human  brain. 

The  sulcus  frontalis  medius  (Eberstaller)  proceeds  horizontally  forwards  in  the 
forepart  of  the  middle  frontal  convolution,  so  as  to  subdivide  it  into  an  upper  and  a 
lower  part.  When  the  furrow  reaches  the  superciliary  margin  of  the  hemisphere 
it  bifurcates,  and  its  terminal  branches  spread  out  widely  and  constitute  a  trans- 
verse furrow,  called  the  fr  onto -marginal  sulcus.  The  sulcus  frontalis  medius  is  only 
found  in  man  and  the  anthropoid  apes.     It  is  not  present  in  any  of  the  lower  apes. 

Owing  to  the  subdivision  of  the  superior  and  middle  frontal  convolutions  ill  the 
manner  indicated,  the  typical  arrangement  of  the  convolutions  in  the  anterior  part 
of  the  outer  surface  of  the  frontal  lobe  is  in  five  horizontal  tiers,  and  not  in  three 
tiers,  as  formerly  described. 

As  a  rule,  the  sulci  on  the  outer  surface  of  the  frontal  lobe  during  the  process  of  development 
appear  in  the  following  order :  (1)  sulcus  prsecentralis  inferior ;  (2)  sulcus  frontalis  inferior  ; 
(3)  sulcus  prajcentralis  superior  and  sulcus  frontalis  superior ;  (4)  sulcus  frontalis  medius ; 
(5)  sulcu.s  paraniedjalis.  This  gives  some  indication  of  the  relative  morphological  importance  of 
these  sulci,  although  it  should  be  borne  in  mind  that  the  period  at  which  sulci  appear  on  the 
foetal  brain  cannot  in  every  case  be  taken  as  affording  an  infallible  guide  in  our  attempts  to 
a.ssign  to  them  their  relative  morpliological  value. 

On  the  mesial  aspect  of  the  frontal  lohe  there  is  an  elongated  more  or  less 
continuous  convolution,  called  the  gyrus  marginalis.  It  lies  between  the  supero- 
mesial  margin  of  the  hemisphere  and  the  calloso-marginal  fissure.  In  the  fore-part 
of  this  gyrus  one  or  two  curved  sulci  are  usually  present.  They  are  termed  the 
sulci  rostrales.  The  posterior  part  of  the  marginal  convolution  is  more  or  less 
completely  cut  off  from  the  portion  wliich  lies  in  front.  This  part  is  called  the 
40 


562 


THE  NEEVOUS  SYSTEM. 


paracentral  lobule,  and  into  it  the  upper  end  of  the  fissure  of  Eolando  is  prolonged 

as  it  turns  over  the  supero-mesial  border  of  the  hemisphere. 

On  the  orbital  aspect  of  the  frontal  lobe  there  are  two  sulci,  viz.  the  olfactory 

and  the  orbital. 

The  olfactory  sulcus  is  a  straight  furrow  which  runs  parallel  to  the  mesial  border 

of  the  hemisphere.     It  is  occupied  by  the  olfactory  tract  and  l)ulb,  and  it  cuts  off  a 

narrow  strip  of  the  orbital  surface  close  to  the  mesial  border,  which  receives  the 

name  of  gryus  rectus. 

The  orbital  sulcus  is  a  composite  furrow  which  assumes  many  different  forms. 

As  a  general  rule  it  presents  a  shape  similar  to  that  of  the  letter  H,  and  is  then 

composed  of  three  parts,  viz.  an  external  limb,  an  internal  limb,  and  a  transverse 

limb.  The  external  limb  (sulcus 
orfjitalis  externiis)  curves  round 
the  orbital  part  of  the  inferior 
frontal  convolution,  so  as  to 
limit  it  on  this  aspect  of  the 
brain.  The  internal  limb  (sulcus 
orbi  talis  intern  us)  is  frequently 
broken  up  into  two  pieces.  It 
marks  off  a  convolution  between 
itself  and  the  olfactory  sulcus, 
called  the  gyrus  orbitalis  in- 
ternus.  The  transverse  limb 
(sulcus  orbitalis  transversus) 
takes  a  curved  course  between 
the  internal  and  external  limbs. 
The  district  in  front  is  termed 
the  gyrus  orbitalis  anterior,  and 
that  behind  the  gyrus  orbitalis 
posterior.  The  latter,  in  its 
outer  part,  corresponds  with  the 
orbital  operculum. 

Parietal  Lobe.  —  The 
parietal  lobe  forms  a  consider- 
able part  of  the  external  surface 
of  the  cerebral  hemisphere,  and 
it  also  appears  on  the  inner 
surface  in  the  form  of  the  pre- 
cuneus or  the  quadrate  lobule. 
In  front,  it  is  bounded  by  the 

Fig.  452.— Gyri  and  Sulci  on  the  tentorial  and  orbital  aspects    fissure  of  Eolando,  which  separ- 
of  the  cerebral  hemispheres.  ^^^^    -^    f^,^^^^    ^^^^    f^,^^^^^    j^^^^ 

Below,  it  is  limited  in  its  fore-part  by  the  posterior  horizontal  limb  of  the  fissure  of 
Sylvius.  Behind  the  upturned  end  of  this  fissure  the  surface  of  the  parietal  lobe 
is  continuous  inferiorly  with  that  of  the  temporal  lobe,  and  an  arbitrary  line  drawn 
backwards  on  the  surface  of  the  brain,  in  continuation  of  the  horizontal  part  of  the 
posterior  limb  of  the  Sylvian  fissure,  is  taken  as  its  inferior  limit.  Posteriorly,  it 
is  separated  from  the  occipital  lobe  at  the  supero-mesial  border  of  the  hemisphere 
by  the  external  parieto-occipital  fissure.  Below  this  fissure  the  surface  of  the 
parietal  lobe  is  continuous  with  that  of  the  occipital  lobe ;  and  an  arbitrary  line 
drawn  across  the  outer  surface  of  the  hemisphere,  from  the  extremity  of  the  external 
parieto-occipital  fissure  to  an  indentation  on  the  infero-lateral  border  of  the  hemi- 
sphere, termed  the  prseoccipital  notch,  may  be  regarded  as  furnishing  a  posterior 
limitation. 

The  prfeoccipital  notcli  is,  as  a  rule,  only  visible  in  brains  that  have  been  hardened  mi  sihi.  It 
is  i^laced  on  the  infero-lateral  border  of  the  hemisphere,  about  an  inch  and  a  half  in  front  of  the 
occipital  pole,  and  is  produced  liy  a  vertical  fold  or  Avrinkle  of  the  dura  mater  on  the  deep  aspect 
of  the  parieto-niastoid  suture,  and  immediately  above  the  hi^diest  part  of  the  lateral  blood-sinus. 

There  is  great  variability  in  the  degree  to  which  this  fold  of  dura  mater  projects  in  different 


PAKIETAL  LOBE. 


;63 


iudividuals.  In  the  child  it  is  always  very  salient,  and  often  produces  a  deep  cleft  in  the  brain, 
but  as  the  full  size  of  the  cranium  is  gradually  attained  it  becomes  much  less  projecting.  In  the 
young  skull  t\yo  or  three  such  folds  in  this  locality  are  frequently  apparent.  Eelated  to  the  prae- 
occipital  notch  there  are  likewise  some  cerebral  veins  which  turn  round  the  infero-lateral  margin 
of  the  hemisphere  to  join  the  lateral  blood-sinus. 

On  the  mesial  surface  of  the  hemis'phere  the  parietal  lobe  is  -represented  by 
the  prsecuneus  or  quadrate  lobule.  This  district,  which  is  somewhat  quadrilateral  in 
form,  hes  between  the  upturned  end  of  the  calloso-marginal  sulcus  and  the  internal 
parieto-occipital  fissure.  It  is  imperfectly  separated  below  from  the  limbic  lobe  by 
a  somewhat  variable  furrow  called  the  post-limbic  sulcus. 

The  gyri  and  sulci,  on  the  outer  surfax,e  of  the  jparietal  lohe,  are  the  following  : — 


Sulcus  intrapari- 
etalis  (of  Tur- 
ner). 


Sulci  i 


Upturned  ends  of- 

(a)  Sylvian  fissure. 

(b)  Parallel  fissure. 

(c)  Second  tempo- 

ral fissure. 


Sulcus  postcentralis 

inferior. 
Sulcus  postcentrahs 

superior. 
Ramus  horizontalis. 
I  Ramus  occipitalis. 


Gyri 


Gyras    ascendens    parietaUs    or    g}Tus 

postcentralis. 
Gyrus  parietalis  superior. 


Gyrus  parietalis  inferior 


Gyrus  supra - 
marginaliij. 

Gyrus  angu- 
laris. 

Gyrus  post- 
parietalis. 


The  intraparietal  sulcus  (of  Turner)  is  a  composite  furrow,  and  is  built  up 
of  four  originally  distinct  factors.  Two  of  these,  termed  the  sulcus  postcentralis 
inferior  and  the  sulcus  postcentralis  superior,  take  a  more  or  less  oblique  course 
across  the  hemisphere,  and  are  most  frequently  united  into  one  continuous  fissure. 
The  other  two  factors  are  placed  horizontally,  one  behind  the  other,  and  are  termed 
the  ramus  horizontalis  and  the  ramus  occipitalis. 

The  sulcus  postcentralis  inferior  lies  behind  the  lower  part  of  the  fissure  of 
Eolando,  whilst  the  sulcus  postcentralis  superior  occupies  a  similar  position  in 
relation  to  the  upper  part  of  that  fissure.  When  confluent  they  form  a  long,  con- 
tinuous fissure,  which  stretches  across  the  hemisphere  behind  the  fissure  of  Eolando 
and  parallel  to  it. 

The  ramus  horizontalis  is  continuous,  as  a  rule,  with  the  upper  end  of  the  sulcus 
X^ostcentralis  inferior,  and  extends  backwards,  with  a  slight  inclination  upwards 
between  the  superior  parietal  gyrus,  which  lies  above  it,  and  the  inferior  parietal 
gyrus,  which  is  jjlaced  below  it.  With  the  two  confluent  postcentral  sulci  it 
presents  a  figure  hke  the  letter  H  placed  on  its  side. 

The  ramus  occipitalis  is  a  curved  sulcus  which  bounds  externally  the  arcus 
parieto-occipitalis,  or,  in  other  words,  the  arching  convolution  which  surrounds  the 
external  parieto-occipital  fissure.  The  ramus  occipitalis  lies  behind  the  ramus 
horizontalis,  and  is  generally  Knked  on  to  it ;  less  frequently  it  is  separate.  The 
posterior  end  of  the  ramus  occipitalis  enters  the  occipital  lobe,  and,  behind  the  arcus 
parieto-occipitaKs,  bifurcates  into  two  widely  spread-out  branches.  These  form  a 
short  transverse  fissure  in  the  occipital  lobe,  termed  the  sulcus  occipitalis  transversus 

In  the  human  braiu  the  intraparietal  sulcus  is  usually  developed  in  four  separate  pieces, 
corresponding  to  the  four  portions  of  the  fissure  which  have  been  described  as  being  present  in 
the  adult  brain.  The  sulcus  postcentralis  inferior  appears  first  (somewhere  about  the  end  of  the 
sixth  month),  then  the  ramus  occipitalis  and  the  ramus  horizontalis  ;  last  of  all  the  sulcus  post- 
centralis superior  comes  into  view.  The  fui-ther  development  of  the  sulcus  consists  in  the 
running  together  of  these  early  pieces.  This  takes  place  in  different  ways,  and  not  infrequently 
union  fails  at  one  or  more  points,  and  thus  a  great  variety  of  combinations  may  be  noted 
in  different  individuals  ;  indeed,  it  may  be  said  that  every  possible  kind  of  combination  may  be 
met  with.  The  most  common  form  which  the  fissure  assumes,  however,  is  that  in  which  all  its 
factors  have  become  confluent  and  one  continuous  furrow  results.  When  such  an  intraparietal 
furrow  is  widely  opened  up,  certain  deep  annectant  gyri,  which  cross  the  bottom  of  the  sulcus, 
come  into  view.  These  inttirrupt  the  sulcus  at  the  points  of  union  between  its  several  pieces  and 
indicate  its  original  multiple  formation. 

There  is  rea.son  to  believe  that  three  of  the  elements  of  the  human  intraparietal  sulcus,  viz. 
the  sulcus  postcentralis  inferior,  the  ramus  horizontalis,  and  the  ramus  occipitalis,  are  disrupted 
portions  of  the  primitive  single  continuous  fissure  which  is  seen  in  certain  of  the  lower  apes 
(Cebus),  whilst  one,  the  sulcus  postcentralis  superior,  is  a  superadded  element. 

There  is  a  strong  analogy  between  the  postcentral  sulcus,  the  fissure  of  Rolando,  and  the 
40  a 


564 


THE  NEEVOUS  SYSTEM. 


prsecentral  sulcus.  They  form  a  group  of  radial  sulci  on  the  outer  surface  of  the  foetal  cerebrum 
above  the  Sylvian  region.  The  fissure  of  Rolando  makes  its  appearance  first,  then  the  prsecentral 
sulcus,  and,  lastly,  the  postcentral  sulcus.  Each  assumes  sliape  in  the  first  instance  in  two  pieces, 
Adz.  an  upper  and  lower.  The  two  pieces  of  the  fissure  of  Eolando  join  early,  and  only  in  very 
rare  instances  remain  separate  ;  the  two  pieces  of  the  postcentral  furrow  usually  join,  but  in  19 
per  cent  of  cerebral  hemispheres  they  remain  separate  ;  the  two  pieces  of  the  prtecentral  furrow, 
as  a  rule,  remain  separate  and  distinct. 

The  sulcus  transversus  occipitalis,  or  bifurcated  extremity  of  the  ramus  occipitalis,  has  been 


Ascending  parietal  gy 


Termination  of  Sylvian  fissure 

Fig.  453. — The  Intraparietal  Sulcus  fully  opened  up,  so  as  to  show  its  several  parts  and  the 
deep  annectant  gyri  intervening  between  them. 

pi.  Sulcus  postcentralis  inferior.  p-*.    Ramus  horizontalis. 

p-.  Sulcus  postcentralis  superior.  p'*.   Ramus  occipitalis. 

until  lately  generally  believed  to  be  the  representative  in  the  human  brain  of  the  conspicuous 
"  Affenspalte,"  in  the  cerebrum  of  the  ape.  The  accuracy  of  this  view  was  challenged,  in  1892 
(Gunninghavi  Memoir,  No.  vii.  Roy.  Irish  Acad.),  and  recently  Elliot  Smith  has  brought  forward 
evidence  of  a  very  convincing  kind  which  seems  to  show  that  in  the  human  brain  the  "  Affen- 
spalte "  is  represented  by  the  sulcus  occipitalis  lateralis  of  Eberstaller. 

The  intraparietal  sulcus  maps  out  three  districts  or  gyri  on  the  external  surface 
of  the  parietal  lobe,  viz.  the  posterior  central  convolution,  the  superior  parietal 
gyrus,  and  the  inferior  parietal  gyrus. 

The  upturned  ends  of  the  fissure  of  Sylvius,  of  the  first  temporal  or  parallel 
sulcus,  and  of  the  second  temporal  sulcus  ascend  for  a  short  distance,  one  behind 
the  other,  into  the  inferior  parietal  gyrus. 

The  posterior  central  convolution  (ascending  parietal  convolution)  is  a  long  gyrus 
which  extends  obliquely  across  the  hemisphere  from  the  supero-mesial  border  above 
to  the  Sylvian  fissure  below.  It  is  bounded  in  front  by  the  fissure  of  Eolando  and 
behind  by  the  superior  and  inferior  postcentral  sulci. 

The  superior  parietal  gyrus  is  the  area  of  cerebral  cortex  which  lies  between  the 
supero-mesial  border  of  the  hemisphere  above  and  the  ramus  horizontahs  below.  In 
front  it  is  bounded  by  the  superior  postcentral  sulcus,  whilst  behind  it  is  connected 
with  the  occipital  lobe  by  the  arcus  parieto-occipitalis.  It  is  continuous  round  the 
supero-mesial  border  with  the  prsecuneus. 

The  inferior  parietal  gyrus  lies  below  the  ramus  horizontalis  and  the  ramus  occi- 
pitalis and  behind  the  inferior  praecentral  sulcus.  It  is  more  or  less  directly  con- 
tinuous with  the  occipital  lobe  behind  and  the  temporal  lobe  below.  From  before 
backwards  it  presents  three  arching  convolutions,  viz.  the  supra-marginal,  the 
angular,  and  the  postparietal.  The  supramarginal  convolution  is  bent  round  the 
upturned  end  of  the  posterior  limb  of  the  Sylvian  fissure,  and  stands  in  continuity 
behind  and  below  this,  with  the  first  temporal  gyrus.  The  angular  convolution 
arches  over  the  upturned  end  of  the  parallel  sulcus  and  becomes  continuous  with 
the  second  temporal  convolution.'  The  postparietal  convolution  winds  round  the 
upturned  end  of  the  second  temporal  sulcus  and  runs  into  the  thu'd  temporal  gyrus. 

Occipital  Lobe. — The  occipital  lobe  forms  the  hinder  pyramidal  part  of  the 


OCCIPITAL  LOBE. 


>65 


cerebral  hemisphere ;  and  although  very  imperfectly  mapped  off  from  the  temporal 
and  parietal  lobes,  which  lie  in  front  of  it,  it  is  nevertheless  one  of  the  most  natural 
subdivisions  of  the  cerebral  hemisphere.  It  is  not  'develoxjed  in  the  brain  of  the 
quadruped.  Man  and  the  ape  alone  possess  a  well-marked  occipital  lobe,  and  it 
may  be  defined  as  being  that  part  of  the  hemisphere  which  encloses  the  jjosterior 
horn  of  the  lateral  ventricle.  Being  pyramidal  in  form,  it  presents  three  surfaces 
and  an  apex  or  occipital  pole.  On  the  mesial  aspect  of  the  hemisphere  it  is 
separated  from  the  parietal  lobe  {i.e.  the  precuneus)  by  the  internal  parieto-occi- 
pital  fissure.  On  the  tentorial  or  inferior  surface  it  is  not  marked  off  in  any  way 
from  the  temporal  lobe  and  the  limbic  lobe,  which  lie  in  front  of  it.  It  is  necessary, 
therefore,  on  this  aspect  to  employ  an  arbitrary  line  of  demarcation ;  one  which 
extends  from  the  prseoccipital  notch  on  the  infero-lateral  border  of  the  hemisphere 
to  the  isthmus  of  the  limbic  lobe  (i.e.  the  narrow  part  of  the  limbic  lobe  immedi- 
ately below  the  hinder  end  of  the  corpus  callosnm)  will  serve  the  purpose.  On  the 
external  surface  the  external  parieto-occipital  fissure,  and  an  arbitrary  line  from 
this  to  the  prseoccipital  notch,  may  be  regarded  as  separating  the  occipital  from  the 
parietal  and  temporal  lobes.  The  upturned  end  of  the  second  temporal  sulcus  may 
Lie  in  the  course  of  this  line. 

On  the  mesial  aspect  of  the  occipital  lobe  we  find :  (1)  the  calcarine  fissure, 
(2)  the  cuneus,  and  (3)  the  gyrus  lingualis. 

The  calcarine  fissure  begins  on  the  occipital  pole  by  a  bifurcated  extremity, 
which  lies  in  the  groove  which  is  formed  on  this  part  of  the  brain  by  the  lateral 
sinus.  From  this  it  pursues  a  slightly  arched  course  forwards,  and  ends  by  cutting 
into  the  limbic  lobe  immediately  below  the  spleuium  or  thickened  hinder  margin  of 
the  corpus  callosum.  The  calcarine  fissure  is  joined  by  the  internal  parieto-occipital 
fissure  at  a  point  som^ewhat  nearer  its  anterior  than  its  posterior  extremity. 
Together,  the  two  fissures  present  a  -<-shaped  figure.  Between  the  two  limbs  of 
the  Y  is  placed  the  cuneus. 

If  tlie  calcarine  and  internal  parieto-occipital  fissures  are  opened  up  so  as  to  expose  the 
bottom  in  each  case,  three  well-marked  deep  or  submerged  annectant  gyri  will  usually  be  dis- 
played.   One  of  these,  the  best  marked,  called  the  gyrus  cunei,  marks  off  the  parieto-occipital  from 


Callosal  gyrus 


Corpus  callosum 


Parieto-occipital  fissure 


Cuneus 

Anterior  cuneo- 

lingual  gyrus 

Posterior  calcariuf; 

'Issure 

Posterior  cuneo- 

liiigual  gyrus 


_♦_  "__3>MiUU«. 


Anterior  calcarine 
fissure 


(iyrus  lingualis 
Collateral  fissure 


Fid.    4.54. — iNTEKNAIy  PaKIETO-OCC'II'ITAI,  ANO  THK  CaI.CAHINK   FiSSUEES  KULLY    Ol'ENEO  UP,  so  as  to  show  tlie 
fleep  annectant  gyri  marking  ofl' tin;  several  cleniciits  of  the  ^-shaped  system. 


the  calcarine  fiHHurc- and  joins  tlie  (;uiieus  witii   the  liiiiljic  lol)e.     In  the  chinipanzc^e  and  in  the 
lower  ajtf.H  the  gyms  cunei   in  on  tlie  Htiri'acc,  and  there  is  no  coniniunication  between  the  two 
fiseures  ;  in  tlie  orang,  gibbon,  and  microcephalic  idiot,  it  may  either  ha  submerged  or  on  the 
40  b 


566 


THE  NERVOUS  SYSTEM. 


surface.  The  second  deep  annectant  gyrus,  termed  the  anterior  cuneo-lingual,  crosses  the  bottom 
of  the  calcarine  fissure  a  short  distance  behind  the  point  where  it  is  joined  by  the  parieto-occi- 
pital  fissure,  and  divides  it  into  an  anterior  and  a  jiosterior  part.  Thu  anterior  calcarine  fissure  is 
slightly  longer  and  much  deeper  than  the  posterior  part.  It  includes  the  whole  of  tlie  stem  of 
the  Y-shaped  fissural  arrangement  and  extends  backwards  for  a  short  distance  into  the  cuneus. 
It  is  the  conqjlete  part  of  the  fissure  and  gives  rise  to  an  elevation  on  the  inner  wall  of  the 
posterior  horn  of  the  lateral  ventricle,  to  which  the  name  of  calcar  avis  or  hippocamijus  minor  is 
given.  The  posterior  calcarine  fissure  is  shallower  and  is  usually  interrupted  by  the  third  deep 
annectant  gyrus,  viz.  the  posterior  cuneo-lingual ;  this  divides  it  into  two  parts,  of  which  the 


■^■^L...,.^^^^l^^^^y^~~--^^  » 


Fig.  455. — Development  of  the  Parieto-occipital  and  tue  Caluauine  Fissures. 

A,  Mesial  aspect  of  a  left  cerebral  hemisphere  of  a  foetus  approaching  the  end  of  the  fifth  month  of  develop- 
ment ;  B,  Mesial  aspect  of  a  right  cerebral  hemisphere  of  a  foetus  in  the  beginning  of  the  seventh 
mouth  of  development. 

S.L.  Septum  luciduni.  c'.      Anterior  calcarine  fissure. 

f.       Fornix.  c'-.  "j 

U.     Uncus.  c'\  j 

g.d.  Gyrus  dentatus.  c.a.    Anterior  collateral  fissure. 

p.o.   Parieto-occiiJital  fissure.  cm.  Mid-collateral  fissure. 


Two  paits  of  posterior  calcarine  fissure. 


hinder  is  little  more  than  the  bifurcated  extremity  of  the  fissure.  Very  frequentlj^  this  deep 
gyrus  reaches  the  surface,  and  then  the  hinder  end  of  the  sulcus  is  completely  cut  off.  The 
posterior  calcarine  fissure  is  not  a  complete  fissure. 

When  the  manner  in  which  the  calcarine  fissure  is  developed  is  studied,  the  various  a2:)pear- 
ances  which  come  into  view  when  the  bottom  of  the  adult  fissure  is  inspected  receiA^e  the  fullest 
explanation.  The  anterior  calcarine  fissure  is  formed  very  early  as  an  infolding  of  the  wall  of 
the  cerebral  hemisphere.  The  posterior  calcarine  fissure  is  a  secondary  formation.  It  appears 
much  later,  and  usually  in  two  pieces,  which  run  together  and  then  join  the  anterior  calcarine 
fissure.     The  points  of  union  are  indicated  in  the  adult  by  the  two  cuneo-lingiial  deep  gyri. 

The  cuneus  is  the  wedge-shaped  or  triangular  district,  on  the  mesial  aspect  of 
the  occipital  lobe,  which  lies  between  the  internal  parieto-occipital  and  calcarine 
fissures. 

The  gyrus  lingualis  is  a  well-marked  convolution  between  the  calcarine  fissure 
above  and  the  posterior  part  of  the  collateral  fissure  below,  which  stretches 
forwards  from  the  occipital  pole.  Anteriorly,  it  becomes  very  narrow  and  joins 
the  hippocampal  part  of  the  limbic  lobe.  It  lies  partly  on  the  mesial  surface  and 
partly  on  the  tentorial  surface  of  the  occipital  lobe. 

On  the  tentorial  surface  of  the  occipital  lohe  there  is  only  one  convolution, 
viz.  the  posterior  part  of  the  occipito- temporal  gyrus.  It  proceeds  continuously 
forwards  into  the  temporal  lobe  on  the  outer  side  of  the  collateral  fissure,  and  is 
bounded  externally  by  the  occipito-temporal  sulcus,  a  furrow  which  is  rarely  con- 
tinuous, but  is  usually  represented  by  a  series  of  detached  pieces. 

There  are  two  well-marked  sulci  on  the  external  surface  of  the  occipital  lohe, 
viz.  the  sulcus  occipitalis  transversus  and  the  sulcus  occipitalis  lateralis.  The  sulcus 
occipitalis  transversus  extends  transversely  across  the  upper  part  of  the  lobe,  behind 
the  arcus  parieto-occipitalis.  As  already  explained,  it  is  the  terminal  bifurcation  of 
the  ramus  occipitalis  of  the  intraparietal  sulcus.  The  sulcus  occipitalis  lateralis- is 
a  short  horizontal,  often  sharply-curved,  furrow,  which  divides  the  outer  surface  of 
the  lobe  into  an  upper  and  a  lower  area  of  very  nearly  equal  exter^t.  These  areas 
are  connected  by  superficial  annectant  gyri  with  the  parietal  and  temporal  lobes. 

Elliot  Smith  has  brought  forward  very  convincing  proof  in  favour  of  regarding  the 
sulcus  occipitalis  lateralis  as  the  representative  of  the  "  AfFenspalte  "  in  the  brain  of  the 


TEMPOEAL  LOBE.  567 

ape.  He  calls  it  the  sulcus  lunatus  occipitalis,  and  shows  that  in  the  brains  of  Egyptian 
Fellaheen  it  not  infrequently  possesses  an  operculum,  and  presents  an  appearance  which 
closely  corresponds  with  the  condition  distinctive  of  the  gorilla.  The  same  may  occasion- 
ally be  seen  in  the  brain  of  the  aboriginal  Australian. 

Temporal  Lobe.- — -The  temporal  lobe  lies  behind  the  stem  and  below  the 
posterior  horizontal  limb  of  the  Sylvian  fissure.  It  is  somewhat  pyramidal  in  form, 
and  presents  an  upper,  an  outer,  and  a  tentorial  surface,  with  a  free  projecting  apex 
or  pole.  Above,  it  is  bounded  by  the  posterior  horizontal  limb  of  the  fissure  of 
Sylvius,  together  with  the  artificial  line  which  is  drawn  backwards  from  this.  On 
the  tentorial  face  it  is  separated  from  the  hippocampal  part  of  the  limbic  lobe  by 
the  collateral  fissure,  whilst  behind  it  is  marked  off  from  the  occipital  lobe  by  the 
artificial  lines  already  described.  The  temporal  pole  projects  forwards  on  the  under 
surface  of  the  brain  beyond  the  stem  of  the  Sylvian  fissure.  It  should  be  noticed 
that  the  recurved  end  of  the  hippocampal  part  of  the  limbic  lobe  (uncus),  which  lies 
to  the  inner  side  of  the  temporal  pole,  does  not  extend  so  far  forwards  as  the  latter, 
and  is  separated  from  the  pole  by  the  incisura  temporalis  or  ecto-rhinal  fissure. 

The  u'p'per  or  opercular  surface  of  the  temporal  lohe  is  turned  towards  the 
island  of  Eeil  and  the  fronto- parietal  operculum.  The  fissure  of  Sylvius  must, 
therefore,  be  widely  opened  up  to  expose  it.  For  the  most  part  the  surface  is 
smooth,  but  towards  the  back  part  there  are  a  few  transverse  furrows,  which 
separate  two  or  three  weakly-expressed  gyri. 

The  anterior  transverse  gyrus  is  much  more  strongly  expressed  in  the  foetal  than  in  the  adult 
brain.  It  appears  in  the  early  part  of  the  seventh  month,  and  is  only  subsequently  completely 
hidden  within  the  Sylvian  fissure.  The  fact  of  the  auditory  centre  being  localised  in  this  region 
of  the  temporal  lobe  makes  this  fact  of  interest. 

On  the  deep  surface  of  the  temporal  pole  there  are  also  a  few  feeble  furrows. 

On  the  outer  surface  of  the  temporal  lohe  there  are  two  horizontal  sulci,  called 
respectively  the  first  temporal  or  parallel  and  the  second  temporal  sulcus. 

The  parallel  sulcus  is  a  long,  continuous,  and  deep  fissure,  which  begins  near  the 
temporal  pole  and  proceeds  backwards  below  the  posterior  limb  of  the  Sylvian 
fissure.  Its  hinder  end  turns  upwards  into  the  parietal  lobe  and  is  surrounded  by 
the  angular  gyrus.  The  second  temporal  sulcus  is  placed  midway  between  the 
parallel  sulcus  and  the  infero-lateral  border  of  the  hemisphere.  It  is  very  rare  to 
find  it  in  the  form  of  a  continuous  cleft ;  usually  it  is  broken  up  into  several 
isolated  pieces,  one  behind  the  other.  Its  hinder  part,  which  turns  upwards  into 
the  parietal  lobe,  lies  close  to  the  artificial  line  of  demarcation  between  the  occipital 
and  parietal  lobes,  and  is  surrounded  by  the  postparietal  gyrus. 

By  the  two  temporal  sulci  the  outer  surface  of  the  temporal  lobe  is  mapped  out 
into  three  tiers  of  horizontal  convolutions,  which  are  termed  the  first,  second,  and 
third  temporal  gyri. 

On  the  tentorial  surface  of  the  temporal  lohe  there  is  one  fissure,  termed  the 
occipito-temporal  sulcus.  The  occipito -temporal  sulcus  lies  to  the  outer  side  of  the 
collateral  fissure  and  close  to  the  infero-lateral  margin  of  the  hemisphere.  It  runs 
in  an  antero- posterior  direction,  and  is  not  confined  to  the  temporal  lobe,  but 
extends  backwards  towards  the  occipital  pole.  It  is  usually  broken  up  into  two 
or  more  separate  pieces. 

The  occipito-temporal  convolution  is  situated  between  the  collateral  fissure  and 
the  occipito-temporal  sulcus.  It  extends  from  the  occipital  pole  behind  to  the 
temporal  pole  in  front. 

The  narrow  strip  of  surface  on  the  outer  side  of  the  occipito-temporal  sulcus  is 
continuous,  round  the  infero-lateral  margin  of  the  hemisj^here,  with  the  third 
temporal  convolution  on  the  outer  surface  of  the  cerebrum,  and  may  be  reckoned 
as  a  part  of  it. 

The  tliree  temporal  convohitJons  and  tlie  occipito-temporal  convolutions  run 
into  each  other  at  the  temporal  pole. 

Island  of  Keil  or  Insula. — The  insula  is  a  triangular  and  somewhat  bulging 
field  of  cerebral  cortex,  which  lies  on  a  deeper  plane  than  the  general  surface  of  the 
hemlHyihere  and  is  hidden  from  view  by  tlx;  four  opcrcula  which  overlap  it.  It  is 
circumscribed  by  a  limiting  sulcus  ^sulcus  circularis),  already  described,  and  its 


568  THE  NERVOUS  SYSTEM. 

dependent  apical  part,  which  is  directed  downwards,  is  in  close  relation  to  the 
anterior  perforated  spot  and  the  Sylvian  vallecula.  Here  the  limiting  sulcus  is 
absent  and  the  gray  matter  on  the  surface  of  the  insula  passes  continuously  into 
the  anterior  perforated  spot.     The  place  of  transition  is  called  the  limen  insulae. 

The  insula  is  divided  into  several  diverging  convolutions  by  a  series  of  radiating 
sulci.  Of  the  latter,  one,  which  presents  the  same  direction  and  lies  in  the  same 
plane  as  the  fissure  of  Eolando,  receives  the  name  of  the  sulcus  centralis  insulse 
(Fig.  447,  0,  p.  557).  It  divides  the  insula  into  an  anterior  frontal  part  aud  a 
posterior  parieto -limbic  part. 

Limbic  Lobe. — This  lobe  is  seen  on  the  mesial  surface  of  the  hemisphere  in  the 
form  of  an  elongated  ring -like  convolution,  the  extremities  of  which  approach 
closely  to  each  other  at  the  locus  perforatus  anticus.  These  extremities  are  con- 
nected by  the  roots  of  the  olfactory  tract,  and  in  this  manner  the  limbic  ring  may 
be  considered  to  be  closed.  The  upper  part  of  the  limbic  lobe  is  placed  in  intimate 
relation  to  the  extremities  and  upper  surface  of  the  corpus  callosum,  and  receives 
the  name  of  callosal  convolution  or  gyrus  fornicatus.  The  lower  portion  of  the 
lobe  is  termed  the  hippocampal  convolution  and  forms  the  inner  part  of  the 
tentorial  surface  of  the  hemisphere.  The  continuity  between  the  hippocampal 
gyrus  and  the  callosal  convolution  is  established  below  the  hinder  end  of  the  corpus 
callosum  by  a  narrow  portion  of  the  limbic  lobe,  called  the  isthmus.  From  this 
point  the  hippocampal  convolution  extends  forwards  towards  the  temporal  pole. 
Finally,  on  the  side  of  the  crus  cerebri,  the  hippocampal  gyrus  is  folded  back  on 
itself  and  ends  in  a  recurved  hook-like  extremity  called  the  uncus.  The  uncus  does 
not  reach  so  far  forwards  as  the  temporal  pole. 

The  callosal  convolution  begins  below  the  anterior  end  of  the  corpus  callosum  at 
the  locus  perforatus  anticus,  and,  winding  round  the  genu  of  the  corpus  callosum,  it 
is  continued  backwards  on  its  upper  surface  to  its  hinder  thickened  extremity  or 
splenium.  Curving  round  this,  it  becomes  greatly  narrowed  through  the  calcarine 
fissure  cutting  into  it.  This  narrow  part  is  termed  the  isthmus,  and  constitutes  the 
link  of  connexion  between  the  callosal  gyrus  and  the  hippocampal  gyrus.  The 
callosal  gyrus  is  separated  from  the  marginal  convolution  by  the  calloso-marginal 
fissure,  and  behind  this  it  is  imperfectly  marked  off  from  the  prsecuneus  by  the 
post-limbic  sulcus.  The  furrow  which  separates  it  from  the  corpus  callosum  is 
termed  the  callosal  sulcus. 

The  hippocampal  convolution  is  bounded  on  the  outer  side  by  the  anterior  part 
of  the  collateral  fissure,  and  in  front  of  this  by  the  incisura  temporalis,  which 
separates  its  hooked  extremity,  or  uncus,  from  the  temporal  pole.  On  the  inner  side 
it  is  limited  by  the  hippocampal  or  dentate  fissure,  whilst  posteriorly  it  is  divided 
into  two  parts  by  the  anterior  extremity  of  the  calcarine  fissure.  Of  these,  the 
upper  is  the  isthmus,  which  connects  it  with  the  callosal  gyrus,  whilst  the  lower 
portion  brings  it  into  continuity  with  the  gyrus  lingualis.  The  surface  of  the 
hippocampal  convolution  is  covered  by  a  white  reticular  stratum  of  fibres,  termed 
the  substantia  reticularis  alba. 

Altliougli  the  hippocampal  convohition  and  uncus  in  descriptive  anatomy  are  classed  together 
there  is  a  marked  morjDhological  distinction  between  them.  The  uncus  is  the  feeble  representative 
in  man  of  the  important  i^yriform  lobe  in  certain  of  the  lower  mammals,  and  consequently  it 
belongs  to  the  rhinencephalon  ;  the  hippocam^^al  convolution,  on  the  other  hand,  is  to  be  regarded 
as  forming  a  part  of  the  neo-jycdUmn  of  Elliot  Smith.  The  unimjjortant  incisura  temporalis  of 
the  human  brain  in  lower  types  of  brain  in  which  the  rhinencephalon  bulks  largely  is  represented 
by  the  conspicuous  ecto-rhinal  fissure. 

Gyrus  Dentatus  and  the  Fimbria. — If  the  dentate  fissure,  which  lies  along 
the  inner  side  of  the  hippocampal  convolution,  be  opened  up,  the  gyrus  dentatus 
and  the  fimbria,  lying  side  by  side,  will  be  brought  into  view  (Fig.  451,  p.  559). 

The  fimbria  is  simply  a  portion  of  the  posterior  pillar  of  the  fornix  prolonged 
into  this  region.  It  is  a  conspicuous  band  of  white  matter,  which  presents  a 
prominent  free  border.  In  front  it  runs  into  the  recurved  extremity  of  the  uncus, 
whilst,  if  traced  backwards,  it  will  be  seen  to  curve  upwards  behind  the  posterior 
end  of  the  optic  thalamus  and  become  continuous  with  the  posterior  pillar  of  the 
fornix  below  the  hinder  part  of  the  corpus  callosum. 


GYKUS  DENTATUS. 


iG9 


The  gyrus  dentatus  is  the  free  edge  of  gray  matter  which  is  placed  between  the 
fimbria  and  the  deep  part  of  the  upper  surface  of  the  hippocampal  convohjtion. 
The  oroove  between  it  and  the  fimbria  is  termed  the  fimbrio- dentate  sulcus,  whilst 
the  furrow  between  it  and  the  hippocampal  convolution  forms  the  bottom  of  the 
dentate  fissure.  The  dentate  gyrus  is  notched  along  the  margin,  whilst  its  surface 
is  scored  by  numerous  parallel  and  closely-placed  transverse  grooves.  It  begins 
behind  in  the  region  of  the  splenium  or  thickened  posterior  margin  of  the  corpus 


Caudate  iiucleu; 


Optic  radiation 

Caudate  nucleus 

Optic  radiation 

Inferior  longitudinal  bundle 


Tapetum 
Descending  horn  of  lateral  ventiicle 


Choroid  plexus  in  lateral 
ventricle 


Corpus  callosuni 
Fornix 

Thalamus  (pulvinar) 
Occipital  corticifugal  tract  to 
superior  quadrigeminal  body 
Superior  quadrigeminal  body- 
Corpus  geniculatum  externum 

Corpus  geniculatum  internum 

Sylvian  gray  matter 

Inferior  brachium 

Lateral  fillet 

Superior  cerebellar  peduncle 

^ —  Cerebellum 


Fimbria' 
Gyrus  dentatus ' 

Dentate  fissure  ' 

Fig.  456. — Coronal  Section  through  the  Left  Side  ov  the  Cerebrum,  Mesencephalon,  and  Pons, 
IN  the  Region  of  the  Pulvinar  of  the  Thalamus  and  the  Corpora  Geniculata  (Chimpanzee  ; 
Weigert-Pal  specimen). 

callosum,  and  is  carried  forwards  into  the  cleft  of  the  uncus.  From  this  it  emerges 
in  the  form  of  a  delicate  band,  which  crosses  the  surface  of  the  recurved  part  of  the 
uncus  in  a  transverse  direction,  thereby  constituting  the  frenuhim  Giacomini. 

The  dentate  fissure  is  a  complete  fissure,  and  the  elevation  on  the  ventricular 
wall  which  corresponds  to  it  is  called  the  hippocampus  major.  It  begins  behind 
the  splenium  of  the  corpus  callosum,  where  it  is  continuous  with  a  shallow  part  of 
the  callosal  fissure,  and  it  proceeds  forwards  between  the  gyrus  dentatus  and  the 
hippocampal  convolution.     Its  anterior  end  is  enclosed  within  the  uncus. 

When  coronal  sections  are  made  through  the  callosal  part  of  the  limbic  lobe  and  the  subjacent 
corpus  callosum,  the  cortical  gray  matter  is  seen  to  be  reflected  from  the  bottom  of  the  callosal 
fissure  in  the  form  of  an  exceedingly  fine  layer,  which  forms  a  thin  coating  for  the  upper  surface 
of  the  corpus  callosum.  In  the  midst  of  this  certain  delicate  strands  of  longitudinal  fibres,  the 
strise  longitudinales,  are  embedded,  and,  with  the  gray  matter  associated  with  them,  they  re- 
present an  aborted  or  vestigial  convolution,  termed  the  gyrus  supracallosus.  This  gyrus  is  con- 
tinuous with  the  gyrus  dentatus  round  the  hinder  margin  of  the  corpus  callosum. 

Olfactory  Lobe. — The  olfactory  lobe  is  small  and  rudimentary  in  the  human 
brain,  and  the  description  which  is  given  here  docs  not  include  all  the  parts  which, 
from  the  morphological  point  of  view,  belong  to  this  portion  of  the  cerebral  liemi- 
sphere  (see  p.  584).  Under  this  heading  we  shall  study  merely :  (1)  the  olfactory 
bulb  and  tract,  with  the  two  roots  of  the  latter ;  (2)  the  trigonum  oliactorium. 

The  olfactory  tract  is  a  narrow,  white,  prismaiic  band,  whicli  expands  anteriorly 
into  a  .swollen  hulbtHis  (extremity,  termed  the  olfactory  bulb.  ]>otli  tlic  tract  and 
the   iMilh  lie   u])on   the  olf';if,tory  sulcus  on  il)c  orl)ital  surface  of  the  frontal  lobe, 


570 


THE  NERVOUS  SYSTEM. 


whilst  the  inferior  surface  of  the  bullj  rests  on  the  cribriform  plate  of  the  ethmoid 
bone,  and  receives  the  numerous  olfactory  nerves  which  reach  it  through  the  foramina 
in  that  part  of  the  cranial  floor. 

Posteriorly,  the  olfactory  tract  divides  into  two  diverging  roots.  The  mesial 
root  curves  abruptly  inwards  and  is  continued  into  the  callosal  and  sub-callosal 
o-yri.  The  lateral  root  runs  outwards  and  backwards  over  the  outer  part  of  the 
locus  perforatus  anticus,  and  gradually  disappears  from  view.  In  animals,  in 
which  the  olfactory  apparatus  is  better  developed  than  in  man,  it  may  be  traced 
into  what  corresponds  to  the  uncinate  extremity  of  the  hippocampal  convolution 
in  man  (Fig.  380,  p.  474). 

The  trigonum  olfactorium  or  olfactory  tubercle  is  the  small  triangular  field  of 
gray  matter  which  occupies  the  interval  between  the  roots  of  the  olfactory  tract 
at  the  point  where  they  begin  to  diverge.  Some  fibres  from  the  posterior  end  of 
the  olfactory  tract  enter  the  trigonum,  and,  in  certain  cases,  these  constitute  a 
more  or  less  distinct  middle  root. 


Corpus  Callosum,  Septum  Lucidum,  and  Foenix. 

Corpus  Callosum. — The  corpus  callosum  is  the  great  transverse  commissure 
which  passes  between  the  two  cerebral  hemispheres.     It  is  placed  nearer  the  anterior 


Cmgulum 


Kiontal  fibres 


Out  biirface 


Fibres  of  corona  ladiata- 


Intersection  of 

callosal  and  corona 

radiata  systems  of 

fibres 


Transverse  fibres 
of  corpus 
callosum 


Corpus  callosum 


Ciuguluni  (cu 


Inferior  longi- 
tudinal bundle 


Forceps  major 


Tapetum 


r    ,  ~^^— -  '^yy,,,j„,,,mmm„i^  Stria  loHi^itudiualis  mesialis 

Spleniuni  ^^^^  ■ssa^jpppn-' 

Fig.  457. — The  Corpus  Callosum,  exposed  from  above  and  the  right  half  dissected, 
to  show  the  course  taken  by  its  tiljres. 

than  the  posterior  aspect  of  the  brain,  and  it  unites  the  inner  surfaces  of  the  hemi- 
spheres throughout  very  nearly  a  haK  of  their  antero-posterior  length.  The  corpus 
callosum  is  highly  arched  from  before  backwards,  and  presents  a  convex  upper 
.surface  and  a  concave  lower  surface. 


COEPUS  CALL08UM.  571 

The  uijper  surface  of  the  corpus  callosuin  forms  the  bottom  of  the  great  longi- 
tudinal fissure,  and  on  each  side  of  this  it  is  covered  by  the  callosal  gyrus.  Only 
in  its  posterior  part  is  it  touched  by  the  falx  cerebri;  in  front,  this  process  of  dara 
mater  falls  considerably  short  of  it.  The  upper  surface  of  the  callosum  is  covered 
by  a  thin  layer  of  gray  matter  continuous  at  the  bottom  of  the  callosal  sulcus  with 
the  gray  cortex  on  the  surface  of  the  hemisphere.  In  this  there  are  embedded  on 
either  side  of  the  mesial  plane  two  delicate  longitudinal  bands  of  fibres,  called 
respectively  the  stria  longitudinalis  medialis  and  lateralis.  The  stria  longitudinalis 
medialis  is  the  more  strongly  marked  of  the  two,  and  it  is  separated  from  its  neigh- 
bour of  the  opposite  side  by  a  faint  mesial  furrow.  The  stria  longitudinalis  lateralis 
is  placed  farther  out,  under  cover  of  the  callosal  gyrus.  The  thin  coating  of  gray 
matter,  with  the  two  striae,  represents  an  aborted  convolution,  termed  the  gyrus 
supracallosus.  So  thin  is  the  gray  coating  supphed  by  this  gyrus  that  the  trans- 
verse direction  pursued  by  the  callosal  fibres  proper  can  be  easily  perceived 
through  it. 

The  two  extremities  of  the  corpus  callosum  are  much  thickened,  whilst  the 
intermediate  part  or  body  is  considerably  thinner.  The  massive  'posterior  end, 
which  is  full  and  rounded,  lies  over  the  mesencephalon  and  extends  backwards  as 
far  as  the  highest  point  of  the  cerebellum.  It  is  called  the  splenium,  and  it  consists 
of  an  upper  and  a  lower  part.  The  latter  is  bent  forwards  under  the  upper  part,  to 
the  inferior  surface  of  which  it  is  closely  appUed.  The  anterior  end  of  the  corpus 
callosum  is  not  quite  so  massive  and  is  folded  downwards  and  backwards  on  itself. 
It  is  termed  the  genu.  The  recurved  lower  part  of  the  genu  is  separated  from  the 
part  of  the  corpus  callosum,  which  lies  above,  by  an  interval.  It  rapidly  thins  as 
it  passes  backwards  and  receives  the  name  of  the  rostrum.  The  fine  terminal  edge 
of  the  rostrum  becomes  connected  with  the  lamina  cinerea. 

The  gyrus  supracallosus,  with  its  contained  medial  and  lateral  longitudinal  strise,  when  traced 
backwards,  is  seen  to  turn  round  the  splenium  and  become  continuous  with  the  gyrus  dentatus. 
In  front  the  mesial  strife,  with  the  associated  gray  matter,  are  carried  round  the  genu  and  then 
backwards  on  the  under  surface  of  the  rostrum.  As  they  turn  I'ound  the  anterior  extremity  of 
the  corpus  callosum,  each  stria  runs  into  the  corresponding  gyrus  subcallosus— a  narrow  cortical 
strip  which  lies  on  the  mesial  surface  of  the  hemisphere  immediately  below  the  genu  of  the 
corpus  callosum.  The  gyrus  subcallosus  is  often  called  the  peduncle  of  the  corpus  callosum,  and 
the  fibres  of  the  stria  which  it  contains,  emerging  from  its  substance,  proceed  backwards  and 
outwards  along  the  posterior  limit  of  the  anterior  perforated  spot  towards  the  anterior  extreniity 
of  the  temporal  lobe.  Elliot  Smith  has  shown  that  these  parts  have  an  important  morphological 
significance. 

The  under  surface  of  the  corpus  callosum  on  either  side  of  the  mesial  plane  is 
for  the  most  part  free,  and,  lined  by  ependyma,  it  forms  the  roof  of  the  anterior 
horn  and  body  of  the  lateral  ventricle.  In  the  mesial  plane,  however,  it  is  attached 
to  subjacent  parts,  viz.  to  the  septum  lucidum  in  front  and  to  the  body  of  the 
fornix  behind. 

The  transverse  fibres  of  the  corpus  callosum,  as  they  enter  the  white  medullary 
centre  of  the  cerebral  hemisphere,  radiate  from  each  other  so  as  to  reach  every  part 
of  the  cerebral  cortex.  This  radiation  is  termed  the  radiatio  corporis  callosi  and 
the  fibres  which  compose  it  intersect  the  fibres  which  form  the  corona  radiata,  or,  in 
other  words,  the  fibres  which  extend  between  the  internal  capsule  and  the  cerebral 
cortex  (Figs.  440,  p.  547  ;  and  468,  p.  582).  The  more  anterior  of  the  fibres  which 
comjjose  the  genu  of  the  corpus  callosum  sweep  forwards  in  a  series  of  curves  into 
the  prefrontal  region  of  the  hemisphere.  A  large  part  of  the  splenium,  forming  a 
solid  bundle  termed  the  forceps  major,  bends  suddenly  and  abruptly  backw.ards 
into  the  occipital  lobe  (Fig.  463,  p.  577).  Fibres  from  the  body  and  upper  part 
of  the  splenium,  curving  round  the  lateral  ventricle,  form  a  very  definite  stratum, 
called  the  tapetum.  Tbis  is  a  tliin  layer  in  the  medulliixy  centre  of  the  hemispliere, 
which  constitutes  the  immediate  roof  and  outer  wall  of  the  posterior  horn  and  the 
outer  wall  of  the  hinder  part  of  the  descending  horn  of  the  lateral  ventricle.  In 
coronal  sections  through  the  occipital  and  hinder  temporal  regions  the  tapetum 
Stands  out  very  distinctly  (Figs.  456,  p.  569  ;  462,  p.  576 ;  and  465,  p.  579). 

Fornix. — 1'he  fornix  is  an  arched  bilateral  structure  composed,  for  the  most 
part,  of  longitudinally-directed  fibres,     in  its    intermediate   part   its  two    lateral 


572  THE  NEEVOUS  SYSTEM. 

halves  are  joined  together  in  the  mesial  plane,  and  form  what  is  called  the  body  of 
the  fornix ;  but  in  front  and  behind  they  are  quite  separate,  and  constitute  the 
anterior  and  posterior  pillars  of  the  fornix. 

The  body  of  the  fornix  is  triangular  in  form.  In  front,  where  it  is  continuous 
with  the  anterior  pillars,  it  is  narrow  ;  whilst  behind  it  broadens  out,  becomes 
flattened,  and  is  finally  prolonged  into  the  posterior  pillars.  The  upper  surface  of 
the  body  of  the  fornix  is  in  contact  with  the  under  surface  of  the  hinder  part  of 
the  body  of  the  corpus  callosum,  and  posteriorly  is  adherent  to  it.  In  front  of  this 
adhesion,  and  in  the  mesial  plane,  it  is  attached  to  the  septum  lucidum.     Beyond 

these  attachments,  on  each  side,  the  upper  surface 

""^^Moiiro    /x^^^^^^~~~~~^^  °^  ^^®   body  of  the  fornix  forms   a  part   of  the 

Anterior  Jr  \\  floor  of  the   lateral  ventricle  and  is  clothed  by 

commissure   u/^ 4/-  vicq'^d^A°ifyr    ^^6  lining  epcudyma.     It  presents  a  sharp  lateral 

kL),.^^,.^^  edge  or   margin,  from  under  which    the  choroid 

(^{~^^^^  plexus    projects  into    the  cavity    of  the  lateral 

/"-^  ventricle   and   with   which    the  epithelial   layer 

Fig.  458. -Diagrammatic  Profile  View   which   COVers    that    plexus    is  continuous.        The 

OF  THE  Fornix.  lower  surface  of  the    body   of   the   fornix   rests 

upon    the  velum    interpositum,   which    separates 

it  from  the  roof  of  the  third  ventricle  and  the  upper  surface  of  the  optic  thalami. 

It  is  not  at  all  an  uncommon  occurrence  to  find  the  two  lateral  portions  of  the 

body  of  the  fornix  of  unequal  size  (Fig.  461,  p.  575). 

The  anterior  pillars  of  the  fornix  (columuse  fornicis)  are  two  rounded  strands 
which  emerge  from  the  anterior  part  of  the  body  of  the  fornix,  and  then  diverge 
very  slightly  from  each  other  as  they  curve  downwards  in  front  of  the  foramina  of 
Monro.  Sinking  into  the  gray  matter  on  the  lateral  waU  of  the  third  ventricle, 
each  anterior  pillar  proceeds  downwards  to  the  base  of  the  brain,  and  in  the  inter- 
peduncular space  protrudes,  to  take  part  in  the  formation  of  the  corpus  mammillare. 
When  the  corpus  mammillare  is  dissected  it  appears  to  be  largely  formed  of  a 
twisted  loop  of  the  anterior  pillar  of  the  fornix,  in  which  the  pillar  bends  upon 
itself,  and  is  then  continued  upwards  and  backwards  into  the  optic  thalamus. 
This  appearance,  however,  is  misleading.  The  fibres  of  the  anterior  pillar  end  in 
the  gray  nucleus  of  the  corpus  mammillare,  and  the  strand  which  passes  from  this 
to  the  thalamus  is  the  bundle  of  Vicq  d'Azyr  (p.  548). 

The  posterior  pillars  of  the  fornix  (crura  fornicis)  are  flattened  bands  which 
diverge  widely  from  each  other.  At  first  they  are  adherent  to  the  under  surface 
of  the  corpus  callosum,  but  soon  they  sweep  downwards  round  the  posterior  ends  of 
the  optic  thalami  and  enter  the  descending  horns  of  the  lateral  ventricles.  Here 
each  pillar  comes  into  relation  with  the  corresponding  hippocampus  major,  and  a 
portion  of  its  fibres  are  spread  out  on  the  surface  of  this  prominence,  thereby 
giving  it  a  white  coating  termed  the  alveus,  whilst  the  remainder  of  the  fibres 
constitute  the  fimbria  or  taenia  fornicis — a  narrow  but  very  distinct  band  of  white 
matter,  which  is  attached  by  its  outer  margin  along  the  inner  border  of  the 
hippocampus  major  and  ends  in  front  by  joining  the  uncus  (p.  568). 

A  certain  number  of  transverse  fibres  enter  into  the  formation  of  the  fornix. 
The  diverging  posterior  pillars  enclose  between  them  a  small  triangular  space  on 
the  under  surface  of  the  hinder  part  of  the  corpus  caUosum.  This  area  is  crossed 
by  transverse  fibres,  which  form  a  thin  lamina  called  the  psalterium  or  lyra.  Some- 
times the  psalterium  is  not  completely  fused  to  the  under  surface  of  the  corpus 
callosum,  and  in  these  cases  a  narrow  space  is  left  between  them,  which  receives  the 
name  of  Verga's  ventricle. 

The  fornix  is  intimately  connected  with  the  olfactory  apparatus.  Its  fibres  for  the  most  part, 
arise  from  the  pyramidal  cells  in  the  cornn  ammonis  or  hippocanijDus  major  and  ascend  in  the 
fimbria  and  posterior  pillar.  In  the  region  of  the  psalterium  numerous  fibres  cross  the  mesial 
plane,  enter  the  opposite  posterior  pillar,  and  in  it  proceed  to  the  opposite  cornu  ammonis. 
These  fibres  constitute  a  commissure  between  the  two  cornua  ammonis.  The  xemainder  of  the 
fibres  proceed  forwards  in  the  body  of  the  fornix,  and  by  means  of  the  anterior  pillar  the 
majority  of  the  fibres  are  carried  downwards,  behind  the  anterior  commissure,  to  the  corpus 
mammillare.  Some,  however,  curve  backwards  into  the  stria  medullaris  (p.  548) ;  whilst  others, 
forming  the  olfactory  bundle  of  the  cornu  ammonis,  pass  in  front  of  the  anterior  commissure  and 


LATEEAL  VENTEICLE.  573 

enter  the  septum  lucidum,  through  which  they  reach  the  subcallosal  gyrus  and  the  locus  per- 
foratus  anticus.  Finally,  this  bundle  divides  into  two  parts,  of  which  one  joins  the  inner  root  of 
the  olfactory  tract,  whilst  the  other  goes  to  the  uncus. 

The  greater  number  of  the  longitudinal  fibres  of  the  fornix  must,  therefore,  be  regarded  as 
establishing  a  connexion  between  the  cornu  ammonis  and  the  optic  thalamus.  The  inner  portion 
of  the  composite  nucleus  of  the  corjius  mammillare  is  an  internode  interposed  in  the  path  of  this 
connecting  tract.  The  bundle  of  Vicq  d'Azyr,  formed  by  the  relay  of  fibres  which  takes  origin 
in  this  internode,  forms  the  second  link  in  the  chain. 

The  striae  longitudinales  in  the  gyrus  supracallosus  on  the  upper  surface  of  the  corpus 
callosum  are  to  be  regarded,  from  a  morphological  point  of  view,  as  forming  an  outlying  part  of 
the  fornix  system. 

There  can  be  little  doubt  that  tlie  gyrus  supracallosus  represents  a  wasted  portion  of  the 
hippocampus  formation.  In  monotremes  and  marsupials  the  hippocampus  occupies  a 
corresj)onding  position,  but,  with  the  greater  development  of  the  corpus  callosum  in  higher 
mammals,  atrophy  and  stretching  occur  and  the  structure  is  reduced  to  a  vestigial  condition 
(Elliot  Smith).  That  fornix  fibres  therefore  should  be  found  in  connexion  with  the  supracallosal 
gyrus  is  not  surprising. 

Septum  Lucidum  (septum  pellucidum). — The  septum  lucidum  is  a  thin  vertical 
partition  which  intervenes  between  the  anterior  cornua  and  foreparts  of  the  bodies 
of  the  two  lateral  ventricles.  It  is  triangular  in  shape,  and  posteriorly  it  is 
prolonged  backwards  for  a  variable  distance  between  the  body  of  the  corpus  callosum 
and  the  fornix,  to  both  of  which  it  is  attached  by  its  upper  and  lower  edges.  In 
front  it  occupies  the  gap  behind  the  genu  of  the  corpus  callosum,  whilst  below,  in 
the  narrow  interval  between  the  posterior  edge  of  the  rostrum  of  the  corpus  callosum 
and  the  fornix,  it  is  prolonged  downwards  towards  the  base  of  the  brain  in  the 
gyrus  subcallosus.  The  septum  lucidum  is  composed  of  two  thin  laminae  in  appo- 
sition with  each  other  in  the  mesial  plane  (Fig.  461,  p.  575). 

Fifth  Ventricle  (cavum  septi  pellucidi). — This  name  is  applied  to  the  mesial 
cleft  between  the  two  laminae  of  the  septum  lucidum.  It  varies  greatly  in  size  in 
different  brains  and  contains  a  little  fluid.  It  is  completely  isolated  and  presents 
no  communication  with  the  otherventricles  of  the  brain.  Indeed, the  term"  ventricle," 
as  applied  to  it,  is  quite  inappropriate,  seeing  that  at  no  period  in  the  development 
of  the  brain  has  it  any  connexion  with  the  general  ventricular  system. 

Lateral  Ventkicle. 

The  cavity  in  the  interior  of  the  cerebral  hemisphere  is  called  the  lateral 
ventricle.  It  is  lined  throughout  by  ependyma  continuous  with  the  ependymal 
lining  of  the  third  ventricle.  In  many  places  the  walls  of  the  cavity  are  in  appo- 
sition, whilst  in  other  localities  spaces  of  varying  capacity,  and  containing  cerebro- 
spinal fluid,  are  left  between  the  bounding  walls. 

The  lateral  ventricle  (ventriculus  lateralis)  communicates  with  the  third  ventricle 
of  the  brain  by  means  of  a  small  foramen,  just  large  enough  to  admit  a  crow-quill, 
which  is  termed  the  foramen  of  Monro.  This  aperture  is  placed  in  front  of  the  fore 
end  of  the  optic  thalamus  and  behind  the  anterior  pillar  of  the  fornix. 

The  highly- irregular  shape  of  the  lateral  ventricle  can  be  best  understood  by  the 
study  of  a  cast  of  its  interior  (Figs.  459  ;  and  444,  p.  551).  It  is  usual  to  describe 
it  as  being  composed  of  a  body  and  three  horns,  viz.  an  anterior,  a  posterior,  and  a 
descending  horn.  The  anterior  horn  is  that  part  of  the  cavity  which  lies  in  front  of 
the  foramen  of  Monro.  The  body  is  the  portion  of  the  ventricle  which  extends 
from  the  foramen  of  Monro  to  the  splenium  of  the  corpus  callosum.  At  this  point 
the  postoiior  and  descending  horns  diverge  from  the  hinder  part  of  the  body.  The 
posterior  liorn  curves  backwards  and  inwards  into  the  occipital  lobe.  It  is  very 
variable  in  its  length  and  capacity.  The  descending  horn  proceeds  with  a  bold  sweep 
round  the  hinder  end  of  the  optic  thalamus,  and  then  tunnels  in  a  forward  and 
inward  direction  through  the  temporal  lobe  towards  the  temporal  pole.  The  early 
foetal  lateral  ventricle  is  very  capacious  and  presents  an  arched  or  semilunar  forn]. 
It  is  composed  of  parts  wliich  correspond  to  the  anterior  horn,  the  body,  and  the 
descending  liorn,  and  tliere  is  little  or  no  demarcation  between  them.  The 
poHterior  horn  is  a  later  production.  It  comes  into  existence  with  the  occipital 
lobe  and  is  produced  as  a  diverticulum  or  elongated  pouch,  which  grows  backwards 
from  tfie  upper  and  hinder  part  (i.e.  the  convexity)  of  the  primitive  cavity. 


574 


THE  NEEVOUS  SYSTEM. 


Anterior  Horn  of  the 
Lateral  Ventricle  (cornu  an- 
terius).  —  The  anterior  horn 
forms  the  foremost  part  of  the 
cavity,  and  extends  in  a  for- 
ward and  outward  direction  in 
the  frontal  lobe.  When  seen 
in  coronal  section  (Fig.  460)  it 
presents  a  triangular  outline, 
the  floor  sloping  upwards  and 
outwards  to  meet  the  roof  at 
;in  acute  angle.  It  is  bounded 
in  front  by  the  posterior  sur- 
face of  the  genu  of  the  corpus 
callosum;  the  ?'oq/ is  also  formed 
by  the  corpus  callosum.  The 
inner  wall,  which  is  vertical, 
is  formed  by  the  septum 
lucidum ;  whilst  the  sloping 
fioor  presents  a  marked  eleva- 
tion or  bulging,  viz.  the  smooth, 
rounded,  and  prominent  ex- 
tremity of  the  pear-shaped 
caudate  nucleus. 

Body  of  the  Lateral  Ven- 
tricle (pars  centralis). — The 
body  of  the  cavity  is  likewise 
roofed  by  the  corpus  callosum. 
On  the  inner  or  mesial  side  it 
is  bounded  by  the  attachment 
of  the  fornix  to  the  under  sur- 
face of  the  corpus  callosum  and 
by  the  hinder  part  of  the 
septum  lucidum.  On  the  outer  side  it  is  closed,  as  in  the  case  of  the  anterior  horn, 
by  the  meeting  of  the  fioor  and  the  roof  of  the  cavity.  On  the  floor  a  number 
of  important  ob- 
jects may  be  re- 
cognised. From 
without  inwards 
these  are  met  in 
the  following 
order:  (1)  the  cau- 
date nucleus ;  (2) 
a  groove  which 
extends  obliquely 
from  before  back- 
wards and  out- 
wards between  the 
caudate  nucleus 
and  the  optic 
thalamus,  and  in 
which  are  placed 
the  vein  of  the 
corpus  striatum 
and  a  white  band 
called  the  taenia 
semicircularis ;  (3) 
a  portion  of  the 
upper    surface    of 


Fig.   459, — Drawing  taken  from  a  Cast  op  the  Ventricular 
System  of  the  Brain,  as  seen  from  above  (after  Retzius). 

Vent.  III.  Third  ventricle.  Vent.  IV.   Fourth  ventricle. 

R.SP.  Recessus  suprapinealis. 


Great  longitudinal  fissure 


s  callosum  (genu) 


Anterior  horn  of 
lateral  ventricle 


Caudate  nucleus 


Caudate  nucleus 
(in  section) 


callosum  (genu) 


Fig.  460. 


Great  longitudinal  fissure 

-Coronal  Section  through  the  Frontal  Lobes  and  the 
Anterior  Horns  of  the  Lateral  Ventricles. 


LATERAL  VENTRICLE. 


575 


the  optic  thalamus;  (4)   tlie  choroid  plexus;    (5)  the  thin,  sharp  lateral  edge  of 
the  fornix. 

The  caudate  nucleus  narrows  rapidly  as  it  proceeds  backwards  on  the  outer  part 
of  the  floor  of  the  body  of  the  lateral  ventricle.  The  vein  of  the  corpus  striatum  is 
covered  over  by  ependyma.  It  joins  the  vein  of  Galen  close  to  the  foramen  of 
Monro.  The  connexions  of  the  taenia  semicircularis  will  be  dealt  with  later.  The 
portion  of  the  upper  surface  of  the  optic  thalamus  which  appears  in  the  floor  of  the 

Corpus  callosum 
Ventricle  V.     ':    Foramen  of  Monro 
;    ;     I     Caudate  nuoleus 


Corpus  callosum 
turned  to  tlie  left  side 


Septum  luoidum 


Optic  thalamus 

;         Cl'.oroid  plexus 

;/~~~^      Ttenia  semicircularis 


Trifronum  ventriculi 


Hippocampus  major 


Calcar  avis 


Hulb  of  the  cornu 


Fimbria  ; 

Forceps  major 


■     Hippocampus  major 
Posterior  pillar  of  the  fornix 

Body  of  the  fornix 


Fig.  461. — Dissection,  to  show  the  fornix  and  lateral  ventricles  ;  the  body  of  the  corpus  callosum 
has  been  turned  over  to  the  left. 


ventricle  is  in  great  part  hidden  by  the  choroid  plexus,  which  lies  upon  it.  The 
choroid  plexus  is  a  rich  vascular  fringe  which  appears  from  under  cover  of  the  sharp 
lateral  edge  of  the  fornix.  In  front  it  is  continuous,  behind  the  foramen  of  Monro, 
with  the  corresponding  choroid  plexus  of  the  opposite  side,  whilst  behind,  it  is 
carried  into  the  descending  horn  of  the  ventricle.  Although  the  choroid  plexus 
has  all  the  ajjpearance  of  lying  free  within  the  ventricle,  it  must  be  borne  in  mind 
that  it  is  invested  by  an  epithelial  layer  which  represents  a  portion  of  the  hemi- 
sphere wall  and  excludes   it  from  the  cavity.     This  thin  layer  is  continuous  on  the 


576 


THE  XEKVOUS  SYSTEM. 


one  hand  with  the  sharp  edge  of  the  fornix,  and  on  the  other  it  is  attached  to  the 
upper  surface  of  the  optic  thalamus. 

Posterior  Horn  of  the  Lateral  Ventricle  (cornu  posterius). — The  posterior 
horn  is  an  elongated  diverticulum  carried  backwards  into  the  occipital  lobe  from  the 
hinder  end  of  the  body  of  the  ventricle.  It  tapers  to  a  point  and  describes  a  gentle 
curve,  the  convexity  of  which  is  directed  outwards.  The  roof  awd  outer  vxdl  of  this 
portion  of  the  ventricular  cavity  are  formed  by  the  tapetum  of  the  corpus  callosum. 
In  coronal  sections  through  the  occipital  lobe  this  is  seen  as  a  thin  but  distinct 
layer  of  white  fibres,  which  lies  immediately  outside  the  ependyma  and  to  the  inner 
side  of  a  much  larger  strand  of  fibres  in  the  medullary  substance  of  the  occipital 
lobe,  viz.  the  optic  radiation. 

On  the  inner  vxdl  two  elongated  curved  elevations  may  be  observed.  The 
uppermost  of  these  is  termed  the  bulb  of  the  cornu  (bulbus  cornu  posterioris),  and  is 
produced  by  the  fibres  of  the  forceps  major  of  the  corpus  callosum  as  they  curve 
abruptly  backwards  from  the  lower  ^mrt  of  the  splenium  of  the  corpus  callosum  into 
the  occipital  lobe.  Below  this  is  the  elevation  known  as  the  calcar  avis.  It  varies 
greatly  in  size  in  different  brains,  and  is  caused  by  an  infolding  of  the  ventricular 
wall  in  correspondence  with  the  anterior  calcarine  fissure  on  the  exterior  of  the 
hemisphere. 

Descending-  Horn  of  the  Lateral  Ventricle  (cornu  inferius). — The  descending 
horn  is  the  continuation  of  the  cavity  into  the  temporal  lobe.  At  first  directed  back- 
wards and  outwards  the  descending  horn  suddenly  sinks  downwards  behind  the  optic 
thalamus  into  the  temporal  lobe,  in  the  centre  of  which  it  takes  a  curved  course  for- 
wards and  inwards  to  a  point  about  an  inch  behind  the  extremity  of  the  temporal  pole. 

In  the  angle  between  the  diverging  posterior  and  descending  horns  the  cavity 
of  the  ventricle  presents  an  expansion  of  a  somewhat  triangular  shape.  To  this 
the  name  of  trigonum  ventriculi  is  sometimes  given. 

The  roof  of  the  descending  horn  is  formed  for  the  most  part  by  the  tapetum  of 


Splenium  of  corpus  callosum 


Bulb  of  the  posterior  cornu 


Bulb  of  the  posterior  cornu 


Fig.   462. 


Inferior  longitudinal  fasciculus. 
-Coronal  Section  through  the  Posterior  Horns  of  the  Lateral  Ventricles. 


the  corpus  callosum.  At  the  extremity  of  the  horn  the  roof  presents  a  bulging 
into  the  cavity.  This  is  the  amygdaloid  tubercle,  and  it  is  produced  by  a  super- 
jacent collection  of  gray  matter  termed  the  amygdaloid  nucleus.  The  taenia  semi- 
circularis  and  the  attenuated  tail  of  the  caudate  nucleus  are  both  prolonged  into  the 
descending  horn  and  are  carried  forwards,  in  its  roof,  to  the  amygdaloid  nucleus. 

On  tlie  floor  of  the  descending  horn  the  following  structures  are  seen :  (i) 
hippocampus  major,  or  the  cornu  ammonis ;  (2)  the  choroid  plexus  ;  (3)  the  fimbria  ; 
and  (4)  the  eminentia  collateralis. 

The  hippocampus  major  (hippocampus)  is  for  the  most  part  covered  by  the 


LATEEAL  VENTEICLE. 


577 


choroid  plexus.  It  is  a  prominent  elevation  on  the  lioor  of  the  descending  horn  of 
the  lateral  ventricle  and  is  strongly  curved,  in  conformity  with  the  course  taken 
by  the  horn  in  which  it  lies.  It  therefore  X->resents  an  internal  concave  margin  and 
an  external  convex  border.  Narrow  behind,  it  enlarges  as  it  is  traced  forwards, 
and  it  ends  below  the  amygdaloid  tubercle  in  a  thickened  extremity,  which 
presents  some  faint  grooves  or  notches  on  its  surface.  In  consequence  of  this,  the 
anterior  end  of  the  hippocampus  major  receives  the  name  of  the  pes  hippocampi. 
The  hippocampus  major  is  the  internal  elevation  which  corresponds  to  the  dentate 
fissure  on  the  exterior  of  the  hemisxahere  (Fig.  464). 

If  an  incision  be  made  along  the  outer  convex  edge  of  the  hippocampus  major,  and  the  surface 
lamina  be  raised,  the  central  core  will  be  seen  to  present  the  curious  appearance  of  two 
corrugated  layers  dove-tailed  into  eacli  other  (M'Carthy). 

The  fimbria  (fimbria  hippocampi)  is  the  narrow  band  of  white  matter  which  is 
attached  by  its  outer  margin  along  the  inner  concave  border  of  the  hippocampus 
major.  The  white  matter  composing  it  is  continuous  with  the  thin  white  layer 
(the  alveus)  which  is  spread  over  the  surface  of  the  hippocampus  major,  and  it 
presents  two  free  surfaces  and  a  sharp  free  inner  border.  The  fimbria  has  already 
been  examined  in  connexion  with  the  hippocampal  fissure  and  the  gyrus  dentatus 


Caudate  nucleu; 


Genu  of  corpus  callosum 

Septum  lucidum 
Ventricle  V. 
Caudate  nucleus 

Foramen  of  Monro 

Taenia  semicircularis 

Optic  thalamus 
Fornix 


Mesial  longitudinal  stria  on  the 
'•>;        splenium  of  the  corpus  callosum 


Fio.  46.'j.— Dissection,  to  sIjow  the  fornix  ami  the  posterior  and  descemliug  conuia 
of  tlie  lateral  ventricle  of  tlie  left  .side. 

(p.  508),  and  the  relations  which  it  presents  to  the  fornix  and  the  uncus  have  been 
pointed  out. 

When  tlie  ))ia  mater  in  the  region  of  the  hi])pocampal  lissure  is  removed  from 
the  Hiirfuce  ol'  the  brain,  the  choroid  plexus  in  the  interior  of  the  descending  horn 
41 


578 


THE  NEKVOUS  SYSTEM. 


of  the  lateral  ventricle  is  usually  withdrawn  with  it,  and  a  j&ssure  appears  between 
the  fimbria  and  the  roof  of  the  ventricular  horn.  This  is  the  choroid  fissure.  It 
appears  at  a  very  early  date  in  the  development  of  the  cerebral  hemisphere,  and 
takes  an  arcuate  course  upwards  and  forwards  round  the  hinder  end  of  the  optic 
thalamus.  In  the  region  of  the  body  of  the  lateral  ventricle  it  extends  as  far 
forwards  as  the  foramen  of  Monro,  and  is  formed  by  the  involution  of  an  epithelial 
part  of  the  wall  of  the  ventricle  over  the  choroid  plexus  (p.  575).  In  the  region  of 
the  descending  horn,  when  the  choroid  plexus  with  the  involuted  epithelial  layer 
which  covers  it  is  withdrawn,  the  choroid  fissure  is  converted  into  an  artificial  gap 
which  leads  directly  into  this  part  of  the  ventricular  cavity. 

The  choroid  plexus  is  a  convoluted  system  of  blood-vessels  in  connexion  with  a 
fold  of  pia  mater,  which  is  prolonged  into  the  descending  horn  of  the  lateral 
ventricle.  It  lies  on  the  surface  of  the  hippocampus  major  and  is  continuous 
behind  the  posterior  part  of  the  optic  thalamus,  with  the  choroid  plexus  in  the  body 
of  the  lateral  ventricle.  But  it  must  not  be  supposed  that  the  choroid  plexus  lies 
free  in  the  ventricular  cavity.  It  is  clothed  in  the  most  intimate  manner  by  an 
epithelial  layer,  which  represents  the  inner  or  mesial  wall  of  the  descending  horn 
involuted  into  the  cavity  over  the  choroid  plexus.  The  ventricle,  therefore,  only 
opens  on  the  surface  through  the  choroid  fissure  when  this  thin  epithelial  layer  is 
torn  away  by  the  withdrawal  of  the  choroid  plexus.  Erom  the  above,  it  will  be 
understood  that  the  arcuate  choroid  fissure,  throughout  its  whole  length  (viz.  from 

the  foramen  of  Monro  to  the 
extremity  of  the  descending 
horn  of  the  lateral  ventricle), 
is  formed  by  the  involution  of 
a  portion  of  the  wall  of  the 
hemisphere  which  remains  epi- 
thelial. In  the  body  of  the 
ventricle  this  layer  is  attached, 
on  the  one  hand,  to  the  sharp 
lateral  margin  of  the  fornix, 
and  on  the  other  to  the  upper 
surface  of  the  optic  thalamus ; 
in  the  descending  horn  it  is 
attached,  in  like  manner,  to  the 
edge  of  the  fimbria  or  posterior 
pillar  of  the  fornix,  whilst  above 
it  joins  the  roof  of  this  portion 
of  the  ventricle  along  the 
line  of  the  taenia  semicircularis. 
The  eminentia  collateralis 
fatfrai'vLSf  shows  Very  great  differences  in 
caicaravis  its  degree  of  development,  and 
it  may  present  two  distinct 
Buiboftiieconiu  forms,  whicli  may  be  distin- 
guished from  each  other  as  the 
eminentia  collateralis  posterior 
and  the  eminentia  collateralis 
anterior. 

The  posterior  collateral 
eminence  is  a  smooth  eleva- 
tion in  the  floor  of  the  tri- 
gonum  ventricuh,  in  the  in- 
terval which  is  left  between 
the  calcar  avis  and  the  hippo- 
campus major  as  they  diverge 
from  each  other.  In  the  fojtal  brain  this  is  always  a  very  strongly -marked 
elevation,  which  corresponds  with  the  mid-collateral  fissure,  but  inj  the  course  of 
growth  it  is  apt  to  lose  much  of  its  prominence. 


Pes  hippocampi 


Hippocampus 

major 


Fi6.  464. — Dissection  from  above,  to  show  the  posterior  and 
desceiidiua;  cornua  of  the  lateral  ventricle. 


B.G. 
F. 


Giacomiui's  band. 
Fimbria. 


F.D.   Gyrus  dentatus. 

H.C.  Hippocampal  convolution. 


BASAL  GANGLIA  OF  THE  CEREBEAL  HEMISPHEEE.  579 


The  anterior  collateral  eminence  is  only  occasionally  present.  It  appears  as  an 
elongated  elevation  of  varying  length  and  prominence,  on  the  floor  of  the  descend- 
ing horn  of  the  lateral  ventricle,  on  the  outer  side  of  the  hippocampus  major.  It 
is  formed  by  the  anterior  portion  of  the  foetal  collateral  sulcus,  when  this  develops 
as  a  complete  fissure. 

Basal  Ganglia  of  the  Ceeebral  Hemispheee. 

Under  this  heading  are  included  certain  masses  of  gray  matter  more  or  less 
completely  embedded  in  the  white  medullary  substance  of  the  hemisphere,  and 
which  are  developed  in  its  wall.  They  compose  the  caudate  and  lenticular  nuclei, 
which  together  form  the  corpus  striatum,  the  claustrum,  and  the  amygdaloid 
nucleus. 

The  caudate 
nucleus  bulges 
into  the  lateral 
ventricle.  It  is  a 
pyriform,  highly- 
arched  mass  of 
gray  matter,  which 
presents  a  thick, 
swollen  head,  or 
anterior  extremity, 

and  a  long,  attenu-    Anterior  limb  of  internal 

atedtail.  The  head  ventrkfieV 

projects  into  the 
anterior  horn  of  the 
lateral  ventricle, 
whilst  its  narrower 
part  is  prolonged 
outwards  and 
backwards  in  the 
floor  of  the  body 
of  the  ventricle, 
where  it  is  separ- 
ated from  the  optic 
thalamus    by    the 


Genu  of  corpus  callosum 

Anterior  horn  of  lateral 
ventricle 

Caudate  nucleus 


Genu  of  internal  capsule 
Anterior  pillars  of  fornix- 
Globus  pallidus 

Bundle  of  Vicq  d'Azyr 

Posterior  limb  of  internal 
capsule 

Thalamus. 

Retrolenticular  part  of 

internal  capsule 


taenia  semicircul- 
aris.  Finally,  its 
tail  curves  down- 
wards with  a  bold 
sweep  and  enters 
the  descending 
horn  of  the  lateral 
ventricle.  In  the 
roof  of  this  horn 
it  is  prolonged 
forwards  to  the 
amygdaloid  nu- 
cleus, the  lower 
part  of  which  it 
joins.  The  caudate 
nucleus  thus  pre- 


Hippocampus  major. 

Splenium 

Choroid  plexus 


Band  of  Vicq  d'Azyr- 


Calcarine  Assure- 


Claustrum 


Putamen 


Tail  of 

caudate 

nucleus 


Optic 

*/       radiation 

/— i Tapetum 
Inferior 

longitudinal 

bundle 


Fig.  465.— Horizontal  Section  through  the  Right  Cerebral  Hemisphere 
AT  the  Level  of  the  Widest  Part  op  the  Lenticulaii  Nucleus. 


sents  a  free  ventricular  surface,  covered  with  ependyma,  and  a  deep  surface 
embedded  in  tlie  white  substance  of  the  cerebral  hemisphere,  and  for  the  most  part 
related  to  the  internal  capsule. 

Owing  to  its  arched  form  it  follows  that,  in  horizontal  sections  through  the 
cerebral  hemisphere  below  a  ])articular  level,  it  is  cut  at  two  points,  and  both  the 
head  and  the  tail  appear  on  the  field  of  the  section  (Fig.  465).     In  coronal  sections 
Ijchind  the  amygdaloid  nucleus,  it  is  also  divided  at  two  ])laces  (Fig.  440,  p.  547). 
41a 


580 


THE  NERVOUS  SYSTEM. 


The  anterior  extremity  of  the  head  of  the  caudate  nucleus  coincides  very  nearly 
with  that  of  the  anterior  horn  of  the  lateral  ventricle.  In  the  region  of  the  locus 
perforatus  anticus,  the  head  of  the  caudate  nucleus  gains  the  surface  and  its  gray 
matter  hecomes  continuous  with  that  of  the  cerebral  cortex. 

The  lenticular  nucleus  lies  on  the  outer  side  of  the  caudate  nucleus  and  optic 
thalamus,  and  is  for  the  UKist  part  embedded  witliiu  the  white  medullary  substance 
of  the  cerel)ral  liemispliere.  It  does  not  extend  either  so  far  forwards  or  so  far 
backwards  as  the  caudate  nucleus.  Indeed,  it  presents  a  very  close  correspondence 
in  point  of  extent  with  the  insula  or  island  of  Eeil  on  the  surface.  When  seen  in 
horizontal  section,  it  presents  a  shape  similar  to  that  of  a  biconvex  lens.  Its 
inner  surface  bulges  more  than  the  outer  surface,  and  its  point  of  highest  convexity 
is  placed  opposite  the  taenia  semicircularis  or  the  interval  between  the  caudate 
nucleus  and  the  optic  thalamus.  In  coronal  section  the  appearance  presented  by 
the  lenticular  nucleus  differs  very  much  in  different  planes  of 

^ 


section.  Fig.  466 
represents  a  sec- 
tion through  its 
anterior  portion. 
Here  it  is  semi- 
1  unar  or  crescen  tic 
in  outline  and  is 
directly  continu- 
ous below  with 
the  head  of  the 
caudate  nucleus ; 
above,  also,  it  is 
intimately  con- 
nected with  the 
caudate  nucleus 
by  bands  of  gray 
matter,  which 
pass  between  the 
two  nuclei  and 
break  up  the  white 
matter  of  the  fore- 
part of  the  inter- 
vening internal 
capsule.  It  is 
due  to  the  ribbed 
ouGH  THE  Cerebral  Hemispheres  so  as  to  ciit  qj,  barred  aDDCar- 
anien)  of  the  lenticular  nucleus  in  front  of  the  ,  .   -,  K^ 

ance,  which  is  pre- 
sented by  such  a 

section  as  this,  that  the  term  corpus  striatum  is  applied  to  the  two  nuclei.  In 
the  region  of  the  locus  perforatus  anticus  both  nuclei  reach  the  surface  and  become 
continuous  with  the  cortex. 

When  a  section  is  made  in  a  plane  further  back  {e.g.  immediately  posterior  to 
the  anterior  commissure,  as  in  Fig.  467)  the  divided  lenticular  nucleus  assumes  an 
altogether  different  shape,  and  is  seen  to  be  completely  cut  oft"  from  the  caudate 
nucleus  by  the  internal  capsule.  It  is  now  triangvilar  or  wedge-shaped.  Its  'base 
is  turned  towards  the  island  of  Eeil  and  is  in  direct  relation  to  a  thin  lamina  of 
white  matter,  termed  the  external  capsule.  Its  internal  surface  is  oblique  and  is 
applied  to  the  internal  capsule,  whilst  its  inferior  surface  is  horizontal  and  is 
directed  downwards  towards  the  base  of  the  brain.  But,  further,  two  white  laminae, 
the  external  and  internal  medullary  laminae,  are  now  evident,  which  traverse  its 
substance  in  a  vertical  direction  and  divide  it  into  three  zones.  The  outer,  basal, 
and  larger  zone  is  termed  the  putamen ;  the  two  inner  portions  together  constitute 
the  globus  pallidus. 

The  putamen  forms  much  the  largest  part  of  the  lenticular  .nucleus.  It  is 
darker  in  colour  than  the  globus  pallidus,  and  in  this  respect  resemltles  the  caudate 
nucleus.     It  is  traversed  by  fine  radiating  bundles  of  fibres,  which  enter  it  from  the 


Great  longi- 
tudinal fissure 


Corpus  callosum 

Lateral  ventricle. 

Anterior  pillar 

of  fornix 

Choroid  plexus 

Foramen  of 
Monro' 


Septum  luciduia 


Caudate  nucleus 
Internal  capsule 

Putamen 
Claustrni 

Fig.  466. — Coronal  Section  thro 
through  the  anterior  part  (putan 
globus  pallidus. 


BASAL  GANGLIA  OF  THE  CEEEBEAL  HEMISPHEEE. 


581 


external  medullary  lamina.  Both  in  point  of  structure  and  in  mode  of  development 
it  is  closely  associated  with  the  caudate  nucleus,  and  it  is  the  only  part  of  the  len- 
ticular nucleus  which  is  connected  by  intervening  bands  of  gray  matter  with  the 
caudate  nucleus.  The  antero-posterior  length,  as  well  as  the  vertical  depth  of  the 
putamen,  is  much  greater  than  in  the  case  of  the  globus  pallidus ;  consequently,  in 


Choroid  plexus 


Lateral  ventricle 


Claustrum 


Bundle  of  Vicq 
d'Azyr 


Great  longitudinal 
assure 

Gorijus  callosum 

Fornix 

Caudate  nucleus 
Vein  of  corpus 
striatum 

V^elum  interpositum 

Thalamus 

Third  ventricle 

Choroid  plexus 

Internal  capsule 

Foramen  of  Monro 

ijiterior  pillar  of 

roruix 

Anterior  commissure 

^  Jptic  tract 

lufundibuhim 
Optic  chiasma 
Optic  nerve 


Locus  perforatus  anticus  Olfactory  peduncle 

Fig.  467. — Coronal  Section  through  the  Cerebrum  so  as  to  cut  through  the  three  divisions  of  the 
lenticular  nucleus  ;  i^osterior  siirface  of  the  section  depicted. 


Globus  pallidus 

Anterior  pillar 
'of  fornix' 


both,  coronal  and  horizontal  sections  through  the  cerebrum  it  is  encountered  before 
the  plane  of  the  globus  pallidus  is  reached. 

The  external  capsule  is  loosely  connected  witli  tlie  outer  surface  of  the  putamen,  and  it  can  be 
readily  strijjped  off.  This  accounts  for  the  tendency,  exhibited  in  htemorrhages  in  this  locality, 
for  the  effused  blood  to  spread  out  in  the  interval  between  these  structures. 

The  globus  pallidus  is  composed  of  the  two  smaller  and  inner  zones  of  the  lenti- 
cular nucleus.  They  present  a  faint  yellowish  tint,  and  are  paler  and  more 
abundantly  traversed  by  fibres  than  the  putamen.  The  zone  next  the  putamen  (i.e. 
the  intermediate  zone)  is  much  larger  than  the  innermost  subdivision.  It  extends 
forwards  to  a  jjoint  a  little  in  front  of  the  plane  of  the  anterior  commissure.  When 
the  lenticular  nucleus  is  cut  in  a  coronal  direction,  and  in  its  widest  part,  the 
innermost  zone  shows  an  indication  of  a  separation  into  two  parts,  so  that  here  the 
globus  pallidus  appears  to  consist  of  three  subdivisions.  The  morphology  of  the 
globus  pallidus  is  by  no  means  clear. 

Connexions  of  the  Corpus  Striatum. — (1)  Numerous  fibres  pass  from  the  optic 
tlialainus  to  the  corpus  striatum,  and  in  the  reverse  direction  from  the  corpus  striatum 
into  the  thalamus  througli  the  anterior  limb  of  the  internal  capsule.  These  may  be 
termed  the  thalamo- striate  and  the  strio- thalamic  fibres.  (2)  Edinger  describes  a 
connexion  Ijctweon  the  caudate  nucleus  and  the  substantia  nigra.  The  connecting  fibres 
pass  through  the  subthalamic  region  and  constitute  a  tract  in  the  mesencephalon,  in  close 
apposition  with  the  substantia  nigra,  called  the  stratum  intermedium.  (3)  The  ansa 
lenticularis  lias  previously  been  mentioned.  It  is  composed  of  fibres  which  come  from  the 
inferior  part  of  the  fore  portion  of  the  thalamus  and  curve  outwards  inider  the  lenticular 
nucleus.  They  stream  ufjwurds  into  this  and  through  its  modidlary  lamiujc.  Many  of 
theru  apparently  proceed  onwards  to  the  cerebral  cortex.  (4)  Fibres  from  the  posterior 
41  h 


582 


THE  NERVOUS  SYSTEM. 


limb  of  the  internal  capsule  (thalamic  fibres  chiefly)  enter  the  lenticular  nucleus  and 
stream  through  it,  and  its  medullary  lamina;,  on  their  way  to  the  cerebral  cortex. 

Claustrum. — This  is  a  thin  plate  of  gray  substance"  emliedded  in  the  white 
matter,  which  intervenes  between  the  lenticular  nucleus  and  the  gray  cortex  of  the 
insula  or  island  of  Reil.  Followed  in  an  upward  direction,  it  becomes  gradually 
thinner   and   ultimately   disappears.      As   it    is    traced   downwards,    Jiowever,    it 


Intersection  of  corona  racliata 
and  callosal  systems  of  fibres 

CoriHisJcallosum 
Caudate  nucleus — ;;^ 

Fornix 
Internal  capsule' 


-  Occipito-frontal  association  bundle 


External  capsule 


Claustrum 


Frontoparietal  operculum 
Insula 


Temporal  operculum 


Globus  pallidus 
Optic  tract- 
Anterior  commissure'^ 


Fig.  468. — Coronal  Section  through  the  Left  Side  of  the  Cerebrum  of  an  Orang 

(Weigert-Pal  specimen). 

The  section  passes  thro^^gll  the  middle  of  the  lenticular  nucleus. 

thickens  considerably,  and  at  the  base  of  the  brain  it  comes  to  the  surface  at  the 
anterior  perforated  spot  and  becomes  continuous  with  the  gray  matter  of  the  cortex. 
Its  extent  corresponds  very  closely  with  the  area  occupied  by  the  insula,  and  its 
surface  towards  this  portion  of  the  cerebral  cortex  shows  ridges  and  depressions 
corresponding  to  the  insular  gyri  and  sulci. 

Amygdaloid  Nucleus. — In  the  forepart  of  the  temporal  lobe,  in  front  of,  and 
to  some  extent  above  the  extremity  of  the  descending  horn  of  the  lateral  ventricle, 
there  is  a  round  mass  of  gray  matter,  called  the  amygdaloid  nucleus.  The  tail  of 
the  caudate  nucleus  joins  its  lower  part,  whilst  above  it  is  carried  up  into  the  puta- 
men.     In  front  it  is  continuous  with  the  gray  cortex  of  the  cerebrum. 

Taenia  Semicircularis. — This  is  a  band  of  fibres  which,  for  the  most  part,  arise 
in  the  amygdaloid  nucleus.  From  this  it  runs  backwards  in  the  roof  of  the  de- 
scending horn  of  the  lateral  ventricle,  and  then  arches  upwards  and  forwards,  so  as 
to  gain  the  floor  of  the  body  of  the  lateral  ventricle.  In  both  situations  it  lies 
close  to  the  inner  side  of  the  nucleus  caudatus,  and  finally,  at  the  foramen  of 
Monro,  it  bends  downwards  towards  the  anterior  commissure.  Some  of  its  fibres 
pass  in  front  and  others  behind  the  commissure,  and  ultimately  they  end  in  the 
locus  perforatus  anticus  (Ko.lliker). 

Internal  Capsule. — This  term  is  applied  to  the  broad  band  of  white  matter 
which  intervenes  between  the  lenticular  nucleus,  on  the  outside,  and  the  optic 


INTEKNAL  CAPSULE.  583 

thalamus,  tsenia  semicircularis,  and  caudate  nucleus  on  the  inner  side.  It  presents 
many  different  appearances,  according  to  the  plane  in  which  the  brain  is  cut.  In 
the  region  of  the  mesencei^halon,  a  C(jronal  section  through  the  brain  shows  that  in 
great  part  the  internal  capsule  is  directly  continuous  with  the  crusta  of  the  crus 
cerebri  (Eig.  440,  p.  547).  In  horizontal  section  the  internal  capsule  is  observed  to 
be  bent  upon  itself  opposite  the  taenia  semicircularis,  or  the  interval  between  the 
caudate  nucleus  and  the  thalamus.  This,  bend,  which  jjoints  inwards,  is  called  the 
genu.  About  one-third  of  the  internal  capsule  lies  in  front  of  the  genu,  and  is 
termed  the  anterior  limb ;  the  remaining  two-thirds,  which  lie  behind  the  genu, 
constitute  the  posterior  limb. 

The  anterior  limb  of  the  internal  capsule  intervenes  between  the  lenticular 
nucleus  and  the  caudate  nucleus.  In  its  lower  and  forepart  it  is  much  broken  up 
by  the  connecting  bands  of  gray  matter  which  pass  between  the  forepart  of  the 
putamen  and  the  lenticular  nucleus. 

The  anterior  limb  of  the  internal  capsule  is  largely  composed  of  corticipetal  fibres 
belonging  to  the  thalamic  radiation.  It  hkewise  contains  corticifugal  fibres.  The 
corticipetal  fibres  are  of  two  kinds,  viz.  thalamo-frontal  and  thalamo-striate.  The 
former,  which  arise  in  the  optic  thalamus,  go  tiirough  the  anterior  limb  of  the  internal 
capsule  to  reach  the  cortex  of  the  frontal  lobe.  The  thalamo-striate  fibres  likewise  arise 
in  the  thalamus  and  enter  the  anterior  limb,  to  reach  the  caudate  and  lenticular  nuclei. 

The  corticifugal  fibres  are  represented  by  the  fronto-thalamic,  the  strio-thalamic,  and 
the  fronto-pontine  tracts. 

The  fronto-pontine  tract  arises  in  the  cortex  of  the  prefrontal  region,  traverses  the 
anterior  limb  of  the  internal  capsule,  forms  the  inner  fifth  of  the  crusta  of  the  crus  cerebri, 
and  finally  ends  in  the  nucleus  pontis. 

The  posterior  limb  of  the  internal  capsule  is  placed  between  the  optic  thalamus 
and  the  lenticular  nucleus,  and  it  extends  backwards  for  a  short  distance  beyond 
the  hinder  end  of  the  putamen  on  the  outer  side  of  the  posterior  part  of  the 
thalamus  and  of  the  tail  of  the  caudate  nucleus.  The  posterior  limb,  therefore,  is 
spoken  of  as  consisting  of  a  lenticular  and  a  retr denticular  part. 

The  lenticular  part  of  the  posterior  limb  is  composed  of  both  corticipetal  and  cortici- 
fugal fibres.  The  corticipetal  fibres  enter  the  internal  capsule  from  the  outer  aspect  of 
the  optic  thalamus,  and  are  composed  of  fibres  which  arise  within  the  thalamus,  and  proceed 
upwards  to  the  cerebral  cortex. 

The  corticifugal  fibres  consist  of  the  pyramidal  tract  and  the  cortico-thalamic  fibres. 

The  great  motor  or  pyramidal  tract,  descending  from  the  Rolandic  area  of  the  cortex, 
occupies  the  anterior  half  of  the  lenticular  part  of  the  internal  capsule.  The  fibres,  which 
go  to  the  nucleus  of  the  facial  nerve,  lie  close  to  the  genu,  and  behind  these  are  the 
fibres  which  go  to  the  hypoglossal  nucleus ;  still  further  back  are  pyramidal  fibres  which 
enter  the  spinal  cord  and  end  around  the  motor  cells  of  the  anterior  horn  of  gray  matter. 
This  pyramidal  tract  has  been  observed  occupying  the  middle  part  of  the  crusta  of  the 
crus  cerebri,  into  which  it  passes  directly  from  the  internal  capsule. 

The  retrolenticular  part  of  the  posterior  limb  coii tains  :  (1)  the  fibres  of  the  optic 
radiation  as  they  pass  to  establish  their  connexions  with  the  thalamus,  superior  quadri- 
geminal  body,  and  corpus  geniculatum  extermmi ;  (2)  the  fibres  of  the  auditory  radiation, 
or  those  which  connect  the  auditory  cortical  field  in  the  temporal  lobe  with  the  corpus 
geniculatum  internum  (Figs.  418,  p.  520,  and  Fig.  439,  p.  546)  ;  (3)  the  temporo-pontine 
tract,  which  is  composed  of  fibres  which  take  origin  in  the  two  upper  convolutions  of  the 
temporal  lobe  and  pass  through  this  section  of  the  internal  capsule  to  reach  the  outer 
part  of  the  crusta  of  the  crus  cerebri.  Through  this  they  reach  the  ventral  part  of  the 
pons,  in  the  gray  matter  of  which  they  end. 

When  the  fibres  of  the  internal  capsule  are  traced  iipwards  they  are  found  to 
spread  out  widely  from  each  other  in  a  radiating  or  fan-sbaped  manner,  so  as  to 
reach  the  various  convolutions  of  the  cerebral  hemisphere.  This  arrangement  is 
termed  the  corona  radiata.  The  callosal  system  of  fibres,  as  they  proceed  into  the 
hemisphere,  also  radiate,  and  they  intersect  the,  fibres  of  the  corona  radiata  (Fig. 
468,  p.  582;. 

External  Capsule. — 'I'Ih;  tbin  lamina  of  white  juatter  between  the  outer  aspect 
of  the  putamen  and  the  claustrum  is  called  the  external  capsule.     This  joins  with 


584  THE  NEEVOUS  SYSTEM. 

the  internal  capsule  in  front  of  and  behind  the  putamen,  and  in  this  manner  the 
lenticular  nucleus  is  encapsulated  by  white  matter. 

Morphological  Subdivision  of  the  Cerebral  Hemisphere. — In  many  respects  the  descrip- 
tive anatomy  of  the  human  cerebral  hemisphere  is  not  in  accord  with  the  facts  which  liave  been 
acquired  regarding  its  morj^hological  evolution ;  and  of  recent  years  this  discrepancy  has  become 
more  marked  through  the  important  researches  of  Elliot  Smith. 

From  the  morj)hological  point  of  view  the  cerebral  hemisphere  may  be  regarded  as  being 
composed  of  three  jiarts,  viz.  the  rhinencephalon,  the  corpus  striatum,  and  the  neo-palli>im. 

The  rhinencephalon  is  the  most  archaic  part  of  the  hemisphere,  and  in  the  brains  of  the 
lower  vertebrates  (fislies,  amphibians,  reptiles)  it  constitutes  its  chief  bulk.  In  the  human  brain 
it  is  represented  by  the  olfactory  Inilb,  olfactory  tract  and  its  roots,  the  anterior  perforated 
space,  the  uncus,  the  gyrus  subcallosus,  the  septum  lucidum,  the  hijipocampus,  fornix,  gyrus 
dentatus,  and  the  gyrus  supracallosus. 

The  uncus,  with  the  aborted  lateral  stria  of  the  olfactory  peduncle,  is  all  that  remains  in  the 
human  brain  of  the  relatively  huge  pyriform  lobe  of  many  of  the  lowei'  mammals.  The  hippo- 
camjtal  convolution  which  lies  to  the  outer  side  of  the  dentate  fissure,  although  it  runs  con- 
tinuously into  the  uncus,  is  not  a  part  of  the  rhinencephalon.  It  belongs  to  the  neo-pallium. 
The  feeble  furrow,  termed  the  incisura  temporalis  which  separates  the  uncus  from  the  tem^aoral 
pole,  is  one  of  the  most  primitive  of  the  cerebral  fissures.  It  represents  the  rhinal  or  ecto-rhinal 
fissure — the  bounding  fissure  of  the  rhinencephalon. 

The  neo-pallium  is  represented  by  the  rest  of  the  hemisphere,  exclusiA^e  of  the  corpus  striatum. 
It  therefore  comprises  almost  the  whole  of  the  convoluted  cortex  on  the  surface  together  with  its 
associated  white  matter.  The  great  development  of  the  neo-pallium  in  man  is  one  of  the  most 
distinctive  characters  of  the  human  brain. 

In  their  jjhylogenetic  evolution  the  rhinencephalon  and  the  neo-pallium  aj^pear  to  develop 
more  or  less  independently  of  each  other.  In  certain  cases  the  former  atrophies,  whilst  the 
neo-pallium  attains  a  high  degree  of  development  {e.g.  man,  monkey,  whale,  etc.),  in  others  the 
reverse  development  occurs  {e.g.  hedgehog  and  many  other  mammals),  in  which  the  rhinencephalon 
forms  a  large  part  of  the  hemisphere  and  the  neo-pallium  is  relatively  small. 

Intimate  Structure  of  the  Cerebral  Hemisphere. 

The  cerebral  hemisphere  is  composed  of  an  external  coating  of  gray  matter, 
termed  the  cortex,  spread  over  an  internal  mass  of  white  matter,  which  is  called  the 
medullary  centre.  The  cortex  is  of  peculiar  interest,  seeing  that  there  is  good  reason 
for  believing  that  in  it  the  higher  functions  of  the  brain,  or  those  which  may  be 
classed  under  the  general  designation  of  the  intellectual  functions,  take  place.  It 
is  within  the  same  layer  of  gray  matter  that  the  influence  of  those  external  impres- 
sions, which  gain  access  to  the  cerebro-spinal  axis  through  the  senses,  finally  take 
shape  as  consciousness ;  and  in  it  also  are  placed  the  centres  which  carry  on  the 
psycho-motor  functions.  The  white  medullary  centre  is  composed  of  nerve-fibres 
which  constitute  the  paths  along  which  the  influence  of  impressions  is  carried  to 
and  from  the  cortex,  and  from  one  part  of  the  cortex  to  another. 

The  Cerebral  Cortex. 

The  gray  cortex  is  spread  over  the  entire  surface  of  the  cerebral  hemisphere,  but 
it  does  not  form  a  layer  of  equal  thickness  in  all  localities.  At  the  summit  of  a 
convolution  it  is  always  thicker  than  at  the  bottom  of  a  furrow.  The  maximum 
thickness  of  cortex  (about  6  mm.)  is  attained  in  tlie  upper  parts  of  the  two  central 
convolutions,  whilst  the  minimum  (about  2-5  mm.)  may  be  observed  in  the  region 
of  the  occipital  pole.  The  amount  of  gray  cortex  differs  considerably  in  different 
individuals,  and  appreciably  diminishes  in  old  age.  It  is  also  stated,  but  upon 
imperfect  evidence,  that  it  is  relatively  more  abundant  in  the  male  than  in  the 
female. 

In  structure,  likewise,  marked  differences  may  be  noted  in  the  gray  cortex  of 
different  regions,  and  excellent  work  has  been  recently  done  in  the  direction 
of  connecting  these  structural  peculiarities  with  the  functional  characteristics 
of  particular  areas  and  applying  them  to  the  determination  of  morpliological 
problems  connected  witli  the  cerebral  surface  (Campbell  and  Bolton).  In  certain 
locahties  this  structural  difference  is  quite  apparent  to  the  naked  eye  when  sections 
are  made  through  the  cortex.  Tliere  are,  however,  no  sharp  transitions  in  structure. 
One  form  of  cortex  passes,  as  a  rule  gradually  and  almost  insensibly,  into  the  variety 
of  cortex  which  is  distinctive  of  an  adjoiniog  region,  and  throughout  the  whole 


STEUCTUIiE  OF  THE  CEEEBEAL  COKTEX.  585 

mass  a  general  ground  type  may  be  recognised.  It  is  only  to  those  general 
structural  features  which  more  or  less  characterise  the  entire  cortical  layer  that  we 
shall  be  able  to  refer. 

When  sections  are  made  through  the  fresh  brain,  and  the  cut  surface  is  closely 
inspected,  it  will  usually  be  apparent  that  the  cortex  is  indistinctly  stratified.  On 
the  outside  there  is  a  thin,  whitish  layer,  and  beneath  this  the  gray  matter  presents 
two  strata  of  very  nearly  equal  thickness,  viz.  a  middle,  gray-coloured  stratum  and 
an  inner,  yellowish-red  stratum.  Between  the  two  latter  layers  a  narrow  white 
band  is,  in  many  places,  visible.  This  is  termed  the  outer  band  of  Baillarger.  When 
the  layers  indicated  above  are  present,  four  strata  superimposed  on  each  other  are 
recognised ;  but  in  certain  regions,  as,  for  instance,  in  the  anterior  central  convolu- 
tion, a  second  white  streak  traverses  the  deep  or  inner  gray  layer  and  divides  it  into 
two.  This  is  termed  the  inner  white  band  of  Baillarger,  and,  when  it  is  present,  the 
gray  cortex  becomes  divided  obscurely  into  six  alternating  white  and  gray  layers. 

The  outer  band  of  Baillarger  is  strongly  marked  in  the  region  of  the  calcarine 
fissure  and  gives  a  characteristic  appearance  to  this  portion  of  the  cortex.  In  this 
locality  it  receives  the  name  of  the  band  of  Vicq  d'Azyr  or  the  stria  of  Gennari 
(Fig.  465,  p.  579). 

According  to  Henschen  the  visual  centre  is  strictly  limited  to  the  region  in 
which  the  stria  of  Gennari  is  present.  Elliot  Smith  applies  the  name  of  "  striated 
area  "  to  this  cortical  district,  and  considers  that  it  affords  a  means  of  identifying 
hom.ologous  sulci  in  the  brains  of  man  and  the  apes. 

To  obtain  a  full  understanding  of  the  minute  structure  of  the  cerebral  cortex  many 
different  methods  must  be  employed,  and  it  is  only  by  combining  the  several  separate 
pictures  which  are  thus  afforded  that  the  end  in  view  is,  in  some  measure,  readied. 

The  stratification  indicated  above  has  little  bearing  upon  the  more  essential  points  of 
the  intimate  structure  of  the  cortex.  The  three  white  layers  are  brought  about  by 
aggregations  of  fibres  running  in  a  tangential  direction,  or,  in  other  words,  in  a  direction 
parallel  to  the  surface  of  the  convolution. 

Nerve-cells. — According  to  the  arrangement  and  the  characters  presented  by  the 
nerve-cells  which  are  met  with  at  different  depths,  it  is  now  usual  to  recognise  four  layers 
in  the  cortex.     These  are  :  (1)  the  stratum  zonale  ;  (2)  the  layer  of  small  pyramidal  cells  ; 

(3)  the  layer  of  large  pyramidal  cells ;  and  (4)  the  layer  of  polymorphic  cells. 

As  the  pyramidal  cells  are  specially  characteristic  of  the  cerebral  cortex,  we  shall,  in 
the  first  iiistance,  describe  the  two  layers  which  contain  them.  The  difference  between 
these  two  layers  largely  depends  upon  the  difference  in  the  size  of  the  constituent  cells. 
Taken  together,  the  second  and  third  layers  constitute  the  chief  part  of  the  cortex ;  they 
merge  insensibly  into  each  other,  and,  in  the  parietal  and  frontal  lobes,  the  layer  of  large 
pyramidal  cells  is  the  thickest  of  all  the  layers.  In  both  of  these  strata  the  pyramidal 
cells  present  the  same  form,  and  apparently  also  similar  connexions. 

A  pyramidal  cell  has  a  triangular  outline.  Its  apex  is  directed  towards  the  surface 
of  the  convolution  and  is  drawn  out  into  a  long,  tapering,  apical,  dendritic  process ;  its 
base  is  turned  towards  the  medullary  centre  of  the  gyrus,  and  from  this  (usually  from  the 
centre)  a  slender  axon  proceeds.  Numerous  lateral  dendrites  are  given  off  from  both  sides 
of  the  cell-body,  and  particularly  from  the  two  basal  corners.  The  apical  dendrite  varies 
in  length,  according  to  the  depth  at  which  the  cell  is  placed  in  the  cortex.  In  every  case 
it  passes  straight  towards  the  surface  of  the  convolution.  Every  here  and  there  fine 
lateral  branches  come  off  from  it,  and  ultimately  it  enters  the  stratum  zonale,  where, 
close  to  the  surface,  it  ends  by  breaking  up  into  a  large  number  of  fine  terminal  filaments, 
which  spread  out  horizontally  in  every  direction  and  interlace  closely  with  the  corre- 
sponding filaments  of  other  pyramidal  cells  and  with  the  other  elements  of  this  layer. 

The  axon  of  the  cell  descends,  gives  off  collatei'als,  assumes  a  medullary  sheath,  and 
enters  the  central  wliite  core  of  the  gyrus  as  a  nerve  fibre. 

The  stratum  zonale  is  chiefly  com[)osed  of  fibres  which  run  in  a  tangential  direction,  or, 
in  other  words,  parallel  to  the  surface.  These  form  an  interlacement  of  considerable  density 
and  extreme  complexity.  The  elements  which  for  the  most  part  enter  into  the  formation 
of  this  fcltwork  are  :  (1)  the  tcrnunal  filaments  of  the  apical  dendrites  of  the  pyramidal 
cells;  (2)  the  terminal  filaments  of  certain  corticipetal  fibres,  which  enter  the  cortex  from 
the  white  centre  of  the  gyrus  ;  (3)  the  axons  of  certain  small  cells  peculiar  to  this  stratum  ; 

(4)  the  axons  of  the  cells  of  Martinotti.  Spread  over  the  surface  of  this  tangential  inter- 
lacement of  fibres,  which  constitutes  the  most  important  part  of  the  stratum  zonale,  there 


586 


THE  NEEVOUS  SYSTEM. 


BAUD   OF 
BECHTEREW 


■z  OUTER  BAND 


^    BAILLARGER 


is  a  thin  layer  of  neuroglia  which  intervenes  between  it  and  the  pia  mater,  which  covers 
the  convolution.  The  stratum  zonale  is  not  devoid  of  nerve-cells,  although  these  are 
small  and  somewhat  indefinite  in  their  connexions.  The  most  characteristic  form  is  a 
small  fusiform  cell  described  by  Cajal,  which  sends  out  from  either  end  a  long  process 

and  which  lies  in  the  deeper 
--     |Sr!~IL__^  NcuRocLiA.       pa.rt    of    the    layer.      The 
"         ^^  long    filamentous   processes 

of  this  cell  thread  their  way 
between  the  other  fibres  in 
a  tangential  direction  and 
give  oft'  minute  branches 
which  pass  towards  the 
surface. 

The  deepest  layer  of  the 
cortex  contains  the  poly- 
morphic cells.  These  cells 
are  not  large,  and  they 
present  many  different 
forms.  Numerous  dendrites 
proceed  from  the  cells  of 
this  group,  but  none  of 
these  reach  the  stratum 
zonale,  and  in  this  respect 
the  polymorphic  cells  offer 
a  marked  contrast  to  the 
pyramidal  cells.  The  axons 
of  the  polymorphic  cells, 
however,  like  those  of  the 
pyramidal  cells,  enter  the 
white  centre  of  the  gyrus 
in  the  shape  of  nerve-fibres. 
In  addition  to  the  cells 
characteristic  of  the  several 
layers,  there  are  two  which, 
may  be  found  amongst  the 
pyramidal  or  amongst  the 
polymorphic  cells.  These 
are  :  (1)  the^  cells  of  Golgi ; 
(2)  the  cells  of  Martinotti. 

A  cell  of  Golgi  has  this 
peculiarity — that  its  axon, 
close  to  its  origin,  begins 
to  divide,  and  very  soon 
loses  its  individuality  by 
breaking  up  into  a  perfect 
maze  of  branches,  none  of 
which  pass  far  from  the 
neighbourhood  of  the  cell- 
body  and  none  of  which 
enter  the  stratum  zonale. 
The  cell  of  Martinotti  is  small  and  is  chiefly  found  in  the  deeper  part  of  the  cortex. 
Its  leading  peculiarity  is,  that  its  slender  axon  runs  in  a  contrary  direction  to  the  axons  of 
the  pyramidal  cells  and  of  the  polymorphic  cells.  In  other  words,  it  proceeds  towards  the 
surface,  and,  entering  into  the  stratum  zonale,  divides  into  terminal  filaments,  which  spread 
out  in  the  tangential  interlacement  characteristic  of  this  layer. 

Nerve-Fibres. — ^The  arrangement  of  the  nerve-fibres  can  best  be  studied  in  vertical 
sections  through  the  gray  cortex,  which  have  been  specially  treated  with  this  end  in 
view.  In  such  preparations  bundles  of  nerve-fibres  are  seen  to  radiate  into  the  gray 
cortex  from  the  surface  of  the  white  centre  of  the  gyrus.  As  these  proceed  through  the 
polymorphic  layer  into  the  layer  of  lai'ge  pyramidal  cells,  they  gradually  become  less 
distinct,  and,  finally,  they  disperse  and  are  lost  to  view  before  they  reach  the  layer  of 
small  pyramidal  cells.  In  the  intervals  between  the  radiating  bundles  the  polymorphic 
and  large  pyramidal  cells  are  arranged  in  columns,  and  in  the  same  intervals  an  open 


INNER   BAND 

OF 
BAILLARGER 


INTRACORTICAL 

ASSOCIATION 

FIBRES 


Fig.  469. 


-DiAGRAjr  TO  Illustrate  Minute  Structure  of  the 
Cerebral  Cortex. 


A  1 

T-,"  I-Neui'oglia  cells. 

C.  Cell  with  short  axon  (N)  which  breaks 

up  in  a  free  arborisation. 

D.  Sijiudle-shaiied  cell  in  stratum  zonale. 


E.  Small  iDyramidal  cell. 

F.  Large  pyramidal  cell. 

G.  Cell  of  Martinotti. 
H.  Polymorphic  cell. 
K.  Corticipetal  fibres. 


THE  OLFACTOEY  TEACT  AND  BULB. 


587 


feltwork  of  intercrossiug  fibres  is  evident.  After  the  radiating  fibre-bundles  have  dis- 
appeared the  same  feltwork  of  fibres  is  visible  in  the  gray  matter,  and  consequently  it  is 
convenient  to  distinguish,  with  Edinger,  an  inter-radial  feltwork  and  a  supra-radial  felt- 
work of  fibres  in  the  cortex.  The  fibres  which  enter  into  the  composition  of  the  diflerent 
radial  bundles  vary  in  number  from  ten  to  twenty,  and  they  gradually  diminish  in  number 
as  they  proceed  onwards.  This  diminution  is  due  to  their  joining  the  various  cells  that 
they  meet  (both  polymorphic  and  pyramidal)  as  their  axons.  The  fiVjres  in  a  given  bundle 
also  vary  much  in  size,  and  it  may  be  noticed  that  the  largest  fibres  disappear  in  the 
vicinity  of  the  large  pyramidal  cells,  which  shows  clearly  that  it  is  with  these  that  they 
are  connected.  But,  in  addition  to  cell-axons,  the  radial  bundles  contain  fibres  of  an 
altogether  difi'erent  type,  viz.  corticipetal  fibres,  which  pass  through  all  the  layers  of  the 
cortex  and  end  in  fine  terminal  filaments  in  the  tangential  interlacement  of  the  stratum 
zonale. 

The  inter-radial  and  supra-radial  feltwork  is  largely  formed  of  the  collaterals  which 
issue  from  the  axons.  By  a  condensation  of  this  feltwork  the  two  bands  of  Baillarger  are 
formed.  The  outer  band,  which  is  the  broader  and  better  marked,  occurs  in  the  deeper 
part  of  the  layer  of  the  large  pyramidal  cells.  The  inner  band,  when  present,  is  formed 
in  the  superficial  part  of  the  layer  of  polymorphic  cells. 

Another  condensation  of  the  fibre-feltwork  in  the  superficial  part  of  the  supra-radial 
region  may  be  noted  in  certain  localities.     This  is  termed  the  band  of  Bechterew. 

It  has  been  noted  that  up  to  a  certain  point  the  tangential  fibres  increase  in  quantity 
as  age  advances,  and  there  is  reason  to  believe  that  upon  the  richness  with  which  the 
gray  cortex  is  supplied  with  fibres — more  especially  of  the  tangential  variety — depends  to 
some  extent  the  intellectual  capacity  of  an  individual. 

Whilst  the  general  mass  of  the  cortex  for  the  most  part  conforms  more  or  less  closely 
to  the  ground-type  described  above,  showing  merely  deviations  characteristic  of  the 
different  regions,  there  is  one  part  of  the  cortex,  viz.  the  cornu  ammonis  and  the  fascia 
dentata,  in  which  the  structural  arrangement  of  the  elements  is  very  markedly  different. 
To  some  extent  this  is  due  to  the  complicated  manner  in  which,  in  this  region,  the  cortex 
is  folded  upon  itself. 

Olfactory  Tract  and  Bulb. 

The  olfactory  tract  and  bulb  arise  as  a  hollow  outgrowth  from  the  primitive  cerebral 
vesicle.  In  many  animals  with  a  well-developed  olfactory  apparatus,  the  tract  and  bulb 
remain  hollow ;  but  in  man  the  central  cavity  becomes 
obliterated,  although  traces  of  the  original  hollow  persist 
in  the  shape  of  ependymal  remains,  visible  in  the  centre 
of  both  tract  and  bulb.  Outside  these  ependymal 
elements  is  a  coating  of  white  matter,  upon  which  is 
laid  the  gray  matter.  The  gray  matter,  however,  is 
by  no  means  uniformly  distributed  over  the  surface. 
In  the  tract,  except  along  the  dorsal  edge,  it  is  so  thinly 
spread  that  it  is  hardly  appreciable.  In  the  bulb,  on 
the  other  hand,  there  is  very  little  gray  matter  on  the 
dorsum,  but  a  considerable  quantity  on  the  ventral 
surface  ;  and  it  is  into  this  that  the  delicate  nerves  which 
enter  the  cranium  through  the  cribriform  plate  of  the 
ethmoid  bone  sink.  A  brief  description  of  the  structure 
of  this  infrabulbar  mass  of  gray  matter,  as  well  as  of 
the  connexions  established  by  its  elements,  now  becomes 
necessary. 

The  fibres  of  the  delicate  olfactory  nerves  are  to 
be  regarded  as  the  axons  of  the  olfactory  cells  of  the 
olfactory  mucous  membrane.  They  enter  the  ventral 
surface  of  the  olfactory  bulb,  and  there  each  breaks  iip 
in  an  arborescent  fashion  into  a  tuft  of  terminal  filaments. 
A  thick  dendrite  from  a  mitral  cell  of  the  bulb  passes 
down  towards  this  terminal  tuft,  and,  coming  into  con- 
tact with  it,  breaks  up  and  terminates  in  a  similar 
manner.  In  this  way  a  large  number  of  globular  bodies, 
formed    by    the    arborescent    terminations    of   a   mitral 

dendrite  and  of  certain  olfactory  nerve-fibres,  are  formed.  These  arc  the  olfactory 
glomeruli  of  the  bulb.     The  mitral  cells  lie  deeper  in  the  olfactory  bulb.     Each  gives 


CRIBRIFORM 
PLATE 


LFACTORY    MUCOUS 
11    MEMBRANE 


Fig.  470. — Diagram  op  the  Minute 
Structuhb  ok  tiih  Or,i''ACT()iiY  Bulb. 


588  THE  NERVOUS  SYSTEM. 

off  several  dendrites  and  one  axon.  Only  one  dendrite  enters  into  the  formation  of  a 
glomerulus,  but  several  nerve-fibres  may  be  connected  with  such  a  body.  It  thus  happens 
that,  through  its  dendrite,  a  mitral  cell  may  stand  in  connexion  with  several  olfactory 
nerve-fibres.  The  axon  of  the  mitral  cell  passes  upwards  to  the  white  matter  of  the 
bulb,  enters  this,  and  is  conducted  through  the  tract  towards  the  cerebral  cortex. 

White  Medullary  Centre  of  the  Cerebral  Hemisphere. 

The  white  matter  of  the  hemisphere  which  lies  subjacent  to  the  gray  cortex  is 
composed  of  medu Hated  nerve-fibres,  arranged  in  a  very  intricate  manner.  Accord- 
ing to  the  connexions  which  they  establish  these  fibres  may  be  classified  into  three 
distinct  groups,  viz.  (1)  commissural  fibres ;  (2)  association  fibres ;  and  (3)  projec- 
tion fibres. 

Commissural  Fibres. — These  are  fibres  which  link  together  portions  of  the 
gray  cortex  of  opposite  cerebral  hemispheres.  They  are  arranged  in  three  groups 
forming  three  definite  structures,  viz.  the  corpus  callosum,  the  anterior  commissure, 
and  the  psalterium  or  the  hippocampal  commissure. 

The  corpus  callosum  has  in  a  great  measure  been  already  studied  (p.  570).  As 
it  enters  each  hemisphere,  its  fibres  spread  out  in  an  extensive  radiation  (the  radia- 
tion of  the  corpus  callosum).  It  thus  comes  about  that  every  part  of  the  cerebral 
cortex,  with  the  exception  of  the  bulbus  olfactorii  and  the  under  and  fore  part  of 
the  temporal  lolie,  is  reached  by  the  callosal  fibres.  But  it  should  be  clearly  under- 
stood that  all  the  regions  of  the  cortex  do  not  receive  an  equal  proportion  of  fibres ; 
in  other  words,  some  cortical  areas  would  appear  to  be  more  plentifully  supplied 
than  others.  Another  point  of  some  importance  consists  in  the  fact  that  the  callosal 
fibres  do  not,  as  a  rule,  connect  together  symmetrical  portions  of  the  gray  cortex. 
As  the  fibres  cross  the  mesial  plane  they  become  greatly  scattered,  so  that  most 
dissimilar  parts  of  the  cortex  of  opposite  hemispheres  come  to  be  associated  with 
each  other. 

Each  callosal  fibre  arises  in  one  hemisphere  and  ends  by  fine  terminal  arborisations 
in  the  cortex  of  the  opposite  hemisphere.  It  may  arise  in  any  one  of  three  ways,  viz. 
(1)  as  the  axon  of  one  of  the  cortical  cells,  either  pyramidal  or  polymorphic;  (2)  as  the 
collateral  of  a  fibre  of  association ;  (3)  as  the  collateral  of  a  fibre  of  projection. 

Many  cases  have  been  recorded  in  which,  through  congenital  defect,  the  corpus 
callosum  has  not  been  developed.  In  the  description  of  this  structure  on  p.  570  attention 
has  been  called  to  a  layer  of  callosal  fibres  which  sweep  over  the  posterior  and  descending 
horns  of  the  lateral  ventricle,  so  as  to  form  the  immediate  outer  wall  of  the  cavity.  This 
layer  is  called  the  tapetum,  and  it  has  been  stated  that  when  the  corpus  callosum  is 
absent  the  tapetum  is  found  in  a  well-developed  condition.  Further,  it  has  been  asserted 
that  in  cases  where  the  corpus  callosum  has  been  experimentally  destroyed  the  tapetum 
suffered  no  degeneration  (Muratoff).  Certain  anatomists  are,  therefore,  inclined  to  argue 
that  the  tapetum  has  little  or  no  connexion  with  the  corpus  callosum.  This  assertion, 
however,  cannot  by  any  means  be  regarded  as  being  proved.  There  is  a  large  amount  of 
evidence  on  the  other  side.  Thus,  Mingazzini  has  seen  a  case  of  failure  of  the  corpus 
callosum  which  was  accompanied  by  a  corresponding  defect  in  the  tapetum,  whilst  soften- 
ing of  the  splenium  and  the  forceps  major  has  been  observed  by  Anton  to  be  accompanied 
by  a  secondary  degeneration  of  the  tapetum.  Further,  the  recent  experimental  evidence 
of  Ferrier  and  Turner  would  appear  to  support  the  older  view  that  the  tapetum  is  associated 
in  the  closest  manner  with  the  corpus  callosum. 

The  anterior  commissure  (commissura  anterior)  is  a  structure  supplemental  to 
the  corpus  callosum.  It  connects  together  the  two  olfactory  lobes,  and  also  portions 
of  opposite  temporal  lobes.  It  presents  a  cord-like  appearance  and  is  arranged  in 
the  form  of  a  horse-shoe,  the  concavity  of  which  looks  backwards.  The  middle  free 
portion  is  placed  immediately  in  front  of  the  anterior  pillars  of  the  fornix  as  they 
curve  downwards,  and  also  in  intimate  relation  to  the  anterior  end  of  the  third 
ventricle.  Posteriorly,  the  small  portion  of  the  anterior  commissure  which  appears 
in  the  ventricle  Ijetween  the  two  pdlars  of  the  fornix  is  clothed  with  the  ventricular 
ependyma ;  anteriorly,  the  commissure  is  connected  with  the  lamina  cinerea  as  it 
stretches  from  the  optic  chiasma  upwards  towards  the  rostrum  of  the  corpus 
callosum. 


COMMISSUEAL  FIBEES 


>89 


The  lateral  part  of  the  anterior  commissure  penetrates  the  cerebral  hemisphere, 
and,  gaining  the  lower  part  of.  the  anterior  end  of  the  internal  capsule,  divides  into 
two  portions,  viz.  a  small  lower  olfactory  part  and  a  much  larger  temporal  part. 

The  olfactory  portion  of  the  anterior  commissure  is  an  exceedingly  small  fasci- 
culus. It  passes  downwards  and  forwards,  and  finally  enters  the  olfactory  tract. 
It  is  composed  (1)  of  true  commissural  fibres,  which  bind  one  olfactory  bulb  to  the 
other ;  and  (2)  of  other  fibres,  which  connect  the  olfactory  bulb  of  one  side  with 
the  temporal  lobe  of  the  other  side. 

The  temporal  portion  is  formed  of  almost  the  whole  of  the  fibres  of  the  com- 
missure. It  is  carried  transversely  outwards,  under  the  lenticular  nucleus,  until  it 
gains  the  interval  between  the  globus  pallidus  and  the  putamen.     At  this  point  it 

Ventricle  V.  Corijus  callosum 

Corpus  callosum  \ 


Lateral  a  entricle 


Lateral  ventricle 


Caudate  nucleus 


Internal 
capsule 


Anterior 
commissure 


Fig.  471. — Two  Coronal  Sections  thbough  the  Cerebral  Hemispheres  of  an  Orang, 
IN  THE  Plane  of  the  Anterior  Commissure. 

A,  Section  through  the  left  hemiKi')here  in  a  plane  a  short  distance  behind  B,  which  is  a  section 
through  the  right  hemisphere. 

changes  its  direction  and  sweeps  backwards.  In  coronal  sections  through  the 
brain,  behind  this  bend,  the  temporal  portion  of  the  anterior  commissure  appears  as 
an  oval  bundle  of  fibres  cut  transversely  and  placed  in  close  contact  with  the  under 
surface  of  the  lenticular  nucleus  (Fig.  468,  p.  582).  Finally,  it  turns  sharply  down- 
wards on  the  outer  aspect  of  the  amygdaloid  nucleus,  and  its  fibres  are  lost  in  the  white 
medullary  centre  of  the  temporal  lobe.  The  precise  part  of  the  cerebral  cortex  with 
which  these  fibres  stand  in  connexion  is  not  known.  When  the  lateral  part  of  the 
anterior  commissure  is  displayed  by  dissection,  it  is  seen  to  be  twisted  like  a  rope. 

The  psalterium,  or  the  hippocampal  commissure,  is  composed  of  fibres  which  con- 
nect the  cornu  ammonis  of  one  side  with  the  corresponding  structure  of  the  opposite 
side.     It  is  described  on  p.  572. 

Association  Fibres. — The  association  fibres  bind  together  different  portions  of 
the  cortex  of  the  same  hemisphere,  'i'hey  are  grouped  into  long  and  short  associa- 
tion bundles. 

The  greater  number  of  the  short  association  fibres  pass  between  adjacent 
convolutions.  They  curve  round  the  bottom  of  the  sulci  in  U-shaped  loops.  Some 
of  these  occupy  the  deepest  part  of  the  gray  cortex  itself,  and  are  termed  intracortical 
association  fibres  (Fig.  469,  p.  586) ;  others  lie  immediately  subjacent  to  the  gray 
matter — between  it  and  the  general  mass  of  the  white  matter — and  receive  the 
name  of  suhcorlicaJ  fiJjres.  Many  groups  of  short  asscjciatioii  fibres,  instead  of  linking 
together  contiguous  convolutions,  pass  between  gyri  more  or  less  remote.     It  is  only 


590 


THE  NEEVOUS  SYSTEM. 


after  birth,  when  intellectual  effort  and  education  have  stimulated  different  portions 
of  the  cortex  to  act  in  harmony  and  in  conjunction  with  each  other,  that  these 
association  fibres  assume  their  sheaths  of  medulla  and  become  functional. 

The  long  association  fibres  are  arranged  in  bundles  which  run  for  considerable 
distances  within  the  white  medullary  centre  of  the  cerebral  hemisphere,  and  unite 
districts  of  gray  cortex  which  may  be  far  removed  from  each  other.  The  better 
known  of  these  fasciculi  are  the  following:  (1)  the  uncinate;  (2)  the  cingulum; 
(3)  the  superior  longitudinal ;  (4)  the  inferior  longitudinal ;  (5)  the  occipito-frontal. 

The  fasciculus  uncinatus  is  composed  of  fibres  which  arch  over  the  stem  of  the 
Sylvian  fissure  and  connect  the  frontal  pole,  and  the  orbital  convolutions  of  the 
frontal  lobe,  with  the  front  portion  of  the  temporal  lobe. 

The  cingulum  is  a  very  well-marked  and  distinct  band,  which  is  closely  associated 
with  the  limbic  lobe.  Beginning  in  front,  in  the  region  of  the  anterior  perforated 
spot,  it  arches  round  the  genu  of  the  corpus  callosum  and  is  carried  backv/ards  on 
the  upper  surface  of  this  structure  at  the  place  where  its  fibres  pass  into  the 


Fig.  472. — Diagram  of  the  Leading  Association  Bundles  of  the  Cerebral  Hemisphere. 
(Founded  on  the  drawings  of  Dejerine.) 

A.   Outer  aspect  of  hemisphere.  B.  Inner  aspect  of  hemisphere. 

callosal  radiation.  The  cingulum,  therefore,  lies  under  cover  of  the  callosal  gyrus 
and  stands  in  intimate  relation  to  the  white  centre  of  this  convolution  (Fig.  457, 
p.  570).  At  the  hinder  end  of  the  corpus  callosum  the  cingulum  turns  round 
the  splenium  and  is  carried  forwards,  in  relation  to  the  hippocampal  gyrus,  to  the 
uncus  and  the  temporal  pole.  The  cingulum  is  composed  of  several  systems  of 
fibres  which  only  run  for  short  distances  within  it. 

The  fasciculus  longitudinalis  superior  is  an  arcuate  bundle  which  is  placed  on  the 
outer  aspect  of  the  foot  or  basal  part  of  the  corona  radiata  and  connects  the  frontal, 
occipital,  and  temporal  regions  of  the  hemisphere.  It  lies  in  the  base  of  the  fronto- 
parietal operculum  and  sweeps  backwards  over  the  insular  region  to  the  posterior 
end  of  the  Sylvian  fissure.  Here  it  bends  downwards  round  the  hinder  end  of  the 
putamen  and  proceeds  forwards  in  the  temporal  lobe,  to  reach  its  anterior  extremity. 
As  it  turns  downwards  to  reach  the  temporal  lobe  numerous  fibres  radiate  from  it 
into  the  occipital  lobe. 

The  fasciculus  longitudinalis  inferior  is  a  very  conspicuous  bundle  which  extends 
along  the  whole  length  of  the  occipital  and  temporal  lobes  (Fig.  457,  p.  570).  In  the 
occipital  lobe  it  is  placed  on  the  outer  aspect  of  the  optic  radiation,  which  takes  a  similar 
direction  and  from  which  it  is  distinguished  by  the  greater  coarseness  of  its  fibres 
(Figs.  462,  p.  576 ;  465,  p.  578 ;  473,  p.  592).  It  is  not  present  in  the  macaque 
monkey  (Ferrier  and  Turner),  but  is  well  developed  in  the  orang  and  the  chimpanzee, 

The  fasciculus  occipito-frontalis  is  a  bundle  of  fibres  which  runs  in  a  sagittal  direction 
in  intimate  relation  to  the  lateral  ventricle  (Fig.  468,  p.  582).  It  has  been  pointed  out 
(Forel,  Onufrowicz,  and  others)  that,  in  cases  where  the  corpus  callosum  fails  to  develop, 
the  tapetum  remains  apparently  unaffected,  and  Dejerine  has  endeavoured  to  prove  that 
the  fibres  of  this  layer  really  belong  to  the  fasciculus  occipito-frontalis.  According  to 
Dejerine,  the  fasciculus  occipito-frontalis  lies  on  the  inner  aspect  of  the  corona  radiata  in 
intimate  relation  to  the  caudate  nucleus,  and  posteriorly  it  spreads  out  over  the  upper 
and  outer  aspect  of  the  lateral  ventricle,  immediately  outside  the  ependyma,  where 
it  constitutes  the  tapetum   (see  p.  588).     There  is  a  considerable  amount  of  Hterature 


PEOJECTION  FIBEES. 


591 


dealing  with  this  subject,  and  the  most  probable  explanation  of  the  difficulty  would 
appear  to  be  that  the  tapetum  is  composed  of  fibres  derived  from  both  the  corpus 
callosum  and  the  fasciculus  occipito-fron talis  of  Dejerine. 

Projection  Fibres. — The  projection  fibres  are  those  which  connect  the  cerebral 
cortex  with  nuclear  masses  placed,  at  a  lower  level.  The  great  bulk  of  these  fibres 
are  found  in  the  corona  radiata.  This  has  already  been  seen  to  be  formed  by  the 
continuation  upwards  of  the  internal  capsule  (p.  583).  In  the  corona  radiata  the 
fibres  which,  lower  down,  are  gathered  together  in  the  compact  mass  which  con- 
stitutes the  internal  capsule,  radiate  in  every  direction,  intersect  the  radiation  of 
the  corpus  callosum,  and  finally  reach  every  region  of  the  cortex.  Although  the 
fibres  of  the  corona  radiata  represent  the  chief  bulk  of  the  projection  fibres,  it  should 
also  be  borne  in  mind  that  a  certain  number  gain  the  cortex  by  a  different  route, 
notably  through  and  under  the  lenticular  nucleus  and  by  the  path  offered  by  the 
external  capsule. 

The  projection  fibres  of  the  cerebral  hemisphere  may  be  classified  into  (1) 
corticipetal,  and  (2)  corticifugal  groups ;  and  under  these  headings  the  following 
great  strands  may  be  arranged  : — 


Corticipetal  Projection  Strands. 

1.  Tbalamo-cortical. 

2.  Corticijjetal  fibres  of  the  optic  radiation. 

3.  The  auditory  radiation. 


Corticifugal  Projection  Strands. 

1.  The  pyramidal  or  great  motor  tract. 

2.  The  cortico-thalamic. 

3.  The  fronto-pontine  strand. 

4.  The  temporo-pontine  strand. 

5.  The  corticifugal  fibres  of  the  optic 

tion. 


radia- 


The  great  motor  or  pyramidal  tract  is  composed  of  fibres  which  arise  from  pyramidal 
cells  in  that  portion  of  the  cortex  which  is  spread  over  the  Eolandic  area,  or,  in 
other  words,  in  the  district  immediately  in  front  of  the  fissure  of  Eolando.  The 
fibres  descend  through  the  corona  radiata  into  the  posterior  limb  of  the  internal 
capsule.  From  this  point  the  further  course  of  the  pyramidal  tract  has  been 
traced,  viz.  through  the  central  part  of  the  crusta  of  the  crus  cerebri,  the  ventral 
part  of  the  pons,  and  the  pyramid  of  the  medulla  oblongata.  At  the  level  of  the 
foramen  magnum  it  decussates  in  the  manner  already  described,  and  enters  the 
spinal  cord  as  the  crossed  and  direct  pyramidal  tracts.  The  fibres  composing  these 
end  in  connexion  with  the  ventral  or  motor  column  of  cells,  from  which  the  fibres 
of  the  anterior  roots  of  the  spinal  nerves  arise. 

The  fronto-pontine  strand  is  composed  of  fibres  which  arise  as  the  axons  of  the 
cells  in  the  cortex  which  covers  the  portion  of  the  frontal  lobe,  which  lies  in  front  of 
the  prsecentral  furrows.  It  descends  in  the  anterior  limb  of  the  internal  capsule, 
enters  the  mesial  part  of  the  crusta  of  the  crus  cerebri,  through  which  it  gains  the 
ventral  part  of  the  pons.  In  this  its  fibres  end,  by  forming  arborisations  around  the 
cells  of  the  nucleus  pontis. 

The  temporo-pontine  tract  consists  of  fibres  which  spring  from  the  cells  of  that 
part  of  the  cortex  which  covers  the  middle  portions  of  the  two  upper  temporal  con- 
volutions. It  probably  represents  a  corticifugal  tract  belonging  to  the  auditory 
system,  seeing  that  it  springs  to  some  extent  from  the  auditory  cortical  area.  The 
temporo-pontine  tract  passes  inwards  under  the  nucleus  lenticularis,  enters  the 
retrolenticular  part  of  the  hinder  limb  of  the  internal  capsule,  and  thus  gains  the 
outer  part  of  the  crusta  of  the  crus  cerebri.  From  this  it  descends  into  the  ventral 
part  of  tfie  pons,  in  which  it  ends  in  the  nucleus  pontis  (Fig.  439,  p.  546). 

The  optic  radiation  forms  a  very  definite  and  easily  demonstrated  tract  of 
longitudinally-directed  fibres  in  the  white  medullary  centre  of  the  occipital  lobe. 
It  lies  on  the  outer  side  of  the  ventricular  cavity,  from  which  it  is  separated  by  the 
fibres  of  the  tapetum  and  tbe  ependyma  of  the  ventricle  (Figs.  462,  p.  576  ;  and  465, 
p.  579).  To  the  outer  side  of,  and  applied  closely  to,  the  o])tic  radiation  is  another 
longitudinal  tract  of  fibres  in  this  part  of  the  medullary  ctuitre  of  the  cerebral  hemi- 
sphere, viz.  the  inferior  longitudinal  association  bundle;  but  the  fibres  of  the  latter 
fasciculus  are  coarser  and  are  stained  more  deeply  by  the  Pal-Weigert  method,  and 
thus  tliey  can,  as  a  rule,  be  easily  distinguished  from  the  optic  radiation.     Traced 


592 


THE  NEEVOUS  SYSTEM. 


in  a  backward  direction,  the  fibres  of  the  optic  radiation  disperse  and  pass  to  the 
cortex  of  the  occipital  lobe  on  both  its  mesial  and  outer  aspects.  This  is  a  matter 
of  interest,  seeing  that  the  visual  centre  is  placed  in  this  cortical  district,  and  more 
particularly  on  the  mesial  aspect  in  the  immediate  neighbourhood  of  the  calcarine 
fissure  (Flechsig  and  Henschen).  When  the  optic  radiation  is  followed  in  a  forward 
direction  it  is  seen  to  enter  the  retrolenticular  part  of  the  posterior  limb  of  the 
internal  capsule,  from  whence  its  fibres  pass  to  the  pulvinar  of  tlie  optic  thalamus, 
to  the  corpus  geniculatum  externum  and  the  superior  quadrigeminal  body. 

As  we  have  noted,  the  optic  radiation  is  composed  partly  of  cortioifugal  and 
partly  of  corticipetal  fibres  (p.  552).  The  former  arise  from  cells  in  the  occipital 
cortex  and  end  in  the  pulvinar  and  the  superior  quadrigeminal  body ;  the  cortici- 
petal fibres  arise  in  the  pulvinar  and  in  the  corpus  geniculatiim  externum  and 
end  in  the  occipital  cortex  (Ferrier  and  Turner). 

The  system  of  fibres  which  belong  to  the  mesial  fillet  and  the  superior  cerebellar 


Caudate  nucleus 


Choroid  plexus  in  lateral 
ventricle 

Corpus  eallosuni 


Thalamus  (pulvinar) 
Occipital  corticifugal  tract  to 
superior  quadrigeminal  body 
Superior  quadrigeminal  body 
Corpus  geniculatum  externum 
—  Coirpus  geniculatum  internum 
Sylvian  gray  matter 
Inferior  brachium 
^j|ir~~^^*'^''^^  fillet 

Superior  cerebellar  i^eduuele 

Cerebellum 
Pons 


Optic  radiation 

Caudate  nucleus 

Optic  radiation 

Inferior  longitudinal  bundle 

Tapetum 

Descending  horn  of  lateral  ventricle 

Fimbria 


Gjrus  dentatus' 

Dentate  Assure 

Fig.  473.  —  Coboxal  Section  through  the  Left  Side  of  the  Cerebrum,  Mesencephalon,  and  Pons, 
IN  THE  Re(jion  of  THE  PuLYiNAR  OF  THE  THALAMUS,  AND  THE  CORPORA  Geniculata  (Chimpanzee  ; 
Weigert-Pal  specimen). 

peduncle  have  been  already  more  or  less  fully  dealt  with  (pp.  535  and  539).  The  fillet 
system  represents  the  continuation  upwards  of  the  posterior  columns  of  the  cord. 
The  first  nuclear  internodes  in  the  system  are  met  with  in  the  medulla  in  the  shape  of 
the  cuneate  and  gracile  nuclei.  It  is  here  that  the  fillet  first  takes  definite  shape,  and, 
as  it  passes  upwards  through  the  tegmental  part  of  the  medulla  and  pons,  it  receives 
many  additions  to  its  strength  in  the  form  of  fibres  from  the  nuclei  of  termination 
of  the  afferent  cranial  nerves.  Finally,  passing  through  the  tegmentum  of  the 
mesencephalon,  it  reaches  the  subthalamic  region  and  enters  the  ventral  aspect  of 
the  thalamus.  This  may  be  looked  upon  as  being  the  second  internode  laid  across 
the  path  of  the  fillet,  and  its  fibres  end  in  arborisations  around  the  thalamic  cells. 

The  fibres  of  the  superior  cerebellar  peduncle  encounter  two  nuclear  internodes  as 
they  pass  towards  the  cerebral  cortex,  viz.  the  red  tegmental  nucleus  and  the  optic 
thalamus  (p.  536). 

The  fibres  of  the  auditory  radiation  arise  as  the  axons  of  cells  situated  in  the 
internal  geniculate  body.  They  enter  the  retrolenticular  part  of  the  posterior  limb 
of  the  internal  capsule  and  proceed  under  the  lenticular  nucleus  towards   the 


PEOJECTION  FIBRES. 


59.' 


temporal  lobe.  Here  they  end  in  the  area  of  cortex  which  constitutes  the  auditory 
centre.  This  corresponds  to  the  middle  portion  of  the  superior  temporal  convolu- 
tion, and  also  to  the  rudimentary  transverse  gyri  of  Heschl,  which  are  present  on 
the  insular  surface  of  the  temporal  operculum. 

The  thalamo-cortical  cortico-thalamic  systems  include  the  fibres  which  constitute 
a  double  bond  of  connexion  between  the  thalamus  and  all  parts  of  the  cortex. 
They  are  sufficiently  described  at  p.  545. 

The  remarkable  researches  of  Flechsig  have  added  greatly  to  our  knowledge  of  the  different 
tracts  of  fibres  in  the  cerebral  hemisphere.  By  studying  the  periods  at  which  these  tracts 
myelinate  he  has  been  able  to  note  the  manner  in  which  the  different  areas  of  the  cortex  are 
boiuid  together  and  also  linked, on  to  subjacent  centres.  He  has  arrived  at  a  highh^  important 
conception  regarding  the  functional  value  of  different  districts  of  the  cortex,  founded  upon  their 
anatomical  connexions.  He  recognises  four  sense-areas  in  the  cortex,  viz.  the  somtesthetic  area, 
the  visual  area,  the  auditory  area,  and  the  olfactory  area. 

The  somsesthetic  area  is  the  field  of  general  sensibility  and  is  the  most  extensive  of  aU.  It 
includes  the  two  central  convolutions,  the  posterior  jDortions  of  the  three  frontal  convolutions,  the 
paracentral  convolution,  and  the  adjoining  jjart  of  the  callosal  convolution. 

The  visual  area  is  placed  on  the  inner  aspect  of  the  occipital  lobe,  and  more  particularly  in 
the  immediate  neighbourhood  of  the  calcarine  fissure. 

The  auditory  area  corresponds  to  the  middle  third  of  the  suj)erior  temporal  convolution 
and  to  the  transverse  gyri  of  Heschl. 

The  olfactory  area  includes  the  locus  perforatus  anticus,  the  trigonum  olfactorium,  the 
anterior  part  of  the  callosal  convolution,  and  the  uncus. 

These  sense-areas  are  peculiarly  rich  in  their  supply  of  projection  fibres,  and  each  is  j^rovided 
with  an  extensive  system  of  both  corticifugal  and  corticipetal  fibres.     Thus  the  somgesthetic  area 


^^5SX^JJ^^— ^R£a 


^.^Hgjnc^ ^£55- 


FiG.  474. 


-Diagrams  to  show  Flechsig's  sensory  and  association  areas  on  the  surface  of  the  cerebral 

hemisphere. 


is  the  field  where  the  motor  pyramidal  tract  takes  origin  and  within  which  the  tracts  of  general 
sensibility  end.  The  visual  area  has  the  corticijjetal  and  corticifugal  fibres  of  the  optic  radiation. 
The  auditory  area  has  the  corticipetal  auditory  radiation  and  also  the  corticifugal  temporo- 
pontine tract.  In  man  the  olfactory  area  is  feebly  develojjed,  and  Flechsig  has  not  been  able 
to  establish,  with  certainty,  its  corticipetal  and  corticifugal  projection  tracts. 

The  sense-areas  differ  greatly  from  each  other  in  the  extent  of  cerebral  surface  which  they 
cover.  The  size  in  each  case  is  in  strict  conformity  with  the  joeripheral  area  with  which  each  is 
in  connexion.  It  can  easily  be  understood,  therefore,  how  the  someesthetic  area,  representing  as 
it  does  on  the  cortex  all  the  parts  of  the  body  outside  the  special  organs  of  sense,  from  which 
sensory  nerves  proceed,  should  be  so  large.  Further,  it  is  manifest  why  the  visual  sensorial  area, 
which  in  the  cortex  is  the  corresj)onding  part  to  the  retina,  should  be  of  greater  extent  than  the 
auditory  field,  which  represents  the  cochlea,  and  the  olfactory  area,  which  represents  a  small 
amount  of  olfactory  mucous  meml^rane  in  the  nasal  chamber. 

The  four  sensorial  areas,  taken  together,  only  form  about  one-third  of  the  entire  cerebral 
surface.  The  remaining  two-thirds  of  the  cortex  constitute  what  Flechsig  has  termed  the 
association  centres.  The  great  extent  of  these  in  man  must  be  regarded  as  a  special  human 
charactei-istic.  Tliese  centres  differ  from  the  sensorial  areas  in  being  jjoorly  provided  with  pro- 
jection fibres.  They  have  little,  direct  connexion  with  the  centres  whiclx  lie  at  a  lower  level. 
Indeed,  the  only  direct  l)ond  of  union  over  a  very  large  extent  of  these  association  areas  with 
lower  centres  consists  of  the  tlialamo-cortical  fibres,  which  pass  to  them  from  the  thalamus. 
But,  on  the  other  hand,  they  are  ricli  in  association  filn'es,  and  are  linked  in  the  most  complete 
and  perfect  manner  ]>y  these  fibres  to  the  sensorial  areas. 

Heclisig  regards  tliese  association  areas  as  constituting  the  portions  of  cortex  in  which  the 
higlier  intellectual  activities  are  carried  on,  and  he  further  believes  that  they  exercise  an 
important  controlling  influence  over  the  sense-areas.  More  particularly  is  this  control  exhibited 
in  the  ca.se  of  the  great  sonuesthetic  area,  within  which  the  influence  of  all  bodily  impressions  is 
received  and  transformed  into  consciou.sness,  and  within  which  the  impulses  which  are  thereby 
42 


594  THE  NEEVOUS  SYSTEM. 

excited  take  definite  form.  These  impulses,  according  to  Fleclisig,  are,  in  a  measure,  in  all 
properly-balanced  minds,  held  in  subjection  by  the  higher  feelings,  which  assume  shape  in  the 
association  centres. 

In  his  study  of  the  fcDctal  and  infantile  brain  Flechsig  has  shown  that  the  fibres  of  the  sensory 
paths  become  medullated  in  the  first  instance  ;  tlien  the  corticifugal  fibres  which  go  out  from  the 
sense-areas  assume  their  sheaths  of  myelin  ;  and,  further,  that  it  is  not  until  a  month  after  birth, 
and  after  the  jsrojection  fibres  in  connexion  with  the  sense-areas  are  myelinated,  that  the  associa- 
tion areas  become  linked  on  by  medullated  association  fibres  with  the  sense-areas. 

Development  of  the  Parts  derived  from  the  Fore-brain. 

It  has  been  previously  noted  that  the  fore-brain  very  early  shows  an  obscure  sub- 
division into  a  front  portion,  termed  the  telencephalon,  and  a  hinder  part,  called  the 
diencephalon,  which  corresponds  more  nearly  to  the  original  cavity  of  the  fore-brain. 
The  cavity  of  third  ventricle  is  derived. from  both,  and  stretches  forwards,  therefore,  to 
the  lamina  terminalis,  Avhich  in  its  lower  part  is  represented  in  the  adult  by  the  lamina 
cinerea. 

The  lateral  Avail  of  both  sections  of  the  primitive  fore-brain  shows  a  subdivision  into 
a  dorsal  or  alar  and  a  ventral  or  basal  lamina.  The  groove  which  indicates  this  separa- 
tion is  the  sulcus  of  Monro,  and  is  evident  even  in  the  adult  brain. 

In  recognising  an  alar  and  basal  lamina  in  the  fore-brain  the  teaching  of  Professor  His  is 
followed.  This  subdivision,  however,  is  not  admitted  by  all  observers,  and  some  hold  that  the 
fore-brain  is  to  be  regarded  as  a  great  diverticular  expansion  which  grows  out  fi'om  the  mid- 
dorsal  and  alar  lamina  of  the  mesencephalon. 

Alar  Lamina. — The  alar  part  of  the  lateral  wall  of  the  telence'pltalon  is  pushed  out 
to  form  the  diverticulum,  which  ultimately  constitutes  the  cerebral  hemisphere,  and  thus 
from  a  very  early  period  the  primitive  position  of  this  part  of  the  lateral  wall  is  indicated 
by  the  wide  foramen  of  Monro,  or  aperture  of  communication  between  the  cavity  of  the 
cerebral  hemisphere  and  the  third  ventricle. 

The  alar  part  of  the  lateral  wall  of  the  diencephalon  is  utilised  for  the  development  of 
the  thalamus,  the  epithalamus,  and  the  metathalamus.  Of  these  the  optic  thalamus  is 
derived  from  the  anterior  and  by  far  the  greatest  part  of  the  alar  wall.  It  arises  as  a 
large  oval  swelling,  which  gradually  approaches  its  fellow  of  the  opposite  side,  and  thus 
diminishes  the  width  of  the  third  ventricle.  Finally,  the  two  bodies  come  into  contact  in 
the  mesial  plane  and  cohere  over  an  area  corresponding  to  the  gray  commissure.  This 
occurs  about  the  end  of  the  second  month. 

From  that  section  of  the  lateral  wall  to  which  the  name  of  metathalamus  is  given  the 
two  geniculate  bodies  arise.  Each  of  these  shows,  in  the  first  place,  as  a  depression  on 
the  inside,  and  a  slight  elevation  on  the  outside,  of  the  wall  of  the  diencephalon.  As  the 
thalamus  grows  backwards,  it  encroaches  greatly  upon  the  territory  occupied  by  the  geni- 
culate bodies.  It  thus  comes  about  that  in  the  adult  brain  the  internal  geniculate  body 
seems  to  hold  a  position  on  the  lateral  aspect  of  the  mesencephalon,  whilst  the  external 
geniculate  body,  viewed  from  the  surface,  appears  to  be  a  part  of  the  thalamus. 

From  the  epithalamic  region  of  the  wall  of  the  diencephalon  are  developed  the  pineal 
gland,  its  peduncle,  and  the  habenular  region.  These  parts  are  relatively  much  more 
evident  in  the  embryonic  than  in  the  adult  brain.  The  pineal  body  is  developed  as  a 
diverticulum  of  the  posterior  part  of  the  roof  of  the  diencephalon.  Viewed  from  the 
dorsal  aspect  of  the  brain-tube,  this  diverticulum  shows  in  the  first  instance  as  a  rounded 
elevation,  from  either  side  of  which  a  broad  ridge  runs  forwards.  This  ridge  becomes 
the  taenia  thalami,  whilst  in  the  region  of  its  junction  with  the  pineal  elevation  the 
trigonum  habenulae  takes  shape.  The  pineal  diverticuhim  ultimately  becomes  solid,  but 
a  small  portion  of  the  original  cavity  is  retained  as  the  recessus  pinealis  of  the  third 
ventricle. 

Basal  Lamina. — The  part  of  the  diencephalon  and  telencephalon  which  represents 
the  basal  lamina  lies  below  the  level  of  the  sulcus  of  Monro,  retains  its  primitive  form,  and 
undergoes  only  slight  change.  Consequently,  when  this  region  in  the  adult  brain  is  com- 
pared with  the  corresponding  region  in  the  embryonic  brain,  the  i-esemblance  between  the 
two  is  very  sti'iking. 

In  the  fore-brain,  therefore,  it  is  the  alar  lamina  wdiich  plays  the  predominant  part  in 
the  formation  of  the  cerebrum.  The  value,  also,  of  the  basal  part  of  the  wall  of  this 
portion  of  the  neural  tube  is  still  further  reduced  by  the  fact  that  it  no  longer  contains 
the  nuclei  of  origin  of  efferent  nerves.  The  highest  of  these  nuclei  (the  oculo-motor)  is 
placed  in  the  mesencephalon. 


DEVELOPMENT  OF  PAIiTS  DERIVED  FROM  FORE-BRAIN.      595 


The  region  of  the  fore-brain  which  lies  below  the  sulcus  of  Monro  is  termed  the  hypo- 
thalamus. The  part  of  this  which  corresponds  to  the  diencephalon  is  called  the  pars 
mam  miliar  is     hypothalami, 

'A, 


whilst  the  part  in  front,  which 
belongs  to  the  telencephalon, 
receives  the  name  of  pars  optica 
hypothalami. 

From  the  pars  mammillaris 
hypothalami  are  derived  the 
corpus  mammillare  and  a 
portion  of  the  tuber  cinereum. 
With  the  pars  optica  hypo- 
thalami are  associated  the 
following  parts,  viz.  the  tuber 
cinereum,  with  the  infundi- 
bulum  and  the  cerebral  part 
of  the  pituitary  body,  the  optic 
chiasma,  the  optic  recess,  and 
the  lamina  cinerea. 

The    corpora  mammillaria 
form,  in  the  first  instance,  a 
relatively      large      downward 
bulging    of    the    floor   of    the 
brain-tube.      As    development 
goes  on  this  bulging  becomes  S- 
relatively  small,  and  about  the   \ 
fourth  month  the  single  pro-    '' 
jection  becomes   divided    into 
the  two  tubercles. 

The  infundibulum  and 
posterior  or  cerebral  lobe  of 
the  pituitary  body  are  de- 
veloped as  a  hollow  downward 
diverticulum  of  the  floor  of 
the  telencephalon  (p.  549).  A 
portion  of  the  original  cavity  ^^ 
is  retained  in  the  upper  part 
of  the  infundibulum,  and  con- 
stitutes the  infundibular  recess 
in  the  floor  of  the  third  ventricle. 

The  optic  nerve  is  chiefly 
formed  by  the  passage  of  fibres 
backwards     from    the    retina 


M, 


Fig.  475. — Two  Drawings  op  the  Embryonic  Brain  (by  His). 

Reconstruction  of  the  fore-brain  and  mid-braiu  of  His's  embryo  KO  ; 
profile  view.  B,  Same  brain  as  A,  divided  along  the  mesial  plane 
and  viewed  upon  its  inner  aspect. 

Mammillary  eminence  ;  T.c,  Tuber  cinereum  ;  Hp,  Hypophysis 
(pituitary  diverticulum  from  buccal  cavity)  ;  Opt,  Optic  stalk ; 
TH,  Optic  thalamus  ;  Tg,  Tegmental  part  of  mesencephalon  ;  P.s, 
Par  subthalamica  ;  C.s,  Corpus  striatum  ;  F.M,  Foramen  of  Monro  ; 
L,  Lamina  terminalis  ;  R.O,  Recessus  opticus  ;  R.i,  Recessus  iufun- 
dibuli. 


in  the  wall  of  the  original  optic  stalk,  whilst  the  chiasma  takes  form  by  the  transit  of 
fibres  across  the  middle  line  in  front  of  the  infundibulum  and  behind  the  optic  recess.  To 
a  large  extent  these  fibres  are  derived  from  the  optic  nerve.  The  optic  recess  of  the  third 
ventricle  marks  the  spot  where  the  hollow  optic  vesicle  originally  bulged  out  from  the 
lower  and  lateral  part  of  the  fore-brain,  and  in  the  adult  it  therefore  represents  a  portion 
of  the  primitive  cavity  of  the  tubular  stalk  of  the  optic  vesicle.  In  the  course  of  develop- 
ment the  optic  nerve  fibres,  which  appear  in  the  stalk  of  the  optic  vesicle  to  form  the 
optic  nerve,  seek  an  attachment  much  further  back,  and  through  the  optic  tract  they  are 
even  carried  as  fur  as  the  mesencephalon. 

The  roof  of  the  fore-brain  remains  thin,  and  does  not  proceed  to  the  development 
of  nervous  elements,  except  in  its  posterior  part.  Here  it  forms  the  pineal  body  and  the 
posterior  commissure.  In  front  of  these  structures  the  roof  of  the  fore-brain  is  epithelial, 
and  remains  so  during  life.  It  constitutes  the  epithelial  roof  of  the  third  ventricle,  and 
it  becomes  involuted  along  the  middle  line  into  the  cavity  by  the  choroid  plexuses  of  the 
ventricle.  The  posterior  commissure  appears  as  a  transverse  tliickening  at  the  bottom  of 
a  transverse  groove  which  appears  in  the  x'oof  of  the  early  brain-tube  behind  the  pineal 
diverticulum. 

Cerebral  Hemisphere. — I'he  cerebral  hemisphere  is  derived  from  the  alar  section 
of  the  lateral  wall  of  tlie  telencephalon.  From  this  it  grows  out  and  soon  assumes  very 
large  dimensions.  At  first  it  grows  forwards  and  upwards,  and  a  distinct  fissure,  the 
42  a 


596 


THE  NEEVOUS  SYSTEM. 


early  incisura  longitudinalis  cerebri,  appears  between  the  cerebral  hemispheres  of 
opposite  sides.  The  separation  of  the  two  cerebral  vesicles  by  the  longitudinal  fissure 
begins  at  the  end  of  the  first  month.  This  fissure  becomes  occupied  by  mesoblastic  tissue, 
wdiicli  later  on  forms  the  falx  cerebri.  The  cerebral  hemisphere,  in  its  further  growth,  is 
carried  progressively  backwards  over  the  hinder  parts  of  the  developing  brain.  At  the 
end  of  the  third  month  it  has  covered  the  optic  thalamus.  A  month  later  it  reaches  the 
corpora  quadrigemina,  and  by  the  seventh  month  it  has  not  only  covered  these,  but  also 
the  entire  upper  surface  of  the  cerebellum. 

At  the  end  of  the  first  month  the  olfactory  lobe  grows  out  as  a  hollow  protrusion  from 


TERMINALIS 


RECESS        CHIASMA 


Fig.  476. — Two  Dkawings  by  His,  illustrating  the  development  of  the  humau  braiu. 

A,  Median  section  through  a  foetal  human  brain  in  the  third  month  of  development. 

B,  Schema  showing  the  directions  in  which  the  cerebral  hemisphere  expands  during  its  growth. 

P.  M.H.  Pars  mammillaris  hypothalami.  M.   Mammillary  region.  0.  Occipital  lobe. 

P.O.H.    Pars  ojjtica  hypothalami.  F.    Frontal  lobe.  T.  Temporal  lobe. 

P.    Parietal  lobe. 


the  lower  and  fore  part  of  the  cerebral  vesicle.  This  in  course  of  time  becomes  solid  and 
forms  the  olfactory  tract  and  bulb.  In  the  adult  brain  the  point  which  corresponds  to 
the  original  connexion  between  the  early  hollow  olfactory  diverticulum  and  the  cavity  of 
the  cerebral  vesicle  is  represented  by  the  extremity  of  the  anterior  cornu  of  the  lateral 
ventricle. 

In  the  floor  of  the  hollow  cerebral  hemisphere  a  thickening  takes  origin,  and  this 
ultimately  is  developed  into  the  corpus  striatum.  On  the  outer  surface  of  the  vesicle  this 
thickening  is  seen  to  correspond  to  a  depression  which  constitutes  the  early  Sylvian  fossa, 
the  further  development  of  which  is  described  on  p.  556. 

In  the  earlier  stages  of  its  development  the  cerebral  hemisphere  is  a  thin-walled  vesicle 
with  a  relatively  large  cavity,  which  represents  the  primitive  condition  of  the  lateral 
ventricle.  At  first  the  vesicle  is  bean-shaped  and  the  cavity  is  curved.  At  this  stage  the 
outline  is  very  similar  to  that  presented  by  the  cerebral  hemisphere  of  a  quadruped,  and 
there  is  little  or  no  trace  of  an  occipital  lobe  or  of  a  posterior  horn  of  the  lateral  ventricle. 
As  development  goes  on,  however,  the  occipital  portion  of  the  hemisphere  grows  backwards 
over  the  cerebellum  in  the  shape  of  a  hollow  protrusion,  and  a  distinct  occipital  lobe 
enclosing  the  posterior  horn  of  the  lateral  ventricle  is  the  result.  This  developmental 
stage,  which  is  distinctive  of  man  and  the  apes,  begins  about  the  fourth  month. 

On  the  mesial  aspect  of  the  cerebral  hemisphere,  in  the  early  stages  of  its  development, 
an  invagination  of  the  wall  of  the  vesicle  takes  place  into  the  cavity  immediately  above 
and  behind  the  large  foramen  of  Monro.  This  is  the  choroidal  fissure,  and  the  fold  of  the 
cerebral  wall,  w'hich  is  thus  thrust  into  the  cavity,  remains  thin  and  entirely  epithelial. 
After  a  time  mesoblastic  tissue  from  the  great  longitudinal  fissure  finds  its  way  into  the 
choroidal  fissure  and  occupies  the  interval  between  the  two  thin  layers  which  form  the  fold. 
This  mesoblastic  tissue  forms  the  choroid  plexus  of  the  lateral  ventricle,  and  in  the  early 
stages  of  the  hemisphere  it  is  so  voluminous  that  it  fills  up  the  relatively  large  cavity  of 
the  lateral  ventricle. 

Development  of  the  Gyri  and  Sulci.— In  the  early  stages  of  its  development,  the 
surface  of  the  cerebral  hemisphere  is  smooth  and  closely  applied  to  the  deep  surface  of 
the  cranial  capsule  within  which  it  is  enclosed. 

After  the  occipital  lobe  is  fully  formed  and  the  fifth  month  is  reached,  the  cranium 
grows  for  a  time  more  rapidly  than  the  brain,  with  the  result  that  a  relatively  wide  space  is 


DEVELOPMENT  OF  PAETS  DEEIVED  FEOM  FOEE-BEAIN.      597 

left  between  the  cerebral  surface  and  the  surrounding  cranial  envelope.  This  is  occupied 
by  sodden  subarachnoid  tissue,  and  when  this  stage  is  reached  (in  the  latter  part  of  the 
fifth  month)  the  sulci  and  gyri  begin  to  make  their  appearance.  The  incomplete  sulci  owe 
their  origin  to  the  upheaval  of  the  cerebral  cortex  on  either  side  of  the  appearing  fissures, 
and  the  gyri  which  bound  them  are  formed  as  the  result  of  an  exuberance  of  surface 
growth  in  localised  areas.  Owing  to  the  wide  interval  between  the  cranial  wall  and  the 
surface  of  the  cerebral  hemisphere,  the  particular  surface  areas  which  grow  and  foreshadow 
the  future  gyri  suffer  no  restriction,  and  they  take  the  form  of  rounded  eminences  which 
rise  from  the  general  surface  level  of  the  cerebral  hemisphere.  As  growth  goes  on,  how- 
ever, the  brain  gradually  assumes  a  bulk  more  nearly  in  accord  with  the  cavity  of  the 
.cranium,  and  the  space  for  extension  becomes  more  limited.  Finally,  about  the  beginning 
of  the  eighth  month,  the  gyral  elevations  come  into  close  contact  with  the  cranial  wall, 
and  a  stage  of  growth-antagonism  between  the  brain  and  its  enclosing  capsule  is  entered 
upon.  As  a  result  of  this  the  gyri  are  pressed  together,  the  fissures  assume  more  definite 
shape,  and  the  ordinary  convolutionary  forms  make  their  app>earance.  So  intimate,  indeed, 
is  the  contact  between  the  cerebral  hemisphere  and  the  skull  capsule  that  the  gyri,  to 
some  extent,  produce  an  imprint  on  the  deep  aspect  of  the  ci-anial  bones. 

As  already  explained,  the  complete  fissures  are  produced  by  an  infolding  of  the  wall 
of  the  cerebral  vesicle. 

Cerebral  Commissures. — The  development  of  the  cerebral  commissures  is  sur- 
rounded with  much  difficulty.  It  would  seem  that  the  corpus  callosum,  the  anterior 
commissure,  and  the  fornix  all  take  origin  in  the  lamina  terminalis.  The  triangular 
interval  which  is  left  between  these  commissures  is  occupied  by  the  septum  lucidum — a 
structure  which  has  an  intimate  developmental  and  morphological  connexion  with  the 
gyrus  subcallosus.  The  great  development  of  the  corpus  callosum  in  man  is  to  be 
associated  with  the  enormous  expansion  of  the  human  neo-pallium  of  which  it  is  the 
commissiire. 

Weight  of  the  Beain. 

The  average  weight  of  the  adult  male  brain  may  be  said  to  be  about  1360 
grammes.  The  female  brain  weighs  rather  less,  but  this  is  to  be  expected  from  the 
smaller  bulk  of  the  female  body.  Probably  the  relative  weight  of  the  brain  in  the 
two  sexes  is  very  much  the  same.  The  variations  met  with  in  brain-weight  are 
very  great,  but  it  is  doubtful  if  normal  intellectual  functions  could  be  carried  on  in 
a  brain  which  weighs  less  than  960  grammes.  In  microcephalic  idiots  brains  of 
extremely  small  size  are  met  with. 

THE  MENINGES  OF  THE  BRAIN  AND  SPINAL  CORD. 

The  brain  and  spinal  cord  are  enclosed  within  three  membranes,  which  are 
termed  the  meninges  or  meningeal  membranes.  From  without  inwards  these  are  : 
(1)  the  dura  mater,  (2)  the  arachnoid  mater,  and  (3)  the  pia  mater.  The  space 
between  the  dura  mater  and  the  arachnoid  receives  the  name  of  subdural  space, 
while  the  much  more  roomy  interval  between  the  arachnoid  and  the  pia  mater  is 
called  the  subarchnoid  space. 

DuKA  Matee. 

The  dura  mater  is  a  dense  and  thick  fibrous  membrane  which  possesses  a  very 
considerable  degree  of  strength.  Its  arrangement  within  the  cranial  cavity  is  so 
different  from  that  within  the  spinal  canal  that  it  is  customary  to  speak  of  it  as 
consisting  of  two  parts,  viz.  a  cranial  and  a  spinal,  although  in  adopting  this  sub- 
division it  must  be  clearly  understood  that  both  portions  are  continuous  with  each 
other  at  the  foranien  magnum. 

Cranial  Dura  Mater  Tdura  mater  cerebri). — The  cranial  dura  mater  is  adherent 
to  the  inner  surl'ac(;  of  the  cranial  wall,  and  performs  a  double  office,  it  serves  as 
an  internal  periosteum  for  the  bones  which  it  lines  and  constitutes  an  envelope 
for  the  brain.  Its  inner  surf;jce,  which  bounds  the  subdural  space,  is  smooth  and 
glistening,  and  is  c(jverod  by  a  layer  of  endothelial  cells.  The  outer  surface,  when 
separated  from  the  cranial  wall,  is  rough,  this  being  due  to  numerous  fine  fibrous 
processes  and  blood-vessels  which  pass  between  it  and  the  bones.  Its  degree  of 
42  & 


598 


THE  NERVOUS  SYSTEM. 


adhesion  to  the  cranial  wall  differs  considerably  in  different  regions.  To  the  vault 
of  the  cranium,  except  along  the  lines  of  the  sutures,  the  connexion  is  by  no  means 
strong,  and  in  the  intervals  between  the  fibrous  processes  which  pass  into  the  bone 
there  are  small  lymph  spaces  (epidural  spaces)  where  the  outer  surface  of  the 
membrane  is  covered  l)y  endotlielial  cells.  So  long  as  the  sutures  are  open  the 
dura  mater  is  connected  with  the  periosteum  on  the  exterior  of  the  skull,  along  the 
sutural  lines,  by  a  thin  layer  of  fibrous  tissue  which  intervenes  between  the  bony 
margins.  Around  the  foramen  magnum,  and  to  the  fl(Jor  of  the  cranium,  the  dura 
mater  is  very  firmly  adherent.  Tliis  is  more  particularly  marked  in  the  case  of  the 
projecting  parts  of  the  cranial  floor,  as,  for  example,  the  petrous  portions  of  the . 
temporal  bones,  the  clinoid  processes,  and  so  on.  This  firm  adhesion  in  these 
regions  is  still  further  strengthened  by  the  fact  that  the  nerves,  as  they  leave  the 
cranium  through  the  various  foramina,  are  followed  by  sheaths  of  the  fibrous  dura 


Inferior  petrosal  sinus 


Superior  petrosal  i 
Lateral  sinus 


Fig.  477. — Sagittal  Section  through  the  Skull,  a  little  to  the  Left  of  the  Mesial  Plane, 
to  show  the  arrangement  of  the  dura  mater. 

The  cranial  nerves  are  indicated  by  numerals. 

mater.  Outside  the  cranium  these  prolongations  of  the  membrane  blend  with  the 
fibrous  sheaths  of  the  nerves,  and  likewise  become  connected  with  the  periosteum  on 
the  exterior  of  the  skull.  In  the  child,  durino;  the  growth  of  the  cranial  bones,  and 
also  in  old  age,  the  dura  mater  is  more  adherent  to  the  cranial  wall  than  during  the 
intermediate  portion  of  life. 

The  cranial  dura  mater  is  composed  of  two  layers  intimately  connected  with 
each  other,  but  yet  capable  of  being  demonstrated  in  most  regions  of  the  cranium. 
Along  certain  lines  these  two  layers  separate  from  each  other  so  as  to  form  channels 
lined  by  endothelium.  These  channels  are  the  venous  blood-sinuses  which  receive  the 
blood  from  veins  which  come  from  various  parts  of  the  brain.  They  are  described 
in  the  section  dealing  with  the  Vascular  System. 

Strong  fibrous  partitions  or  septa  are  given  off  along  certain  lines  from  the  deep 
surface  of  the  dura  niater.  These  project  into  the  cranial  cavity,  and  subdivide  it 
partially  into  compartments  which  all  freely  communicate  with  each  other,  and 


DUEA  MATEE.  599 

each  of  which  contains  a  definite  subdivision  of  the  brain.  These  septa  are  :  (1)  the 
falx  cerebri;  (2)  the  tentorium  cerebelh;  (3)  the  falx  cerebelU;  and  (4)  the 
diaphragma  sellse. 

The  falx  cerebri  is  a  sickle-shaped  partition  which  descends  in  the  great  longi- 
tudinal fissure  between  the  two  hemispheres  of  the  cerebrum.  In  front  it  is  narrow, 
and  attached  to  the  crista  galli  of  the  ethmoid  bone.  As  it  is  followed  backwards 
it  increases  in  breadth,  and  behind  it  is  attached  along  the  mesial  plane  to  the 
upper  surface  of  the  tentorium.  The  anterior  narrow  part  of  the  falx  is  frequently 
cribriform,  and  is  sometimes  perforated  by  apertures  to  such  an  extent  that  it  almost 
resembles  lace-work.  Along  each  border  it  splits  into  two  layers,  so  as  to  enclose  a 
blood-sinus.  Along  its  upper  convex  attached  border  runs  the  great  longitudinal 
sinus ;  along  its  concave  free  border  courses  the  much  smaller  inferior  longitudinal 
sinus ;  whilst  along  its  attachment  to  the  tentorium  is  enclosed  the  straight  sinus. 

The  tentorium  cerebelli  is  a  large  crescentic  partition  of  dura  mater,  which  forms 
a  membranous  tent-like  roof  for  the  posterior  cranial  fossa,  and  thus  intervenes 
between  the  posterior  portions  of  the  cerebral  hemispheres  and  the  cerebellum.  It 
is  accurately  applied  to  the  upper  surface  of  the  cerebellum.  Thus  its  highest  point 
is  in  front  and  in  the  mesial  plane,  and  from  this  it  slopes  downwards  towards  its 
attached  border.  It  is  kept  at  a  high  degree  of  tension,  and  this  depends  on  the 
integrity  of  the  falx  cerebri,  which  is  attached  to  its  upper  aspect  in  the  mesial 
plane. 

The  posterior  border  of  the  tentorium  is  convex,  and  is  attached  to  the  hori- 
zontal ridge  which  marks  the  deep  surface  of  the  occipital  bone.  Beyond  this,  on 
each  side,  it  is  fixed  to  the  postero-inferior  angle  of  the  parietal  bone,  and  then 
forwards  along  the  superior  border  of  the  petrous  portion  of  the  temporal  bone. 
From  the  internal  occipital  protuberance  to  the  postero-inferior  angle  of  the 
parietal  bone  this  border  encloses  the  lateral  blood-sinus,  whilst  along  the  upper 
border  of  the  petrous  bone  it  encloses  the  superior  petrosal  sinus.  The  anterior 
border  of  the  tentorium  is  sharp,  free,  and  concave,  and  forms  with  the  dorsum 
sellse  an  oval  opening  shaped  posteriorly  like  a  pointed  arch.  This  opening  receives 
the  name  of  the  incisura  tentorii,  and  within  it  is  placed  the  mesencephalon,  or  the 
stalk  of  connexion  between  the  parts  which  lie  in  the  posterior  cranial  fossa  and 
the  cerebrum.  Beyond  the  apex  of  the  petrous  part  of  the  temporal  bone  the  two 
margins  of  the  tentorium  cross  each  other  like  the  limbs  of  the  letter  X ;  the  free 
margin  is  continued  forwards,  to  be  attached  to  the  anterior  clinoid  process,  whilst 
the  attached  border  proceeds  inwards,  to  be  fixed  to  the  ]Dosterior  clinoid  process. 

The  falx  cerebelli  is  a  small,  sickle-shaped  process  of  dura  mater  placed  below 
the  tentorium,  which  projects  forwards  in  the  mesial  plane  from  the  internal  occi- 
pital crest.  It  occupies  the  notch  which  separates  the  two  hemispheres  of  the 
cerebellum  posteriorly.  Inferiorly  it  bifurcates  into  two  small  diverging  ridges 
which  gradually  fade  away  as  they  are  traced  forwards  on  either  side  of  the  foramen 
magnum. 

The  diaphragma  sellse  is  a  small  circular  fold  of  dura  mater  which  forms  a  roof 
for  the  pituitary  fossa.  A  small  opening  is  left  in  its  centre  for  the  transmission 
of  the  infundibulum. 

Spinal  Dura  Mater  (dura  mater  spinalis). — In  the  spinal  canal  the  dura  mater 
forms  a  tube  which  encloses  the  spinal  cord,  and  which  extends  from  the  foramen 
magnum  above  to  the  level  of  the  second  or  third  piece  of  the  sacrum  below.  It 
is  very  loosely  applied  to  the  spinal  cord  and  the  nerve-roots  which  form  the 
Cauda  equina ;  in  other  words,  it  is  very  capacious  in  comparison  with  the  volume 
of  its  contents.  Moreover,  its  calibre  is  not  uniform.  In  the  cervical  and  lumbar 
regions  it  is  considerably  wider  than  in  the  dorsal  region,  whilst  in  the  sacral 
canal  it  rapidly  contracts,  and  finally  ends  by  blending  with  the  fijuni  terminale 
externum,  the  chief  bulk  of  which  it  forms.  At  the  upper  end  of  the  spinal 
canal  the  s^jinal  dura  mater  is  firmly  fixed  to  the  third  cervical  vertebra,  to  the 
axis  vertebra,  and  around  the  margin  of  the  foramen  magnum.  In  the  sacral 
canal  the  filnm  terminale  externum,  with  wliicli  it  })lends,  extends  downwards  to 
the  ]«xck  of  the  coccyx,  to  the  ])eriostoum  of  whicli  it  is  fixed.  The  lower  end  of 
•the  tube  is  thus  securely  anchored  and  held  in  its  place. 
42  c 


600  THE  NERVOUS  SYSTEM. 

Within  the  cranial  cavity  the  dura  mater  is  closely  adherent  to  the  bones,  and 
forms  for  them  an  internal  periosteum.  As  it  is  followed  into  the  spinal  canal  its 
two  constituent  layers  separate.  The  inner  layer  is  carried  downwards  as  the  long 
cylindrical  tube  which  encloses  the  spinal  cord.  The  outer  layer,  which  is  much 
thinner,  becomes  continuous  behind  and  on  each  side  of  the  foramen  magnum  with 
the  periosteum  on  the  exterior  of  the  cranium,  whilst  in  front  it  is  prolonged 
downwards  into  the  vertebral  canal  in  connexion  with  the  periosteum  and  ligaments 
on  the  anterior  wall  of  the  canal.  The  spinal  dura  mater,  therefore,  corresponds  to 
the  inner  layer  of  the  cranial  dura  mater,  and  to  it  alone.  It  is  separated  from  the 
walls  of  the  spinal  canal  by  an  interval,  the  epidural  space,  which  is  occupied  by 
soft  fat  and  a  plexus  of  thin-walled  veins.  In  connexion  with  the  S])inal  dura 
mater  there  are  no  blood-sinuses  such  as  are  present  in  the  cranial  cavity,  but  it 
should  be  noted  that  the  veins  in  the  epidural  space,  placed  as  they  are  between 
the  periosteum  of  the  spinal  canal  and  tube  of  dura  mater,  occupy  the  same 
morphological  plane  as  the  cranial  blood-sinuses.  Another  feature  which  serves  to 
distinguish  the  spinal  dura  mater  from  the  cranial  dura  mater  consists  in  the  fact 
that  it  gives  off  from  its  deep  surface  no  partitions  or  septa. 

The  cylindrical  tube  of  spinal  dura  mater  does  not  lie  absolutely  free  within 
the  vertebral  canal.  Its  attachments,  however,  are  of  such  a  character  that  they 
in  no  way  interfere  with  the  free  movement  of  the  vertebral  column.  On  either 
side  the  spinal  nerve-roots,  as  they  pierce  the  dura  mater,  carry  with  them  into  the 
intervertebral  foramina  tubular  sheaths  of  the  membrane,  whilst  in  front  loose 
fibrous  prolongations — more  numerous  above  and  below  than  in  the  dorsal  region — 
connect  the  tube  of  dura  mater  to  the  posterior  common  ligament  of  the  A'ertebral 
column.  No  connexion  of  any  kind  exists  between  the  dura  mater  and  the  posterior 
wall  of  the  spinal  canal. 

When  the  interior  of  the  tube  of  spinal  dura  mater  is  inspected,  the  series  of 
apertures  of  exit  for  the  roots  of  the  spinal  nerves  is  seen.  These  are  ranged  in 
pairs  opposite  each  intervertebral  foramen. 

Viewed  from  the  inside  of  the  tube  of  dura  mater,  each  of  the  two  roots  of  a 
spinal  nerve  is  seen  to  carry  with  it  a  special  and  distinct  sheath.  When  examined 
on  the  outside,  however,  the  appearance  is  such  that  one  miglit  be  led  to  conclude 
that  both  roots  are  enveloped  in  one  sheath  of  dura  mater.  This  is  due  to  the  fact 
that  the  two  sheaths  are  firmly  held  together  by  intervening  connective  tissue. 
The  two  tubular  sheaths  remain  distinct  as  far  as  the  ganglion  on  the  posterior 
root,  and  then  blend  with  each  other. 

Subdural  Space. — The  dura  mater  and  the  arachnoid  mater  are  closely  applied 
to  each  other,  and  the  capillary  interval  between  them  is  termed  the  subdural 
space.  It  contains  a  minute  quantity  of  fluid,  which  is  just  sufficient  in  amount  to 
moisten  the  opposed  surfaces  of  the  two  bounding  membranes. 

The  subdural  space  in  iio  way  communicates  with  the  subarachnoid  space. 
The  fluid  which  it  contains  is  led  into  the  venous  blood-sinuses  around  the 
Pacchionian  bodies,  and  thus  gains  exit.  The  subdural  space  is  carried  outwards 
for  a  very  short  distance  on  the  various  nerves  which  are  connected  with  the 
brain  and  the  spinal  cord,  and  it  has  a  free  communication  with  the  lymph-paths 
present  in  these  nerves.  In  the  case  of  the  optic  nerve  the  sheath  of  dura  mater 
is  carried  along  its  whole  length,  and  with  it  the  subdural  space  is  likewise  pro- 
longed to  the  back  of  the  eyeball. 

• 

The  Arachnoidea. 

The  arachnoid  mater  is  a  very  thin  membrane,  remarkable  for  its  delicacy  and 
transparency,  which  envelopes  both  the  brain  and  the  cord  between  the  dura  mater 
and  the  pia  mater.  The  cranial  part  of  the  arachnoid  mater  or  the  araclmoidea 
encephali,  except  in  the  case  of  the  great  longitudinal  and  the  Sylvian  fissures,  does 
not  dip  into  the  sulci  on  the  surface  of  the  brain.  In  this  respect  it  differs  from 
the  pia  mater.  It  bridges  over  the  inequalities  on  the  surface  of  the  brain. 
Consequently,  on  the  basal  aspect  of  the  encephalon  it  is  spread  out  in  the  form  of 
a  very  distinct  sheet  over  the  medulla,  the  pons  Varolii,  and  the  hollow  which  lies 


THE  ARACHNOIDEA. 


601 


in  front  of  the  pons,  and  in  certain  of  these  regions  it  is  separated  from  the  brain- 
surface  by  wide  intervals. 

The  spinal  part  of  the  arachnoid  mater  or  arachnoidea  spinalis,  which  is  directly 
continuous  with  the  cranial  arachnoidea,  forms  a  loose  wide  investment  for  the 
spinal  cord.  This  arachnoidal  sac  is  most  capacious  towards  its  lower  part,  where  it 
envelopes  the  lower  end  of  the  cord  and  the  collection  of  long  nerve-roots  which 
constitute  the  cauda  equina. 

As  the  nerves,  both  from  the  brain  and  the  cord,  pass  outwards  they  receive  an 
investment  from  the  arachnoid,  which  runs  for  a  short  distance  upon  them  and 
then  comes  to  an  end. 

Subarachnoid  Space  (cavum  subarachnoidale). — The  interval  between  the 
arachnoidea  and  the  pia  mater  receives  the  name  of  the  subarachnoid  space.     It 


Pacchionian  body 


Lacuna  lateialis. 


Dura  niatei 


Subdural  space 

Arachnoidea 

Subarach 
noid  space — ^ 
and  tissue   /  ^ 

Pia  matei 


Fig.  478. — Diagram  to  show  the  relations  of  the  membranes  of  the  brain  to  the  cranial  wall  and  the  cerebral 
convolutions,  and  also  of  the  Pacchionian  bodies  to  the  superior  longitudinal  sinus  and  the  lateral  lacunte. 

contains  the  cerebro-spinal  fluid,  and  communicates  freely  through  certain  well- 
defined  apertures  with  the  ventricular  cavities  in  the  interior  of  the  brain.  Three 
of  these  (viz.  the  foramen  of  Majendie  and  another  at  the  extremity  of  each  lateral 
recess)  are  in  connexion  with  the  fourth  ventricle ;  two  are  slit-like  openings  into 
the  lateral  ventricles,  and  are  placed  at  the  extremity  of  each  descending  horn. 

Wiihin  the  cranium  the  subarachnoid  space  is  broken  up  by  a  meshwork  of  fine 
filaments  and  trabeculse,  which  connects  the  two  bounding  membranes  (viz.  the 
arachnoidea  and  the  pia  mater)  in  the  most  intimate  manner,  and  forms  a  delicate 
sponge-like  interlacement  between  them.  "Where  the  arachnoidea  passes  over  the 
summit  of  a  cerebral  convolution,  and  is  consequently  closely  applied  to  the  sub- 
jacent pia  mater,  the  meshwork  is  so  dense  and  the  trabeculEc  so  short  that  it  is 
hardly  possible  to  discriminate  between  the  two  membranes.  To  all  intents  and 
purposes  tliey  form  in  these  localities  one  lamina.  In  the  intervals  between  the 
rounded  margins  of  adjoining  convolutions,  however,  distinct  angular  spaces  exist, 
where  the  subarachnoid  trabecular  tissue  can  be  studied  to  great  advantage.  These 
intervals  on  the  surface  of  the  cerebrum  constitute  numerous  communicating 
channels  which  serve  for  the  free  passage  of  the  subarachnoid  fluid  from  one  part  of 
the  brain  to  anotlnjr.  The  larger  branches  of  the  arteries  and  veins  of  the  brain 
traverse  the  subarachnoid  space ;  their  walls  are  directly  connected  with  the  sub- 
arachnoid trabecular,  and  are  batlied  by  subarachnoid  fluid. 

In  certain  situatiojis  within  the  cranium  the  arachnoidea  is  separated  from  the 


602 


THE  NEKVOUS  SYSTEM. 


pia  mater  by  intervals  of  considerable  width  and  extent.  These  expanded  portions 
of  the  subarachnoid  space  are  termed  cisternse  subarachnoidales.  In  these  the  sub- 
arachnoid tissue  is  much  reduced.  There  is  no  longer  a  close  meshwork;  the 
trabeculse  connecting  the  two  bounding  membranes  take  the  form  of  long  fila- 
mentous intersecting  threads  which  traverse  the  spaces.  All  the  subarachnoid 
cisterns  communicate  in  the  freest  manner  with  each  other  and  also  with  the 
narrow  channels  on  the  surface  of  the  cerebrum. 

Certain  of  these  cisterns  require  special  mention.  The  largest  and  most  con- 
spicuous is  the  cistema  magna.  It  is  formed  by  the  arachnoid  membrane  bridging 
over  the  wide  interval  between  the  back  part  of  the  under  surface  of  the  cerebellum 
and  the  medulla.  It  is  continuous  through  the  foramen  magnum  with  the  posterior 
part  of  the  wide  subarachnoid  space  of  the  cord. 

The  cistema  pontis  is  the  continuation  upwards  on  the  floor  of  the  cranium  of 
the  anterior  part  of  the  subarachnoid  space  of  the  spinal  cord.  In  the  region  of 
the  medulla  it  is  continuous  behind  with  the  cisterna  magna,  so  that  this  sub- 
division of  the  brain,  like  the  spinal  cord,  is  surrounded  by  a  wide  subarachnoid 
space. 

In  front  of  the  pons  Varolii  the  arachnoidea  bridges  across  between  the  pro- 
jecting temporal  lobes,  and  covers  in  the  deep  hollow  in  this  region  of  the  brain. 
This  space  is  called  the  cisterna  basalis,  and  within  it  are  placed  the  large  arteries 
which  take  part  in  the  formation  of  the  circle  of  Willis.  Leading  out  from  the 
cisterna  basalis  there  are  certain  wide  subarachnoid  channels.  Two  of  these  are 
prolonged  into  the  Sylvian  fissures,  and  in  these  are  accommodated  the  middle 
cerebral  arteries.  Anteriorly  the  basal  cistern  passes  into  a  space  in  front  of  the 
optic  chiasma,  and  from  this  it  is  continued  into  the  great  longitudinal  fissure 
above  the  corpus  callosum.  In  this  subarachnoid  passage  the  anterior  cerebral 
arteries  are  lodged. 

The  spinal  part  of  the  subarachnoid  space  is  a  very  wide  interval  which  is 
partially  subdivided  into  compartments  by  three  incomplete  septa.  One  of  these 
is  a  mesial  partition  called  the  septum  posticum,  which  connects  the  pia  mater 
covering  the  posterior  aspect  of  the  cord  with  the  arachnoid  mater.  In  the  upper 
part  of  the  cervical  region  the  septum  posticum  is  imperfect,  and  is  merely  repre- 

Duva  mater  seutcd  by  somc  strauds  pass- 

-Aracimoid  iug  betwccn  the  two  mem- 

-Ligamentum  denticuiatum  i^^ancs ;  in  the  lowcr  part  of 
the  cervical  region  and  in 
the  dorsal  region  it  becomes 
tolerably  complete.  The 
other  two  septa  are  formed 
by  the  ligamenta  denticulata 
which  spread  outwards  from 
either  side  of  the  spinal  cord. 
These  will  be  described  with 
the  pia  mater. 

Pacchionian  Bodies 
(granulationes  arach- 
noidales). — When  the  sur- 
face of  the  dura  mater  is 
inspected  after  the  removal 
of  the  calvaria,  a  number  of 
small  fleshy-looking  excres- 
cences, purplish-red  in  colour, 
are  seen  ranged  in  clusters  on 
either  side  of  the  superior 
longitudinal  sinus,  and  when 
this  sinus  is  opened  they  are 
also  observed  protruding  in  considerable  numbers  into  its  interior.  ■  These  are  the 
Pacchionian  bodies,  and  they  are  also  found  in  smaller  number  and  distinctly 
smaller  size  in  connexion  with  other  blood-sinuses,  such  as  the  lateral  sinus,  the 


Arachno 


Posterior  nerve-root— 


Spinal  ganglion 


Anterior  divisioi 
of  nerve 

Posterior  division 
of  nerve 


Anterior  nerve- 
root  (cut) 
Posterior  nerve- 
root 

Anterior  nerve- 
root  (cut) 


Ligamentuni 
denticuiatum 


Pia  mater 


Anterior  nerve-root 


Fig.  479. 


-Membranes  of  the  Spinal  Coed,  and  the  mode  of 
Origin  of  the  Spinal  Nerves. 


THE  ARACHNOIDEA.  603 

straight  sinus,  and  the  cavernous  sinus.  At  first  sight  they  appear  to  belong  to 
the  dura  mater,  but  in  reality  they  are  projections  from  the  arachnoidea.  In  the 
child  they  are  exceedingly  small  and  rudimentary,  and  it  is  only  as  life  advances 
that  they  become  large  and  conspicuous. 

Each  Pacchionian  body  is  a  bulbous  protrusion  of  the  arachnoid  membrane. 
It  is  attached  to  the  arachnoidea  by  a  narrow  pedicle,  and  into  its  interior  is  pro- 
longed through  this  a  continuation  of  the  subarachnoid  space  and  its  characteristic 
meshwork.  The  Pacchionian  bodies  do  not  pierce  the  dura  mater.  As  they  push 
their  way  into  a  blood -sin  us  they  carry  before  them  a  thin  covering  continuous 
with  the  sinus  wall.  On  either  side  of  the  superior  longitudinal  sinus  there  are  a 
number  of  irregular  spaces  in  the  dura  mater  which  communicate  with  the  sinus 
either  by  a  small  aperture  or  a  narrow  channel.  These  spaces  are  called  the 
parasinoidal  sinuses  or  the  lacunas  laterales,  and  certain  of  the  meningeal  veins  and 
some  of  the  diploic  veins  open  into  them.  Pacchionian  bodies  push  themselves 
into  the  parasinoidal  sinuses  from  below  in  such  a  manner  that  they  receive  a 

Pacchionian  body  Mouth  of  a  vein 


Bone 


^g    Superior 
^'tf     longitudinal 


Fig.  480. — Mesial  Section  through  the  Cranial  Vault  in  the  Frontal  Region.     Displays  a  portion 
of  the  superior  longitudinal  sinus  and  the  Pacchionian  bodies  protruding  into  it  (enlarged). 

complete  covering  from  the  layer  of  dura  mater  which  forms  the  sinus  floor.  Nor 
does  the  bone  escape.  As  the  Pacchionian  bodies  enlarge  they  cause  absorption 
of  the  cranial  wall,  and  suiall  pits  are  hollowed  out  on  its  deep  surface  for  their 
reception.  It  must  be  clearly  understood,  however,  that  in  such  cases  the 
Pacchionian  body  is  separated  from  the  bone  by  the  following  : — (1)  A  con- 
tinuation round  the  Pacchionian  body  of  the  subdural  space  ;  (2)  the  thinned 
floor  of  the  parasinoidal  sinus ;  (3)  the  lumen  of  the  sinus ;  and  (4)  the  greatly 
thinned  upper  wall  of  the  sinus. 

The  Pacchionian  bodies  have  a  special  function  to  perform.  Through  them 
fluid  can  pass  from  the  subarachnoid  space  into  the  venous  sinuses  with  which  they 
stand  in  connexion.  Whenever  the  pressure  of  blood  in  the  sinuses  is  lower  than 
that  of  the  fluid  in  the  subarachnoid  space  and  the  ventricles  of  the  brain,  the 
cerebro-spinal  fluid  filtrates  through  the  Pacchionian  bodies  into  the  blood-sinuses. 
This  is  not  the  only  way  that  subarachnoid  fluid  may  obtain  exit.  The  sub- 
arachnoid space  is  carried  outwards  for  a  short  distance  on  the  nerves  in  connexion 
with  their  arachnoidal  sheaths,  and  communicates  with  the  lymph  channels  of  the 
nerves.  This  connexion  is  more  complete  in  the  case  of  the  olfactory,  the  optic, 
and  the  auditory  nerves,  than  in  other  nerves.  A  very  free  communication  between 
the  subarachnoid  space  and  the  lymphatics  of  the  nasal  mucous  membrane  is  said 
to  exist. 

The  Pia  Mater. 

The  pia  mater  forms  the  immediate  investment  of  the  brain  and  cord.  It  is  a 
delicate  and  very  vascular  membrane. 

Pia  mater  encephali. — The  pia  mater  which  covers  the  brain  is  finer  and 
more  delicate  than  that  which  clothes  the  spinal  cord.  It  follows  closely  all  the 
inequalities  on  the  surface  of  the  })rain,  and  in  the  case  of  the  cerebrum  it  dips 
into  each  sulcus  in  the  form  of  a  fVjld  which  lines  it  completely.  On  the  cerebellum 
the  relation  is  not  so  intimate;  it  is  only  into  the  larger  lissures  that  it  penetrates 
in  the  form  of  folds. 


604 


THE  NEEVOUS  SYSTEM. 


The  larger  blood-vessels  of  the  brain  lie  in  the  subarachnoid  space.  The  finer 
twigs  ramify  in  the  pia  mater  before  they  proceed  into  the  substance  of  the  brain. 
As  they  enter  they  carry  with  them  sheaths  derived  from  the  pia  mater.  When 
a  portion  of  the  membrane  is  raised  from  the  surface  of  the  encephalou,  numerous 
fine  processes  are  withdrawn  from  the  cerebral  surface.  These  are  the  blood-vessels 
with  their  sheaths,  and  they  give  the  deep  surface  of  tlie  pia  mater  a  rough  and 
flocculent  appearance. 

As  the  pia  mater  is  carried  over  the  lower  part  of  the  roof  or  jjosterior  wall  of 
the  fourth  ventricle  of  the  brain  it  receives  the  name  of  the  tela  choroidea  inferior, 
and  it  is  in  connexion  with  this  portion  of  the  pia  mater  that  the  choroid  plexuses 
of  that  cavity  are  developed.  The  tela  choroidea  superior  or  velum  iuterpositum 
is  a  fold  of  pia  mater  which  is  invagiuated  into  the  brain,  so  that  it  comes  to  lie 
over  the  third  ventricle  and  project  in  the  shape  of  choroid  plexuses  into  the 
lateral  ventricles.     This  invagination  requires  special  notice. 

The  velum  interpositum  (tela  choroidea  superior)  is  a  double  layer  or  fold  of  pia 
mater  which  intervenes  between  the  body  of  the  fornix  which  lies  above  it  and  the 
epithelial  roof  of  tbe  third  ventricle,  and  the  two  optic  thalami  which  lie  below  it. 
Between  its  two  layers  are  blood-vessels,  and  some  subarachnoidal  trabecular 
tissue.  In  shape  the  velum  interpositum  is  triangular,  and  the  narrow  anterior 
end  or  apex  reaches  forwards  as  far  as  the  foramina  of  Monro.     The  base  lies 

under  the  splenium  of  the  corpus 
callosum,  and  here  the  two  layers 
of  the  velum  separate  and  become 
continuous  with  the  investing  nia 
mater  on  the  surface  of  the  brain 
by  passing  out  through  a  cleft 
called  the  transverse  fissure. 

Along  each  lateral  margin  the 
velum  interpositum  is  bordered 
by  the  choroid  plexus  of  the  body 
of  the  lateral  ventricle,  which 
projects  into  the  ventricular  cavity 
from  under  cover  of  the  free 
lateral  margin  of  the  fornix.  It 
should  be  borne  in  mind  that  the 
epithelial  hning  of  the  ventricle 
gives  a  complete  covering  to  the 
choroid  plexus.  Posteriorly  the 
choroid  plexus  is  continuous  with 
the  similar  structure  in  the  de- 
scending horn  of  the  ventricle, 
whilst  in  front  it  narrows  greatly, 
and  becomes  continuous  across  the 
mesial  plane  with  the  correspond- 
ing plexus  of  the  opposite  side, 
behind  the  epithelial  layer  which 
lines  the  foramen  of  Monro.  From 
this  median  junction  two  much 
smaller  choroid  plexuses  run  back- 
wards on  the  under  surface  of  the  velum  interpositum,  and  project  downwards  into 
the  third  ventricle.     These  are  the  choroid  plexuses  of  the  third  ventricle. 

The  most  conspicuous  blood-vessels  in  the  velum  interpositum  are  the  two 
veins  of  Galen,  which  run  backwards,  one  on  either  side  of  the  mesial  plane.  In 
front,  each  is  formed  at  the  apex  of  the  fold  by  the  union  of  the  vein  of  the 
corpus  striatum  and  a  large  vein  issuing  from  the  choroid  plexus  ;  behind,  they 
unite  to  form  the  vena  magna  Galeni,  and  this  pours  its  blood  into  the  anterior 
end  of  the  straight  sinus  (Eig.  477,  p.  598). 

The  continuous  cleft  in  the  brain  through  which  the  velum  interpositum  and 
the  choroid  plexuses  of  the  two  descending  horns  of  the  lateral  ventricles   are 


Genu  of  corpus 
callosum 


Ventricle  V. 
Septum  lucidum 
Caudate  nucleus 


Anterior  pillar  of  fornix 
Vein  of  corfjus  striatum 

Optic  thalamus 

Velum  interpositum 
Vein  of  Galen 


Choroid  plexus  oi 
lateral  ventricle 


— ^Lyra 

Posterior  pillar  of  fornix 
(under  surface) 


Body  of  fornix  (thrown 
backwards) 


Fig. 


481. — Dissection  to  show  the  Velum  Interpositum, 
AND  THE  Parts  in  immediate  Relation  to  it. 


THE  PIA  MATEi;. 


GOr 


introduced  into  the  interior  of  the  Vjrain  is  sometimes  called  the  transverse  fissure. 
It  consists  of  an  upper  intermediate  part  and  two  lateral  parts.  The  former 
passes  forwards  between  the 


Lateral  ventricle 


Choroid  plexus  of  lateral  ventj  ii 
\ 


Position  of  teen 
semicircularis 


TiKuia  tbalami 


Choroid  jjlexus  Vent, 


Veins  of  Galen 


Fiu.  482. — Diagrammatic  Coronal  Section  through  the  optic 
thalami,  and  the  parts  hi  immediate  relatiou  to  them.  The  inter- 
mediate part  of  the  great  transverse  fissure  holding  the  velum 
interpositum  is  seen,  and  also  the  manner  in  which  this  fissure  is 
shut  out  from  the  lateral  ventricles  Ijy  the  epithelium  which  covers 
the  choroid  plexus  on  each  side. 


corpus  callosum  and  the 
fornix  above  and  the  roof  of 
the  third  ventricle  and  the 
optic  thalami  below.  It  is 
limited  on  either  side  by 
the  epithelial  covering  of  the 
choroid  plexuses,  which  shuts 
out  these  structures  from 
the  cavity  of  the  lateral  ven- 
tricles. The  lateral  part  is 
the  choroidal  fissure.  This 
is  continuous  with  the  in- 
termediate part,  and  has 
already  been  described  in 
connexion  with  the  descend- 
ing horn  of  the  lateral 
ventricle  (p.  578). 

Pia  mater  spinalis. — 
The  pia  mater  of  the  cord 
is  thicker  and  denser  than 
that  of  the  brain.  This  is 
largely  due  to  the  addition  of  an  outside  fibrous  layer,  in  which  the  fibres  run 
chiefly  in  the  longitudinal  direction.  The  pia  mater  is  very  firmly  adherent  to 
the  surface  of  the  cord,  and  in  front  it  sends  a  fold  into  the  antero-median  fissure 
of  the  cord.     The  septum  which  occupies  the  postero-median  fissure  is   likewise 

Dura  mater  ^^^7    attachcd    tO    itS     dcCp 

^^/Aiachnoid  surfacc.       In    front    of    the 

-L.4amentuiudenticuiatuni    autcro  -  median     furrow     of 

the  cord  the  pia  mater  is 
thickened  in  the  form  of 
a  longitudinal  glistening 
band,  termed  the  linea 
splendens,  which  runs  along 
the  whole  length  of  the 
cord,  and  blends  with  the 
filum  terminale  below.  The 
blood-vessels  of  the  spinal 
cord  lie  between  the  two 
layers  of  the  pia  mater. 

The  nerves  v/hich  leave 
both  the  brain  and  cord 
receive  closely -applied 
sheaths  from  the  pia  mater. 
These  blend  with  the  con- 
nective-tissue sheaths  of  the 
nerves. 

The  ligamentum  denticu- 
latum  is  a  strong  fibrous 
band  which  stretches  out 
like  a  wing  from  the  pia  mater  on  either  side  of  the  spinal  cord,  so  as  to  connect 
the  pia  mater  with  the  dura  mater.  The  pial  or  inner  attachment  of  the  ligament 
extends  in  a  continuous  line  between  the  anterior  and  posterior  nerve-roots,  from 
the  level  of  the  foramen  magnum  a])Ove  to  the  level  of  the  first  lumbar  vertebra 
below.  Its  outer  margin  is  serrated  or  denticulated,  and  for  the  most  part  free. 
From  twenty  to  twciity-two  denticulations  may  be  recognised.  They  occur  in  the 
intervals  between  the  spinal  nerves,  and  pushing  tlie  arachnoid  before  them,  they 


Arachnoi 


Posterior  iierve-r 


Spinal  gangl 

Anterior  division 

of  nerve 

Posterior  division 

of  nerve 


Anterior  nerve- 
root  (cut) 
Posterior  nerve- 
root 

Anterior  nerve- 
root  (cut) 


Ligamenturu 
denticulatuiu 


Fig. 


483.— Membranes  of  the  Spinal  Cord,  and  the  modk  ok 
Okkun  of  the  Spinal  Nerves. 


606  THE  NEEVOUS  SYSTEM. 

are  attached  by  their  pointed  ends  to  the  inner  surface  of  the  dura  mater.  The 
hgamenta  denticulata  partially  subdivide  the  wide  subarachnoid  space  in  the  spinal 
canal  into  an  anterior  and  a  posterior  compartment.  The  anterior  nerve-roots 
traverse  the  anterior  compartment,  whilst  the  posterior  nerve-roots  traverse  the 
posterior  compartment.  Further,  the  posterior  compartment  is  imperfectly  sub-' 
divided  into  a  right  and  a  left  lateral  part  by  the  septum  posticum. 

By  means  of  the  ligamenta  denticulata  the   spinal  cord  is  suspended  in   the 
middle  of  the  tube  of  dura  mater. 


THE   PERIPHERAL   NERVES  AND   THE   SYMPATHETIC 
NERVOUS   SYSTEM. 

By  A.  M,  Paterson. 


Arising  from  the  brain  and  spinal  cord  respectively,  the  cranial  and  spinal 
nerves  are  responsible,  collectively,  for  the  central  localisation  of  peripheral 
stimuli,  or  for  the  transmission  peripherally  of  central  impulses.  The  sense 
organs  and  the  somatic  regions  of  the  body  are  in  direct  communication  by 
the    nerves  with    the 


Dorsal  nerve-root 
Ligamentum 
denticulatum 
Ventral  nerve-root 


Dorsal  nerve-root 
Ventral  nerve-root 

Ventral  nerve-root 
Ligamentum 
denticulatum 
Arachnoid 


brain  and  spinal  cord. 
The  splanchnic  area, 
and  the  viscera  which 
it  contains,  are  gov- 
erned by  nerves  con- 
nected with  the  central 
nervous  system.  By 
means  of  the  sym- 
pathetic nervous  sys- 
tem, the  nerves  from 
the  cerebro-spinal  sys- 
tem are  directed  to 
their  several  destina- 
tions in  the  splanchnic 
area :  and  connexions 
are  effected  with  the 
roots  of  the  nerves  on 
the  one  hand,  and 
through  their  peri- 
pheral branches,  with 
the  somatic  region,  on 
the  other  hand. 

THE   SPINAL 
NERVES. 

The  spinal  nerves 

are  arranged  in  pairs, 
of  which  there  are 
usually  thirty  -  one. 
Each  nerve  arises  by 
two  roots  from  the 
spinal  cord,  which 
separately  pierce  tiie  dura  mater.  Enclosed  in  a  tubular  investment  of  this 
monibrane,  the  nerve  emerges  from  the  spinal  canal  through  tlie  intervertel)ral 
foramen,  and  is  distributed  to  the  trunk  and  limbs  in  a  manner  to  be  described  below. 
The  nerves  are  designated  cervical,  thoracic,  lumbar,  sacral,  and  coccygeal,  in  rela- 
tion to  the  vertcbrie  Ijetwecn  which  thijy  emerge  from  the  spinal  canal.  Each  nerve 
appears  below  the  corresjionding  vertebra,  except  the  first  of  the  cervical  series, 

007 


Posterior  primary 
division 

Anterior  jiriinary 
division 


—Pia  mater 


Dorsal  nerve-root 


Dorsal  ganglion 

Posterior  primary 
division 


Anterior  primary  division 
\  entral  nerve-root 


Spinal  coril 


Fio.  484. — Scheme  of  the  Auhangement  of  the  Membranes  of  the 
SciNAL  Cord  and  the  Roots  of  the  Spinal  Nerves. 


608 


THE  NEEVOUS  SYSTEM. 


which  passes  out  of  the  spinal  caual  between  the  occipital  bone  and  the  atlas. 
There  are  thus  eight  cervical  nerves  (the  last  appearing  between  the  seventh 
cervical  and  first  thoracic  vertebrte)  ;  there  are  twelve  thoracic, /ve  lumbar,  _^'ye 
sacral,  and  one  coccygeal  nerve,  all  appearing  below  the  corresponding  vertebra?. 

The  thirty-first  nerve  is  occasionally  absent ;  and  there 
are  sometimes  one  or  two  additional  pairs  of  minute 
filaments  below  the  thirty-first,  which,  however,  do  not 
emerge  from  the  spinal  canal.  These  are  rudimentary 
caudal  nerves. 

The  size  of  the  spinal  nerves  varies  extremely.  The 
lai-gest  are  those  which  take  part  in  the  formation  of  the 
great  nerve -trunks  for  the  supply  of  the  limbs  (lower 
cervical  and  first  thoracic,  and  lower  lumbar  and  upper 
sacral  nerves) ;  and  of  these  the  nerves  destined  for  the 
lower  limbs  are  the  larger.  The  coccygeal  nerve  is  the 
smallest  of  the  spinal  nerves ;  the  thoracic  nerves  (except 
the  first)  are  much  more  slender  than  the  limb  nerves ; 
and  the  cervical  nerves  diminish  in  size  from  below  up- 
wards. 

Origin    of    the    Spinal    Nerves.— Each    spinal 

nerve  is  attached  to  the  spinal  cord  by  two  roots, 
called  respectively  dorsal  (posterior)  and  ventral 
(anterior). 

The  dorsal  root  is  larger  than  the  ventral  root ; 
it  contains  a  larger  number  of  rootlets,  and  the  in- 
dividual rootlets  are  of  larger  size  than  in  the  ventral 
root.  It  has  a  vertical  linear  attachment  to  the 
postero-lateral  sulcus  of  the  spinal  cord.  The  rootlets 
of  contiguous  dorsal  roots  are  in  close  relation,  and,  in 
some  instances,  overlap.  The  dorsal  root  separates  as 
it  passes  away  from  the  cord  into  two  bundles,  both 
of  which  become  connected  with  the  inner  end  of  a 
spinal  ganglion.  From  the  outer  end  of  this  ganglion 
the  dorsal  root  proceeds  to  its  junction  with  the 
ventral  root  in  the  intervertebral  foraimen. 

The  spinal  ganglia  are  found  on  the  dorsal  roots 
of  all  the  spinal  nerves.  (In  the  case  of  the  first 
cervical  or  sub-occipital  nerve,  the  spinal  ganglion  may 
be  rudimentary  or  absent ;  and  the  dorsal  root  itself 
may  be  wanting,  or  derived  from  the  spinal  accessory 
nerve.)  They  occupy  the  intervertebral  foramina, 
except  in  the  case  of  the  sacral  and  coccygeal  nerves, 
the  ganglia  of  which  lie  within  the  vertebral  canal : 
and  the  first  and  second  cervical  nerves,  the  ganglia 
of  which  lie  upon  the  neural  arches  of  the  atlas  and 
axis  respectively.  With  the  exception  of  the  coccygeal 
ganglia  they  are  outside  the  cavity  of  the  dura  mater, 
but  are  invested  by  the  membrane.  The  ganglia 
are  of  ovoid  form,  bifurcated  in  some  cases  at  their 
inner  ends.  They  consist  of  unipolar  nerve -cells, 
whose  processes,  after  a  very  short  course,  divide  into 
central  (root)  and  peripheral  (trunk)  fibres.  The 
central  fibres  form  the  portion  of  the  root  entering 
the  spinal  cord  ;  the  peripheral  fibres  are  continued  in 
an  outward  direction  from  the  ganglion  into  the  spinal  nerve. 

Accessory  spinal  ganglia  (ganglia  aberrantia). — Between  the  spinal  ganglion  and  the  spinal 
cord  small  collections  of  cells  are  occasionally  found  on  the  dorsal  roots,  either  as  scattered  cells 
or  distinct  ganglia.  They  are  niost  frequently  met  with  on  the  dorsal  roots  of  the  lumbar  and 
sacral  nerves. 


Fig.    485. — Diagrammatic     Repre- 
sentation  OF  THE   ORIGIN  OF  THE 

Spinal  Nerves,  showing  the  posi- 
tion of  their  roots  and  ganglia 
respectively  in  relation  to  the  spinal 
column.  Tlie  nerves  are  shown  as 
thick  black  lines  on  the  left  side. 


DIVISIONS  OF  A  SPINAL  NERVE. 


609 


BffAAICf/ 


The  ventral  root  is  smaller  than  tlie  dorsal  root.  It  arises  from  the  anterior 
surface  of  the  spinal  cord  {cmterior  root  zone)  by  means  of  scattered  bundles  of 
nerve-fibres,  which  occupy  a  greater  horizontal  area  and  are  more  irregular  in  their 
arrangement  than  the  fascicles  of  the  dorsal  root.  It  possesses  no  ganglion  in  its 
course.  The  rootlets  sometimes  overlap,  and  are  not  unfrequently  connected  with 
neighbouring  rootlets  above  and  below. 

The  dorsal  and  ventral  roots,  from  their  attachment  to  the  spinal  cord,  proceed 
outwards  in  the  spinal  canal  towards  the  intervertebral  foramina,  where  they 
unite  to  form  the  spinal  nerve.  The  direction  of  the  roots  of  the  firsfc  tw^o  nerves 
is  upwards  and  outwards ;  the  roots  of  the  remaining  nerves  course  obliquely 
downwards  and  outwards,  the  obliquity  gradually  increasing  until,  in  the  case  of 
the  lower  lumbar,  the  sacral  and  coccygeal  nerve-roots,  their  course  is  vertically 
downwards  in  the  spinal  canal.  The  collection  of  nerve-roots  which  occupies 
the  lower  part  of  the  canal  below  the  first  lumbar  vertebra,  and  comprises  all  the 
nerve-roots  below  those  of  the  first  lumbar  nerve,  is  designated  the  cauda  equina. 
They  arise  from  the  lumbar  enlarge- 
ment and  conus  meduUaris,  and  sur- 
round the  filum  terminale  of  the  spinal 
cord. 

Within  the  spinal  canal  the  nerve- 
roots  are  in  relation  with  the  meninges 
of  the  cord,  and  are  separated  from  one 
another  by  the  ligamentuni  denti- 
culatum,  and,  in  the  neck,  by  the  spinal 
part  of  the  spinal  accessory  nerve.  Each 
receives  a  covering  of  pia  mater,  con- 
tinuous with  the  neurilemma ;  the 
arachnoid  invests  each  root  as  far  as 
the  point  where  it  meets  with  the  dura 
mater ;  and  each  root  pierces  the  dura 
mater  separately.  The  two  roots  are 
thereafter  enclosed  in  a  single  tubular 
sheath  of  dura  mater,  in  which  is  included 
the  spinal  ganglion  of  the  dorsal  root. 
The  spinal  nerve  thus  formed  lies  in 
the  intervertebral  foramen,  except  in 
the  case  of  the  first  two  cervical  and 
the  sacral  and  coccygeal  nerves. 

Divisions  of  a  Spinal  Nerve. — 
After  emerging  from  the  intervertebral 
foramen  the  nerve  immediately  divides 
into  two  primary  divisions,  named  respectively  the  posterior  and  anterior 
primary  divisions.  Just  before  its  division  each  nerve  gives  off  a  minute 
recurrent  branch,  which  re-enters  the  vertebral  canal  after  effecting  a  junction 
with  a  branch  from  the  sympathetic  cord,  and  is  distributed  to  the  spinal  cord 
and  its  membranes. 

The  posterior  and  anterior  primary  divisions  of  the  spinal  nerve  are  responsible 
for  the  innervation  of  the  skeletal  muscles  and  the  skin  covering  the  trunk 
and  limbs.  They  are  thus,  properly  speaking,  the  somatic  branches  of  the 
spinal  nerve. 

In  ]-elatioii  to  certain  of  the  nerves,  a  series  of  much  smaller  branches  exist  which  are  connected 
with  tlie  sympathetic  system  (Fig.  486,  SY),  in  a  way  to  be  described  later.  These  constitute  the 
white  rami  communicantes,  and  may  Ije  ti.-rnied  the  visceral  divisions  of  the  sjjinal  nerves.  They 
are  dci-ived  from  tlie  aiit('rior  pi'iniary  divisions  of  the  nerves,  and  receive  their  fibres  mainly 
from  tlie  ventral  roots,  thougli,  at  least  in  the  case  of  certain  nerves,  from  the  dorsal  I'oots  as  well. 
Tliese  nerves  are  directed  inwards  from  the  intervertebral  foramen  over  the  vertebral  colunni,  and, 
becoming  connected  willi  the  symjjathetic  cord,  convey  spinal  fibres  to  the  organs  and  tissues  in 
tlie  splanchnic  area. 

The  posterior  and  anterior  primary  divisions  of  the  nerves  contain  fibres  from 
43 


B/VINCH 


Fig.  486. — Scheme  of  the  Distribution  of  a 
Typical  Spinal  Nerve. 


610  THE  NEEVOUS  SYSTEM. 

both  dorsal  and  ventral  roots.  Indeed,  each  root  can  be  seen,  on  removal  of  its 
sheath,  to  divide  into  two  portions,  of  which  one  portion  enters  into  the  formation 
of  the  posterior,  the  other  into  the  formation  of  the  anterior  primary  division. 
The  posterior  primary  divisions,  with  the  exception  of  the  first  two,  are  smaller 
than  the  anterior  primary  divisions ;  and  they  are,  generally  speaking,  responsible  for 
the  innervation  of  the  skin  and  muscles  of  the  back.  They  do  not  supply  the  muscles 
of  the  limbs;  although  in  their  cutaneous  distribution  they  are  prolonged  on  to 
the  back  of  the  head,  tlie  shoulder,  and  the  buttock.  Tbey  form  two  small  plexuses 
— the  posterior  cervical  and  the  posterior  sacral  plexuses.  The  anterior  primary 
divisions  are,  with  the  exception  of  t]ie  first  two  cervical  nerves,  much  larger  than 
the  posterior  primary  divisions.  They  supply  the  sides  and  fore-parts  of  the  body, 
the  limbs,  and  the  perineum.  For  the  most  part  they  have  a  complicated 
arrangement.  The  thoracic  or  intercostal  nerves  alone  have  a  simple  mode  of  dis- 
tribution ;  the  other  nerves  give  rise  to  the  three  great  plexuses — cervical,  brachial, 
and  lumbo-sacral. 

Distribution  of  the  Spinal  Nerves. — The  distribution,  like  the  origin  of  the 
posterior  and  anterior  primaiy  divisions  of  the  spinal  nerves,  presents  primarily  and 
essentially  a  segmental  arrangement,  masked  and  in  some  cases  obliterated  by  develop- 
mental changes  which  have  occurred  in  the  parts  supplied.  In  no  region  can  a  single 
nerve  be  traced  to  a  complete  segment.  In  the  trunk  between  the  Hmbs  the  nearest 
approach  to  a  complete  girdle  is  formed  by  such  a  nerve  as  the  sixth  thoracic  nerve. 
In  its  cutaneous  distribution  it  forms  a  perfect  belt,  the  nerve  by  its  posterior  and 
anterior  primary  divisions  supplying  a  distinctly  segmental  area  from  the  middle  line 
of  the  trunk  behind  to  the  sternum  in  front.  Its  muscular  distribution,  also,  is 
almost  perfectly  segmental.  The  anterior  primary  division  supplies,  unaided,  the 
intercostal  muscles  of  the  segment  in  Avhich  it  lies.  The  posterior  primary  division 
supplies  muscles  in  the  back,  not,  however,  in  a  strictly  segmental  manner,  on  account 
of  the  fact  that  the  segmental  myotomes  have  fused  together  in  the  back  to  give  rise 
to  complex  longitudinal  muscles,  which  are  together  supplied  by  the  series  of  muscular 
branches  derived  from  the  posterior  primary  divisions  of  contiguous  nerves.  In  other 
regions  greater  changes  cause  more  marked  deviations  from  a  simple  segmental  type  of 
distribution  and  give  rise  to  the  various  plexuses,  by  which  the  trunk,  and  more  particu- 
larly the  limbs,  are  innervated. 


POSTERIOE  PRIMARY  DIVISIONS  OF  THE  SPINAL  NERVES. 

The  posterior  primary  divisions  of  the  spinal  nerves  are  distributed  generally  to 
the  skin  of  the  back  of  the  trunk,  the  back  of  the  head,  the  shoulder  and  the 
buttock,  and  to  the  longitudinal  muscles  of  the  back,  but  not  to  the  muscles  of  the 
limbs. 

Each  posterior  primary  division  divides  as  a  rule  into  two  parts,  an  internal  and 
an  external  trunk  (Fig.  486,  p.  609).  In  the  upper  half  of  the  body  the  internal 
trunks  generally  supply  the  cutaneous  branches,  while  the  external  trunks  are 
purely  muscular  nerves.  In  the  lower  part  of  the  body  the  opposite  is  the  case : 
the  external  trunks  provide  the  cutaneous  nerves  and  the  internal  trunks  are 
distributed  entirely  to  muscles.  The  cutaneous  branches  have  a  different  course 
in  the  two  cases.  In  the  upper  half  of  the  back  they  course  inwards  and  back- 
wards beneath  and  among  the  muscles  to  within  a  short  distance  of  the  spinous 
processes  of  the  vertebras,  close  to  which  they  become  superficial.  They  then 
extend  outwards  in  the  superficial  fascia.  In  the  lower  half  of  the  back  the 
cutaneous  nerves  are  directed  downwards  and  outwards  among  the  muscles,  and 
become  superficial  at  a  greater  distance  from  the  middle  line. 


CEEVICAL  NEEVE8. 


611 


CERVICAL  NERVES. 

First  Cervical  Nerve  (n.  sub-occipi- 
talis). — It  has  already  been  pointed  out 
that  the  dorsal  root  of  this  nerve  may 
be  rudimentary,  or  even  absent  altogether. 
Its  posterior  primary  division  is  larger 
than  the  anterior  primary  division ;  it 
does  not  divide  into  internal  or  external 
branches,  and  it  does  not  directly  supply 
any  cutaneous  branch. 

Passing  backwards  in   the  space  be- 
tween the  occipital  bone  and  the  posterior 
arch  of  the  atlas,  the  nerve  occupies  the 
sub  -  occipital 
triangle,    and   is 
placed      below 
and    behind   the 
vertebral  artery, 
and  under  cover 
of  the  complexus 
muscle.     It  sup- 
plies the  follow- 
ing branches : — 

(a)  Muscular 
branches  to  the 
complexus,  recti 
capitis  postici, 
major  and  minor, 
and  obliqui, 
superior  and  in- 
ferior. 

(c)  A  commu- 
nicating- brancli 
descends  to  join 
the  second  cervi- 
cal nerve. 

The     communi- 
cating brancli  may 

arise     in     common 

witb  the  nerve  to 

the     obhquus     in- 
ferior,   and     reach 

the  second  cervical 

nerve    by  piercing 

or  passing  over  or 

beneath    the    obli- 

quus  inferior.      Or 

it  may  accompany 

the    nerve    to    the 

complexus,     and 

communicate    with 

the  great  occipital 

nerve,   after   pierc- 
ing that  muscle. 

Fig.  487. — The  Distribution  of  Cutaneous  Nerves  on  the  Back  of  the  Trunk. 
On  one  side  the  di.stribntion  of  the  several  nerves  is  represented,  the  letters  indicating  their  nomenclature. 

G.O  (C.2j,  Great  occipital  ;  C.3,  Least  occipital ;  T.l  et  ser/.,  Posterior  primary  divisions  of  thoracic  nerves  ; 
L.l  ei  neq.,  Posterior  primary  divisions  of  first  tljree  lumltar  nerves  ;  S.l  ei  xrr/.,  Posterior  primnrj 
divisions  of  sacral  nerves  ;  Aci',  Acromial  branches  from  cervical  plexus  ;  T.2-12,  Lateral  brandies  of 
thoracic  nerves;  (Jirc,  Cutaneous  V>raiiches  of  circumflex  nerve;  L.l,  Iliac  branch  of  ilio-]iypof,'astric 
nerve  ;  E.C,  External  cutaneous  nerve  ;  S.Sc,  .Small  sciatic  nerve. 

On  the  other  side  a  schematic  rei)resentation  is;,'iven  of  the  areas  sup])Ued  by  the  aljove  nerves,  the  numerals 
indicating  the  spinal  origin  of  the  branches  of  distrilmtion  to  each  area. 


612 


THE  NEEVOUS  SYSTEM. 


Second  Cervical  Nerve. — The  posterior  primary  division  of  this  nerve  is 
larger  than  the  corresponding  anterior  primary  division.  It  passes  backwards 
between  the  atlas  and  axis,  and  in  the  interval  between  the  obliquus  inferior 
and  the  semispinalis  colli  muscles,  under  cover  of  the  complex  us  muscle.  In  this 
situation  the  nerve  gives  off  several  small  muscular  and  communicating  branches. 
The  main  trunk,  after  piercing  the  complexus  and  trapezius  muscles,  accompanies 
the  occipital  artery  to  the  scalp  as  the  great  occipital  nerve  (n.  occipitalis  major). 
This  is  the  chief  cutaneous  nerve  for  the  back  part  of  the  scalp.  It  enters  the 
superficial  fascia  at  the  level  of  the  superior  curved  line  of  the  occipital  bone  and 
about  an  inch  from  the  external  occipital  protuberance.  Ramifying  over  the 
surface,  it  supplies  the  skin  of  the  scalp  as  far  as  the  vertex.      It  communicates  on 


d'J//MmmS    Occipital  attachment  of 
trapezius 
Insertion  of  complexus 


Insertion  of  stern  o 
mastoid 
Splenius  capitis. 

Trachelo-mastoid 


Complexus 
Least  occipital  nekve 


Splenius  capitis 


Trachelo-mastoid 


Great  occipital  nerve 

Obliquus  superior 

Rectus  capitis  posticus  major 
Rectus  capitis  posticus  minor 
Vtrtebial  artery 


Slboccipital  nerve 
Postenoi  arch  of  atlas 

Obliquus  inferior 

Posterior  division  of  second  cervical 

nerve 


Posterior  division  of  third  cervical 
ner\e 

Deep  ceT\  ical  artery 

Posterior  division  of  fourth  cervical 

NER%E 


Semispinalis  colli 


Fig.  488. — Posterior  Cervical  Plexus. 


the  scalp  with   the   following  nerves  :  great   auricular,  small   occipital,  posterior 
auricular,  and  least  occipital. 

The  muscular  branches  of  the  second  cervical  nerve  are  destined  for  the  com- 
plexus, obliquus  inferior,  semispinalis  colli,  and  multifidus  spinse. 

Its  communicating  branches  form  the  posterior  cervical  plexus.  Descending  over 
the  posterior  arch  of  tlie  atlas  is  a  branch  from  the  sub-occipital  nerve  which  forms  a  loop 
or  network  Avith  a  corresponding  branch  of  the  second  nerve.  From  this  loop  twigs  are 
supplied  to  the  surrounding  muscles.  A  similar  loop  is  formed  by  a  communication 
between  branches  of  the  second  and  third  nerves,  from  which  muscles  are  also  supplied. 
Occasionally  an  additional  loop  is  formed  between  branches  of  the  third  and  fourth  nerves. 

Third  Cervical  Nerve. — This  is  much  smaller  than  the  second  nerve.  Near 
its  origin  it  forms  a  loop  of  communication  with  the  second,  and  it  may  give  off 
a  similar  communicating  branch  to  the  fourth  nerve.  The  main  trunk  divides 
into  internal  cutaneous  and  external  muscular  branches.  The  external  musctilar 
branch  enters  contiguous  muscles  ;  the  internal  cutaneous  branch  passes  backwards 
and  inwards,  and  becomes  superficial  as  the  third  or  least  occipital  nerve  (n.  occipi- 
talis minimus),  close  to  the  middle  line  of  the  neck.  It  supplies  fine  branches  to 
the  neck  and  scalp,  and  communicates  with  the  great  occipital  nerve. 


LUMBAE  NERVES.  613 

The  fourth,  fifth,  and  sixth  cervical  nerves  are  still  smaller.  Beneath  the  com- 
plexus  each  divides  into  external  muscular  and  internal  cutaneous  branches.  The 
muscular  branches  supply  neighbouring  muscles ;  the  cutaneous  branches  are  small 
nerves,  which,  passing  backwards,  become  superficial  close  to  the  middle  line.  They 
supply  the  skin  of  the  back  of  the  neck.  The  sixth  is  the  smallest,  and  its  cutaneous 
branch  is  minute,  and  may  be  absent  altogether.  In  certain  cases  the  fourth  nerve 
forms,  with  the  third,  a  loop  of  communication  from  which  muscles  are  supplied. 

Seventh  and  Eighth  Cervical  Nerves. — These  are  the  smallest  of  the  posterior 
primary  divisions  of  the  cervical  nerves.  They  give  off  ordinarily  no  cutaneous 
branches,  and  end  in  the  deep  muscles  of  the  back. 

THORACIC  NERVES. 

The  posterior  primary  division  of  each  thoracic  nerve  divides  into  an  internal 
and  external  branch.  In  the  case  of  the  upper  six  thoracic  nerves  the  internal 
branches  are  chietiy  distributed  as  cutaneous  nerves, — only  giving  off  small  muscular 
branches — while  the  external  branches  are  wholly  muscular  in  their  distribution  ; 
in  the  case  of  the  lower  six  thoracic  nerves  the  opposite  is  the  case.  In  all  cases 
the  muscular  branches  serve  to  innervate  the  longitudinal  muscles  of  the  back. 
The  distribution  of  the  cutaneous  branches  is  different  in  the  upper  and  lower 
part  of  the  back.  The  upper  six  or  seven  thoracic  nerves  innervate  the  skin  of 
the  scapular  region.  The  internal  cutaneous  branches,  after  passing  backwards  from 
their  origin  among  the  dorsal  muscles,  reach  the  surface  near  the  spines  of  the 
vertebrae  and  are  directed  almost  horizontally  outwards  over  the  vertebral  border 
of  the  scapula.  The  first  is  small ;  the  second  is  very "  large  and  reaches  to  the 
acromion  process.  The  rest  diminish  in  size,  from  above  downwards,  and  become 
more  and  more  oblique  in  direction.  The  external  cutaneous  branches  of  the  lovjer 
five  or  six  thoracic  nerves  are  directed  from  their  origin  obliquely  downwards  and 
outwards  among  the  parts  of  the  erector  spinae  muscle.  Becoming  cutaneous  by 
piercing  the  latissimus  dorsi  at  some  distance  from  the  middle  line,  they  supply 
the  skin  of  the  back  in  the  lower  part  of  the  chest  and  loin,  the  lowest  nerves 
(eleventh  and  twelfth)  reaching  over  the  iliac  crest  on  to  the  buttock.  The  lower 
nerves  often  subdivide  into  two  branches  before  or  after  their  emergence  from  the 
latissimus  dorsi  muscle. 

LUMBAR  NERVES. 

First  three  Lumbar  Nerves. — The  posterior  primary  divisions  of  the  first 
three  lumbar  nerves  subdivide  into  internal  and  external  branches,  in  the  same 
way  as  the  lower  thoracic  nerves.  The  internal  branches  are  muscular  and 
innervate  the  deep  muscles  of  the  back.  The  external  branches  are  chiefly 
cutaneous.  They  are  directed  obliquely  downwards  and  outwards  among  the 
fibres  of  the  erector  spinse  and  become  superficial  by  piercing  the  vertebral 
aponeurosis,  just  above  the  iliac  crest  and  a  short  distance  in  front  of  the  posterior 
iliac  spine.  They  are  then  directed  downwards  in  the  superficial  fascia  of  the 
buttock,  and  supply  a  lengthy  strip  of  skin,  extending  from  the  middle  line  above 
the  iliac  crest  to  a  point  below  and  behind  the  great  trochanter  of  the  femur. 

The  fourth  and  fifth  lumbar  nerves  (like  the  last  two  cervical  nerves)  usually 
supply  only  muscular  branches  to  the  longitudinal  muscles  of  the  back.  The  fifth 
nerve  in  many  cases  sends  a  minute  branch  to  form  a  loop  of  connexion  with  the 
posterior  primary  division  of  the  first  sacral  nerve  (posterior  sacral  plexus). 

SACRAL  AND  COCCYGEAL  NERVES. 

The  posterior  primary  divisions  of  the  sacral  nerves  issue  from  the  posterior 
sacral  forfimina.  As  in  the  case  of  the  thoracic  and  lumbar  nerves,  the  upper 
sacral  nerves  differ  from  the  lower  in  their  distribution. 

The  first  three  sacral  nerves  sup])]y  internal  iiiuscular  branches  for  the 
niiiltifiduH  K})inai,  and  cxtcjrnal  cutaneous  branches  which  pierce  the  fibres  of  the 
sacro-sciatic  ligamoit  iind  the  gluteus  maximus  muscle,  and  supply  the  skin  over 


614  THE  NEEVOUS  SYSTEM. 

the  back  of  the  sacrum  and  contiguous  part  of  the  buttock,  giving   rise  to  the 
posterior  sacral  plexus. 

The  posterior  sacral  plexus  consists,  like  the  posterior  cervical  plexus,  of  Ioojds 
or  plexiform  communications  over  the  back  of  the  sacrum  between  the  posterior  primary 
divisions  of  the  first  three  sacral  nerves,  to  which  are  frequently  joined  branches  of  the 
last  lumbar  nerve  and  fourth  sacral  nerve.  From  these  loops  branches  proceed  to 
supply  the  multifidus  spina;  muscle  ;  others,  piercing  the  great  sacro-sciatic  ligament,  form 
secondary  loops  beneath  the  gluteus  maximus  muscle.  From  the  secondar}^  loops,  two  or 
more  cutaneous  branches  arise,  which,  after  traversing  the  muscle,  supply  the  skin  over 
the  sacrum  and  inner  part  of  the  buttock. 

Posterior  Sacro-coccygeal  Nerve. — The  posterior  divisions  of  the  fourth  and 
fifth  sacral  nerves  do  not  divide  into  internal  and  external  branches.  They  unite 
together  to  form  a  cord  which,  descending  behind  the  coccyx,  receives  the  minute 
posterior  primary  division  of  the  coccygeal  nerve.  The  union  of  the  three  nerves 
constitutes  the  posterior  sacro-coccygeal  nerve,  which,  after  perforating  the  sacro- 
sciatic  ligament,  is  distributed  to  the  skin  in  the  neighbourhood  of  the  coccyx.  It 
supplies  no  muscles.  This  nerve  is  the  representative  of  the  superior  caudal  trunk 
of  tailed  animals. 

Morphology  of  the  Posterior  Primary  Divisions. 

There  are  several  points  of  morphological  interest  in  relation  to  the  posterior  primary 
divisions  of  the  spinal  nerves. 

1.  Muscular  Distribution. — In  their  muscular  distribution  they  are  strictly  limited  to  the 
longitudinal  muscles  of  the  back  :  namely,  those  associated  with  the  axial  skeleton  alone. 

2.  Cutaneous  Distribution. — Their  cutaneous  distribution  represents  two  points  of  interest. 

A.  In  the  first  place,  while  the  skin  of  the  back  is  supplied  in  a  regularly  segmental  manner 
by  the  several  nerves,  certain  of  them  fail  to  reach  the  surface  at  all.  The  absence  of  a  cutaneous 
branch  from  the  sub-occipital  nerve  may  be  due  either  to  the  absence  of  a  perfect  dorsal  root,  or 
to  its  communication  with  the  second  nerve.  The  other  nerves,  w^hich  do  not  usually  supply  the 
skin,  are  the  seventh  and  eighth  cervical,  and  the  fourth  and  fifth  lumbar  nerves.  These  nerves 
are  j)laced  in  the  centre  of  regions  in  which  the  upper  and  lower  limbs  are  developed.  They  are 
minute  nerves,  while  the  corresponding  anterior  primary  divisions  are  among  the  largest  of  the 
spinal  nerves.  Thus,  opposite  the  centre  of  each  limb,  posteriorly,  there  is  a  hiatus  in  the 
segmental  distribution  of  the  posterior  primary  divisions  of  the  spinal  nerves  to  the  skin  of  the 
shoulder  and  buttock,  attributable  to  the  formation  of  the  limbs,  and  the  extension  into 
them  of  the  greater  part  of  the  nerves  of  the  region.  This  gap,  in  the  case  of  the  U2:)per  limb, 
commences  at  the  level  of  the  vertebra  j)rominens ;  in  the  case  of  the  lower  limb  it  commences 
opposite  the  level  of  the  posterior  superior  iliac  spine.  It  can  be  con^ued  on  to  each  limb  as 
a  hj'-pothetical  area  (the  dorsal  axial  line),  which  indicates  the  area  of  contact  (and  overlapping) 
of  cutaneous  nerves  not  in  strictly  numerical  sequence.  Thus,  in  the  region  of  the  shoulder,  the 
sixth  (or  fifth)  cervical  nerve  innervates  an  area  of  skin  adjoining  that  supplied  by  the  first 
thoracic  nerve  ;  in  the  region  of  the  buttock  the  third  lumbar  nerve  supplies  an  area  contiguous 
with  that  supplied  by  the  first  sacral  nerve. 

B.  The  cutaneous  branches  of  the  posterior  primary  divisions  of  the  spinal  nerves  differ  from 
the  muscular  branches  in  respect  of  their  penetration  into  regions  beyond  those  sujiplied  by 
their  motor  roots.  The  cutaneous  branches,  in  regions  where  outgrowths  or  extensions  from  the 
trunk  have  occurred,  follow  these  extensions ;  and,  in  consequence,  suj)ply  skin  covering  parts 
which  do  not  belong  to  segments  represented  by  the  nerves  in  question.  Thus  the  second  and 
third  cervical  nerves  (great  and  least  occipital)  are  drawn  upwards  so  as  to  supply  the  posterior 
part  of  the  scalii ;  the  upper  thoracic  nerves  are  drawn  outwards  over  the  scapular  region ;  the 
upper  lumbar  and  sacral  nerves  sujiply  the  skin  of  the  buttock ;  and  the  sacro-coccygeal  nerve 
forms  a  rudimentary  caudal  nerve. 

3.  Plexuses. — The  plexuses  formed  by  the  posterior  primary  divisions  of  the  upper 
cervical  and  ujiper  sacral  nerves  are  the  simplest  met  with  in  the  human  body.  The  posterior 
cervical  plexus  is  one  from  which  muscular  branches  are  supplied  ;  the  posterior  sacral  jjlexus  is 
mainly  concerned  in  producing  cutaneous  offsets.  In  the  case  of  the  posterior  cervical  plexus 
the  loops  of  communication  between  the  first  three  or  four  cervical  nerves  result  in  the  formation 
of  a  series  of  nerves  for  the  supply  of  the  semispinalis,  complexus,  and  other  muscles,  wdiich 
bring  into  contact  with  these  muscles,  simultaneously,  a  considerable  area  of  the  spinal  cord,  and 
provide  a  combined  and  simultaneous  innervation  for  the  several  jDarts  of  each  muscle.  In  the  case 
of  the  posterior  sacral  plexus,  the  formation  of  loops  between  the  nerves  results  in  the  innerva- 
tion of  any  given  spot  in  the  cutaneous  area  supplied  from  these  loops  by  more  than  one  spinal 
nerve.  As  has  been  said  already,  the  cutaneous  nerves,  even  without  the  formation  of  plexuses, 
overlap  in  their  cutaneous  distribution.  The  formation  of  a  plexus  causes  a'  more  intimate 
union  of  neighbouring  spinal  nerves,  so  that  stimulation  of  the  surface  aftects  a  wider  area  in 
the  spinal  cord  than  if  the  nerves  passed  separately  to  it  from  the  surface.  While  segmentation 
becomes  less  obvious,  increased  co-ordination  is  effected  both  of  movement  and  sensation. 


ANTEEIOE  PEIMARY  DIVISIONS  OF  THE  SPINAL  NERVES.     615 


ANTEPJOR   PRIMARY   DIVISIONS   OF   THE   SPINAL   NERVES. 

The  anterior  prim- 
ary divisions  of  the 
spinal  nerves,  are,  with 
the  exception  of  the 
first  two  cervical 
nerves,  much  larger 
than  the  corresponding 
posterior  primary  divi- 
sions. Composed  of 
elements  of  both  dorsal 
and  ventral  roots,  each 
nerve  separates  from 
the  posterior  primary 
division  on  emerging 
from  the  intervertebral 
foramen,  and,  proceed- 
ing outwards,  is  dis- 
tributed to  structures 
on  the  lateral  and 
anterior  aspects  of  the 
body, — including  the 
limbs. 

Each  nerve  is  joined 
near  its  origin  by  a 
gray  ramus  communi- 
cans  from  the  sym- 
pathetic gangliated 
cord ;  and  in  the  case 
of  certain  thoracic, 
lumbar,  and  sacral 
nerves,  the  anterior 
primary  division  gives 
off  a  delicate  bundle 
of  fibres,  which  forms 
the  white  ramus  com- 
municans  of  the  sym- 
pathetic cord.  That 
part  of  the  spinal  nerve 
which  is  distributed  to 
the  body  wall  andlimbs 
may  be  termed  somatic; 
the  small  white  ramus 
communicans,  in- 
nervating the  struc- 
tures in  the  splanchnic 
area,  may  be  termed  the 
visceral  or  splanchnic 
jjart  of  the  spinal  nerve. 


Fia.  489. 


-The  Distribution  of  Cutaneous  Nerves  on  the  Front  of 
THE  Trunk. 

Ine  anterior  prim-    On  one  .side  the  distribution  of  the  several  nerves  is  represented,  the  letters 
ary    divisions      of     the  indicating  their  nomenclature. 

spinal  nerves  are  only,  G.A,  Great  auricular  nerve  ;  S.C,  Superficial  cervical  nerve  ;  S.Cl,  Supra- 
clavicular nerves  ;  AcR,  Acromial  ;  Cl,  Clavicular  ;  St,  Sternal ;  T.2-12, 
Lateral  and  anterioi-  branches  of  thoracic  nerves  ;  I.H,  Ilio-hypogastric  nerve  ;  I.I,  Ilio-inguinal  nerve  ;  CiRC, 
Cutaneous  branch  of  circumflex  nerve  ;  L.I.C,  Lesser  internal  cutaneous  nerve  ;  I.H,  Intercosto-liumeral ;  LC, 
Internal  cutaneous  ;  M.H,  Cutaneous  branch  of  musculo-spiral  nerve  ;  E.C,  External  cutaneous  nerves  ;  G.C, 
Genito-criiral  nerve  ;  M,C'  '\  Middle  ciitaTieous  nerves  ;  I.C^,  Branch  of  internal  cutaneous  nerve  ;  P,  Branches 
of  pudic  nerve  ;  S.Sc,  Jiranches  of  small  sciatic  nerve. 

On  the  otlier  wide  a  scljematic  rejireseutation  is  given  of  tlie  areas  supplied  by  the  al)ove  nerves,  tlie  numerals 
indicating  the  Hpinal  origin  of  the  brandies  of  distribution  to  each  area. 


616 


THE  NEEVOUS  SYSTEM. 


in  certain  cases,  distributed  in  a  regular  segmental  manner.  Except  in  the  case  of 
the  thoracic^  nerves,  the  anterior  primary  divisions  ccmibine  to  form  the  three  great 
plexuses — cervical,  brachial,  and  lumbo-sacral — and  their  arrangement  and  distribu- 
tion is  rendered  exceedingly  complex. 

A  thoracic  nerve,   such  as  the  fifth  or  sixth,   may  be  regarded  as  a  type  to 

illustrate  the  mode 
'^^'  of    distribution    of 

the  anterior  primary 
divisions  of  the 
spinal  nerves  (Fig. 
486,  p.  609).  It 
occupies  an  inter- 
costal space ;  near 
its  origin  it  possesses 
gray  and  white  rami 
comniunicantes ;  it 
courses  through  the 
interval  between  the 
intercostal  muscles ; 
it  supplies  branches 
to  these  muscles 
and  gives  off,  when 
it  reaches  the  side 
of  the  chest, a  lateral 
hranch,  which,  after 
supplying  small 
muscular  branches, 
pierces  the  external 
intercostal  muscle, 
and  is  distributed 
to  an  area  of  skin 
over  the  lateral  part 
of  the  trunk,  con- 
tiguous dorsally 
with  a  similar  area, 
innervated  by  the 
cutaneous  branches 
of  the  posterior 
primary  division  of 
the  same  nerve. 
The  lateral  branch 
generally  subdivides 
into  a  smaller  j905- 
terior  and  a  larger 
anterior  trunk,  as  it 
pierces  the  muscles 
clothing  the  wall  of 
the  chest.  The  an- 
terior primary  divi- 
sion of  the  nerve 
then  pursues  its 
course  obliquely  for- 
wards to  the  side  of 
the  sternum,  where, 
after  piercing  the 
pectoral  muscles,  it 

appears  superficially  as  the  anterior  terminal  cutaneous  hranch.  This  supplies  an  area 
of  skin  continuous  with  that  supplied  by  the  anterior  part  of  the  lateral  branch  of 
the  same  nerve.     Such  a  nerve  thus  supplies,,  by  means  of  its  lateral  and  anterior 


3Jfy 


fhr 

Fig.  490. 

Superficial  Division. 

A.scendiug  branches  (Asc. ) — 
S.O.    Small  occipital. 
G.A.  Great  auricular. 
S.C.    Superficial  cervical. 


Descending  (supra-clavicular)  branches 
(Desc.)— 
Acr.   Acromial. 
C).     Clavicular. 
St.      Sternal. 

Deep  Division. 

External  branches — 

Communicating  (C.)  to  spinal  acces- 
sory nerve  (Sj).  Ace). 

Muscular — 

S.M.      Sterno-mastoid. 

Tr.         Trapezius. 

L.A.S.   Levator  anguli  scapulae. 

Sc.M.     Scalenus  medius. 


-The  Cervical  Plexus. 

Internal  branches — 
Communicating  to 
Hy.  Hyjioglossal. 

Va.  Vagus. 

Sy.  Sympathetic  ganglion. 

D.Cerv.    Descendens  cervicis. 


Muscular- 
Mi. 

W. 

Sc.A. 

Phr. 

G.Hy. 

Th.Hy. 

D.Hy. 

Ansa. 

S.Th. 

S.Hy. 

O.Hy. 


Rectus  capitis  anticus  minor, 

and  lateralis. 
Lougus    colli,    and    rectus 

capitis  anticus  major. 
Scalenus  anticus. 
Phrenic  nerve. 
Nerve  to  genio-hyoid. 
Xerve  to  thyro-hyoid. 
Descendens  hyi^oglossi. 
Ansa  hypoglossi. 
Nerve  to  sterno-thyroid. 
Nerve  to  steruo-hyoid. 
Nerves  to  omo-liyoid. 


THE  CERVICAL  PLEXUS.  617 

branches,  an  area  of  skin  which  (with  the  area  supplied  by  the  cutaneous  branch 
of  its  posterior  primary  division)  forms  a  continuous  and  uninterrupted  belt, 
extending  from  the  middle  line  behind  to  the  middle  line  in  front.  The  lateral 
and  anterior  branches  of  the  nerve  innervate  in  their  course  the  intercostal  and  other 
muscles,  to  be  afterwards  mentioned  in  detail. 

CERVICAL   NERVES. 

The  anterior  primary  divisions  of  the  cervical  nerves,  together  with  parts  of  the 
first  and  second  thoracic  nerves,  are  distributed  to  the  head,  neck,  and  upper 
extremity.  The  first  four  cervical  nerves,  by  means  of  the  cervical  plexus,  innervate 
the  neck;  the  last  four  cervical  nerves,  together  with  a  large  part  of  the  first 
thoracic  nerve,  through  the  brachial  plexus,  supply  the  upper  limb.  The  second 
thoracic  nerve  may  contribute  a  trunk  to  this  plexus,  and  always  assists  in  the 
innervation  of  the  arm. 

THE   CERVICAL    PLEXUS. 

The  anterior  primary  divisions  of  the  first  four  cervical  nerves  are  concerned 
in  forming  the  cervical  plexus.  Each  nerve  emerges  from  the  spinal  canal  behind 
the  vertebral  artery.  Each  is  joined  on  its  emergence  from  the  intervertebral 
foramen,  at  the  side  of  the  vertebral  column,  by  a  gray  ramus  communicans  from  the 
superior  cervical  ganglion  of  the  sympathetic.  In  the  neck  the  cervical  nerves  are 
concealed  by  the  sterno-mastoid  muscle;  in  front  lies  the  rectus  capitis  anticus 
major,  and  .behind  are  the  scalenus  medius,  and  (behind  the  first  or  sub-occipital 
nerve)  the  rectus  capitis  lateralis.  The  cervical  plexus  is  constituted  by  the  com- 
bination of  these  nerves  in  an  irregular  series  of  loops  under  cover  of  the  sterno- 
mastoid  muscle. 

From  these  loops  the  branches  of  distribution  arise,  as  (a)  cutaneous  branches  to 
the  head,  neck,  and  shoulder ;  (&)  muscular  branches  to  the  muscles  of  the  neck  and 
the  diaphragm ;  and  (c)  communicating  branches  to  the  vagus,  spinal  accessory, 
hypoglossal,  and  sympathetic  nerves. 

For  convenience  of  description,  the  nerves  derived  from  the  plexus  may  be 
classified  as  follows  : — 

I.  Superficial  (cutaneous)  Branches — 

A.  Ascending  Branches  (C.  2,  3).       B.  Descending  (supra-clavicular)  Branches  (C.  3,  4). 

Small  occipital,  Acromial, 

Great  auricular,  '  Clavicular, 

Superficial  cervical.  Sternal. 

II.  Deep  (muscular  and  communicating)  Branches — 

A.  External  Branches.  B.  Internal  Branches. 

1.  Muscular  V^ranches  to  1.     Muscular  to 

Sterno-mastoid  (C.  2),  Prevertebral  muscles  (C.  1,  2,  3,  4), 

Trapezius  (C.  3,  4),  Infra-hyoid  muscles  (C.  1,  2,  3) 
Levator  anguli  scapulse  (C.  3,  4),  (ansa  hypoglossi), 

Scaleni  (medius  and  posticus)  (C.  3,  4).  Diaphragm  (C.  3,  4)  (phrenic 

2.  Communicating  branches  to  nerve). 

Spinal  accessory  nerve  (C.  2,  3,  4).  2.   Communicating  branches  to 

Vagus  nerve  (C.  1,  2), 
Hypoglossal  nerve  (C.  1,2), 
C.  Hypoglossi  (C.  2,  3), 
Sympathetic  (C.  1,  2,  3,  4). 

The  second,  third,  and  i'ourth  cervical  nerves  arc  the  chief  nerves  engaged  in 
forming  the  plexus.  T'h(;  first  cervical  nerve  only  enters  into  the  formation  of  a 
small  part — tlie  internal  jjortion  of  the  deep  part  of  the  plexus. 

Superficial  Cutaneous  Branches. — These  nerves,  six  in  number,  are  entirely 
cutaneous.     T\u;y  radiate  f'roin  the  plexus,  and  appear  in  the  posterior  triangle  of 


618 


THE  NERVOUS  SYSTEM. 


the  neck  at  the  posterior  border  of  the  sterno-mastoid  muscle.  They  are  divisible 
into  two  series,  the  one  ascending :  small  occipital,  great  auricular,  and  superficial 
cervical ;  the  other  descending  (supra-clavicular) :  sternal,  clavicular,  and  acromial. 
Ascending  Branches. — The  small  occipital  nerve  (n.  occipitalis  minor)  is  variable 
in  size  and  is  sometimes  double.  Its  origin  is  from  the  second  and  third  cervical 
nerves  (more  rarely  from  the  second  only).  It  extends  backwards  beneath  the 
sterno-mastoid,  and  then  upwards  along  its  posterior  border.  Piercing  the  deep 
fascia  near  the  apex  of  the  posterior  triangle,  it  divides  into  auricular,  mastoid,  and 

occipital  branches,  and  supplies  small 
cervical  branches  to  the  upper  part 
of  the  neck.  The  auricular  branch 
supplies  the  skin  of  the  deep  surface 
of  the  pinna  ;  the  mastoid  and  occipital 
branches  supply  the  scalp.  The  nerve 
communicates  on  the  scalp  with  the 
great  occipital  and  great  auricular 
nerves,  and  with  the  posterior  auricular 
branch  of  the  facial  nerve. 

The  great  auricular  nerve  (n.  auri- 
cularis  magnus)  is  the  largest  of  the 
cutaneous  branches.  It  arises  from 
the  second  and  third  cervical  nerves 
(or,  more  rarely,  from  the  tbird  alone). 
Winding  round  the  posterior  border 
of  the  sterno-mastoid  muscle,it  courses 
vertically  upwards  towards  the  ear. 
In  this  course  it  crosses  the  sterno- 
mastoid  muscle  obliquely  and  is 
covered  by  the  platysma  myoides. 
Before  arriving  at  the  ear  it  subdivides 
into  mastoid,  auricular,  and  facial 
branches.  The  mastoid  branches  ascend 
over  the  mastoid  process  and  supply 
the  skin  of  the  scalp  behind  the  ear, 
communicating  with  the  small  oc- 
cipital and  posterior  auricular  nerves. 
The  auricular  branches  ascend  to  the 
ear  and  supply  the  lower  part  of  the 
pinna  on  both  aspects ;  they  com- 
municate with  the  same  nerves.  The 
facial  branches,  passing  over  the  angle 
of  the  jaw  and  through  the  substance 

I.O,  Infra-orbital  branch  ;  Inf.  Max,  Inferior  maxillary    of   the  parotid  gland,  supply  the  skin 

Slit'^'M'M  '^^'T''7^°■*^"^n'?i''''^'^'^^'^^?v^  of  the  cheek  over  the  lower  part  of 

branch  ;  M,  Mental  branch  ;  C.2,  3,  Branches  of  the      ,  i      i  •  i 

second  and  third  cervical  nerves  ;  G.O,  Great  occipital    the    maSSCtcr  niUSCle  and   the   parotid 
nerve;     S.O,     Small    occipital    nerve;     G.A,     Great    gland.  They       COmmunicatC       with 

aimcukr  nerve  ;  S.C^  Superficial  cervical^  branches     of    the    facial    ncrve    in    the 

Least    occipital   nerve;    4,    5,    6,    Posterior   primary 
divisions  of  4th,  5th,  and  6th  cervical  nerves.  parotid  gland. 

The  superficial  cervical  nerve  (n. 
cutaneus  colli)  arises  from  the  second  and  third  cervical  nerves.  It  winds  round 
the  posterior  border  of  the  sterno-mastoid  muscle,  and  crosses  the  muscle  to  reach 
the  anterior  triangle,  under  cover  of  the  platysma  myoides  muscle  and  the  external 
jugular  vein.  It  divides  near  the  anterior  edge  of  the  sterno-mastoid  muscle  into 
upper  and  lower  branches,  which  are  distributed  through  the  platysma  myoides  to 
the  skin  covering  the  anterior  triangle  of  the  neck.  The  upper  branches  com- 
municate freely  beneath  the  platysma  myoides  with  the  infra-mandibular  branch  of 
the  facial  nerve. 

Descending  (supra-clavicular)  Branches. — By  the  union  of  two  roots  derived 
from  the  third  and  fourth  cervical  nerves  a  considerable  trunk  is  formed,  which 


Fig.  491. — Distribution  of  Cutaneous  Nerves  to 
THE  Head  and  Neck. 

Oplith,  Ophthalmic  division  of  the  fifth  nerve  ;  S.T,  Supra- 
trochlear branch  ;  S.O,  Supra-orbital  branch ;  I.T, 
Infra-trochlear  branch  ;  L,  Lachrymal  branch  ;  N, 
External  nasal  branch  ;  Sup.  Max,  Superior  maxillary 
division  ;    T,   Temporal  branch  ;    M,    Malar   branch  ; 


THE  CETiVICAL  PLEXUS. 


619 


emerges  from  under  cover  of  the  sterno-mastoid  muscle  and  extends  obliquely 
downwards  through  the  lower  part  of  the  posterior  triangle  of  the  neck.  It  sub- 
divides into  radiating  branches — sternal,  clavicular,  and  acromial — which  pierce  the 
deep  fascia  of  the  neck  above  the  clavicle,  and  are  distributed  to  the  skin  of  the 
lower  part  of  the  side  of  the  neck,  the  front  of  the  chest,  and  the  shoulder.  The 
sternal  branches  (rami  supra-sternales)  are  the  smallest.  Passing  over  the  inner 
end  of  the  clavicle,  they  supply  the  skin  of  the  neck  and  chest  as  far  down  as 
the  manubrio-sternal  joint.  The  clavicular  branches  (rr.  supra-claviculares)  pass 
over  the   middle  third  of  the  clavicle,  beneath  the  platysma,  and  can  be  traced 


Great  occipital 
nerve 

Small  occipital 
nerve 

Great  auricular 
nerve 

Nerves  to  levator 
anguli  scapulfe" 

Superficial  cervical 
nerve 

Spinal  accessory- 
Nerve  to  trapezius 


Acromial"!  branches 

Clavicular  I    fr- J. 

Sternal  J    plexus 


Posterior  scapular 
nerve 

Posterior  thoracic 
nerve 


Fig.  492. — The  Triangles  of  the  Neck  (Nerves). 

as  low  as  the  nipple.  The  acromial  branches  (rr.  supra-acromiales)  pass  over  or 
through  the  insertion  of  the  trapezius  muscle,  and  over  the  outer  third  of  the 
clavicle,  to  the  shoulder,  where  they  supply  the  skin  as  far  down  as  the  lower  third 
of  the  deltoid  muscle. 

Deep  Branches. — The  deep  branches  of  the  cervical  plexus  are  naturally 
separated  into  an  external  and  itn  internal  set  by  tlieir  relation  to  the  sterno-mastoid 
muscle.  P(!neatli  the  muscle,  the  external  branches  are  directed  outwards  towards 
the  posterior  triangle,  the  internal  branches  inwards  towards  the  anterior  triangle. 

The  external  branches  consist  of  muscular  and  communicating  nerves,  which 
for  the  most  part  occupy  the  post(!rior  triangle. 

The  muscular  branches  are  the  following:  (1)  To  the  sterno-mastoid,  \xom  the 
second  cervical  ucrvf;.     'i'bis  enters  the  muscle  on  its  deep  surface  and  communicates 


620 


THE  NEEVOUS  SYSTEM. 


with  the  spinal  accessory  nerve.  (2)  To  the  trapezius,  from  the  third  and  fourth 
cervical  nerves.  These  nerves  cross  the  posterior  triangle  and  end  in  the  trapezius, 
after  having  communicated  with  the  spinal  accessory  nerve,  in  the  posterior  triangle, 
and  beneath  the  muscle.  (3)  To  the  levator  angicli  scapula,  from  the  third  and 
fourth  cervical  nerves.  Two  independent  branches  enter  the  outer  surface  of  the 
muscle  in  the  posterior  triangle.  (4)  To  the  scaleni  (medius  and  posticus),  from 
tlie  third  and  fourth  cervical  nerves. 

The  communicating  branches,  already  mentioned,  are  three  in   number.     They 


Hypoglossal  nervl 
Recurrent  brancli 


Vagus  nervk 
I      Superior  cervical  ganglion  of  the  synipatlietic 


First  CERVifAL  nerve 


Second  rERvicAi.  nervk 


Glosso-phar^-moeai. 
nerve 


Third  cervical  nerv 

Stylopharyngeii 


Pharyngeal  branch  ov  vag-TJS — 
Digastric 

DeSCENDENS  HYPOGLOSSr 

Mifldle  consti-ictor 
Descendens  cervicis 

Internal  laryngeal  nerve 
Ansa  hypoglossi 

Inferior  constrictor 


Omo-hyoid 


j-^  .  Hyoglossus 

— Genio-hyoglossns 

Genio-hyoiil 
Mylo-liyoid  (cut) 
Digastric 

Th3rro-hyoi(l 


Fig.  493. — The  Muscles  of  the  Htoid  Bone  and  Styloid  Process,  and  the  Extrinsic   Muscles'op 

THE  Tongue,  with  their  Nerves. 

join  the  spinal  accessory  nerve  in  three  situations : — (a)  A  branch  from  the  second 
cervical  nerve  to  the  sterno-mastoid  joins  the  spinal  accessory  nerve  heneath  that 
muscle,  (b)  Branches  to  the  trapezius  from  the  third  and  fourth  nerves  are  con- 
nected with  the  spinal  accessory  nerve  in  the  posterior  triangle,  (c)  Branches  from 
the  same  nerves  join  the  spinal  accessory  nerve  heneath  the  trapezius  rmiscle. 

The  internal  branches  of  the  plexus  also  comprise  muscular  and  communi- 
cating branches.  The  first  cervical  nerve  assists  in  the  formation  of  this  series  of 
nerves,  forming  a  slender  loop  with  part  of  the  second  nerve  in  front  of  the  trans- 
verse process  of  the  atlas. 

Communicating  Branches.  (a)  With  the  sympathetic. — Gray  rami  communi- 
cantes  pass  to  each  of  the  first  four  cervical  nerves,  near  their  origins,  from  the 


rilKENIC  NEliVK  G21 

superior  cervical  ganglion  or  from  the  cord  below  the  ganglion.  (/>)  With  the 
pneumo gastric  nerve.— The  ganglion  of  the  trunk  of  the  pneuinogastric  nerve  may 
be  connected  by  a  slender  nerve  with  the  loop  between  the  first  two  cervical  nerves. 
This  communication  is  not  constant,  (c)  With  the  hypoglossal. — An  important 
communication  occurs  between  the  hypoglossal  nerve  and  the  loop  between  the  first 
and  second  cervical  nerves  (Fig.  493).  A  trunk  from  the  last-named  nerves  joins  the 
hypoglossal  just  beyond  its  exit  from  the  skull.  One  fine  branch  from  this  trunk 
passes  upwards  along  the  hypoglossal  nerve  towards  the  skull  (^meningeal  hranchj. 
The  main  part  of  the  trunk  accompanies  the  hypoglossal  and  sejjarates  from  it  succes- 
sively in  three  nerves — the  descendens  hypoglossi,  and  the  nerves  to  the  thyro-hyoid 
and  genio-Lyoid  muscles.  The  portion  of  the  nerve  which  remains  accompanies  the 
hypoglossal  to  the  muscles  of  the  tongue.  It  is  probable  that  no  part  of  the  hypo- 
glossal nerve  itself  is  concerned  in  the  formation  of  these  three  branches.  The 
descending  branch  of  the  hypoglossal  (r.  descendens  hypogiossi)  descends  in  front  of 
the  common  carotid  artery,  and  is  joined  in  the  anterior  triangle  of  the  neck  by 
the  descending  cervical  nerve,  to  form  the  ansa  hypogiossi,  from  which  the  infra- 
hyoid muscles  are  innervated.  (The  descending  branch  of  the  hypoglossal,  in  some 
cases,  arises  from  the  pneumogastric  nerve.) 

Muscular  Branches. — The  muscles  supplied  by  the  internal  branches  of  the 
plexus  are  the  prevertebral  muscles,  the  genio-hyoid  and  infra-hyoid  muscles,  and 
the  diaphragm. 

(ft)  Prevertebral  Muscles. — 1.  From  the  loop  between  the  first  and  second 
cervical  nerves  a  small  branch  arises,  for  the  supply  of  the  rectus  capitis  lateralis 
and  the  recti  capitis  antici  (major  and  minor).  2.  From  the  second,  third,  and 
fourth  nerves  small  branches  supply  the  inter- transversales,  longus  colli,  and  rectus 
capitis  anticus  major.  3.  From  the  fourth  nerve  a  branch  arises  for  the  upper  part 
of  the  scalenus  anticus. 

(&)  Genio-hyoid  and  Infra-hyoid  Muscles. — The  descending  cervical  nerve  (n. 
cervicalis  descendens)  is  formed  in  front  of  the  internal  jugular  vein  by  the  union 
of  tw^o  slender  trunks  from  the  second  and  third  cervical  nerves.  It  forms  a  loop 
of  communication  in  front  of  the  carotid  sheath  with  the  descending  branch  of  the 
hypoglossal  nerve  (derived  ultimately  from  the  first  two  cervical  nerves).  This 
loop  of  communication  is  called  the  ansa  hypogiossi.  It  is  often  plexiform ;  and 
from  it  branches  are  given  to  the  sterno-hyoid,  sterno- thyroid,  and  omo-hyoid 
muscles.  The  nerve  to  the  sterno-hyoid  muscle  is  often  continued  behind  the 
sternum,  to  join  in  the  thorax  with  the  phrenic  nerve  or  the  cardiac  plexus. 

The  thyro-hyoid  muscle  and  the  genio-hyoid  muscle  are  supplied  by  branches  of 
the  hypoglossal  nerve,  which  are  also  traceable  back  to  the  communication  between 
the  hypoglossal  and  the  first  two  cervical  nerves. 

The  anterior  muscles  in  immediate  relation  to  the  middle  line  of  the  neck, 
between  the  chin  and  the  sternum,  are  thus  continuously  supplied  by  the  first 
three  cervical  nerves.  The  hypoglossal  is  the  nerve  of  the  muscles  of  the  tongue, 
and  it  is  not  certain  that  it  contributes  any  fibres  to  the  above-named  muscles. 

(c)  Diaphragm. — The  phrenic  nerve  supplies  the  diaphragm. 

Phrenic  Nekve. 

The  phrenic  nerve  (n.  phrenicus)  is  derived  mainly  from  the  fourth  cervical 
nerve,  reinforced  by  roots  from  the  third  (either  directly  or  through  the  nerve  to 
the  sterno-hyoid)  and  fifth  (either  directly  or  through  the  nerve  to  the  subclavius 
muscle).  It  passes  downwards  in  the  neck  upon  the  scalenus  anticus  muscle ;  at 
the  root  of  the  neck  it  enters  the  thorax  between  the  subclavian  artery  and  vein, 
and  traverses  the  mediastinum  to  reach  the  diaphragm,  lying  in  the  middle 
mediastinum  Vjetween  the  pericardium  and  pleura,  and  in  front  of  the  root  of  the 
lung.  In  its  course  it  presents  certain  differences  on  tlie  tw(j  sides.  In  the  neck, 
on  the  left  side,  it  crosses  the  first  ]>art  of  the  subclavia,n  artery :  on  the  right  side 
it  crosses  the  second  ]jart.  In  the  superior  mediastinum,  on  the  left  side,  it  lies 
between  the  left  subclavian  and  carotid  arteries,  and  crosses  the  pneumogastric 
nerve  and  the  aortic  arch.     On  the  right  side  it  accompanies  the  innominate  vein 


622  THE  NEEVOUS  SYSTEM. 

and  superior  vena  cava,  and  is  entirely  separate  from  the  pneumogastric  nerve. 
The  left  nerve  is  longer  than  the  right,  owing  to  the  position  of  the  heart  and  the 
left  half  of  the  diaphragm.  The  right  nerve  sends  fibres  along  the  inferior  vena 
cava  through  the  foramen  quadratum.  Reaching  the  diaphragm  the  nerve  separates 
into  numerous  branches  for  the  supply  of  the  muscle ;  some  enter  its  thoracic 
surface  (siib-pleural  branches),  but  most  of  the  fibres  supply  it  after  piercing  the 
muscle  (sub-peritoneal  branches). 

The  branches  of  the  phrenic  nerve  are — ^1.  Muscular  (to  the  diaphragm) ;  2. 
pleural;  3.  pericardiac;  4.  inferior  vena  caval ;  5.  capsular;  and  6.  hepatic. 

The  branches  to  the  pleura  and  pericardium  arise  as  the  phrenic  nerve 
traverses  the  mediastinum.  The  branches  to  the  inferior  vena  cava,  suprarenal 
capsule,  and  liver  arise  after  communication  of  the  phrenic  nerve  with  tlie 
diaphragmatic  plexus  of  the  sympathetic  on  the  abdominal  surface  of  the 
diaphragm. 

Communications  of  the  Phrenic  Nerve. — 1.  Tlie  plirenic  nerve  may  communicate 
with  the  nerve  to  the  subclavius  muscle.  2.  It  may  communicate  with  the  ansa 
hyjMnlossi,  or  a  branch  from  it  (the  nerve  to  the  sterno-hyoid).  3.  It  frequently  com- 
municates with  the  cervical  part  of  the  sympathetic.  4.  It  communicates  with  the 
solar  plexus  by  a  junction  upon  the  abdominal  surface  of  the  diaplu-agm  with  the 
diaphragmatic  plexus  on  the  inferior  phrenic  artery,  in  which  a  small  diaphragmatic 
ganglion  is  found  on  the  right  side.  From  this  junction  branches  are  given  off  to  the 
inferior  vena  cava,  suprarenal  capsule,  and  hepatic  plexus. 

MOKPHOLOGY    OF   THE    CERVICAL   PlEXUS. 

The  characteristic  feature  of  the  cervical  plexus  is  the  comloinatiou  of  parts  of  adjacent  nerves 
into  compound  nerve-trunks  by  the  formation  of  series  of  looj^s.  The  result  of  the  formation  of 
these  loops  is  that  parts  (particularly  cutaneous  areas)  are  supplied  by  branches  of  more  than  one 
sj)inal  nerve. 

A.  Cutaneous  Distribution. — By  the  combinations  of  the  nerves  into  loops  the  discrimination 
of  the  elements  in  the  upper  cervical  nerves,  corresponding  to  the  lateral  and  anterior  branches 
of  a  typical  thoracic  nerve,  is  made  a  matter  of  some  difficulty.  The  second,  third,  and 
fourth  nerves,  through  the  cervical  plexus,  supply  an  area  of  skin  extending,  laterally,  from  the 
side  of  the  head  to  the  shoulder  ;  anteriorly,  from  the  face  to  the  level  of  the  nipi^le.  The  higher 
nerves  supply  the  upper  region  (second  and  third) ;  the  lower  nerves  supj)ly  the  lower  region 
(third  and  fourth).  It  is  not  possible  to  strictly  compare  the  individual  nerves  with  the  lateral 
and  anterior  branches  of  a  thoracic  nerve.  A  line  drawn  from  the  ear  to  the  middle  of  the 
clavicle  sejaai-ates,  however,  a  lateral  from  an  anterior  cutaneous  area ;  and  certain  of  the 
cutaneous  nerves  fall  naturally  into  one  of  these  two  categories.  The  nerves  homologous  with 
anterior  branches  of  intercostal  nerves  are  the  superficial  cervical  and  the  sternal  branches  of 
the  sujjra-clavicular  series ;  those  homologous  with  lateral  branches  are  the  small  occipital  and 
acromial  branches.  The  great  auricular  and  clavicular  branches  are  mixed  nerves,  comprising 
elements  belonging  to  both  sets. 

B.  Muscular  Distribution. — The  nerves  from  the  cervical  jjlexus,  supjalying  muscles,  are 
simpler  in  their  arrangement.  They  are  not  generally  in  the  form  of  looj)s,  and  they  are  easily 
separated  into  lateral  and  anterior  series.  The  lateral  nerves  comprise  the  branches  to  the 
rectus  capitis  lateralis,  sterno-mastoid,  traj^ezius,  levator  anguli  scapulae.  The  nerves  in  the 
anterior  series  are  those  to  the  recti  antici,  the  hyoid  muscles,  and  the  diaphragm. 

It  is  noteworthy  that  the  last-named  muscles — genio-hyoid,  thyro-hyoid,  sterno-hyoid,  omo- 
hyoid, sterno-thyroid,  and  diaj^hragm — are  continuously  supplied  by  branches  from  the  first  five 
cervical  nerves  :  the  higher  muscles  by  the  higher  nerves  ;  the  lower  muscles  by  the  lower  nerves. 


THE   BRACHIAL   PLEXUS. 

The  brachial  plexus  is  formed  by  the  anterior  primary  divisions  of  the  fifth, 
sixth,  seventh,  and  eighth  cervical  nerves,  along  with  the  greater  part  of  the  first 
thoracic  nerve.  In  some  cases  a  slender  branch  of  the  fourth  cervical  nerve  is  also 
engaged ;  and  the  second  thoracic  nerve,  in  all  cases,  also  contributes  to  the 
innervation  of  the  arm,  through  the  intercosto-humeral  nerve.  It  many  cases  it 
contributes  also  directly  to  the  plexus,  by  an  intra-thoracic  communication  with 
the  first  thoracic  nerve. 

Position  of  the  Plexus — The  nerves  forming  tlie  bracliial  plexus  appear  in 
the   posterior   triangle  of  the  neck  between   the  scalenus  anticus  and  scalenus 


THE  BEACHIAL  PLEXUS. 


623 


medius  muscles ;  the  plexus  is  formed  in  close  relation  to  the  subclavian  and 
axillary  arteries  ;  the  nerves  emanating  from  it  accompany  the  artery  to  the  axilla, 
where  they  are  distributed  to  the  shoulder  and  upper  limb. 

Communication  with  the  Sympathetic. — The  lower  four  cervical  nerves  comniunicate 
with  the  cervical  portion  of  the  sympathetic  by  means  of  gray  rami  communicantes. 
Two  branches  arise  from  the  middle  cervical  ganglion,  and  join  the  anterior  primary 
divisions  of  the  fifth  and  sixth  nerves.  Two  arising  from  the  inferior  cervical  ganglion 
join  the  seventh  and  eighth  nerves.  They  reach  the  nerves  either  by  piercing  the 
prevertebral  muscles  or  by  passing  round  the  border  of  the  scalenus  anticus  muscle. 

Composition  of  the  Brachial  Plexus. — In  an  analysis  of  the  brachial  plexus 
four  stages  may  be  always  seen  : — 
(1)  The  undivided  nerves. 


Fig.  494. — The  Nerves  op  the  Brachial  Plexus. 

Sy,  Sympathetic  gangliated  cord  ;  Phr,  Phrenic  nerve  ;  C.4,  5,  6,  7,  8,  T.l,  2,  3,  Anterior  primary  divisions  of  the 

lower  cervical   and  upper  thoracic  nerves  ;  M\  M^,  Muscular  branches  to  axial  muscles  ;  P.  T,  Long 

thoracic  nerve  ;  Rh,   Nerve  to  rhomboids  (posterior  scapular)  ;    Subcl,  Nerve  to  subclavhis  muscle  ; 

nit,  Intercostal  nerves  ;  S.Sc,  Supra-scapular  nerve.     The  intercostal  part  of  the  first  thoracic  nerve 

is  omitted. 
Outer  Cord. — E.A.T,  External  anterior  thoracic  nerve  ;  M.C,  Musculo-cutaneous  nerve  ;  Cb,  ^erve  to  coraco- 

brachialis  ;  M,  Median  nerve. 
Inner  Cord. — I.A.T,  Internal  anterior  thoracic  nerve  ;  U,  Ulnar  nerve  ;  I.C,  Internal  cutaneous  nerve  ;  L.I.C, 

Lesser  internal  cutaneous  nerve. 
Posterior  Cord. — Circ,  Circumflex  nerve  ;  M.S,  Musculo-spiral  nerve  ;  S.Sub,  Short  subscapular  nerve  ;  M.Sub, 

Lower  subscapular  nerve  ;  L.Sub,  Long  subscapular,  nerve  ;  I.H,  Intercosto-humeral  nerve  ;  Lat,  Lateral 

branch  of  third  intercostal  nerve. 

(2)  The  separation  of  the  nerves  into  ventral  (anterior)  and  dorsal  (posterior) 

trunks  ;  and  the  formation  of  three  primary  cords. 

(3)  The  formation  of  three  secondary  cords — outer,  inner,  and  posterior. 

(4)  The  origin  of  the  nerves  of  distribution. 

(1)  The  undivided  nerves  have  only  a  very  short  independent  course  at  the  side 
of  the  neck,  after  passing  between  the  scalene  muscles. 

(2)  Almost  immediately  after  entering  the  posterior  triangle  there  are  formed 
three  primary  cords :  the  first  cord  is  formed  by  the  union  of  the  fifth  and  sixth 
n(!rves  togetber  ;  the  second,  by  the  seventh  nerve  alone ;  and  the  third,  by  the 
union  of  the  eighth  cervical  and  first  thoracic  nerves  together.  "While  these  cords 
are  being  ibrmed,  a  divisi(jn  oc(;urs  in  each  of  tlie  last  ibur  cervical  nerves,  into 
ventral  fanterior)  and  dorsal  (posterior)  trunks;  the  lii'st  thoracic  nerve  usually 
gives  rise  to  no  dorsal  trunk.     The  ventral   and   doi'sal   trunks  of  tlie  iil'th,  sixth, 


624  THE  NERVOUS  SYSTEM. 

and  seventh   nerves  are  nearly  equal  in  size.     The   dorsal  trunk   of  the  eighth 
cervical  nerve  is  much  smaller. 

(3)  The  secondary  cords  of  the  plexus  are  formed  by  combinations  of  these 
ventral  and  dorsal  trunks  in  relation  to  the  axillary  artery.  They  are  three  in 
numljer.  The  outer  cord  (fasciculus  lateralis)  is  formed  by  a  combination  of  the 
ventral  trunks  of  the  tilth,  sixth,  and  seventli  nerves,  and  lies  on  the  outer  side  of 
the  axillary  artery.  The  inner  cord  (fasciculus  medialis)  is  formed  by  a  combination 
of  the  ventral  trunk  of  the  eighth  cervical  with  the  part  of  the  first  thoracic 
nerve  engaged  in  the  formation  of  the  plexus;  it  lies  on  the  inner  side  of  the 
axillary  artery.  The  posterior  cord  (fasciculus  posterior)  is  made  up  of  all  the 
dorsal  trunks  from  the  fifth,  sixth,  seventh,  and  eighth  cervical  nerves,  and  lies 
Ijeliind  the  axillary  artery.  The  first  thoracic  nerve  does  not  usually  contribute  to 
the  posterior  cord,  and  the  branch  when  present  is  a  fine  nerve. 

(4)  The  nerves  of  distribution  for  the  shoulder  and  arm  are  derived  from  these 
secondary  cords,  and  receive  in  this  way  various  contributions  from  the  constituent 
spinal  nerves.  From  the  outer  cord  arise  the  external  anterior  thoracic  and  musculo- 
cutaneous nerves,  and  the  outer  head  of  the  median  nerve.  From  tlie  inner  cord 
arise  the  inner  head  of  the  median,  the  ulnar,  internal  cutaneous,  lesser  internal 
cutaneous,  and  the  internal  anterior  thoracic  nerves.  From  the  2JOsterior  cord  arise 
the  circumflex,  the  three  subscapular,  and  the  musculo-spiral  nerves. 

It  is  to  be  remembered  tliat,  altliough  derived  from  a  secondary  cord  formed  by  a  certain 
set  of  spinal  nerves,  any  given  nerve  does  not  necessarily  contain  fibres  from  all  the  constituent 
nerves ;  e.g.  both  the  musculo-cutaneous  and  circumflex  nerves,  from  the  outer  and  posterior 
cords  respectively,  are  ultimately  derived  only  from  the  fifth  and  sixth  cervical  nerves. 

The  Branches  of  the  Brachial  Plexus. 

It  is  customary  to  separate  artificially  the  nerves  of  distribution  of  the  brachial 
plexus  into  two  sets :  (1)  supra-clavicular  and  (2)  infra-clavicular.  Clinically  it  is 
important  to  realise  the  position  of  origin  of  certain  nerves.  The  nerves  to  the 
prevertebral  muscles,  the  communication  with  the  phrenic,  the  posterior  scapular, 
and  long  thoracic  nerves,  arise  from  the  roots  of  the  nerves  involved  in  the  plexus. 
The  supra-scapular  and  the  nerve  to  the  subclavius  arise  at  the  level  of  formation  of 
the  secondary  cords ;  and  the  anterior  thoracic  and  subscapular  nerves  arise  from  the 
secondary  cords,  prior  to  their  ultimate  subdivision  into  the  nerves  of  distribution 
for  the  upper  limb. 

Supra-clavicular  Nerves. — The  nerves  derived  from  the  plexus  above  the 
level  of  the  clavicle  are,  like  the  main  trunks,  divisible  into  two  series ;  anterior 
branches  arising  from  the  front,  and  posterior  branches  arising  from  the  back  of  the 
plexus  (Fig.  494,  p.  623). 

Anterior  Branches.  Posterior  Branches. 

1.  Nerves  to  scalenus  anticus  and  1.   Nerves  to  scaleni,  medius  and 

longus  colli.  posticus. 

2.  Communicating  nerve  to  join  2.   Posterior  scapular  nerve. 

the  phrenic  nerve.  3.  Long  thoracic    nerve. 

3.  Nerve  to  the  subclavius  rnuscle.  4.   Supra-scapular  nerve. 

The  muscular  twigs  to  the  scalenus  anticus  and  longus  colli  arise  from  the  lower 
four  cervical  nerves,  as  they  emerge  from  the  intervertebral  foramina. 

The  communicating  nerve  to  the  phrenic  arises  usually  from  the  fifth  cervical 
nerve  at  the  outer  border  of  the  scalenus  anticus.  It  is  sometimes  absent,  and 
occasionally  an  additional  root  is  present  from  the  sixth  cervical  nerve.  In  some 
instances  the  nerve  is  replaced  by  a  branch  from  the  nerve  to  the  subclavius, 
which  passes  inwards  behind  the  sterno-mastoid  muscle  to  join  the  phrenic  at  the 
inlet  of  the  thorax. 

The  nerve  to  the  subclavius  is  a  slender  nerve,  which  arises  from  the  front  of 
the  cord  formed  by  the  fifth  and  sixth  cervical  nerves.  It  descends'  in  the  posterior 
triangle  of  the  neck  over  the  third  part  of  the  subclavian  artery.  It  often  com- 
municates with  the  phrenic  nerve. 


THE  ANTEEIOR  THORACIC  NERVES. 


625 


€.8    Inner 
Cord 


The  branches  to  the  scaleni,  medius  and  posticus,  are  small  trunks  which  arise 
from  the  lower  four  cervical  nerves  as  they  emerge  from  the  intervertebral  foramina. 

The  posterior  scapular  nerve  (n.  dorsalis  scapulse,  nerve  to  the  rhomboids) 
arises  from  the  back  of  the  fifth  cervical  nerve,  as  it  emerges  from  the  intervertebral 
foramen.  It  appears  in  the  posterior  triangle  of  the  neck,  after  piercing  the 
scalenus  medius  muscle.  It  is  directed  downwards,  under  cover  of  the  levator 
anguli  scapulse  and  rhomboid  muscles,  and  along  the  vertebral  border  of  the 
scapula,  to  be  distributed  to  the  levator  anguli  scapulas,  rhomboideus  minor,  and 
rhomboideus  major  muscles.     It  occasionally  pierces  the  levator  anguli  scajjuke. 

The  long  thoracic  nerve  (n.  thoracalis  longus,  external  res^jiratory  nerve  of 
Bell)  arises  by  three  roots,  of  which  the  middle  one  is  usually  the  largest,  from  the 
back  of  the  fifth,  sixth,  and  seventh  nerves,  as  they 
emerge  from  the  intervertebral  foramina.  The  nerve 
pierces  the  scalenus  medius  as  two  trunks,  of  which 
the  lower  represents  the  contribution  from  the  seventh 
cervical  nerve,  and,  descending  along  the  side  of  the 
neck  behind  the  cords  of  the  brachial  plexus,  it 
enters  the  axilla  between  the  upper  edge  of  the 
serratus  magnus  and  the  axillary  artery.  It  con- 
tinues its  downward  course  over  the  outer  surface 
of  the  serratus  magnus,  to  which  it  is  distributed. 

There  is  a  more  or  less  definite  relation  between  the  roots 
of  this  nerve  and  the  parts  of  the  serratus  magnus.  The  first 
part  of  the  muscle  is  innervated  by  the  fifth  nerve  alone  ; 
the  second  part  by  the  fifth  and  sixth,  or  the  sixth  alone  ; 
the  third  part  by  the  sixth  and  seventh,  or  the  seventh 
nerve  alone. 

The  suprascapular  nerve  (n.  suprascapularis) 
arises  from  the  back  of  the  cord  formed  by  the 
fifth   and   sixth   cervical    nerves  in   the   posterior 

triangle  of  the  neck.  It  occupies  a  xjosition  above  Fig.  495.— Diagh^ux  of^  the  ^origin 
the  main  cords  of  the  brachial  plexus,  and  courses 
downwards  and  outwards  parallel  to  them  towards 
the  superior  border  of  the  scapula.  It  passes  through 
the  suprascapular  foramen  to  reach  the  dorsum  of 
the  scapula.  After  supplying  the  supraspinatus 
muscle  it  winds  round  the  great  scapular  notch  in 
company  with  the  suprascapular  artery  and  terminates 
in  the  infraspinatus  muscle.  It  also  supplies  articular 
branches  to  the  back  of  the  shoulder  joint. 

Infra -clavicular  Nerves. — The  so-called  infra -clavicular  branches  of  the 
brachial  plexus  are  distributed  to  the  chest,  shoulder,  and  arm.  According  to 
their  origin  they  are  divisible  into  two  sets — an  anterior  set,  derived  from  the 
outer  and  inner  cords,  and  a  posterior  set,  derived  from  the  posterior  cord.  In 
their  distribution  the  same  division  is  maintained.  The  anterior  nerves  of 
distribution,  springing  from  the  outer  and  inner  cords,  supply  generally  the  chest 
and  the  front  of  the  limb ;  the  posterior  nerves,  springing  from  the  posterior  cord, 
sujjply  the  shoulder  and  the  back  of  the  limb. 

Anterior  Branches. 
Nerves  from  the  Outer  Cord. 
K.xternal  anterior  thoracic.  Outer  head  of  median.  Musculo-cutaneous. 

Nerves  from  the  Inner  Cord. 
Jntoriial  anterior  thoracic.  Ulnar.  I inier  head  of  median. 

Intenial  cutaneous.  Lesser  internal  cutaneous. 


AND  Distribution  of  the  Nerves 
TO  the  Pectoral  Muscles. 

E.A.T,  External  anterior  thoracic  nerve  ; 
I.A.T,  Internal  anterior  thoracic 
nerve  ;  C.5,  6,  7,  C.8,  T.l,  Nerves  of 
the  brachial  lolexus  ;  Art,  Axillary 
artery ;  Cl,  Clavicle  ;  Scl,  Sub- 
clavius  muscle  ;  P.  Ml,  Pectoralis 
minor,  joined  to  subclavius  by 
costo-coracoid  membrane  ;  P. Ma, 
Pectoralis  major. 


(/ircumjflex. 
44 


Posterior    Branches. 
Nerves  from  the  Posterior  Cord. 

Musculo-spii'al.  Three  subscapular  nerves. 


626 


THE  NERVOUS  SYSTEM. 


Anterior  Thoracic  JSTerves. 

The  anterior  thoracic  nerves  (nn.  thoracicales  anteriores)  are  two  in  number, 
external  and  internal.     The  external  anterior  thoracic  nerve  arises  from  the  outer 


Tiapeziu' 
C'la\Kle  (cut 

Coraco-claviculav  lig  uiients. 
Pectoralis  iiiinoi 
Coracoid  process] 
Coraco-acromial  ligament 

Circumflex  artery"-j'^' 

Circumflex  nerve- 


Suprascapular  nerve 


H      ^^^Seriatus  maguu.s 
^^^^^^-Uoi  al  scapulE*-  artery 


Subseapularis 
.Teres  major 


Peotoralis  major 
Coraco-brachialis  .^ 


r  Short  liead.^ 
Biceps  -j  ^< 


Posterior  cord  of  brachial 

I  1 EXUS 

Short  subscapular  nurve 

Long  subscapular  nerve 
Lower  subscapulak  nerve 


Latissimus  dorsi 


Internal 
cutaneous  branch 
of  musculo-spiral 
nerve 


liiceps  (long  head) 

Nerve  to  inner  head  of 
'triceps  (ulnar  collateral) 

cord  of  the  brachial  plexus  by  three 
roots — from  the  fifth,  sixth,  and 
seventh  cervical  nerves.  The  in- 
(iunerhead)  Vernal  anterior  thoracic  nerve  arises 
from  the  inner  cord  of  the  plexus, 
from  the  eighth  cervical  and  first 
thoracic  nerves.  Each  courses  down- 
wards and  forwards  on  either  side 
of  the  axillary  artery.  A  loop  of 
communication  is  formed  between 
them  over  the  artery.  They  are 
finally  distributed  to  the  pectoralis 
major  and  minor  muscles  (Eig.  495). 

The  nerves  are  distributed  to  the 
pectoral  muscles  in  the  following 
way  : — Two  sets  of  branches  from  the 
external  anterior  thoracic  nerve  pierce 
the  costo- coracoid  membrane.  The 
upper  branches  supply  the  clavicular 
part  of  the  pectoralis  major  ;  the  lower 
branches  are  distributed  to  the  upper 
fibres  of  the  sternal  portion  of  the 
muscle.  The  upper  branches  come 
from  the  fifth  and  sixth  cervical  nerves; 
the  lower  branches,  from  the  fifth, 
sixth,  and  seventh  nerves.  The  pectoralis  minor  is  pierced  by  two  sets  of  nerves — the 
upper  set  is  derived  from  the  loop  of  communication  betAveen  the  external  and  internal 
anterior  thoracic  nerves  over  the  axillary  artery ;  the  lower  set  is  derived  from  the 
internal  anterior  thoracic  nerve  alone.  These  nerves  supply  the  x)ectoralis  minor  muscle, 
and,  after  piercing  it,  supply  the  sternal  2:>art  oi  the  pectoralis  major.     The  lower  nerve,  in 


Musculo-cutaneous. 
nerve 


Brachialis  anticus 


Musculo-spiral  nerve 


Brachio-radialis 
Biceps  (cut)- 

Extensor  carpi  radialis 
lonaior 


Posterior  interosseous 

nerve' 

Radial  nerve 

Supinator  radii  brevis 


Flexor 

■profundus 

digitorum 


Fig.  496. — The  Posterior  Wall  of  the  Axilla  and  the 
Front  of  thk  Arm  (the  biceps  being  divided). 


MEDIAN  NERVE.  627 

many  cases,  sends  its  branches  to  the  pectoralis  major  round  the  lower  border  of  the 
pectoralis  minor,  and  it  may  supply  on  its  Avay  the  axillary  arches,  if  present.  These  two 
branches  are  derived — the  upper  from  the  seventh,  eighth  cervical,  and  first  thoracic 
nerves ;  the  lower  from  the  eighth  cervical  and  first  thoracic  nerves.  The  pectoral 
muscles  are  thus  both  supplied  by  the  two  anterior  thoracic  nerves.  The  clavicular  fibres  of 
the  pectoralis  major  are  innervated  by  the  fifth  and  sixth  nerves ;  the  sternal  fibres,  from 
above  downwards,  by  the  fifth,  sixth,  seventh,  and  eighth  cervical,  and  first  thoracic 
nerves ;  and  the  pectoralis  minor  is  supplied  by  the  seventh  and  eighth  cervical,  and 
first  thoracic  nerves. 

MUSCULO-CUTANEOTJS    NeEVE. 

The  musculo-cutaneous  nerve  (n.  musculo-cutaneus)  takes  origin  from  the 
outer  cord  of  the  plexus,  from  the  fifth  and  sixth  cervical  nerves  (Fig.  496).  The 
nerve  to  the  coraco-brachialis  muscle,  arising  from  the  seventh  or  sixth  and  seventh 
nerves,  is  usually  associated  with  it.  Separating  from  the  outer  head  of  the 
median  nerve,  the  musculo-cutaneous  nerve  lies  at  first  between  the  coraco- 
brachialis  muscle  and  the  axillary  artery.  It  is  then  directed  downwards  between 
the  two  parts  of  the  coraco-brachialis,  and  passes  between  the  biceps  and  brachialis 
anticus  muscles,  to  the  bend  of  the  elbow.  In  its  course  it  may  send  a  branch 
under  the  biceps  to  join  the  median  nerve.  It  pierces  the  deep  fascia  over  the 
front  of  the  elbow,  between  the  biceps  and  brachio-radiaHs,  and  terminates  in 
cutaneous  branches  for  the  supply  of  the  outer  side  of  the  forearm. 

The  branches  of  the  nerve  are  muscular  and  cutaneous.  The  muscular  branches 
are  supplied  to  the  two  heads  of  the  biceps  and  the  brachiaHs  anticus,  as  the  nerve 
lies  between  the  muscles.  The  nerve  to  the  coraco-brachialis  (usually  incorporated 
with  the  trunk  of  the  musculo-cutaneous  nerve)  has  an  independent  origin  from 
the  seventh  or  sixth  and  seventh  nerves.  It  is  usually  double,  one  branch  entering 
each  portion  of  the  muscle.  The  cutaneous  branches  are  anterior  and  posterior 
(Fig.  497,  p.  628).  The  anterior  branch  descends  along  the  front  of  the  outer  side 
of  the  forearm  to  the  wrist,  and  supplies  an  area  extending  inwards  to  the  middle 
line  of  the  forearm  anteriorly,  and  downwards  so  as  to  include  the  ball  of  the 
thumb.  It  communicates  above  the  wrist  with  the  radial  nerve,  and  supplies 
branches  to  the  radial  artery.  The  posterior  branch  passes  backwards  and 
downwards  over  the  extensor  muscles  and  supplies  the  skin  on  the  outer  aspect 
of  the  forearm  posteriorly  in  its  upper  three-fourths,  communicating  with  the 
cutaneous  branches  of  the  musculo-spiral  nerve. 

In  addition  to  the  above  branches,  the  musculo-cutaneous  nerve  supplies  in  many 
cases  the  following  small  twigs  in  the  arm  :  (1)  a  medullary  branch  to  the  humerus ;  (2) 
a  periosteal  branch  to  the  lower  end  of  the  humerus  on  its  anterior  surface ;  and  (3)  a 
branch  to  the  brachial  artery. 

Median  Nerye. 

The  median  nerve  (n.  medianus)  arises  by  two  roots — one  from  the  outer 
cord,  the  other  from  the  inner  cord  of  the  brachial  plexus.  The  outer  head,  from 
the  (fifth),  sixth,  and  seventh  nerves,  descends  along  the  outer  side  of  the  axillary 
artery ;  the  inner  head,  from  the  eighth  cervical  and  first  thoracic  nerves,  crosses 
the  end  of  the  axillary  artery  or  the  beginning  of  the  brachial  artery,  to  join  the  other 
head  in  the  upper  part  of  the  arm.  Descending  along  the  outer  side  of  the  brachial 
artery,  the  nerve  crosses  over  it  obliquely  in  the  lower  half  of  the  arm.  In  the 
hollow  of  tlie  elbow,  it  lies  internal  to  the  brachial  artery,  beneath  the  bicipital 
fascia  'uid  the  median  Ijasilic  vein.  It  passes  into  the  forearm  between  the  two 
heads  of  the  pronator  radii  teres  muscle,  separated  from  the  ulnar  artery  by  the 
deep  origin  of  that  muscle.  Extending  down  the  middle  of  the  forearm,  between 
the  sup;'rficial  and  deep  muscles  to  the  wrist,  it  enters  the  palm  of  the  hand  on  the 
outer  side  of  tlie  llexor  tendons  of  the  finuers  beneath  the  anterior  annular 
ligament.  In  the  hand  it  spreads  out  at  the  lower  border  of  the  annular  ligament 
beneath  the  palmar  fascia  and  superficial  palmar  arch,  and  separates  into  its  six 
terminal  }»ranches.  In  the  forearm  a  small  artery  accompanies  it, — the  comes  nervi 
median].  Above  the  wrist  it  is  comparatively  superficial,  lying  on  the  outer  side  of 
the  superficial  flexor  tendons  and  directly  beneath  the  tendon  of  the  palmaris  longus. 


628 


THE  NEEVOUS  SYSTEM. 


Communications. — (1)  The  median,  in  some  cases,  receives  a  commmiicating  branch 
from  tlie  musculo-cutaneous  nerve  in  the  arm.  (2)  It  communicates  in  some  cases,  in 
the  upper  part  of  the  forearm,  with  the  uhiar  nerve  Leneath  the  flexor  muscles.  (3)  It 
communicates  by  means  of  its  cutaneous  branches  with  the  ulnar  nerve  in  the  palm  of 
the  hand. 

Branches.— 'J'he  mediau  uer^■e  usually  gives  oil'  no  branches  in  the  upper  arm. 
Branches  in  the  Forearm. — (1)  Articular  Branclies. — Minute  articular  filaments 

are  distributed  to  the 
front  of  the  elbow-joint. 
(2)  Muscular  Bran- 
ches.—  Just  below  the 
elbow  a  bundle  of  nerves 
arise  which  is  distributed 
to  the  following  muscles: 
pronator  radii  teres, 
flexor  carpi  radialis,  pal- 
maris  longus,  flexor  sub- 
limis  digitorum.  Nerves 
are  also  generally  trace- 
able from  this  bundle  to 
the  upper  fibres  of  the 
flexor  longus  poUicis 
and  flexor  profundus 
digitorum.  The  nerve 
to  the  pronator  radii 
teres  often  arises  inde- 
pendently in  the  hollow 
of  the  elbow. 

(3)  The  anterior  in- 
terosseous nerve  arises 
from  the  buck  of  the 
median  nerve  in  the 
forearm,  descends  in 
front  of  the  interosseous 
membrane  along  with 
the  anterior  interosseous 
artery,  passes  behind 
the  pronator  quadratus 
muscle,  and  terminates 
by  supplying  articular 
filaments  to  the  radio- 
carpal articulation.  In 
its  course  the  nerve 
supplies  muscular 
branches   to   the   fiexor 

(A)  represents  the  distribution  of  the  several  nerves,  the  letters  indicating    ;[qqo-uS  pollicis,  the  OUtCr 

their  nomenclature.     AcR,  Acromial  branch  (cervical  plexus)  ;   CiRC,  »        J-  flo^nr    ^-^rn 

Cutaneous    branch    of    circumflex    nerve;     M.Se,    Superior    external  Hail    01    tne    nexoi     pio- 

cutaneous  branch  of  musculo-spiral  nerve  ;    M.C,   Musculo-cutaneous  funduS     digitOrum,    and 

nerve;  M,  Median  nerve;  U,  Ulnar  nerve;  I.C,  Internal  cutaneous  ^^^  pronator    QUadratUS, 
nerve  ;  L.I.C,  Lesser  internal  cutaneous  nerve  ( Wrisberg)  ;  I.H,  Inter-         •    ^   ,  _  „,  „  ,3  „  1  ]  „  ^,^ 

costo-humeral  nerve  ;  T.2,  3,  4,  5,  6,  Anterior  and  lateral  branches  of  mmUtC  meauiiciiy 

intercostal  nerves.  branches  to  the   radius 

(B)  is  a  schematic  representation  of  the  areas  supplied  by  the  above  nerves,    and    ulna,    and   tWlgS  ^  tO 

the  lettering  indicating  the  spinal  origin  of  the  branches  of  distribution    ^^iq    peiiosteum    and    in- 
to each  area.     V.A.L,  Ventral  axial  line.  tCrOSSCOUS  membrane. 

(4)  Palmar  Cutaneous  Brancli. — In  the  lower  third  of  the  forearm  a  small 
cutaneous  branch  arises,  which  pierces  the  deep  fascia  and  crosses  the  anterior 
annular  ligament  to  reach  the  palm  of  the  hand.  It  supplies  the  skin  of  the  palm 
and  communicates  with  a  similar  branch  of  the  ulnar  nerve.  This  branch  is  not 
always  present. 


Fig.  497.— The  Distribution  of  Cutaneous  Nerves  on  the  Front  of 
THE  Arm  and  Hand. 


ULNAR  NERVE.  629 

Branches  in  the  Hand. — In  the  hand  the  median  nerve  gives  off  its  terminal 
branches.     These  are  muscular  and  cutaneous. 

The  main  muscular  branch  arises  just  below  the  anterior  annular  ligament  and 
passes  outwards  to  the  base  of  the  thenar  eminence  ;  entering  the  ball  of  the  thumb 
superficially  on  the  inner  side,  it  supplies  branches  to  the  abductor  pollicis, 
opponens  pollicis,  and  the  superficial  head  of  the  flexor  brevis  pollicis. 

The  cutaneous  branches  are  five  in  number.  Three  separate  branches  supply  each 
side  of  the  thumb  and  the  radial  side  of  the  index  finger.  The  two  remaining 
branches  subdivide  at  the  cleft  between  the  second  and  third,  and  the  third  and 
fourth  fingers  respectively,  into  branches  which  supply  the  adjacent  sides  of  the 
second,  and  third,  and  the  third  and  fourth  fingers.  From  the  nerves  which  supply 
respectively  the  radial  side  of  the  index  finger,  and  the  contiguous  sides  of  the 
index  and  third  fingers,  fine  muscular  branches  arise  for  the  two  outer  lumbrical 
muscles.  The  cutaneous  branches  of  the  median  nerve  are  placed  in  the  palm 
between  the  superficial  palmar  arch  and  the  flexor  tendons.  They  become  super- 
ficial at  the  roots  of  the  fingers  between  the  slips  of  the  palmar  fascia,  or,  in  the 
case  of  the  nerves  to  the  thumb  and  radial  side  of  the  index  finger,  at  the  outer 
edge  of  the  central  portion  of  the  palmar  fascia.  In  the  fingers  they  are  placed 
superficial  to  the  digital  arteries,  and  are  distributed  to  the  sides  and  front  of  the 
fingers.  Each  nerve  supplies  one  or  more  dorsal  branches,  distributed  to  the  skin 
on  the  dorsal  aspect  of  the  terminal  phalanx  of  the  thumb  and  the  two  distal 
phalanges  of  the  first  two  and  a  half  fingers,  thus  making  up  for  the  deficiency  of 
the  radial  nerve  in  these  situations. 

Ulnae  Nerve. 

The  ulnar  nerve  (n.  ulnaris)  arises  from  the  inner  cord  of  the  brachial  plexus, 
from  the  eighth  cervical  and  first  thoracic  nerves.  It  also  occasionally  has  a  root 
from  the  outer  cord  of  the  plexus  (seventh  cervical  nerve).  In  the  axilla  it  hes 
between  the  axillary  artery  and  vein,  and  behind  the  internal  cutaneous  nerve ;  in 
the  upper  half  of  the  upper  arm  it  lies  on  the  inner  side  of  the  brachial  artery  in 
front  of  the  triceps  muscle.  In  the  lower  half  of  the  arm  it  is  separated  from  the 
brachial  artery ;  and  passing  behind  the  intermuscular  septum,  and  in  front  of  the 
inner  head  of  the  triceps  in  company  with  the  inferior  profunda  artery,  it  reaches  the 
interval  between  the  internal  condyle  of  the  humerus  and  the  olecranon  process.  It 
is  here  protected  by  an  arch  of  deep  fascia  stretching  between  the  internal  condyle 
and  the  olecranon  process.  It  enters  the  forearm  between  the  humeral  and  ulnar 
origins  of  the  flexor  carpi  ulnaris,  and  courses  downwards  between  the  flexor  carpi 
ulnaris  and  flexor  profundus  digitorum.  In  the  lower  half  of  the  forearm  it  becomes 
comparatively  superficial,  lying  on  the  inner  side  of  the  ulnar  artery  beneath  the 
tendon  of  the  flexor  carpi  ulnaris.  Just  above  the  anterior  annular  ligament  of  the 
wrist,  and  external  to  the  pisiform  bone,  it  pierces  the  deep  fascia  in  company  with 
the  artery  and  passes  into  the  hand  over  the  anterior  annular  ligament.  Eeaching 
the  palm  it  divides  beneath  the  palmaris  brevis  muscle  into  its  two  terminal 
branches,  superficial  and  deep. 

Communications. — (1)  The  ulnar  nerve  communicates  in  some  cases  with  the  median 
nerve  in  the  forearm ;  (2)  with  the  internal  ctitaneous  and  sometimes  the  median  nerve 
hj  its  palmar  cutaneous  branch  ;  (3)  with  the  cutaneous  part  of  the  median  nerve  in  the 
palm  by  means  of  its  terminal  cutaneous  branches  ;  (4)  with  the  radial  nerve  on  the 
dorsum  of  the  hand  by  means  of  its  dorsal  brancli. 

Branches. — The  ulnar  nerve  gives  off  no  branches  till  it  reaches  the  forearm. 

In  the  forearm  it  gives  off  articular,  muscular,  and  cutaneous  branches. 

'J'he  articular  branch  is  distributed  to  the  elbow  joint  and  arises  as  the  nerve 
yjasHcH  Ijobind  the  intonial  condyle. 

T\ui  muscular  branches  arise  as  soon  as  the  nerve  enters  the  forearm.  They  are 
distributed  to  the  muscles  between  which  the  ulnar  nerve  lies — the  flexor  carpi 
ulnaris  and  th(!  inn(;r  half  of  the  flexor  profundus  digitorum. 

The  cutaneous  branches  are  two  in  number,  palmar  and  dorsal. 


630 


THE  NEKVOUS  SYSTEM. 


The  palmar  cutaneous  branch  is  variable  in  size  and  position.  It  pierces  the 
deep  fascia  in  the  lower  third  of  the  forearm  and  passes  to  the  hypothenar 
eminence  and  palm  of  the  hand,  to  the  skin  over  which  it  is  distributed.     It  gives 

branches  to  the 
ulnar  artery,  and 
communicates  often 
with  the  internal 
cutaneous  and 
palmar  branch  of 
the  median  nerve. 

The  dorsal  cut- 
aneous brancli  is 
much  larger  (Fig. 
498).  It  arises 
fromtlie  ulnar  nerve 
in  the  middle  third 
of  the  forearm; 
and,  directed  ob- 
liquely downwards 
and  backwards  be- 
neath the  tendon  of 
the  flexor  carpi 
ulnaris,  it  becomes 
cutaneous  on  the 
inner  side  of  the 
forearm  in  its  lower 
fourth.  It  passes 
on  to  the  back  of  the 
hand,  and  after  giv- 
ing off  branches  to 
the  skin  of  the  wrist 
and  hand,  which 
communicate  with 
the  radial  nerve,  it 
terminates  in  two 
branches,  to  supply 
the  little  finger  and 
half  the  ring-finger 
in  the  following 
way  :  —  the  inner 
branch  courses 
along  the  inner  side 
of  the  dorsum  of 
the  hand  and  little 
finger :  the  outer 
branch     subdivides 


Fig.  498. 


B  A 

-The  Distribution  of  Cutaneous  Nerves  on  the  Back  of  the 
Arm  and  Hand. 


(A)  represents  the  distribution  of  the  several  nerves,  the  letters  indicating  their 
nomenclature.  ACR,  Acromial  branches  (cervical  plexus)  ;  CiRC,  Cutaneous 
branch  of  circumflex  nerve  ;  Ms.E.C.s,  Ms.E.C.i,  Superior  and  inferior  external 
cutaneous  branches  of  mnscnlo-spiral  nerve  ;  M.C,  Musculo-cutaneons  nerve  : 
R,  Radial  nerve  ;  M,  Branches  of  median  nerve  to  fingers  ;  U,  Ulnar  nerve  ; 
I.C,  Internal  cutaneous  nerve  ;  Ms.I.C,  Internal  cutaneous  branch  of  musculo- 
spii-al  nerve  ;  L.I.C,  Lesser  internal  cutaneous  nerve  (Wrisberg)  ;  I.H,  Inter- 

costo-humeral  ;  T.l.  2,  3,  4,  5,  6,  Lateral  and  posterior  branches  of  upper    at  the  clcft  between 
thoracic  nerves.  ^\-^q   j^i^g   and   little 

(B)  is  a  schematic  representation  of  the  areas  supplied  by  the  above  nerves,  the    fingers     to      supply 

lettering  indicating  the  spinal  origin  of  the  branches  of  distribution  to  each    ^^^^    adiacent     sidcS 
area.     D.A.L,  Dorsal  axial  line.  „       ^ ,    •'  ^ 

oi  these  fingers ; 
this  branch  communicates  with  the  radial  nerve.  The  nerve  may  supply  two  and 
a  half  fingers  on  the  dorsum  of  the  hand. 

In  the  palra  the  ulnar  nerve  supplies  a  small  muscular  branch  to  the  palmans 
brevis  muscle,  and  then  subdivides  into  its  terminal  branches,  which  are  named 
superficial  and  deep. 

The  superficial  brancli  is  purely  cutaneous;  it  passes  downwards  beneath  the 
palmar  fascia,  and  subdivides  into  an  inner  and  an  outer  branch.  The  inner 
branch  courses  along  the  inner  border  of  the  little  finger,  which  it  supphes  on   its 


INTERNAL  CUTANEOUS  NERVE. 


631 


palmar  aspect.  The  outer  braiicli  becomes  superficial  at  the  cleft  between  the 
fourth  and  fifth  lingers,  between  the  slips  of  the  palmar  fascia,  and  subdivides  into 
two  branches  which  supply  the  adjacent  sides  of  these  fingers  on  their  palmar  aspect. 
It  communicates  with  the  adjacent  digital  branch  of  the  median  nerve. 

The  deep  branch  is  purely  muscular.     It  separates  from  the  superficial  branch, 


Levator  anguli  scapiilse 


Bhomboideus 
major 

Scapular  fascia 

Dorsal  Scapular 
artery  (branch  of) 

Teres  major  — 


Latissimus  dorsl- 


Supraspmatus  mi]  sole 
Scapular  spine  (cut) 

— lufiaspinatus 


Teres  minor 

^j£j. Nerve  to  teres  minor 

Circumflex  nerve  and 


Deltoid  (reflected) 

Cutaneous  branch 
of  circumflex 

Triceps  (outer  head) 


Triceps  (long  head) 

MUSCULO-SPIRAL 

liiceps  (outer  head) 
Brachialis  anticus 

Tiiceps  (inner  head) 
xternal  intermuscular  septum 

External  cutaneous 
branches  of  musculo- 
SPIRAL 


Plexor 
carpi . 
ulnaris 


Brachio-radialis 


Extensor  carpi  radialis  longior 


Extensor  muscles  of  forearm 
(common  tendon) 


and  passes  deeply  between  the 
flexor  brevis  and  abductor  minimi 
digiti  muscles ;  it  supplies  these 
muscles  and  the  opponens  minimi 
digiti,  and,  turning  outwards  along 
the  line  of  the  deep  palmar  arch 
and  under  cover  of  the  deep  flexor 
tendons,  it  supplies  branches  to  ulnar 
the  following  muscles  :  interossei,  ^^^^^ 
two  inner  (third  and  fourth)  lum- 
bricales  (on  their  deep  surf  aces),  th  e 
adductores  pollicis,  obliquus  and 
transversus,  and  deep  part  of  the 
flexor  brevis  ])ollicis. 

Internal  Cutaneous  Nerve. 

The  internal  cutaneous  nerve  (n.  cutaneus  brachii  medialis)  arises  from 
the  inner  cord  of  the  brachial  plexus,  from  the  eighth  cervical  and  first  thoracic 
nerves  (Figs.  497  and  498).  In  the  axilla  and  upper  half  of  the  arm  it  lies  superficial 
to  the  main  artery.  It  becom3S  cutaneous  by  ])iercing  the  deep  fascia  about  the 
middle  of  the  inner  side  of  the  upper  arm,  and  accom])anying  the  basilic  vein 
throijgl)  thf;  lower  half  of  the  arm,  it  divides  at  the  I'ront  of  the  elbow  into  its  two 
teniiiii!!,]  hrunches. 

Communication. — Tlic  internal  cutaneous  nerve  communicates  with  the  pahnar 
Ijranch  of  thi;  ulnar  nerve  in  the  lower  part  of  the  forearm. 


Fig.  499.  -  -Deltoid  Rkgion  and  Back  of  Arm. 


632  THE  NEEVOUS  SYSTEM. 

Branches. — In  the  arm,  as  soon  as  it  becomes  superficial,  the  internal  cutaneous 
nerve  gives  off  a  l)ranch  which  supplies  the  skin  of  the  lower  half  of  the  anterior 
surface  of  the  arm  on  its  inner  side.  At  the  elbow  it  divides  into  two  terminal 
branches — anterior  and  internal,  which,  crossing  over  or  under  the  median  basilic 
vein,  are  distributed  to  the  inner  side  of  the  forearm. 

The  anterior  branch  can  be  followed  to  the  wrist  and  supplies  the  whole  of  the 
front  of  the  forearm  in  the  inner  half;  the  internal  branch,  is  not  so  large,  and, 
passing  obliquely  backwards  and  downwards  over  the  origins  of  the  pronator  and 
flexor  muscles,  it  is  distributed  to  the  upper  two-thirds  or  three-fourths  of  the 
posterior  aspect  of  the  forearm  on  the  inner  side. 

Lessee  Inteknal  Cutaneous  Nerve. 

The  lesser  internal  cutaneous  nerve  (n.  cutaneus  brachii  medialis  minor) 
arises  from  the  inner  cord  of  the  brachial  plexus,  and  ultimately  from  the  first 
thoracic  nerve  (Eig.  494,  p.  624).  It  lies  at  first  between  the  axillary  artery  and 
vein  ;  and  after  descending  over,  under,  or  even,  in  some  cases,  through  the  axillary 
vein,  it  perforates  the  deep  fascia  on  the  inner  side  of  the  arm,  and  is  distributed  to 
the  skin  of  the  arm  for  the  upper  half  or  more  on  its  inner  side. 

The  nerve  varies  considerably  in  size.  It  may  be  absent,  its  place  being  taken  by  branches 
of  the  intercosto-humeral  or  by  branches  from  the  internal  cutaneous  offset  of  the  musculo- 
spiral  nerve.  It  generally  bears  a  distinct  relation  in  size  to  the  intercosto-humeral,  due  to  the  fact 
that  the  size  of  the  latter  depends  upon  the  size  of  the  part  of  the  second  thoracic  nerve  con- 
nected with  the  first  in  the  thorax.  If  an  intra-thoracic  connexion  occurs  between  the  first  and 
second  thoracic  nerves,  the  intercosto-humeral  may  be  deprived  of  a  certain  number  of  its 
fibres,  which  in  that  case  reach  the  ujaper  limb  through  the  lesser  internal  cutaneous  nerve. 
When  traced  uj)  to  the  plexus  the  lesser  internal  cutaneous  is  found  to  have  an  origin  from  the 
back  of  the  cord  formed  by  the  eighth  cervical  and  first  thoracic  nerves,  and  usually  receives 
fibres  from  the  first  thoracic  nerve  only.  In  cases  where  "  axillary  arches  "  are  present  they  may 
be  supplied  by  this  nerve.    , 

Circumflex  ISTerve. 

The  circumflex  nerve  (u.  axillaris),  at  its  origin  is  just  below  the  supra- 
scapular and  comes  from  the  same  spinal  nerves — the  fifth  and  sixth  cervical 
nerves  (Fig.  494,  p.  623).  Extending  downwards  and  outwards  behind  the  axillary 
artery,  it  leaves  the  axilla  by  passing  round  the  external  border  of  the  subscapularis 
muscle,  in  company  with  the  posterior  circumflex  artery,  in  a  quadrilateral  space 
bounded  by  the  humerus,  subscapularis,  triceps  (long  head),  and  teres  major. 
Winding  round  the  surgical  neck  of  the  humerus  from  within  outwards,  it 
terminates  under  the  deltoid  by  supplying  that  muscle  (Fig.  499,  p.  631). 

Branches. — Muscular  branches  are  supplied  to  the  teres  minor  and  deltoid 
muscles.  The  nerve  to  the  teres  minor  enters  the  outer  side  of  the  muscle.  It 
possesses  a  pseudo-ganglion,  a  thickening  of  fibrous  tissue,  on  its  trunk. 

Articular  branches  enter  the  back  part  of  the  capsule  of  the  shoulder-joint. 

A  cutaneous  branch  (n.  cutaneus  brachii  lateralis)  of  considerable  size  passes 
obliquely  downwards  and  forwards  from  beneath  the  deltoid  muscle,  becoming 
superficial  at  its  posterior  border.  Sometimes  the  branches  pierce  the  muscle.  It 
supplies  the  skin  over  the  insertion  of  the  deltoid  and  the  upper  half  of  the  arm 
on  the  outer  side  (Fig.  498,  p.  630). 

Musculo-Spiral  Nerve. 

The  musculo-spiral  nerve  (n.  radialis)  appears  to  be  the  continuation  into  the 
upper  limb  of  the  posterior  cord  of  the  brachial  plexus.  It  usually  takes  origin 
from  all  the  nerves  which  form  the  posterior  cord — the  fifth,  sixth,  seventh,  and 
eighth  cervical  nerves  (Fig.  494,  p.  623).  In  a  minority  of  cases  the  first  thoracic 
contributes  a  few  fibres,  and  more  frequently  the  fifth  cervical  nerve  is  excluded 
from  it.  It  extends  from  the  axilla  round  the  back  of  the  humerus  to  the  bend  of 
the  elbow,  where  it  ends  by  dividing  into  its  terminal  branches. 

In  the  axilla  it  lies  behind  the  axillary  artery,  and  in  front  of  the  subscapularis, 
teres  major,  and  latissimus  dorsi  muscles. 


TIFE  MUSCULO-SriRAL  NERVE. 


633 


In  the  arm.,  in  the  upper  third,  it  lies  on  the  inner  side  of  the  humerus  l^ehind 
the  brachial  artery,  and  upon  the  long  head  of  the  triceps.  In  the  middle  third  of 
the  arm  it  courses  obliquely  outwards  and  downwards  in  the  spiral  groove  of  the 
humerus,  along  with  the  superior  profunda  artery,  separating  the  long,  external, 
and  internal  heads  of  the  triceps  muscle  (Fig.  499,  p.  631).  In  the  lower  third  of 
the  arm,  piercing  the  upper  part  of  the  intermuscular 
septum  at  the  outer  border  of  the  triceps  muscle,  it 
descends  to  the  bend  of  the  elbow  in  front  of  the  external 
condyle  of  the  humerus,  in  the  interval  between  the 
brachio-radialis  and  brachialis  anticus  muscles.  Under 
cover  of  the  former  muscle,  in  the  hollow  of  the  elbow, 
it  divides  into  its  two  terminal  branches,  the  radial  and 
posterior  interosseous  nerves. 

The  collateral  branches  are  in  three  sets,  arising 
(a)  on  the  inner  side,  (&)  on  the  back,  and  (c)  on  the 
outer  side  of  the  humerus  (Fig.  500). 

Branches  arising  internal  to  the  humerus.— 1. 
Internal  cutaneous  (n.  cutaneus  brachii  posterior). — This 
branch,  arising  in  common  with  one  of  the  following,  or 
independently,  pierces  the  fascia  on  the  inner  side  of 
the  arm  near  the  axilla.  It  supplies  the  skin  of  the 
inner  side  of  the  arm  in  the  upper  third,  above  and 
behind  the  area  supplied  by  the  lesser  internal  cutaneous 
nerve  (Fig.  498,  p.  630).  This  nerve  varies  in  size, 
according  to  the  bulk  of  the  lesser  internal  cutaneous 
and  intercosto-humeral  nerves. 

2.  Muscular  branches  (rr.  musculares). — These  are 
in  two  sets.  One  series  supplies  the  long  head  of  the 
triceps  muscle  near  its  origin ;  the  other  series  enters 
the  inner  head  of  the  muscle.  One  of  the  latter, 
separating  itself  from  the  rest,  accompanies  the  ulnar 
nerve  in  the  middle  third  of  the  arm,  and  supplies  the 
lower  part  of  the  muscle.  This  is  sometimes  called  the 
collateral  ulnar  nerve. 

Branches  arising  on  the  back  of  the  humerus. — 
Muscular  branches  arise  from  the  nerve  in  the  musculo- 
spiral  groove  for  the  supply  of  all  three  heads  of  the 
triceps  muscle.  The  branch  which  enters  the  inner 
head  of  the  muscle,  besides  supplying  it,  passes  through 
the  muscle  and  behind  the  external  condyle  of  the 
humerus,  to  terminate  in  the  anconeus. 

Branches  arising  at  the  outer  side  of  the 
humerus.  —  1.  The  cutaneous  branches  (n.  cutaneus 
antibrachii  dorsalis)  are  two  in  number,  superior  and 
inferior.  Arising  from  the  musculo-spiral  nerve  before 
it  pierces  the  external  intermuscular  septum,  these 
branches  pierce  the  deep  fascia  close  together  on  the 
outer  side  of  the  arm  in  its  lower  half.  Descending 
over  the  back  of  the  external  condyle,  the  superior 
lyranch  supplies  the  skin  of  the  outer  side  and  Ijack  of 
the  arm  in  its  lower  third,  and  the  back  of  the  Ibrearm  in  its  upper  half.  The 
inferior  branch  supplies  an  area  of  skin  on  the  back  of  the  forearm  in  the  upper 
two-thirds  internal  to  the  area  innervated  by  tJie  musculo  -  cutaneous  nerve 
(Fig.  498,  p.  630). 

2.  Muscular  branches. — The  musculo-sydral  nerve,  as  it  lies  in  the  interval 
between  the  braohiah's  Jinticus  and  Itraohio-radialis,  supplies  a  small  branch  to  the 
bracliialis  anticus  (which  in  some  cases  is  not  ])rescnt)  and  nerves  to  the  brachio- 
radialis  and  extensor  carpi  radialis  longior.  It  may  also  provide  the  nerve  to  the 
extensor  carpi  radialis  brevior. 


^j:  n. 


Fig.  500. — Diagrammatic  Eepre- 
sentation    of   the    branches 

OP  THE  MtJSCULO-SPIRAL  NeRVE. 

M.S,  Musculo-spiral  nerve  ;  L.H, 
Nerve  to  long  head  of  triceps  ; 
I.C,  Internal  cutaneous  branch  ; 
I.H,  Nerve  to  inner  head  of 
triceps;  O.H,  Nerve  to  outer  head 
of  triceps  ;  I.H,  Second  nerve 
to  inner  head  of  triceps  ;  Anc. 
Nerve  to  anconeus  ;  Art,  Ar- 
ticular branch  ;  E.Cs,  Superior, 
external  cutaneous  branch  ;  E.Ci, 
Inferior  external  cutaneous 
branch  ;  B.A,  Nerve  to  brachialis 
anticus  ;  Br,  Nerve  to  brachio- 
radialis  ;  E.C.R.L,  Nerve  to  ex- 
tensor carpi  radialis  longior  ;  P.I, 
Posterior  interosseous  nerve  ;  R, 
Radial  nerve. 


634 


THE  NEEVOUS  SYSTEM. 


Eadial  Nerve. 
The  radial   nerve  (r.  superficialis)  is  entirely 


Extfirnal  condyle 


Insertion  of 
trice]  IS 

Extensor  lunscles 
(origin) 


Supinator  rad 
brevis" 


Extensor  carpi 
ulnari 


iriceps  (long  liead) 
I'^riiceps  (outer  head) 
Biachio-radialis 

~Bricliialis  anticus 
Biceps 
rriceps  (inner  head) 


Extensor  carpi  radialis 
longioi  (origin) 

\)j|_r\tensor  carpi  radialis 
bieMor  (origin) 

'dJ^MUSCULO-SPIRAL  NERVE 


Ill  Posterior  interosseous 

NEEVP 


Extensor  ossis  metacarpi 
polhcis 

Extensor  carpi  radialis 
longioi  (tendon) 


Dorsal  branch  oi' 

ulnar  ndrvi 

Extensor  minimi 

digiti  (teiiil(iii) 

B-'ctensor  commun 

digitorum  (tendon) 


Extensoi  carpi  radialis 
bre\ior  (tendon) 

Extensor  brevis  pollicis 


Extensor  carpi  radialis 
ongior  (tendon) 
Extensor  ossis  metacarpi 
pollicis 

Extensor  carpi  radialis 
brevior  (tendon) 
^\^Extensor  brevis  pollicis 

Extensor  longus 
pollicis 

^     First  dorsal  inter- 
osseous muscle 


Fig.  501. — The  Muscles  of  the  Back  of  the  Forearm 
(the  superficial  muscles  have  been  reflected). 

and   articular   in    its    distribution,    and   it   arises 


cutaneous  in  its  distribution- 
Arising  in  the  hollow  of  the 
elbow  beneath  the  brachio- 
radialis,  it  courses  downwards 
under  cover  of  that  muscle 
through  the  upper  two-thirds 
of  the  arm,  and  accompanies- 
the  radial  artery  in  the  middle 
third  of  the  forearm.  It  then 
passes  backwards  beneath  the 
tendon  of  the  bracliio-radialis- 
and  pierces  the  deep  fascia  in 
the  outer  side  of  the  forearm 
in  the  lower  third.  It  is 
distributed  to  the  skin  of  the 
back  of  the  wrist,  the  outer 
side  and  the  back  of  the  hand, 
and  the  back  of  the  thumb  and 
outer  two  and  a  half  fingers 
(Fig.  498,  p.  630).  Its  branches 
communicate  on  the  ball  of 
the  thumb  with  the  musculo- 
cutaneous nerve,  and  on  the 
back  of  the  hand  with  the 
dorsal  branch  of  the  ulnar 
nerve.  The  digital  branches 
are  small,  and  are  five  in 
number.  Two  pass  to  the 
back  of  the  thumb  and  reach 
the  inter-phalangeal  articula- 
tion. One  supplies  the  radial 
side  of  the  index  finger  as  far 
as  the  second  phalanx.  The 
remaining  two  branches  divide 
at  the  clefts  between  the  second 
and  third,  and  third  and  fourth 
fingers  respectively,  and  in- 
nervate the  adjacent  sides  of 
these  fingers  as  far  as  the  second 
phalanx.  The  rest  of  the  skin 
of  these  digits  to  the  tips  is 
supplied  by  digital  branches 
of  the  median  nerve.  The 
nerve  may  only  supply  one 
and  a  half  fiuojers,  being  re- 
placed  by  branches  from  the 
ulnar  nerve. 

Posterior  Interosseous 
Nerve. 

The    posterior    inter- 
osseous nerve  (r.  profundus, 
n.       interosseus       antibrachii 
dorsalis)  is  entirely  muscular 
like    the   radial    beneath    the 


brachio  -  radialis    muscle.      Directed    obliquely    downwards    and     backwards,    it 


THOEAGIC  NERVES.  635 

reaches  the  back  of  the  forearm,  after  passing  round  the  outer  side  of  the 
radius,  by  piercing  the  fibres  of  the  supinator  radii  brevis  muscle  (Fig.  501). 
On  the  back  of  the  forearm  it  is  placed  in  the  upper  part  of  its  course  beneath  the 
superficial  extensor  muscles,  arid  upon  the  supinator  radii  brevis  and  extensor  ossis 
metacarpi  pollicis,  along  with  the  posterior  interosseous  artery.  In  the  lower  half 
of  the  forearm  it  pisses  beneath  the  extensor  longus  pollicis,  and  lies  upon  the 
interosseous  membrane.  At  the  wrist  it  passes  beneath  the  extensor  tendons  on  to 
the  back  of  the  carpus,  where  it  terminates  in  a  gangliform  enlargement  of  small 
size,  from  which  branches  pass  to  the  inter-carpal  articulations.  The  posterior  inter- 
osseous nerve  supplies  the  following  branches: — 

(1)  Terminal  articular  brandies  to  the  carpal  joints. 

(2)  Muscular  branches,  in  its  course  through  the  forearm.  Thus  on  the  outer 
side  of  the  radius  it  supplies  the  extensor  carpi  radialis  brevior  and  the  supinator 
brevis  muscle  before  it  enters  the  fibres  of  the  last-named  muscle.  After  emerging 
from  the  supinator  brevis  it  supplies  a  large  bundle  of  nerves  which  enter  the 
extensor  communis  digitorum,  extensor  minimi  digiti,  and  extensor  carpi  ulnaris 
near  their  origins.  Lower  down  the  forearm  the  nerve  gives  off  branches  to  the 
extensor  ossis  metacarpi  pollicis,  extensor  longus  and  extensor  brevis  pollicis,  and 
extensor  indicis. 

SUBSCAPULAE    NeRVES. 

There  are  three  subscapular  nerves  (nn.  subscapulares)  (Eigs.  494  and  496). 

The  first  or  short  subscapular  nerve  is  generally  double,  and  there  may  be 
three  trunks  present.  It  arises  from  the  posterior  cord  of  the  plexus  behind  the 
circumflex  nerve,  and  comes  from  the  fifth  and  sixth  cervical  nerves.  It  passes 
downwards  behind  the  axillary  artery  and  enters  the  subscapularis  muscle. 

The  second  or  lower  subscapular  nerve  also  arises  behind  the  circumflex 
from  the  posterior  cord  of  the  plexus,  and  from  the  fifth  and  sixth  cervical  nerves. 
Its  origin  is  below  and  external  to  that  of  the  first  nerve.  It  courses  outwards  and 
downwards  behind  the  axillary  artery,  and  the  circumflex  and  musculo-spiral 
nerves  to  the  teres  major  muscle.  It  supplies  branches  to  the  outer  part  of  the 
subscapularis  muscle  and  ends  in  the  teres  major. 

The  third  or  long  subscapular  nerve  (n.  thoraco-dorsalis)  arises  from  the  back 
of  the  posterior  cord  of  the  plexus,  behind  the  musculo-spiral  nerve,  and  from  the 
sixth,  seventh,  and  eighth  cervical  nerves,  or  from  the  seventh  and  eighth  nerves 
only.  It  is  directed  downwards  and  outwards  between  the  two  previous  nerves, 
behind  the  axillary  artery  and  over  the  posterior  wall  of  the  axilla,  in  company 
with  the  subscapular  artery,  to  the  latissimus  dorsi  muscle,  which  it  supplies  on  its 
anterior  (inner)  surface. 

THORACIC  NERVES. 

The  thoracic  nerves  are  twelve  in  number,  each  nerve  emerging  below  the 
corresponding  vertebra  and  rib.  Eleven  of  the  series  are  intercostal,  the  twelfth 
lying  below  the  last  rib.  The  first,  second,  third,  and  twelfth  nerves  present 
peculiarities  in  their  course  and  distribution.  The  other  thoracic  nerves,  as  already 
stated,  are  simple,  and  may  be  regarded  as  types  both  in  course  and  distribution. 

The  first  thoracic  nerve  is  the  largest  of  the  series.  It  emerges  from  the 
spinal  canal  below  the  neck  of  the  first  rib,  and  divides  in  the  first  intercostal 
space  into  two  very  unequal,  upper  and  lower,  parts.  The  upper  larger  part  ascends 
obliquely  over  the  neck  of  the  first  rib,  lying  external  to  the  superior  intercostal 
artery,  and  enters  the  neck  behind  the  suljclavian  artery  and  the  pleura.  It  pro- 
ceeds outwanls  upon  the  scalenus  medius  muscle  and  enters  into  the  formation  of 
tlic  brachial  plexus,  as  already  described. 

The  lotver,  intercoslal  part  of  the  nerve  is  much  smaller  in  size!  It  courses 
forwards  in  the  first  intercostal  space  and  supplies  the  intercostal  muscles.  It 
usually  gives  off  no  nritorior  branch  to  the  skin  of  the  chest  and  no  lateral 
cutaneous  branch. 


636 


THE  XEEYOUS  SYSTEM. 


In  some  cases  a  lateral  cutaneous  branch  emerges  from  the  side  of  the  first  intercostal  space. 
This  may  be  derived  from  the  first  nerve,  or  it  may  be  the  intercosto-humeral  nerve,  derived 
from  the'second  thoracic  nerve.  In  many  cases  an  anterior  cutaneous  branch  perforates  the  first 
intercostal  space  and  supplies  the  skin  on  the  front  of  the  chest.  This  branch,  similarly,  is  some- 
times traceable  to  the  second  thoracic  nerve. 

Commimicatioiis. — Besides  its  junction  with  the  eighth  cervical  to  form  the 
brachial  plexus,  the  first  thoracic  nerve  effects  the  following  communications : — (a)  The 
last  cervical  or  first  thoracic  ganglion  of  the  sympathetic  sends  a  gray  ramus  commuui- 
cans  to  join  the  nerve  on  its  appearance  in  the  thorax,  (b)  The  second  thoracic  nerve  in 
a  majority  of  cases  communicates  with  the  fii^t.  This  communication  varies  considerably 
in  size  and  distribution.  It  may  reinforce  the  intercostal  branch  of  the  nerve,  it  may 
send  one  branch  to  the  intercostal  portion  and  another  to  the  part  of  the  nerve  joining  the 
brachial  plexus,  or  it  may  consist  of  a  nerve  proceeding  solely  to  join  the  brachial  plexus  by 
a  junction  in  the  first  intercostal  space  with  the  part  of  the  first  thoracic  nerve,  which  is 
engaged  in  forming  the  plexus,  (c)  It  is  possible  that  the  first  white  ramus  communicans 
in  the  thoracic  region  connects  the  first  thoracic  nerve  with  the  gangliated  cord  of  the 
sympathetic,  but  this  is  not  known  with  certainty. 


The  second  thoracic  nerve  is  of  large  size,  though  much  smaller  than  the 
first.  It  passes  forwards  in  the  second  intercostal  space,  lying  at  first  in  the  sub- 
costal groove  between  the  external  and  internal  intercostal  muscles.  At  the  level 
of  the  mid-axillary  line  it  gives  off  a  large  lateral  branch ;  continuing  its  course 
it  pierces  the  internal  intercostal  muscle  and  Ues  upon  the  pleura ;  finally,  at  the 
lateral  border  of  the  sternum,  it  passes  forwards  in  front  of  the  internal  mammary 
artery  and  through  the  internal  intercostal  muscle,  and  the  aponeurosis  of  the 
external  intercostal  muscle,  and  ends  by  supplying  the  skin  of  the  front  of  the 
chest  over  the  second  intercostal  space. 

The  nerA'e  supplies  the  following  branches : — 


eXTSKNAL 


lMfT£KfOfi 


JitfTERIOR 
SfiAMCf/ 


1.  Muscular  branches  to  the  muscles 
of  the  second  intercostal  space. 

2.  Cutaneous  branches,  (a)  Anterior 
terminal  branches  (it.  cutaneus  anterior)  to 
the  skiu  over  the  second  intercostal  space 
(Fig.  503).  (6)  A  larire  lateral  cutaneous 
branch,  the  intercosto-htuneral  nerve  (n. 
intercosto-brachiahs)  (Fig.  494,  p.  623). 
This  nerve  pierces  the  intercostal  muscles 
and  the  serratus  magnus,  and,  crossing  the 
axilla,  extends  to  the  arm.  It  pierces  the 
deep  fascia  jiist  beyond  the  posterior  fold  of 
the  axilla,  and  can  be  traced  down  the  arm 
as  far  as  the  interval  between  the  internal 
condyle  of  the  humerus  and  the  olecranon 
process.  It  supplies  an  area  of  skiu  stretch- 
ing across  the  armpit  and  along  the  posterior 
surface  of  the  arm  on  the  inner  side  as  far 
as  the  elbow  (Fig.  497,  p.  628). 

The  intercosto-humeral  nerve  varies  in  size. 
It  may  pierce  the  first  intercostal  space,  and  it  is 
often  divisible  into  anterior  and  posterior 
branches,  like  the  lateral  branch  of  an  ordinary 

intercostal  nerve. 


Fig.  502.- 


-scheme  of  the  dlstribctiox  of  a 
Typical  Spixal  Nerve. 


Communications.  —  (1)  The  intercosto- 
humeral  nerve  communicates  with  two 
adjacent  nerves.  Either  before  or  after 
piercing  the  fascia  of  the  axilla  it  is  joined  by 
the  lesser  internal  cutaneous  nerve  of  the  brachial  plexus.  It  also  communicates  with  the 
posterior  part  of  the  lateral  branch  of  the  third  intercostal  nerve  by  means  of  the  branches 
distributed  to  the  floor  and  boundaries  of  the  axilla.  It  may  supply  the  axillary  arches, 
when  present.     (2)  Besides  the  branches  referred  to,  the  second  thoracic  nerve  in  many 


THORACIC  NERVES. 


637 


cases  transmits  a  nerve  to 
the  brachial  plexus,  which 
becomes  incorporated 
with  the  first  thoracic 
nerve  after  passing  over 
the  neck  of  the  second  rib. 
This  branch  is  inconstant. 
As  already  mentioned,  it 
may  join  only  the  inter- 
costal part  of  the  first 
thoracic  nerve,  it  may  join 
the  brachial  plexus  only, 
or  it  may  send  branches 
to  both  parts  of  the  first 
thoracic  nerve.  (3)  Be- 
sides the  communications 
effected  by  branches  of  the 
second  thoracic  nerve  in 
its  course,  it  also  receives 
a  gray  ramu  s  conununicans 
from  the  second  thoracic 
ganglion  of  the  sym- 
pathetic cord  in  the 
thorax.  It  probably  also 
sends  to  the  sympathetic 
the  first  vjhite  ramus  corri- 
'inu7iicans,  though  this  is 
not  known  with  certainty. 

The  third  thoracic 
nerve  only  differs  from 
a  typical  thoracic  nerve 
in  one  respect.  Its 
lateral  branch  divides 
in  the  usual  way  into 
anterior  and  posterior 
parts,  of  which  the  latter 
is  carried  to  the  arm  and 
supplies  an  area  of  skin 
on  the  posterior  half  of 
the  inner  side  near  the 
root  of  the  limb.  It 
effects  a  junction  with 
the  intercosto-humeral 
nerve  (Fig.  494,  p.  623). 

The  fourth,  fifth, 
and  sixth  thoracic 
nerves  have  a  course 
and  distribution  which 
is  simple  and  typical. 
Excejjt  for  the  peculi- 
arities above  mentioned, 
the  second  and  third 
thoracic  nerves  have  a 
similar  distribution. 

The  nerves  apyjear 
on  the  ])Osterior  wall  of 
the  tiiorax,  in  tlie  sub- 
costal groove  of  the  cor- 
reHyjonding  rib.  They 
extend  forwards  be- 
tween   tlie    intercostal 


-The  Distribution  ob'  Cutaneous  Nerves  on  the  Front  op 
THE  Trunk. 

On  one  side  tlie  distribution  of  the  several  nerves  is  rejjiesented,  the  letters 
indicating  their  nonienclature. 

G.A,  Great  auricular  nerve  ;  S.C,  Superficial  cervical  nerve  ;  S.Cl,  Supra- 
clavicular nerves  ;  Acu,  Acromial  ;  Cl,  Clavicular  ;  St,  Sternal  ;  T.2-12, 
Lateral  and  anterior  branches  of  thoracic  nerves  ;  I.H,  Ilio-hypogastric 
nerve  ;  l.I,  Ilio-inguinal  nerve  ;  Circ,  Cutaneous  branch  of  circumflex 
nerve  ;  L.I.C,  Lesser  internal  cutaneous  nerve  ;  LH,  intercosto-humeral  ; 
f.( ',  Internal  cutaneous  ;  M.S,  Cutaneous  branch  of  musculo-spiral  nerve, 
VjS',  External  cutaneous  nerves ;  G.C,  Genito-crural  nerve  ;  M.C'  '•*,  Middle 
cutaneous  nerves  ;  I.C",  Branch  of  internal  cutaneous  nerve  ;  P,  Branches 
of  pudic  nerve  ;  S.Sc,  Branches  of  small  sciatic  nerve. 

On  tlic  other  side  a  schematic  representation  is  given  of  the  areas  snp])lied  liy 
tlie  above  nerves,  the  numerals  indicating  tint  spinal  oi'igin  of  the  branches 
of  distribution  to  each  area. 


638  THE  NEEVOUS  SYSTEM. 

muscles  as  far  as  the  middle  of  the  chest  wall,  lying  at  a  lower  level  than  the  inter- 
costal vessels.  At  the  side  of  the  chest  each  nerve  passes  obliquely  through  the  internal 
intercostal  muscle,  and  comes  to  lie  upon  the  pleura,  triangularis  sterni  muscle, 
and  internal  mammary  artery.  Thereafter,  piercing  the  fibres  of  the  internal 
intercostal  muscle  and  the  aponeurosis  of  the  external  intercostal  muscle,  each 
nerve  ends  by  supplying  the  skin  of  the  front  of  the  chest,  over  an  area  correspond- 
ing to  the  inner  or  anterior  part  of  the  intercostal  space  to  which  it  belongs. 

Branches. — Each  intercostal  nerve  supplies,  in  addition  to  the  anterior  terminal 
cutaneous  branches,  muscular  branches  to  the  intercostal  muscles  and  a  lateral 
trunk  (r.  cutaneus,  lateralis),  which,  piercing  the  intercostal  'muscles  and  the 
serratus  maguus,  divides  into  anterior  and  posterior  branches  for  the  innervation 
of  the  skin  over  the  side  of  the  chest.  Each  area  of  skin  thus  innervated  is 
continuous  anteriorly  with  the  area  innervated  by  the  anterior  terminal  branches 
of  the  same  nerves,  and  posteriorly  with  the  areas  supplied  by  their  posterior 
primary  divisions. 

The  upper  six  intercostal  nerves  supply  the  muscles  of  the  first  six  intercostal 
spaces  and  the  triangularis  sterni  (3,  4,  5,  6).  The  second,  third,  fourth,  fifth,  and 
sixtli  nerves  supply  the  skin  of  the  front  of  the  chest :  the  second,  opposite  the 
manubrio-sternal  joint;  the  sixth,  opposite  the  base  of  the  xiphoid  cartilage.  Their 
lateral  branches  supply  branches  to  the  intercostal  muscles  and  tiie  skin  of  the  side 
of  the  chest,  the  second  (intercosto-humeral)  and  the  third  in  part  being  drawn  out 
on  to  the  arm.     The  fourth  supplies  the  nipple  (Fig.  503). 

Communications. — Each  of  these  intercostal  nerves  communicates  with  the  sympathetic 
cord  and  gangUa  by  two  branches — a  ivhite  7-amus  cominunicans  to  the  corresponding  sym- 
pathetic ganglion  or  the  adjacent  part  of  the  sympathetic  cord ;  and  a  gray  ramus  com- 
municans,  which  passes  to  each  nerve  from  the  corresponding  ganglion. 

The  seventh,  eighth,  ninth,  tenth,  and  eleventh  thoracic  nerves  only  differ 
from  the  preceding  nerves  in  regard  to  a  part  of  their  course  and  distribution.  Each 
has  the  same  course  and  communications  as  the  preceding  nerves  in  the  thoracic  wall. 
In  addition,  these  nerves  have  a  further  course  and  distribution  in  the  abdominal 
wall.  Each  nerve  traverses  its  intercostal  space  in  the  way  described.  At  the 
anterior  end  of  the  space,  the  nerve  pierces  the  attachment  of  the  diaphragm  and 
the  transveralis  abdominis  muscles  to  the  costal  cartilages,  and  courses  forwards  in 
the  abdominal  wall  between  the  transversalis  and  obliquus  internus  muscles.  The 
nerve  then  passes  between  the  rectus  muscle  and  the  posterior  layer  of  its  sheath, 
and  eventually  reaches  the  anterior  abdominal  wall  and  becomes  cutaneous  by 
piercing  the  rectus  itself  and  the  anterior  layer  of  its  sheath. 

Muscular  Branches. — The  lower  intercostal  nerves  supply  the  intercostal 
muscles  of  the  spaces  in  which  they  lie ;  and  in  the  abdominal  wall  they  innervate 
the  transversalis,  obliqui,  and  rectus  abdominis.  The  branches  arise  from  the 
main  trunk  as  well  as  from  its  lateral  and  anterior  branches.  (The  ninth,  tenth, 
and  eleventh  nerves  are  described  as  assisting  in  the  innervation  of  the  diaphragm 
by  communications  with  the  plirenic  nerve.) 

Cutaneous  Branches. — These  are  lateral  and  anterior.  The  lateral  branches 
divide  into  anterior  and  posterior  parts,  and,  becoming  superficial  along  the  line  of 
inter-digitation  of  the  obliquus  externus  muscle  with  the  serratus  magnus  and 
latissimus  dorsi,  they  are  directed  more  obliquely  downwards  than  the  lateral 
branches  of  the  higher  intercostal  nerves,  and  are  distributed  to  the  skin  of  the 
loin  as  low  down  as  the  buttock.  The  lateral  branch  of  the  eleventh  nerve  can  be 
traced  over  the  iliac  crest  (Fig.  503). 

The  anterior  branches  are  small.  That  of  the  seventh  nerve  innervates  the  skin 
at  the  level  of  the  ensiform  cartilage.  The  eighth  and  ninth  appear  between  the 
ensiform  cartilage  and  the  umbilicus ;  the  tenth  nerve  supplies  the  region  of  the 
umbilicus ;  and  the  eleventh,  the  area  immediately  below  the  umbilicus. 

The  cutaneous  branches  of  these  nerves,  including  the  posterior  primary  divisions,  thus  supply 
continuous  belts  of  skin,  which  can  be  mapped  out  on  the  body  from  the.  vertebral  column 
behind  to  the  middle  line  in  front.  These  areas  are  not  jilaced  horizontally,  but  tend  to  be 
drawn  downwards  as  the  series  is  followed  from  the  upper  to  the  lower  nerves. 

The  twelfth  thoracic  nerve  is  peculiar  in  its  course  and  distribution.     It 


THE  LUMBO-SACEAL  PLEXUS.  639 

emerges  below  the  last  rib  (Fig.  504),  and  passes  outwards  and  downwards  in  the 
posterior  abdominal  wail  under  cover  of  the  psoas  muscle,  and  between  the  external 
•arcuate  ligament  and  the  quadratus  lumborum  muscle ;  it  pierces  the  transversalis 
muscle,  and  courses  forwards  in  the  interval  between  it  and  the  obliquus  internus 
as  far  as  the  sheath  of  the  rectus  muscle.  After  piercing  the  posterior  layer  of  the 
sheath,  the  rectus  muscle,  and  the  anterior  layer  of  the  sheath,  it  terminates  hj 
supplying  the  skin  of  the  anterior  abdominal  wall  midway  between  the  umbilicus 
and  the  pubis.  The  branches  of  the  nerve  are  muscular,  to  the  transversalis, 
obliqui,  rectus,  and  pyramidalis  muscles  of  the  abdominal  wall,  and  cutaneous 
"branches,  two  in  number — an  anterior  terininal  branch,  which  supplies  the  skin  of 
the  anterior  abdominal  wall  midway  between  the  umbilicus  and  the  pubis,  and  a 
large  latei^al  cutaneous  (iliac)  branch,  which,  passing  obliquely  downwards  through 
the  lateral  muscles  of  the  abdominal  wall,  becomes  superficial  above  the  iliac  crest, 
a  couple  of  inches  behind  the  anterior  superior  spine.  It  supplies  the  skin  of  the 
buttock  as  far  down  as  a  point  below  and  in  front  of  the  great  trochanter  of  the 
femur  (Fig.  507,  p.  645). 

The  twelfth  thoracic  nerve,  in  many  cases,  receives  a  communicating  branch  from  the  eleventh, 
near  its  origin,  and  still  more  frequently  sends  a  fine  branch  to  join  the  origin  of  the  first 
lumbar  nerve  in  the  psoas  muscle.  It  may  communicate  also  with  the  ilio-hypogastric  nerve,  as 
they  lie  together  in  the  abdominal  wall. 

THE  LUMBO-SACEAL  PLEXUS. 

The  lumbo-sacral  plexus  is  formed  by  the  union  of  the  anterior  primary  divisions 
of  the  remaining  spinal  nerves  —  five  lumbar,  five  sacral,  and  one  coccygeal. 
Frequently,  a  fine  communicating  branch  of  the  twelfth  thoracic  nerve  joins  the 
first  lumbar  nerve  near  its  origin. 

Of  the  nerves  in  question  the  first  sacral  is  generally  the  largest  in  size,  the 
nerves  diminishing  gradually  above  and  rapidly  below  the  first  sacral.  The  plexus, 
for  the  most  part,  forms  the  nerves  destined  for  the  supply  of  the  lower  limb.  In 
addition,  however,  nerves  arise  at  its  upper  limit  which  are  distributed  to  the  trunk 
above  the  level  of  the  limb,  and  at  the  lower  end  of  the  plexus  nerves  arise  for  the 
supply  of  the  perineum. 

Partly  for  convenience  of  description,  and  partly  on  account  of  the  differences 
in  position  and  course  of  some  of  the  nerves  emanating  from  it,  the  plexus  is  sub- 
divided into  three  subordinate  parts  —  lumbar,  sacral  or  sciatic,  and  pudendal 
plexuses.     There  is,  however,  no  strict  line  of  demarcation  between  the  three  parts. 

The  lumbar  plexus  is  formed  by  the  first  four  lumbar  nerves,  and  is  often 
joined  by  a  branch  from  the  twelfth  thoracic  nerve  as  well,  [t  is  limited  below  by 
the  fourth  lumbar  nerve  (n.  furcalis),  which  also  enters  into  the  composition  of  the 
sciatic  or  sacral  plexus.  The  nerves  of  the  lumbar  plexus  are  formed  in  the  loin, 
and  supply  that  region  as  well  as  part  of  the  lower  limb.  They  are  separated  from 
the  nerves  of  the  sacral  portion  of  the  plexus  by  the  articulation  of  the  innominate 
bone  with  the  sacrum. 

The  sacral  or  sciatic  plexus  is  formed  by  the  fourth  and  fifth  lumbar,  and  the 
first  two  or  three  sacral  nerves.  .  It  is  generally  limited  below  by  the  third  sacral 
nerve  (n.  bigeminus),  which  also  assists  in  forming  the  pudendal  plexus.  The  nerves 
of  the  sacral  plexus  are  placed  on  the  posterior  wall  of  the  pelvis,  and  are  destined 
almost  entirely  for  the  lower  limb. 

The  pudendal  plexus  is  formed  by  the  second,  third,  fourth,  and  fifth  sacral 
nerves,  and  the  minute  coccygeal  nerve.  It  is  placed  on  the  back  wall  of  the  pelvis 
and  supplies  branches  mainly  to  the  perineum. 

Communications  with  the  Sympathetic. — Each  of  these  nerves  has  communica- 
tions with  the  g;ujffli;ited  cord  of  tlie  syrnpathetic  in  the  abdomen  and  pelvis. 

Gray  Rami  Communicantes.  — From  the  lumbar  and  sacral  ganglia  long  slender  ,yray 
rarai  ro/iu/tim/iraa/r's  nn^  dii'ccted  backwards  and  outwards  over  the  bodies  of  the  vertebra;, 
and  (in  the  bimbar  region)  beneath  the  origins  of  the  psoas  nuiscle,  to  reach  the  anterior 
primjiry  divi.sious  of  the  nerves.  These  branches  arc  irregular  in  their  arrangement.  A 
given  nerve  may  receive  branches  from  two  ganglia,  or  one  ganglion  may  send  branches 
to  two  nerves.  The  rami  arc  longer  in  tlie  loin  thati  in  the  pelvis,  owing  to  the  prf)jcction 
of  the  lumbar  portion  of  the  vei'tebral  column. 


640 


THE  NEEVOUS  SYSTEM. 


White  Rami  Communicantes. — Certain  lumbar  and  sacral  nerves  are  also  connected 
with  the  abdominal  and  pelvic  sympathethic  by  means  of  tvhite  rami  covimtmicantts.  From 
the  first  two,  and  possibly  also  the  third  and  fourtli  lumbar  nerves,  white  rami  conununi- 


FiG.  504. — NBmT:s  of  the  Lumbo-Sacral  Plexus. 

Sy,  Sympathetic  cord  ;  T.12,  L.l,  2,  3,  4,  5,  S.l,  2,  3,  4,  5,  Co,  Anterior  primary  divisions  of  the  last  thoracic, 
the  lumbar,  sacral,  and  coccygeal  nerves  ;  Q,  Nerves  to  quadratus  Inmborum  ;  Ps,  Nerves  to  psoas 
muscle  ;  G.C,  Genito-crural  nerve  ;  II,  Iliac  branches  of  last  thoracic  and  ilio-hj'pog'astric  nerves  ;  Hy, 
Hypogastric  branch  of  Ilio-hypogastric  nerve  ;  I.I,  Ilio-inguinal  nerve  ;  E.C,  External  cutaneous  nerve  ; 
A.  C,  Anterior  crural  nerve  ;  Obt,  Obturator  nerve  ;  Py,  Nerves  to  pyriformis  muscle  ;  O.I,  Nerve  to 
obturator  internus  ;  Q.F,  Nerve  to  quadratus  femoris  muscle  ;  Art,  Articular  branch  ;  S.G,  Superior 
gluteal  nerve  ;  I.G,  Inferior  gluteal  nerve  ;  P,  Peroneal  nerve  ;  Bi.2,  Nerve  to  ^hort  head  of  biceps 
muscle  ;  T,  Tibial  nerve  ;  Art,  Articular  branch  ;  H.S,  Nerve  to  the  hamstring  nrascles  ;  Bi.l,  Nerves 
to  biceps  (long  head),  and  St.l,  to  semitendinosus  ;  St. 2,  Semitendiuosus  ;  Sm,  Semimembranosus  ; 
A.m,  Adductor  magnus  ;  S.Sc,  Small  sciatic  nerve  ;  Pert,  Pei-forating  cutaneous  nerve  ;  Pud,  Pudic  nerve  ; 
M.  Muscular  branches  ;  Per,  Perineal  branch  of  fourth  sacral ;  A. Co,  Anterior  sacro-coccygeal  nerve. 


THE  LUMBAE  PLEXUS. 


641 


cante.s  are  directed  forwards,  either  independently  or  incorporated  with  the  corresponding 
gray  rami,  to  join  the  upper  part  of  the  lumbar  gangliated  cord.  The  fifth  lumbar  nerve 
and  the  first  sacral  nerves  are  unprovided  with  white  rami  communicantes.  From  the 
third,  and  usually  also  the  second  or  fourth  sacral  nerves,  white  rami  (visceral  branches) 
pass  inwards,  and,  crossing  over  (without  joining)  the  gangliated  cord,  enter  the  pelvic 
plexus  of  the  sympathetic.  The  fifth  sacral  and  coccygeal  nerves  possess  no  white  rami 
communicantes. 

THE  LUMBAR  PLEXUS. 

The  lumbar  plexus  is  formed  by  the  anterior  primary  divisions  of  the  first  three 

Vena  caval  opening     CEsophageal  opening    Central  tendon  (middle  part) 

Diaphragm  (right  cms) 

lliddlp  arcuate  ligament 
Aortic  opening 
Central  tendon 
(left  part) 
Diaphragm  (left 

Central  tendon  (right  part) ^.uv^. 

Diaphragm  (costal  fibres) 
Internal  arcuate  ligament 


External  arcuate  ligament- 
End  of  last  nb 
Last  thoracic  nervi. 
Ant.  layer  of  lumbar  fascia 
Lumbar  fascia 

iLIO-HYPOOASTRIf 

Lumbar  vessels  and  sympa 

thetic  communicating  neives 

Ilio-inguinal 

Quadratus  lumborum 


External  cutaneous  nerve- 

Psoas  magnus 

Iliacus 

lumbo-sacral  cord 

Genito-crural  ner\  e 

Anterior  crural  nerve. 

Obturator  nerve. 

Great  sciatic  nerve 


Last  thoracic 
lTTT     nerve 
■-"     End  of  last  rib 
Lumbar  nerve  I. 
Ilio-hypogastric 
Lumbar  nerve  II. 

Ilio-inouinal 
Quadratus 
'lumborum 
Lumbar  nerve  III. 

Genito-crural 

Lumbar  nerve  IV. 


Lumbo-sacral  cord 

External  cutaneous 

nerve 

Ant.  crural  nerve 

Obturator  nerve 
Gre  vt  sciatic  nerve 


Flo.  505. 


Obturator  nerve 
,  Adductor  longus  (origin) 
,    Adductor  brevis  (origin) 
,    Gracilis  (origin) 
Adductor  magnus  (origin) 
Tectineus  (cut) 
j      I    Superficial  branch  of  obturator  nerve 
I     Dekp  branch  of  obturator  nerve 
•Jbtiirator  extenius 

-VjeW    ok   the    POSTKIUOIt   ABDOMINAL   WaLL,    TO   SHOW   THE   MUSCLES   AND   THE    NERVES   OF 

THE  Lumbo-Hackal  Plexus. 


and  a  x^art  of  the  fourth  lumbar  nerves,  with  the  addition,  in  some  cases,  of  a  small 
branch  I'rom  the  twelfth  thoracic  nerve.  The  nerves  incirease  in  size  from  aljove 
downwards  {'FJcr.  .505;. 

Position  and  Constitution.— The  plexus  is  placed  deeply  in  the  substance  of 
the  psoas  muscle,  in  front  of  the  transverse  processes  of  the  lumbar  vertebrae.     The 
45 


642  THE  NEEVOUS  SYSTEM. 

nerves,  on  emerging  from  the  interverteVjral  foramina,  are  connected  as  above 
described  with  the  sympathetic  system,  and  then  divide  in  the  following  manner  in 
the  substance  of  the  psoas  muscle.  The  first  and  second  nerves  divide  into  upper 
and  lower  branches.  The  upper  branch  of  the  first  nerve  (which  may  be  joined  by 
the  branch  from  the  twelfth  thoracic  nerve)  forms  two  nerves,  ilio-hypogastric  and 
ilio-inguinal.  The  lower  branch  of  the  first  joins  the  upper  branch  of  the  second 
nerve,  to  produce  the  genito-crural  nerve.  The  lower  Ijranch  of  the  second  nerve, 
the  whole  of  the  third,  and  that  part  of  the  fourth  nerve  engaged  in  the  con- 
stitution of  the  plexus  divide  each  into  two  unequal  parts — smaller  anterior  and 
larger  posterior  parts.  The  smaller  anterior  portions  combine  together  to  form 
the  obturator  nerve,  which  is  thus  formed  by  the  second,  third,  and  fourth  lumbar 
nerves.  The  root  from  the  second  nerve  is  not  always  present.  The  larger 
posterior  portions  of  the  same  nerves  combine  together  to  form  the  anterior 
crural  nerve.  From  the  back  of  the  posterior  parts  of  the  second  and  third 
nerves,  the  external  cutaneous  nerve  arises.  The  nerves  also  provide,  near  their 
origins,  irregular  muscular  branches,  for  the  psoas  and  quadratus  lumborum 
muscles.  The  following  is  a  list  of  the  nerves  which  spring  from  the  lumbar 
plexus  (Figs.  504  and  505) : — 

(1)  Muscular  branches  to  the  quadratus  (4)  Genito-crural. 

lumborum  and  psoas.  (5)  External  cutaneous. 

(2)  Ilio-hypogastric.  (6)  Obturator. 

(3)  Ilio-inguinal.  (7)  Anterior  crural. 

Muscular  Branches. — The  nerves  to  the  quadratus  lumborum  muscle  arise 
independently  from  the  first  three  or  four  lumbar  nerves  (and  sometimes  also  from 
the  twelfth  thoracic  nerve).  The  nerves  to  the  psoas  muscles  arise  from  the  second 
and  third  lumbar  nerves,  with  additions,  in  some  cases,  from  the  first  or  fourth. 
They  are  often  associated  in  their  origin  with  the  nerve  to  the  iliacus  from  the 
anterior  crural.  The  psoas  minor,  when  present,  is  innervated  by  the  first  or 
second  lumbar  nerve. 

The  ilio-hypogastric  and  ilio-inguinal  nerves  closely  resemble  in  their  course 
and  distribution  the  lower  thoracic  nerves,  with  which  they  are  in  series. 

The  ilio-hypogastric  nerve  (n.  ilio-hypogastricus)  is  the  highest  branch  of 
the  first  lumbar  nerve.  It  receives  fibres  also  from  the  twelfth  thoracic,  when  that 
nerve  communicates  with  the  first  lumbar  nerve.  After  traversing  the  psoas  muscle 
obliquely,  it  appears  at  its  outer  border  on  the  surface  of  the  quadratus  lumborum 
and  behind  the  kidney.  It  courses  through  the  loin,  lying  between  the  transversalis 
and  obliquus  internus  muscles,  above  the  crest  of  the  ilium.  About  an  inch  in  front  of 
the  anterior  superior  spine  it  pierces  the  obliquus  internus,  and  continues  its  course 
in  the  groin  beneath  the  aponeurosis  of  the  obliquus  externus.  It  finally  becomes 
cutaneous  in  the  anterior  abdominal  wall,  by  piercing  the  aponeurosis  of  the  obliquus 
externus  about  an  inch  and  a  half  above  the  external  abdominal  ring  (Fig.  507  p.  645). 
Its  branches  are — (1)  muscular  to  the  muscles  of  the  abdominal  wall ;  and  (2) 
cutaneous  branches,  two  in  number.  The  iliac  branch  corresponds  with  the  lateral 
branch  of  an  intercostal  nerve,  and,  after  piercing  the  obliquus  internus  and 
obliquus  externus,  becomes  cutaneous  just  above  the  iliac  crest,  below  and  behind 
the  iliac  branch  of  the  last  thoracic  nerve.  It  is  small,  and  may  be  absent.  It  is 
distributed  to  the  skin  over  the  upper  part  of  the  outer  side  of  the  buttock,  in  con- 
tinuity with  the  cutaneous  branch  of  the  posterior  primary  division  of  the  first 
lumbar  nerve.  The  hypogastric  branch  is  the  anterior  terminal  branch  of  the  nerve. 
It  supplies  the  skin  of  the  anterior  abdominal  wall  below  the  level  of  the  last 
thoracic  nerve  and  above  the  pubis. 

The  ilio-inguinal  nerve  (n.  ilio-inguinalis)  is  the  second  branch  given  off 
from  the  first  lumbEir  nerve.  It  also  may  receive  fibres  from  the  last  thoracic 
nerve.  Not  unfrequently  the  ilio-hypogastric  and  ilio-inguinal  nerves  are  repre- 
sented for  a  longer  or  shorter  part  of  their  course  by  a  single  trunk.  ,  When  separate 
the  nerve  takes  a  course  similar  to  that  of  the  ilio-hypogastric  nerve,  but  at  a  lower 
level,  as  far  as  the  anterior  abdominal  wall.  It  then  pierces  the  obliquus  internus 
farther  forward  and  lower  down  than  the  ilio-hypogastric ;  and  coursing  forwards 


OBTUEATOR  NERVE.  643 

beneath  the  aponeurosis  of  the  obhquus  externus,  just  above  Poupart's  hgainent,  it 
becomes  superficial  after  passing  through  the  external  abdominal  ring  and  external 
spermatic  fascia  (Fig.  507,  p.  645). 

Its  branches  are  muscular  to  the  muscles  of  the  abdominal  wall,  among  which  it 
passes,  and  cutaneous  hranches,  which  innervate  the  skin  (1)  of  the  anterior  abdominal 
wall  over  the  symphysis  pubis,  (2)  of  the  thigh  over  the  upper  and  inner  part  of 
Scarpa's  triangle,  and  (3)  of  the  upper  part  of  the  scrotum,  and  root  and  dorsum  of 
the  penis  (of  the  mons  Veneris  and  labium  majus  in  the  female).  These  last-named 
branches  are  contiguous  to  branches  of  the  pudendal  and  pudic  nerves.  No  lateral 
cutaneous  branch  arises  from  the  ilio-inguinal  nerve.  It  thus  corresponds,  like  the 
hypogastric  part  of  the  ilio-hypogastric  nerve,  to  the  anterior  trunk  of  a  typical 
thoracic  nerve. 

The  genito-crural  nerve  (n.  genito-femoralis)  usually  arises  by  two  independent 
roots  from  the  front  of  the  first  and  second  lumbar  nerves,  which  unite  in  the  substance 
of  the  psoas  to  form  a  slender  trunk.  It  appears  on  the  posterior  abdominal  wall, 
lying  on  the  psoas  magnus,  internal  to  the  psoas  parvus,  and,  piercing  the  psoas 
fascia,  it  extends  downwards  on  the  outer  side  of  the  common  and  external  iliac  vessels 
and  behind  the  ureter  to  Poupart's  ligament  (Fig.  505,  p.  641).  At  a  variable  point 
above  that  ligament  it  divides  into  genital  and  crural  branches.  The  genital  branch 
is  a  minute  nerve.  It  crosses  the  terminations  of  the  external  iliac  vessels,  and, 
along  with  the  vas  deferens  and  spermatic  vessels,  enters  the  inguinal  canal  through 
the  internal  abdominal  ring.  It  terminates  by  supplying  small  branches  to  the 
skin  of  the  scrotum  and  adjacent  part  of  the  thigh.  In  the  female  it  accompanies 
the  round  ligament  to  the  labium  majus.  This  nerve  gives  off  in  its  course  the 
following  small  branches :  (1)  to  the  external  iliac  artery ;  (2)  to  the  cremaster 
muscle ;  (3)  to  communicate  with  the  spermatic  plexus  of  the  sympathetic.  The 
crural  branch  continues  the  course  of  the  parent  nerve  into  the  thigh,  lying  on  the 
outer  side  of  the  femoral  artery.  It  becomes  cutaneous  by  passing  through  the 
saphenous  opening  or  the  iliac  portion  of  the  fascia  lata,  and  supplies  an  area  of 
skin  over  Scarpa's  triangle,  external  to  that  supplied  by  the  ilio-inguinal  nerve 
(Fig.  507,  p.  645).  It  communicates  in  the  thigh  with  the  middle  cutaneous 
branch  of  the  anterior  crural  nerve.  Before  piercing  the  deep  fascia  it  gives  a 
minute  branch  to  the  femoral  artery. 

The  external  cutaneous  nerve  (n.  cutaneus  femoris  lateralis)  is  only  distri- 
buted to  skin  (Fig.  505).  It  arises  from  the  back  of  the  lumbar  plexus,  and  usually 
from  the  second  and  third  lumbar  nerves.  Emerging  from  the  psoas  muscle  at  its 
outer  border,  the  nerve  crosses  the  iliacus  muscle,  beneath  the  fascia  iliaca,  to  reach 
the  anterior  superior  iliac  spine.  It  enters  the  thigh  beneath  the  outer  extremity 
of  Poupart's  ligament,  and  either  over,  under,  or  through  the  origin  of  the  sartorius 
muscle.  It  extends  down  the  outer  side  of  the  front  of  the  thigh  for  a  few  inches, 
lying  at  first  beneath  the  fascia  lata,  and  afterwards  in  a  tubular  investment  of  the 
fascia.  It  gives  off  small  branches  in  this  part  of  its  course,  and  finally,  piercing  the 
fascia  about  four  inches  below  the  anterior  superior  iliac  spine,it  separates  intoanterior 
and  posterior  terminal  branches.  The  anterior  branch  is  the  larger,  and  is  distributed 
on  the  outer  side  of  the  front  of  the  thigh  almost  to  the  knee.  The  smaller  posterior 
branch  supplies  the  skin  of  the  outer  side  of  the  buttock  below  the  great  trochanter 
and  of  the  upper  two-thirds  of  the  outer  side  of  the  thigh  (Fig.  507,  p.  645). 

Obturator  Nerve. 

The  obturator  nerve  (n.  obturatorius)  supplies  the  muscles  and  skin  on  the 
inner  side  of  the  thigh.  It  arises  in  the  substance  of  the  psoas  muscle  by  three 
roots  jjlaced  in  front  of  those  of  the  anterior  crural  nerve,  and  derived  from  the 
second,  third,  and  fourth  lumbar  nerves  (Fig.  505,  p.  641).  Sometimes  the  root 
from  the  second  nerve  is  aljsent.  Passing  vertically  downwards,  the  nerve  emerges 
from  tbe  psoas  at  its  inner  border,  behind  the  common  iliac,  and  on  the  outer  side 
of  the  internal  iliac  vessels.  It  passes  forwards  below  the  pelvic  brim  in  company 
with  the  obturator  artery  to  the  obturator  groove  of  the  thyroid  foramen,  through 
which  it  reaches  the  thigh.  While  in  the  obturator  groove  it  separates  into  its 
two  main  l)ranches,  named  superficial  and  deep  (Fig.  506,  p.  644). 
45  a 


644 


THE  NEKVOUS  SYSTEM. 


The  superficial  branch  enters  the  thigh  in  front  of  the  obturator  externus  and 
adductor  hrevis  muscles,  and  beneath  the  pectineus  and  adductor  longus.  In  the 
middle  third  of  the  thigh  it  is  found  coursing  along  the  inner  border  of  the  adductor 
longus,  anterior  to  the  gracilis;  and  it  finally  divides  iuto  two  slender  terminal 
filaments,  of  which  one  enters  Hunter's  canal  and  ends  on  the  femoral  artery,  while 
the  other  supplies  the  skin  for  a  variable  distance  on  the  inner  side  of  the  thigh  and 
joins  in  the  obturator  (sub-sartorial)  plexus. 

The  branches  (jf  the  siiperficial  part  of  the  nerve  are  : — 

1.  An  articular  branch  to  the  hip-joint  which  arises  from  the  nerve  as  soon  as 
it  enters  the  thigh,  and  supplies  the  joint  through  the  acetabular  notch. 


Obturator  nervk 


Psoas  magnus  ,\\ 

Branch  to  hip-joint 
Deep  branch 

Superficial  branch Luri^s^ 

Descending  muscular  brandies 


Ascending  branch  to  obturator 
externus 


Internal  circumflex  arterj 
Adductor  longu^ 


Pyriforniis 

Gluteus  inaximus 
Pelvic  fascia 
Obturator  internus 
Obturator  externus 

^?^J>^^V^Ischium 

Ascending  branch  of  internal 
circumflex  artery 
Quadratus  femoris 
Internal  circumflex  artery 


Descending  muscular  branches 
Adductor  magnus 


Branch  to  knee-joint 


Branch  to  femoral  artery  Gracilis 

Fig.  506. — Scheme  of  the  Course  and  Djstribution  of  the  Obturator  Nerve. 

2.  Muscular  branches  to  the  adductor  longus,  gracilis,  adductor  brevis  (usually), 
pectineus  (occasionally).  The  last-named  muscle  is  not  usually  supplied  from  the 
obturator  nerve. 

3.  A  cutaneous  branch  of  very  variable  size  forms  one  of  the  terminal  branches 
(Eig.  507).  It  becomes  superficial  between  the  gracilis  and  adductor  longus,  in  the 
middle  third  of  the  thigh,  and  may  supply  the  skin  of  the  lower  two-thirds  of  the 
thigh  in  its  inner  side.  It  is  generally  of  small  size,. and  is  connected  with 
branches  of  the  internal  cutaneous  and  internal  saphenous  nerves  behind  the 
sartorius  muscle  to  form  the  obturator  (sub-sartorial)  plexus.  The  branch  from  the 
internal  saphenous  nerve  to  the  plexus  passes  inwards  behind  the  sartorius  after 
piercing  the  aponeurotic  covering  of  Hunter's  canal.  The  branch  from  the  internal 
cutaneous  nerve  is  generally  superficial  at  the  point  of  formation  of  the  plexus. 

4.  The  branch  to  the  femoral  artery  is  the  other  terminal  branch  of  the 
nerve.  It  enters  Hunter's  canal  along  the  inner  edge  of  the  adductor  longus,  and 
ramifies  over  the  lower  part  of  the  artery. 

5.  A  fine  communicating  branch  sometimes  joins  the  anterior  crural  nerve  in 
front  of  the  hip-joint. 

The  deep  part  of  the  obturator  nerve  reaches  the  thigh  by  piercing  the 


ANTERIOR  CRURAL  NERVE. 


645 


obturator  extern  us  muscle.  It  passes  downwards  between  the  adductor  brevis  and 
adductor  magnus  muscles.  After  passing  obliquely 
through  the  adductor  magnus,  it  appears  in  the  popliteal 
spaceonthe  popliteal  vessels,  and  terminates  byxDiercing 
the  posterior  ligament  and  supplying  the  knee-joint. 
Its  branches  are : — (1)  muscular  "branches  to  the 
obturator  externus,  adductor  magnus,  and  (when  the 
muscle  is  not  supplied  by  the  superficial  part  of  the 
nerve)  the  adductor  brevis.  The  branch  to  the  obturator 
externus  arises  before  the  nerve  enters  the  muscle,  in 
the  obturator  groove.  The  nerve  to  the  adductor 
magnus  is  given  off  as  the  obturator  nerve  passes 
through  the  substance  of  the  muscle.  (2)  An  articular 
terminal  branch  is  supplied  to  the  back  of  the  knee-joint. 

Anteeioe  Crural  Nerve. 

The  anterior  crural  nerve  (n.  femoralis)  is  the 
great  nerve  for  the  muscles  and  skin  of  the  front  of 
the  thigh.  It  arises  in  the  substance  of  the  psoas 
muscle,  from  the  back  of  the  second,  third,  and  fourth 
lumbar  nerves,  behind  the  obturator  nerve.  Passing 
obhquely  through  the  psoas  muscle,  it  emerges  from 
its  outer  border  in  the  false  pelvis  (Fig.  505,  p.  641). 
Passing  downwards  in  the  groove  between  the  psoas 
and  iliacus,  it  enters  the  thigh  beneath  Poupart's  liga- 
ment, external  to  the  femoral  sheath  and  femoral 
vessels.  In  Scarpa's  triangle  it  breaks  up  into  a  large 
number  of  branches,  among  which  the  external  cir- 
cumflex artery  passes. 

The  branches  of  the  anterior  crural  nerve,  which 
are  (1)  muscular,  (2)  articular,  and  (3)  cutaneous, 
arise  in  the  following  way : — 

In  the  abdomen  a  muscular  branch  arises  from 
the  outer  side  of  the  nerve  and  enters  the  iliacus 
muscle. 

In  Scarpa's  triangle  the  terminal  muscular, 
articular,  and  cutaneous  branches  arise  in  the  form 
of  a  large  bundle  of  nerves. 

1.  The   muscular  branches   supply  the  pectineus.  Fig.  507.- Distribution   of   Cuta- 

,.  T  T-  ,  rm  j_j.i  NEOus  Nerves  on    the  Front  of 

sartorius,  and  quadriceps  extensor,     ihe  nerve  to  the      ^^^  lower  Limb. 

pectineus  arises  close  to  Poupart's  ligament,  and  ^^^  ^he  one  side  the  distribntion  of  the 
coursing  obliquely  downwards  and  inwards  behind 
the  femoral  vessels  enters  the  muscle  at  its  outer 
border.  It  is  not  infrequently  double.  It  some- 
times gives  off  a  fine  communicating  branch  to  the 
superficial  part  of  the  obturator  nerve.  The  nerves 
to  the  sartorius  are  in  two  sets  :  an  outer  short  set  of 
nerves  associated  with  the  outer  part  of  the  middle 
cutaneous  nerve,  which  enter  the  upper  part  of  the 
muscle ;  and  an  inner  longer  set  which  are  associated 
with  the  inner  part  of  the  middle  cutaneous  nerve, 
and  supply  the  middle  of  the  muscle.  The  parts  of 
the  quadriceps  extensor  are  supplied  by  several 
branches.  The  vastus  externus  and  rectus  femoris 
are  supplied  on  their  dee])  surface  by  separate  nerves 
whicli  are  uccomjjanied  by  jjranches  of  the  external 
circumlliix  artery.  The  crureus  muscle  is  supplied 
superficially  by  a  nerve  which    passes    through   the 

muscle,  and  innervates  also  the  subcrureus.     It   also  receives  fibres  from  one  of 
45  5 


several    nerves    is    represented,  the 
letters  indicating  their  nomenclature. 

T.ll,  Branches  of  eleventh  thoracic 
nerve;  T.  12,  Branches  of  twelfth 
thoracic  nerve  ;  l.H,  Ilio-hypogastric ; 
I.I,  Uio-inguinal ;  E.C,  External  cuta- 
neous ;  G.  C,  Genito-crnral ;  M.C^,"^, 
Middle  cutaneous  ;  I.C^,''^,  Internal 
cutaneous  ;  Obt,  Obturator  ;  S.Sc, 
Small  sciatic  ;  Pat.  Plex,  Patellar 
plexus ;  Pat.  Patellar  branch  of 
internal  saphenous;  E. P.S,  Sural 
branches  of  peroneal  nerve  ;  I.  S, 
Internal  saplienous  ;  M.O,  Musculo- 
cutaneous ;  E.S, Externalsaphenous; 
A.T,  Anterior  tibial. 

On  the  other  side  a  schematic  repre- 
sentation is  given  of  the  areas  sup- 
plied by  the  above  nerves,  the  ligiires 
indicating  the  spinal  origin  of  the 
branches  of  distribution  to  each  area. 


646  THE  NEEVOUS  SYSTEM. 

the  nerves  to  the  vastus  interims.  The  vastus  internus  muscle  is  supplied  by  two 
nerves  :  an  upper  trunk,  which  supplies  the  higher  part  of  the  muscle,  and  sends  fibres 
to  the  crureus  as  well ;  and  a  lower  trunk,  which  descends  on  the  outer  side  of  the 
femoral  artery  along  with  the  internal  saphenous  nerve,  and  passing  beneath  the 
sartorius,  over  or  under  the  aponeurotic  covering  of  Hunter's  canal,  enters  the  inner 
side  of  the  vastus  internus  muscle.  This  nerve  gives  off  a  small  branch  which  enters 
the  medullary  canal  of  tlie  femur. 

2.  The  articular  branches  supply  the  hip  aiid  knee-joints.  The  articular  branch  to 
the  hip-joint  arises  from  the  nerve  to  the  rectus  femoris,  and  is  accompanied  by 
branches  from  the  external  circumflex  artery.  The  articular  branches  to  the  knee- 
joint  are  four  in  number.  Three  of  them  arise  from  the  nerves  to  the  vastus  externus, 
crureus,  and  vastus  internus,  which,  after  the  muscular  nerves  are  given  off,  are 
continued  downwards  to  the  knee-joint  along  the  front  of  the  femur.  A  fourth 
articular  branch  arises  (sometimes)  from  the  internal  saphenous  nerve. 

3.  The  cutaneous  branches  are  the  middle  and  internal  cutaneous,  and  the 
internal  saphenous  nerves  (Fig.  507). 

The  middle  cutaneous  nerve  arises  in  two  parts,  an  external  and  an  internal 
hranch,  in  the  upper  part  of  Scarpa's  triangle.  The  two  branches  descend  vertically 
and  become  cutaneous  by  piercing  the  fascia  lata  over  the  upper  third  of  the 
sartorius  muscle.  They  carry  muscular  branches  to  the  sartorius,  and  the  external 
branch  in  many  cases  pierces  the  muscle.  These  two  nerves  supply  the  skin  of 
the  lower  three-fourths  of  the  front  of  the  thigh,  between  the  external  cutaneous 
nerve  on  the  outer  side  and  the  internal  cutaneous  on  the  inner  side.  They 
reach  down  to  the  front  of  the  patella,  and  there  assist  in  the  formation  of  the 
patellar  plexus.  The  external  branch  communicates  in  the  upper  third  of  the 
thigh  with  twigs  from  the  crural  branch  of  the  genito-crural  nerve. 

The  internal  cutaneous  nerve  lies  at  first  in  Scarpa's  triangle  on  the  outer  side 
of  the  femoral  vessels.  At  the  apex  of  the  triangle  it  crosses  over  the  femoral  vessels, 
and  is  directed  downwards  over  or  through  the  sartorius  muscle,  and  beneath  the 
fascia  lata,  to  the  lower  third  of  the  thigh.  It  is  distributed  to  the  skin  of  the 
lower  two-thirds  of  the  thigh  on  the  inner  side  by  means  of  three  branches — upper, 
middle,  and  lower. 

The  wpper  branch  may  be  represented  by  two  or  more  twigs.  It  arises  from  the 
main  nerve  near  its  origin,  and  pierces  the  fascia  lata  near  the  apex  of  Scarpa's 
triangle.  It  is  distributed  to  the  skin  of  the  upper  part  of  the  thigh,  along  the 
line  of  the  saphenous  vein.  The  middle  or  anterior  branch  is  a  larger  nerve.  It 
separates  from  the  lower  branch  at  the  apex  of  Scarpa's  triangle,  and  passing  over 
the  sartorius  muscle  becomes  cutaneous  in  the  middle  third  of  the  thigh  on  the 
inner  side.  It  supplies  the  skin  of  the  lower  half  of  the  thigh  on  the  inner  side, 
extending  as  low  as  the  knee,  where  it  joins  in  the  formation  of  the  patellar  plexus. 

The  lower  or  internal  branch  represents  the  termination  of  the  nerve.  It  passes 
down  the  inner  side  of  the  thigh  over  the  sartorius  muscle,  and  communicates  in 
the  middle  third  of  the  thigh  with  the  internal  saphenous  and  obturator  nerves  to 
form  the  obturator  plexus.  Piercing  the  fascia  lata  on  the  inner  side  of  the  thigh 
in  the  lower  third,  it  ramifies  over  the  inner  side  of  the  knee,  and  assists  in  the 
formation  of  the  patellar  plexus. 

The  size  of  the  internal  cutaneous  nerve  varies  with  the  size  of  the  cutaneous 
part  of  the  obturator,  and  of  the  internal  saphenous  nerve. 

The  long  or  internal  saphenous  nerve  (n.  saphenus)  may  be  regarded  as  the 
terminal  branch  of  the  anterior  crural  nerve.  It  is  destined  for  the  skin  of  the  leg 
and  foot.  From  its  origin  in  Scarpa's  triangle  it  descends  alongside  the  femoral 
vessels  to  Hunter's  canal.  In  the  canal  it  crosses  over  the  femoral  sheath  from 
without  inwards.  At  the  lower  end  of  the  canal,  accompanied  by  the  superficial 
branch  of  the  anastomotic  artery,  it  passes  over  the  tendon  of  the  adductor  magnus, 
and  opposite  the  inner  side  of  the  knee-joint  becomes  cutaneous  by  passing  between 
the  sartorius  and  gracilis  muscles.  The  nerve  then  extends  down  the  leg  along 
with  the  internal  saphenous  vein,  and  coursing  over  the  front  of  the  inner  ankle  it 
terminates  at  the  middle  of  the  inner  border  of  the  foot. 

Branches. — 1.  A  communicating  branch  arises  in  Hunter's  canal,  and  passing 


THE  SACRAL  OR  SCIATIC  PLEXUS.  647 

inwards  beneath  the  sartorius  joins  with  branches  of  the  obturator  nerve  in  forming 
the  obturator  plexus. 

2.  The  patellar  branch  arises  at  the  lower  end  of  Hunter's  canal,  and  piercing  the 
sartorius  muscle  is  directed  downwards  and  forwards  below  the  patella,  and  over 
the  inner  tuberosity  of  the  tibia  to  the  front  of  the  knee  and  upper  part  of  the 
leg.     It  enters  into  the  formation  of  the  patellar  plexus. 

3.  An  articular  branch  sometimes  arises  from  the  nerve  at  the  inner  side  of  the  knee. 

4.  The  terminal  branches  of  the  internal  saphenous  nerve  are  distributed  to  the 
skin  of  the  front  and,  inner  side  of  the  leg,  and  the  posterior  half  of  the  dorsum 
and  inner  side  of  the  foot. 

Patellar  plexus. — This  plexus  consists  of  fine  communications  beneath  the 
skin  in  front  of  the  knee,  between  the  branches  of  the  cutaneous  nerves  supplying 
that  region.  The  nerves  which  enter  into  its  formation  are  the  patellar  branch  of 
the  internal  saphenous,  internal  and  middle  cutaneous  nerves,  and  sometimes  the 
external  cutaneous  nerve. 

The  accessory  obturator  nerve  (n.  obturatoriiis  accessorius,  n.  accessorius  anterioris  cniralis 
Winslow)  is  only  occasionally  present  (29  per  cent,  Eisler).  It  arises  from  the  third,  or  third  and 
fourth  lumbar  nerves,  between  the  roots  of  the  obturator  and  anterior  crural  nerves.  Associating 
itself  with  the  obturator,  from  which,  however,  it  is  quite  separable,  it  appears  in  the  abdomen 
at  the  inner  side  of  the  psoas  muscle,  and  coursing  over  the  pelvic  brim  behind  the  external  iliac 
vessels,  it  leaves  the  obturator  nerve,  and  enters  the  thigh  in  front  of  the  pubis. 

In  the  thigh,  behind  the  femoral  vessels,  it  usually  ends  in  three  branches :  a  nerve  which 
replaces  the  branch  from  the  anterior  crural  to  the  j)ectineus,  a  nerve  to  the  hip -joint,  and  a 
nerve  which  communicates  with  the  superficial  part  of  the  obturator  nerve.  In  some  cases  it 
only  supj)lies  the  nerve  to  the  pectineus  ;  more  rarely  it  is  of  considerable  size,  and  reinforces  the 
obturator  nerve  in  the  innervation  of  the  adductor  muscles. 

The  accessory  obturator  nerve  was  first  described  by  Winslow  as  the  ii.  accessorius  anterioris 
cruralis.  Schmidt  later  described  it  in  great  detail,  and  gave  it  the  name  it  now  bears.  It  is 
more  closely  associated  with  the  anterior  crural  than  with  the  obturator.  Its  origin  is  behind 
the  roots  of  the  obturator :  it  is  separated,  like  the  anterior  crural,  from  the  obturator  by  the 
pubic  bone,  and  its  chief  branch,  to  the  pectineus  muscle,  replaces  the  normal  branch  from  the 
anterior  crural  nerve.  On  the  other  hand,  for  a  part  of  its  course  it  accompanies  the  obturator, 
and  in  rare  cases  it  may  rejDlace  branches  of  that  nerve. 

THE  SACRAL  OR  SCIATIC  PLEXUS. 

The  sacral  or  sciatic  portion  of  the  lumbo-sacral  plexus  is  destined  almost 
entirely  for  the  lower  limb.  It  is  usually  formed  by  the  anterior  primary  divisions 
of  a  part  of  the  fourth  lumbar  nerve  (n.  furcalis),  the  fifth  lumbar,  the  first,  and 
parts  of  the  second,  and  third  sacral  nerves  (u.  bigeminus). 

Communications  with  the  Sympathetic. — Each  of  the  nerves  named  is  connected 
to  the  lumbar  or  pelvic  sympathetic  by  gray  rami  communicantes,  as  already  described  ; 
and  tvhite  I'ami  communicantes  pass  usually  from  the  third  and  usually  also  from  the 
second  or  fourth  sacral  nerves  to  join  the  pelvic  plexus  of  the  sympathetic. 

Position  and  Constitution.- — ^The  plexus  is  placed  on  the  back  wall  of  the 
pelvis  between  the  parietal  pelvic  fascia  and  the  pyriformis  muscle.  In  front  of  it 
are  the  pelvic  colon,  the  internal  iliac  vessels,  and  the  ureter. 

The  plexus  is  constituted  by  the  convergence  of  the  nerves  concerned  towards 
the  lower  part  of  the  great  sacro-sciatic  foramen,  and  their  union  to  form  a  broad 
triangular  band,  the  apex  of  which  is  continued  through  the  great  sacro-sciatic 
foramen  below  the  pyriformis  muscle  into  the  buttock,  as  the  great  sciatic  nerve. 
From  the  anterior  and  posterior  surfaces  of  this  triangular  band  numerous  small 
branches  arise,  which  are  distributed  to  the  parts  in  the  neighbourhood  of  the 
origin  of  the  nerve. 

The  great  sciatic  nerve  ends  in  the  thigh  by  dividing  into  two  large  nerves,  the 
tibial  ^internal  popliteal),  and  peroneal  (external  popliteal).  In  many  cases  these 
two  nerves  are  distinct  from  their  origin,  and  are  separated  sometimes  by  fibres 
of  the  pyriformiH  muscle.  In  all  cases  on  removal  of  the  sheath  investing  the 
great  sciatic  nerve  the  tibial  and  peroneal  nerves  can  be  traced  up  to  the  plexus, 
from  which  they  invariably  take  origin  by  distinct  and  separate  roots. 

The  (JfiHccMding  branch  of  the  fourth  lumbar  nerve  (n.  furcalis)  after  emergiug 
from  the  inner  border  of  the  psoas  muscle  iiit(!riia]  to  the  ol)turator  nerve,  divides 


648  THE  NEEVOUS  SYSTEM. 

behind  the  iUac  vessels  into  anterior  and  posterior  (ventral  and  dorsal)  parts,  each 
of  which  joins  a  corresponding  part  of  the  fifth  lumbar  nerve.  The  anterior 
primary  division  of  the  fifth  lumbar  nerve  descends  over  the  ala  of  the  sacrum,  and 
divides  into  anterior  and  posterior  parts,  which  are  joined  by  the  corresponding  parts 
of  the  fourth  lumbar  nerve.  The  two  resulting  trunks  are  sometimes  called  the 
lumbo-sacral  cord.  The  first  and  second  sacral  nerves  pass  almost  horizontally  out- 
wards from  the  anterior  sacral  foramina,  and  divide  in  front  of  the  pyriformis  into 
similar  anterior  and  posterior  parts.  The  third  sacral  nerve  (n.  bigeminus)  divides 
into  upper  and  lower  parts.  The  lower  part  is  concerned  in  forming  the  pudendal 
plexus.  The  upper  part  is  directed  outwards,  and  slightly  upwards,  towards  the 
preceding  nerve,  and  does  not  separate  into  two  parts,  but  remains  undivided. 

These  trunks  combine  to  form  the  sciatic  or  sacral  plexus,  and  its  main  sub- 
divisions, in  the  following  way.  Lying  in  apposition,  and  converging  to  the  lower 
part  of  the  great  sacro-sciatic  foramen,  the  posterior  (dorsal)  trunks  of  the  fourth  and 
fifth  lumbar  nerves  (lumbo-sacral  cord),  and  of  the  first  and  second  sacral  nerves, 
combine  to  form  the  peroneal  nerve  and  the  subordinate  nerves  which  arise  from  the 
posterior  aspect  of  the  plexus.  The  anterior  (ventral)  trunks  of  the  fourth  and  fifth 
lumbar  nerves  (lumbo-sacral  cord),  and  of  the  first  and  second  sacral  nerves,  together 
with  that  part  of  the  third  sacral  nerve  which  is  contributed  to  the  plexus,  unite  to 
form  the  tibial  nerve  and  the  subordinate  nerves  arising  from  the  front  of  the  plexus. 
Of  these  nerves  the  fifth  lumbar  and  first  sacral  are  the  largest ;  the  others 
diminishing  in  size  as  they  are  traced  upwards  and  downwards.  There  is  no 
distinct  demarcation  between  the  sacral  and  pudendal  plexuses.  The  second  and 
third  sacral  nerves  (and  in  some  cases  the  first  sacral  also)  are  concerned  in  the 
formation  of  both  plexuses. 

Branches.  —  The  nerves  of  distribution  derived  from  the  sacral  plexus  are 
divided  according  to  their  origin  into  an  anterior  (ventral)  and  a  posterior  (dorsal) 
series.     Each  set  comprises  one  of  the  two  essential  terminal  parts — peroneal  and 
tibial  nerves — of  the  great  sciatic,  and  numerous  smaller  collateral  branches. 
Anterior  Branches.  Posterior  Branches. 

Tibial  (internal  popHteal)  nerve  Peroneal  (external  popliteal)  nerve 

Muscular  branches —  Muscidar  branches — 

Nerves  to  hamstring  muscles  Nerves  to  short  head  of  biceps 

„  quadratus  femoris  „  pyriformis 

„  gemelli  Superior  gluteal  nerve 

„  obturator  internus  Inferior  gluteal  nerve 

Articular  branches  (to  hip-joint)  Articular  branches  (to  knee-joint) 

GrEEAT  Sciatic  Nerve. 

The  great  sciatic  nerve  (n.  ischiadicus). — It  has  already  been  shown  how 
this  nerve  is  formed.  It  comprises  the  two  main  nerves  of  the  sacral  plexus,  bound 
together  by  an  investing  sheath,  which  contains,  in  addition  to  the  peroneal  and 
tibial  nerves,  a  subordinate  branch  of  each,  the  nerve  to  the  hamstring  muscles, 
from  the  tibial,  and  the  nerve  to  the  short  head  of  the  biceps  flexor  cruris,  from 
the  peroneal  nerve.  A  thick  band  about  half  an  inch  in  breadth  is  formed,  con- 
sisting from  within  outwards  of  (1)  nerves  to  the  hamstring  muscles,  (2)  tibial 
(internal  popliteal),  (3)  peroneal  (external  popliteal),  (4)  nerve  to  the  short  head  of  the 
biceps  muscle.  The  great  sciatic  nerve  extends  through  the  buttock  and  the  back 
of  the  thigh.  Forming  a  continuation  of  the  sacral  plexus,  it  enters  the  buttock 
by  passing  through  the  great  sacro-sciatic  foramen,  in  the  interval  between  the 
pyriformis  and  superior  gemellus.  Concealed  by  the  gluteus  maximus  muscle,  it 
passes  downwards  to  the,  thigh,  accompanied  by  the  sciatic  artery,  and  the  arteria 
comes  nervi  ischiadici.  It  lies  in  the  hollow  between  the  great  trochanter  of  the 
femur  and  the  tuberosity  of  the  ischium,  and  enters  the  thigh  beneath  the  fold  of  the 
nates  at  the  lower  border  of  the  gluteus  maximus.  At  this  spot  it  is  comparatively 
superficial,  lying  in  the  angle  between  the  edge  of  the  gluteus  maximus  above  and 
externally,  and  the  origins  of  the  hamstring  muscles  internally.  In  the  thigh  it 
is  placed  upon  the  adductor  magnus  beneath  the  hamstring  muscles,  and  it 
terminates  at  a  variable  point  by  dividing  into  the  tibial  and  peroneal  nerves.     As 


NEEVES  OF  DISTEIBUTION  FROM  THE  SACKAL  PLEXUS.     649 

already  stated,  these  two  nerves  may  be  separate  from  their  origins,  and  their 
separation  may  occur  at  any  point  between  the  great  sacro-sciatic  foramen  and  the 
upper  part  of  the  popliteal  space. 

The  Nerves  of  Distkibution  from  the  Sacral  Plexus. 

These  are  divisible  into  two  series — collateral  and  terminal  branclies.  Each 
subdivision  consists  of  a  series  of  anterior  (ventral)  and  posterior  (dorsal)  trunks. 

Collateral  Branches. — The  anterior  Iranches  are  (a)  muscular  branches  (to  the 
quadratus  femoris,  gemelli,  obturator  internus,  and  hamstring  muscles) ;  and  (Jb) 
articular  branches  (to  the  hip -joint).  These  nerves  all  arise  from  the  anterior 
aspect  of  the  sacral  plexus. 

The  nerve  to  the  quadratus  femoris  (and  inferior  gemellus)  arises  from  the 
front  of  the  fourth  and  fifth  lumbar  and  first  sacral  nerves.  It  passes  downwards 
over  the  back  of  the  capsule  of  the  hip-joint  (to  which  it  sends  a  fine  branch)  beneath 
the  sacral  plexus,  gemelli,  and  obturator  internus  muscles.  It  supplies  a  nerve  to 
the  inferior  gemellus,  and  terminates  in  the  deep  surface  of  the  quadratus  femoris. 

The  nerve  to  the  obturator  internus  (and  superior  gemellus)  arises  from  the 
anterior  aspect  of  the  fifth  lumbar  and  first  two  sacral  nerves.  In  the  buttock  it 
lies  below  the  great  sciatic  nerve  on  the  outer  side  of  the  pudic  vessels ;  crossing 
the  ischial  spine,  it  enters  the  ischio-rectal  fossa  through  the  lesser  sciatic  foramen. 
The  nerve  supplies  in  the  buttock  a  branch  to  the  superior  gemellus,  and  terminates 
by  entering  the  pelvic  surface  of  the  obturator  internus. 

The  nerve  to  the  hamstring  muscles  forms  the  innermost  part  of  the  great 
sciatic  trunk  in  the  lower  part  of  the  buttock.  It  arises  from  all  the  roots  of  the 
tibial  nerve  on  their  anterior  aspect,  viz.,  from  the  fourth  and  fifth  lumbar  and 
the  first  three  sacral  nerves.  These  roots  unite  to  form  a  cord  which  is  closely 
associated  with  the  tibial  nerve  and  is  placed  in  front  of  and  afterwards  on  its 
inner  side.  Extending  into  the  thigh,  the  trunk  is  distributed  to  the  hamstring 
muscles  by  means  of  two  sets  of  branches.  Just  below  the  level  of  the  ischial 
tuberosity  an  upper  set  of  nerves  passes  inwards  to  enter  the  upper  part  of  the 
semi-tendinosus  and  the  ischial  head  of  the  biceps.  Lower  down  in  the  thigh  the 
remaining  portion  of  the  nerve  separates  off  from  the  great  sciatic  (tibial)  trunk 
and  supplies  branches  to  the  semi-membranosus,  the  lower  part  of  the  semi-tendi- 
nosus, and  the  adductor  magnus. 

Articular  branches  for  the  hip-joint  arise  from  the  nerve  to  the  quadratus 
femoris,  and  often  directly  from  the  front  of  the  great  sciatic  (tibial)  nerve  near  its 
origin.     They  enter  the  back  of  the  capsule  of  the  joint  in  the  region  of  the  buttock. 

The  'posterior  tranches  are  :  (a)  muscular  branches,  viz.  a  nerve  to  the  pyriformis, 
the  superior  gluteal  nerve,  the  inferior  gluteal  nerve,  and  a  nerve  to  the  short  head 
of  the  biceps ;  (b)  articular  branches  (to  the  knee-joint). 

These  nerves  all  arise  from  the  posterior  aspect  of  those  roots  of  the  sacral 
plexus,  which  are  associated  with  the  origin  of  the  peroneal  nerve. 

The  nerve  to  the  pyriformis  muscle  may  be  double.  It  arises  from  the  back 
of  the  second,  or  first  and  second  sacral  nerves,  and  at  once  enters  the  anterior 
surface  of  the  muscle. 

The  superior  gluteal  nerve  (n.  gluteus  superior)  arises  from  the  back  of  the 
fourth  and  fifth  lumbar  and  first  sacral  nerves,  and  is  directed  backwards  and 
outwards  into  the  buttock,  above  the  pyriformis  muscle,  along  with  the  gluteal 
artery.  Under  cover  of  the  gluteus  maximus  and  gluteus  medius,  it  extends 
outwards  over  the  gluteus  minimus,  along  with  the  inferior  part  of  the  deep  gluteal 
artery,  to  the  under  surface  of  the  tensor  vaginae  femoris,  in  which  it  ends.  On 
its  way  it  supplies  branches  to  the  gluteus  medius  and  gluteus  minimus. 

The  inferior  gluteal  nerve  (n.  glutaeus  inferior)  arises  from  the  back  of  the  fifth 
lumbar  and  first  two  sacral  nerves.  It  appears  in  the  buttock  at  the  lower  border 
of  the  pyriformis  muscle,  superficial  to  the  great  sciatic  nerve,  and  at  once  breaks 
up  into  a  number  of  branches  for  the  supply  of  the  gluteus  maximus.  In  its  course 
in  the  Imttock  it  is  closely  associated  with  the  small  sciatic  nerve.  Its  origin  is 
sometimes  combined  with  that  of  the  following  nerve. 

The  nerve  to  the  short  head  of  the  biceps  springs  irom  the  outer  side  of  the 


650  THE  NEEVOUS  SYSTEM. 

great  sciatic  (peroneal)  trunk  in  the  upper  part  of  the  thigh.  When  traced  to  its 
origin,  it  is  found  to  arise  (sometimes  in  combination  with  the  inferior  gluteal  nerve) 
from  the  fifth  lumbar  and  first  two  sacral  nerves.  In  its  course  it  is  closely 
applied  to  the  outer  side  of  the  peroneal  nerve,  from  which  it  separates  in  the 
middle  third  of  the  thigh,  usually  in  combination  with  the  articular  branches  of 
that  nerve  for  the  knee-joint.  In  some  cases  it  has  an  independent  course  in  the 
thigh,  and  it  may  be  associated  in  the  buttock  with  the  inferior  gluteal  nerve. 

An  articular  branch  for  the  outer  side  and  i'ront  of  the  knee-joint  generally 
arises  from  the  great  sciatic  or  peroneal  nerve  in  common  with  the  nerve  to  the 
short  head  of  the  biceps.  When  traced  up  to  the  plexus,  it  is  found  to  arise  from 
the  back  of  the  fourth  and  fifth  lumbar  and  first  sacral  nerves.  It  passes  through 
the  upper  part  of  the  popliteal  space  concealed  by  the  biceps  muscle,  and  separates 
into  upper  and  lower  branches,  which  accompany  the  upper  and  lower  external 
articular  arteries  to  the  outer  side  of  the  knee-joint. 

Terminal  Branches. — ^The  peroneal  (external  popliteal)  and  tibial  (internal 
popliteal)  nerves  are  the  two  main  trunks  resulting  from  the  combination  of  the 
posterior  and  anterior  cords  respectively  of  the  sacral  plexus.  The  peroneal  nerve 
is  homologous  with  the  musculo-spiral  nerve  in  the  upper  limb  ;  the  tibial  nerve 
represents  a  medio-ulnar  trunk  ;  and,  as  already  stated,  the  two  nerves,  constituting 
the  great  sciatic  nerve,  are  enveloped  in  a  common  sheath  for  a  variable  distance 
before  pursuing  an  independent  course  in  the  leg. 

Peroneal  Nerve. 

The  peroneal  or  external  popliteal  nerve  (n.  peronteus  communis)  arises  from 
the  back  of  the  sacral  plexus  from  the  fourth  and  fifth  lumbar  and  first  two 
sacral  nerves.  Incorporated  with  the  great  sciatic  nerve  in  the  buttock  and 
upper  half  of  the  thigh,  it  passes  downwards  from  the  bifurcation  of  that  nerve 
through  the  popliteal  space,  to  its  termination  at  a  point  about  an  inch  below  the 
head  of  the  fibula.  It  is  concealed  at  first  by  the  biceps  muscle.  Following 
the  tendon  of  that  muscle,  it  passes  obliquely  through  the  upper  and  outer  part 
of  the  popliteal  space  and  over  the  outer  head  of  the  gastrocnemius  muscle  to  the 
back  of  the  head  of  the  fibula.  1  n  the  lower  part  of  its  course  and  at  its  termination 
it  is  directly  beneath  the  deep  fascia. 

Collateral  Branches. — These  are  divided  into  two  sets  :  («)  Nerves  arising  from 
the  roots  or  trunk  of  the  nerve  while  it  is  in  combination  with  the  tibial  nerve  in 
the  great  sciatic  trunk.  These  have  been  already  described,  viz.  a  muscular  branch 
to  the  short  head  of  the  biceps,  and  an  articular  branch  to  the  knee-joint,  (b)  Nerves 
arising  in  the  popliteal  space.  These  are  cutaneous  branches,  viz.  a  sural  branch  and 
the  peroneal  communicating. 

The  sural  branch  (n.  cutaneus  sura3  lateralis)  is  irregular  in  size  and  distribution, 
and  may  be  represented  by  two  or  more  branches  (Fig.  507,  p.  645).  Arising  from 
the  peroneal  nerve  in  the  popliteal  space,  often  in  common  with  the  succeeding 
nerve,  it  pierces  the  deep  fascia  over  the  outer  head  of  the  gastrocnemius,  and  is 
distributed  to  the  skin  on  the  outer  aspect  of  the  back  of  the  leg  in  the  upper 
two-thirds.  The  extent  of  its  distribution  varies  with  that  of  the  small  sciatic 
and  external  saphenous  nerves. 

The  peroneal  communicating  nerve  (r.  anastomoticus  peronteus,  r.  communicans 
fibuiaris),  arising  in  the  popliteal  space,  passes  over  the  outer  head  of  the  gastro- 
cnemius beneath  the  deep  fascia  to  the  middle  third  of  the  leg,  where  it  assists  in 
forming  the  external  saphenous  nerve  by  its  union  with  the  tibial  communicating 
branch  of  the  tibial  nerve.  In  many  cases  the  two  branches  do  not  unite.  In  such 
cases  the  peroneal  communicating  nerve  may  be  limited  in  its  distribution  to  the 
skin  of  the  outer  side  of  the  leg,  heel,  and  ankle,  or  it  may  be  distributed  to  the 
area  usually  supplied  by  the  external  saphenous  nerve. 

Terminal  Branches.  —  The  terminal  branches  of  the  peroneal  nerve  are 
recurrent  tibial,  anterior  tibial,  and  musculo-cutaneous.  They  arise  just  below 
the  head  of  the  fibula,  and  are  directed  forwards,  diverging  in  their  course, 
beneath  the  peroneus  longus  muscle. 

The  recurrent  tibial  nerve  is  the  smallest  branch.     Passing  forwards  beneath 


MUSCULO-CUTANEOUS  NEIiVE. 


651 


the  origin  of  the  peroneus  longus  aud  the  extensor  longus  digitorum  muscles,  it 
divides  below  the  outer  tuberosity  of  the  tibia  into  branches  which  supply  the  upper 
fibres  of  the  tiliialis  anticus  muscle,  the  tibio-fibular  articulation,  and  the  knee-joint. 

Antepjoii  Tibial  Nerve. 

The  anterior  tibial  nerve  (n.  peroneeus  profundus;  passes  downwards  and  in- 
wards, beneath  the  peroneus  longus,  extensor  longus  digitorum,  and  extensor  proprius 
hallucis  muscles,  to  the  front  of  the  leg.  In  its  course  down  the  leg  it  is  deeply 
placed  upon  the  interosseous  membrane  and  the  lower  part  of  the  tibia,  in  company 
with  the  anterior  tibial  artery.  At  the  ankle  it  lies  beneath  the  anterior  annular 
ligament  and  the  tendon  of  the  extensor  proprius  hallucis,  and  crossing  over  the 
ankle-joint,  it  divides  on  the  dorsum  of  the  foot  into  its  terminal  branches. 

1.  Collateral  Branches  (in  the  leg). — These  are  given  off  to  the  muscles  between 
which  the  anterior  tibial  nerve  passes :  tibialis  anticus,  extensor  proprius  hallucis, 
extensor  longus  digitorum,  and  peroneus  tertius.  A  fine  articular  branch  supplies 
the  ankle-joint. 

2.  Terminal  Branches  (on  the  foot). — -The  terminal  branches  are  internal  and 
external.  The  internal  branch  passes  along  the  dorsum  of  the  foot  on  the  outer 
side  of  the  dorsalis  pedis  artery  to  the  first  interosseous  space,  where  it  divides  into 
two  dorsal  digital  branches  for  the  supply  of  the  skin  of  the  outer  side  of  the  great 
toe  and  the  inner  side  of  the  second  toe.      Each  of  these 

branches  communicates  with  branches  of  the  musculo- 
cutaneous nerve.  It  gives  off  one  or  two  dorsal  inter- 
osseous tranches,  which  supply  the  inner  tarso-metatarsal 
and  metatarso-phalangeal  articulations,  and  also  enter  the 
first  dorsal  interosseous  muscle. 

The  external  brancli  passes  outwards  over  the  tarsus 
beneath  the  extensor  brevis  digitorum,  and  ends  in  a 
gangliform  enlargement  (similar  to  the  gangliform  enlarge- 
ment on  the  posterior  interosseous  nerve  at  the  back  of  the 
wrist).  Erom  this  enlargement  muscular  branches  arise 
for  the  supply  of  the  extensor  brevis  digitorum,  along  with 
branches  for  the  tarsal,  tarso-metatarsal,  and  metatarso- 
phalangeal articulations.  Its  dorsal  interosseous  branches 
may  be  as  many  as  four  in  number.  Of  these  the  outer  two, 
extremely  small,  may  only  reach  the  tarso-metatarsal 
articulations.  The  inner  two  are  fine  branches,  which, 
besides  supplying  the  articulations,  may  give  branches  to 
the  second  and  third  dorsal  interosseous  muscles. 

The  branches  from  the  anterior  tibial  nerve  to  the 
interosseous  muscles  are  probably  sensory,  the  motor  supply 
of  these  muscles  being  certainly  derived  from  the  external 
plantar  nerve. 

MUSCULO-CUTANEOUS    NeRVE. 

The  musculo-cutaneous  nerve  (n.  peronasus  super-  fig.  508.— distribution  of 
ficialis),  the  last  of  the  branches  of  the  peroneal  nerve.  Cutaneous  Nerves  on 
passes  below  the  head  of  the  fibula  and  beneath  the  upper     p^^^^        '  '  ™^ 

fibres  of  the  peroneus  longus  muscle.     Lying  in  a  sheath  in  j,.^  internal  saphenous  nerve  ; 
the  intermuscular  septum,  Ijetween  the  peronei  externally     m.c,    Musculo  -  cutaneous 
and  the  extensor   longus  digitorum  internally,  it  proceeds 
downwards  in   front   of  the   fibula  to  the  lower   third   of 
the  leg,  where  it  pierces  the  deep  fascia  in  two  branches, 
internal  and  external. 

Its  branches  are :  (i)  collateral  muscular  branches  dis- 
tributed to  th(!  peroneus  longus  and  ])eroneus  brevis,  as  the   nerve  lies  in  relation 
to  thew!  muscles ;  (2)  terminal  cutaneous  branches,  internal  and  external. 

The  internal  terminal  branch  courses  downwards  over  the  anterior  annular  liga- 


nerve  ;  A.T,  Anterior  tibial 
nerve  ;  E.S,  External  sa- 
phenous nerve.  The  ex- 
tremities of  the  toes  are 
supplied  by  the  plantar 
nerves  (I.P,  E.P). 


652  THE  NERVOUS  SYSTEM. 

ment  of  the  ankle,  and  after  supplying  offsets  to  the  lower  third  of  the  leg  and  dorsum 
of  the  foot,  divides  into  three  branches.  (1)  The  internal  Ijranch  supplies  the  skin 
of  the  dorsum  of  the  foot  and  the  inner  side  of  the  great  toe,  and  communicates 
with  the  internal  saphenous  nerve.  (2)  The  intermediate  branch  passes  to  the 
interval  between  the  great  toe  and  the  second,  and  divides  into  two  branches  which 
communicate  with  the  internal  branch  of  the  anterior  tibial  nerve.  (3)  Tlie 
external  branch  passes  to  the  interval  between  the  second  and  third  toes,  and 
divides  into  two  digital  branches  to  supply  the  adjacent  sides  of  these  toes. 

The  external  terminal  brancli  of  the  nerve  descends  over  the  anterior  annular 
ligament,  and  after  supplying  branches  to  the  lower  part  of  the  leg  and  the 
dorsum  of  the  foot,  divides  into  two  parts,  internal  and  external,  which,  passing  to 
the  intervals  between  the  third  and  fourth,  and  fourth  and  fifth  toes  respectively, 
divide  into  dorsal  digital  branches  for  the  adjacent  sides  of  these  toes.  These 
branches  communicate  with  offsets  of  the  external  saphenous  nerve. 

The  arrangement  of  the  cutaneous  branches  of  the  musculo-cutaneous  is  liable  to  considerable 
variation.  The  outer  division  of  the  nerA'e  may  be  increased  in  size,  and  may  supply  the  nerve 
to  the  adjacent  sides  of  the  second  and  third  toes  ;  or  in  other  cases,  it  may  be  reduced  in  size,  in 
which  case  the  external  saphenous  nerve  takes  its  place  on  the  dorsum  of  the  foot,  often  supplying 
as  many  as  two  and  a  half  toes  on  the  oiiter  side. 

The  cutaneous  nerves  on  the  dorsum  of  the  toes  from  the  anterior  tibial  and  musculo-cutaneous 
nerves  are  much  smaller  than  the  corresponding  plantar  digital  nerves.  They  are  reinforced  on 
the  dorsum  of  the  terminal  phalanges  by  twigs  from  the  plantar  nerves,  which  supply  the  tips  of 
the  toes  and  the  nails. 

Tibial  Nerve. 

The  tibial  or  internal  popliteal  nerve  (n.  tibialis)  arises  from  the  front  of 
the  sacral  plexus,  usually  from  the  fourth  and  fifth  lumbar  and  first  three  sacral 
nerves  (Fig.  511,  p.  656).  It  is  incorporated  in  the  great  sciatic  trunk  in  the 
buttock  and  upper  part  of  the  thigh.  At  the  bifurcation  of  the  great  sciatic  nerve 
it  passes  onwards  through  the  popliteal  space  and  the  back  of  the  leg.  The  part 
of  the  nerve  from  its  origin  from  the  plexus  or  the  bifurcation  of  the  great  sciatic 
nerve  to  the  lower  border  of  the  popliteus  muscle,  is  sometimes  called  internal 
popliteal;  the  part  of  the  nerve  in  the  back  of  the  leg  being  then  designated 
posterior  tibial.  The  course  of  the  nerve  through  the  buttock  and  thigh  has  already 
been  described  (p.  648).  In  the  popliteal  space  it  is  concealed  at  first  by  the 
semi-mem branosus  and  other  hamstring  muscles.  It  crosses  the  popliteal  vessels 
from  without  inwards,  and  is  thereafter  found  upon  the  popliteus  muscle,  under 
cover  of  the  gastrocnemius  and  plantaris.  In  the  back  of  the  leg,  from  the  lower 
border  of  the  popliteus  muscle  to  the  ankle,  the  tibial  (or  posterior  tibial)  nerve 
lies  on  the  tibialis  posticus  muscle  and  the  tibia,  and,  along  with  the  posterior 
tibial  vessels,  occupies  a  sheath  in  the  intermuscular  septum  separating  the  super- 
ficial and  deep  muscles  of  the  back  of  the  leg.  In  the  upper  part  of  the  leg  the 
nerve  is  internal  to  the  vessels,  but,  crossing  over  them,  it  lies  on  their  outer  side 
in  the  lower  portion  of  its  course.  It  terminates  beneath  the  internal  annular 
ligament  by  dividing  into  the  external  and  internal  plantar  nerves. 

The  collateral  branches  may  be  divided  into  three  series  arising  respectively 
in  the  region  of  the  thigh,  the  popliteal  space,  and  the  back  of  the  leg : — 

(a)  Branches  arising  from  the  Roots  or  Trunk  of  the  Nerve  while  it  is  incor- 
porated toith  the  Great  Sciatic  Nerve. — These  have  been  already  described,  viz. 
muscular  branches  to  the  quadratus  femoris,  gemelli,  obturator  internus,  and  the 
hamstring  muscles,  and  an  articular  branch  to  the  hip-joint  (Fig.  511,  p.  656). 

(b)  Branches  arising  in  the  Popliteal  Space  above  tJi.e  Knee-Joint. — These  are 
in  three  sets — articular,  muscular,  cutaneous. 

1.  The  articular  branches  are  slender  nerves,  variable  in  number.  There  are 
usually  two,  an  azygos  branch  which  pierces  the  posterior  ligament  of  the  knee- 
joint,  and  an  internal  branch,  a  long  fine  nerve  which,  crossing  the  popliteal  vessels, 
descends  on  the  inner  side  of  the  space  to  accompany  the  lower  internal  articular 
artery  to  the  knee-joint.  In  its  course  it  gives  off  a  branch,  often  absent,  which 
accompanies  the  upper  internal  articular  artery. 

2.  The  muscular  branches  are  five  in  number.  Nerves  for  the  two  heads  of  the 
gastrocnemius,  and  the  plantaris  enter  these  muscles  at  the  borders  of  the  popliteal 


TIBIAL  NEEVE. 


653 


space.  A  nerve  for  the  soleus  enters  the  superficial  surface  of  the  muscle.  A 
nerve  for  the  popliteus  muscle  passes  over  the  surface  of  that  muscle,  and  after 
winding  round  its  lovs'er  border,  supplies  it  on  its  deep  (anterior)  surface.  As  this 
nerve  passes  beneath  the  popliteus  it  supplies  branches 
to  the  tibialis  posticus  muscle,  an  interosseous  branch 
for  the  interosseous  membrane,  which  can  be  traced  as 
far  as  the  lower  tibio-fibular  articulation,  an  articular 
branch  for  the  upper  tibio-fibular  joint,  and  a  medullary 
branch  for  the  shaft  of  the  tibia. 

3.  The  cutaneous  branch  is  the  tibial  communicating 
nerve  (n.  communicans  tibialis,  n.  cutaneus  surse 
medialis).  This  nerve  passes  from  the  popliteal  sjjace 
in  the  groove  between  the  two  heads  of  the  gastro- 
cnemius muscle,  and  afterwards  lies  upon  the  tendo 
achillis.  It  pierces  the  deep  fascia  in  the  middle  third 
of  the  back  of  the  leg,  and  is  joined  immediately 
afterwards  by  the  peroneal  communicating  nerve 
from  the  peroneal  nerve.  From  their  union  the 
external  or  short  saphenous  nerve  results,  which 
reaches  the  foot,  winding  round  the  back  of  the 
external  malleolus  along  with  the  external  saphenous 
vein.  The  external  saphenous  nerve  supplies  cuta- 
neous branches  to  the  outer  side  and  back  of  the 
lower  third  of  the  leg,  the  ankle  and  heel,  and  the 
outer  side  of  the  foot  and  little  toe,  as  well  as  ar- 
ticular branches  to  the  ankle  and  tarsal  joints. 

The  external  saphenous  nerve  communicates  on  the 
foot  with  the  musculo-cutaneous  nerve,  and  its  size  varies 
with  the  size  of  that  nerve.  It  may  extend  on  to  the 
dorsum  of  the  foot  for  a  considerable  distance,  and  may 
either  reinforce  or  replace  the  branches  of  the  musculo- 
cutaneous nerve  to  the  intervals  between  the  fourth  and 
fifth  and  the  third  and  fourth  toes.  The  mode  of  forma- 
tion of  the  external  saphenous  nerve  is  very  variable.  The 
usual  arrangement  is  that  described.  Frequently  the 
peroneal  and  tibial  commixnicating  nerves  do  not  unite, 
and  in  such  cases  the  more  usual  arrangement  is  for  the 
tibial  communicating  nerve  to  form  alone  the  external 
saphenous  nerve,  the  peroneal  communicating  nerve  ex- 
tending only  to  the  ankle  and  heel.  It  is  less  usual  for 
the  peroneal  communicating  nerve  to  form  alone  the  ex- 
ternal saphenous  nerve,  the  tibial  communicating  nerve  in 
these  cases  ending  at  the  heel. 

(c)  Branclhes  arising  in  the  Back  of  the  Leg  heloiv 
the  Knee- Joint. — These  branches  are  mainly  muscular 
and  cutaneous. 

The  muscular  branches  are  four  in  number,  com- 
prising nerves  to  the  soleus  (entering  its  deep  surface) 
and  tibialis  posticus,  often  arising  by  a  common  trunk, 
and  nerves  to  the  flexor  longus  digitorum  and  flexor 
longus  hallucis,  the  latter  generally  accompanying 
tlie  peroneal  artery  for  some  distance. 

The  cutaneous  branch  is  th(!  internal  calcanean  nerve 
frr.  calcanei  mediales),  whicli  pierces  the  internal 
annular  ligament,  and  is  distributed  to  the  skin  of 
the  heel  and  back  part  of  the  sole  of  the  foot. 


saphenous  ; 
tibial  ;  I.P 


Fig.  509. — Distribution  of  Cuta- 
neous Nerves  on  the  Back  op 
THE  Lower  Limb. 

On  the  one  side  the  distributiou  of 
the  several  nerves  is  represented, 
the  letters  indicating  their  nomen- 
clature. 

L.l,  2,  3,  S.l,  2,  3,  Posterior  primary 
divisions  of  lumbar  and.  sacral 
nerves  ;  I.H,  Ilio-hypogastric;  T.12, 
Lateral  and  posterior  branches  of 
last  thoracic  nerve;  A. Co',  Posterior 
sacro-coccygeal  nerve  ;  A.Co",  An- 
terior sacro-coccygeal  nerve ;  Perf, 
Perforating  cutaneous  nerve  ;  S.Sc, 
Small  sciatic  ;  E.C,  External  cuta- 
neous ;  Obt,  Obturator  ;  I.C,  In- 
ternal cutaneous  ;  E.  P.S,  Sural 
branches  of  peroneal  ;  l.S,  Internal 

Calc,  Calcanean  branch  of  posterior 


E.S,  External  saphenous  ;  M.C,  Musculo-cutaneous 
Internal  jilantar  ;  E.P,  Kxternal  plantar  nerve. 
On  the  other  side  a  schematic  representation  is  given  of  the  areas  supplied  by  the  above  nerves,  the  figures 
indicating  the  spinal  origin  of  the  branches  of  distribution  to  each  area. 


654 


THE  NERVOUS  SYSTEM. 


In  addition  a  medullary  nerve  to  the  fibala,  and  a  small  articular  branch  to 
the  ankle-joint,  are  supplied  by  the  posterior  tibial  nerve. 

The  terminal  branches  of  the  tibial  nerve  are  the  internal  and  external 
plantar  nerves. 

Internal  Plantar  Nerve. 

The  internal  plantar  nerve  (n.  plantaris  medialis)  is  homologous  with  the 
median  nerve  in  the  hand  (Fig.  510,  p.  654).  It  is  rather  larger  than  the  external 
plantar.  It  courses  forwards  in  the  sole  of  the  foot  beneath  the  internal  annular 
ligament  and  abductor  hallucis  to  the  interval  between  that  muscle  and  the  flexor 
brevis  digitorum,  in  company  with  the  internal  plantar  artery. 

The  collateral  branches  are  muscular,  cutaneous,  and  articular.  The  muscular 
branches  supply  the  abductor  hallucis  and  the  flexor  brevis  digitorum.  The  plantar 
cutaneous  branches  are  small  twigs  which  pierce  the  plantar  fascia  in  the  interval 
between  these  muscles  to  supply  the  inner  part  of  the  sole  of  the  foot.  The  arti- 
cular branches  are  minute  twigs  which  supply  the  inner  tarsal  and  tarso-metatarsal 
articulations. 

The  terminal  branches  are  four  in  number,  and  may  be  designated  first, 
second,  third,  and  fourth,  from  within  outwards. 

The  first  (most  internal)  branch  separates  from  the  nerve  before  the  others, 
and  pierces  the  plantar  fascia  behind  the  ball  of  the  great 
toe.  It  supplies  a  muscular  branch  to  the  flexor  brevis 
hallucis,  and  cutaneous  branches  to  the  inner  side  of  the 
foot  and  ball  of  the  great  toe.  It  terminates  as  the 
plantar  digital  nerve  for  the  inner  side  of  the  great  toe. 

The  second  branch  arises  along  with  the  third  and 
fourth ;  after  supplying  a  branch  to  the  first  lumbrical 
muscle,  it  becomes  superficial  in  the  interval  between  the 
first  and  second  toes,  and  terminates  by  dividing  into  two 
collateral  digital  nerves  for  the  supply  of  the  adjacent  sides 
of  these  toes. 

The  third  and  fourth  branches  are  entirely  cutaneous  in 
their  distribution.  They  become  superficial  in  the  intervals 
between  the  second  and  third  and  the  third  and  fourth 
toes  respectively,  and  there  divide  into  collateral  digital 
branches  for  the  supply  of  the  adjacent  sides  of  these  toes. 
The  plantar  digital  nerves  supply  the  whole  length  of 
the  toes  on  the  plantar  aspect,  and,  in  relation  to  the 
terminal  phalanges,  furnish  minute  dorsal  offsets  for  the 
supply  of  the  nails  and  tips  of  the  toes  on  their  dorsal 
surface.  The  internal  plantar  nerve  thus  supplies  the  skin 
of  the  three  and  a  half  inner  toes  in  the  sole  of  the  foot ; 
and  four  muscles  : — the  abductor  hallucis  and  flexor  brevis 
digitorum,  the  flexor  brevis  hallucis,  and  the  first  lumbrical 
muscle. 

External  Plantar  Nerve. 


rS.M.D. 


Id.m.d. 


Fig.  510. — Scheme  ok  Distri- 
bution OF  THE  Plantar 
Nerves. 

I. PI,  Internal  plantar  nerve,  and 
its  cutaneous  and  muscular 
branches;  F.B.D,  Flexor 
brevis  digitorum  ;  Abd.H, 
AbdiTctor  hallucis;  F.B.H, 
Flexor  brevis  hallucis;  L.I, 
First  lumbricalis  ;  E.Pl,  Ex- 
ternal plantar  nerve,  and  its 
cutaneous  and  muscular 
branches  ;  Ace,  Accessorius  ; 
Abd.m.d,  Abductor  minimi 
digiti ;  F.B.M.D,  Flexor  brevis 
minimi  digiti  ;  R.  P,  Ramus 
profundus. 


The  external  plantar  nerve  (n.  plantaris   lateralis) 

is  homologous  with  the  ulnar  nerve  in  the  hand.     From 

its   origin    beneath    the   internal    annular    ligament    it 

extends  forwards  and  outwards  in  the  sole,  in  company 

with  the  external  plantar  artery,  between  the  flexor  brevis 

digitorum  and  accessorius  muscles,  towards  the   head  of 

the  flffch  metatarsal  bone.     Here  it  terminates  by  dividing 

into  superficial  and  deep  branches. 

Collateral  Branches. — Muscular  branches  are  given  off  from  the  undivided  nerve 

to   the   accessorius   and   abductor   minimi   digiti    muscles.       Cutaneous   h'anches 

pierce  the  plantar  fascia  at  intervals  along  the  line  of  the  intermuscular  septum, 

between  the  flexor  brevis  digitorum  and  abductor  minimi  digiti. 

Terminal  Branches. — The  superficial  branch  (r.  superficialis)  is  mainly  cutaneous. 


THE  PUDENDAL  PLEXUS.  655 

Passing  forwards  between  the  tlexor  brevis  digitorum  and  abductor  minimi  digiti, 
it  divides  into  external  and  internal  parts. 

The  external  branch,  after  supplying  the  flexor  brevis  minimi  digiti  muscle,  and 
sometimes  one  or  both  interossei  of  the  fourth  space,  becomes  superficial  behind 
the  ball  of  the  little  toe,  and  supplies  cutaneous  twigs  to  the  sole  of  the  foot  and  ball 
of  the  toe.     It  terminates  as  the  digital  branch  for  the  outer  side  of  the  little  toe. 

The  internal  branch  passes  forwards  to  the  interval  between  the  fourth  and  fifth 
toes,  where  it  becomes  cutaneous,  and  divides  into  two  collateral  digital  branches  for 
the  supply  of  the  adjacent  sides  of  these  toes.  It  communicates  with  the  fourth 
terminal  branch  of  the  internal  plantar  nerve. 

The  deep  branch  (r.  profundus)  of  the  external  plantar  nerve,  passing  deeply 
along  with  the  external  plantar  artery,  extends  inwards  towards  the  great  toe, 
beneath  the  accessorius  and  adductor  obliquus  hallucis.  It  gives  off  articular 
branches  to  the  tarsal  and  tarso-metatarsal  articulations,  and  inuscular  branches 
to  the  interossei  of  each  space  (except  in  some  cases  the  muscles  of  the  fourth 
space) :  to  the  adductor  obliquus  and  adductor  transversus  hallucis,  and  the  outer 
three  lumbrical  muscles.  These  nerves  enter  the  deep  surface  of  the  muscles,  that 
to  the  second  lumbrical  reaching  its  muscle  after  passing  forwards  beneath  the 
adductor  transversus  hallucis. 

THE  PUDENDAL  PLEXUS. 

The  pudendal  plexus  constitutes  the  third  and  last  subdivision  of  the  lumbo- 
sacral plexus.  It  is  composed  for  the  most  part  of  the  spinal  nerves  below  those 
which  form  the  sacral  plexus ;  but,  as  already  stated,  there  is  no  distinct  point  of 
separation  between  the  two  plexuses.  On  the  contrary,  there  is  considerable  over- 
lapping, so  that  two  and  sometimes  three  of  the  principal  nerves  derived  from  the 
pudendal  plexus  have  their  origin  in  common  with  nerves  of  the  sacral  plexus. 

The  plexus  is  formed  by  fibres  from  the  anterior  primary  divisions  of  the  first 
three  sacral  nerves,  and  by  the  whole  of  the  anterior  primary  divisions  of  the  fourth 
and  fifth  sacral  and  coccygeal  nerves.  The  size  of  the  nerves  diminishes  rapidly 
from  the  first  sacral  to  the  coccygeal,  which  is  extremely  slender. 

Position  and  Constitution. — The  plexus  is  formed  on  the  back  wall  of  the 
pelvis.  Of  the  nerves  forming  it,  the  upper  ones  emerge  from  the  anterior  sacral 
foramina ;  the  fifth  sacral  nerve  appears  between  the  last  sacral  and  first  coccygeal 
vertebra ;  and  the  coccygeal  nerve  appears  below  the  transverse  process  of  that 
vertebra.     The  nerves  of  distribution  derived  from  the  plexus  are  the  following : — 

1.  Visceral  branches.  4.   Pudic  nerve. 

2.  Small  sciatic  nerve.  5.  Muscular  branches. 

3.  Perforating  cutaneous  nerve.  6.   Sacro-coccygeal  nerve. 

Omitting  the  visceral  branches,  all  the  nerves  are  distributed  to  the  perineum. 
Only  two,  the  small  sciatic  and  perforating  cutaneous  nerves,  send  branches  to  the 
lower  limb. 

Visceral  Branches. — Like  the  other  spinal  nerves,  the  fourth  and  fifth  sacral 
and  coccygeal  nerves  are  provided  with  fine  gray  rami  communicantes  from 
the  sacral  gangliated  cord,  which  joins  them  after  a  short  course  on  the  front  of 
tlie  sacrum.  The  third  (along  with  the  second  or  fourth)  sacral  nerve  in  addition 
sends  a  considerable  toldte  ramus  communicans  or  visceral  branch  inwards  to  the 
pelvic  plexus  and  viscera. 

Small  Sciatic  Nerve  (n.  cutaneus  femoris  posterior). — This  nerve  is  complex 
both  in  origin  and  distribution  (Fig.  511,  p.  656).  Springing  from  the  junction  of 
the  sacral  and  pudendal  plexuses,  it  is  derived  from  the  first  three  or  second  and 
third  sacral  nerves.  It  is  distributed  to  the  lower  limb  and  perineum,  and  is 
associated  with  other  nerves  belonging  to  both  regions.  It  arises  from  the  back  of 
the  roots  of  the  sacral  ])lexus  in  the  pelvis.  Its  higher  roots  from  the  first  and 
second  sacral  nerves  are  intimately  associated  with  the  origin  of  the  inferior  gluteal 
nerve ;  its  lowest  root  from  the  third  sacral  nerve  is  associated  with  the  origins  of 
the  perforating  cutaneous  or  pudic  nerve.  It  enters  the  buttock  through  the  great 
sciatic  notch  below  tlic  pyriformis,  along  with  the  sciatic  artery  and  inferior  gluteal 


656 


THE  NEEVOUS  SYSTEM. 


nerve.  Proceeding  downwards  behind  the  great  sciatic  nerve,  it  enters  the  thigh 
at  the  lower  border  of  the  ghiteus  maximus  muscle,  where  it  gives  off  considerable 
branches.     Becoming  gradually  smaller  as  it  courses  downwards  over  the  hamstring 


Fig.  511. — Nerves  of  the  Lumbo-Sacral  Plexus. 

Sy,  Sympathetic  cord  ;  T.12,  L.l,  2,  3,  4,  5,  S.l,  2,  3,  4,  5,  Co,  Anterior  primary  divisions  of  the  last  thoracic, 
the  lumbar,  sacral,  and  coccygeal  nerves  ;  Q,  Nerves  to  quadratus  lumborum  ;  Ps,  Nerves  to  psoas 
muscle  ;  G.C,  Genito-cniral  nerve  ;  II,  Iliac  branches  of  last  thoracic  and  ilio-hypogastric  nerves  ;  Hy, 
Hypograstic  branch  of  ilio-hypogastric  nerve  ;  I.I,  Ilio-inguinal  nerve;  E.C,  External  cutaneous  nerve  ; 
A.C,  Anterior  crural  nerve  ;  Obt,  Obturator  nerve  ;  Py,  Nerves  to  pyriformis  muscle  ;  O.I,  Nerve  to 
obturator  internus  ;  Q.F,  Nerve  to  quadratus  femoris  muscle  ;  Art,  Articular  branch  ;  S.G,  Superior 
gluteal  nerve  ;  1.6.  Inferior  gluteal  nerve  ;  P,  Peroneal  nerve  ;  Bi.2,  Nerve  to  short 'head  of  biceps  muscle  ; 
T,  Tibial  nerve  ;  Art,  Articular  branch  ;  H.S,  Nerve  to  the  hamstring  muscles  ;  Bi.l,  Nerves  to  biceps 
(long  head),  and  St.l,  to  semi-tendinosus  ;  St.2,  Semi-tendinosus  ;  Sm,  Semi-membranosus  ;  A.m, 
Adductor  maguus  ;  S.Sc,  Small  sciatic  nerve  ;  Perf,  Perforating  cutaneous  nerve  ;  Pud,  Pudic  nerve  ; 
M,  Muscular  branches  ;  Per,  Perineal  branch  of  fourth  sacral  ;  A.Co,  Anterior  sacro-coccj'geal  nerve. 


PUDENDAL  PLEXUS.  657 

muscles  to  the  popliteal  space,  it  finally  pierces  the  popliteal  fascia  in  one  or  more 
cutaneous  branches,  which  supply  the  skin  over  the  calf  of  the  leg  for  a  variable 
distance  (Fig.  509,  p.  653). 

Branches. — The  small  sciatic  is  a  purely  cutaneous  nerve.  It  supplies  branches 
to  the  perineum,  buttock,  thigh,  and  leg. 

The  perineal  branch  (rr.  perinseales ;  inferior  pudendal  nerve :  long  scrotal 
nerve)  arises  from  the  small  sciatic  nerve  at  the  lower  border  of  the  gluteus 
maximus  muscle  (Fig.  512,  p.  658).  It  sweeps  inwards  towards  the  perineum, 
lying  on  the  origin  of  the  hamstring  muscles  below  the  ischial  tuberosity,  and 
becomes  subcutaneous  after  passing  over  the  pubic  arch.  Its  terminal  branches 
supply  the  skin  of  the  scrotum  and  root  of  the  penis,  or  in  the  female  the  labium 
majus  and  clitoris,  some  of  them  being  directed  backwards  towards  the  anus  and 
central  point  of  the  perineum.  They  communicate  with  the  inferior  haemorrhoidal 
and  perineal  branches  of  the  pudic  nerve,  and  with  the  ilio-inguinal  nerve.  In  its 
course  to  the  perineum  the  nerve  gives  off  collateral  Iranclies  to  the  skin  of  the 
upper  and  inner  part  of  the  thigh. 

The  gluteal  branches  (rr.  clunium  inferiores)  are  large  and  numerous  (Fig. 
509,  p.  653).  They  arise  from  the  small  sciatic  nerve  beneath  the  gluteus 
maximus,  and  become  subcutaneous  by  piercing  the  fascia  lata  at  different  points 
along  its  lower  border.  They  supply  the  skin  of  the  lower  half  of  the  buttock. 
The  outermost  branches,  reaching  to  the  back  of  the  great  trochanter,  overlap  the 
terminal  filaments  of  the  gluteal  branches  of  the  external  cutaneous  nerve,  and  the 
posterior  primary  divisions  of  the  first  three  lumbar  nerves.  The  innermost  branches, 
which  may  pierce  the  great  sacro-sciatic  ligament,  reach  nearly  to  the  coccyx,  and 
are  co-terminous  in  their  distribution  with  the  branches  of  the  perforating  cutaneous 
nerve,  which  they  reinforce  and  not  infrequently  replace. 

The  femoral  branches  are  divisible  into  two  sets — internal  and  external.  They 
pierce  the  fascia  lata  of  the  thigh  at  intervals,  and  supply  the  skin  of  the  back  of 
the  thigh  on  its  inner  and  outer  sides  respectively. 

The  sural  branches  are  two  or  more  slender  nerves  which  pierce  the  fascia 
over  the  popliteal  space,  and  are  distributed  for  a  variable  extent  to  the  skin  of 
the  back  of  the  leg.  They  may  stop  short  over  the  popliteal  space,  or  may  extend 
as  far  as  the  ankle.  Usually  they  innervate  the  skin  as  far  as  the  middle  of  the 
calf.     They  communicate  with  the  external  saphenous  nerve. 

In  cases  where  the  great  sciatic  nerve  is  naturally  divided  at  its  origin  into  tibial  (internal 
popliteal)  and  peroneal  (external  popliteal)  nerves  {e.g.  by  the  pyriformis  muscle),  the  small 
sciatic  nerve  is  also  separated  into  two  parts  :  a  dorsal  part,  associated  with  the  peroneal  nerve 
and  arising  in  common  with  the  lower  roots  of  the  inferior  gkiteal  nerve  (usually  from  the  first 
and  second  sacral  nerves),  and  comprising  the  gluteal  and  external  femoral  branches  ;  and  a 
ventral  part,  associated  with  the  tibial  nerve  and  arising  usually  from  the  second  and  third 
sacral  nerves,  along  with  the  perforating  cutaneous  and  pudic  nerves,  and  comprising  the 
perineal  and  internal  femoral  branches. 

Perforating  Cutaneous  Nerve  (n.  perforans  ligamenti  tuberoso  -  sacri 
(Schwalbe),  n.  cutaneus  clunium  inferior  medialis  (Eisler)). — This  nerve  arises 
from  the  back  of  the  second  and  third  sacral  nerves  (Fig.  512,  p.  658).  At  its 
origin  it  is  associated  with  the  lower  roots  of  the  small  sciatic  nerve.  Passing  down- 
wards it  pierces  the  great  sacro-sciatic  ligament,  along  with  the  coccygeal  branch 
of  the  sciatic  artery ;  and  after  winding  round  the  lower  border  of  the  gluteus 
maximus  muscle,  or  in  some  cases  piercing  its  lower  fibres,  it  becomes  subcutaneous 
a  little  distance  from  the  coccyx,  and  supplies  the  skin  over  the  lower  part  of  the 
buttock  and  the  inner  part  of  the  fold  of  the  nates. 

The  perforating  cutaneous  nei've  is  not  always  present.  In  a  minority  of  cases  it  is  associated 
at  its  origin  with  tlie  pudic  nerve.  When  absent  as  a  separate  nerve,  its  jDlace  is  taken  by  (1) 
gluteal  branches  of  the  small  sciatic  nerve,  or  (2)  a  branch  from  the  pudic  nerve,  or  (3)  a  small 
nerve  (n.  perforans  coccygeus  major,  Eisler),  arising  separately  from  the  back  of  the  third  and 
fourlli  .sacral  nerves. 

Muscular  Branches. — Between  the  third  and  fourtli  sacral  nerves  (occasion- 
ally reinforced  by  the  second,  Eisler)  a  plexiibrm  loop  is  formed,  from  which 
mu.scular  nerves  are  given  off  to  the  levator  ani  (supplying  the  muscle  on  its  pelvic 
surface),  coccygeus,  and  external  sphincter.     The  nerve  to  the  external  sphincter 
46 


658 


THE  NERVOUS  SYSTEM. 


{periyieal  branch  of  fourth  sacral)  pierces  the  great  sacro-sciatic  ligament  and  the 
coccygeus  muscle,  to  which  it  gives  olfsets,  and  appears  in  the  ischio-rectal  fossa 
between  the  gluteus  niaximus  and  the  external  sphincter.  Besides  supplying  the 
posterior  fibres  of  the  external  sphincter,  it  distributes  cutaneous  offsets  to  the  skin 
of  the  ischio-rectal  fossa  and  the  fold  of  the  nates  behind  the  anus.  This  nerve 
replaces  in  some  instances  the  perforating  cutaneous  nerve. 

Anterior  Sacro-coccyg'eal  Nerves  (nn.  ano-coccygei). — By  the  union  of  the 
remaining  part  of  the  fourtli  with  the  fifth  sacral  and  coccygeal  nerves,  the 
so-called  coccygeal  plexus  is  formed.  A  tine  descending  branch  of  the  fourth 
sacral  nerve  passes  over  or  through  the  great  sacro-sciatic  ligament,  to  join  the 
fifth  sacral  nerve.  This  fifth  sacral  nerve,  joined  by  the  descending  branch  of 
the  fourth,  descends  alongside  the  coccyx  and  is  again  joined  by  the  coccygeal 
nerve,  so  that  a  plexiform  cord  results,  homologous  with  the  inferior  caudal  trunk 
of  tailed  animals.  Fine  twigs  arise  from  it,  which  pierce  the  sacro-sciatic  ligament 
and  supply  the  skin  in  the  neighbourhood  of  the  coccyx,  internal  to  the  perforating 
cutaneous  nerves  and  behind  the  anus. 


The  Pudic  Nerve. 

The  pudic  nerve  (n.  pudendus)  is  the  principal  nerve  for  the  supply  of  the 
perineum.     It  arises  in  the  pelvis  usually  by  three  roots  from  the  second,  third,  and 


Perineal  branch  ok  small 

SCIATIC 


Anterior 

superficial 
perineal 

NERVE 


Posterior 

superficiai 

perineal 

NERVE 

Gluteal 
branches 

OF  SMALL' 
SCIATIC 
NERVE 


Ischial  tuberosity 


Lexator  ani 


P.iuptal  pelvic 
fascia 


Inferior  h^morli 

NER\ 

Perforating  CUT  tvE 

Perineal  branch  of  fourth  sacral  nerve 
Fig.  512 


Levator  ani 
External  spliiucter  aui 


Anterior  sacro-coccygeal  nerve 
The  Muscles  and  Nerves  of  the  Male  Perineum. 


fourth  sacral  nerves  (Fig.  511,  p.  656).  (Frequently  one  of  its  branches,  the  inferior 
hemorrhoidal  nerve,  arises  independently  from  the  third  and  fourth  sacral  nerves). 
The  nerve  passes  to  the  buttock  through  the  great  sacro-sciatic  foramen  below  the 
great  sciatic  nerve,  and  lies  on  the  lesser  sacro-sciatic  ligament,  or  the  spine  of  the 
ischium,  internal  to  the  internal  pudic  artery.  It  enters  the  perineum  along  with 
the  pudic  artery  through  the  small  sacro-sciatic  foramen.  In  the  perineum  it  is 
deeply  placed  in  the  outer  wall  of  the  ischio-rectal  fossa,  enclosed  in  a  special 
sheath  derived  from  the  parietal  pelvic  fascia  covering  the  inner  surface  of  the 
obturator  internus  muscle.  At  the  anterior  limit  of  the  ischio-rectal  fossa,  the 
nerve  approaches  the  surface  and  divides  at  the  base  of  the  triangular  ligament 
into  its  terminal  branches,  the  perineal  nerve  and  the  dorsal  nerve  of  the  penis. 


THE  PUDIC  NERVE. 


659 


The  branches  of  the  pvidic  uerve  are  essentially  the  same  in  the  two  sexes.  As 
a  rule  no  branches  are  given  off  till  the  nerve  enters  the  perineum,  but  sometimes 
the  inferior  hsemorrhoidal  nerve  has  an  independent  origin  from  the  plexus,  merely 
accompanying  the  pudic  nerve  in  the  first  part  of  its  course ;  and  in  exceptional 
cases  the  perforating  cutaneous  nerve  of  the  buttock  is  a  branch  of  the  pudic  nerve. 

The  inferior  hsemorrhoidal  nerve  (n.  hsemorrhoidalis  inferior)  arises  from  the 
pudic  nerve  under  cover  of  the  gluteus  maximus,  at  the  posterior  part  of  the 
ischio-rectal  fossa.  In  cases  in  which  it  has  an  independent  origin  from  the  plexus, 
it  arises  from  the  third  and  fourth  sacral  nerves.  It  crosses  the  ischio-rectal  fossa 
in  company  with  the  inferior  hsemorrhoidal  vessels,  and  separates  into  numerous 
branches — muscular,  cutaneous,  and  communicating. 

The  muscular  branches  end  in  the  external  sphincter  ani  muscle.  The  cutaneous 
branches  supply  the  skin  around  the  anus.  The  communicating  branches  connect 
the  inferior  hsemorrhoidal  with  three  other  nerves — the  perineal  branches  of  the 
small  sciatic,  pudic,  and  fourth  sacral  nerves. 

The  perineal  nerve  (n.  perineus),  one  of  the  two  terminal  branches  of  the 
pudic  nerve,  arises  near  the  base  of  the  triangular  ligament.  It  almost  immediately 
divides  into  two  parts,  superficial  and  deep. 

The  superficial  part  is  purely  cutaneous  and  consists  of  two  nerves,  the  posterior 


Corpus  cavernosum 

(cut) 

Nerve  to  corpus 

cavernosum 

Nerve  to  dorsum 

OF  PENIS 

Compressor  urethrse 

Nerve  to  bulb 

Triangular  ligament 

(posterior  layer) 

Internal  pudic  nerve 


Bulb  of  penis 

Triangular  ligament 
(anterior  layer) 

Crus  penis 


Fig.  513. — The  Triangular  Ligament  op  the  Perineum.  , 

or  external  and  the  anterior  or  internal  superficial  perineal  nerves,  which  pass, 
along  with  the  superficial  perineal  vessels,  to  the  anterior  part  of  the  perineum. 
The  posterior  or  external  superficial  perineal  nerve,  at  the  anterior  limit  of  the  ischio- 
rectal fossa,  usually  passes  over  the  base  of  the  triangular  ligament  and  over  the 
transversus  perinei  muscle.  The  anterior  or  internal  superficial  perineal  nerve,  lying 
more  deeply,  pierces  the  base  of  the  triangular  ligament  and  goes  underneath  or 
through  the  transversus  perinei  muscle.  Becoming  superficial  in  the  anterior 
(urethral)  triangle  of  the  perineum,  they  are  distributed  to  the  skin  of  the  scrotum 
(or  labium  majus),  and  communicate  with  the  perineal  branch  of  the  small  sciatic 
nerve  and  with  the  inferior  hasmorrhoidal  nerve. 

The  deep  part  of  the  perineal  nerve  is  mainly  but  not  entirely  muscular. 
Coursing  forwards  through  the  anterior  part  of  the  ischio-rectal  foss:T,  it  passes 
between  the  two  layers  of  tlie  triangular  ligament  towards  the  urethra.  It  supplies 
muscular  branches  to  the  anterior  parts  of  the  levator  ani  and  external  sphincter, 
to  the  transversus  perinei,  erector  penis  (or  clitoridis),  bulbo-cavernosus  (ejaculator 
urinaj  or  sphincter  vaginai),  and  compressor  urethrte.  It  terminates  as  the  nerve 
to  the  bulb,  which,  piercing  the  triangular  ligament,  enters  the  bulb  of  the  urethra 


660 


THE  NERVOUS  SYSTEM. 


and  supplies  the  erectile  tissue  of  the  bulb  and  corpus  spongiosum,  as  well  as  the 
mucous  membrane  of  the  urethra  as  far  as  the  glans  penis  (or  clitoridis). 

The  dorsal  nerve  of  the  penis,  the  other  terminal  branch  of  the  pudic  nerve, 
accompanies  the  internal  pudic  artery  beneath  the  superficial  layer  of  the  triangular 
ligament.  It  passes  forward  close  to  the  pubic  arch,  lying  beneath  the  crus  and 
erector  penis  (or  clitoridis),  and  triangular  ligament,  and  upon  the  compressor 
urethras  muscle ;  piercing  the  triangular  ligament  near  its  apex,  at  the  outer  side 
of  the  dorsal  artery  of  the  penis  (or  clitoris),  it  passes  on  to  the  dorsum  of  the 
penis  or  clitoris,  to  which  it  is  distributed  in  its  distal  two-thirds,  sending  branches 
round  the  sides  of  the  organ  to  reach  its  under  surface.  In  the  female  the  nerve  is 
much  smaller  than  in  the  male.  The  dorsal  nerve  of  the  penis  supplies  one  branch, 
the  nerve  to  the  corpus  cavernosum,  as  it  lies  beneath  the  triangular  ligament. 
This  is  a  slender  nerve,  which,  piercing  the  triangular  ligament,  supplies  the 
erectile  tissue  of  the  crus  and  corpus  cavernosum. 

Morphology  of  the  Pudendal  Plexus. — The  structures  occupying  the  perineum  are  placed 
in  the  ventral  axis  of  the  body,  and  comprise  from  before  backwards,  the  penis  and  scrotum,  or 
nions  Veneris  and  vulva,  the  central  point  of  the  perineum,  the  anus  and  ischio-rectal  fossa,  and 
the  coccyx.  They  are  placed  on  the  mesial  side  of  the  attachment  of  the  lower  limbs — the  penis 
or  mons  Veneris  in  relation  to  the  preaxial  border  ;  the  coccyx  in  relation  to  the  postaxial  border 
of  the  limb. 

The  nerves  of  the  perineum,  thus  reaching  the  ventral  axis  of  the  trunk,  are  homologous  with 
the  anterior  (ventral)  terminations  of  other  nerves.     They  are  sejiarated  into  two  series.     Mainly 

supplied  through  the  pudendal  plexus  by  the  last  four  sacral 
and  the  coccygeal  nerves,  the  perineum  is  also  innervated 
to  a  minor  extent  by  the  first  lumbar  nerve  through  the 
ilio -inguinal  nerve,  which  reaches  the  root  of  the  penis  and 
the  scrotum.  The  region  is  thus  supplied  by  two  series 
of  widely  separated  nerves,  which  have  their  meeting-place 
on  the  dorsum  and  side  of  the  penis  and  scrotum.  This 
junction  of  the  ilio-inguinal  and  pudendal  nerves  constitutes 
the  beginning  of  the  ventral  axial  area  or  line,  which 
extends  peripherally  along  the  inner  side  of  the  lower  limb. 
AjDart  from  this  break  in  their  distribution,  a  definite 
numerical  order  may  be  followed  in  the  arrangement  of  the 
Fig.  514. -Scheme  of  the  innervation  perineal  nerves.  The  higher  parts  of  the  perineum  are  in- 
of  the  hinder  portion  of  the  truulv  nervated  by  the  higher  spinal  nerves  ;  the  lower  parts,  by  the 
and  of  the  perineum,  and  the  iu-  lower  nerves.  This  is  best  exemplified  in  the  distribution  ot 
terruption  of  the  segmental  arrange-  the  cutaneous  nerves.  The  base  of  the  penis  and  scrotum 
ment  of  the  nerves  associated  with  (or  mons  Veneris)  is  supplied  by  the  first  lumbar  nerve  (ilio- 
the  formation  of  the  limb.  inguinal).     The  dorsal  nerve  of  the  penis  (or  clitoris),  when 

T.IO   11    12    The  areas  of  distribution    traced  back  to  the  jjudendal  plexus,  is  found  to  come  from 
of  the'  lower  thoracic  nerves  ;  L.  1,  2,    the  second,  and  to  a  less  extent  from  the  third  sacral  nerves  ; 

3,  The  posterior  primary  divisions  of  the  scrotal  nerves  (perineal  branches  of  the  pudic  and  small 
the  first  three  lumbar  nerves  ;  L.  1,  sciatic)  similarly  arise  from  the  third,  and  to  a  less  extent 
The  ilio-inguinal  nerve;  S.l,  2,  3,    from  the  second  sacral  nerves;    the  skin  of  the  ischio-rectal 

4,  5,  6,  The  posterior  primary  divi-  fossa  and  anus  is  innervated  by  the  inferior  hsemorrhoidal 
sions  of  the  sacral  and  coccygeal  (third  and  fourth  sacral  nerves),  and  the  perineal  branch  of 
nerves  (6)  ;  S.3,  2,  S.3,  2,  Branches    ^^^^  fourth  sacral  nerve.     The  coccygeal  plexus,  lastly,  supplies 

the  skin  round  the  coccyx  (fourth  and  iifth  sacral  and 
coccygeal  nerves).  Judged  from  its  nerve  sujiply  the  perineum 
is  to  be  regarded  as  occupying,  for  the  most  part,  a  position 
behind  or  more  caudal  than  that  of  the  lower  limb  in  relation 
to  the  trunk.  There  is  here  a  remarkable  gap  in  the 
numerical  sequence  of  the  nerves  supj^lying  the  ventral  axis 
of  the  body.  All  the  nerves  between  the  first  lumbar  and  the  second  sacral  fail  to  reach  the  mid 
ventral  line  of  the  trunk  and  are  wholly  concerned  in  the  innervation  of  the  lower  limb. 

At  the  preaxial  border  of  the  limb  (groin)  the  first  lumbar  nerve,  the  highest  nerve  supplying 
the  perineum,  is  concerned  also  in  innervating  the  skin  of  the  limb.  At  the  postaxial  border  of 
the  limb  (fold  of  the  nates  and  back  of  the  thigh),  the  nerves  which  are  the  highest  of  those  con- 
stituting the  pudendal  plexus  (the  second  and  third  sacral  nerves)  are  also  implicated  in  inner- 
vating that  border  of  the  limb.  The  fourth  sacral  nerve  is  only  concerned  to  a  very  slight 
extent  in  the  innervation  of  the  limb  by  means  of  the  perineal  branch,  which  reaches  the 
beginning  of  its  postaxial  border ;  the  last  two  spinal  nerves  are  wliolly  unrepresented  in  the 
limb  proper  and  end  entirely  in  the  trunk  behind  the  limb. 

Development  of  the  Spinal  Nerves. 
I.  Origin  of  the  Spinal  Nerve  Roots. — The  process  of  development  of  the  spinal 


of  pudic  nerve  to  penis  and  scrotum  ; 
S.3,  4,  Inferior  hsemorrhoidal  nerve  ; 
4,  Perineal  branch  of  the  fourth 
sacral  nerve  ;  4,  5,  6,  Anterior  sacro- 
coccygeal nerve  ;  D.A.L,  Dorsal  axial 
line  ;  V.A.L,  Ventral  axial  line. 


DEVELOPMENT  OF  THE  SPINAL  NERVES. 


6G1 


nerves  commences  by  means  of  the  outgrowth  of  the  dorsal  and  ventral  roots  from  the 
medullary  tube.      The  two  roots  take  origin  in  quite  different  ways. 

The  dorsal  root  is  the  first  to  appear, — before,  during,  or  after  the  union  of  the 
medullary  plates  and  the  formation  of  the  neural  tube.  It  takes  origin  as  a  cellular  bud 
from  the  dorsal  surface  of  the  medullary  tube  in  one  of  three  ways : — (1)  It  may  arise 
from  the  junction  of  the  medullary  plate  and  surface  epiblast  before  the  closure  of  the 
medullary  groove.  (2)  It  may  spring  from  the  neural  crest,  a  ridge  on  the  dorsal  aspect 
of  the  medullary  tube,  after  its  closure  is  complete.  (3)  It  may  be  simply  a  direct  out- 
growth from  the  dorsal  surface  of  the  medullary  tube.  Pyriform  in  shape,  the  bud 
enlarges  and  becomes  separated  from  the  medullary  tube,  and  projects  ventrally  in  the 
space  between  the  myotome  and  the  medullary  tube.  Each  bud  is  separated  by  only  a 
slight  interval  from  its  neighboiir. 

The  cells  (neuroblasts)  composing  the  bud  become  rapidly  spindle-shaped,  and  by  the 
middle  of  the  fourth  week  give  rise  to  tioo  sets  of  j^'rocesses ;  (1)  a  central  series,  which 


A, 


Fig.   515. — Development  of 
Formation  of  nerve  roots. 


C, 


D.E,  Dorsal  root. 
V.R.  Ventral  root. 
N.T,  Neural  tnlje. 
No,    Notochord. 

Formation  of  nerves. 


Al.C,  Alimentary  canal. 

Ao,  Aorta. 

V,  Cardinal  vein. 

M.P,  Muscle  plate. 

,   E,   Foniiation  of  subordinate 
branches. 

Lat,   Lateral,  and 

Ant,  Anterior,  Ijranches. 


THE  Spinal  Nerves. 

B,  Formation  of  nerve  trunk  (N). 
D.G,     Dorsal  ganglion. 


Sy,       Sympathetic  cord. 
W.D,  Wolffian  duct. 
Co,       Cceloni. 

Formation  of  nerve  trunks  in  relation 
to  the  limb  :  dorsal  and  ventral 
trunks  corresponding  to  lateral  and 
anterior  trunks  in  D  and  E. 


So,  Somatic  division. 
Vi,  Visceral  branch. 
P,    Posterior  jiriiMary  division. 

grow  backwards  and  are  secondarily  connected  with  the  dorso-lateral  aspect  of  tlie 
medullary  tube  as  the  fiVjres  of  the  dorsal  root;  and  (2)  a  peripheral  series,  which  con- 
stitute the  dorsal  root  tiVires  of  the  spinal  nerve  and  join  the  ventral  root,  to  form  the 
spinal  nerve  proper.     The  intermediate  cellular  mass  remains  as  the  spinal  ganglion. 

The  ventral  root  of  a  spinal  nerve  arises  in  quite  a  different  way,  from  cells  (neuro- 
blasts) in  the  HuVjstance  of  the  medullary  tube.  In  the  account  of  the  development  of  the 
spinal  cord  it  has  Ijeen  shown  how  the  cellular  constituents  of  the  medullary  tube  are  con- 
verted into  two  classes  of  cells:  (1)  spongioblasts,  which  produce  the  matrix  (neuroglia)  of 
the  spinal  cord  ;  and  (2)  germ-cells  or  neuroblasts,  which  produce  the  nerve-cells  of  the 
gray  matter  of   the   cord.     Th(;  neuroblasts  give  rise   to   the  axis-cylinder  processes  or 


662  THE  NEEVOUS  SYSTEM. 

axons,  which,  penetrating  the  spongy  tissue  of  the  medullary  tube  and  the  outer  limiting 
membrane,  find  their  way  into  the  mesoblastie  tissue  on  the  ventro-lateral  surface  of  the 
tube.  Fibrous  from  their  earliest  origin  and  derived  from  nerve-cells  which  remain  within 
the  medullary  tube,  the  axons  of  which  the  ventral  root  is  composed  become  surrounded  by 
mesoblastie  cells  immediately  on  their  emergence,  which  give  rise  to  the  sheaths  of  the  nerve. 
The  ventral  root  is  a  little  later  in  its  date  of  appearance  than  the  dorsal  root.  It  begins 
to  be  evident  at  the  twenty-fourth  day  and  is  completely  formed  by  the  twenty-eighth  day. 

II.  Formation  of  the  Spinal  Nerve. — The  fibres  of  the  dorsal  root  ganglion  and 
the  ventral  root  grow  by  extension  from  the  cells  with  which  they  are  respectively  con- 
nected, and  meet  in  the  space  between  the  myotome  and  the  side  of  the  medullary  tube 
to  form  the  spinal  nerve.  It  has  been  already  shown  that  in  the  adult  there  is  a  funda- 
mental division  of  the  spinal  nerve  into  posterior  and  anterior  primary  divisions.  In  the 
process  of  development  this  separation  is  even  more  obvious.  As  the  fibres  of  the  dorsal 
and  ventral  roots  approximate,  they  separate  at  the  same  time  each  into  two  unequal 
portions  :  the  smaller  parts  of  the  two  roots  unite  together  to  form  the  posterior,  and  the 
larger  parts  unite  to  form  the  anterior  primary  division  of  the  spinal  nerve. 

The  posterior  primary  division,  curving  outwards  and  dorsally,  passes  through  the 
myotome  and  is  connected  with  it.  In  the  substance  of  the  myotome  it  separates  into 
branches  as  it  proceeds  towards  the  dorsal  wall  of  the  embryo.  At  a  later  stage,  the 
branches  are  definitely  arranged  into  an  outer  and  an  inner  set. 

The  anterior  primary  division  grows  gradually  in  a  ventral  direction  to  reach  the 
somato-splanchnopleuric  angle,  under  cover  of  the  growing  myotome.  It  spreads  out  at 
its  distal  end  and  eventually  separates  into  two  portions  :  a  smaller,  splanchnic,  or  visceral ; 
and  a  larger,  somatic,  or  parietal  portion.  (1)  The  smaller,  splanchnic,  or  visceral  portion 
grows  inwards,  dorsal  to  the  AVolflfian  ridge,  to  be  connected  with  the  sympathetic  cord 
and  the  innervation  of  organs  in  the  splanchnic  area.  This  branch  of  the  spinal  nerve 
becomes  the  white  ramus  communicans  of  the  sympathetic.  It  is  not  present  in  the  case 
of  all  the  spinal  nerves  (cervical,  lower  lumbar,  and  xipper  sacral).  It  will  be  referred  to 
again  in  connexion  with  the  syixipathetic  system.  (2)  The  larger,  somatic,  or  parietal 
portion  becomes  the  main  part  of  the  anterior  primary  division  of  the  nerve.  It 
continues  the  original  ventral  course  of  the  nerve,  and,  reaching  the  body  wall,  sub- 
divides into  two  terminal  branches — a  lateral  branch,  which  grows  outwards  and  down- 
wards and  reaches  the  lateral  aspect  of  the  trunk,  after  piercing  the  myotome ;  and  a 
ventral  or  anterior  branch,  -which  grows  onwards  in  the  body  wall  to  reach  the  ventral 
axis.     This  arrangement  is  met  with  in  the  trunk  between  the  limbs  and  in  the  neck. 

III.  Formation  of  Limb-plexuses. — The  method  of  growth  of  the  spinal  nerves, 
just  described,  is  modified  in  the  regions  where  the  limbs  are  developed.  In  relation  to 
the  limbs,  which  exist  in  the  form  of  buds  of  cellular  undifferentiated  mesoblast  before 
the  spinal  nerves  have  any  connexion  with  them,  the  development  of  the  nerve  proceeds 
exactly  in  the  way  described  up  to  the  point  of  formation  of  somatic  and  splanchnic 
branches.  The  somatic  branches  then  stream  out  into  the  limb  bud,  passing  into  it 
below  the  ends  of  the  myotomes  and  spreading  out  into  a  bundle  of  fibres  at  the  basal 
attachment  of  the  limb.  Later  on,  the  nerves  separate  each  into  a  pair  of  definite  trunks, 
which  are  named  dorsal  and  ventral,  and  which,  dividing  round  a  central  core  of  meso- 
blast, proceed  to  the  dorsal  and  ventral  surfaces  respectively  of  the  limb  bud.  While  this 
process  is  going  on,  a  secondary  union  takes  place  between  (parts  of)  adjacent  dorsal  and 
ventral  trunks.  Dorsal  trunks  nnite  with  dorsal  trunks,  ventral  trunks  unite  with  ventral 
trunks,  to  form  the  nerves  distributed  ultimately  to  the  surfaces  and  periphery  of  the 
limb.  These  dorsal  and  ventral  trunks  are  homologous  with  the  lateral  and  ventral 
branches  of  the  somatic  nerves  in  other  regions. 

Morphology  of  the  Limb-plexuses. 

The  arrangement  of  the  limb  nerves  is  rendered  complex  and  the  significance  of  the  plexuses 
is  obscured  by  the  changes  through  which,  coincidently,  the  nerves  on  the  one  hand  and  the 
parts  supplied  by  them  on  the  other  hand  have  jaassed  in  the  course  of  develojDment. 

Nature  of  the  Limbs. — As  already  described,  the  mammalian  limbs  arise  as  flattened  buds 
from  the  extremities  of  the  'Wolffian  ridge.  Each  bud  possesses  a  preaxial  and  a  jjostaxial  border, 
and  a  dorsal  and  a  ventral  surface,  continuous  with  the  dorsal  and  ventral  aspects  of  the  trunk 
and  homologous  with  its  lateral  and  ventral  surfaces.  Each  bud  consists  at  first  of  a  mass  of 
undifferentiated,  unsegmented  mesoblast,  covered  by  epithelium.  Around  the  central  core  of 
mesoblast  which  produces  the  skeletal  axis,  the  vessels  and  muscles  of  the  limb  are  formed 
in  situ,  the  muscles  as  double  dorsal  and  ventral  strata,  beneath  the  corresponding  surfaces  of 
the  bud. 

Each  limb  bud  is  connected  to  the  lateral  and  ventral  aspects  of  the  trunk,  and  is  associated 
with  a  number  of  body  segments,  varying  in  the  two  extremities  and  in  different  animals. 


MOEPHOL(XIY  OF  THE  LIMB-PLEXUSES. 


663 


Although  the  mesoblastic  material  of  which  the  limb  bud  is  composed  exhiljits  in  itself  no 
segmental  divisions  at  any  period  of  its  development,  a  clear  indication  of  the  segmental  relations 
of  the  limbs  is  obtained  from  the  arrangement  of  the  limb  nerves.  Taking  the  nerves  which 
supply  the  limbs  as  a  guide,  the  segments  engaged  in  the  formation  of  the  upper  extremity  are 
the  last  five  cervical  and  first  two  thoracic.  The  lower  extremity  is  related  by  its  nerves  to  all 
the  lumbar  and  the  first  three  sacral  segments.  In  each  limb,  the  segments  at  the  preaxial  and 
postaxial  borders  are  only  partially  concerned  in  limb  formation. 

It  has  been  already  shown  that  the  somatic  brandies  of  the  nerves  enter  the  substance  of  the 
embryonic  limb  and  divide  in  their  course  into  dorsal  and  ventral  trunks,  which  supply  the 
dorsal  and  ventral  surfaces  of  the  limb  bud.  The  higher  nerves  supply  the  preaxial  border,  the 
lower  nerves  sujsply  the  postaxial  border,  while  the  nerves  most  centrally  situated  extend  furthest 
towards  the  periphery  of  the  limb. 

In  order  to  understand  properly  the  constitution  of  the  limb-plexuses,  it  is  necessary  further 
to  make  a  comparison  of  the  surfaces  and  borders  of  the  embryonic  and  adult  limbs. 

Upper  Limb. — (A)  Borders. — The  preaxial  border  of  the  ujoj^er  extremity  extends  from  the 
middle  of  the  clavicle,  in  the  line  of  the  cephalic  vein,  down  the  front  of  the  shoulder,  the  outer 
side  of  the  arm,  forearm  and  hand,  to  the  outer  border  of  the  thumb.  The  postaxial  border 
extends  from  the  middle  of  the  axilla  along  the  inner  side  of  the  arm  (in  the  line  of  the  basilic 
vein),  the  inner  side  of  the  forearm  and  hand,  to  the  inner  border  of  the  little  finger. 

(B)  Surfaces. — The  areas  of  the  limb  between  these  lines,  anteriorly  and  posteriorly,  coiTespond 
to  the  ventral  and  dorsal  surfaces  of  the  embryonic  limb  bud.  The  ventral  surface  is  represented 
by  the  front  of  the  chest,  arm,  and  forearm,  and  the  palm  of  the  hand.  The  dorsal  surface  is 
represented  by  the  scapular  and  deltoid  regions,  the  back  of  the  arm,  forearm,  and  hand. 

Lower  Limb. — (A)  Borders. — The  preaxial  border  of  the  lower  limb  extends  from  the  middle 
of  Poupart's  ligament  down  the  inner  side  of  the  thigh  and  leg  in  the  line  of  the  internal 
saphenous  vein,  to  the  inner  side  of  the  great  toe.  The  postaxial  border,  beginning  at  the  coccyx, 
extends  along  the  fold  of  the  nates  and  the  outer  side  and  back  of  the  thigh  and  leg  (in  the  line 
of  the  external  saphenous  vein)  to  the  outer  border  of  the  foot  and  little  toe. 

(-B)  Surfaces. — The  areas  between  these  lines  correspond  to  the  ^Drimitive  dorsal  and  ventral 
surfaces  of  the  embryonic  limb  bud.  The  unequal  amount  of  rotation  in  the  parts  of  the  lower 
limb  obscures  the  relation  of  foetal  and  adult  surfaces,  which  are  most  easily  made  out  in  the 
infantile  position  of  the  limbs,  with  the  thighs  and  knees  flexed  and  the  soles  of  the  feet 
inverted.  The  ventral  surface  of  the  embyronic  limb  is  represented  by  the  inner  side  and 
back  of  the  thigh,  the  back  of  the  leg,  and  the  sole  of  the  foot.  The  dorsal  surface  is  represented 
by  the  front  of  the  thigh  and  buttock,  the  front  of  the  leg,  and  the  dorsum  of  the  foot. 

Composition  of  the  Limb-plexuses. — In  all  mammals  the  same  definite  plan  underlies  the 
constitution  of  the  limb-plexuses.  The  nerves  concerned  are  the  anterior  primary  divisions  of 
certain  segmental  spinal  nerves,  which  (with  certain  exceptions  at  the  preaxial  and  postaxial 
borders)  are  destined  wholly  and  solely  for  the  innervation  of  the  limb.  Each  of  the  anterior 
primary  divisions  engaged  divides  into  a  pair  of  secondary  trunks,  named  dorsal  or  posterior, 
ventral  or  anterior.  The  dorsal  and  ventral  trunks  again  subdivide  into  tertiary  trunks,  which 
combine  with  the  corresponding  subdivisions  of  neighbouring  dorsal  and  ventral  trunks  to  form 
the  nerves  of  distribution.  The  combinations  of  dorsal  trunks  jarovide  a  series  of  nerves  for  the 
supply  of  that  part  of  the  limb  which  is  derived  from  the  dorsal  surface  of  the  embryonic  limb 
bud  ;  the  combinations  of  ventral  trunks  give  rise  to  nerves  of  distribution  to  the  regions 
corresponding  to  its  ventral  surface.  The  relation  of  the  nerves  derived  from  the  limb-plexuses 
to  the  areas  of  the  limbs  is  given  in  the  accompanying  tables  : — 

T.  Upper  Limb. 


Origin. 

Nerves. 

Distribution. 

Brachial 
Plexus 

1 
1 

Dorsal  trunks 

{Posterior  cord) 

^Posterior  scapular         .         .  V 
Posterior  thoracic 
Suprascapular       .         .         .     ' 
Subscapular  (3)     . 
Circumflex    .         .         .         .  ■' 
(Lesser  internal  cutaneous  (?) )  \ 
(Intercosto-humeral  (?) )           J 

Musculo-spiral      .        .        .  I 

Scapular  region  and 
shoulder 

Arm,  inner  side 

Back  of  arm,  fore- 
arm, and  hand 

Front  of  chest 

Front   of   arm   and 

forearm 
Inner  side  of  arm 
Front   of  arm   and 

forearm 
P>ont  of  forearm  and 

hand                        ^ 

Dorsal 
surface 

Ventral  trunks 

(Outer  and 
J    inner  cords)    ' 

/•Nerve  to  subclavius  1 
Anterior  thoracic  (2)/   ' 

Musculo-cutaneous 

-  Lesser  internal  cutaneous 

Internal  cutaneous        .         .    | 

Median f 

^  Ulnar \ 

Ventral 
surface 

664 


THE  NEEVOUS  SYSTEM. 


II.  Lower  Limb. 


Origin.              ; 

Nerves. 

Distribution. 

Lumbo- 
sacral    ' 
Plexus 

Dorsal 
trunks 

Ventral ' 
trunks 

'Ilio-hypogastric  (iliac  brancli)' 
Superior  gluteal 
Inferior  gluteal 
Nerve  to  ijyriforini.s 
Small  sciatic          .         .         .    -' 

External  cutaneous       .         .   / 

Genito-crural  (crural  Ijrancli) 

Anterior  crural      .         .         .    [ 

Peroneal        .... 

Buttock 

Buttock  and  thigh,  outer  side  ' 

and  front 
Front  of  thigh 
Front  and  inner  side  of  thigh, 

leg,  and  foot 
Front  of  leg  and  foot 

Dorsal 
surface 

Allio-hypogastric   (hypogastric 
branch) 

Ilio-inguinal         .         .         .    j 

Genito-crural  (genital  Ijranch) 

Obturator      .         .         .         .  i 

Nerve  to  obturator  internus- 
and  superior  gemellus 

Nerve   to  quadratus   femoris 
and  inferior  gemellus 

Nerve  to  hamstrings 

Small  sciatic 

tibial 1 

Abdominal  wall  (ventral  sur- 
face) 

Abdominal  wall,  thigh,  and 
perineum 

Groin 

Thigh  (inner  side)  and  knee 
(back) 

Buttock  and  back  of  thigh 

Back  of  thigh  and  perineum 
Back  of  knee,  leg,  and  sole  of 
foot                                            ^ 

1 

Ventral 
surface 

In  the  regions  of  the  limbs  no  anterior  cutaneous  branches,  derived  fi'om  the  limb  nerves, 
supply  the  trunk.  The  whole  of  the  nerve  is  carried  into  the  limb  and  is  absorbed  in  its 
innervation,  and  the  dorsal  and  ventral  trunks  forming  the  liml^-plexuses  are  to  he  looked  upon 
as  homologous  with  the  lateral  and  anterior  trunks  of  an  intercostal  nerve.  Two  series  of 
anomalies  in  relation  to  the  formation  and  distribution  of  the  nerves  to  the  limbs  must,  however, 
be  considered,  because  it  has  been  suggested  (Goodsir)  that  the  nerves  of  the  limbs  are  serially 
homologous  with  not  the  whole,  but  with  only  the  lateral  branches  of  the  anterior  primary 
divisions  of  the  intercostal  nerves. 

(1)  Nerves  in  connexion  with  the  primitive  borders  of  the  Limbs. — At  the  preaxial 
border  of  the  upper  limb,  at  its  root,  the  fourth  cervical  nerve,  which  supplies  the  anterior  and 
lateral  surfaces  of  the  neck,  is  also  distributed  through  the  supraclavicular  nerves  to  the  skin  of 
Iwth  ventral  and  dorsal  surfaces  of  the  limb.  The  nerves  and  surfaces  are  here  not  merely 
homologous,  but  in  actual  continuity. 

At  the  preaxial  border  of  the  lower  limb,  similarly,  the  first  lumbar  nerve,  by  means  of  the 
ilio-hypogastric  and  ilio-inguinal  branches,  supplies  on  the  one  hand  the  buttock,  in  series  with 
the  lateral  branches  of  the  lower  thoracic  nerves,  and,  on  the  other  hand,  the  lower  part  of  the 
abdominal  wall  and  the  adjacent  inner  side  of  the  thigh,  in  series  with  the  anterior  terminal 
branches  of  the  lower  thoracic  nerves. 

At  the  postaxial  border  of  the  upper  limb  the  first  and  second  thoracic  nerves  are  concerned 
in  supplying  trunk  segments  as  well  as  parts  of  the  limb.  The  first  thoracic  nerve,  besides 
sui)j)lying  the  limb  through  the  inner  cord  of  the  jilexus,  also  innervates  at  least  the  muscles  of 
the  first  intercostal  space  ;  the  second  thoracic  nerve  is  concerned  in  the  innervation  of  the  limb, 
principally  by  means  of  its  lateral  branch  only,  which,  as  the  intercosto-humeral  nerve,  supplies 
the  skin  along  the  postaxial  border  of  the  limb  and  on  its  dorscd  side.  At  the  postaxial  border  of 
the  lower  limb,  in  the  same  way,  the  third  and  fourth  sacral  nerves,  jjartially  implicated  in  the 
innervation  of  the  limb  (through  the  tibial,  small  sciatic,  perforating  cutaneous  nerve,  and 
perineal  branch  of  the  fourth  sacral  nerve),  are  also  engaged  in  supplying  the  trunk  (perineum) 
through  the  pudic  nerve.  These  peculiarities  of  arrangement  of  the  nerves  at  the  borders  of  the 
limbs  may  be  explained  on  the  sxipposition  that  the  segment  corresponding  to  the  nerve  named 
is  only  partially  concerned  in  limb  formation,  and  is,  at  the  same  time,  imj)licated  to  a  greater 
or  less  extent  in  the  formation  of  structures  belonging  to  the  trunk. 

(2)  The  origin  and  distribution  of  the  nerves  at  the  postaxial  border  of  the  limbs  present 
a  special  difficulty.  In  the  composition  respectively  of  the  brachial  and  lumbo-sacral  plexuses, 
the  first  thoracic  and  third  sacral  nerves  do  not  as  a  rule  divide  into  ventral  and  dorsal  trunks, 
but  contribute  only  to  the  formation  of  the  ventral  series  of  nerves.  A  solution  of  this  difficulty 
may  be  found  in  the  examination  of  the  areas  of  distribution  of  the  nerves  derived  from  the 
first  thoracic  and  third  sacral  nerves.     In  the  case  of  the  brachial  plexus  (the  inner  cord  of  which 


THE  DISTRIBUTION  OF  THE  SPINAL  NEEVES. 


665 


receives  normally  the  whole  contribution  of  the  first  thoracic  nerve)  the  lesser  internal  cutaneous, 
the  inner  branch  of  the  internal  cutaneous,  and  the  dorsal  l^ranch  of  the  ulnar  nerve  supply  the 
dorsal  aspect  of  the  limb  on  its  postaxial  border.  These  nerves  are  in  serial  homology  with  the 
intercosto-humeral  and  lateral  trunks  of  intercostal  nerves.  In  the  case  of  the  lumbo-sacral  plexus 
similarly,  in  which  the  third  sacral  nerve  does  not  divide  into  ventral  and  dorsal  trunks,  the 
small  sciatic  and  tibial  nerves  containing  the  contribution  from  the  third  sacral  nerves  innervate, 
by  means  of  the  gluteal  and  external  femoral  branches  of  the  former  and  the  tibial  communi- 
cating branch  of  the  latter,  the  dorsal  surface  of  the  limb  along  the  postaxial  border,  in  series 
with  the  perforating  cutaneous  nerve  and  the  perineal  branch  of  the  fourth  sacral. 

These  a23parent  anomalies  appear  to  indicate  that,  instead  of  dividing  into  its  proper  dorsal 
and  ventral  trunks,  the  entire  contribution  of  the  spinal  nerve  concerned  is  in  these  instances 
carried  undivided  along  the  postaxial  border  of  the  limb  in  association  with  the  ventral  trunks, 
and  that  the  dorsal  subdivisions  are  thrown  off  successively  as  the  plexus  cords  approach  the 
periphery.  Indeed,  in  the  case  of  the  small  sciatic  nerve,  Eisler  has  shown  that,  when  the 
peroneal  and  tibial  nerves  are  separated  at  their  origin,  its  gluteal  and  external  femoral  branches 
arise  from  and  are  connected  with  the  dorsal,  and  the  perineal  and  internal  femoral  branches 
with  the  ventral  trunk. 


The  Disteibution  of  the  Spinal  Nerves  to  the  Muscles  and  Skin 

OF  the  Limbs. 

By  dissection,  experiment,  and  clinical  observation,  it  is  conclusively  proved  that 
as  a  rule  each  nerve  of  distribution  in  the  limb,  whether  to  muscle  or  skin,  is  made  up  of 
fibres  derived  from  more  than  one  spinal  nerve  ;  and,  further,  that  in  cutaneous  distribution 
a  considerable  overlapping  occurs  in  the  course  of  the  several  peripheral  nerves.  Moreover, 
the  arrangement  of  the  distribution  of  the  nerves  to  skin  and  to  muscles  is  not  identical. 
In  the  case  of  the  skin  of  the  limbs,  by  the  covering  of  the  limb  being  drawn  on  to  it  from 
adjacent  parts  in  the  process  of  growth,  cutaneous  nerves  are  engaged,  which  are  derived 
from  sources  not  represented  in  the  muscular  innervation  of  the  limbs.  Again,  among  the 
muscles,  some  have  undergone  fusion,  others  have  become  rudimentary,  and  others  again 
have  altered  their  position  in  the  limb.  Bearing  these  qualifications  in  mind,  it  is 
possible  to  formulate  a  definite  plan  for  the  innervation  of  the  skin  and  muscles  of  the 
upper  and  lower  limb.  The  accompanying  tables  give  an  analysis  of  the  distribution  of 
the  spinal  nerves  to  the  skin  and  muscles  of  the  upper  and  lower  limb  respectively : — 


T.  Upper  Limb. 

A.  Cutaneous  Nerves. 

1.  Dorsal  (Posterior)  Surface. 


Regions. 


Scapular 


Deltoid 


Upper  arm 


Upper  jmrt 

{preaxicd) 

Lower  part 

(postaxial) 


j  Upper  jjart 
idJ 


(preaxial) 
Lower  part 
(postaxial) 

Outer  side 
(preaxial) 

Inner  side 
( pOHtaxial) 


Nerves. 


Posterior  primary  divisions, 
cervical     .... 

Cervical  plexus,  acromial 

Posterior  primary  divisions, 
thoracic     .... 

Intercostal  nerves,  lateral  branches 

Cervical  plexus,  acromial 
Circumflex     .... 
Intercostal         nerves,  lateral 

branches   .... 

Circumflex     .... 
Musculo-spiral,     upper     external 

branch       .... 
Musculo-spii'al,  internal  branch 
Lesser  internal  cutanxious 
Intercosto-humeral 


Spinal  Origins. 


Preaxial 
Nerves. 


C.  4.  5.  6. 
C.  3.  4. 

T.  1.-7. 
T.  2.  3.  4. 

C.  3.  4. 
C.  5.  6. 


C.  5.  6. 


Postaxial 
Nerves. 


T.  2.  3. 


C.  (5).  6. 

C.  8. 
T.  1. 
T.  2. 


666 


THE  NEEVOUS  SYSTEM. 
1.  Dorsal  (Posterior)  Surface — continued. 


Regions. 


'Outer  side 

{jjreaxial) 


Forearm- 


Hand 


Inner  side 

(postaxial) 

r  Outer  side 
I      (preaxiaT) 
I  Inner  side 
I     (postaxial) 


Nerves. 


Musculo-spiral,     upper 

branch 
Musculo-spiral,     lower 

branch 
Musculo  -  cutaneous, 

brancli 
Radial    . 
Internal       cutaneous, 

branch 
Ulnar,  dorsal  branch 

Radial    . 


Ulnar 


external 
external 
posterior 


internal 


Spinal  Origins. 

Preaxial  Postaxial 

Nerves.  Nerves. 


C.  (5).  6. 

C.  6.  7. 

C.  5.  6. 
C.  6.  7. 


C.  6.  7. 


C.  8.  T.  1. 
C.  8. 


C.  8. 


Regions. 


I.  Upper  Limb. 

A.  Cutaneous  Nerves. 

2,  Ventral  (Anterior)  Surface. 


Chest 


Upper  arm 


Forearm 


{Uj^per  part 
(preaxial) 
Lower  part 
(postaxial) 

Outer  part 

(p)reaxial) 

Inner  part 
(postaxial) 

rOiTter  part 
.1      (preaxial) 
I  Inner  part 
^     (postaxial) 
"Outer  part 
(preaxial) 


Hand 


Inner  part 
(j)ostasRial)' 


Nerves. 


Cervical    plexus,    supraclavicular 

branches   .... 
Intercostal        nerves,        anterior 

branches   .... 
Intercostal  nerves,  lateral  branches 
Circumflex     .... 
Musculo  -  spiral,     upper     external 

branch       .... 
Internal  cutaneous 
Lesser  internal  cutaneous 
Intercosto-humeral 
Musculo  -  cutaneous,  anterior 

branch      .... 
Internal       cutaneous,       anterior 

branch      .... 
Musculo -cutaneous,  ball  of  thumb 
Median,  palmar  branch 
digital  branches 
thumb,  outer  side    . 

„       inner  side) 
index,  outer  side  / 
,,       inner  side) 
middle,  outer  side/ 
„       inner  side~^ 
ring,  outer  side      ( 
Ulnar,  palmar  branch   . 
„      digital  branches 


Spinal  Origins. 

Preaxial  Postaxial 

Nerves.  Nerves. 


C.  3.  4. 

) 

C.  5.  6. 
C.  5.  6. 

C.  5.  6. 


T.  2.-7. 


C.  8.  T.  1. 
T.  1. 
T.  2. 


C.  8.  T.  1. 


I  C.  5.  6. 
C.  6.  7. 
C.  6.  7.  8.  T.  1. 

■  C.  6.  (7). 

C.  6.  7. 

C  (6).  7.  8.  (T.  1). 

C.  8,  T.  1. 

T.  1. 
T.  1. 


THE  DISTRIBUTION  OF  THE  SPINAL  NEEVES. 


667 


I.  Upper  Limb. 

B.  Muscular  Nerves. 
1.  Dorsal  (Posterior)  Surface. 


Spinal  Origins. 

Regions. 

Muscles. 

Nerves.             ! 

Preaxial  Postaxial 

] 

Nerves.      Nerves.   ' 

1 

'Upper  part 

Trapezius        .... 

Cervical  plexus     . 

i 

C.  3.  4. 

(preaxial 
muscles) 

Levator  anguli  scapulse 

/Cervical  plexus    . 
I  Posterior  scapular 

C.  3.  4. 
C.  5. 

Ehomboidei    .         .         .         .  | 

Posterior  scapular 

C.  5. 

( 

Serratus  niagnus    . 

Posterior  thoracic 

C.  5.  6.  7. 

Shoulder- 

Supraspinatus  "1 
Infraspinatus  J      '         '        ' 

Suprascapular 

Subscapular  is 

f  Short  subscapular 
I  Lower        „              j 

-C.  5.  6. 

Teres  major    . 

Lower  subscapular 

Lower  part 

{postaxial 

Teres  minor  ) 

Deltoid          /         •         ■         ■ 

Circumflex    . 

J 

^     muscles) 

Latissimus  dorsi     . 

Long  subscapular 

C.  6.  7.  8. 

Triceps 

* 

Outer  head 

] 

C.  (6).  7.  8. 

Upper  arm         .        .  " 

Middle  head       .         . 

Musculo-spiral 

I        C.  7.  8. 

Inner  head 

Anconeus        .... 

. 

' 

Brachio-radialis 

] 

C.  6.  6. 

Extensor        carpi        radialis 

j-Musculo-spiral 

longior       .... 

C.  (5).  6.  7.  8. 

Extensor        carpi        radialis 

' 

brevior      .... 

C.  (5).  6.  7.  (8). 

Supinator  radii  brevis   . 

C.  (5).  6.                ! 

Forearm     . 

Extensor  communis  digitorum 

' 

„         minimi  digiti  . 
„         carpi  ulnaris    . 

Posterior      inter- 

' 

Extensor  ossis  metacarpi  pol- 

osseous 

,C.  (5).  6.  7.  8.       1 

licis  

■ 

Extensor  longus  pollicis 

„          brevis  laollicis 

„          indicis     . 

> 

I.  Upper  Limb. 

B.  Muscular  Nerves. 
2.  Ventral  (Anterior)  Surface. 


Regions. 


Muscles. 


Pectoral 
Region 


Upper  part 
{preaxial 
muscles) 


Lower  part 

{postaxial 
muscles) 


Stemo-mastoid 
Omo-hyoid      \ 
Sterno-hyoid  ) 
Subclavius    . 
Pcctoralis  major 
Clavicular  j)art 
SteiTial  pait 
Pectoral  is  minor 


Nerves. 


Cervical  plexus 
Ansa  hypoglossi     . 
Brachial  plexus 

^Anterior    thoracic 
nerves 


Spinal  Origins. 

Preaxial    Postaxial 
Nerves.      Nerves. 


C.  2. 

C.  1.  2.  3. 

C.  5.  6. 

C.  5.  6.  7.  8.  T.  1. 

C.  5.  6. 

C.  .O.  6.  7.  8.  T.  1. 
C.  7.  8.  T.  1. 


668 


THE  NEEVOUS  SYSTEM. 
2.  Ventral  (Anterior)  Surface — continued. 


Regions. 


Upper 


Outer  part 

{preaxial) 


Inner  jjart 

{postaxial) 

Outer  part 

(preaxial) 


Muscles. 


Forearm- 


Inner  part 

{•postaxial) 
'Outer  jDart 
iineaxial) 


Hand     - 


Inner  part 

(postaxial) 


Biceps  . 

Bracliialis  anticus 
Coraco-bracliialis  . 


Axillary  arches 


Pronator  radii  teres 
Flexor  carpi  radialis     . 
Palmaris  longus    . 
Flexor  sublimis  digitorum    . 

Flexor  profundus  digitorum 

Flexor  carpi  ulnaris 
Flexor  longus  poUicis  . 
Pronator  quadratus 
Abductor  poUicis  . 
Opponens  pollicis 
Flexor  brevis  jjoUicis    . 
Two  outer  lumbricales . 
Two  inner  hinibricales . 
Interossei       .         .         .         . 
Adductores    pollicis    (traus- 

versus  et  obliquus) 
Abductor  minimi  digiti 
Opponens  minimi  digiti 
Flexor  brevis  minimi  digiti 


Nerves. 


Musculo-cutaneous 
/  Musculo-cutaneous 
IMusculo-spiral 

Musculo-cutaneous 
r Internal  anterior 


thoracic,  or  lesser 
internal  cutane- 
ous, or  inter- 
costo-liumeral 


Spinal  Origins. 

Prea.vicd  Pa^f axial 
Nerves.      Nerves. 


|C.  5.  6. 

'  C.  (5).  6. 
C.  7. 


C.  8.  T.  1.  (2). 


^Median 

/Anterior 
I     osseous : 
Ulnar     . 
1  Anterior 
J      osseous 

■  Median  . 


Ulnar 


C.  6. 
C.  6. 


inter- 
Ulnar 

inter-    \ 


C.  7.  8.  T.  1. 
C.  8.  T.  1. 
C.  8.  T.  1. 

C.  7.  8.  T.  1. 


-C.  6.  7. 


C.  8.  (T.  1). 


II.  Lower  Limb. 

A.  Cutaneous  Nerves. 
1.  Dorsal  Surface. 

{Front  and  cuter  side  of  thigh,  buttock,  front  of  leg,  dorsuon  of  foot.) 


Regions. 


Nerves. 


Front  of  thigh  and 
front  part  of  but- 
tock 

{freaxial  nerves) 


Thigh - 


Buttock  J 


Outer  side  of  thigh  r 
and  buttock,  back ) 
and  lower  part      i 

{postaxial  nerves)      [ 


Leg 


Dorsum 
foot 


•1 


of 


Inner  side 

{preaxial) 
Outer  side 

{jyostaxial) 
Inner  side 

{preaxial) 
Outer  side 

{postaxial) 


Genito-crural,  crural  branch 
Anterior  crural,  internal  branch    . 
Anterior  crural,  middle  branch 
External  cutaneous 
Twelfth  thoracic,  iliac  branch 
Ilio-hy2:)ogastric,  iliac  branch 
Posterior       primary       diA'isiont^, 

lumbar     ..... 
Posterior       primary       divisions, 

sacral        ..... 
Posterior        primary        divisions, 

coccygeal ..... 
Small  sciatic  :  gluteal,  and  femoral 

branches  ..... 
Internal  saphenous 

Patellar  branch 
Musculo-cutaneous 
Peroneal,  sural  branches 
Internal  saphenous 
Anterior  tibial  .... 
Musculo-cutaneous 
External  saphenous 


Spinal  Origins. 

Preaxial  Postaxial 

Nerves.  Nerves. 


L.  1.  2. 

L.  2.  3. 

T.  12. 
L.  1. 


L.  1.  2.  3. 


S.  1.-5. 
Co. 


S.  1.  2.  3. 


\l. 


3.  4. 


S.  1. 

5.  s. ; 


L.  4.  5. 
L.  (4). 
,  3.  4. 
L.'4.  5.  (S. 
L.  4.  5.  S.  1. 

S.  1.  (2). 


!)• 


THE  DISTKIBUTION  OF  THE  SPINAL  NERVES. 


669 


n.  Iiower  Limb. 

A.  Cutaneous  Nerves. 

2.  Ventral  Surface. 

{Inner  side  and  hack  of  thigh,  hade  of  leg,  and  sole  of  foot.) 


Spinal  Origins.              ' 

Regions. 

Nerves. 

Preaxial           Postaxial 

)f 

1        Nerves.               Nerves.         j 

1 

'  Inner  side   ( 

|Ilio-inguinal          .... 
/obturator      ..... 

,   L.  1. 

Inner      side 

thigh 

L.  2.  3.  (4). 

and  back  of 

(preaxial) 

thigh 

Back  of  thig 
(postaxial) 

ti 

■Small  sciatic,  femoral  branches     . 

S.  1.  2.  3. 

. 

Peroneal,  sural  branches  . 

Jl.  (4).  5.  S.  1. 
S.  1.  2.  3. 

Back  of  leg 

Peroneal,  communicans  fibularis  . 
Small  sciatic          .... 

External  saphenous 

S.  1.  (2). 

/■Inner  side 

Internal  saphenous 

,    L.  3.  4. 

(preaxial) 

Posterior  tibial,  calcanean 
Internal  plantar    . 
Great  toe,  inner  side . 
„        ,,    outer  side. 

S.  1.  2. 
\   L.  4.  5.  S.  1. 
L.  4.  5. 

JL.  4.  5.  S.  1. 

Second  toe,  inner  side 

Sole  of  foot  - 

„         ,,     outer  side 
Third  toe,  inner  side 

■L.  5.  S.  1. 

„         „     outer  side 

Fourth  toe,  inner  side 

J                                               ' 

External  plantar  . 

]                                              1 

Fou.rth  toe,  outer  side 

Vs.  1.  2. 

Outer  side 

Fifth  toe,  inner  side  . 

(postaxial) 

„       „    outer  side  . 

J                                               i 

External  saphenous 

S  1.  (2). 

11.  Lower  Limb. 

B.  Muscular  Nerves. 
1.  Dorsal  Surface. 

{Front  and  outer  side  of  thigh,  huttock,  front  and  outer  side  of  leg,  dorsum  of  foot?) 


! 

Spinal  Origins. 

Regions. 

Muscles. 

Nerves. 

Preaxial      Postaxial 

Nerves.         Nerves. 

i    Pectineus 

\ 
JL.  2.  3.                      i 

Sartorius  . 

Front  of  thigh 

{preaxial) 

Iliacus 

Psoas 

Quadriceps  extensor 

^Anterior  crural 

JL.  2.  3.  4. 

Vastus  internus    . 

Rectus  femoris 

II.  3.  4. 

Crureus 

Vastus  externus    . 

j 

Tensor  f'ascite  femoi'is 

) 

i     L.  4.  5.  S.  1 

Glut(!iis  Illiniums 

rSupej'ioi'  gluteal 

Buttockand  outer  side  of  thigh            „       mediiis 

{;i)()slaxial) 

,,        iiiaxiiiiiis 

1 11  f'ci'ioi- gluteal    . 

1          !_,  5   S    1    2 

Bice])8,  kIioiI  head    . 

Peroneal 

Pyrifoniiis 

i                                            i 

Sacral  jilexus 

S.  1.  2. 

670 


THE  NEEVOUS  SYSTEM. 
1.  Dorsal  Surface — continued. 


Regions. 


Front  of  leg 


Dorsum  of  foot 


Inner  side 

{preaxial) 


Outer  side 
(postaxial) 


Muscles. 


Tibialis  anticus 
Extensor      j^^^-'Pi'i'^i'^ 

hallucis 
Extensor  longus 

digitorum 
Peroneus  tertius 
Peroneus  longus 
Peroneus  brevis 
Extensor  brevis  digi 

torum    . 


Nerves. 


:-  Anterior  tibial 


Spinal  Origins. 

I'rea.ckd  JVcrces. 


>L.  4.  5.  S.  1. 


Musculo-cutaneous 
Anterior  tibial  .    1 


II.  Lower  Limb. 

B.  Muscular  Nerves. 
2.  Ventral  Surface. 

(Inner  side  and  hack  of  thigh,  hack  of  leg,  and  sole  of  foot.) 


Regions. 


Thigb,  inner 
side  \ 

(preaxial) 

mx.  •  -u  J      Thigh,  outer  I 

Thigh      and         g.^^'  ) 

(postaxial)  I 


Buttock 


Muscles. 


Back  of  leg 


Inner  side 

{preaxial) 


Sole  of  foot 


Outer  side 

(postaxial) 


Adductor  longus 

Gracilis    . 
Adductor  brevis 

Obturator  externus  . 

Adductor  magnus     . 

Adductor  magnus     . 

Semi-membranosus  . 

Semi-tendinosus 

Biceps,  long  head     . 

Quadratus  femoris 
and  superior  gem- 
ellus 

Inferior  gemellus 
and  obturator  in- 
ternus   . 

Plantaris  . 

Popliteus . 

Flexor  longus  digi- 
torum  . 

Tibialis  posticus 

Flexor  longus  hal- 
lucis 

Soleus 

Soleus 

Gastrocnemius  (each 
head)     . 

Abductor  hallucis     . 

Flexor  brevis  digi- 
torum   . 

Flexor  brevis  hal- 
lucis 

First  lumbricalis 

Second,  third,  and 
fourth  lumbricales 

Flexor  accessorius    . 

Adductores  hallucis . 

Interossei 

Flexor  brevis  minimi 
digiti    . 

Abductor  minimi 
digiti    . 


Nerves. 


Spinal  Origins. 

Preaxial       Postaxial 

Nerves.  Nerves. 


-  Obturator 


Nerve   to    ham- 
strings    . 


Sacral  plexus 


Tibial 


Posterior  tibial 


Tibial 


-  Internal  plantar 


L 
L 
L 

2. 
2. 
3. 

3. 
3. 

4. 

4. 

L. 
L. 

4. 
5. 

S. 

5. 

S. 
1. 

S. 
1. 
2. 

1. 
2. 
3. 

L 

4 

5. 

S 

1 

S. 

1. 

2. 

3. 

L.  4.  5.  S.  1. 
L.  5.  S.  1. 

L.  5.  S.  1.  2. 

S.  1.  2. 

L.  4.  5.  S.  1. 


►  External  plantar 


S.  1.  2. 


THE  DISTKIBUTION  OF  THE  SPINAL  NERVES. 


071 


A.  Innervation  of  the  Muscles  of  the  Limbs. — The  loll  owing  laws  appear  to  be  applicable 
to  the  upper  and  lower  limbs  alike  : — • 

1.  No  limb-muscle  receives  its  nerve-swpply  from  posterior  primary  divisions. 

2.  The  dorsal  and  ventral  strata  of  muscles  are  aliuays  supplied  by  the  corresponding  dorsal  and 
ventral  branches  of  the  nerves  concerned.  The  ventral  muscular  stratum  is  more  extensive  than  the 
dorsal ;  the  ventral  nerves  are  the  more  numerous,  and  the  additional  nerves  are  postaxially  placed. 
The  spinal  nerves  supplying  muscles  of  the  upper  limb  are  C.  5,  6,  7,  8  (dorsal),  and  C.  5,  6,  7,  8, 
T.  1  (ventral) ;  the  nerves  for  the  muscles  of  the  lower  limb  are  L.  2,  3,  4,  5,  S.  1,  2  (dorsal),  and 
L.  2,  3,  4,  5,  S.  1,  2,  3  (ventral). 

3.  The  dorsal  and  ventral  trunks  of  the  nerves  are  distributed  in  the  limb  in  a  continuous, 
segmental  m,anner  ;  so  that,  "  of  two  muscles,  that  nearer  the  head  end  of  the  body  tends  to  be 
supplied  by  the  higher  nerve,  and  that  nearer  the  tail  end  by  the  lower  nerve"  (Herringham). 

4.  The  nerves  pilaced  m,ost  centrally  in  the  plexus  extend  furthest  into  the  limb,  and  the  more 
preaxial  nerves  terminate  sooner  in  the  limb  than  the  more  postaxial  nerves. 


Upper  Limb 
Dorsal  Surface. 

Muscles  of  shoulder     .     C.  3,  4,  5,  6,  7,  8. 
„         arm    .         .     C.  6,  7,  8. 
„  forearm      .     C.  6,  7. 


Ventral  Surface. 


Muscles  of  thigh  and 

buttock    . 
Muscles  of  leg  and  foot 


Muscles  of  chest  .  C.  .5,  6,  7,  8,  T.  1. 

„         arm  .  C.  .5,  6,  7. 

forearm  .  C.  6,  7,  8,  T.  1. 

hand  .  C.  6,  7,  8  (T.  1). 
Lower  Limb. 

Muscles  of  thigh  .  L.  2,  3,  4,  5,  S.  1, 

L.  2,  3,  4,  5,  S.  1,  2.                 „         leg  .  L.  4,  5,  S.  1,  2. 

L.  4,  5,  S.  1.                             „         foot  .  L.  5,  S.  1,  2. 


2,  3. 


The  only  exception  to  this  rule  is  on  the  ventral  (anterior)  surface  of  the  upper  arm,  where  a 
suppression  of  the  muscle  elements  leads  to  an  absence  of  the  regular  series  of  segmental  nerves 
^C.  8,  T.  1)  on  its  postaxial  border.     These  nerves  reappear  in  the  forearm,  and  the  occasional 


Shovilder 

DORSAL 
Arm 

SURFACE 
Forearm 

1               ! 

Hand. 

C.3 

4 

5 

1 

6 

:                ;                 \             \ 

7 

i                      :                       \                 \ 

8 

1 

i              \ 

1 

\ 

Chest 


VENTRAL    SURFACE 
u4rm.  Forearm 


If  and 


DORSAL      SURFACE 
ThiCfh.    &•    Buttock.         Leff 


J'oot 


L.2 
3 
4 
5 

S.I 
2 


VENT 
ThigJi 

RAL 

SURFACE 

L.2 

] 

3 

4 

i                            \                           ! 

,S 

SI 

'                             '                          ) 

2 

'                             1                          J 

3 

\                  i                ! 

Fig.  516. — Scheme  of  the  segmental  distribution  of  the  muscular  nerves  of  the  upper  and  lower  limbs. 

"  axillary  arches "  may  be  regarded  as  the  muscular  elements  usually  suppressed,  and,  when 
present,  supplied  by  these  nerves. 

Muscles  with  a  Double  Nerve-supply. — The  existence  of  more  than  one  nerve  to  a  muscle 
indicates  usually  that  the  muscle  is  composite  and  is  the  representative  of  originally  separate 
elements,  belonging  to  more  than  one  segment  or  to  both  surfaces  of  the  limb.  In  the  case  of 
the  pectoralis  major,  subscapularis  and  flexor  profundus  digitorum,  adductor  magnus,  and  soleus, 
parts  of  the  same  (ventral  or  dorsal)  stratum  have  fused,  to  form  muscles  innervated  from  the 
coiTesponding  ventral  or  dorsal  nerves.  The  other  muscles  having  a  double  nerve-supply — 
brachial  is  anticus,  biceps  flexor  cruris,  and  (sometimes)  pectineus — are  examples  of  fusion  at  the 
preaxial  or  postaxial  border  of  muscular  elements  derived  from  the  dorsal  and  ventral  surfaces  of 
the  limb,  which  are  correspondingly  innervated  by  branches  from  both  dorsal  and  venlral  series  : 
e.g.  the  brachialis  anticus  is  innervated  ))y  the  muscuhi-cutaneous  and  musculo-spiral  nerves  ;  the 
bicejw  flexor  criiixs,  Ijy  the,  perrnie;!,!  (short  head)  and  tibial  (long  head)  nerves  ;  and  the  pectineus, 
by  tlie,  anfi-rJor  ci'iiral  and  (soun-.tinics)  fjhtiirator  nerves. 

B.  Innervation  of  the  Skin  of  the  Limbs. — While  the  scheme  of  cutaneous  innervation  of 
the  liinbs  is  fuiiflanientally  segmental,  yet  the  arrangement  is  confused  and  complicated  by 
various  causes.  The  grfjwtli  of  tlie  linil)  from  the  trunk  has  caused  the  skin  to  be  drawn  out 
over  it  like  a  Kti'(d'',he,fl  sheet  of  india-ruijljer  (H(aTingliam),  and  at  the  same  time  the  extent  of 
tlie  dorsal  area  of  the  linilj  is  jncreas<'d  at  tlie  expense  of  the  ventral  area.  The  ccaitral  nerves  of 
the  plexus  remain  buiied  deejily  in  the  substance;  of  the  limlj,  only  coming  to  the  surface  towards 
the  periphery.     The  proximal  parts  of  both  suifaces  of  the  limb  thus  become  innervated   by 


672 


THE  NEEVOUS  SYSTEM. 


cutaneous  nerves  otherwise  not  necessarily  concerned  in  the  innervation  of  the  limbs.  Herring- 
ham  has  shown  tliat — (A)  Of  hvo  spots  on  the  skin,  that  nearer  the  preaxial  harder  tends  to  he 
supplied  by  the  higher  nerve.  (B)  Of  two  s])ots  in  the  preaxial  area,  the  loiver  tends  to  he  supplied  by 
the  lower  nerve;  and  of  tiuo  spots  in  the  'postaxial  area,  the  lower  tends  to  he  su])plied  by  the  higher 
nerve.  In  other  words,  from  the  root  of  the  limb  do^vn  the  preaxial  border  to  its  distal  extremity, 
and  up  the  j^ostaxial  border  to  the  root  of  the  limlj  again,  there  is  a  definite  numerical  sequence 
of  spinal  nerves  supi^lying  skin  areas  through  nerves  of  the  limb-plexuses.  A  similar  numerical 
sequence  in  the  arrangement  of  the  nerves  is  also  found  extending  over  the  dorsal  and  ventral 
surfaces  of  the  limbs  from  jireaxial  to  postaxial  Ijorder,  excej)t  in  certain  situations. 

On  the  dorsal  and  ventral  surfaces  of  both  uj^per  and  lower  limbs  there  is  a  hiatus,  for  a 
certain  distance,  in  the  numerical  sequence  of  tlie  spinal  nerves  in  their  cutaneous  distribution, 
explicable  on  tlie  ground  tliat  the  central  nerves  of  tlie  i)lexus,  which  fail  to  reach  the  surface  in 
these  situations,  are  replaced  by  cutaneous  brandies  from  neighbouring  nerves.  This  hiatus  has 
been  named  tlie  axial  area  or  line. 

In  the  upper  limb,  the  dorsal  axial  area  or  line  extends  from  the  middle  line  of  the  back, 
oi3i30site  the  vertebra  promineiis,  to  the  insertion  of  the  deltoid. 

The  ventral  axial  area  or  line  extends  anterioidy  from  the  middle  line  of  the  trunk,  at  the 
manubrio-sternal  joint,  across  the  chest,  down  the  front  of  the  arm  and  forearm  to  the  wrist. 

In  the  lower  limb,  the  dorsal  axial  area  or  line  may  be  traced  from  the  middle  line  of  tlie 
back  over  tlie  posterior  suj^erior  iliac  sj^ine,  across  the  buttock  and  thigh,  to  the  head  of  the 
fibula. 

A  ventral  axial  area  or  line  can  also  be  traced  from  tlie  root  of  the  penis  along  the  inner  side 
of  the  thigh  and  knee,  and  down  the  back  of  the  leg  to  the  heel. 

These  areas  or  lines  represent  the  meeting-place  and  overlapping  of  nerves,  which  are  not  in 
numerical  sequence  ;  and  it  is  only  at  the  peripheral  parts  of  the  limbs,  on  the  dorsal  and  ventral 
surfaces,  that  the  nerves  appear  in  numerical  sequence  from  the  preaxial  to  the  postaxial  border. 
In  the  case  of  the  upjDer  limb  the  hiatus  is  caused,  in  both  surfaces  of  the  limb,  by  the  absence  of 
cutaneous  branches  of  the  seventh  cervical  nerve  ;  in  the  case  of  the  lower  limb  the  hiatus  is  due 
to  the  absence  of  branches  from  the  fifth  lumbar  nerve  on  both  surfaces  of  the  limb,  and  the 
absence  of  branches  from  the  fourth  lumbar  nerve,  in  addition,  on  the  dorsal  surface. 

Understanding  the  significance  of  these  dorsal  and  ventral  axial  areas  or  lines,  and  at  the 
same  time  bearing  in  mind  the  overlapping  which  occurs  in  tlie  cutaneous  distribution  of  each 
spinal  nerve,  the  areas  of  skin  supplied  through  the  limb-ijlexuses  can  be  mapped  out  with  con- 
siderable i^recision,  as  indicated  in  the  following  tables  : — 

A.  Upper  Limb. 
Cutaneous  Distribution. 


Nerves. 

Spinal  Origin. 

Distribution. 

f 

Supraclavicular  nerves 

C. 

3.  4. 

Chest,   shoulder,    deltoid,    and 
scapular  regions. 

Circumflex  . 

C. 

5.  6. 

Deltoid  region,  outer  side  of  arm. 

Preaxial  border 

Musculo-spiral    (upper 

C. 

(5).  6. 

Outer  side  and  back  of  arm  and 

from  neck  to     - 

external) 

forearm. 

hand 

Musculo-spiral    (lower 

C. 

6.  7.  8. 

Outer  side  and  back  of  elbow 

i 

external) 

and  forearm. 

Musculo-cutaneous 

C. 

5.  6. 

Outer  side  of  forearm,  in  front 

V 

and  behind. 

r  Dorsum  1 
Hand  -> 

I  Palm      - 

Eadial 

Ulnar  .... 

C. 
C. 

6.  7. 

8. 

?^^t«^^!t|  of  dorsum  of  hand, 
inner  side  } 

Musculo-cutaneous 

C. 

5.  6. 

Ball  of  thumb. 

Median 

Ulnar  .... 

C. 
T. 

6.  7. 
1. 

?^^t«^'^!^^|of  palm  of  hand. 
Inner  side  J      ^ 

r 

Thumb          C.  6.  7. 

First  finger,  C.  6.  7.  8. 

Digits       . 

Median 

C. 

6.  7.  8.  T.  1. 

Second   „      C.  7.  8.  T.  1. 

Ulnar 

c. 

8.  T.  1. 

Third     „      C.  8.  T.  1. 
Fourth    „    1  m  -■ 
Fifth       „   i^-  ^■ 

. 

t 

Internal  cutaneous 

c. 

8.  T.   1. 

Inner  side  of  forearm,  in  front 

and  behind. 

Musculo-spiral    (inter- 

c. 

8. 

nal) 

Postaxial  border 

Lesser  internal  cutane- 

T. 

1. 

Inner  side  of  arm. 

from  hand  to 

ous 

chest 

Intercosto-humeral 

T. 

2. 

^ 

Intercosto-humeral 

T. 

2. 
3. 
4. 

■ 

Third  intercostal 

T. 

Axillary  folds. 

^ 

Fourth         „ 

T. 

VARIATIONS  IN  THE  POSITION  OF  THE  LIMB-PLEXUSES.      673 


B.  Lower  Limb. 
Cutaneous  Distribution. 


Nerves. 

Spinal  Origin. 

Distribution. 

r 

Iliac  branch  of  twelfth 

T. 

12. 

Outer  side  of  buttock. 

thoracic 

Iliac    branch    of    ilio- 

L. 

1. 

Outer  side  of  buttock. 

hypogastric 

Ilio-inguinal 

L. 

1. 

Groin  and  over  Scarpa's  triangle. 

Preaxial  border 

Genito-crural 

L. 

1.  2. 

Front  of  thigh,  upper  third. 

from  trunk  to    ' 

i  External  cutaneous 

L. 

2.  3. 

Front  and  outer  side  of  thigh. 

foot 

Anterior  crural  (middle 

L. 

2.  3. 

Front  and  inner  side  of  thigh, 

i 

and  internal) 

lower  two-thirds. 

Obturator     . 

L. 

2.  3.  (4). 

Inner    side    of    thigh,   middle 

third. 
Knee  and  leg,  inner  side  and 

Anterior  crural  (inter- 

L. 

3.  4. 

nal  saphenous) 

front. 

Internal  saphenous 

L. 

3.  4. 

Inner  side  of  foot. 

Anterior  tibial     . 

L. 

4.  5.  S.  (1). 

Interval      between      first     and 

r  Dorsum  - 

1 

second  toes. 

Musculo-cutaneous 

L. 

4.  5.  S.   1. 

Dorsum  of  foot  and  toes. 

Foot- 

'^Sole 

External  sajjlienous 

S. 

1.  (2). 

Outer  side  of  foot. 

Internal  plantar 

L. 

4.  5.  S.  1. 

Inner  part                 \ 
Outer  part                  -of  sole. 
Heel  and  back  part  J 

External  plantar 

S. 

1.  2. 

Posterior    tibial    (cal- 

s. 

1.  2. 

canean) 

■ 

4.  5.  S.   1.      , 
1.  2. 

Great  toe,    L.  4.  5.  S.  1. 

Digits 

Internal  and  external 
plantar 

L. 

S. 

Second  toe,  L.  4.  5.  S.  1. 
Third      „    L.  5.  S.  1. 
Fourth    „    L.  5.  S.  1.  2. 

Fifth       „    S.  1.  2. 

External  saphenous 

s. 

1.  (2). 

Outer  side  of  foot  and  leg,  lower 

Postaxial  border 

third. 

from  foot  to    •; 

i  Small  sciatic 

s. 

1.  2.  3. 

Back  of  leg,  thigh,  and  buttock. 

coccyx 

Perforating  cutaneous . 

s. 

2.  3. 

Buttock   (fold   of  nates,   inner 

^ 

half). 

Sacro-coccygeal    . 

s. 

4.  5.  Co.  1. 

Anal  fold. 

Vaeiations  in  the  Position  of  the  Limb-plexuses. 

Two  different  kinds  of  variations  occur  in  relation  to  the  limb-nerves. 

(1)  Individual  variations,  in  both  the  extent  of  origin  and  in  the  area  of  distribution  of  a 
given  nerve,  are  not  uncommon  ;  these  variations  are  usually  concomitant  with  comjsensatory 
variations  in  adjacent  nerves,  and  are  due  to  the  fibres  of  a  given  sj^inal  nerve  taking  an 
abnormal  course  in  the  trunk  of  another  nerve  of  distribution  and  effecting  a  communication 
with  the  proper  nerve  peripherally.  In  this  way  the  variations  in  the  origin  and  distribution 
of  the  intercosto -humeral  nerve  may  be  explained ;  and,  similarly,  the  ulnar  nerve  may  have 
some  of  its  fibres  carried  as  far  as  the  forearm  incorporated  with  the  median  and  transferred  to 
it  by  a  communication  between  the  two  nerves  in  that  region. 

(2)  Variations  in  the  limb-plexus,  in  relation  to  the  vertebral  column,  are  the  chief  cause  of 
variations  in  the  constitution  of  the  limb-nerves.  These  variations  affect  more  or  less  the  whole 
series  of  nerves  in  the  plexus. 

The  brachial  plexus  is  subject  only  to  very  slight  variation  in  position  and  arrangement. 
It  may  be  reiufoi/ced  at  the  upper  end  by  a  slender  trunk  from  the  fourth  cervical  nerve,  and, 
more  frequently,  by  an  intra  -  thoracic  communication  between  the  second  and  first  thoracic 
nerves.  The  presence  of  one  or  other  of  these  nerves  is  an  indication  of  a  slight  tendency 
towards  a  cephalic  or  caudal  shifting  of  the  whole  plexus  in  relation  to  the  spinal  cord.  It  is, 
liowever,  never  sufficient  to  cause  the  exclusion  to  any  extent  of  the  nerves  normally  implicated. 
The  presence  of  a  c(a-vical  rib  may  coincide  with  little  or  no  change  in  the  relation  of  the  nerves. 
lu'Jced,  the  inclusion  of  the  second  thoracic  nerve  in  the  plexus  may  be,  as  already  stated, 
merely  an  individual  variation,  a  change  m  the  jjath  to  the  limb  of  the  intercosto-humeral 
nerve.  Concomitant  variations  occur  among  gi'oups  of  nerves,  however,  whicli  indicate  a  certain 
tendency  to  variation  in  tlie  jjosition  of  tlie  wliole  jjh^xus.  At  onci  cmd,  the  suprascapular  and 
mu.sculo-ciitaneous  nerves  may  arise  from  the  iburth  and  fiftli,  fiftli  alone,  or  fifth  and  sixth 
cervical  nerve.s.  At  tlie  otlier  end  of  the  ])lexus,  the  musculo-sjjiral  may  or  may  not  rticeive  a 
root  from  the  first  thoracic  niirve,  and  this  addition  is  ratlier  more  likely  to  occur  wlien  tlie 
fiea;nd  thoracic  nerve  is  iinp]icat(!d  in  the  plexus. 

Tin;  lumbo-sacral  plexus  shows  a  very  considerable  variability  in  position  and  constitution. 
Ei.sler  ri'cords  concomitant  variations  in  tlie  j'ltjxus  in  18  \)('X  cent  of  tlie  cases  examined  by  him. 
47 


674 


THE  NERVOUS  SYSTEM. 


The  variations  occur  within  wide  limits.  The  plexus  may  begin  at  the  eleventh  or  twelftli 
thoracic  or  first  lumbar  nerve.  The  last  nerve  in  the  great  sciatic  cord  may  be  the  second,  third, 
or  fourth  sacral  nerve.  The  j^osition  of  the  n.  furcalis  is  a  guide  to  the  arrangement  of  the 
plexus.  It  may  be  formed  by  tlie  third,  third  and  fourth,  fourth,  fourtli  and  fifth,  or  fifth 
lumbar  nerves.     The  resulting  variations  are  illustrated  by  tlie  following  extreme  cases  : — 

(1)  Prefixed  Variety.  (2)  Postfixed  Variety. 
Nervus  furcalis     .         .         .         L.  3  aud  4  (double).  L.  5. 

Obturator     .         .         .         .         L.  1,  2,  3.  L.  2,  3,  4,  5. 

Anterior  crural     .         .         .         T.  12,  L.  1,  2,  3,  4.  L.  2,  3,  4,  5. 

Tibial L.  3,  4,  5,  S.  1,  2.  L.  5,  S.  1,  2,  3,  4. 

Peroneal       .  .  L.  3,  4,  5,  S.  1.  L.  5,  S.  1,  2,  3. 

Those  variations  in  the  constitution  of  the  lumbo-sacral  plexus  are  most  numerous  which 
are  due  to  the  inclusion  of  nerves  more  caudally  placed.  Thus,  out  of  twenty-two  variations 
in  the  position  of  the  n.  furcalis,  in  nineteen  Eisler  found  it  formed  by  the  fifth  lumbar  nerve  ; 
in  two  cases  only,  by  the  third  lumbar  nerve.  There  is  further  evidence  that  variations  in  the 
position  of  the  plexus  are  accompanied  by  variations  in  the  vertebral  column  itself.  Out  of  the 
twenty -two  abnormal  jjlexuses  examined  by  Eisler,  sixteen  were  coincident  with  abnormal 
arrangement  of  the  associated  vertebrte. 

Significance  of  the  Limb-plexuses. 

From  the  above  considerations,  it  is  oljvious  that  something  more  than  convenience  of  transit 
for  the  spinal  nerves  to  skin  and  muscles  is  secured  by  the  formation  of  the  limb-plexuses.  It 
has  been  shown  that  by  their  combinations  in  the  j^lexuses,  every  spot  or  area  of  skin  in  the 
limbs  is  innervated  by  more  than  one  spinal  nerve ;  and  generally,  also,  each  limb-muscle  is 
supplied  by  more  than  one  spinal  nerve.  Each  cutaneous  area  and  each  limb -muscle  is  thus 
brought  into  relationship  with  a  wider  area  of  the  spinal  cord  than  would  occur  if  the 
plexuses  were  non-existent.  A  simultaneous  record  of  sensation  is  thus  transmitted  from  any 
given  point  on  the  surface  of  the  limb  through  more  than  one  dorsal  root ;  and  a  more  ready 
co-ordination  of  muscular  movement  is  brought  about  by  the  transmission  of  motor  impulses 
from  the  ventral  root  of  a  given  spinal  nerve  to  more  than  one  muscle  at  the  same  time.  In  a 
word,  a  plexus  exists  to  suj)ply  the  whole  limb  and  the  limb  as  a  whole,  as  an  organ  which  has 
its  different  active  parts  connected  with  the  central  nervous  system  by  means  of  the  limb-plexus. 


THE  CEANIAL  NEEVES. 

The  series  of  cranial  nerves  is  arranged  in  twelve  pairs,  which  present  striking 
differences  in  origin,  in  distribution,  and  in  functions. 


Number. 

Name. 

Function. 

Superficial  Attachment 

to  Brain. 

I. 

Olfactory- 

SmeU 

Olfactory  bulb. 

II. 

Optic    . 

Sight        

Optic  thalamus. 

III. 

Oculo-motor 

Motor  to  the  muscles  of  eyeball  and 

orbit 
Motor  to  superior  oblique  muscle  of 

Crus  cerebri. 

IV. 

Trochlear    . 

Superior      meduUary 

eyeball 

velum. 

V. 

Trigeminal  . 

Sensory  to  face,  tongue,  and  teeth  ; 
motor  to  muscles  of  mastication 

Pons  Varolii. 

VI. 

Abducent    . 

Motor  to  external  rectus  muscle  of 

Junction  of  pons  and 

eyeball 

medulla. 

VII. 

Facial  . 

Motor  to  muscles  of  scalp  and  face. 

Posterior     border     of 

sensory  to  tongue 

pons  Varolii. 

VIII. 

Auditory 

Hearing  and  equilibrium 

Posterior     border     of 
pons  Varolii 

IX. 

Glossopharyngeal 

Sensory  to  tongue  and  j)har}mx 

Medulla  oblongata. 

X. 

Pneumogastric    . 

Sensory  to  pharynx,  oesophagus  and 
stomach,  and  respiratory  organs 

Medulla  oblongata. 

XI. 

Spinal  accessory 

(«)  Accessory  to  vagus. — Motor  to 
muscles  of  palate,  pharynx,  oeso- 
phagus, stomach  and   intestines, 
and  respiratory  organs ;  inhibitory 
for  heart 

Medulla  oblongata. 

(6)  Spinal  part :  motor  to  trapezius 

Spinal  cord. 

and  sterno -mastoid  muscles 

XII. 

Hypoglossal 

Motor  to  muscles  of  the  tongue 

Medulla  oblongata. 

THE  EIEST  Oli  OLFACTORY  NERVE. 


im 


The  deep  cerebral  connexions  of  the  cranial  nerves  are  dealt  with  in  the 
section  which  treats  of  the  Brain  (pp.  514  and  540).  Certain  general  points  in 
connexion  with  these  nerves  are  also  touched  upon  in  the  chapter  introductory  to 
the  Nervous  System  (p.  443). 


The  Eiest  or  Olfactory  Nerve. 

The  olfactory  nerve  (n.  olfactorius)  consists  of  several  parts  :  (1)  a  series  of  fine 
nerves,  which  arise  from  (2)  the  olfactory  bulb.     This  again  is  connected  by  (3) 


Olfactory  bulb 


Olfactory  tract- 


Olfactory  tubercle  —jJlhiM,  ~  ^' 
Optic  nerve 
Optic  cliiasma 


Oculo-motor  neive 


Trochlear  uei 


Trigemiual  nerve-j||| 
Abducent  nerve 

Facial  nerve, ...-. 
Pars  intermediaJiWtV 
Auditory  nerveJj 


Olfactory  bulb 


-Olfactory  tract 
.Broca's  area 
il factory  tubercle 
^ii  sial  root  of  olfactory 
neive 

■Lateral  root 
-Optic  chiasjna 
.^^4— Ant.  perforated  spot 
_3_  *»'-.Temporal  lobe  (cut) 
jOptic  tract 
>Oculo-motor  nerve 

■Trochlear  nerve 
TT-Ttenia  semicircularis 
—Trigeminal  nerve 
Ext.  geniculate  body 
Abducent  nerve 
lut.  geniculate  body 
Pulvinar 
Facial  nerve 
Pars  intermedia 
Auditory  nerve 

Lateral  ventricle 

Mid.  cerebellar  peduncle 

Glosso-pharyngeal  nerve 

Vagus  nerve 

Spinal  accessory  nerve 

(accessory) 

Spinal  accessory  nerve 

(spinal) 

'Occipital  lobe  (cut) 


Glosso-phaiyngeal  nei\ 

Vagus  nLi\ 


Hypoglossal  nerve 
Spinal  cord 
Vermis  of  cerebellum  (cut) 


Spinal  accessory  neive  (accessory) 

Spinal  accessory  nerve  (spinal)      | 
Hypoglossal  nerve 

Fia.  517. — View  of  the  Under  Surface  of  the  Brain, 

with  the  lower  portion  of  the  temporal  and  occipital  lobes,  and  the  cerebellum  on  the  left  side  removed, 

to  show  the  origins  of  the  cranial  nerves. 

the  olfactory  tract  with  the  brain,  to  which  it  is  attached  by  (4)  two  roots  (Eig.  517). 

The  anatomy  of  the  roots,  tract,  and  bulb  of  the  olfactory  nerve  are  described 
elsewhere  (pp.  569  and  587). 

The  olfactory  nerves,  about  twenty  in  number,  arise  from  the  under  surface  of 
the  olfactory  bulb.  The  fibres  are  non-medullated.  Piercing  the  cribriform  plate 
of  the  ethmoid  bone,  enveloped  in  sheaths  of  dura  mater,  they  are  distributed  in 
tiie  nasal  cavity  as  the  nerves  of  smell.  The  fibres  form  fine  plexuses  over  a  limited 
area  on  the  upper  portion  of  the  nasal  septum,  and  to  even  a  less  extent  over  the 
outer  wall  of  the  nose. 

The  Second  ou  Optic  Nerve. 

Tlie  optic  nerve  (n.  o])ticus)  arises  from  tlie  brain  l)y  means  of  the  optic  tract 
(Fig.  551).     This  takes  (jrigin  from  tfioi  external  and  internal  geniculate  bodies, 


676 


THE  NERVOUS  SYSTEM. 


situated  on  the  under  surface  of  the  optic  thalamus  at  its  posterior  end,  and  also 
from  the  brachium  of  the  upper  of  the  two  corpora  quadrigemina  (vide  pp.  532 
and  551).     The  optic  tract  reaches  the  base  of  the  brain  after  sweeping  round 


ljlri[  Olfactory  nerves 

Superior  nasal  nerve  Branches  ( 

\  Interior  nasal  neive 


Olfactoi 


Fig.  518. — Innervation  of  the  Nasal  Cavity. 

between  the  crus  cerebri  and  the  hippocampal  convolution  of  the  temporal  lobe. 
The  two  optic  tracts  converge  in  front  of  the  inter-peduncular  space,  internal  to 
the  anterior  perforated  spot  and  the  termination  of  the  internal  carotid  artery, 

and  unite  to  form  the  optic  cMasma  or 
commissure.  This  adheres  to  the  under 
surface  of  the  floor  of  the  third  ventricle  in 
front  of  the  tuber  cinereum,  and  gives 
rise  at  each  end  to  the  optic  nerve.  The 
optic  nerve,  directed  outwards  and  for- 
ward, pierces  the  dura  mater,  and  passes 
from  the  cranial  cavity  into  the  orbit 
through  the  optic  foramen  in  company  with 
the  ophthalmic  artery.  In  the  orbit  the 
nerve  is  imbedded  in  the  fat  behind  the 
eyeball,  and  is  surrounded  by  the  ocular 
muscles.  It  is  connected  with  the  globe  of 
the  eye  at  a  point  one-eighth  of  an  inch 
on  the  inner  side  of  the  axis  of  the  eyeball. 
After  piercing  the  fibrous  and  vascular  coats, 
the  nerve  spreads  out  at  the  optic  disc  to 
form  the  innermost  layer  of  the  retina. 
In  the  orbit  the  nerve  is  crossed  by  the 
ophthalmic  artery  and  the  nasal  nerve,  and 
nearer  to  its  termination  it  is  surrounded 
by  the  ciliary  vessels  and  nerves,  and  by 
the  capsule  of  Tenon.  It  is  pierced  ob- 
liquely on  its  under  surface  by  the  central 
artery  of  the  retina. 

Decussation  in  the  Optic  Commissure.— In 

the  optic  commissure  tlie  fibres  of  the  two  optic 
tracts  separate,  the  inner  half  of  each  tract  de- 
cussating to  form  the  mesial  half  of  the  opposite 
oj)tic  nerve.  The  other,  outer  half  of  each  tract, 
continues  its  course  to  form  the  outer  half  of  the 
optic  nerve  on  the  same  side.  At  the  back  of 
the  commissure  another  bundle  of  fibres  is  found 

passing   from  tract  to  tract  behind  the  decussating  fibres,  and  known  as  Gudden's  commissure 

(see  p.  552). 

The  Thikd  or  Oculo-motor  Nerve. 
The  oculo-motor  nerve  (n.  oculo-motorius)  arises  from  the  brain,  in  the  region 
of  the  posterior  perforated  spot,  by  several  radicles  emerging  from  the  oculo-motor 


Fig 


519.' — Diagram  of  the  Central  Connexions 
OF  THE  Optic  Nerve  and  Optic  Tract. 


thp:  third  oil  oculo-motok  nerve. 


677 


sulcus,  on  the  inner  side  of  the  crus  cere?jri,  just  in  front  of  the  pons  Varohi  TFig. 
517).  Passing  forwards  between  the  posterior  cerebral  and  superior  cerebellar 
arteries,  the  nerve  pierces  the  dura  mater  on  the  outer  side  of  the  posterior  clinoid 
process,  in  a  small  triangular  space  between  the  free  and  attached  Ijorders  of  the 
tentorium  cerebelli.  Beneath  the  dura  mater  the  nerve  courses  through  the  outer 
wall  of  the  cavernous  sinus,  and  enters  the  orbit  througii  the  sphenoidal  fissure 


Internal  carotid  artery    Optic  nerve 


Trochlear  ner\' 
Oculo-motor  nerve 


Diaphragma  sellse 


Pituitary  fossa — 


Oijhthalmic  artery 
I       I       J       Anteiior  clinoid  process 
<ai  — N  r\      /       /'       Trochlear  nerve 
-VSaSWi      /         /         Frontal  branch 


Sphenoidal  sinui 


Sphenoid  bone- 


Internal  carotid  artery 

Abducent  nerve 

Cavernous  sinus 
Ophthalmic  division  of  trigeminal  nerve 
Superior  maxillary  division  of  trigeminal  nerve 
Inferior  maxillary  division  of  trigeminal  nerve 


Ijdchiymal  branch 


<Jculo-niotor  nerve 
(superior  division) 

Nasal  branch  of  ophthalmic 

nerve 
Oculo-motor  nerve 
(mferior  division) 
Abducent  nerve 

Superior  maxillary  division  of 
trigeminal  nerve 


Foramen  ovale 
1.    Inferior  maxillary  division  of  trigeminal  nerve 
Motor  root 


Fig.  520. — Relations  op  Structures  in  the  Cavernous  Sinus  and  Sphenoidal  Fissure. 


Posterior 
commissure- 


and  between  the  two  heads  of  the  external  rectus  muscle.     As  it  enters  the  orbit 
it  divides  into  upper  and  lower  branches,  separated  by  the  nasal  nerve. 

Branches. — The  superior  brancli  of  the  nerve  supplies  two  muscles  of  the  orbit 
— the  superior  rectus  and  the  levator  palpebrse  superioris. 

The  inferior  branch 
passes  forwards,  and  after 
giving  branches  to  the 
internal  and  inferior  recti, 
ends  in  the  inferior  oblique 
muscle.  The  short  root  of 
the  ciliary  ganglion  arises 
from  the  terminal  branch 
which  goes  to  the  last- 
named  muscle. 


Communications. — 1.  In 

the  cavernous  sinus  the  third 
nerve  communicates  with  the 
cavernous  plexus  on  the  in- 
ternal carotid  artery.  2.  In 
the  cavernous  sinus  it  also 
receives  a  slender  communi- 
cation from  the  ophthalmic 
division  of  the  fifth  nerve. 


Optic  thalamus 


Frenulum  veli 
Superior  medullary  velum 


Brachia  conjunctiva 

Fourth  nerve 

Fillet 

Superior  peduncle  of 

cerebellum 

Crus  cerebri 

Lingula 


Fig.  521. 


-Dorsal  Surface  op  the  Mid-Brain,  to  show  the  origin 
of  the  trochlear  (fourth)  nerve. 


3.    The  short  root  of  the  ciliary  ganglion  passes  upwards 


from  the  branch  of  the  nerve  which  supplies  the  inferior  oblique  muscle. 


The  Fourth  or  Trochlear  Nerve. 

The  trochlear  nerve  (n.  trochlearis  or  patheticus)  emerges  from  the  dorsal 
surface  of  the  mid-brain.  It  springs  at  the  side  of  the  frenulum  from  the 
anterior  end  of  the  superior  medullary  velum,  just  behind  the  corpora  quadri- 
gemina  (I'or  deoj)  origin,  see  p.  540).  It  is  extremely  slender,  and  of  consider- 
able length.  Passing  round  the  crus  cerebri,  the  nerve  n.ppears  in  the  base  of 
the  brain  behind  the  optic  tract,  in  the  interval  between  the  crus  cerebri  internally 
and  the  temporal  lobe  of  tlie  cerebrum  externally.  Continued  forwards  to  the  base 
of  the  skull,  it  pierces  the  I'ree  border  of  the  tentorium  cerebelli,  on  the  outer  side 
47  a 


678 


THE  NEEVOUS  SYSTEM. 


of  the  third  nerve,  and  proceeds  forwards  in  the  outer  wall  of  the  cavernous  sinus, 
to  the  sphenoidal  fissure  lying  between  the  third  and  ophthalmic  nerves.  It 
enters  the  orbit  aljove  the  muscles  of  the  eyeball,  and  terunnates  in  the  orbital 
(superior)  surface  of  the  superior  oblique  muscle. 

Communications. — In   the   cavernous  sinus   the  nerve  receives  (1)  a  communicating 


Olfactnij  bull 


Optic  nene 

Optic  comiiiissuie 
Anterior  cerebral 
artery 
Middle  cerebral 
artei\ 
Posterior 
communi- 
cating artery 
Oculo-motor 
iier\e 
Posterior  ceie 
bral  arter-\ 
Superior  cere 
bellar  artei  v 
Trochleii 


Infra  trochlear  nerve 

Supra-trochlear  nerve 

Oculo-motor  nerve 

Spbeno-parietal  sinus 
Ophthalmic  vein 

Anterior  cliTioid 
pi ocess 

'I'roclilear  nerve 

Oculo-motor 
nerve 

Abducent  nerve 

Circular  sinus 

Ophthalmic  nerve 

Superior 

;naxillary  nerve 

Inferior 

maxillary  nerve 

Cavei-nous  sinus 
Basilar  sinus 
Gasserian 
sransrlion 


Glosso-pharyn- 
geal  nerve 
Pneuujogastiic 
nei  \  p 
Spinal  accessoi  v  nei  \  e 

Hypoglobvil  nc^i  \ 


reutorium  cerebelli 
(.cut) 

Occipital  suiuses 


Lateral  sinu'5 
Veitebral  aitei\ 

Spiml  <  01 

Openings  ot  occipital  hinusts 


Falx  cerebri  (cut) 
Fig.  522. — The  Base  of  the  Skull,  to  show  the  dura 


Stiai^ht  sinus 
Poiculai  Heiophili 


bupeuoi  longitudinal  sinub 

ater,  sinuses,  arteries,  and  nerves. 


branch  from  the  cavernous  or  carotid  plexus  on  the  internal  carotid  artery,  and  (2)  a 
slender  filament  from  the  ophthalmic  division  of  the  fifth  nerve. 

The  Fifth,  Trigeminal  or  Trifacial  Nerve. 

The  trigeminal  nerve  (n.  trigeminus)  arises  from  the  surface  of  the  pons 'Varolii  in 
its  outer  part  by  two  roots,  a  large  sensory  root  (portio  major)  and  a  small  motor  root 
(portio  minor)  (Fig.  517,  p.  675).  The  two  roots  proceed  forward's  in  the  posterior 
fossa  of  the  base  of  the  skull,  and  piercing  the  dura  mater  beneath  the  attachment 
of  the  tentorium  cerebelli  to  the  superior  border  of  the  petrous  portion  of  the 


THE  FIFTH,  TEIGEMINAL  OE  TEIFACIAL  NEEVE. 


679 


temporal  bone,  enter  a  cavity  in  the  dura  mater  (cavum  Meckelii)  over  the  apex  of 
the  petrous  bone.  The  large  sensory  root  gradually  conceals  the  small  motor  root 
in  its  course  forwards,  and  expands  beneath  the  dura  mater  into  a  large  flattened 
ganglion, — ^the  Gasserian  ganglion  (ganglion  semilunare).  This  ganglion  occupies 
an  impression  on  the  apex  of  the  petrous  portion  of  the  temporal  bone,  and  from  it 
three  large  trunks  arise — theophthalmic 
or  first,  the  superior  maxillary  or  second, 
and  the  inferior  maxillary  or  third 
divisions  of  the  nerve.  The  small 
motor  root  of  the  nerve  passes  forward 
beneath  the  Gasserian  ganglion,  and  is 
wholly  incorporated  with  the  inferior 
maxillary  division  of  the  nerve. 

Ophthalmic  Division  (n.  ophthal- 
micus).— The  ophthalmic  nerve  passes 
forwards  to  the  orbit  through  the  middle 
fossa  of  the  base  of  the  skull,  beneath 
the  dura  mater.  It  lies  in  the  outer 
wall  of  the  cavernous  sinus,  at  a  lower 
level  than  the  fourth  nerve,  and  reaches 
the  orbit  through  the  sphenoidal  fissure 
(Fig.  520). 

In  the  wall  of  the  cavernous  sinus  the 
ophthalmic  nerve  gives  off  (1)  a  small 
recurrent  branch  to  the  dura  mater  (n. 
tentorii),  (2)  communicating  branches  to 
the  cavernous  plexus  of  the  sympathetic 
on  the  internal  carotid  artery,  and  (3) 
small  communicating  twigs  to  the  trunks 
of  the  third,  fourth,  and  sixth  nerves. 

In  the  sphenoidal  fissure  the  nerve 
divides  into  'three  main  branches — 
lachrymal,  frontal,  and  nasal  (Fig.  524). 

The  lachrymal  nerve  (n.  lacrymalis) 
enters  the  orbit  through  the  outer  angle 
of  the  sphenoidal  fissure,  above  the 
orbital  muscles.  Passing  forwards  be- 
neath the  periosteum  to  the  anterior 
part  of  the  orbit,  the  nerve  ends  by 
supplying  branches  (a)  to  the  lachrymal 
gland,  (&)  to  the  conjunctiva,  and  (c) 
to  the  skin  of  the  outer  canthus  of 
the  eye. 


Fig 


-DiSTEIBUTION    OF    SbNSORT    NeRVES    TO    THE 

Head  and  Neck. 

Oplith,  Ophthalmic  division  of  the  fifth  nerve  ;  St,  Supra- 
trochlear branch  ;  S.O,  Supra -orbital  branch  ;  I.T, 
Infra-trochlear  branch  ;  L,  Lachrymal  branch  ;  N, 
External  nasal  branch  ;  Sup. Max,  Superior  maxillary- 
division  ;  T,  Temporal  branch ;  M,  Malar  branch  ; 
I.O,  Infra-orbital  branch  ;  Inf.Max,  Inferior  maxillary 
division  ;  A.T,  Auriculo-temi3oral  branch  ;  B,  Buccal 
branch  ;  M,  Mental  branch  ;  C2,  3,  Branches  of  the 
second  and  third  cervical  nerves  ;  G.  0,  Great  occipital 
nerve  ;  S.O,  Small  occipital  nerve  ;  G.A,  Great 
auricular  nerve  ;  S.C,  Superficial  cervical  nerve  ;  03, 
Least  occipital  nerve ;  4,  5,  6,  Posterior  primary 
division  of  4th,  5th,  and  6th  cervical  nerves. 


The  lachrymal  nerve  communicates  in  the 
orhit  with  the  orbital  branch  of  the  su^ierior 

maxillary  nerve,    and   on   the   face,   by   its  terminal    branches,   with    the   temporal   branches 
of  the  facial  nerve  (Fig.  523). 

The  frontal  nerve  (n.  frontalis),  entering  the  orbital  cavity  through  the 
sphenoidal  fissure,  courses  forwards  above  the  ocular  muscles,  and  divides  at  a 
variable  point  into  two  branches — a  larger  supra-orbital  and  a  smaller  supra- 
trochlear nerve.  The  supra-orbital  nerve  (n.  siipra-orbitalis)  passes  directly  forwards, 
and  leaves  the  orbit  tlirough  the  supra-orbital  groove  or  foramen  to  reach  the  fore- 
head. It  gives  off  the.  following  secondary  branches :  (1)  the  principal  branches 
(rr.  frontales)  are  distributed  to  the  forehead  and  scalp,  reaching  backwards  as  far 
as  the  vertex;  (2)  small  branches  supply  the  upper  eyelid;  and  (3)  twigs  are 
distributfid  to  the  frontal  sinus.  On  the  forehtiful  the  supra-orbital  nerve  com- 
municates  with  the  temporal  liranches  of  the  facial  nerve.  Ti)e  supra-trochlear 
nerve  (n.  supra-trochlearis)  courses  oblif[nely  forwards  and  inwards  over  the  tendon 
47  & 


680 


THE  NEKVOUS  SYSTEM. 


of  the  superior  oblique  muscle  to  reach  the  inner  side  of  the  supra-orbital  arch. 
Leaving  the  cavity  of  the  orbit,  the  nerve  is  distributed  to  the  skin  of  the  mesial 
part  of  the  forehead,  the  root  of  the  nose,  and  the  inner  canthus  of  the  eye. 

It  communicatee  with  the  iiifra-trochlear  branch  of  the  nasal  nerve,  either  before  or 
after  leaving  the  orbital  cavity. 

The  nasal  nerve  (n.  naso-ciliaris)  enters  the  orbit  through  the  sphenoidal 
fissure,  between  the  heads  of  the  external  rectus  muscle,  and  between  the  two 
divisions  of  the  third  nerve  (Eig.  520,  p.  677).  It  crosses  the  orbital  cavity 
obliquely  to  reach  the  anterior  ethmoidal  foramen,  lying  in  its  course  below  the 
superior  rectus  and  superior  oblique  muscles,  and  above  the  optic  nerve  and  internal 
rectus  muscle.  The  nerve  is  transmitted  through  the  anterior  ethmoidal  foramen 
into  the  cranial  cavity,  where  it  lies  on  the  cribriform  plate  of  the  ethmoid  bone. 

It  enters  the  nasal  cavity 
through  the  nasal  fissure,  and 
terminates  by  dividing  into 
internal  and  external  branches. 
The  internal  division  supplies 
the  mucous  membrane  over  the 
upper  and  anterior  part  of  the 
nasal  septum  (rr.  mediales). 
The  external  branch,  after 
supplying  collateral  offsets  to 
the  outer  wall  of  the  nose  (rr. 
laterales),  finally  appears  on 
the  face  between  the  nasal 
bone  and  lateral  cartilage,  and 
supplies  branches  to  the  skin 
of  tbe  lower  part  and  tip  of 
the  nose. 

The  branches  of  the  nasal 
nerve  may  be  divided  into 
three  sets,  arising  (a)  in  the 
orbit,  (&)  in  the  nose,  and  (c) 
on  the  face. 

In  the  orbit  the  branches 
are  given  off  in  three  situa- 

Nasal  nerve  ;  L.G,  Long  root  to  lenticular  ganglion  ;  Sy,   Root  tionS — external    to,    OVer,    and 

from  sympathetic  (on  carotid  artery);   III,  Slmrt  root  from  motor  ij^te^al     tO     the    Optic    nerve. 

ocnli  nerve  ;  C,  Snort  ciliary  branches  ;  L.C,  Long  ciliary  nerves  ;  .    "      .  ,  ^  ,. 

I.T,    Infra-trochlear   nerve  ;    E.N,   External,    and    I.N,    Internal  («)    As     the    Uasal     nerVB    lieS 

nasal  nerves.      Lachrymal  nerve  ;  0,  Orbital  branch  of  superior  external    tO     the    Optic    nerVC 

Erch"'L."Z:i  £?J'euSSe.  '"""'•■'  "•  "°'*'""""'  it  gives  oft-  the  long  root  of  the 

ciliary  ganglion  (radix  longa). 
(h)  As  it  crosses  the:  optic  nerve  two  long  ciliary  branches  (nn.  ciliaris  longi)  arise, 
and  pass  forwards  alongside  the  optic  nerve  to  the  eyeball,  (c)  On  the  inner  side 
of  the  optic  nerve  the  infra-trochlear  nerve  (n.  infra-trochlearis)  arises,  a  slender 
branch  which  courses  forward  beneath  the  pulley  of  the  superior  oblique  muscle  to 
the  front  of  the  orbit.  It  ends  on  the  face  by  supplying  the  skin  of  the  root  of  the 
nose  and  the  eyelids,  and  communicates  either  in  the  orbit  or  on  the  face  with 
the  supra- trochlear  nerve.  On  the  face  it  also  communicates  with  infra-orbital 
branches  of  the  facial  nerve. 

In  the  nose  the  internal  nasal  branch  supplies  the  mucous  membrane  of  the 
fore-part  of  the  nasal  septum ;  the  external  nasal  branch  supplies  the  fore-part  of 
the  outer  wall  of  the  nose. 

On  the  face  the  terminal  filaments  of  the  nerve  are  distributed  to  the  skin  of 
the  lower  half  and  tip  of  the  nose.  The  superficial  terminal  branch  communicates 
with  the  infra-orbital  branches  of  the  facial  nerve  (Fig.  523). 

The  ciliary  or  lenticular  ganglion  (ganglion  ciliare)  is  associated  with  the 
nasal  branch  of  the  ophthalmic  nerve  and  with  the  lower  division  of  the  third 
nerve.     It  is  a  small  reddish  ganglion,  placed  between  the  external  rectus  muscle 


Fig.  524. 


-Scheme  of  the  Distribution  of  the  Ophthalmic 
Nerve. 


Vs,  Trigeminal  nerve,  afferent  root ;  Mo,  Efferent  root ;  G.G,  Gasserian 
ganglion  ;  M,  Meningeal  branch  ;  I.C,  Branch  to  internal  carotid 
artery  ;  Opli,  Ophthalmic  nerve  ;  S.M,  Superior  maxillary  nerve  ; 
I.  M,  Inferior  maxillary  nerve  ;  III,  Communication  to  oculo- 
motor nerve  ;  IV,  To  trochlear  nerve  ;  VI,  To  abducent  nerve. 
Frontal  nerve;  f.s.  Branches  to  frontal  sinus  ;  S.o,  Supra-orbital 
nerve  ;  S.t,  Supra-trochlear  nerve ;   L,  Branches  to  upper  eyelid. 


THE  FIFTH,  TRIGEMINAL  OR  TRIFACIAL  NERVE. 


681 


and  the  optic  nerve,  and  in  front  of  the  o^jhthahnic  artery.  Its  roots  are  three  in 
number:  (1)  sensory  or  long  (radix  longa),  derived  from  the  nasal  branch  of  the 
ophthalmic  nerve ;  (2)  motor  or  short  (radix  Ijrevis),  derived  from  the  inferior 
division  of  the  third  nerve ;  and  (3)  sympathetic,  a  slender  filament  from  the 
cavernous  plexus  on  the  internal  carotid  artery,  which  may  exist  as  an  independent 
root  or  may  be  incorporated  v^ith  the  long  root  from  the  nasal  nerve.  The  branches 
from  the  ganglion  are  twelve  to  fifteen  short  ciliary  nerves  (nn.  ciliares  breves), 
which  pass  to  the  eyeball  in  two  groups  above  and  below  the  optic  nerve.  They 
supply  the  coats  of  the  eyeball,  including  the  iris  and  ciliary  muscles.  The  circular 
fibres  of  the  iris  and  the  ciliary  muscle  are  innervated  by  the  third  nerve  ;  the 
radial  fibres  of  the  iris  by  the  sympathetic. 

Superior  Maxillary  Division  of  the  Fifth  Nerve  (n.  maxillaris). — This  large 
nerve  courses  forwards  from  its  origin  in  the  Gasserian  ganglion  through  the  middle 
fossa  of  the  base  of  the  skull,  beneath  the  dura  mater,  and  in  relation  to  the  lower 
part  of  the  cavernous  sinus  (Fig.  520,  p.  677).  Passing  through  the  foramen 
rotundum  in  the  root  of  the  pterygoid  process,  it  traverses  the  spheno-maxillary 
fossa.     It  enters  the  orbit  as  the  infra-orbital  nerve,  through  the  spheno-maxillary 


Lachrymal  gland 


Frontal  nerve 


Supra-orbital  nerve 


Lachrymal  nerve. 

Nerves  to  superior  rectus  and 

levator  palpebrte  superioris, 

from  oculo-motor  nerve, 

superior  division 

Trochlear  nerve- 


Rectus  externu' 


Abducent  nerve 

Oculo-motor  nerve 
(inferior  division) 

Lenticular  ganglion 

Nerve  to  rectus  inferior,  from 
oculo-motor  nerve' 

Nerve  to  obliquus  inferior, 
from  oculo-motor  nerve 


Supra-trochlear  nerve 
Levator  palpebrae  superioris 
Rectus  superior 
Obliquus  superior 
Nasal  nerve 
Infra-trochlear  nerve 

Rectus  internus 

Nerve  to  rectus  internus  from 

'oculo-motor 

Ophthalmic  artery 

Optic  nerve 

Long  ciliary  nerves 

Rectus  inferior 


Obliquus  inferior 
Fig.  525. — Schematic  Representation  of  the  Nerves  which  traverse  the  Cavity  of  the  Orbit. 


fissure,  and  occupying  successively  the  infra-orbital  groove  and  canal,  it  finally 
appears  on  the  face  through  the  infra-orbital  foramen  (Fig.  526). 

The  branches  and  communications  of  this  nerve  occur  (a)  in  the  cavity  of  the 
cranium,  (b)  in  the  spheno-maxillary  fossa,  (c)  in  the  infra-orbital  canal,  and  (d) 
on  the  face. 

In  the  cavity  of  the  cranium  the  nerve  gives  off  a  minute  recurrent  branch  (n. 
meningeus)  to  the  dura  mater  of  the  middle  fossa  of  the  base  of  the  skull. 

In  the  spheno-maxillary  fossa  the  nerve  gives  off — (1)  two  short  thick  spheno- 
palatine nerves  (nn.  spheno-palatini),  the  short  or  sensory  roots  of  the  spheno- 
palatine (Meckel's)  ganglion.  (2)  A  posterior  dental  nerve,  which  may  be  double 
(niL  alveolares  superiores),  descends  through  the  ptery go-maxillary  fissure  to  the 
outer  side  of  the  upper  jaw,  and  proceeds  forwards  along  the  alveolar  arch,  in 
company  with  the  posterior  dental  artery.  It  supplies  the  gum  and  the  upper 
molar  teeth  by  branches  which  perforate  the  bone  to  reach  the  alveoli.  The  nerve 
forms  a  fine  plexus  joined  by  the  middle  dental  nerve  before  finally  reaching  the 
teeth.  (13)  A  small  orbital  branch  (n.  zygomaticus)  enters  the  orbital  cavity  through 
the  spheno-maxillary  fissure,  and  proceeding  along  the  outer  wall,  communicates 
with  the  lachrymal  nerv(3,  and  j)asses  through  the  orbital  canal  in  the  malar  bone, 
where  it  divides  into  malar  and  tcmjjoral  branches.  The  malar  branch  (n.  zygo- 
matico-facialisj  apj tears  on  the  face,  after  traversing  the  malar  bone,  and  suitplies 
the  skin  over  that  boiKi.  It  communicates  with  the  malar  branches  of  the  facial 
nerve.     The  temporal  branch  (w.  zygomatico-temporalis)  perforates  the  zygomatic 


682 


THE  NEEVOUS  SYSTEM. 


surface  of  the  malar  bone,  and  is  distributed,  after  piercing  the  temporal  fascia,  to 
the  skin  over  the  fore-part  of  the  temple.  It  communicates  with  the  temporal 
branches  of  the  facial  nerve.  It  may  be  very  minute,  and  not  pass  further  than 
the  temporal  fascia,  between  the  two  layers  of  which  it  may  form  a  communication 
with  the  facial  nerve.  (4)  The  infra-orbital  nerve  (n.  infra-orbitalis)  is  the  terminal 
branch  of  the  superior  maxillary  nerve,  which  enters  the  orbit  through  the  spheno- 
maxillary fissure  and  traverses  the  infra-orbital  canal  to  reach  the  face. 

In  the  infra-orhital  canal  the  infra-orbital  nerve  supplies  one  and  sometimes 
two  branches  to  the  teeth — the  middle  and  anterior  dental  nerves  (rr.  alveolares 
superiores  medius  and  anterior).  The  former  may  be  only  a  secondary  branch  of 
the  latter  nerve,  or  they  may  arise  independently  from  the  infra-orljital  nerve. 

However  formed, 
the  nerves  descend 
in  Ijony  canals  in 
the  wall  of  the  an- 
trum of  Highmore 
(to  the  lining  of 
which  branches  are 
given),  and  reach 
the  alveolar  arch, 
where  they  form 
minute  plexuses 
and  supply  the 
teeth  (joining  pos- 
teriorly with  the 
branches  of  the 
posterior  dental 
nerve).  The  an- 
terior dental  nerve 
supplies  the  incisor 
and  canine  teeth ; 
the  middle  dental 
nerve  supplies  the 
premolar  teeth. 

After  emerging 
on  the  face  from  the 
infra-orbital    fora- 


FiG.  526.- 


palatine  nerve  ;  Ace,  Accessory  posterior  palatine  nerve  ;  Vid,  Vidian  nerve 
Pt.Pal,  Pterygo-palatine  branch. 


-Scheme  of  the  Course  and  Distribution  of  the  Superior 
Maxillary  Nerve. 

Rec,  Recurrent  branch  in  the  middle  fossa  of  the  skull  ;  M.G,  Meckel's  ganglion  in  HlCn,      tlie      intra  - 

the  spheno-maxillary  fossa  ;  S.P,  Spheno-palatine  nerves  ;  S.N,  Superior  nasal  orbital     nerVC     di- 

branch  ;  Orb,   Orbital   nerve  ;  T,    Temporal,   and   M,    Malar   branches  ;  I.O,  yj(1gg    iri to  a  num- 

lufra-orbital  nerve,    ajspearing   on  the   face  ;  P,  Palpebral  ;  N,  Nasal,    and  ,              „           ^■^.■ 

L,    Labial   branches;   A.D,    Anterior  dental   branch;    M.D,    Middle    dental  ^^r   01    radiating 

branch;  N.P,  Naso-palatine  nerve  ;  P.D,  Posterior  dental  branch  ;  I.N,  Inferior  branches   arranged 

nasal  branch  ;  L.P.P,  Large  posterior  palatine  nerve  ;  S.P. P,  Small  posterior   jp    three    sets (a^ 

palpebral,    for    the 
lower    eyelid ;    (&) 

nasal,  for  the  skin  of  the  side  of  the  nose  ;  and  (c)  labial,  for  the  cheek  and  upper  lip. 
These  branches  form  communications  with  the  infra-orbital  branches  of  the  facial 
nerve,  and  give  rise  to  the  infra-orhital  plexus  (Fig.  523,  p.  679). 

The  spheno-palatine  or  Meckel's  ganglion  (g.  spheno-palatinum)  occupies  the 
upper  part  of  the  spheno-maxillary  fossa.  It  is  a  small  reddish-gray  ganglion, 
suspended  from  the  superior  maxillary  nerve  by  the  two  spheno-palatine  branches 
which  constitute  its  sensory  roots.  The  motor  and  sympathetic  roots  of  the  ganglion 
are  derived  from  the  vidian  nerve.  This  nerve  is  formed  in  the  cavity  of  the  skull 
upon  the  cartilage  filling  up  the  foramen  lacerum  medium,  by  the  union  of  the 
great  superficial  p)etrosal  nerve  from  the  geniculate  ganglion  of  the  facial  nerve 
(emerging  from  the  temporal  bone  through  the  hiatus  Fallopii)  with  the  great  deep 
petrosal  nerve,  a  branch  of  the  carotid  plexus  of  the  sympathetic  on  the  internal 
carotid  artery.  The  vidian  nerve  passes  through  the  vidian  canal  to  the  spheno- 
maxillary fossa,  where  it  ends  in  Meckel's  ganglion. 


THE  FIFTH,  TRIGEMINAL  OR  TRIFACIAL  NERVE.  683 

The  branches  from  the  ganghon  are  seven  in  number,  (a)  The  pterygo-palatine 
or  pharyngeal  branch  passes  backwards  through  the  jjterygo-palatine  canal  to 
supply  the  mucous  membrane  of  the  roof  of  the  pharynx. 

(&)  The  posterior  palatine  nerves,  three  in  number,  are  directed  downwards  to  the 
palate  through  the  posterior  palatine  canals.  The  large  posterior  palatine  nerve  emerges 
on  the  under  surface  of  the  palate  through  the  large  posterior  palatine  canal,  and  at 
once  separates  into  numerous  branches  for  the  supply  of  the  mucous  membrane  of  the 
soft  and  the  hard  palate.  Its  anterior  filaments  communicate  with  branches  of  the 
naso-palatine  nerve.  The  main  nerve  gives  off,  as  it  lies  in  the  posterior  palatine  canal, 
a  small  inferior  nasal  nerve  which  enters  the  nasal  cavity  and  supplies  the  mucous 
membrane  of  the  lower  part  of  the  outer  wall  of  the  nose.  The  small  posterior 
palatine  nerve  descends  through  the  small  posterior  palatine  canal,  and,  piercing 
the  tuberosity  of  the  palate  bone,  is  distributed  to  the  mucous  membrane  of  the 
soft  palate,  uvula,  and  tonsil.  It  possibly  conveys  motor  fibres  to  the  levator  palati 
and  azygos  uvulae  muscles.  The  accessory  posterior  palatine  nerves  are  one  or 
more  small  twigs  which  pass  through  accessory  posterior  palatine  canals,  and 
supply  branches  to  the  mucous  membrane  of  the  tonsil,  soft  palate,  and  uvula. 

(c)  The  branches  directed  inwards  from  Meckel's  ganglion  enter  the  nasal 
cavity  through  the  spheno -palatine  foramen.  They  are  two  in  number — the 
superior  nasal  and  the  naso-palatine.  The  superior  nasal  nerve  is  a  small  nerve 
destined  for  the  mucous  membrane  of  the  upper  and  back  part  of  the  outer  wall  of 
the  nose.  The  naso-palatine  nerve,  after  passing  through  the  spheno-palatine 
foramen,  crosses  the  roof  of  the  nose,  and  extends  obliquely  downwards  and 
forwards  along  the  nasal  septum,  grooving  the  vomer  in  its  course,  to  reach  the 
incisor  foramen  near  the  front  of  the  hard  palate.  The  nerves  pass  through  the 
subordinate  mesial  foramina  (of  Scarpa),  the  left  nerve  in  front  of  the  right.  In 
the  incisor  foramen  the  two  nerves  communicate  together.  They  then  turn  back- 
wards and  supply  the  mucous  membrane  of  the  hard  palate.  They  communicate 
posteriorly  with  terminal  filaments  of  the  large  posterior  palatine  nerves.  In  its 
course  through  the  nasal  cavity  the  naso-palatine  nerve  furnishes  collateral  branches 
to  the  mucous  membrane  of  the  roof  and  septum  of  the  nose  (Fig.  518,  p.  676). 

(d)  The  orbital  branches,  one  or  more  minute  branches,  pass  upwards  to  the 
periosteum  of  the  orbit  from  Meckel's  ganglion. 

Inferior  Maxillary  Nerve  (n.  mandibularis). — The  inferior  maxillary  nerve 
is  formed  by  the  union  of  two  roots :  a  large  sensory  root,  from  the  Gasserian 
ganglion,  and  the  small  motor  root  of  the  trigeminal  nerve,  which  is  wholly 
incorporated  with  this  trunk.  The  two  roots  pass  together  beneath  the  dura  mater 
of  the  middle  fossa  of  the  base  of  the  skull  to  the  foramen  ovale,  through  which 
they  emerge  into  the  pterygoid  region.  Outside  the  skull  they  combine  to  form  a 
single  trunk,  which  soon  separates  into  anterior  and  posterior  divisions. 

At  its  emergence  from  the  skull  the  nerve  is  deeply  placed  beneath  the  middle 
of  the  zygomatic  arch,  and  is  concealed  by  the  ramus  of  the  lower  jaw,  and  by  the 
temporal,  masseter,  and  external  pterygoid  muscles. 

The  branches  of  the  inferior  maxillary  nerve  may  be  divided  into  two  series — 
(1)  those  derived  from  the  undivided  nerve,  and  (2)  those  derived  from  the  terminal 
divisions  of  the  nerve. 

The  branches  of  the  undivided  nerve  are  two  in  number,  (a)  A  small 
recurrent  branch  (n.  spinosus)  arises  just  outside  the  skull,  and  accompanying  the 
middle  meningeal  artery  through  the  foramen  spinosum,  supplies  the  dura  mater. 
(b)  In  the  pterygoid  region  a  small  branch  arises  for  the  supply  of  the  internal 
pterygoid  muscle.     This  nerve  forms  a  connexion  with  the  otic  ganglion. 

The  tcrmina,]  divisions  of  the  nerve  are  a  small  anterior  and  a  large  posterior 
trunk. 

The  small  anterior  trunk  passes  downwards  and  forwards  beneath  the  external 
pterygoid  muscle,  and  separates  into  the  following  Imanches  : — (1)  A  branch  for  the 
external  pterygoid  muscle  (n.  pterygoideus  externus),  whicli  supplies  it  on  its  deep 
surface ;  (2)  a  branch  to  the  njasseter  muscle  (n.  massetericus),  which  passes  over 
the  upper  border  of  the  external  ytterygoid  and  through  the  sigmoid  notch  of  the 
lower  jaw ;  (3)  and  (4)  two  branches  to  the  temporal  muscle  (nn.  temporales  pro- 


684 


THE  NERVOUS  SYSTEM. 


fundi,  anterior  et  x^osterior),  which  also  ascend  above  the  external  pterygoid 
muscle ;  and  (5)  the  buccal  nerve  (n.  buccinatorius),  which  passes  obliquely 
forwards  between  the  two  heads  of  the  external  pterygoid  to  reach  the  buccinator 
muscle.  This  nerve  is  sensory,  and  its  fibres  are  in  j)art  distributed  to  the  skin  of 
the  cheek  (communicating  with  buccal  branches  of  the  facial  nerve) ;  they  are  also 
in  part  distributed  to  the  mucous  membrane  of  the  inside  of  the  mouth,  to  reach 
which  tliey  pierce  the  filjres  of  the  buccinator  muscle.     The  buccal  nerve  usually 

supphes  a  third  branch  to 
the  temporal  muscle,  after 
emerging  between  the  two 
heads  of  the  external 
pterygoid  muscle  (Eig.  523, 
p.  679). 

The  large  posterior 
trunk  extends  downwards 
a  short  way  beneath  the 
external  pterygoid  muscle. 
After  giving  off  by  two 
roots  the  auriculo-temporal 
nerve,  it  ends  by  dividing 
into  two,  the  lingual  and 
the  inferior  dental  nerves. 
The  auriculo-temporal 
nerve  (n.  auriculo-tempor- 
alis)  is  formed  by  the  union 
of  two  roots  which  embrace 
the  middle  meningeal 
artery.  The  nerve  passes 
backwards  beneath  the 
external  pterygoid  muscle 
and  between  the  internal 
lateral  ligament  and  the 
neck  of  the  lower  jaw. 
Entering  the  substance  of 
the  parotid  gland,  it  is 
directed  upwards  to  the 
temple  over  the  zygoma  in 


Fig. 


527.— Scheme  of  the  Distribution  of  the  Inferior 
Maxillary  Nerve. 


V.I.M,  Inferior  maxillary  nerve  ;  S,  Afferent,  and  Mo,  Efferent  roots  ;  M, 
Meningeal  branch  ;  O.G,  Otic  ganglion  ;  I.Pt,  Nerve  to  internal  ptery- 
goid ;  S.S.P,  Small  superficial  petrosal  nerve  ;  T.T,  Nerves  to  tensor 

tympani,  and  T.P,  Tensor  palati ;  Ty.Plex,  Tympanic  plexus  ;  I.C,  company  witll  the  temporal 
Internal  carotid  artery;  S.D.P,  Small  deep  petrosal  nerve;  G.G,  „_,j.^„„  t^-  ;„  finnllv  His- 
Geniculate  ganglion  ;  F,  Facial  nerve  ;  Ty,  Tympanic  branch  ;  G.Ph,    ailCl}  .       it     lb     nudii^ 

-  A.T, 


Glosso-pharyngeal  nerve  ;  M.M,  Middle  meningeal  artery  ; 
Auriculo-temporal  nerve  ;  F,  Communication  with  facial  nerve  ;  Par, 
Nerve  to  parotid  gland  ;  Me,  Branch  to  meatus  of  ear  ;  Pi,  Branch 
to  pinna  ;  T,  Temporal  branch  ;  A,  Anterior  division  of  inferior 
maxillary  nerve  ;  E.Pt,  Nerves  to  external  pterygoid  ;  M,  Masseter  : 
T.T.T,  Temporal,  and  Bucc,  Buccinator  muscles  ;  Po,  Posterior 
division  of  inferior  maxillary  nerve  ;  L,  Lingual  nerve  ;  C.T,  Chorda 
tympani  nerve  ;  Sub.G,  Sub-maxillary  ganglion  ;  Hy,  Hypoglossal 
nerve  ;  I.D,  Inferior  dental  nerve  ;  My.hy,  Mylohyoid  nerve  ;  My, 
Nerve  to  mylohyoid  ;  Di,  Nerve  to  digastric  (anterior  belly)  ; 
Ment.,  Mental  Branch  ;  Sty.Gl,  Stylo-glossus  ;  H.Gl,  Hyoglossus  ; 
G.H.G,  Genio-hyoglossus  muscles. 


tributed  as  a  cutaneous 
nerve  of  the  temple  and 
scalp,  and  reaches  almost  to 
the  vertex  of  the  skull. 

Th e  auriculo  -  temporal 
nerve  gives  off  the  follow- 
ing branches: — (1)  A  small 
branch  to  the  temporo- 
maxillary  articulation.  (2) 
the    parotid 


Branches    to 

gland.  (3)  A  twig  for  the  supply  of  the  skin  of  the  external  auditory  meatus 
(and  membrana  tympani).  (4). Branches  to  the  upper  half  of  the  pinna  on  its 
outer  aspect.     (5)  Terminal  branches  to  the  skin  of  the  temple  and  scalp. 

It  has  the  following  communications  with  other  nerves  :— (1)  Important  commuuica- 
tions  are  effected  by  the  roots  of  the  nerve,  which  are  separately  joined  by  small  branches 
from  the  otic  ganglion.  (2)  The  parotid  branches  of  the  nerve  are  connected  with  branches 
of  the  facial  nerve  in  the  substance  of  the  gland.  (3)  The  temporal  branch  of  the  nerve 
is  in  communication  superficially  with  the  temporal  branches  of  the  facial  nerve. 

The  lingual  nerve  (n.  lingualis)  is  the  smaller  of  the  two  terminal  branches 


THE  FIFTH,  TETGEMINAL  OE  TRIFACIAL  NERVE.  685 

of  the  posterior  division  of  the  inferior  maxillary  nerve.  It  proceeds  downwards  in 
front  of  the  inferior  dental  nerve,  beneath  the  external  pterygoid  muscle,  to  its  lower 
border.  After  passing  between  the  internal  pterygoid  muscle,  and  the  ramus  of  the 
lower  jaw,  it  crosses  beneath  the  mucous  membrane  of  the  floor  of  the  moutli  in  the 
interval  between  the  mylohyoid  and  hyoglossus  muscles  and  beneath  the  duct  of 
the  submaxillary  gland.  It  sweeps  forwards  and  inwards  to  the  side  of  the 
tongue,  to  the  mucous  membrane  over  the  anterior  two-thirds  of  which  it  is 
distributed. 

Two  nerves  communicate  with  the  lingual  nerve  in  its  course  to  the  tongue  : — 

(1)  The  chorda  tympani  branch  of  the  facial  nerve  joins  it  beneath  the  external 
pterygoid  muscle,  and  is  incorporated  with  it  in  its  distribution  to  the  tongue. 

(2)  The  hypoglossal  nerve  forms  larger  or  smaller  loops  of  communication  with 
the  lingual  nerve  as  they  course  forwards  together  over  the  hyoglossus  muscle. 

Besides  supplying  the  aforesaid  branches  to  the  mucous  membrane  over  the 
sides  and  dorsum  of  the  tongue  in  its  anterior  two-thirds,  the  lingual  nerve  supplies 
the  mucous  membrane  of  the  outer  wall  and  floor  of  the  mouth.  It  also  assists, 
along  with  the  chorda  tympani  nerve,  in  forming  the  roots  of  the  submaxillary 
ganglion. 

The  submaxillary  ganglion  (ganglion  submaxillare)  is  a  minute  reddish 
ganglion  placed  on  the  hyoglossus  muscle,  between  the  lingual  nerve  and  the 
duct  of  the  submaxillary  gland.  It  is  suspended  from  the  former  by  two  trunks, 
consisting  for  the  most  part  of  fibres  of  the  lingual  and  chorda  tympani  nerves 
which  at  this  point  become  separated  from  the  lingual  nerve  and  incorporated  with 
the  ganglion.  The  roots  of  the  ganglion  are — (1)  an  afferent  root,  derived  from 
the  lingual  nerve  ;  (2)  an  efferent  root,  derived  from  the  chorda  tympani ;  and  (3)  a 
sympathetic  root,  from  the  sympathetic  plexus  upon  the  facial  artery. 

The  branches  from  the  ganglion  are  distributed  to  the  submaxillary  gland  and 
Wharton's  duct,  and  by  fibres  which  become  reunited  with  the  trunk  of  the  lingual 
nerve,  to  the  sublingual  gland. 

The  inferior  dental  nerve  (n.  alveolaris  inferior)  is  larger  than  the  lingual 
nerve.  It  passes  from  beneath  the  lower  border  of  the  external  pterygoid  muscle 
to  reach  the  interval  between  the  ramus  and  internal  lateral  ligament  of  the  lower 
jaw.  Entering  the  inferior  dental  canal  through  the  inferior  dental  foramen,  it 
traverses  the  substance  of  the  ramus  and  body  of  the  lower  jaw,  distributing 
branches  in  its  course  to  the  teeth.  A  fine  plexus  is  formed  by  the  dental  branches 
before  they  finally  supply  the  teeth. 

Branches  and  Communications. — (1)  The  mylohyoid  nerve  is  a  small  branch 
arising  just  before  the  inferior  dental  nerve  passes  through  the  inferior  dental 
foramen.  Grooving  the  ramus  of  the  jaw  in  its  course,  it  descends  into  the 
submaxillary  triangle  on  the  superficial  aspect  of  the  mylohyoid  muscle.  Concealed 
in  this  situation  by  the  submaxillary  gland  and  the  facial  artery,  it  is  distributed 
to  the  mylohyoid  and  anterior  belly  of  the  digastric  muscles.  (2)  The  mental 
branch  of  the  inferior  dental  nerve  is  a  trunk  of  considerable  size  arising  from  the 
main  nerve  in  the  inferior  dental  canal.  It  emerges  from  the  lower  jaw  through 
the  mental  foramen,  and  is  distributed  by  many  branches  to  the  chin  and  lower 
lip.  It  communicates  beneath  the  facial  muscles  with  the  supra-mandibular 
branches  of  the  facial  nerve  (Fig.  523,  p.  679).  (3)  The  incisor  branch  is  the  terminal 
part  of  the  inferior  dental  nerve  remaining  after  the  origin  of  the  mental  branch. 
It  supplies  the  incisor  and  canine  teeth. 

The  otic  ganglion  (g.  oticum)  is  situated  beneath  the  inferior  maxillary  nerve 
just  below  the  foramen  ovale.  Like  the  other  ganglia  described  above,  it  possesses 
three  roots : — (1)  A  motor  roof,  derived  from  the  nerve  to  the  internal  pterygoid 
muscle;  (2)  a  sensor^/  root,  formed  by  the  s^ncdl  super/lcial  petrosal  nerve  from  the 
tympanic  plexus  (through  which  communications  are  effected  with  the  tympanic 
Ijranch  of  the  glosso-jjharyngeal  nerve,  and  a  branch  from  the  geniculate  ganglion 
of  the  facial  nerve);  (3)  a  symjxithetic  root,  from  the  plexus  on  the  middle 
meningeal  artery  (Fig.  527). 

Five  branches  arise  IVoin  jJio  gaiiglion — three  communicating  and  two  motor 
l^ranches.    Tiio  three  communicating  nerves  are  fine  branches  which  join  respectively 


686  THE  NEEVOUS  SYSTEM. 

the  vidian  nerve,  the  roots  of  the  auriculo-temporal,  and  the  chorda  tympani 
nerve.  The  two  motor  nerves  supply  the  tensor  tympani  and  tensor  palati 
muscles. 

Summary. — The  trigeminal,  the  largest  and  most  complex  of  the  cranial  nerves,  is  (1)  the 
chief  sensory  nerve  for  the  face,  the  anterior  half  of  the  scalp,  the  orbit  and  eyeball,  the  nose  and 
nasal  cavity,  the  lips,  teeth,  mouth,  and  two-thirds  of  the  tongue  ;  (2)  the  motor  fibres  of  the 
nerve  supply  the  muscles  of  mastication,  the  mylohyoid  and  anterior  belly  of  the  digastric, 
possibly  the  levator  palati  and  azygos  uvulae  (througli  Meckel's  ganglion),  and  the  tensor  tympani 
and  tensor  jjalati  muscles  (through  the  otic  ganglion) ;  (3)  througli  the  ganglia  j)laced  on  the 
three  divisions  of  the  nerve,  not  only  are  important  organs,  areas,  and  muscles  innervated,  but 
communications  are  also  effected  with  the  sympathetic  system,  with  the  third  nerve  (lenticular 
ganglion),  facial  nerve  (spheno -palatine  and  otic  ganglia),  and  glosso-pharyiageal  nerve  (otic 
ganglion). 

In  its  distribution  to  the  skin  of  the  face  the  branches  of  the  fifth  nerve  present  two  striking 
peculiarities  : — (1)  While  the  branches  to  the  skin  reach  the  surface  at  many  j^oints  and  in 
diverse  ways,  the  three  main  divisions  are  severally,  by  their  bi-anches,  responsible  for  the  su^jply 
of  three  clearly  demarcated  cutaneous  areas  (Fig.  523,  p.  679).  (2)  By  numerous  communications 
with  the  facial  nerve,  sensory  fibres  arej  given  to  the  muscles  of  expression  supjjlied  by  the 
facial  nerve. 

The  Sixth  or  Abducent  Nerve. 

The  abducent  nerve  (u.  abducens)  issues  from  the  brain  at  the  lower  border  of 
the  pons  Varolii,  just  above  the  pyramid  of  the  medulla  oblongata  (for  deep  origin, 
see  p.  524).  It  is  directed  forwards,  and  pierces  the  dura  mater  in  the  posterior 
fossa  of  the  base  of  the  skull  alongside  the  dorsum  sellse  (Fig.  522,  p.  678).  It 
then  occupies  the  inner  wall  of  the  cavernous  sinus  and  is  placed  on  the  outer 
side  of  the  internal  carotid  artery.  It  passes  through  the  sphenoidal  fissure  below 
the  third  and  nasal  nerves  and  between  the  two  heads  of  the  external  rectus 
muscle  (Fig.  520,  p.  677).  In  the  cavity  of  the  orbit  it  supplies  the  external  rectus 
muscle  on  its  inner  (ocular)  surface. 

Communications. — In  the  wall  of  the  cavernous  sinus  the  sixth  nerve  receives  two 
conimunicating  filaments  : — (1)  From  the  carotid  plexus  of  the  sympathetic,  and  (2)  from 
the  ophthalmic  division  of  the  trigeminal  nerve. 

The  Seventh  or  Facial  Nerve. 

The  facial  nerve  (n.  facialis)  emerges  from  the  brain  at  the  posterior  border  of 
the  pons  Varolii,  below  the  trigeminal  nerve  and  internal  to  the  auditory  nerve  (for 
deep  origin,  see  p.  522).  Between  it  and  the  latter  nerve  is  the  minute  pars  intermedia 
of  Wrisberg  (Fig.  517,  p.  675).  The  nerve  passes  outwards  through  the  internal 
auditory  meatus,  courses  through  the  aqueduct  of  Fallopius  in  the  petrous  portion 
of  the  temporal  bone,  emerges  in  the  base  of  the  skull  by  the  stylo-mastoid  foramen, 
and  passes  forwards  through  the  parotid  gland  to  supply  the  muscles  of  the  face. 
In  the  internal  auditory  meatus  the  nerve  is  placed  upon  the  auditory  nerve,  the 
pars  intermedia  intervening.  In  the  aqueduct  of  Fallopius  the  nerve  first  passes 
backwards  on  the  inner  side  of  the  tympanum,  and  then  downwards  behind  the 
tympanum,  in  the  inner  wall  of  the  tympanic  antrum.  In  the  parotid  gland 
the  nerve  crosses  superficially  the  external  carotid  artery  and  the  temporo-maxillary 
vein.  On  the  face  its  branches  radiate  from  the  anterior  border  of  the  parotid  gland 
and  enter  the  deep  surface  of  the  facial  muscles. 

Branches  and  Communications. — (i.)  In  the  internal  auditory  meatus  the  'pars 
intermedia  (n.  intermedius),  lying  l3etween  the  facial  and  auditory,  sends  com- 
municating branches  to  both  nerves.  The  branch  to  the  auditory  nerve  probably 
separates  from  it  again  to  join  the  geniculate  ganglion  of  the  facial  nerve. 

(ii.)  In  the  aqueduct  of  Fallopius  the  geniculate  ganglion  (g.  geniculi)  is  formed 
at  the  point  where  the  facial  nerve  bends  backwards  (geniculum  n.  facialis).  It  is 
an  oval  swelling  on  the  nerve,  and  is  joined  by  a  branch  from  the  upper  (vestibular) 
trunk  of  the  auditory  nerve,  by  which  it  probably  receives  fibres  of  the  pars  iiiter- 
media.  From  the  ganglion  three  small  nerves  arise : — (1)  The  large  superficial 
petrosal  nerve  passes  forwards  through  the  hiatus  Fallopii  to  the  middle  fossa  of  the 
base   of  the  skull.     On  the  upper  surface  of  the  foramen  lacerum  medium  it  is 


THE  SEVENTH  OR  FACIAL  NERVE. 


687 


joined  by  the  great  deep  petrosal  nerve  from  the  sympathetic  plexus  on  the  internal 
carotid  artery  to  form  the  vidian  nerve,  which,  after  traversing  the  vidian  canal, 
ends  in  Meckel's  ganglion.  (2)  A  minute  nerve  pierces  the  temporal  bone  and  joins 
the  tympanic  branch  of  the  glosso-pharyngeal  in  the  substance  of  the  bone.  By 
their  union  the  small  superficial  petrosal  nerve  is  formed,  which  pierces  the  temporal 
bone  and  ends  in  the  otic  ganglion.  (3)  The  external  superficial  petrosal  nerve  is  a 
minute  inconstant  branch  which  joins  the 
sympathetic  plexus  on  the  middle  meningeal 
artery. 

In  the  course  of  the  facial  nerve  in  the 
lower  part  of  the  aqueduct  of  Fallopius, 
behind  the  tympanum,  three  branches  arise — 
(1)  The  small  nerve  to  the  stapedius  muscle, 
which  passes  forwards  to  the  tympanum.  (2) 
The  chorda  tympani  nerve  (probably  associated 
with  the  pars  intermedia),  which  enters  the 
tympanic  cavity  through  the  iter  chorclce 
posterius,  passes  over  the  membrana  tympani 
and  the  handle  of  the  malleus,  and  leaves 
the  cavity  through  the  iter  chordm  anterius 
to  reach  the  pterygoid  region.  Beneath  the 
external  pterygoid  muscle  it  becomes  incor- 
porated with  the  lingual  branch  of  the  in- 
ferior maxillary  nerve,  and  in  its  further 
course  is  inseparable  from  that  nerve.  It 
supplies  a  root  to  the  sub-maxillary  ganglion, 
and  is  finally  distributed  (probably  as  a 
nerve  of  taste)  to  the  side  and  dorsum  of 
the  tongue  in  its  anterior  two-thirds.  The 
chorda  tympani  nerve  receives  beneath  the 
external  pterygoid  muscle  a  fine  communica- 
tion from  the  otic  ganglion.  (3)  Before  it 
leaves  the  aqueduct  of  Eallopius  a  fine  com- 
municating branch  arises  from  the  facial  nerve 
to  join  the  auricular  branch  of  the  pneumo- 
gastric  nerve. 

(iii.)  In  the  neck  the  facial  nerve  gives  off 
three  muscular  branches :  (1)  and  (2)  small 
branches  supply  the  stylo- hyoid  and  the 
posterior  belly  of  the  digastric,  the  latter 
nerve  sometimes  communicating  with  the 
glosso-pharyngeal.  (3)  The  posterior  auricular 
nerve  bends  backwards  and  upwards  over 
the  anterior  border  of  the  mastoid  process 
along  with  the  posterior  auricular  artery. 
It  divides  into  two  branches — an  auricular 
Irranch  for  the  retrahens  aurem  and  the  intrinsic  muscles  of  the  pinna,  and  an 
occipital  hranch  for  the  posterior  belly  of  the  occipito-frontalis  muscle.  The 
posterior  auricular  nerve  communicates  with  the  great  auricular,  small  occipital, 
and  auricular  branch  of  the  pneumogastric  nerves  in  its  course. 

(iv.)  In  the  parotid  gland  the  facial  nerve  spreads  out  in  an  irregular  series  of 
branches  Tpes  anserinusj,  indefinitely  divided  into  a  temporo-facial  and  a  cervico- 
facial division.  Communications  occur  in  the  substance  of  the  gland  between  the 
main  trunks  and  the  great  auricular  and  auriculo-temporal  nerves. 

The  temporo-facial  division  gives  off  three  series  of  subordinate  branches 
which  radiate  forwards  and  upwards  from  the  parotid  gland. 

1.  The  temporal  branches  are  of  large  size,  and,  sweeping  out  of  the  j)arotid  gland 
over  the  zygomatic  firch,  are  distributed  to  the  orbicularis  palpebrarum,  frontalis, 
corrugator  supercilii,  attrahens,  and  attollens  aurem.     The  temporal  branches  com- 


I.M. 

Fig.  528. —  The  Facial  Nerve  with  its 
Branches  and  Communications  [in  the 
Aqueduct  of  Fallopius.  i 

VII,  Facial  nerve  ;  P.I,  Pars  intermedia  ;  VIII, 
Auditory  nerve  ;  Aq.Fal,  Aqueduct  of  Fallo- 
pius ;  G.G-,  Geniculate  ganglion  ;  E.S.P,  Ex- 
ternal superficial  petrosal  nerve  ;  M.M,  Middle 
meningeal  artery  ;  G.S.P,  Great  superficial 
petrosal  nerve  :  G.  P.  D,  Great  deep  petrosal 
nerve  ;  I.C,  Internal  carotid  artery  ;  Vid, 
Vidian  nerve ;  M.G,  Meckel's  ganglion  ;  Ty.  PI, 
Tympanic  plexus  ;  S.D.P,  Small  deep  petrosal 
nerve  ;  G.Ph,  Glosso-pharyngeal  nerve  ;  Ty, 
Tympanic  branch  ;  S.S.P,  Small  superficial 
petrosal  nerve  ;  O.G,  Otic  ganglion  ;  Stap, 
Nerve  to  stapedius  ;  C.T,  Chorda  tympani 
nerve ;  L,  Lingual  nerve ;  A.Va,  Communication 
with  auricular  branch  of  vagus  ;  P.  A,  Posterior 
auricular  nerve  ;  Sty.hy,  Nerve  to  stylo-hyoid  ; 
Di,  Nerve  to  digastric  (posterior  belly)  ;  T.F, 
Temporo-facial  division  ;  C.F,  Cervico-facial 
division  ;  T.  Temporal  ;  M,  Malar  ;  I.O,  Infra- 
orbital ;  B.  Buccal  ;  S.M,  Supra-mandibular, 
and  I.M,  Infra-mandibular  branches. 


688 


THE  NEEVOUS  SYSTEM. 


municate  in   their  course   with  tlie    auriculo-temporal,  temporal  (of  the  superior 
maxillary),  lachrymal,  and  supra-orbital  branches  of  the  trigeminal  nerve. 

2.  The  malar  branclies  are  small,  and  sometimes  are  inseparable  from  the  temporal 
or  infra-orbital  nerves.  Extending  forwards  across  the  malar  bone,  they  supply 
the  orbicularis  palpebrarum  and  zygomatic  muscles,  and  communicate  with  the  malar 

branch  of  the  superior  maxillary  nerve. 
3.  The  infra-orbital  branclies  are  of 
considerable  size.  Passing  forwards  over 
the  masseter  muscle  in  company  with 
Stenson's  duct,  they  supply  the  orbi- 
cularis palpebrarum,  the  zygomatici, 
buccinator,  and  the  muscles  of  the  nose 
and  upper  lip.  The  infra-orbital  plexus 
is  formed  by  the  union  of  these  nerves 
with  the  infra-orbital  branch  of  the 
superior  maxillary  nerve  below  the 
lower  eyelid.  Smaller  communica- 
tions occur  with  the  infra-trochlear  and 
nasal  nerves  on  the  side  of  the  nose. 

The  cervico-facial  division  of  the 
facial  nerve  also  supplies  three  series 
of  secondary  branches. 

1.  The  buccal  branch  (or  branches) 
extends  forwards  to  the  angle  of  the 
mouth  to  supply  the  muscles  con- 
verging to  the  mouth,  including  the 
buccinator.  It  communicates  with  the 
buccal  branch  of  the  inferior  maxillary 
nerve  in  front  of  the  anterior  border 
of  the  masseter  muscle. 
Fig.   529. -Distribution   of  Facial  Nerve  outside  .^    ,p,         sunra  -  mandibular      branch 

THE  Skull,  and  Communications  with  Trigeminal  -^-    -^"^^      supra    manaiDUiar      orancn 

Nerve  on  the  Face.  passes  along  thelower  jaw  to  the  interval 

Facial   nerve. —P. A,  Posterior  auricular  nerve;   S.H,    between    the    lower   lip  and    chin,   and 

Nerve  to  stylo-hyoid  ;  Di,  Nerve  to  digastric  (posterior    supplies    the    depreSSOr    anguli   Oris,  de- 

T«^Jf{.^S:°^tl;2Z:^.r:Z:t  pressor  laWi  imenoris,  and  orbicularis 

facial  division  ;    B,    Buccal  ;    Sm,    Supra-mandibular  ;    OriS.      it  COmmuniCateS  With  the  mental 

im,  lufra-maudibuiar  branches.  branch  of  the  inferior  dental  nerve. 
Trigeminal  nerve -Ophth,  Ophthalmic  divisio.yS^^^  o     rj.^         infra  -  mandibular      branch 

Supra-orbital  ;    I.T,     Infra  -  trochlear  ;     N,    Eixternal 

nasal;    L,    Lachrymal  branches.       Sup. Max,    Superior  emerges    Irom    the    parOtld    gland    near 

maxillary  division  ;     T,   Temporal  ;    M,    Malar  ;    I.O,  i^S     lower    end,    and     SWCCpS     forwards 

Infra-orbital  branches.       Inf.Max,   Ingrio^r^ maxillary  ^^^^^  ^^^  ^^^^^^  ^^  ^^^   .,^^  ^^  ^j^^  ^^,^^^ 

of  the  neck.     It  supplies  the  platysma 
myoides,  and  forms  loops  of  communica- 
tion with  the  superficial  cervical  nerve  from  the  cervical  plexus. 


division  ;    A.T,    Auriculo-temporal  ;    B,    Buccal  ; 
Mental  branches  ;  S.C,  Superficial  cervical  nerve. 


The  Eighth  or  Auditory  JSTerve. 

The  auditory  nerve  (u.  acusticus)  arises  from  the  brain  by  two  roots,  mesial  and 
lateral.  The  mesial  root  (radix  vestibularis)  emerges  between  the  olive  and  the 
restiform  body.  The  lateral  root  (radix  cochlearis),  continuous  through  the  cochlear 
nucleus  with  the  strise  acusticse  of  the  fourth  ventricle,  winds  round  the  outer  side 
of  the  restiform  body  (for  deep  connexions,  see  p.  519).  The  two  roots  become 
incorporated  to  form  the  trunk  of  the  nerve,  wliich  is  attached  to  the  brain  on  the 
outer  side  of  the  facial  nerve  and  pars  intermedia  at  the  posterior  border  of  the 
pons  Varolii  (Fig.  517,  p.  675). 

The  nerve  extends  outwards  through  the  internal  auditory  meatus,  lying  beneath 
the  facial  nerve  and  pars  intermedia  (Fig.  522,  p.  678).  In  the  meatus  its  two 
component  parts  separate  from  one  another,  forming  a  superior  or  vestibular  trunk 
continuous  with  the  mesial  root,  and  an  inferior  or  cochlear  trunk  continuous  with 


TI-TE  NINTH  OR  GLOSSO-PHAEYNGEAL  NERVE. 


089 


the  lateral  root.     These  trunks  again  subdivide,  and  xoiercing  the  lamina  criljrosa, 
supply  the  several  parts  of  the  labyrinth. 

The  superior  or  vestibular  trunk  (n.  vestibuli)  in  the  internal  auditory  meatus 
usually  receives  fibres  from  the  'pars  intermedia, and  gives  off  a  communicating  branch 


-Scheme  of  the  Origin  and  Distribution 
OF  THE  Auditory  Nerve. 
Py,  Pyramicl ;  01,  Olive  ;  R.B,  Kestiform  body ;  A.St,  Striae acustica- ; 
Do,  Dorsal  nucleus  ;  G,  Lateral  cochlear  nucleus  ;  Ve,  Ventral  nu- 
cleus ;  P.I,  Pars  intermedia;  G.G,  Geniculate  ganglion;  Co,  Cochlea  ; 
Sacc,  Saccvile  ;  Po,  Posterior  semicircular  canal ;  Ext,  External 
semicircular  canal ;  Sup,  Superior  semicircular  canal ;  Utr,  Utricle. 

to  the  geniculate  ganglion  of  the  facial  nerve.  It  then  separates  into  three  terminal 
branches  which  pierce  the  lamina  cribrosa,  and  supply  (1)  the  macula  acustica  of 
the  utricle  and  the  ampullae  of  (2)  the  superior  and  (3)  external  semicircular  canals. 

The  inferior  or  cochlear  trunk  (n.  cochleae)  gives  off  branches  (1)  to  the 
macula  acustica  of  the  saccule,  (2)  to  the  ampulla  of  the  posterior  semicircular  canal, 
and  (3)  is  continued  through  the  lamina  cribrosa  to  the  labyrinth  as  the  cochlea-r 
nerve,  which  is  distributed  through  the  modiolus  and  osseous  spiral  lamina  to  the 
organ  of  Corti  in  the  cochlea. 

Both  the  vestibular  and  cochlear  nerves  contain  among  their  fibres  collections  of  nerve 
cells,  forming  in  each  nerve  a  distinct  ganglion — the  vestibular  ganglion  (g.  vestibulare)  on 
the  vestibular  trunk,  and  the  spiral  ganglion  of  the  cochlea  (g.  spirale)  on  the  cochlear  trunk. 

The  Ninth  or  Glosso-pharyngeal  Nerve. 

The  glosso-pharyngeal  nerve  (n.  glosso-pharyngeus)  (Fig.  517,  p.  675)  arises  from 
the  brain  by  five  or  six  fine  radicles  which  emerge  from  the  medulla  oblongata  between 
the  olive  and  the  restiform  body,  close  to  the  facial  nerve  above,  and  in  series  with 
the  roots  of  the  pneumogastric  nerve  below  (for  deep  connexions,  seep.  517).  The 
rootlets  combine  to  form  a  nerve  which  extends  outwards  to  the  jugular  foramen, 
through  which  it  passes,  along  with  the  pneumogastric  and  spinal  accessory  nerves, 
but  enveloped  in  a  separate  sheath  of  dura  mater  (Fig.  522,  p.  678).  Reaching  the 
neck,  the  nerve  arches  downwards  and  forwards  to  the  interval  between  the  hyoid 
bone  and  the  lower  jaw.  It  lies  at  first  between  the  internal  carotid  artery  and 
the  internal  jugular  vein,  and  then  between  the  internal  and  external  carotid 
arteries,  in  its  course  to  the  side  of  the  pharynx.  It  sweeps  round  the  stylo- 
pharyngeus  muscle  and  the  stylo-hyoid  ligament,  and  disappears  beneath  the 
hyoglossus  muscle,  to  reach  its  termination  in  the  tongue. 

The  branches  of  the  nerve  may  be  classified  in  three  series  according  to  their 
origin — (i.)  in  the  jugular  foramen  ;  (ii.)  in  the  neck ;  (iii.)  in  relation  to  the  tongue. 

In  the  jvgular  foramen  there  are  two  enlargements  upon  the  trunk  of  the  nerve 
— the  jugular  and  petrous  ganglia.  The  jugular  ganglion  (g.  superius)  is  small,  does 
not  implicate  the  whole  width  of  the  nerve,  and  may  be  fused  with  the  petrous 
ganglion,  or  even  absent  altogether.     No  branches  arise  from  it. 

The  petrous  ganglion  (g.  petrosum)  is  distinct  and  constant.  It  is  placed 
ujjon  the  nerve  at  the  lower  part  of  its  course  through  the  jugular  foramen. 

Branches  and  Communications  of  the  Petrous  Ganglion. — The  tympanic  branch  (n. 
tympanicuH,  Jacojtson's  nerve)  is  the  most  important  offset  from  this  ganglion.  It 
passes  tlirough  a  small  canal  in  the  bridge  of  bone  between  the  jugular  foramen 
and  the  carotid  canal  to  reach  the  cavity  of  the  tymy)anuni,  where  it  breaks  u])  into 
branches,  to  form,  along  with  branches  from  the  cnrotid  ])lexus  of  the  sym})athctic  on 
the  internal  carotid  artery  fsmall  deep  petrosal  nerve),  the  tympanic  plexusforthc  supply 
of  the  mucous  lining  of  tlui  tympanum,  mastoid  cells,  and  Eustacliian  tube  (Fig.  528, 
48 


690 


THE  NEEVOUS  SYSTEM. 


p.  687).  The  fibres  of  the  tympanic  branch  of  the  glosso-pharyngeal  nerve  become 
reunited  to  form,  by  their  union  with  a  small  nerve  from  the  geniculate  ganglion  of  the 
facial  nerve,  the  small  superficial  petrosal  nerve  in  the  substance  of  the  temporal  bone. 
This  passes  forwards  through  the  temporal  bone,  and  eventually  joins  the  otic  ganghon. 

Besides  forming  the  tympanic  branch,  the  petrous  ganglion  of  the  glosso-pharyngeal 
nerve  communicates  witli  tln-ee  other  nerves — (1)  with  the  superior  cervical  ganglion  of 

the      sympathetic  ;      (2)     with      the 
auricular     branch    of    the    pneumo  - 
P'-^-  gastric;  and  (3)  sometimes  with  the 

Aur.N^     \\iii//'%nil//       yTv^Tpiex^V  ^i;f  ganglion  of  the  root  of  the  pneumo- 

gastric. 

In  the  neck  the  glosso-pharyngeal 
nerve  gives  off  two  branches.  (1) 
As  it  crosses  over  the  stylo-pharyn- 
geus  muscle  it  supplies  the  nerve 
to  that  muscle,  which  sends  fibres 
through  it  to  reach  the  mucous 
membrane  of  the  pharynx.  (2) 
The  pharyngeal  branches  of  the  nerve 
supply  the  mucous  membrane  of 
the  pharynx  directly  after  piercing 
the  superior  constrictor  muscle,  and 
indirectly  after  joining,  along  with 
the  pharyngeal  offsets  from  the 
pneumogastric  and  the  superior 
cervical  ganglion  of  the  sym- 
pathetic, in  the  formation  of  the 
pharyngeal  plexus. 

The  terminal  branches  of  the 
nerve  supply  the  mucous  mem- 
brane of  the  tongue  and  adjacent 
parts.  A  tonsillitic  branch  forms  a 
plexus  (circulus  tonsillaris)  to 
supply  the  mucous  membrane 
covering  the  tonsil,  the  adjacent 
part  of  the  soft  palate,  and  the 
pillars  of  the  fauces.  Lingual 
branches  supply  the  mucous  mem- 
brane of  the  dorsal  third  and 
lateral  half  of  the  tongue,  extend-  • 
ing  backwards  to  the  glosso-epi- 
giottidean  folds  and  the  front  of 
the  epiglottis. 


Fig.  531. — Scheme  of  the  Distribution  of  the  Glosso- 

PHARTNGEAL   NeRVE. 

G.Ph,  Glosso-pharyngeal  nerve  ;  J,  Jugular,  and  P,  Petrous 
ganglia ;  Ty,  Tympanic  branch  (Jacobson's  nerve)  ; 
Ty.Plex.,  Tympanic  plexus  ;  Fa,  Eoot  from  geniculate 
ganglion  of  facial  nerve  ;  S.S.P,  Small  superficial  petrosal 
nerve  to  the  otic  ganglion  ;  S.D.P,  Small  deep  petrosal 
nerve  ;  I.C,  Internal  carotid  artery  ;  Va,  Pneumogastric 
nerve  ;  Aur.,  Auricular  branch  (Arnold's  nerve)  ;  Sy., 
Superior  cervical  sympathetic  ganglion  ;  F,  Communi- 
cating branch  to  facial  nerve  ;  Ph,  Pharyngeal  branch  of 
vagus  ;  E.C,  External  carotid  artery  ;  Ph. PI,  Pharyngeal 
plexus;  S.Ph,  Stylo-pharyngeus  muscle;  S. H.L,  Stylo- 
liyoid  ligament;  H.G,  Hyo-glossus  ;  S.G,  Stylo-glossus  ; 
Ton,  Tonsil  ;  S.  Pal.,  Soft  palate  ;  G.  H.G,  Genio-hyoglossus  ; 
G.H,  Genio-hyoid  ;  Hy,  Hyoid  bone. 


The  Tenth  or  Pneumogastric  Nerve. 

The  pneumogastric  or  vagus  nerve  (n.  vagus)  arises  from  the  brain  by  numerous 
radicles  attached  to  the  front  of  the  restiform  body  of  the  medulla  oblongata,  in  series 
with  the  glosso-pharyngeal  nerve  above  and  the  spinal  accessory  nerve  below  it  (ibr 
deep  connexions,  see  p.  517).  Uniting  to  form  a  single  trunk,  the  roots  of  the  nerve 
pass  outwards  to  the  jugular  foramen,  through  which  they  emerge  into  the  neck. 

In  the  jugular  foramen  the  nerve  occupies  the  same  sheath  of  dura  mater  as  the 
spinal  accessory  nerve,  and  is  placed  behind  the  glosso-pharyngeal  nerve.  Two 
ganglia  are  present  on  the  trunk  in  this  situation.  The  higher  and  smaller  is  the 
ganglion  of  the  root  (g.  jugulare)  ;  the  lower  and  larger  is  the  ganglion  of  the  trunk 
of  the  nerve  (g.  nodosum). 

In  the  neck  the  pneumogastric  nerve  pursues  a  vertical  coarse  in  front  of  the 
spinal  column.  It  occupies  the  carotid  sheath,  lying  between  and  behind  the 
internal  and  common  carotid  arteries  and  the  internal  jugular  vein.     It  enters  the 


THE  TENTH  OE  PNEUMOGASTRIC  NERVE. 


691 


thorax  behind  the  large  veins  :  on 
the  right  side,  after  crossing  over 
the  subclavian  artery ;  on  the  left 
side,  in  the  interval  Ijetween  the 
left  common  carotid  and  subclavian 
arteries. 

In     the    thorax    the    nerves 
occupy  the  superior  and  posterior 
mediastinal  spaces,  and  their  re- 
lations are    different   on   the  iwo 
sides,     (a)  In  the  superior  media- 
stinum the  right  nerve  continues 
its  course  alongside  the  innominate 
artery  and  the  trachea,  and  behind 
the    right    innominate    vein    and 
superior  vena  cava,  to  the  back  of 
the  root  of   the  lung.      The    left 
nerve  courses  downwards  between 
the  left  common  carotid  and  sub- 
clavian   arteries,  and  behind  the 
left    innominate    vein    and    the 
phrenic  nerve.     It  passes  over  the 
aortic  arch,  and  then  proceeds  to 
the  back  of  the  root  of  the  left 
lung.     (&)  In  the  posterior  media- 
stinum the  pneumogastric  nerves 
are  concerned  in  the  formation  of 
two  great  plexuses — the  pulmon- 
ary and  the  oesophageal.     Behind 
the  root  of  each  lung  the  nerve 
breaks    up    to    form    the    large 
posterior    pulmonary    plexus,  from 
the  lower  end  of  which  two  nerves 
emerge  on  each  side.    These  nerves 
on  the   right  side  pass  obliquely 
over  the  vena  azygos  major;   on 
the  left  side  they  cross  the  thoracic 
aorta.     Both  series  reach  the  oeso- 
phagus,   and    divide    into    small 
anastomosing  branches  which  form 
the.  oesophageal   plexus.      At    the 
cesophageal   opening  of  the   dia- 
phragm  the   two  nerves   become 
separated   from    the   plexus,  and 
entering   the  abdomen — the  left 
nerve  in  front  of  the  oesophagus, 
the  right  nerve  behind  it — they  ter- 
minate by  supplying  the  stomach 
and  other  abdominal  organs. 

The  communications  and 
branches  of  the  pneumogastric 
nerve  may  be  described  as  (i.)  gan- 
glionic, (ii.)  cervical,  (iii.)  thoracic, 
and  (iv.)  afxlominal  (Fig.  532). 


Fig.  532. — The  Distribution  of  the  Pneumogastkic  Nerve, 
Var.R,  Va.L,  Right  and  left  vagi ;  r,  Ganglion  of  the  root  and 
connexions  with  Sy,  Sympathetic,  superior  cervical  gang- 
lion ;  G.Ph,  Glosso-pharyngeal  ;  Ace,  Spinal  accessory 
nerve  ;  m,  Meningeal  branch  ;  Aur,  Anricular  branch  ;  t, 
Ganglion  of  the  trunk  and  connexions  with  Hy,  Hypo- 
glossal nerve  ;  CI,  C2,  Loop  between  the  first  two  cervical 
nerves  ;  Sy,  Sympathetic  ;  Ace,  Spinal  accessory  nerve  ;  Ph,  Pharyngeal  branch  ;  Ph. PI,  Pharyngeal 
plexus  ;  S.Jj,  Superior  laryngeal  nerve  ;  I.L,  Internal  laryngeal  branch  ;  E.  L,  External  laryngeal  branch  ; 
I.C,  Internal,  and  E.C,  External  carotid  arteries;  Gal,  Sujicrior  cervical  cardiac  branch;  Ca'2,  Inferior 
cervical  cardiac  branch  ;  ILL,  Recurrent  laryngeal  nerve  ;  CaB,  Cardiac  branches  from  recurrent  laryngeal 
nerves  ;  Ca4,  Thoracic  canliac  branch  (right  vagus)  ;  A.P.Pl,  Anterior,  and  P.P.Pl,  Posterior  ])ulmonary 
plexuses  ;  Oes.Pl,  filsophageal  plexus  ;  Gast.R,  and  Gast.Ij,  Gastric  branches  of  vagus  (right  and  left)  ; 
Coe.Pl,  Cwliac  plexus;   Hep. PI,  Hepatic  plexus  ;  Spl.Pl,  Splenic  jilexus  ;  fieu.Pl,  Renal  plexus, 

48  a 


692  THE  NEEVOUS  SYSTEM. 

The  ganglion  of  the  root  (g.  jugulare)  is  small  and  spherical.  It  occupies 
the  jugular  foramen,  and  gives  oft"  two  branches — meningeal  and  auricular. 

The  meningeal  branch  passes  backwards  to  supply  the  dura  mater  of  the  posterior 
fossa  of  the  liase  ol'  the  skull. 

The  auricular  branch  (Arnold's  nerve)  ascends  to  the  ear  in  a  fissure  between  the 
jugular  and  stylo-mastoid  foramina.  It  receives  near  its  origin  a  twig  from  the 
tympanic  branch  of  the  glosso-pharyngeal  nerve,  and  usually  communicates  mth 
the  facial  nerve  by  a  branch  arising  from  the  latter  in  the  aqueduct  of  Fallopius. 
The  nerve  is  distri]  )uted  to  the  l:)ack  of  the  pinna  and  the  external  auditory  meatus, 
and  communicates  superficially  with  the  posterior  auricular  nerve. 

Communications. — Besides  STipplying  the  meningeal  and  aiu'icular  branches,  the 
ganglion  of  the  root  of  the  pneumogastric  nerve  receives  communications  from  (1)  the 
superior  cervical  ganglion  of  the  sympathetic  ;  (2)  the  spinal  accessory  nerve  ;  and  (3)  the 
petrous  ganglion  of  the  glosso-pharyngeal  nerve  (sometimes). 

The  ganglion  of  the  trunk  of  the  nerve  (g.  nodosum),  placed  immediately 
below  the  preceding,  is  large  and  fusiform.  Like  the  previous  ganglion,  it  supplies 
two  branches — the  pharyngeal  and  superior  laryngeal  nerves. 

The  pharyngeal  branch  receives  its  fibres  (through  the  ganglion)  from  the  spinal 
accessory  nerve.  It  passes  obliquely  downwards  and  inwards  to  the  pharynx 
between  the  internal  and  external  carotid  arteries,  and  combines  with  the  pharyn- 
geal nerves  from  the  glosso-pharyngeal  and  superior  cervical  ganglion  of  the 
sympathetic  to  form  the  pharyngeal  plexus.  From  this  plexus  the  muscles  of  the 
pharynx  and  soft  palate  (except  the  stylo-pharyngeus  and  tensor  palati)  are 
supplied.  The  lingual  branch  is  a  small  nerve  which  separates  itself  from  the 
plexus  and  joins  the  hypoglossal  nerve  in  the  anterior  triangle  of  the  neck. 

The  superior  laryngeal  nerve  (n.  laryngeus  superior)  passes  obhquely  down- 
wards and  inwards,  behind  the  external  and  internal  carotid  arteries,  towards  the 
thyroid  cartilage.  It  divides  in  its  course  into  two  unequal  parts — a  larger  internal 
and  a  smaller  external  laryngeal  nerve. 

The  internal  laryngeal  nerve  (ramus  internus)  passes  inwards  into  the  larynx 
between  the  middle  and  inferior  constrictor  muscles  of  the  pharynx  and  through  the 
thyro-hyoid  membrane.  It  supplies  the  mucous  membrane  of  the  larynx,  reaching 
upwards  to  the  epiglottis  and  base  of  the  tongue,  and  forms  communications  beneath 
the  ala  of  the  thyroid  cartilage  with  the  branches  of  the  inferior  laryngeal  nerve. 

The  external  laryngeal  nerve  (ramus  externus)  passes  downwards  upon  the 
inferior  constrictor  muscle  of  the  pharynx.  It  supplies  branches  to  that  muscle, 
and  ends  in  the  crico-thyroid  muscle. 

Communications. — Besides  supplying  these  pharyngeal  and  laryngeal  nerves,  the 
ganglion  of  the  trunk  of  the  pneumogastric  has  the  following  communications  with  other 
nerves:  (1)  with  the  superior  cervical  ganglion  of  the  sympathetic ;  (2)  w4th  the  hypo- 
glossal ;  (3)  with  the  loop  between  the  first  and  second  cervical  nerves ;  and  (-1)  with  the 
accessory  part  of  the  spinal  accessory  nerve.  This  part  of  the  nerve  appHes  itself  to  the 
ganglion,  and  thereby  supplies  to  the  vagus  nerve  the  inhibitory  fibres  for  the  heart,  as 
well  as  the  motor  fibres  for  the  pharynx,  oesophagus,  stomach  and  intestines,  larynx  and 
respiratory  organs. 

Branches  of  the  Pneumogastric  in  the  Neck. — In  the  neck  the  pneumo- 
gastric nerve  supplies  cardiac  branches  and  (on  the  right  side)  the  inferior  or 
recurrent  laryngeal  nerve  (Fig.  532). 

The  cardiac  branches  are  superior  and  inferior.  On  the  right  side  both  cardiac 
branches  pass  downwards  into  the  thorax  behind  the  subclavian  artery,  and  proceed 
alongside  the  trachea  to  join  the  deep  cardiac  plexus.  On  the  left  side  the  two 
nerves  separate  on  reaching  the  thorax.  The  sujyerior  nerve  passes  deeply  along- 
side the  trachea  to  join  the  deep  cardiac  plexus.  The  inferior  nerve  accompanies 
the  pneumogastric  nerve  over  the  aortic  arch,  along  with  the  superior  cervical 
cardiac  branch  of  the  sympathetic,  to  end  in  the  superficial  cardiac  plexus. 

The  right  inferior  laryngeal  nerve  arises  at  the  root  of  the  neck,  as  the 
pneumogastric  nerve  crosses  over  the  first  part  of  the  subclavian  artery.  It  hooks 
round  the  artery,  and  passes  obliquely  upwards  and  inwards  behind  the  subclavian, 


THE  THOEACIC  PLEXUSES.  693 

the  common  carotid,  and  the  inferior  thyroid  artery  and  the  thyroid  body.  It  finally 
disappears  beneath  the  lower  border  of  the  inferior  constrictor  muscle,  and  ends 
in  supplying  the  muscles  of  the  larynx.  In  its  course  it  gives  off  the  following 
branches : — 

(1)  Cardiac  branches  arise  as  the  nerve  winds  round  the  subclavian  artery,  and 
course  downwards  alongside  the  trachea  to  end  in  the  deep  cardiac  plexus. 

(2)  Communicating  branches  to  the  inferior  cervical  ganglion  of  the  sympathetic 
arise  from  the  nerve  behind  the  subclavian  artery. 

(3)  Muscular  branches  supply  the  trachea,  oesophagus,  and  the  inferior  constrictor 
of  the  pharynx. 

(4)  Terminal  branches  supply  the  muscles  of  the  larynx  (except  the  crico-thyroid) 
and  communicate  beneath  the  ala  of  the  thyroid  cartilage  with  branches  of  the 
internal  laryngeal  nerve. 

Branches  of  the  Vagus  in  the  Thorax. — In  the  thorax  the  pneumogastric 
nerve  forms  the  great  pulmonary  and  oesophageal  plexuses.  The  right  nerve,  in 
addition,  furnishes  cardiac  branches ;  and  the  left  nerve  gives  off  the  inferior  or 
recurrent  laryngeal  nerve. 

The  left  inferior  laryngeal  nerve  differs  from  the  nerve  of  the  right  side  only 
in  its  point  of  origin  and  in  the  early  part  of  its  course.  It  springs  from  the 
pneumogastric  nerve  as  it  crosses  the  aortic  arch,  and,  after  hooking  round  the 
arch  external  to  the  ligamentum  arteriosum,  it  passes  upwards  in  the  superior 
mediastinum  in  the  interval  between  the  trachea  and  oesophagus  to  the  neck.  In 
the  neck  its  course  and  relations  are  similar  to  those  of  the  nerve  of  the  right  side. 
The  branches  of  the  nerve  are  the  same  as  those  of  the  right  nerve.  The  cardiac 
branches  are  larger,  and,  arising  below  the  aortic  arch,  proceed  to  the  deep  cardiac 
plexus. 

Cardiac  branches  from  the  right  pneumogastric  nerve  arise  in  the  superior 
mediastinum,  and  pass  downwards  alongside  the  trachea  to  join  the  deep  cardiac 
plexus.  On  the  right  side  thoracic  cardiac  branches  are  thus  supplied  from  both 
the  trunk  of  the  nerve  and  its  recurrent  branch  ;  on  the  left  side  the  cardiac  branches 
in  the  thorax  arise  solely  from  the  recurrent  branch. 

Abdominal  Branches. — After  the  formation  of  the  oesophageal  plexus  the 
two  pneumogastric  nerves  resume  their  course,  and  passing  along  with  the  gullet 
through  the  diaphragm,  terminate  by  supplying  the  stomach.  The  right  nerve 
enters  the  abdominal  cavity  behind  the  gullet,  and  is  distributed  to  the  posterior 
surface  of  the  stomach.  It  sends  communicating  offsets  to  the  cceliac,  splenic,  and 
renal  plexuses.  The  left  nerve  applies  itself  to  the  anterior  surface  and  lesser  cur- 
vature of  the  stomach,  to  which  it  is  distributed.  It  sends  communicating  offsets 
along  the  lesser  curvature  of  the  stomach  to  the  right  pneumogastric,  and  between 
the  layers  of  the  small  omentum  to  the  hepatic  plexus. 

The  Thoracic  Plexuses. 

Cardiac  Plexuses. — The  cardiac  branches  of  the  pneumogastric  nerve  (both 
cervical  and  thoracic)  combine  with  the  cervical  cardiac  branches  of  the  sympathetic 
to  form  the  superficial  and  deep  cardiac  plexuses. 

The  superficial  cardiac  plexus  is  placed  in  the  hollow  of  the  aortic  arch, 
superficial  to  the  pericardium.  It  contains  a  small  ganglion  (ganglion  of  Wrisberg), 
and  is  joined  by  two  small  nerves — (1)  the  cardiac  branch  from  the  superior 
cervical  ganglion  of  the  sympathetic,  and  (2)  the  inferior  cervical  cardiac  branch 
of  the  jjneumogastric— both  of  the  left  side — which  reach  it  after  passing  over  the 
arch  of  the  aorta. 

Branches  and  Communications. — From  tlie  plexus  branches  of  communication 
pass  (l)  to  the  left  hall'  of  the  deep  cardiac  plexus,  between  the  aortic  arch  and  the 
bifurcation  of  the  pulmonary  artery ;  (2)  to  the  left  anterior  pulmonary  plexus 
along  the  left  branch  of  the  pulmonary  artery ;  (3)  the  branches  of  distribidiion  to 
the  heart  extend  along  the  pulmonary  artery  to  join  the  anterior  or  right  coronary- 
plexus,  which  supplies  the  substance  of  the  heart  in  tlie  course  of  the  right 
coronary  artery. 
48 /> 


694 


THE  NEEVOUS  SYSTEM. 


The  deep  cardiac  plexus  is  much  the  larger.  It  is  placed  behind  the  arch  of 
the  aorta,  on  the  sides  of  the  trachea,  just  above  its  bifurcation.  It  consists  of 
two  lateral  parts,  joined  together  by  numerous  communications  around  the  termina- 
tion of  the  ti'achea.  The  two  portions  of  the  plexus 
are  different  in  their  constitution  and  distribution. 
The  right  half  of  the  plexus  is  joined  by  both  the 
cervical  and  thoracic  branches  of  the  right  pneumo- 
gastric  and  by  the  branches  of  the  riglit  inferior 
laryngeal  nerve,  as  well  as  by  branches  from  the 
superior,  middle,  and  inferior  cervical  ganglia  of  the 
sympathetic.  The  left  half  of  the  plexus  is  joined  by 
the  superi(^r  cervical  cardiac  Ijranch  of  the  left  pneumo- 
gastric,  by  branches  from  the  left  inferior  laryngeal 
nerve,  and  by  branches  from  the  middle  and  inferior 
cervical  ganglia  of  the  left  sympathetic ;  it  also 
receives  a  contribution  from  the  su]3erficial  cardiac 
plexus. 

The  deep  cardiac  plexus  is  distributed  to  the 
heart  and  lungs.  The  right  half  of  the  plexus  for 
the  most  part  constitutes  the  anterior  or  riglit  coronary- 
plexus,  reaching  the  heart  alongside  the  ascending 
aorta,  and  is  distributed  to  the  heart  substance  in 
the  course  of  the  right  coronary  artery.  It  is  rein- 
forced by  fibres  from  the  superficial  cardiac  plexus, 
which  reach  the  heart  along  the  pulmonary  artery. 
Fibres  from  the  right  half  of  the  deep  cardiac  plexus 
pass  also  to  join  the  posterior  or  left  coronary  plexus, 
and  others  extend  outwards  to  join  the  anterior 
pulmonary  plexus  of  the  right  side. 

The  l(ft  half  of  the  deep  cardiac  plexus,  reinforced 
by  fibres  from  the  superficial  cardiac  plexus,  is  dis- 
tributed to  the  heart  in  the  form  of  the  left  or 
posterior  coronary  plexus,  which  is  joined  by  a  few 
fibres  behind  the  pulmonary  artery  from  the  right 
half  of  the  plexus,  and  supplies  the  heart  substance 
in  the  course  of  the  left  coronary  artery.  The  left 
half  of  the  plexus  contributes  also  to  the  left  anterior 
pulmonary  plexus  by  fibres  which  extend  outwards  to 
the  root  of  the  lung  along  the  left  branch  of  the 
pulmonary  artery. 

Pulmonary  Plexuses. — As  already  stated,  the 
pneumogastric  nerve  on  each  side,  on  reaching  the 
back  of  the  root  of  the  lung,  breaks  up  into  numerous 
Superior,  C.2  Middle,  aud  C.3,  In-  piexiform  branches  for  the  formation  of  the  posterior 

fenor  cervical  ganglia ;  Car.  1,  Su-    -■-     ,  ,  „  ,  p         ,.1 

perior,  Car.  2,  Middle,  and  Car. 3,   pulmonary  piexus.     Jbrom  each  ncrvc  a  lew  fibres  pass 

Inferior    cervical    cardiac    syinpa-    tO  the    front  of    the  rOOt  of   the  lung,  aboVC    itS    Upper 

thetic  branches ;  Va,  Pneumogastric  j^grder,  to  form  the  much  Smaller  anterior  pulmonary 

nerve  ;    K.L,    Kecurrent    laryngeal       .  '  1  ^ 

nerve ;  s,  Superior,  and  i,  Inferior    piCXUS. 

cervical  cardiac  branches  of  vagus ;  The  anterior  pulmonary  plexus  on  each  side  is 

p.  C.P  Deep  cardiac  plexus  ;S.C.P,  JQi^e,;^  y^y  a  fesv  fibres  from  the  corresponding  part  of 

Anterior  pulmonary  plexus';  v.v.v,  the  deep  cardiac  plcxus,  and  on  the  left  side  from 

Posterior      pulmonary      plexus ;  the  Superficial  cardiac  plexus  as  well.     It  surrounds 

R.Car.p,  Right,  and  L.Car.p,  Left  ^^^  supplies  the  Constituents  of  the  root  of  the  lung 

coronary  jHexuses  ;    Art.Pul,    Pul-  .  ^^  " 

monary  artery.  anteriorly. 

The  posterior  pulmonary  plexus,  placed  behind 
the  root  of  the  lung,  is  formed  by  the  greater  part  of  the  pneumogastric  nerve, 
reinforced  by  fine  branches  from  the  second,  third,  and  fourth  thoracic  ganglia 
of  the  sympathetic.  Numerous  branches  proceed  from  it  in  a  piexiform  manner 
alons  the  bronchi  and  vessels  into  the  substance  of  the  lung. 


Fig.  533. — The  Constitution  op 
THE  Cardiac  Plexuses. 

:Sy,  Cervical  sympathetic  cord  ;    C.l, 


THE  ELEVENTH  OE  SPINAL  ACCE880KY  NERVE. 


m: 


(Esophageal  Plexus  (plexus 
guhe).  —  Tlie  oesophagus  in  the 
thorax  is  supplied  by  the  pneu mo- 
gastric  nerve  both  in  the  superior 
and  posterior  mediastinum.  In 
theswperiof  mediastinum  it  receives 
branches  from  the  pneumogastric 
nerve  on  the  right  side,  and  from 
its  recurrent  laryngeal  branch  on 
the  left  side. 

In  the  'posterior  mediastinum 
it  is  surrounded  by  the  cesophageal 
plexus,  formed  from  the  trunks  of 
the  pneumogastric  nerves  emerg- 
ing from  the  posterior  pulmonary 
plexus,  which  form  a  large  plexus 
surrounding  the  gullet.  This  part 
of  the  oesophagus  also  receives  fibres 
from  the  great  splanchnic  nerve 
andganglion.  From  the  oesophageal 
plexus  branches  supply  the  mus- 
cular wall  and  mucous  membrane 
of  the  cesox^hagus. 

Pericardiac  branches  are  also 
supplied  from  the  plexus  to  the 
posterior  surface  of  the  peri- 
cardium. 

The  Eleventh  or  Spinal 
Accessory  Nerve. 

The  spinal  accessory  nerve  (n. 
accessorius)  consists  of  two  es- 
sentially separate  parts,  different 
both  in  origin  and  in  distribution. 
One  portion  is  accessory  to  the 
vagus  nerve,  and  arises,  in  series 
with  the  fibres  of  that  nerve,  from 
the  side  of  the  medulla  oblongata. 
The  other,  spinal  portion,  arises 
from  the  lateral  aspect  of  the 
spinal  cord,  between  the  ventral  ^! 
and  dorsal  roots  of  the  spinal 
nerves,  its  origin  extending  from 
the  level  of  the  accessory  portion 
as  low  as  the  origin  of  the  sixth 
cervical  nerve  (for  the  deep  origin, 
see  J)-  516).     Successively  joining 

together,  the  rootlets  form  a  trunk  p^,,  534.__the  Distribution  of  the  Pneumogastkic  Nekve. 
which  ascends  m  the  subdural  Va.R,  Va.L,  Right  and  left  vagi  ;  r,  Ganglion  of  the  root  and 
space    or    the    spinal    cord,    Ijellind  connexions  with  Sy,  Sympathetic,  superior  cervical  gang- 

the    ligamentum   denticulatum,  to  li^^"  ;    ^^■^'^,    Glosso-pharyngeal  ;    Ace,    Spinal    accessory 

the  foramen  magnum.     There  the  "f''"",i  •"'  flf'f^^  /'^''f  '  Aur,  Auricular  branch  ;  t, 

'^  Ganglion  ot   the  trunk   and   connexions  with    Hy,   Hypo- 

glossal nerve  ;  CI,  C2,  Loop  between  the  first  two  cervical 
nerves  ;  Sy,  Sympathetic  ;  Ace,  Spinal  accessory  nerve  ;  Ph.  Pliaryngeal  branch  ;  Ph. PI,  Pharyngeal  plexus  ; 
S. L,  Superior  laryngeal  nerve;  I.L,  Internal  laryngeal  branch;  E.L,  External  laryngeal  brancli  ;  I.C, 
Interna),  aiul  E.C,  External  carotid  arteries  ;  Cal,  Siqierior  cervical  cardiac  branch  ;  Ca2,  Inferior  cervical 
r.ardiac  branch  ;  R.L,  Recurrent  laryngeal  nerve  ;  Ca^S,  Cardiac  brandies  from  recurrent  laryngeal  nerves  ; 
Ca4,  Thoracic  cardiac  Ijraiich  (right  vagus)  ;  A.P.PI,  Anterior,  and  P.P. PI,  Posterior  pulmonary  plexnse.s  ; 
Oes.J'I,  Oesophageal  jilexus  ;  Gast.R,  and  Gast.L,  Gastric  branches  of  vagus  (right  and  left)  ;  CVrt.Pl, 
CVeliae  plexus  ;  Hep.  PI,  Hepatic  plexus  ;  Spl.Pl,  Splenic  plexus  ;  Ren.  PI,  Renal  i)lexus. 

48  c 


696 


THE  NERVOUS  SYSTEM. 


accessory  and  spinal  portions  unite  into  a  single  trunk,  which  leaves  the  cranial 
cavity  through  the  jugular  foramen  in  the  same  compartment  of  dura  mater 
as  the  pneumogastric  nerve  (Fig.  522,  p.  678). 

In  the  jugular  foramen  the  accessory  portion 
of  the  nerve  (after  furnishing  a  small  branch  to 
the  ganglion  of  the  root  of  the  pneumogastric 
nerve)  applies  itself  to  the  ganglion  of  the  trunk, 
and  in  part  joins  the  ganglion,  in  part  the  trunk 
of  the  nerve  beyond  the  ganglion.  By  means  of 
these  connexions  the  pneumogastric  receives 
viscero-motor  and  cardio-inhibitory  fibres. 

The  spinal  portion  of  the  nerve  extends  into 
tlie  neck,  where  at  first  it  lies  along  with  other 
nerves,  in  the  interval  between  the  internal 
carotid  artery  and  the  internal  jugular  vein. 
Passing  obliquely  downwards  and  outwards  over 
the  vein,  it  descends  beneath  the  sterno-mastoid 
muscle,  w^hich  it  supplies  as  it  pierces  it  on  its 
deep  surface.  After  crossing  the  posterior 
triangle  the  nerve  ends  by  supplying  the 
trapezius  muscle  on  its  under  surface.  The 
spinal  portion  of  the  nerve  communicates  in  three 
situations  with  nerves  from  the  cervical  plexus — 
(1)  in  or  beneath  the  sterno-mastoid,  with  the 
branch  for  the  muscle  derived  from  the  second 
cervical  nerve  ;  (2)  in  the  posterior  triangle,  with 
branches  from  the  third  and  fourth  cervical 
nerves ;  (3)  beneath  the  trapezius,  with  the 
branches  for  the  muscle  derived  from  the  third 
and  fourth  cervical  nerves. 


Fig.    535. — Scheme  of  the  Origin,  Con- 
nexions,   AND   Distribution   of  the 


The  Twelfth  or  Hypoglossal  Nerve. 


Spinal  Accessory  Nerve. 

>.Acc,  Spinal  accessory  nerve  ;  C.1-4,  First 
iowv  cervical  nerves  (dorsal  roots)  ; 
Va,  Pneumogastric  nerve  ;  R,  Ganglion  mii  ii  /i  ^  \        • 

of  the  root ;  T,  Ganglion  of  the  trunk  ;  The  hypoglossal  ncrve  (n.  hypoglossus)  arises 
G.Ph,  Giosso-pharyngeai  nerve;  s.M,  \)j  numerous  radicles  from  the  front  of  the  med- 
Nerves  to  sterno-cieido^mastoid  ;   Tr,   ^^j^  oblongata  between  the  pyramid  and  the  olive 

Nerves    to    trapezius;    J.M,    Foramen  o  iJ 


magnum  ;  J.F,  Jugular  foramen. 


(Fig.  517,  p.  675)  (for  deep  origin,  see  p.  515). 


The  root  fibres  arrange  themselves  in  two  bundles 


which  separately  pierce  the  dura  mater,  and  unite  in  the  anterior  condyloid  foramen, 
or  after  emerging  from  the  skull.  In  the  neck  the  nerve  arches  dowhw^ards 
and  forwards  towards  the  hyoid  bone,  and  then  turns  inwards  among  the  supra- 
hyoid muscles  to  the  tongue.  At  first  it  is  placed  deeply,  along  with  other  cranial 
nerves,  on  the  outer  side  of  the  internal  carotid  artery ;  it  then  curves  forwards 
and  downwards  over  the  two  carotid  arteries  lying  beneath  the  digastric  and  stylo- 
hyoid muscles.  As  it  crosses  the  external  carotid  artery  it  hooks  round  the  occipital 
artery.  Above  the  great  cornu  of  the  hyoid  bone  the  nerve  conceals  the  lingual 
artery ;  and  it  then  disappears  between  the  mylo-hyoid  and  hyo-glossus  muscles  to 
reach  the  tongue,  in  the  muscular  substance  of  which  it  terminates. 


Communications. — In  its  course  the  hypoglossal  nerve  has  the  following  communica- 
tions with  other  nerves : — Near  the  base  of  the  skull  it  is  connected  by  small  branches 
with  (1)  the  superior  cervical  ganglion  of  the  sympathetic ;  (2)  the  ganglion  of  the  trunk 
of  the  pneumogastric  ;  (3)  by  a  larger  branch,  with  the  loop  between  the  first  two  cervical 
nerves ;  (4)  as  it  crosses  the  external  carotid  artery  it  receives  a  communication  from  the 
pharyngeal  plexus  {lingual  branch  of  the  vagus) ;  and  (5)  beneath  the  mylo-hyoid  muscle, 
at  the  anterior  border  of  the  hyo-glossus,  it  forms  loops  of  communication  with  the  lingual 
branch  of  the  inferior  maxillary  nerve. 


The  branches  of  the  nerve  are 
hyoid  ;  and  (4)  Lingual. 


-(1)  Eecurrent ;  (2)  Descending;  (3)  Thyro- 


THE  TWELFTH  OK  HYPOGLOSSAL  NERVE. 


G97 


The  recurrent  branch  passes  from  the  uerve  near  its  orign  to  supply  the  dura 
mater  of  the  posterior  fossa  of  the  base  of  the  skull.  It  probably  derives  its  fibres 
from  the  communication  with  the  first  and  second  cervical  nerves. 

The  descending  hypoglossal  nerve  (n.  descendens)  is  the  chief  branch  given  off  in 
the  neck.  It  arises  from  the  hypoglossal  nerve  as  it  crosses  the  internal  carotid 
artery,  and  descends  in  the  anterior  triangle  in  front  of  the  carotid  sheath.  It  is 
joined  about  the  middle  of  the  neck  by  the  descending  cervical  nerve  (from  the 
second  and    third    cervical  nerves).     By  their    union   the   hypoglossal   loop   (ansa 


Hypoglossal  nerve 
Recurrent  branch     | 


First  cervical  nerve 


Second  cervical  nerve 


Glosso-pharyngeal 

nerve 


Third  cervical  nerve  v?^ 
Stylo-pharyngeus'.- 


Pharyngeal  branch  of  vagus — ' 
Digastric 
Descendens  hypoglossi 

Middle  constrictor 
Descendens  cerviois 


Internal  laryngeal  nerve 
Ansa  hypoglossi 

Inferior  constrictor 


Oiao-hyoid 


Vagus  nerve 

Superior  cervical  ganglion  of  the  sympathetic 


Genio-hyoglossus 


cut) 


Fig.  536. — The  Mdscles  of  the  Hyoid  Bone  and  Styloid  Process,  and  the  Extrinsic  Muscles  of 

THE  Tongue  with  their  Nerves. 


hypoglo-isij  is  formed,  from  which  branches  are  distributed  to  the  majority  of  the 
infra-hyoid  muscles — Ijotli  bellies  of  the  omo-hyoid,  the  sterno-hyoid,  and  the 
sterno- thyroid.  The  descending  hypoglossal  nerve  derives  its  fibres  from  the  com- 
munication to  the  hypoglossal  nerve  from  the  loop  between  the  first  and  second 
cervical  nerves;  so  that  the  ansa  liypoglossi  is  made  up  of  fibres  of  the  first  three 
cervical  nerves. 

The  nerve  to  the  thyro-hyoid  muscle  is  a  small  branch  which  arises  from  the 
hypoglossal  nerve  before  it  passes  biineath  tlie  mylo-hyoid  muscle.  It  descends 
behind  the  great  cornu  of  the  hyoid  bone  to  reach  the  muscle.  When  traced 
Vjack\v;i.rds  this  nerve  is  found  associated  with  tlie  loop  Ijetwuen  the  first  and  second 
cervical  nerves. 


.698  THE  NERVOUS  SYSTEM. 

The  lingual  branches  of  the  hypoglossal  nerve  are  distributed  to  the  hyo-glossus, 
gehio-hyoid,  and  genio-hyo-glossus,  and  to  all  the  intrinsic  muscles  of  the  tongue. 
The  nerve  to  the  genio-hyoid  is  said  to  be  derived  from  the  loop  between  the 
first  and  second  cervical  nerves.  It  is  not  known  if  these  two  nerves  are  implicated 
in  the  innervation  of  the  proper  muscles  of  the  tongue,  but  it  appears  certain  that 
the  muscles  named — the  genio-liyoid,  thyro-hyoid,  sterno-hyoid,  omo-hyoid,  and 
sterno-thyroid — are  not  supplied  by  the  hypoglossal,  but  only  by  cervical  nerves, 
the  genio-hyoid  by  the  first  two,  the  otlier  muscles  by  the  first  three  cervical  nerves. 

THE  DEVELOPMENT  OF  THE  CRANIAL  NERVES. 

Omitting  the  first  and  second  nerves,  there  is  an  obvious  likeness  in  the 
development  of  the  several  cranial  nerves  to  the  formation  of  the  dorsal,  afferent  or 
sensory,  and  the  ventral,  efferent  or  motor,  roots  of  the  spinal  nerves.  The  afferent 
roots  of  the  cranial  nerves  arise  from  collections  of  cells  which  bud  off  from  the 
alar  lamina  of  the  brain,  homologous  with  the  dorso-lateral  part  of  the  spinal  cord. 
These  cells  give  rise  to  central  and  peripheral  processes,  like  the  similar  processes 
from  the  dorsal  ganglia  of  the  spinal  nerves,  producing  on  the  one  hand  the  root 
fibres  connected  with  the  brain,  and  on  the  other  hand  the  fibres  of  the  nerve 
proceeding  to  the  periphery.  The  efferent  roots,  like  the  ventral  roots  of  the  spinal 
nerves,  arise  as  the  peripheral  processes  of  neuroblasts  located  in  the  basal  lamina 
of  the  primitive  brain,  which  is  homologous  with  the  ventro-lateral  portion  of  the 
spinal  cord.  The  different  efferent  nerves  may  be  separated  into  two  series, 
according  as  they  arise  from  the  mesial  or  lateral  parts  of  the  basal  lamina.  The 
third,  fourth,  sixth,  and  twelfth  nerves  arise  from  the  mesial  part  of  the  lamina  ;  the 
efferent  fibres  of  the  fifth,  seventh,  ninth,  tenth,  and  eleventh  nerves  arise  from  the 
lateral  part  of  the  lamina. 

Tlie  olfactory  nerves  are  associated  in  their  development  witli  tlie  formation  of  the 
nasal  pit  and  the  olfactory  bulb. 

The  nasal  pits  appear  in  each  side  of  the  front  of  the  head  at  a  little  later  period  than 
the  formation  of  the  lens  and  the  auditory  vesicle.  They  become  converted  into  the  nasal 
cavities  by  the  formation  of  the  pre-oral  viscei'al  clefts  and  arches, — fronto-nasal  and 
ethmo-vomerine  in  tlie  middle  line,  and  lateral  ethmoid  and  maxillary  processes  at  the 
sides  (p.  38). 

The  Rhinencephalon  or  olfactory  bulb  is  a  hollow  outgrowth  from  each  telencephalon 
or  cerebral  hemisphere,  which  appears  in  the  first  month.  It  grows  forwards  into  relation 
with  the  deep  surface  of  the  nasal  pit.  In  many  animals  (as  in  the  horse)  the  olfactory 
bulb  remains  hollow  ;  but  in  the  human  subject  it  loses  its  lumen  and  becomes  a  solid 
bulb  (olfactory  bulb)  connected  to  the  brain  by  a  narrow  stalk,  the  olfactory  tract. 

The  epithelium  of  the  nasal  pit  is  responsible  for  the  formation  of  the  olfactor}-  nerves. 
There  are  two  views  as  to  the  mode  of  their  development  from  the  epithelial  cells.  Both 
views  admit  the  proliferation  of  the  epithelium  of  the  nasal  pit  so  as  to  produce  neuroblasts. 
According  to  the  one  view  these  neuroblasts  detach  themselves  from  the  epithelial  surface, 
and  constitute  an  olfactory  ganglion  which  becomes  applied  to  and  incorporated  with  the 
olfactory  bulb.  The  cells  of  the  ganglion  become  bi-polar,  and  the  peripheral  axons 
constitute  the  olfactory  nerves,  while  the  central  axons  (in  the  second  month)  proceed  back- 
wards to  the  brain  along  the  olfactory  tract.  According  to  the  other  view  (based  on  Disse's 
investigations),  the  proliferating  cells  of  the  nasal  epithelium  remain  in  the  wall  of  the 
nasal  pit,  and  become  the  olfactory  cells  of  the  nasal  cavity,  with  peripheral  processes 
projecting  to  the  surface  of  the  epithelium.  Their  central  axons  become  the  olfactory 
nerve  fibres  which  end  in  the  olfactory  bulb,  forming  dendrites  associated  with  the  dendritic 
processes  of  the  nerve-cells  of  the  bulb.  The  central  axons  of  these  latter  cells  develop 
into  the  fibres  of  the  olfactory  tract. 

The  optic  nerve  is  developed  wholly  from  the  brain.  Its  formation  begins  with  the 
outgrowth  of  the  optic  vesicle,  a  paired  hollow  outgrowth  from  the  ventral  surface  of  the 
thalamencephalon.  The  epiblastic  invagination  of  the  lens,  growing  inwards  from  the 
surface  of  the  head,  causes  the  collapse  of  the  vesicle  and  its  conversion  into  the  optic 
cup,  the  narrow  tube  connecting  the  vesicle  to  the  brain  becoming  the  optic  stalk.  This 
stalk  becomes  solid,  and  forms  the  basis  of  the  optic  tract,  optic  commissui-e,  and  optic 
nerve.  The  optic  cup,  bilaminar  in  form,  and  by  its  edge  clasping  the  lens,  is  embedded 
in  mesoblastic  tissue,  which  gives  rise  to  the  envelopes  of  the  eyeball,  etc.     The  outer 


TPIE  DEVELOPMENT  OF  THE  CRANIAL  NERVES.  699 

layer  of  the  optic  cup  produces  the  layer  of  hexagonal  pigment  cells  of  the  retina.  The 
cells  of  the  inner  layer  produce  the  tissue  of  the  retina  proper.  They  form  neuroblasts 
witli  peripiieral  and  central  processes.  The  peripheral  processes  are  converted  into  retinal 
nerve  tissues ;  the  central  processes  extend  backwai-ds  along  the  optic  stalk,  and  give  rise 
to  the  fibrous  structure  of  the  optic  nerve,  optic  commissure,  and  optic  tract.  Spongio- 
blasts in  the  inner  lamina  of  the  optic  cup  produce  the  sustentacular  tissue  of  the  retina 
(Mliller's  fibres).  The  mesoblastic  tissue  surrounding  the  optic  cup  and  lens  gives  rise  to 
the  rest  of  the  structure  of  the  eyeball,  the  formation  of  which  is  described  in  the  section 
which  deals  with  the  organs  of  sense. 

The  oculo-motor  nerve  arises,  like  the  ventral  root  of  a  spinal  nerve,  from  a  group 
of  neuroblasts  in  the  mesial  part  of  the  basal  lamina  of  the  mid-brain.  The  peripheral 
fibres  extend  forwards,  to  end  around  the  optic  cup  in  the  mesoblastic  tissue,  from  which 
tlie  eye  muscles  are  derived.  Numerous  cells  are  carried  along  with  the  cell  processes  in 
their  course,  and  these  have  been  described  as  being  concerned  in  the  formation  of  the 
ciliary  ganglion. 

The  trochlear  nerve  also  arises  from  a  group  of  neuroblasts  occupying  the  mesial 
part  of  the  basal  lamina  of  the  mid-brain,  close  to  its  junction  with  the  hind-brain.  The 
peripheral  processes  do  not  emerge  directly  from  the  brain,  but  extend  dorsally  from  their 
origin  along  the  side  of  the  brain  to  its  dorsal  aspect,  where  they  appear,  after  decussating 
with  the  fibres  of  the  opposite  nerve,  just  behind  the  quadrigeminal  lamina. 

The  trigeminal  nerve  is  developed  by  means  of  a  large  dorsal  and  a  small  ventral 
root.  Their  origin  to  a  large  extent  resembles  the  mods  of  formation  of  the  roots  of  a 
spinal  nerve. 

The  large  dorsal  (afferent)  root  is  formed  by  means  of  a  cellular  bud  from  the  alar 
lamina  of  the  hind-brain.  This  bud  separates  from  the  brain,  and  forms  the  Gasserian 
ganglion.  Its  cells  becoming  bipolar,  like  the  cells  of  a  spinal  ganglion,  are  secondarily 
connected  with  the  brain  by  means  of  their  central  processes ;  while  the  peripheral  pro- 
cesses, separating  into  three  groups,  proceed  along  the  fronto-nasal  and  maxillary  processes, 
and  along  the  mandibular  arch,  to  form  the  three  main  divisions  of  the  nerve.  Numerous 
cells  accompany  each  main  division  in  its  course  from  the  ganglion,  and  form  eventually 
the  subordinate  ganglia — the  ciliary  on  the  ophthalmic  nerve,  the  &pheno-palatine  on  the 
superior  maxillary  nerve,  and  the  otic  ganglion  on  the  inferior  maxillary  nerve. 

The  small  ventral  (efferent)  root  of  the  trigeminal  nerve,  like  the  motor  ventral  root 
of  a  spinal  nerve,  is  later  in  its  appearance  than  the  sensory  root.  It  arises  as  the  peri- 
pheral fibres  of  a  group  of  neuroblasts  occupying  the  lateral  part  of  the  basal  lamina  of 
the  hind-brain,  which  proceed  directly  to  the  surface  to  join  the  inferior  maxillary  division 
of  the  nerve. 

The  abducent  nerve  resembles  in  its  mode  of  development  the  oculo-motor  and 
trochlear  nerves  with  which  in  its  origin  it  is  in  series.  It  is  formed  by  the  peripheral 
processes  of  a  group  of  neuroblasts  in  the  mesial  part  of  the  basal  lamina  in  the  upper 
part  of  the  hind-brain.  These  processes  pierce  the  part  of  the  brain  in  which,  at  a  later 
stage,  the  fibres  of  the  pyramid  are  developed.  They  then  proceed  to  the  mesoblastic 
tissue  round  the  optic  cup,  which  is  destined  to  form  the  eye  muscles. 

The  facial  nerve  has  developmen tally  a  double  origin.  (1)  In  connexion  with 
the  formation  of  the  auditory  nerve  a  group  of  cells  becomes  separated  from  the  alar 
lamina  of  the  hind-brain  opposite  the  auditory  vesicle.  This  group  becomes  separated 
into  three  parts,  of  which  the  middle  portion  is  the  rudiment  of  the  geniculate  ganglion 
(or  afferent  root).  (2)  The  efferent  root  of  the  nerve  arises  from  a  group  of  neuroblasts 
in  the  lateral  part  of  the  basal  lamina  of  the  hind-brain,  in  series  with  efferent  fibres  of 
the  vago-glosso- pharyngeal  nerves;  after  a  tortuous  course  within  the  brain  its  fibres 
emerge  beneath  the  above-mentioned  cellular  mass,  opposite  the  auditory  vesicle.  They 
are  joined  by  the  ganglionic  root,  and  in  their  course  round  the  auditory  vesicle  become 
embedded  in  the  auditory  capsule  (aqueduct  of  Fallopius).  The  chorda  tympani  nerve 
appears  early  as  a  branch  of  the  facial  nerve.  It  is  probable  that  the  pars  intermedia, 
the  geniculate  ganglion,  and  the  chorda  tympani  nerve  together  represent  the  dorsal 
afferent  element  in  the  constitution  of  this  nerve. 

'J'he  auditory  nerve  arises  as  a  cellular  bud  from  the  alar  lamina  of  the  hind-brain, 
dorsal  to  the  eO'erent  portion  of  the  facial  nerve  and  opposite  to  the  auditory  vesicle,  and 
in  close  association  with  the  latter. 

Becoming  separated  from  the  brain,  the  cellular  mass  separates  into  tliree  portions,  of 
which  the  middle  part  is  associated  with  the  facial  nerve  and  pars  intermedia  (as  the 
geniculate  ganglion),  while  tlie  mesial  and  lateral  parts  are  converted  into  the  mesial 
(vestibular)  and   lateral  (cochlear)  ganglia  and  roots  of  the  auditory  nerve.     The  cells 


700 


THE  NEEVOUS  SYSTEM. 


becoming  bipolar,  their  central  processes  are  secondarily  connected  witli  the  brain  on 
the  dorsal  (lateral)  aspect  of  the  facial  nerve ;  the  peripheral  processes  proceed  to  the 
auditory  vesicle,  to  which  they  are  distributed  as  the  vestibular  and  cochlear  nerves. 
Numerous  cells  are  carried  along  with  the  nerve  trunks  into  relation  with  the  auditory 
capsule,  and  constitute  the  vestibular  and  cochlear  ganglia. 

The  glosso-pharyngeal  and  pneumogastric  nerves  are  developed  from  the  side 
of  the  hind-brain,  both  in  the  same  way,  and  each  by  two  roots.  A  collection  of  cells 
separates  itself  from  the  alar  lamina  of  the  hind-brain  behind  the  auditory  vesicle  to  form 
the  ganglionic  aflferent  root.  The  ganglion  of  the  pneumogastric  is  much  larger  than  that 
of  the  glosso-pharyngeal.  Each  ganglion  becomes  divided  into  two  parts,  a  proximal  and  a 
distal  portion,  connected  together  by  a  commissural  band  of  fibres.  The  proximal  ganglion 
(jugular  ganglion  of  the  glosso-pharyngeal ;  ganglion  of  tlie  root  of  the  pneumogastric) 
is  secondarily  connected  by  centripetal  fibres  to  the  hind-brain.  From  the  distal  ganglion 
(petrous  ganglion  of  the  glosso-pharyngeal ;  ganglion  of  the  trunk  of  the  pneumogastric) 
peripheral  fibres  grow  outwards  to  form  the  nerve  ti'unk. 

Each  nerve  is  also  provided  with  a  small  efferent  root,  consisting  of  nerve  fibres, 
arising  from  a  collection  of  neuroblasts  in  the  lateral  part  of  the  basal  lamina  of  the  hind- 


LATERAL  AREA        "I 

I    BASAL 
I  LAMINA 
MESIAL  AREA  J 


i'ENTRAL    ROOT 
DORSAL    ROOT  V.VEVIII.IJC.X. 

A 


Fig.  537. — Compaeison  of  Origins  op  Nerve  Roots  from  Spinal  Cord  and  Hind-Brain  (after  His). 

A.  Spinal  cord  ;  B.    Hind-brain. 

brain,  and  emerging  beneath  the  ganglionic  root  at  the  junction  of  the  alar  and  basal 
laminae  (in  series  with  the  fibres  of  the  efferent  root  of  the  facial  nerve  above  and  of  the 
spinal  accessory  nerve  below). 

The  spinal  accessory  nerve  arises  in  two  parts — one  medullary,  the  other  spinal. 
The  medullary  (accessory)  portion  develops  as  the  processes  of  a  series  of  neuroblasts  in 
the  lateral  portion  of  the  basal  lamina  of  the  hind-brain,  which  emerge  in  series  with  the 
efferent  roots  of  the  glosso-pharyngeal  and  pneumogastric  nerves.  The  spinal  portion 
arises  as  the  processes  of  a  grouj)  of  neuroblasts  in  the  ventral  part  of  the  medullary  tube 
(anterior  cornu),  which,  turning  outwards,  emerge  as  a  series  of  roots  on  the  lateral  aspect 
of  the  spinal  cord. 

The  hypoglossal  nerve  is  developed,  not  in  series  with  the  nerves  above  mentioned, 
but  like  the  third,  fourth,  and  sixth  nerves,  from  the  mesial  part  of  the  basal  lamina 
of  the  hind-brain,  in  the  space  between  the  glosso-pharyngeal  and  other  nerves  above, 
and  the  first  cervical  nerve  below.  It  is  formed  as  a  series  of  peripheral  processes  fi'om  a 
collection  of  neuroblasts  occupying  the  hind -brain.  Froriep's  ganglion  is  a  transitor}- 
collection  of  nerve  cells  developed  from  the  alar  lamina  of  the  hind-brain  on  the  dorsal 
aspect  of  the  nerve,  and  represents  in  a  rudimentary  condition  its  doi'sal  ganglionic  root. 
It  gives  off  no  branches  and  soon  disappears. 


THE  MOEPHOLOGY  OF  THE  CKANIAL  NERVES. 

The  head  and  face,  possibly  the  oldest,  and  from  every  point  of  view  the  most  fundamental 
and  important  portion  of  the  bodily  fabric,  present  in  some  respects  a  more  conservative  type  of 
structure,  and  in  other  asjiects  have  been  subject  to  more  profound  alterations  than  other  parts 


THE  MOEPHOLOGY  OF  THE  CEANIAL  NERVES.      701 

of  the  body.  Segmentation  is  charactei'istic  of  tlie  trunk,  pervading  bones,  muscles,  vessels,  and 
nerves.  An  absence  of  true  segmentation  is  characteristic  of  the  head  region — omitting  for  the 
moment  tlie  cranial  nerves.  The  head  is  characterised  by  the  possession  of  an  unsegmented 
tubular  nervous  system,  enclosed  in  a  bony  capsule  not  obviously  segmental,  with  which  the 
cajjsules  of  the  sense-organs  become  united.  Tlie  pre-oral  and  post-oral  visceral  arches  and  clefts 
are  not  truly  segmental  like  the  costal  arches  of  the  trunk.  The  branchial  clefts  are  said  to  be 
inter -segmental ;  and  their  muscles  (associated  with  the  myoblast  surrounding  the  developing 
heart)  are  described  as  visceral,  and  not  myotomic,  so  that  the  branchial  vessels  and  nerves 
(similarly)  are  not  to  be  regarded  as  comparable  to  the  segmental  vessels  and  nerves  of  the  trunk. 
The  truly  segmental  structures  present  are  certain  persistent  myotomes  or  muscle  plates,  Avliic]) 
give  rise  to  muscles  innervated  by  the  third,  fourtli,  sixth,  and  twelfth  cranial  nerves. 

Another  difl&culty  in  the  morphology  of  the  head  arises  in  the  absence  of  Ijody  cavity,  and 
the  consequent  difficulty  of  differentiating  the  somatic  and  splanchnic  mesoblast,  and  the  somatic 
and  splanchnic  distribution  of  a  given  nerve. 

Under  these  circumstances  there  is  little  help  to  be  derived  from  head  structures  other  than 
the  nerves  themselves  in  seeking  a  solution  of  the  question  of  the  morphological  relations  of  the 
cranial  nerves.  The  S23inal  nerves  are,  generally  speaking,  all  alike.  The  cranial  nerves,  on  the 
other  hand,  are  all  different.  Scarcely  any  two  nerves  are  alike  ;  and  no  single  cranial  nerve 
possesses  in  itself  all  the  characteristic  features  of  a  spinal  nerve.  As  seen  in  relation  to  their 
development,  the  cranial  nervous  system  possesses  a  series  of  dorsal  ganglia,  comparable  in 
position  and  develojjment  to  the  sj)inal  ganglia  from  which  afferent  nerves  arise  ;  and  the 
efferent  roots  are  developed  in  the  same  way,  and  occupy  somewhat  the  same  position  as  the 
ventral  roots  of  the  spinal  nerves.  But  there  is  no  single  complete  segmental  nerve  in  the  head. 
The  very  essence  of  the  architecture  of  the  head  is  a  want  of  segmentation ;  and  this  character 
is  shared  by  the  cranial  nerves.  In  addition  it  must  be  borne  in  mind  that,  in  relation  to  the 
mammalian  head,  there  are  organs  which  have  no  homologues  in  the  trunk,  and  on  whose 
existence  the  arrangement  of  the  cranial  nerves  depends — e.g.  sense-organs  and  gill-arches. 

Among  the  cranial  nerves  there  are  several  which  jaossess  a  resemblance  to  one  or  other  of 
the  elements  of  a  tyjjical  sjaiiial  nerve.  In  the  neck  the  origin  of  the  fibres  of  the  spinal 
accessory  nerve  is  from  the  side  of  the  spinal  cord,  and  it  is  iir  series  with  the  motor  roots  of 
the  vago-glosso-pharyngeal,  facial,  and  fifth  nerves.  His  (as  shown  in  the  account  of  the 
development  of  the  nerves)  has  described  the  neuroblastic  origin  of  the  motor  roots  of  these 
nerves  from  the  lateral  j^art  of  the  basal  lamina  of  the  primitiA'e  brain.  They  thus  form  a  series 
apart — lateral  motor  roots — sej^arable  from  the  series  of  motor  roots  originating  from  the  mesial 
part  of  the  basal  lamina,  comprising  those  of  the  third,  fourth,  sixth,  and  twelfth  nerves ;  the 
latter  nerve  roots  being  comparable  to  and  in  series  with  the  ventral  roots  of  the  spinal  nerves. 
The  lateral  motor  roots  are  not  represented  in  the  spinal  series  except  in  the  neck.  It  is 
questionable  if  there  is  any  fundamental  distinction  between  the  lateral  and  ventral  motor  roots 
of  the  cranial  nerves.  The  sj^inal  accessory  fibres,  for  example,  when  traced  into  the  spinal  cord, 
have  an  origin  from  the  anterior  cornu  of  the  cord,  and  only  differ  from  the  motor  or  ventral 
root  fibres  of  a  spinal  nerve  in  their  different  course  to  the  surface.  The  ganglia  in  association 
with  the  cranial  nerves  are  comparable  to  the  spinal  ganglia.  The  fifth  nerve,  with  the  Gasserian 
ganglion,  the  ganglion  of  the  facial,  the  ganglia  of  the  auditory,  of  the  glosso-pharyngeal  and  the 
vagus,  and  the  transitory  (Froriep's)  ganglion  of  the  hypoglossal  nerves,  arise  from  the  brain  in  a 
comparable  position,  and  in  the  same  way  as  the  spinal  ganglia.  But  another  series  of  structures 
— the  sense  organs  of  the  lateral  line,  and  the  so-called  "  ej)ibranchial "  organs  which  are  highly 
developed  in  lower  vertebrates  (e.g.  elasmobranchs),  and  which  appear  transitorily  only,  or  are 
absent  altogether  in  mammalian  development,  may  possibly  have  a  share  in  the  formation  of 
certain  of  these  ganglia  or  parts  of  them  {e.g.  ciliary  ganglion,  geniculate  ganglion,  ganglia  of  the 
auditory  nerve,  petrosal  ganglion  of  the  glosso-pharyngeal,  and  the  ganglion  of  the  trunk  of  the 
vagus). 

Cej'tain  of  the  cranial  nerves  are  apj^arently  distinctly  segmental,  supplying  muscles  derived 
from  the  persisting  myotomes  of  tlie  head.  The  first  three  myotomes  are  said  to  give  rise  to  the 
muscles  of  the  eyeball.  The  first  jaroduces  the  superior  rectus,  inferior  rectus,  internal  rectus, 
and  inferior  oblique  muscles,  and  its  segmental  nerve  is  the  oculo-motor.  The  second  myotome 
is  said  to  i:)roduce  tlie  superior  oblique  muscle,  and  its  segmental  nerve  is  the  trochlear.  The 
third  myotome  is  said  to  produce  the  external  rectus  muscle,  and  its  segmental  nerve  is  the 
abducent.  It  has  been  asserted  that  the  tongue  muscles  are  derived  from  the  last  three  or  four 
cephalic  and  first  cervical  myotomes,  and  tliat  the  hypoglossal  nerve  is  the  segmental  nerve  for 
the.-ie  myotomes,  comprising  tlie  motor  elements  of  several  (four  or  five)  segmental  nerves.  The 
intervening  myotonies  between  the  first  three  and  this  occipital  series  disappearing,  the  corre- 
sponding (elements  of  segmental  nerves  are  sujjposed  to  be  absent  also  (Fig.  538). 

Certain  of  the  cranial  nerves  are  essentially  related  to  the  structures  derived  from  and  asso- 
ciated with  the  j)re-oral  and  post-oral  visceral  clefts  and  arches  (Fig.  539).  The  trigeminal  nerve 
is  essentially  the  lujrve  of  tlie  mandibular  arch.  By  its  efferent  root  it  supplies  the  muscles  of 
that  arch.  By  its  afferent  rocjt  and  bi;uic,hes  it  is  related  to  (1)  the  fronto-nasal  jirocess  (oph- 
thalmic division  and  ciliaiy  ganglion) ;  (2)  the  maxillary  arch  (superior  maxillary  nerve) ;  and 
(3)  tlie  mandiltiihiv  arch  (inferior  maxillary  nerve).  The  mandibular  is  at  first  the  main  nerve  ; 
and  the  maxillary  divisitm  is  sometimcH  regarded  as  a  subordinate  branch  (prai-branchial,  pra;- 
trematicj  for  the  siip])ly  of  th(j  anterior  margin  of  the  cleft  (mouth),  with  which  the  nerve  is  in 
relation.  The  ophthalmic  nerve  is  sonjcjtimes  regarded  as  a  morphologically  separate  nerve. 
The  ncn-es  to  tliese  ar^hfiS  have  been  compared   to  the  anterior  primary  divisions  of  spinal 


702 


THE  NERVOUS  SYSTEM. 


nerves,  tlie  brandies  which  they  sujDply  to  the  forehead  and  temple  (frontal,  orliital,  and 
auriculo-temporal)  representmg  the  posterior  primary  divisions.  The  ganglia  on  each  division 
of  the  nerve  are  formed  as  extensions  from  the  Gasserian  ganglion. 

Tlie  facial  nerve  is  essentially  the  nerve  of  the  second  (hyoid)  arch,  and  the  cleft  in  front  of 
that  arch  (spiracnlar  cleft,  Enstachian  tube).  Its  motor  root  supplies  the  muscles  of  that  arch 
(stapedius,  stylo-hyoid,  and  digastric),  and  the  epicranial  and  facial  muscles  and  platysma 
myoides,  which  are  developments  from  the  hyoid  arch  (Rabl).  The  chorda  tympani  nerve  is 
regarded  as  the  subordinate  (prag-branchial,  prse-trematic)  branch  to  supjjly  the  anterior  margin 
of  the  first  post-oral  cleft.  It  is  possible  that  the  geniculate  ganglion,  with  the  pars  intermedia 
and  tlie  chorda  tympani,  may,  in  part  at  least,  represent  the  ganglionic  and  afferent  element  of 

the  nerve.  Or  the 
geniculate  ganglion,  and 
the  nerves  in  relation 
to  it,  may  be  associated 
with  an  "  epibranchial " 
sense-organ. 

The  auditory  nerve, 
on  the  other  hand,  may 
be  either  the  sensory 
element  of  the  branchial 
nerve,  associated  with  the 
hyoid  arch  and  first  post- 
oral  cleft,  or  it  may  repre- 
sent the  nerve  or  nerves 
belonging  to  ancestral 
sense  -  organs  of  the 
lateral  line. 

The  glosso- pharyn- 
geal is  the  branchial 
nerve  of  the  third  post- 
oral  (thyro -hyoid)  arch 
and  the  cleft  in  front. 
Its  efferent  fibres  supply 
the  muscle  of  this  arch, 
— the  stylo-phar}Tigeus. 
The  superior  constrictor 
of  the  pharjTix  is  also 
assigned  to  this  arch  ; 
the  middle  and  inferior 
muscles  to  the  fourth  (first 
branchial)  arch.  The 
afferent  portion  of  the 
nerve  is  possibly  com- 
posed of  two  separate 
parts  ;  the  petrous  gan- 
glion being  associated 
with  an  epibranchial  or 
lateral  line  sense-organ, 
and  the  rest  of  the  nerve 
forming  the  afferent 
fibres  for  the  giU- cleft 
and  arch.  The  lingual 
branches  are  regarded  as 
the  main  stem  (post  - 
trematic),  the  pharyngeal 


Fig.  538. — Scheme  to  illustrate  the  Disposition  of  the  Myotomes  in 
THE  Embryo  in  Relation  to  the  Heab,  Trunk,  ANn  Limbs. 
A,  B,  C,  First  three  cephalic  myotomes  ;  N,  1,  2,  3,  4,  Last  jDersisting  cephalic 
myotomes  ;  C,  T,  L,  S,  Co,  The  myotomes  of  the  cervical,  thoracic, 
lumbar,  sacral,  and  caudal  regions  ;  I.,  II.,  III.,  IV.,  V.,  VI.,  VII.,  VIII. , 
IX.,  X.,  XL,  XII.,  refer  to  the  cranial  nerves,  and  the  structures  with 
which  they  may  be  emtaryologically  associated. 

branches  as  subordinate  branches  ;  the  tympanic  branch  being  the  prse -branchial  or  prse-trematic 
branch  for  the  anterior  margin  of  the  third  gill-cleft. 

The  pneumogastric  nerve  is  generally  regarded  as  representing  the  fusion  of  all  the  branchial 
nerves  behind  the  glosso-pharyngeal.  Its  efi'erent  fibres  are  in  series  with  those  of  the  glosso- 
pharyngeal above  and  the  spinal  accessory  nerve  below,  and  belong  to  the  lateral  series  of  His. 
Its  aflferent  fibres,  like  those  of  the  glosso-i^haryngeal,  represent  two  elements.  The-  lower 
ganglion  has  possible  connexions  with  epibranchial  sense-organs — the  rest  of  the  nerve  repre- 
senting the  fused  branchial  branches  of  fishes.  The  superior  laryngeal  nerve  is  looked  upon 
as  the  branchial  nerve  of  the  fourth,  and  the  inferior  laryngeal  nerve  as  the  branchial  nerve 
of  the  fifth  arch.  While  the  relation  of  the  nerve  to  the  hinder  gill-arches  and  clefts  makes 
it  possible  to  understand  the  innervation  by  the  vagus  of  the  heart  and  lungs,  no  satisfactory 
explanation  is  forthcoming  of  the  passage  of  the  nerve  into  the  abdomen,  and  its  distribution  to 
the  stomach  and  other  organs  below  the  diaphragm. 

The  spinal  accessory  nerve  consists  of  two  parts.  The  accessory  portion  of  the  nerve 
consists  of  efterent  filjres  for  the  branchial  region,  in  series  with  the  lateral  motor  roots  of  the 
glosso-pharyngeal  and  vagus  nerves.  The  spinal  portion  of  the  nerve  is  also  composed  of  efterent 
fibres,  and  represents  the  only  lateral  motor  elements  arising  from  the  spinal  cord. 


THE  SYMPATHETIC  NEEVOUS  SYSTEM. 


703 


Olfactory  Nerve. — There  is  absolute  imcertainty  regarding  the  morphology  of  this  nerve. 
It  consists  of  three  elements  :  (1)  the  olfactory  bulb,  derived  from  the  cerebral  liemiBphere, 
solid  in  man,  but  a  hollow  cereljral  diverticulum  in  certain  animals,  and  forming  the 
rhinencephalon  ;  (2)  the  olfactory  ganglion,  with  its  central  and  peripheral  processes,  derived 
from  the  ectoderm  ;  (3)  the  nasal  pit.  Attention  has  been  specially  fixed  on  the  olfactory 
ganglion,  which  has  been  compared  to  (1)  a  dorsal  spinal  ganglion,  derived  from  the  anterior  end 
of  the  medullary  groove  ;  and  to  (2)  a  lateral  line  sense-organ. 

The  optic  nerve  also  presents  an  insoluble  problem  in  regard  to  its  morphological  position 
in  the  series  of  cranial  nerves.  The  optic  stalk  and  optic  cup  have  been  regarded  as  a  highly- 
modified  dorsal  ganglion ;  but  there  is  insuperable  difficulty  in  accepting  this  view.  The 
peripheral  processes  do  not  become  connected  with  either  ectodermal  or  mesoblastic  structures, 
but  become  the  tissue  of  the  retina ;  while  the  central  processes,  growing  backwards,  envelop 
the  optic  stalk,  and  obtain  connexions  with  the  brain.  The  retina  must  be  regarded  as  a  highly- 
modified  layer,  morphologically  in  series  with  the  wall  of  the  fore-brain  ;  and  the  ectodermal 
structure  of  superficial  origin  comparable  to  the  olfactory  ganglion  or  the  auditory  vesicle  is  the 
lens  (which  may  possibly  be  homologous  with  a  lateral  line  sense-organ).  Tlie  optic  nerve,  optic 
commissure,  and  optic  tract  are  then  to 
be  looked  upon  as  cerebral  commissures, 
and  not  as  nerves  in  the  ordinary  sense. 

The  simplest  and  most  primitive  con- 
dition of  the  head,  in  relation  to  the 
morphology  of  the  cranial  nerves,  is  found 
before  the  formation  of  the  gill-clefts,  when 
the  salient  features  are  a  tubular  and  simple 
brain,  and  a  series  of  superficial  invagina- 
tions which  pass  from  the  surface  inwards 
to  become  connected  with  outgrowths  cor- 
responding to  them  from  the  primitive 
brain.  On  either  side  of  the  head  three 
hollow  invaginations  occur : — (1)  The  nasal 
pit  bearing  the  olfactory  epithelium  becomes 
connected  by  the  olfactory  ganglion  with  the 
rhinencephalon,  an  outgrowthfrom  the  fore- 
brain,  and  so  forms  the  basis  of  an  olfactory 
organ  and  nerve  ;  (2)  a  similar  invagination 
produces  the  lens,  connected  with  a  pro- 
trusion of  the  ojatic  vesicle  from  the  fore- 
brain,  by  which  the  basis  of  the  eye  and 
the  optic  nerve  is  formed  ;  (3)  behind  the 
buccal  cavity  a  third  invagination  forms 
the  auditory  vesicle,  which  is  connected 
with  the  solid  extension  from  the  hind- 
brain  of  the  acoustic  ganglia,  to  form  the 
essentials  of  the  organ  of  hearing  and 
auditory  ner-A^e. 

The  trigeminal  nerve  is  essentially  the 
nerve  of  the  buccal  cavity  and  the  sub- 
ordinate cavities,  nasal  and  oral,  derived 
from  it.  The  branchial  arches  and  clefts 
are  secondary  structures,  and  tlieir  nerves  I.  to  XII.  Cranial  Nerves  ;  Fr,  Froriep's  ganglion  ;  CI.,  Roots 
are  (1)  the  trigeminal  for  the  first  (mandi-  and  trunk  of  the  first  cervical  nerve, 

bular)  arch  and  the  cleft  in  front  of  it ; 

(2)  the  facial  for  the  second  (hyoid)  arch  and  cleft ;  (3)  the  glosso-pharyngeal  for  the  third 
(thyro-hyoid)  arch  and  cleft ;  and  (4)  the  jmeumogastric  for  the  succeeding  arches  and  clefts. 
The  bulbar  part  of  the  spinal  accessory  nerve  is  inseparable  from  the  motor  portion  of  the  vago- 
glosso-pharyngeal  nerves  ;  the  spinal  part  is  beyond  the  series  of  the  cranial  nerves. 

Lastly,  there  are  certain  truly  segmental  nerve  elements,  motor  fibres  which,  remaining 
associaterl  with  certain  ]>ersistent  cejjhalic  myotomes,  give  rise  to  the  oculo-motor,  trochlear, 
abducent,  and  liypoglossal  nerves. 


Fig. 


)39. — Scheme  to  illustrate  the  Embrtological 
Arrangement  of  the  Cranial  Nerves. 


THE   SYMPATHETIC   NERVOUS   SYSTEM. 


The  .syiiipatlictic  nervous  system  consists  of  a  pair  of  elongated  gangliated 
cords  Tnervi  8yni])atl)Joi_),  extending  from  the  base  of  the  skull  to  the  coccyx;  con- 
nected, on  th(;  one  hand,  Ity  a  series  of  branches  to  the  spinal  nervous  system,  and 
on  the  other  liand  giving  off  nu  irregular  series  of  })ranches  to  the  viscera.  At  its 
cephalic  end  each  sympathetic  cord  is  continued  in  a  plexiform  manner  into  the 
cranial  cavity  along  with  the  internal  carotid  nrtery,  and  i'orins  complex  relation- 


704 


THE  NEEVOUS  SYSTEM. 


ships  with  certain  cranial  nerves.  At  their  caudal  ends  the  two  sympathetic 
cords  become  joined  together  by  fine  filaments,  and  are  connected  by  the  coccygeal 
ganglion  (g.  impar). 

The  sympathetic  system  (1)  serves  to  rearrange  and  distribute  fibres  derived 
from  the  cerebro-spinal  system  to  the  viscera  and  vessels  of  the  splanchnic  area ; 

(2)  it  transmits  to  the  cerebro-spinal  system  afferent  fibres  from  the  viscera ;  and 

(3)  it  transmits  fibres  to  the  vessels,  involuntary  muscles,  and  glands,  in  the  course 
of  the  somatic  divisions  of  the  spinal  nerves. 

General  Structure  of  the  Sympathetic  System. — The  sympathetic  system  is 
composed  of  two  elements — ganglia  and  nerve  fibres. 

The  ganglia  (g.  trunci  sympathici)  are  variable  in  number,  form,  size,  and 

position.  They  are  not  definitely  segmental  in 
position,  but  they  are  always  connected  together 
by  a  system  of  narrow  commissural  cords  of  nerve 
fibres.  A  ganglion  consists  of  a  larger  or  smaller 
number  of  multipolar  nerve  cells,  enclosed  in  a 
capsule  of  connective  tissue.  Each  cell  is  pro- 
vided with  one  axon  and  a  number  of  dendrites. 
The  axon  may  enter  into  the  composition  of 
(a)  the  commissural  cord ;  (b)  a  central  branch 
(gray  ramus  communicans) ;  or  (c)  a  peripheral 
branch  from  the  sympathetic  cord.  These  axons 
are  commonly  medullated  at  their  origin,  but 
become  non-medullated  in  their  course  from  the 
parent  cell.  Besides  these  ganglia,  two  other 
series  of  ganglia  are  present  in  connexion  with 
the  peripheral  branches  of  the  sympathetic : 
intermediate  or  collateral  ganglia,  on  the  branches 
or  in  the  sympathetic  plexuses ;  and  terminal 
ganglia,  in  close  relation  to  the  endings  of  the 
nerves  in  the  viscera. 

The  nerve  fibres  in  the  sympathetic  system 
are  of  two  classes,  medullated  and  non-medul- 
lated. The  distinction  is  not  absolute.  The 
medullated  fibres  may  lose  their  medullary 
sheaths  before  reaching  their  terminations ;  and 
the  non-medullated  fibres  may  at  their  origin 
possess  a  medullary  sheath.  The  medullated 
fibres  form  the  series  of  white  rami  communi- 
cantes  (the  visceral  branches  of  the  spinal  nerves). 
They  take  origin  from  the  anterior  primary 
divisions  of  certain  spinal  nerves  in  two  streams  ; 
thoracico-lumbar  from  the  first  or  second  thoracic 
to  the  second  or  third  lumbar  nerve,  and  pelvic, 
or  sacral,  from  the  second  and  third,  or  third  and 
fourth  sacral  nerves.  The  roots  of  these  nerves 
arise  from  both  dorsal  and  ventral  roots  of  the  spinal  nerves,  but  in  largest  numbers 
from  the  ventral  root.  The  Jibres  from  the  ventral  root  are  of  very  small  size.  They 
are  the  axons  of  nerve  cells  within  the  spinal  cord,  which  enter  the  sympathetic  cord 
through  the  white  ramus,  and  end  by  forming  arborisations  around  the  cells  of  a  sym- 
pathetic ganglion.  There  are  three  known  courses  for  such  a  fibre  to  take  in  relation 
to  the  sympathetic  system — (a)  It  may  end  in  the  ganglion  with  which  it  is  im- 
mediately related  ;  (b)  it  may  course  upwards  or  downwards  in  the  commissural  cord 
to  reach  a  neighbouring  ganglion  ;  (c)  it  may  pass  beyond  the  gangliated  cord  to  end 
in  relation  to  cells  of  the  peripheral  (collateral)  ganglia  along  with  fibres  of  distribu- 
tion from  the  sympathetic  ganglia.  These  fibres  are  splanch'nic  efferent  fibres ;  motor 
for  the  unstriped  muscular  tissue  of  the  vessels  and  viscera,  and  secretory  for  the 
glands  in  the  splanchnic  area.  The  fibres  from  the  dorsal  root  of  the  spinal  nerve 
entering  into  the  composition  of  the  white  ramus  communicans  are  the  axons  of  spinal 


Fig.  540.—  Scheme  of  the  Constitution  of 
THE  White  Ramus  Communicans  of  the 
Sympathetic. 

The  roots  and  trunks  of  a  spinal  nerve  are 
sho'wn,  with  the  white  ramus  passing  be- 
tween the  spinal  nerve  and  a  sympathetic 
ganglion  (Sy).  The  splanchnic  eifereut 
fibres  (in  red)  are  shown,  partly  ending 
in  the  ganglion,  and  partly  passing  be- 
yond the  ganglion  into  a  peripheral  branch. 
The  splanchnic  afferent  fibres  (in  blue)  are 
shown,  partly  entering  the  ganglion,  and 
passing  upwards  or  downwards  in  the 
gangliated  cord  ;  partly  passing  over  the 
cord  into  peripheral  branches. 


THE  SYMPATHETIC  NEEVOUS  SYSTEM. 


Y05 


ganglion  cells.  They  constitute  the  splanchnic  afferent  fibres,  and  probahly  traverse 
the  sympathetic  garigliated  cord,  passing  upwards,  downwards,  and  outwards,  without 
being  connected  with  its  cells.  They  are  the  sensory  fibres  for  the  viscera,  which 
they  reach  along  with  the  peripheral  branches  arising  from  the  symxjathetic 
cord  itself.  It  is  not  certain  that  fibres  from  the  dorsal  ganglia  are  only  found  in 
connexion  with  nerves  provided  with  distinct  white  rami.  Similar  medullated 
fibres  are  found  also  in  the  gray  rami  communicantes. 

The  non-medullated  fibres  in  the  sympathetic  system  are  derived  from  the  axons 
of  the  sympathetic  ganglion  cells.  They  have  different  destinations,  (a)  Some 
fibres  appear  to  contribute  to  the  formation  of  the  commissural  cord  connecting 
the  ganglia  together, 
and  to  end  in  arborisa- 
tions round  the  cells 
of  a  neighbouring 
ganglion,  (h)  Non- 
medullated  fibres 
form  a  large  part  of 
the  system  of  peri- 
pheral (sp)lanchnic 
efferent)  branches, 
streaming  into  the 
splanchnic  area  in  an 
irregular  manner, 
both  from  the  gangha 
and  the  connecting 
commissures,  (c)  The 
gray  rami  communi- 
cantes form  a  series 
of  non  -  medullated 
fibres  (with  a  small 
number  of  medullated 
fibres  intermingled) 
proceeding  centrally 
from  the  ganglia  to  the 
spinal  nerves.  These 
gray  rami  are  found 
in  connexion  with 
each  and  all  of  the 
spinal  nerves.  Their 
origin  from  the  gan- 
gliated  cord  is  ir- 
regular :  they  may 
come  from  the  gan- 
glia or  tlie  commis- 
sure; they  may  divide 
after  their  origin,  so 
that  two  spinal  nerves 
are  supplied  from  one 
ganglion  ;  or  two 
ganglia  may  supply 
branches  to  a  single 
spinal  nerve.  The 
gray  ramus  is  distri- 
buted along  the  somatic  divisions  of  the  spinal  nerves,  supplying  branches  to 
uristriped  muscular  fibres  (vaso-motor,  j)ilo-motor)  and  glands  (secretory).  They 
also  jjrovide  small  recurrent  branches,  ending  in  the  membranes  enveloping  the 
spinal  nerve-roots.  Mingled  with  the  non-medullated  fibres  of  the  gray  rami 
are  found  a  small  number  of  iiKulullatod  fibres,  regarded  as  mcMlullated  sympathetic 
fibres,  and  axons  from  the  dorsal  spinal  ganglia  incorporated  with  this  ranms. 
49 


-Scheme  of  the  Constitution  and  Connexions  op  the 
Gangliated  Cord  of  the  Sympathetic. 

The  gangliated  cord  is  indicated  ou  the  right,  with  the  arrangement  of  the  fibres 
arising  from  the  ganglion  cells.  On  the  left  the  roots  and  trunks  of 
spinal  nerves  are  shown,  with  the  arrangement  of  the  white  ramiis  com- 
inunicans  above  and  of  the  yrav  ramus  below. 


706  THE  NERVOUS  SYSTEM. 

The  commissural  cords  of  the  sympathetic  system  are  composed  of  white  and 
gray  fibres.  The  ichite  fibres  are :  (1)  splanchnic  efferent  fibres,  passing  to  a 
ganglion  above  or  below  the  point  of  entrance  into  the  sympathetic  system ;  (2) 
splanchnic  afferent  fibres,  guided  along  the  commissure  and  over  or  through  the 
ganglia.  The  gray  fibres  are  the  axons  of  sympathetic  ganglion  cells :  (1)  true 
commissural  filjres  passing  into  connexion  with  the  cells  of  a  neighbouring 
ganglion ;  (2)  fibres  passing  along  the  commissure  for  a  certain  distance  upwards 
or  downwards  before  entering  the  splanchnic  area  as  peripheral  branches. 

The  peripheral  (splanchnic)  branches  from  the  sympathetic  cord  consist  of — 

(1)  white  fibres — splanchnic  afferent  fibres  unconnected  with  cells,  and  splanchnic 
efferent  fibres  which,  after  passing  over  the  gangliated  cord,  are  on  their  way  to 
join  peripheral  (collateral)  or  terminal  ganglia  in  relation  to  the  viscera  ;  and  of 

(2)  gray  fibres,  splanchnic  efferent  branches,  the  axons  of  sympathetic  ganglion 
cells  distributed  to  the  vessels  and  viscera  in  the  splanchnic  area. 

THE  CEEVICAL  PAET  OF  THE  SYMPATHETIC  COED. 

The  cervical  part  of  the  sympathetic  cord  may  be  regarded  as  an  upward 
prolongation  of  the  primitive  sympathetic  system  along  the  great  vessels  of  the 
neck.  It  is  characterised  by  the  absence  of  white  rami  communicantes  connecting 
it  with  the  cervical  spinal  nerves.  Its  spinal  fibres  ascend  in  the  commissural 
cord  from  the  upper  thoracic  nerves  to  be  connected  with  the  cells  of  the 
cervical  ganglia.  The  branches  from  the  ganglia  in  the  neck  are  distributed  to 
structures  in  the  head,  neck,  and  thorax :  (1)  motor  fibres  to  involuntary  muscles 
(e.g.  dilator  of  the  pupil) ;  (2)  vaso-motor  fibres  along  the  arteries  of  the  head  and 
neck  and  upper  limbs ;  (3)  pilo-motor  fibres  along  the  cervical  spinal  nerves  to  the 
skin  of  the  head  and  neck ;  (4)  cardio-rnotor  fibres ;  (5)  and  secretory  fibres  (for 
the  submaxillary  gland). 

The  gangliated  cord  in  the  neck  is  placed  upon  the  prevertebral  muscles  and 
behind  the  carotid  vessels.  It  extends  from  the  root  of  the  neck,  where  it  is  con- 
tinuous behind  the  subclavian  artery  with  the  thoracic  portion  of  the  cord,  to  the 
base  of  the  skull,  where  it  ends  in  the  formation  of  plexiform  branches  upon  the 
internal  carotid  artery.  It  consists  of  a  narrow  commissural  cord  composed  of 
medullated  and  non-meduUated  fibres,  on  which  are  two  or  three  ganglia — a 
superior  ganglion  at  the  upper  end,  an  inferior  ganglion  at  the  point  of  junction 
with  the  thoracic  portion  of  the  cord,  and  an  intermediate  middle-  ganglion  varying 
in  position  and  often  absent. 

The  superior  cervical  ganglion  (g.  cervicale  superius)  situated  at  the  base  of  the 
skull,  lies  between  the  internal  jugular  vein  and  the  internal  carotid  artery.  It  is 
the  largest  of  the  sympathetic  ganglia,  measuring  an  inch  or  more  in  length.  The 
commissural  cord  connects  it  with  the  middle  ganglion  (g.  cervicale  medium),  which  is 
of  small  size,  is  frequently  absent,  and  may  be  divided  into  two  parts.  It  is  usually 
placed  over  the  inferior  thyroid  artery  as  it  passes  behind  the  carotid  sheath. 

The  inferior  ganglion  (g.  cervicale  inferius)  is  joined  by  the  commissural  cord  to 
the  middle  (or  superior)  ganglion  above,  and  is  only  imperfectly  separated  from  the 
first  thoracic  ganglion  loelow.  It  is  of  considerable  size,  irregular  in  shape,  and  is 
placed  behind  the  first  part  of  the  subclavian  artery  in  the  interval  between  the 
last  cervical  transverse  process  and  the  neck  of  the  first  rib. 

The  branches  from  the  cervical  sympathetic  ganglia  and  cord  are  divisible  into 
two  sets — {A)  Central  communicating  branches  for  other  nerves ;  {B)  peripheral 
branches  of  distribution,  which  alone,  or  along  with  other  nerves,  form  plexuses, 
accompanying  and  supplying  vessels  and  viscera  of  the  head,  neck,  and  thorax. 
Although  this  distinction  is  made,  it  is  to  be  borne  in  mind  that  the  branches  of 
communication  are  as  much  nerves  of  distribution  as  the  others. 

SuPERiOE  Cekvical  Ganglion. 

Central  Communicating'  Branches. — 1.  Gray  rami  communicantes  pass  from 
the  ganglion  to  the  anterior  primary  divisions  of  the  first  four  cervical  nerves. 

2.  Communications  with  Cranial  Nerves. — Just  outside  the  skull,  in  the  deep 


SUPERIOK  CERVICAL  GANGLION. 


707 


part  of  the  neck,  communicating  branches  pass  to  the  following  cranial  nerves :  (a) 
to  the  petrous  ganglion  of  the  glosso-jjharyngeal  and  the  ganglion  of  the  root  of 
the  pneumogastric  (n.  jugularis) ;  (&)  to  the  ganglion  of  the  trunk  of  the  pneumo- 
gastric  ;  (c)  to  the  hypoglossal  nerve. 

Peripheral  Branches  of  Distribution. — 1.  Pharynx. — A  pharyngeal  branch 
courses  downwards  and  inwards  behind  the  carotid  sheath  to  reach  the  wall  of  the 
pharynx,  where  it  joins  (along  with  the 
pharyngeal  branches  of  the  glosso-pharyngeal 
and  pneumogastric  nerves)  in  the  formation 
of  the  pharyngeal  plexus,  and  assists  in  supply- 
ing the  muscles  and  mucous  membrane  of  the 
pharynx. 

2.  Heart. — The  superior  cervical  cardiac 
branch  is  a  slender  nerve  which,  on  the  fight 
side,  descends  behind  the  large  vessels  into 
the  thorax  to  join  the  deep  cardiac  plexus. 
On  the  left  side  the  course  of  the  nerve  is 
similar  in  the  neck,  but  in  the  superior 
mediastinum  it  passes  between  the  left 
carotid  and  subclavian  arteries,  and  over  the 
aortic  arch,  to  join  with  the  inferior  cervical 
cardiac  branch  of  the  pneumogastric  in  the 
formation  of  the  superficial  cardiac  plexus. 
In  their  course  both  nerves  form  connexions 
with  the  other  cervical  cardiac  nerves  of  the 
sympathetic,  and  with  cardiac  and  other 
branches  of  the  pneumogastric  (external  and 
inferior  laryngeal). 

3.  Vessels.  —  (a)  The  external  carotid 
branch  passes  forwards  to  the  external  carotid 
artery,  and  forms  the  external  carotid  plexus, 
which  supplies  offsets  to  that  artery  and  its 
branches,  as  well  as  to  the  inter-carotid  body. 
From  the  subordinate  plexuses  on  the  facial 
and  middle  meningeal  arteries  sympathetic 
fibres  are  supplied  to  the  submaxillary  and 
otic  ganglia  respectively. 

(&)  The  internal  carotid  branches  form  an 
upward  prolongation  of  the  ganglion,  which 
applies  itself  in  the  form  of  bundles  of  nerve- 
fibres  to  the  internal  carotid  artery  as  it 
enters  the  carotid  canal  in  the  temporal  bone. 
The  branches  separate  into  outer  and  inner 
parts,  which  form  plexuses  investing  the 
artery  in  the  cranium.  The  outer  division 
forms  the  lower  or  carotid  plexus  (pi.  caroticus 
internus) ;  the  inner  division  gives  rise  to 
the  upper  or  cavernous  plexus  (pi.  cavernosus). 
Both  plexuses  sup])ly  offsets  to  the  artery  and 
its  branches,  and  form  communications  with 
certain  crani;il  nerves. 

The  carotid  plexus  communicates  by  fine  branches  with  {a)  Ihe  abducent  nerve, 
and  (1)  the  Gass(Tiau  ganglion,  and  gives  off  (c)  the  great  deep  petrosal  and  {d) 
the  small  deep  petrosal  nerves.  The  great  deep  petrosal  nerve  joins  the  great 
superficial  petrosal  nerve  from  the  geniculate  ganglion  of  the  facial,  over  the 
foramen  laccrum  medium.  By  their  union  the  Vidian  nerve  is  formed,  which, 
after  traversing  the  Vidian  canal,  ends  in  Meckel's  ganglion.  The  small  deep 
petrosal  nerve  passes  to  tin;  tympanic  plexus.  Tliis  i)]cxnH,  formed  by  the  small 
deep  pctiosal   nerve,  the  tympanic^   hran(;li  of  the  glosso-pharyngoal,  and  a  twig 


Fig.  542. — The  Distribution  op  the  Sympa- 
thetic Gangliated  Cord  in  the  Neck. 

Sy.l,  Superior  cervical  ganglion,  and  connexions 
and  branches  ;  I.C,  Internal  carotid  artery  ; 
G.Ph,  Glosso-pharyngeal  ;  Va,  Vagus  ;  Hy, 
Hypoglossal  ;  C.l,  2,  3,  4,  First  four  cervical 
nerves;  Plex,  Pharyngeal  jjlexus ;  G.Ph, 
Glosso-pharyngeal  nerve  ;  E.C,  To  external 
carotid  artery  ;  Sy.2,  Middle  cervical  gang- 
lion, connexions,  and  branches  ;  C.5,  6,  Fifth 
and  sixth  cervical  nerves  ;  I. Thy,  Inferior 
thyroid  artery ;  A.V,  Ansa  Vieussenii;  Sy.3, 
.  Inferior  cervical  ganglion,  connexiojis,  and 
branches;  C.7,  8,  Seventh  and  eighth  cer- 
vical nerves  ;  Vert,  Vertebral  plexus  ;  Car, 
Cardiac  branches. 


708 


THE  NEEVOUS  SYSTEM. 


from  the  geniculate  ganglion  of  the  facial  nerve,  is  placed  on  the  inner  wall  of  the 
tympanum.  It  supplies  the  mucous  lining  of  the  tympanum  and  Eustachian 
tube ;  and  the  small  superficial  petrosal  nerve  passes  from  it  to  the  otic  ganglion. 

The  cavernous  plexus  communicates  with  (a)  the 
oculo- motor,  and  (h)  the  trochlear  nerves,  and  (c) 
the  ophthalmic  division  of  the  trigeminal  nerve ;  it 
also  (d)  supplies  twigs  to  the  pituitary  body,  and  (e) 
forms  the  sympathetic  root  of  the  ciliary  ganglion. 
This  may  pass  to  the  ganglion  independently,  or  it 
may  be  incorporated  in  the  long  root  of  the  ganglion 
from  the  nasal  branch  of  the  ophthalmic  nerve. 

Middle  Cervical  Ganglion. 

Central  Communicating  Branches. — 1.  Gray 
rami  communicantes  arise  from  the  ganglion  or  from 
the  cord  for  the  anterior  primary  divisions  of  the 
fifth  and  sixth  cervical  nerves.  2.  The  subclavian 
loop  (ansa  Vieussenii)  is  a  loop  of  communication  from 
this  ganglion,  which,  after  passing  over  and  supplying 
offsets  to  the  subclavian  artery  and  its  branches,  joins 
the  inferior  cervical  ganglion. 

Peripheral  Branches  of  Distribution. — 1.  Heart. 
— A  slender  middle  cervical  cardiac  branch  descends, 
either  separately  or  in  company  with  other  cardiac 
nerves,  behind  the  large  vessels  into  the  thorax, 
where  it  ends  in  the  deep  part  of  the  cardiac  plexus 
on  each  side. 

2.  Thyroid  Body.  —  Branches  extend  inwards 
along  the  inferior  thyroid  artery  to  supply  the  thyroid 
body. 

When  the  middle  ganglion  is  absent  the  branches 
described  arise  from  the  commissural  cord. 


Inferior  Cervical  Ganglion. 

Central  Communicating  Branches. — 1.  G-ray 
rami  communicantes  arise  from  this  ganglion  for  the 
anterior  primary  divisions  of  the  seventh  and  eighth 
cervical  nerves.  2.  The  subclavian  loop  already 
mentioned  connects  the  middle  and  inferior  ganglia 
over  the  front  of  the  subclavian  artery.  3.  A  com- 
munication frequently  occurs  with  the  inferior 
laryngeal  nerve. 

Peripheral  Branches  of  Distribution. — 1.  Heart. 
— ^An  inferior  cervical  cardiac  branch  is  given  off  on 
each  side  to  enter  the  deep  cardiac  plexus. 

2.  Vessels. — (a)  The  vertebral  plexus  is  a  dense 
Superficial  cardiac  plexus;  A.P.P,  plexus  of  fibres  surroundiug  the  vertebral  artery  and 
pr,t''"'";ZVa!r  Views'";  accompanying  its  branches  in  the  neck  and  the 
R.Car.p,  Right,  and  L.Car.p,  Left  Cranial  cavity.  (6)  The  subclavian  plexus  is  derived 
coronary  piexu.ses ;  Art.Pui,  Pui-  from  the  Subclavian  loop,  and  supplies  small  offsets  to 
monary  artery.  ^^^^   Subclavian   artery.       It   gives  branches    to   the 

internal  mammary  artery,  and  communicates  with  the  phrenic  nerve. 

THE  THORACIC  PAET  OF  THE  SYMPATHETIC  CORD. 

The  thoracic  part  of  the  sympathetic  cord  consists  of  a  variable  number  of 
ganglia  of  an  irregularly  angular  or  fusiform  shape,  joined  together  by  commissural 


Fig.  543. — The  Constitdtion  of 
THE  Cardiac  Plexuses. 

Sy,  Cervical  symj^athetic  cord  ;  C.l, 
Superior,  C'.2,  Middle,  and  C.3,  In- 
ferior cervical  ganglia ;  Car.  1, 
Superior,  Car.  2,  Middle,  and  Car.3, 
Inferior  cervical  cardiac  sympa- 
thetic branches ;  Ya,  Pneumogastric 
nerve  ;  R.L,  Recurrent  laryngeal 
nerve  ;  s,  Superior,  and  i,  Inferior 
cervical  cardiac  branches  of  vagus  ; 
D.C.P,  Deep  cardiac  plexus  ;  S.C.P, 


THE  THORACIC  PART  OF  THE  SYMPATHETIC  CORD. 


709 


cords  of  considerable  thickness.     The  number 

of  ganglia  is  usually  ten  or  eleven  ;  but  the  first 

and  sometimes  others  may  be  so  fused  with  the 

neighbouring  ganglia  as  to  still  further  reduce 

the  number.     This  part  of  the  sympathetic  cord 

is  characterised  by  its  union  with  the  thoracic 

spinal  nerves.     Each  thoracic  nerve,  with  the 

possible  exception  of  the  first,  sends  a  visceral 

brancli  (white  ramus  communicans)  to  join  the 

p'anffliated  cord  in  the  thorax.      These  white 

•  ■        1     • 

rami  separate  into  two  mam  streams  m  relation 

to  the  sympathetic  cord.  Those  of  the  upjjer 
five  nerves  are  for  the  most  part  directed 
upwards  to  be  distributed  through  the  cervical 
part  of  the  sympathetic  gangliated  cord  in 
the  manner  already  described.  The  white  rami 
of  the  loiuer  thoracic  nerves  are  for  the  most 
part  directed  downwards  in  the  lower  part  of 
the  sympathetic  cord  and  its  branches,  to  be 
distril)uted  in  the  abdomen ;  at  the  same  time 
some  of  their  fibres  are  directly  associated  with 
the  supply  of  certain  thoracic  viscera, — lungs, 
aorta,  oesophagus. 

These  white  rami  are  composed  of  (1) 
splanclmic  afferent  fibres  passing  from  its  peri- 
pheral branches  through  the  sympathetic  cord 
into  the  dorsal  ganglia  of  the  spinal  nerves — 
medullated  nerve-fibres  unconnected  with  sym- 
pathetic ganglion  cells ;  and  (2)  somatic  and 
splanchnic  efferent  fibres,-  small  medullated 
nerves  which,  after  a  longer  or  shorter  course 
in  the  gangliated  cord  or  its  peripheral 
branches,  become  connected  with  the  sym- 
pathetic ganglion  cells,  or  with  the  cells  of 
peripheral  (collateral  or  terminal)  ganglia,  from 
which  again  (non-meduUated)  axons  proceed  to 
supply  branches  to  viscera  and  vessels.  The 
ultimate  destination  of  the  upper  stream  of 
white  rami  from  the  thoracic  nerves  has  been 
mentioned  in  the  description  of  the  cervical 
sympathetic;  the  peripheral  branches  supply- 
ing thoracic  organs  contain  vaso-motor  fibres 
for  the  lungs  and  aorta.  The  peripheral  branches 
from  the  lower  part  of  the  sympathetic  cord 
in  the  thorax,  receiving  white  rami  from  the 
lower  thoracic  nerves,  are  mainly  destined  for 
distribution  to  structures  below  the  diaphragm. 
They  comprise  (a)  viscero-inhibitory  fibres  for 
the  .stomach  and  intestines;  {h)  motor  fibres  for  p^^_  544.  -The  ArrIng^emkn^t  'of  the 
XJart  of  the  rectum  ;   (c)  pilo-motor  fibres  for  the  Sympathetic   System  in  the  Thorax, 

lower  part  of  the  body;  (cl)  vaso-motor  fibres         Abdomen,  and  Pelvis. 
for  the  abdominal  aorta  and  its  branches,  and   T.i-12;  L.i-5  ;  S.l-5  ;  Co,  Anterior  prinuu-y 

divisions  of  s[iinal  nerves,  connected  to  the 
gangliated  cord  of  the  sympathetic  by 
rami  comumnicantes,  wliitc  (double  lines)  and  gray  (single  lines)  ;  Oes,  (Esophagus  and  u.'.sophageal 
plexus  ;  Ao,  Aorta  and  aorta  ple.xu.s  ;  Va,  Vagus  nerve  joining  oesophageal  plexus  ;  S.l,  Great  splanchnic 
nerve  ;  X,  Great  sjilaiichnic  ganglion  ;  S.2,  Small  splanchnic  nerve  ;  S.3,  Least  siilanchnic  nerve  ;  Co, 
Coronary  artery  and  i)]exus  ;  Si'L,  Sjjlenic  artery  and  jjlexus  ;  H,  Hepatic  artery  and  plexus  ;  SL,  Semi- 
lunar ganglion  ;  Di,  Diapliragm  ;  S.li,  Suprarenal  capsule  ;  He,  Renal  artery  and  plexus  ;  S.M,  Superior 
mesenteric  artery  and  plexus  ;  Si',  Spermatic  artery  and  plexus  ;  I.M,  Inferior  mesenteric  artery  and 
Iilexus  ;  Hy,  Hypoga.stric  nerves  and  jdexus  ;  Rue,  Rectal  plexus;  Ut,  Uterine  plexus;  Ves,  Vesical 
(jIcxus  ;   V.  V.V,  Visceral  branches  from  sacral  nerves. 

40  a 


710  THE  NERVOUS  SYSTEM. 

fur  the  lower  limbs ;  (e)  secretory,  and  (/)  sensory  fibres  for  the  abdominal  viscera. 
The  thoracic  part  of  the  sympathetic  cord  is  placed  upon  the  heads  of  the  ribs, 
and  is  covered  over  by  the  pleura. 

The  branches  from  the  gangliated  cord  are,  as  in  the  neck,  divisible  into  two 
sets — (^A)  Central  branches,  communicating  with  other  nerves,  and  (B)  peripheral 
branches,  distributed  in  a  plexiform  manner  to  the  thoracic  and  abdominal  viscera. 

Central  Communicating  Branches.— -The  white  rami  communicantes  from 
the  thoracic  nerves  have  already  been  described.  I'assing  forwards  from  the 
beginning  of  the  anterior  primary  divisions  of  the  nerves,  they  become  connected 
with  the  ganglia  or  the  commissural  cord  of  the  sympathetic. 

The  gray  rami  communicantes  are  branches  arising  irregularly  from  each  thoracic 
ganglion,  which,  passing  backwards  along  with  the  white  rami,  join  the  anterior 
primary  divisions  of  the  thoracic  nerves. 

Peripheral  Branches  of  Distribution. — These  branches  arise  irregularly 
from  the  ganglia  and  the  commissural  cord.  They  are  composed  of  non-medullated 
fibres  (splanchnic  efferent)  derived  from  the  ganglion  cells,  and  medullated  fil^res 
(splanchnic  efferent  and  afferent)  derived  directly  from  the  white  rami,  without 
the  intervention  of  the  cells  of  the  ganglia. 

1.  Pulmonary  Branches. — From  the  gangliated  cord  opposite  the  second,  third, 
and  fourth  ganglia  fine  filaments  arise  which  join  the  posterior  pulmonary  plexus. 

2.  Aortic  Branches. — The  upper  part  of  the  thoracic  aorta  receives  fine  branches 
from  the  upper  five  thoracic  ganglia. 

3.  Splanchnic  Nerves. — Three  nerves  arise  from  the  lower  part  of  the 
gangliated  cord,  partly  from  the  ganglia  themselves,  and  partly  from  the  com- 
missural cord  between  the  ganglia.  Passing  downwards  over  the  bodies  of  the 
thoracic  vertebrae  they  pierce  the  diaphragm,  to  end  in  the  abdomen. 

(a)  The  great  splanchnic  nerve  (n.  splanchnicus  major)  arises  from  the 
gangliated  cord  between  the  fifth  and  ninth  ganglia.  By  the  union  of  several 
irregular  strands  a  nerve  of  considerable  size  is  formed,  which  descends  in  the 
posterior  mediastinum,  and  piercing  the  crus  of  the  diaphragm,  joins  at  once  the 
upper  end  of  the  semihinar  ganglion  of  the  solar  plexus.  In  its  course  in  the 
thorax  the  great  splanchnic  ganglion  (g.  splanchnicum)  is  formed  upon  the  nerve. 
It  is  more  prominent  in  the  fostus  than  in  the  adult.  Erom  both  nerve  and  ganglion 
branches  arise  in  the  thorax  for  the  supply  of  the  oesophagus  and  descending 
thoracic  aorta  (Fig.  544). 

(h)  The  small  splanchnic  nerve  (n.  splanchnicus  minor)  arises  from  the  gangliated 
cord  opposite  to  the  ninth  and  tenth  ganglia.  It  passes  over  the  bodies  of  the 
lower  thoracic  vertebrae,  pierces  the  diaphragm  near  or  along  with  the  great 
splanchnic  nerve,  and  ends  in  the  solar  plexus  {aortico-renal  gajiglioTi). 

(c)  The  least  splanchnic  nerve  (n.  splanchnicus  imus)  arises  from  the  last 
thoracic  ganglion  of  the  sympathetic,  or  it  may  be  a  branch  of  the  smaller 
splanchnic  nerve.     It  pierces  the  diaphragm,  and  ends  in  the  renal  2}lexus. 


THE  LUMBAE  PAET  OF  THE  SYMPATHETIC  CORD. 

The  lumbar  part  of  the  sympathetic  cord  is  placed  upon  the  bodies  of  the 
lumbar  vertebras,  internal  to  the  origins  of  the  psoas  muscle,  and  in  front 
of  the  lumbar  vessels.  It  is  connected  with  the  thoracic  portion  of  the  cord  by  an 
attenuated  commissural  cord,  which  either  pierces  or  passes  behind  the  diaphragm. 
It  is  continuous  below  with  the  sacral  portion  of  the  cord  by  a  commissure,  which 
passes  behind  the  common  iliac  artery.  It  is  joined  by  medullated  fibres  (white 
rami  communicantes)  from  the  first  two  lumbar  spinal  nerves,  and  it  contains  as 
well  medullated  fibres  continued  down  from  the  lower  part  of  the  thoracic 
gangliated  cord,  and  derived  from  the  visceral  branches  (white  rami  com- 
municantes) of  the  lower  thoracic  nerves.  This  part  of  the  gangliated  cord  is 
characterised  by  great  irregularity  in  the  number  of  the  ganglia.  They  are  usually 
four  in  number,  but  there   are  frequently  more  (up  to  eight) ;  and  in   extreme 


thp:  saceal  part  of  the  gangliated  cord. 


71 J 


cases  fusion  may  occur  to  such  an  extent  that  the  separation  of  individual  ganglia 
becomes  impossible. 

WMte  rami  communicantes. — The  first  two  (or  three)  lumbar  spinal  nerves 
possess  visceral  branches  which  form 
white  rami  communicantes  joining 
the  upper  lumbar  ganglia  or  the 
gangliated  cord.  These  nerves 
form  the  lower  limit  of  the  thoracic- 
lumbar  visceral  branches  of  the 
spinal  nerves.  They  comprise  vaso- 
motor fibres  (for  the  genital  organs), 
and  motor  fibres  for  the  bladder  and 
uterus. 

Central  Communicating- 
Branches.  —  Gray  rami  communi- 
cantes pass  from  the  gangliated  cord 
to  the  anterior  primary  divisions 
of  the  lumbar  nerves  in  an  ir- 
regular manner.  One  ramus  may 
divide  so  as  to  supply  branches  to 
two  adjacent  spinal  nerves ;  or  a 
spinal  nerve  may  be  joined  by  two 
to  five  separate  gray  rami  from  the 
gangliated  cord. 

The  rami  course  beneath  the 
origin  of  the  psoas  magnus  muscle 
and  over  the  bodies  of  the  vertebrae. 
Gray  rami  sometimes  pierce  the 
fibres  of  the  psoas  muscle. 

Peripheral  Branches  of  Dis- 
tribution.— From  the  lumbar  gan- 
gliated. cord  numbers  of  small 
branches  arise  irregularly,  and 
pass  inwards  to  supply  the  ab- 
dominal aorta,  reinforcing  the 
aortic  plexus  (from  the  solar 
plexus). 


THE  SACRAL  PART  OF 
GANGLIATED  CORD. 


Fig.  545. — The  Lumbar  Portion  of  the  Sympathetic 
Gangliated  Cord  and  Lumbar  Plexus.  (From  a  dissection.) 

^   T.ll,  T.12,  L.l,  L.2,  L.3,  L.4,  L.5,  Anterior  primary  divisions 
of  spinal  nerves,  with  white  and  gray  rami  communicantes. 

THE  ^^''  Sympathetic  gangliated  cord  ;  Va,  Vagus  nerve  ;  G.S,  Great 
splanchnic  nerve,  joining  semilunar  ganglion  ;  S.R.C,  Supra- 
renal capsule  and  plexus  ;  R.Pl,  Renal  plexus  ;  Ao.Pl, 
Aortic  plexus;  S. M,  Superior  mesenteric  plexus;  I.M, 
Inferior  mesenteric  plexus;  Hy. PI,  Hypogastric  plexus; 
Q,  Nerves  to  quadratus  lumborum  ;  I.H,  Ilio-hypogastric 
nerve  ;  I.I,  Ilio-inguinal  nerve  ;  G.C,  Genito-crural  nerve  ; 
E.C,  External  ciitaneous  nerve  ;  A.C,  Anterior  crural  nerve  ; 
Ace.  Obt,  Accessory  obturator  nerve  ;  Obt,  Obturator  nerve 
4,  5,  Lumbo-sacral  cord. 


The  sacral  part  of  the  gan- 
gliated cord,  like  the  cervical  and 
lower  lumbar  portions  of  this 
system,  receives  no  white  rami 
communicantes  from  the  spinal 
nerves.  The  visceral  branches  (pelvic  qjlanchnic)  of  the  third,  and  usually,  also 
the  second  or  fourth  sacral  nerves,  enter  the  pelvic  plexus  without  being  directly 
connected  with  the  gangliated  cord.  These  nerves,  however,  are  to  be  regarded  as 
homologous  with  the  white  rami  communicantes  of  the  thoracico-lumbar  nerves 
(abdominal  sidanchnic).  They  convey  to  tlie  pelvic  viscera — (1)  motor  and 
inhibitory  fibres  for  rectum,  uterus,  and  bladder,  (2)  vaso-dilator  fibres  for  the 
genitals,  and  (.'3J  secretory  fibres  for  the  prostate  gland. 

This  portion  of  the  cord  is  placed  in  front  of  the  sacrum,  internal  to  the  anterior 
sacral  foramina.  It  is  connected  above  by  a  commissural  cord  with  the  lumbar 
portion  of  the  sympathetic,  and  below  it  ends  in  a  plexiform  union  over  the  coccyx 
svitb  till!  cord  of  tln!  otbcr  si(](;,  the  two  being  frequently  connected  by  the 
ganglion  impar  oi-  coccygeal  ganglion.     The  number  of  ganglia  is  variable;  there  are 


712  THE  NERVOUS  SYSTEM. 

commonly  four.  They  are  of  small  size,  gradually  diminishing  from  above  down- 
wards. 

Central  communicating  branches  arise  irregularly  in  the  form  of  gray  rami 
communicantes  from  the  sacral  ganglia,  and  join  the  anterior  primary  divisions  of 
the  sacral  and  coccygeal  nerves. 

Peripheral  Branches  of  Distribution. — (1)  Visceral  branches  of  small  size  arise 
from  the  upper  part  of  the  gaugiiated  cord,  and  pass  inwards  to  join  the  pelvic 
plexus  (see  l)elow). 

(2)  Parietal  branches,  also  of  small  size,  ramify  over  tlie  front  of  the  sacrum,  and 
form,  in  relation  to  the  middle  sacral  artery,  a  plexiform  union  with  liranches  from 
the  crangliated  cord  of  the  other  side. 

SYMPATHETIC  PLEXUSES. 

It  has  already  been  seen  that  the  peripheral  branches  of  the  sympathetic 
gangliated  cord  throughout  its  length  are  characterised  by  forming  or  joining 
plexuses  in  their  neighbourhood. 

The  cervical  sympathetic  ganglia  and  nerves  give  rise  to  the  carotid  and 
cavernous  plexuses ;  the  external  carotid,  pharyngeal,  thyroid,  vertebral,  and 
subclavian  plexuses ;  and  they  send  important  branches  to  the  cardiac  plexuses 
(described  along  with  the  pneumogastric  nerve). 

The  thoracic  ganglia  send  branches  to  join  the  pulmonary  and  oe.sophageal 
plexuses  (described  along  wiLh  the  pneumogastric  nerve).  They  form  plexuses  on 
the  thoracic  aorta,  and  by  means  of  the  splanchnic  nerves  they  form  the  chief 
source  of  the  solar  plexus. 

The  Solar  and  Pelvic  Plexuses. 

These  great  plexuses  serve  to  distribute  nerves  to  the  viscera  and  vessels  of  the 
abdominal  and  pelvic  cavities.  Taken  together  they  include  three  plexuses — the 
solar  plexus,  hypogastric  plexus,  and  the  pelvic  plexuses.  They  are  constituted 
by  peripheral  branches  of  the  lower  thoracic,  lumbar,  and  upper  sacral  parts  of  the 
gangliated  cord  of  the  sympathetic ;  and  they  are  related  to  the  central  nervous 
system  by  means  of  the  visceral  branches  (white  rami  communicantes)  of  the  lower 
thoracic  and  upper  lumbar  nerves  on  the  one  hand,  and  by  the  visceral  branches 
of  the  second  and  third,  or  third  and  fourth  sacral  nerves,  on  the  other  hand.  The 
thoracico-lumbar  series  join  the  sympathetic  cord,  and  reach  the  solar  plexus 
mainly  through  the  splanchnic  nerves,  and  to  a  lesser  extent  through  the  lumbar 
gangliated  cord.  The  sacral  series  enter  the  pelvic  plexus  without  connexion  with 
the  sympathetic  cord.  The  hypogastric  plexus  serves  as  a  connecting  link  between 
the  solar  and  pelvic  plexuses. 

The  solar  plexus  lies  on  the  posterior  abdominal  wall  in  relation  to  the 
abdominal  aorta  and  behind  the  stomach.  It  is  composed  of  three  elements  :  the 
cceliac  plexus  surrounding  the  origin  of  tlie  coeliac  axis  between  the  crura  of  the 
diaphragm,  and  two  semilunar  ganglia,  each  lying  on  the  corresponding  crus  of 
the  diaphragm,  and  overlapped  by  the  suprarenal  capsule,  and  on  the  right  side 
by  the  inferior  vena  cava.  The  plexus  is  continuous  with  subordinate  plexuses, 
diaphragmatic,  suprarenal,  renal,  superior  mesenteric  and  aortic ;  and  by  means  of 
the  hypogastric  nerves  the  aortic  plexus  becomes  continued  into  the  hypogastric 
plexus,  which  again  forms  the  chief  origin  of  the  pelvic  plexuses. 

The  semilunar  ganglia  constitute  the  chief  ganglionic  centres  in  the  solar 
plexus.  They  are  irregular  in  form.  They  are  often  partially  subdivided,  and  one 
detached  portion  at  the  lower  end  is  named  the  aortico-renal  ganglion.  Other  small 
scattered  masses  of  cells  are  present  in  the  coeliac  plexus  (ganglia  cceliaca).  At 
the  upper  end  the  semilunar  ganglion  receives  the  great  splanchnic  nerve.  The 
aortico-renal  ganglion  at  its  lower  end  receives  the  smaller  splanchnic  nerve. 
Branches  from  the  ganglion  radiate  in  all  directions — inwards  to  join  the  cceliac 
plexus,  upwards  to  form  the  diaphragmatic  plexus,  outwards  to  the  suprarenal 
plexus,  downwards  to  the  renal,  superior  mesenteric,  and  aortic  plexuses. 


THE  SOLAE  AND  rEJ.VIC  PLEXUSES. 


7i: 


Tlie  coeliac  plexus  i'oims  a  cousiderable 
plexiturm  mass  surroundiug  the  coeliac  axis.  It 
consists  of  a  dense  nieshwork  of  fibres  with 
ganglia  intermingled  (g.  ca3liaca),  joined  by 
numerous  branches  from  the  semilunar  gantjlion 
on  each  side,  and  by  branches  from  the  right 
pneumogastric  nerve.  It  is  continuous  below 
with  the  superior  mesenteric  and  aortic  plexuses. 
Investing  the  coeliac  axis,  it  forms  subsidiary 
plexuses  which  accompany  the  branches  of 
the  artery.  The  coronary  plexus  supplies 
branches  to  the  oesophagus  and  stomach;  the 
hepatic  plexus  supplies  branches  to  the  liver  and 
gall-bladder,  stomach,  duodenum,  anol  pancreas  ; 
and  the  splenic  plexus  sends  offsets  to  the  spleen, 
pancreas,  and  stomach. 

Subordinate  plexuses  are  formed  on  the 
aorta  and  its  branches  by  nerves  derived  from 
the  solar  plexus  (semilunar  ganglia  and  coeliac 
plexus). 

a.  The  diapkragmatic  plexus  consists  of 
fibres  arising  from  the  semilunar  ganglion,  and 
accompanies  the  inferior  phrenic  artery.  Besides 
supplying  the  diaphragm,  it  gives  branches  to 
the  suprarenal  plexus,  and  (on  the  right  side) 
to  the  inferior  vena  cava,  (on  the  left  side)  to 
the  oesophagus.  It  communicates  on  each  side 
with  the  phrenic  nerve.  At  the  junction  of  the 
plexus  and  the  phrenic  nerve  of  the  right  side 
a  ganglion  is  formed  (diapkragmatic  ganglion). 

h.  The  suprarenal  plexus  is  of  most  con- 
siderable size.  It  is  mainly  derived  from 
branches  of  the  semilunar  ganglion,  reinforced 
by  nerves  from  the  lower  part  of  the  solar  plexus 
which  stream  outwards  on  the  capsular  arteries. 
It  is  joined  by  branches  from  the  diaphragmatic 
plexus  above  and  from  the  renal  plexus  below. 
The  nerves  enter  the  substance  of  the  suprarenal 
capsule. 

c.  Therenalplexusisclerivedfrom(l)  branches 
of  the  semilunar  ganglion,  and  (2)  fibres  from 
the  aortic  plexus,  extending  outwards  along  the 
renal  artery  to  the  hilum  of  the  kidney.  It 
receives  also  the  least  splanchnic  nerve,  and  is 
connected  by  numerous  branches  to  the  supra- 
renal plexus. 

6..  The  superior  mesenteric  plexus  is  insepar- 
able above  from  the  cfjeliac  plexus,  and  is  joined 
on  either  side  by  fibres  from  the  semilunar 
ganglion.  It  is  continuous  below  with  the 
aortic  plexus.  A  separate  detached  ganglionic 
mass  Tsuperior  mesenteric  ganglion)  is  rjresent  in  T.i-12  ;  L.i-5  ;  s.i  o  ;  Co,  Anterior  primary 

divisions  of  .spinal  nerves,  connected  to  the 
gangliated  cord  of  the  .sympathetic  by 
rami  communicantcs,  wliite  (donble  lines)  and  gray  (single  lines)  ;  Oes,  (Esophagus  and  oesophageal 
plexus  ;  Ao,  Aorta  and  aortic  plexus  ;  Va,  Vagus  nerve  joining  r«soi)hageal  plexus  ;  S.  1,  Great  splanchnic 
nerve;  X,  Great  splanchnic  ganglion;  S.  2,  Small  splanchnic  nerve;  S.3,  Least  splanchnic  nerve;  Co, 
Coronary  artery  and  jilexus  ;  Si'L,  Splenic  artery  and  plexus  ;  H,  Hepatic  artery  and  jdexus  ;  S.  L,  Semi- 
lunar ganglion  ;  Di,  Diaphragm  ;  S.  li,  Suprarenal  capsule  ;  Re,  Renal  artery  and  jtlexus  ;  S.M,  Superior 
mesenteric  artery  and  ])lexus  ;  Sr,  Spermatic  artery  and  plexus;  I.M,  Inferior  mesenteric  artery  and 
plexus  ;  Hy,  Hypogastric  nerves  and  plexu.s  ;  Rec,  Rectal  plexus  ;  Ut,  Uterine  plexus  ;  Vbs,  Vesical 
plexus  ;  V.V.V,  Vi.scera!  branches  from  sacral  nerves. 


Fig. 


nEC.      UT       VES, 
546. — The     Arrangement    ok    the 
Sympathetic  System  in  the   Thorax, 
Abdomen,  and  Pelvis. 


714  THE  NEKVOUS  SYSTEM. 

the  plexus.  Accompanying  the  superior  mesenteric  arterj  the  plexus  forms 
subordinate  plexuses  around  the  branches  of  the  vessel.  The  plexuses  in  the 
mesentery  at  lirst  surround  the  intestinal  arteries,  but  near  the  intestine  they 
form  fine  plexuses  between  the  layers  of  the  mesentery,  from  which  branches  pass 
to  the  wall  of  the  gut.  This  plexus  supplies  the  small  intestine,  ceecum,  vermiform 
appendix,  ascending  and  transverse  portions  of  the  colon. 

e.  The  aortic  plexus  is  the  continuation  downwards  of  the  solar  plexus  around 
the  abdominal  aorta.  It  is  continuous  above  with  the  superior  mesenteric  and 
solar  plexuses;  it  is  reinforced  by  the  peripheral  branches  of  the  lumbar  gangliated 
cord  of  the  sympathetic ;  and  it  is  connected  with  the  hypogastric  plexus  below 
by  the  hypogastric  nerves.  Besides  investing  and  supplying  the  aorta,  the  plexus 
contributes  to  various  subordinate  plexuses  on  the  branches  of  the  artery.  It 
contributes  to  the  suprarenal  and  renal  plexuses,  and  it  gives  rise  to  the  spermatic 
or  ovarian  and  the  inferior  mesenteric  plexuses. 

The  spermatic  plexus  invests  and  accompanies  the  spermatic  artery.  It  is 
derived  from  the  aortic  plexus,  and  receives  a  contribution  from  the  renal  plexus. 
It  supplies  the  spermatic  cord  and  testicle. 

The  ovarian  plexus  in  the  female  arises  like  the  spermatic  plexus.  It  accom- 
panies the  ovarian  artery  to  the  pelvis,  and  supplies  the  ovary,  broad  ligament,  and 
Fallopian  tube.  It  forms  communications  in  the  broad  ligament  with  the  uterine 
plexus  (from  the  pelvic  plexus),  and  sends  fibres  to  the  uterus. 

The  inferior  mesenteric  plexus  is  a  derivative  from  the  aortic  plexus,'prolonged 
along  the  inferior  mesenteric  artery.  It  forms  subordinate  plexuses  on  the 
branches  of  the  artery  (colic,  sigmoid,  and  superior  hsemorrhoidal),  and  is  dis- 
tributed to  the  descending  colon,  iliac  colon,  pelvic  colon,  and  upper  part  of  the 
rectum. 

The  hypogastric  nerves  form  the  continuation  of  the  aortic  plexus  into  the 
pelvic  cavity.  They  consist  of  numerous  plexiform  bundles  of  nerve-fibres  which 
descend  along  the  front  and  back  of  the  bifurcation  of  the  aorta  and  the  origin  of 
the  common  iliac  arteries,  and  over  the  sacral  promontory,  where,  becoming  in- 
extricably mingled,  they  constitute  the  hypogastric  plexus. 

The  hypogastric  plexus  is  continued  downwards  in  front  of  the  sacrum  on  either 
side  of  the  rectum,  and  ends  in  the  pelvic  plexuses. 

The  pelvic  plexuses  are  formed  by  the  separation  of  the  hypogastric  plexus 
into  two  halves  on  either  side  of  the  rectum.  Each  is  joined  by  fibres  from  the 
upper  part  of  the  sacral  portion  of  the  gangliated  cord  of  the  sympathetic,  and  by 
the  visceral  branches  (white  rami  communicantes)  from  the  second  and  third  or 
third  and  fourth  sacral  nerves.  Accompanying  the  internal  iliac  artery  and  its 
branches  each  pelvic  plexus  gives  off  subordinate  plexuses  for  the  pelvic  viscera. 

a.  The  haemorrhoidal  plexus  supplies  the  rectum,  and  joins  the  superior  hsemor- 
rhoidal  plexus  from  the  inferior  mesenteric  plexus. 

&.  The  vesical  plexus  accompanies  the  vesical  arteries  to  the  bladder-wall. 
Besides  supplying  the  muscular  wall  and  mucous  membrane  of  the  bladder,  it 
forms  subordinate  plexuses  for  the  lower  part  of  the  ureter,  the  vesicula  seminalis, 
and  the  vas  deferens. 

c.  The  prostatic  plexus  is  of  considerable  size.  It  is  placed  on  either  side  of 
the  gland,  and  in  addition  to  supplying  its  substance  and  the  prostatic  urethra,  it 
sends  offsets  to  the  neck  of  the  bladder  and  the  vesicula  seminalis.  It  is  continued 
forwards  on  each  side  to  form  the  cavernous  plexus  of  the  penis  (plex.  cavernosus 
penis).  Bundles  of  nerves  pierce  the  layers  of  the  triangular  ligament,  and  after 
supplying  the  membranous  urethra  at  the  root  of  the  penis,  give  off  branches  which 
enter  and  supply  the  corpus  cavernosum.  The  cavernous  nerves  communicate  with 
branches  of  the  pudic  nerve,  and  give  offsets  to  the  corpus  spongiosum  and  the 
spongy  portion  of  the  urethra. 

d.  The  uterine  plexus  passes  upwards  for  a  short  distance  with  the  uterine  artery 
between  the  layers  of  the  broad  ligament,  and  is  then  distributed  to  the  surfaces 
and  su.bstance  of  the  organ.  It  communicates  between  the  layers  of  the  broad 
ligament  with  the  ovarian  plexus. 

The  vaginal  plexus  is  formed  mainly  by  the  visceral  branches  of  the  sacral 


DEVELOPMENT  OF  THE  SYMPATHETIC  >SYSTEM. 


715 


nerves  entering  the  pelvic  plexus.  It  supplies  the  wall  and  mucous  memljrane 
of  the  vagina  and  urethra,  and  provides  a  cavernous  plexus  lor  the  clitoris  (plex. 
cavernosus  clitoridis).  The  uterine  and  vaginal  plexuses  of  the  female  correspond 
to  the  prostatic  plexus  of  the  male. 


DEVELOPMENT  OF  THE  SYMPATHETIC  SYSTEM. 

There  are  two  diametrically  opposite  views  of  the  mode  of  development  of  the  sym- 
pathetic system. 

In  birds  and  mammals  the  first  rudiment  of  the  sympathetic  cord  occurs  in  the 
formation  of  a  longitudinal  unsegmented  column  of  mesoblastic  cells  (which  stain  more 
deeply  than  the  mesoblast  in  which  they  He)  on  either  side  of  the  aorta,  and  coterminous 
with  it.  This  column  of  cells  becomes  joined  at 
an  early  stage  by  the  visceral  branches  of  the 
spinal  nerves  which  grow  inwards  from  the  main 
nerve  trunks  into  the  splanchnic  area,  and  result 
from  the  division  of  the  nerve  into  somatic  and 
visceral  parts.  These  visceral  branches  constitute 
the  white  rami  communicantes.  They  receive 
contributions  usually  from  both  dorsal  and  ventral 
roots,  and  gradually  approaching  the  above-men- 
tioned column  of  mesoblastic  cells,  they  become 
intimately  associated  witii  the  cells.  In  some 
cases  fibres  of  the  visceral  nerves  pass  over  the 
cellular  column  into  the  splanchnic  area  without 
connexion  with  it  (Fig.  548).  By  the  junction  of 
these  visceral  nerves  with  the  cells  of  the  column, 
certain  cells  persist  and  produce  the  ganglia. 
The  intervening  portions  of  the  column,  by 
changes  in  the  cells,  and  by  the  addition  possibly 
of  fibres  belonging  to  the  visceral  nerves,  give 
rise  to  the  commissural  cords.  The  cellular 
column,  besides  producing  the  gangiiated  cord, 
by  the  further  growth  of  its  cells  and  their  ex- 
tension centrally  and  peripherally,  produces  the 
gray  rami  communicantes,  parts  of  the  peripheral 
branches,  and  the  peripheral  (collateral  and 
terminal)  ganglia,  as  well  as  the  medullaiy 
portion  of  the  suprarenal  capsule.  The  cervical, 
lower  lumbal',  and  sacral  portions  of  the  sym- 
pathetic gangiiated  cord  are  secondary  extensions 
from  the  more  primitive  condition,  gradually 
growing  upwards  and  downwards  along  the  main 
vessels.  These  portions  of  the  system  are  not 
provided  with  white  rami  communicantes.  The 
ganglia  of  the  sympathetic  assume  their  seg- 
mented appearance  (1)  from  the  persistence  of 
the  primitive  cells  and  their  connexion  with  the 
spinal  nerves  by  means  of  the  white  and  gray 
rami  communicantes,  and  (2)  from  the  way  in  which  the  primitive  column  is  moulded 
by  the  surrounding  structures  (bones,  segmental  arteries,  etc.) 

Another  account  of  the  development  of  the  sympathetic  system,  supported  by  liigh 
authority,  describes  the  gangiiated  cord  as  an  outgrowth  of  the  dorsal  ganglia  of  the 
spinal  nerves.  It  is  said  that  each  ganglion  gives  oft'  a  bud  at  its  lower  end,  which, 
growing  inwards  into  the  splanchnic  area,  becomes  attached  to  the  trunk  of  the  spinal 
nerve  just  beyond  the  union  of  the  dorsal  and  ventral  roots.  The  bud  still  extending 
inwards  into  the  splanchnic  area,  remains  associated  with  the  nerve  by  an  attenuated 
stalk.  These  buds,  it  is  said,  become  the  ganglia,  which,  after  reaching  their  permanent 
fjlace  in  the  splanchnic  area,  are  supposed  to  extend  upwards  and  downwards  so  as  to 
coalesce  and  form  a  beaded  chain  of  ganglia.  '^I'lie  stalks  connecting  the  ganglia  with  the 
s[)inal  nerves  Vjecome  the  white  rami  communicantes.  This  mode  of  development  does 
not  satisfactorily  accoiuit  for  several  important  features  of  the  sym])athetic  system — the 
development  of  those  parts  of  the   gangiiated   cord  which   possess  no   white    rami,    the 


Fig.   547. — The  Development  of  the 
Sympathetic  Gangliated  Cord. 

Sy,  Sympathetic  cord  ;  Spl,  Splauchiiic  branches 
of  spinal  nerves  (white  rami  communi- 
cantes) ;  V.S,  Vertebral  segments;  D.G, 
Dorsal  ganglia. 


716 


THE  NERVOUS  SYSTEM. 


absence  of  a  real  segmental  character  in  the  cord  (remarkably  shown  in  the  foetus),  and 
the  constancy  of  continuity  in  the  gangiiated  cord.     No  instance  is  recorded  of  a  hiatus 

between  two  ganglia.  It  is  a 
tempting  view  on  the  other  hand, 
as  it  ascribes  to  the  one  germinal 
layer  (epiblast)  the  formation  of  all 
the  elements  of  the  nervous  system, 
and  it  brings  the  sympathetic 
ganglia  into  serial  homology  with 
isolated  ganglia  on  the  cranial  nerves 
{e.g.  the  ciliary,  spheno-palatine,  and 
otic,  on  the  trigeminal  nerve). 

The  Morphology  of  the  Sym- 
pathetic System. 

From  a  consideration  of  its  struc- 
ture, functions,  and  development,  there 
appear  to  be  two  separate  structures 
represented  in  the  sympathetic  nervous 
system — the  spinal  and  the  sympathetic 
elements.  The  structiu-e  of  the  system 
13 resents  a  union  of  two  distinct  elements 
— fibres  of  cerebro-S2:)inal  origin  and 
"  sympathetic  "  cells  and  fibres.  While 
the  function  of  the  gangiiated  cord  and 
its  branches  seems  to  be  absolutely  de- 
pendent upon  the  cerebro-spinalnervous 
system,  it  is  certain  that  the  cells  and 

11.-.   i;uiuiuLiinutuis  loui;  ,   ictj  a,   puruiuu  ui    him   ramus  loiii-     ni  n  ,  n  j  i     _,  • 

-,  the  ganglion;  (/3)  fibres  passing  over  the  cord,  accom-  fibres  of  the  sympathetic  systein  possess 
panied  by  a  stream  of  cells  ;  (7)  continuous  with  those  of  ^  ^'^}'^^  activity  apart  h-oni  their  con- 
the  ganglion ;  (Ao)  Aorta.  '  nexioii  with  the  central  nervous  system. 

In  the  develoj)ment  of  the  sympathetic 
it  is  at-  least  highly  probable  that  a  mesoblastic  rudiment  or  precursor  forms  the  basis  of  the 
sympathetic  system,  which  is  secondarily  joined  l^y  nerve-fibres  from  the  roots  of  the  spinal 
nerves. 

Morphologically  this  part  of  the  nervous  system  is  essentially  a  longitudinal  cord  or  column, 
associated  with  involuntary  muscles  and  glandular  tissues,  and  jjarticularly  related  to  the  organs 
in  the  splanchnic  area.  Like  other  longitudinal  structures  in  the  body,  and  esi^ecially  like  the 
organs  of  the  si^lanclinic  area,  the  symjiathetic  system  is  not  truly  segmental.  The  gangiiated 
cord  is  only  quasi-segmental,  the  segmentation  being  attributable  to  its  junction  with  the 
visceral  branches  of  the  spinal  nerves.  The  jjeripheral  branches  from  the  gangiiated  cord  are 
not  segmental ;  even  the  gray  rami  are  not  properly  metameric,  but,  like  the  ganglia,  assume  a 
segmental  character  in  consequence  of  their  connexions  with  the  spinal  nerves. 

_  The  phylogenetic  relation  of  the  sympathetic  and  the  cerebro-spinal  elements  in  the  system 
it  is  impossible  to  determine.  It  may  be  that  the  sympathetic  system  is  the  representative  of 
an  ancient  architecture  independent  of  the  cerebro-sjomal  nervous  system,  the  materials  of  which 
are  utilised  for  a  more  modern  nervous  system  ;  or  it  may  be  that  the  correlation  of  spinal 
nerves  and  sympathetic  are  both  the  consequences  of  the  formation  of  new  organs  and  structures 
in  the  splanchnic  area.  Examined  in  every  light,  it  possesses  features  which  effectually  difter- 
entiate  it  from  the  cerebro-spinal  system,  although  it  has  become  inextricably  united' with  it 
and  subservient  to  it. 


548. — ^Section  through  the  Sympathetic  Gangliated 
Cord  of  an  Embryo. 

Showing   the    connexion   with    the    ganglion    (Sy)    of   the   white 
ramus  communicans  (Spl)  ;  (a)  a  portion  of  the  ranuis  join 


COLUMBIA  UNIVERSITY  LIBRARIES  (hsi.stx) 

QIVI23C91  1905C.1v.  1 


i 


BFC  1  0  1986 


-A 


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